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The effects of 50 kilovolt x-rays on the alkali metal borohydrides Walker, Leonard George 1959

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THE EFFECTS OF 50 KILOVOLT X-RAYS ON THE ALKALI METAL BOROHYDRIDES by Leonard George Walker B.A., University o f B r i t i s h Columbia, 1957  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS POR THE DEGREE OF MASTER OF SCIENCE i n the Department of  •  CHEMISTRY  We accept t h i s t h e s i s as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October, 1959  ABSTRACT The marked physical changes i n potassium borohydride such as decrepitation and the development o f a deep blue coloration when the s o l i d compound i s exposed to i o n i z i n g radiation stimulated a study of the e f f e c t s of 50 Kvp X-rays on the a l k a l i metal borohydrides to determine the nature of the radiation induced changes such as color center formation and chemical decomposition. Methods were developed to prepare the a l k a l i metal borohydrides i n a form suitable f o r r a d i a t i o n studies.  Solvents studies showed that anhydrous hydra-  zine was an exceptionally good solvent f o r potassium borohydride, the s o l u b i l i t y being 2S.3 grams KBH^ per 100 grams  a  t  c  »  T  h  e  handling of hydrazine  as a solvent required the construction of special apparatus.  A study of the use o f hydrazine as a solvent f o r  other i o n i c borohydrides and/or the growth of c r y s t a l s suitable f o r spectroscopic work i s incomplete.  Therefore,  the spectroscopic studies on r a d i a t i o n induced absorption bands was done mainly with t h i n pressed p e l l e t s .  The  borohydrides of rubidium and cesium were prepared by metathesis reactions from potassium borohydride v i a a sulfonium borohydride.  The preparation of the previously  unreported trimethylsulfonium borohydride i s described. Color center formation was studied by spectroscopic methods only and the F and U type centers have been tentatively identified.  The thermal s t a b i l i t y and o p t i c a l  b l e a c h a b i l i t y of some of the radiation induced absorption bands were examined.  Chemical studies of radiation damage  i n potassium borohydride f a i l e d to show the presence of free a l k a l i metal. undetectable.  Gaseous boron hydrides were also  Mass spectrometric examination of gaseous .  material evolved during i r r a d i a t i o n showed only hydrogen to be present.  No gas was evolved when heavily i r r a d i a t e d  samples of potassium borohydride were dissolved i n l i q u i d ammonia• A discussion o f methods and apparatus characteri s t i c to the radiation studies such as the X-ray generator, radiation vessels, vacuum system, and a section on r a d i a t i o n dosimetry i s included i n the t h e s i s .  The i n t e n s i t y o f X-rays  generated by the Machlett OEG-60 X-ray tube was  determined  by the application of the included dosimetry data together with a calorimetric measurement of the output f l u x of the tube.  At 50 Kvp and 28 milliamperes the i n t e n s i t y output  was found to be 0.220 cal.min.  cm. * at the tube port.  Some suggestions f o r further work are outlined at the end dT the study.  In  presenting  the' r e q u i r e m e n t s of B r i t i s h it  this thesis f o r an  Columbia,  freely available  agree that for  Department  copying  gain  shall  Department  or  not  his  for reference  and  study.  I  for  extensive be  granted  representatives. of  a l l o w e d w i t h o u t my  ,/^T?.  by  Columbia,  of  the  It  this thesis  of  /?-&rtUsL  copying  of  University shall  The U n i v e r s i t y o f B r i t i s h Vancouver Canada. Date  the  Library  publication be  degree at the  p u r p o s e s may  o r by  that  advanced  fulfilment  I agree that  permission  scholarly  in partial  make  further this  Head o f  thesis my  i s understood for financial  written  permission.  J  ACKNOWLEDGMENTS I wish to express my appreciation to Dr. H. G. Heal for his guidance and encouragement during the course of this work and especially for the opportunity he has given me to learn something of the effects of ionizing radiation i n solids, valuable discussions.  I wish to thank Professor C. A. McDowell for many Thanks are due to Professor J . A. Harris for informa-  tion on the syntheses involved i n this work and also for samples of cesium compounds.  I also wish to thank Dr. B. A* Dune 11 for samples of compounds  used i n the experimental work. Pringle were of great benefit.  The many discussions I have had with Mr. J . I should also like to thank Messrs. Hawkins,  Muehlchen, and Sawford for their assistance i n the design and construction of apparatus.  TABLE OF CONTENTS Page i i i  LIST OF TABLES LIST OF FIGURES  iv  LIST OF PLATES  vii  Chapter I.  INTRODUCTION  1  A. B. C.  1 2  D. II.  III.  The Problem . .Methods o f Investigation The Interaction o f Ionizing Radiation with Matter Radiation Induced L a t t i c e Imperfections . .  APPARATUS AND METHODS CHARACTERISTIC OF THE RADIATION STUDIES ON THE ALKALI METAL BOROHYDRIDES  13  A. B. C. D.  13 24 29 34  The X-Ray Generator Radiation Vessels The Vacuum System and A n c i l l a r y Equipment . Radiation Dosimetry  EXPERIMENTAL A. B. C.  The Preparation o f the A l k a l i Metal Borohydrides Galorimetric Determination of the Radiation Flux from the 0EG-60 X-ray Tube Spectroscopic Examination of the Irradiated Borohydrides 1. 2. 3•  D.  V i s i b l e and u l t r a v i o l e t absorption spectra Infra-red spectra Paramagnetic resonance spectrum . . . .  51 52 72 77 77 98 98  Examination o f Irradiated KBRV f o r Chemical Changes  IV.  4 7  DISCUSSION  BIBLIOGRAPHY  100 104 115  LIST OF TABLES Table 1.  Page C h a r a c t e r i s t i c s of the AEG-50 and the OEG-60 X-ray tubes  15  2.  High tension primary operating c i r c u i t components  17  3.  High tension secondary c i r c u i t components. . .  22  4*  Mass absorption c o e f f i c i e n t s of selected elements  40  Mass absorption c o e f f i c i e n t s of the a l k a l i metal borohydrides  44  5. 6.  Parameters f o r the De Waard Formula and the Klein-Nashina Formula  48  7.  Summary of solvent study  53  8.  Assay of some of the i o n i c borohydrides. . . .  66  9.  Energy f l u x f o r samples i n the radiation vessel f o r chemical studies. Application of the Ivey Formulas to the r a d i a t i o n induced changes i n the a l k a l i metal borohydrides •  10*  iii  76 108  LIST OF FIGURES Figure 1.  Page Defects i n a simple l a t t i c e .  The a l k a l i  metal borohydride l a t t i c e  8  2.  Color centers i n the a l k a l i metal halides . . .  10  3.  Schematic view o f AEG-50 X-ray tube  14  4*  Schematic view o f OEG-60 X-ray tube  14  5.  Angular d i s t r i b u t i o n of i n t e n s i t y from 16  6.  AEG-50 X-ray tube Angular d i s t r i b u t i o n of i n t e n s i t y from OEG-60 X-ray tube  16  7.  High tension primary operating c i r c u i t  18  8*  High tension secondary c i r c u i t  19  9.  Radiation vessel f o r chemical studies  25  10* 11.  Radiation vessel f o r spectroscopic studies. . . Carriage f o r mounting spectroscopic radiation vessel i n recording spectrophotometer  27  12.  Vacuum system used i n radiation studies • . • • 30  13.  Klein-Nashina scattering f a c t o r  43  14. 15.  De Waard parameter, Bp Energy d i s t r i b u t i o n o f Bremsstrahlung f o r various f i l t r a t i o n s  47  16.  Infra-red spectrum of ammonia  56  17.  Infra-red spectrum o f hydrazine  56  18.  Infra-red spectrum of KBHA extracted with  19.  l i q u i d ammonia Infra-red spectrum o f commercial KBH^  iv  28  50  56 57  Figure 20.  Page Infra-red spectrum o f KBH^ extracted with anhydrous hydrazine  57  Infra-red spectrum o f trimethylsulfonium iodide  57  22.  Infra-red spectrum of trimethylsulfonium borohydride.  59  23.  Infra-red spectrum of vacuum pyrolised  21.  .  product  59  24.  Infra-red spectrum of a i r pyrolised product. . .  59  25.  Infra-red spectrum o f Reinecke's s a l t  68  26.  Infra-red spectrum of rubidium Reineckate. . . .  68  27.  Infra-red spectrum of ammonium iodide  68  28.  Infra-red spectrum of rubidium borohydride . . .  70  29.  Infra-red spectrum of cesium borohydride . . . .  70  30.  Cooling curve f o r s i l v e r d i s c i n calorimetric f l u x determination Radiation induced changes i n lithium borohydride Radiation induced changes i n sodium borohydride  31. 32.  74 80 82  33.  Radiation induced changes i n potassium borohydride c r y s t a l .  84  34*  Radiation induced changes i n potassium borohydride c r y s t a l (continued)  86  Radiation induced changed i n potassium borohydride pressed p e l l e t  88  Radiation induced changes i n potassium borohydride pressed p e l l e t (continued)  90  Radiation induced changes i n rubidium borohydride.  92  3,5. 36. 37*  v  Figure 38. 39* 40. 41*  Page Radiation induced changes i n rubidium borohydride (continued)  • • .  94  Radiation induced changes i n cesium borohydride  96  Electron spin resonance spectrum of irradiated KB(powdered)  99  Calibration graph f o r small amounts of hydrogen collected i n chemical decomposition studies  vi  103  LIST OF PLATES Plate I. II, III.  Page Liquid ammonia metathesis apparatus  32  Low temperature colorimeter f o r use with l i q u i d ammonia  35  Apparatus f o r c r y s t a l growth from anhydrous hydrazine. . . .  36  vii  1  I. A.  INTRODUCTION  The Problem The e f f e c t s o f high energy radiations on matter i n  the condensed phase has assumed, i n recent years, a very p r a c t i c a l importance as indicated by the interest i n r a d i a t i o n damage to engineering s t r u c t u r a l materials (1,2) and to b i o l o g i c a l systems  (3,4,5,6),  isotopes f o r m i l i t a r y purposes and research programs  and i n the production o f  (7,8),  (9,10,11)•  i n d u s t r i a l operations  Concurrent with t h i s  growth of i n t e r e s t i n the gross e f f e c t s of r a d i a t i o n , physical chemists have turned t h e i r attention to a study of r a d i a t i o n damage at the molecular l e v e l to correlate chemical e f f e c t s with the mode o f interaction of high energy p a r t i c l e s i n matter, the state of aggregation o f the i r r a d iated material, and the r e a c t i v i t y o f r e s u l t i n g excited and ionized molecules and ions  (12,13,14)*  This study i s concerned with the effects o f 50 k i l o v o l t (Kvp) X-radiation on some i o n i c borohydrides.  H. G. Heal  (15)  observed that s o l i d potassium borohydride developed an intense blue coloration on short exposure to 50 Kvp X-rays at room temperature.  On dissolving c r y s t a l s of the i r r a d i a t e d  material i n cold water a vigorous evolution of gas occurs i n d i c a t i n g the p o s s i b i l i t y o f chemical decomposition i n the s o l i d .  products  This work attempts to elucidate the nature o f  2  t h e c h e m i c a l d e c o m p o s i t i o n and t h e p h y s i c a l changes as c o l o r c e n t e r f o r m a t i o n i n the a l k a l i m e t a l on e x p o s u r e t o X - r a y s .  such  borohydrides  H o w e v e r , no t h o r o u g h s t u d y  on  k i n e t i c a s p e c t s o f t h e r a d i a t i o n e f f e c t s was u n d e r t a k e n . The m a j o r p o r t i o n o f t h e e x p e r i m e n t a l w o r k i n v o l v e d  develop-  i n g methods f o r t h e p r e p a r a t i o n and p u r i f i c a t i o n o f  ionic  borohydrides B.  used i n the r a d i a t i o n  Methods o f In  studies.  Investigation  s t u d y i n g t h e e f f e c t s o f 50 K v p X - r a y s o n t h e  i o n i c borohydrides  s e v e r a l methods o f a n a l y s i s were  applied  t o determine t h e k i n d and q u a n t i t y o f change i n d u c e d .  These  were: 1) I n f r a - r e d a b s o r p t i o n s p e c t r a o f i r r a d i a t e d m a t e r i a l s to determine the nature of the primary products i n the  decomposition  solid.  2) U l t r a - v i o l e t a n d v i s i b l e a b s o r p t i o n s p e c t r a (2000 X t o a p p r o x i m a t e l y 7000 the color  2) t o  determine the nature  of  centers.  3) C o l o r i m e t r i c e s t i m a t i o n o f n o n - v o l a t i l e t i o n products  (e.g.,  potassium metal)  decomposi-  and  quantitative  measurement and a n a l y s i s o f gaseous p r o d u c t s  result-  i n g from i r r a d i a t i o n . 4)  Paramagnetic resonance spectra of i r r a d i a t e d  crystals  to help e l u c i d a t e the nature of primary decomposition products i n the i o n i c  crystals.  3  Methods were developed f o r the preparation, p u r i f i c a t i o n and c r y s t a l l i z a t i o n of the i o n i c borohydrides.  During  the period of t h i s study, the only borohydride commercially available was the potassium s a l t .  A simple procedure f o r  the preparation of other a l k a l i metal borohydrides from the potassium s a l t and other e a s i l y available materials was devised.  An extensive search for suitable solvents to  purify and to c r y s t a l l i z e the i o n i c borohydrides was undertaken.  The most s a t i s f a c t o r y solvents found were anhydrous  l i q u i d ammonia and anhydrous hydrazine.  The use o f these  materials as solvents entailed construction of special apparatus as described i n Chapter I I , Section G. Dosimetry data have been worked out f o r the r a d i a t i o n source, a Machlett OEG-60 beryllium windowed tube, which was used f o r the chemical decomposition studies.  Although l i t t l e  use was made of t h i s information i n the present study, i t has been included because of i t s possible value i n l a t e r quantitative work using t h i s source.  A discussion of X-radiation  dosimetry has also been included f o r reference. The interpretation of changes i n the o p t i c a l properties induced i n the borohydrides by X-radiation i s based mainly on models developed from studies of r a d i a t i o n damage i n the simpler a l k a l i metal halides.  The remaining sections of t h i s  introduction w i l l outline the theory of radiation i n t e r actions i n matter and survey some l a t t i c e imperfections and t h e i r properties.  4  C. The Interaction of Ionizing Radiation with Matter  (16,17)  Ionizing radiations are high energy emanations which can be generally classified as electromagnetic or corpuscular. Because of the wave-particle duality of matter this division is not precise. Photons, however, can be distinguished from other ionizing radiations by their property of zero rest mass. The interaction of two particles, in the rigorous sense, should always be treated in terms of the electromagnetic fields set up by the particles and the effect of these fields on the particles themselves.  Electromagnetic  interactions, in view of the corpuscular nature of the radiation field, should be described as processes of photon absorption and emission. Whenever a charged particle passes in the vicinity of an atom, one of several distinct effects may occur. If the distance of closest approach is large compared to the dimensions of the atom, the atom (or molecule) as a whole reacts to the field of the passing particle resulting in excitation or ionization. When the particle approaches within distances of the order of atomic dimensions the interaction involves the passing particle and one of the atomic electrons, the latter being removed with considerable energy from the bound state. If the binding energy of the emitted electron is small in comparison to the energy obtained in the "knock-on" process, then the interaction may be considered as occurring between the bombarding particle and a free electron.  5  In such close c o l l i s i o n processes the magnetic moments and spins o f the interacting p a r t i c l e s cannot be neglected (18). When the distance o f closest approach becomes smaller than the atomic radius, the d e f l e c t i o n o f the passing p a r t i c l e by the f i e l d of the nucleus becomes the most important e f f e c t . As a r e s u l t o f the p a r t i c l e ' s d e f l e c t i o n , numerous low energy photons known c o l l e c t i v e l y as "Bremsstrahlung" are generated. The interaction o f high energy photons with matter produces results analogous to those o f charged p a r t i c l e s . The i n t e r a c t i o n of the photon with the atom (or molecule) as a whole gives the photoelectric  effect i n which the photon  i s annihilated, i t s energy appearing as electronic energy of the atom (or molecule) and possibly p a r t l y as k i n e t i c energy of an emitted electron. energies ( <50 Kev).  This effect i s important only at low  The interaction o f a photon with a free  electron leads to the Compton effect i n which the photon transfers only a part o f i t s energy and momentum to the electron which i s considered at r e s t .  The interaction o f  a photon with a coulomb f i e l d can lead to pair production whereby the photon i s annihilated with the simultaneous formation o f a positive and a negative electron.  This  process occurs only when the energy o f the photon exceeds the r e s t energy of the two electrons (1.02 Mev).  Irradiation  of matter with neutrons produces i o n i z a t i o n only by secondary processes, the primary e f f e c t being momentum transfer to the  6  nucleus of the c o l l i d i n g atom.  However, the f i n a l r e s u l t s  of neutron capture may be a f i s s i o n reaction or an energetic gamma emission which can cause tremendous structural damage to the molecule or i n the s o l i d . Whenever high energy radiation i s absorbed i n matter secondary electrons w i l l r e s u l t from i o n i z a t i o n processes which w i l l produce secondary ionizations which frequently swamp the e f f e c t s a r i s i n g from primary absorption. This i s always the case with high energy photons.  Primary penetra-  t i o n processes f o r high energy radiation absorption has been excellently outlined by Platzman (19).  The absorption of  i o n i z i n g r a d i a t i o n and subsequent transformations i n a material can be studied conveniently i n a time  sequence  consisting of three stages (20): a) Physical stage involving the highly inhomogeneous d i s s i p a t i o n of the radiation i n the system within a period of 10*^5  second.  b) Physi co chemical stage l a s t i n g f o r 10""* second 2  during which thermal equilibrium i s established. c) Chemical stage leading to the establishment o f chemical equilibrium through d i f f u s i o n and chemical reaction of reactive species. greater than 1 0 ~  12  This requires a time  second for macroscopic  systems  and may be of extreme duration e s p e c i a l l y i n condensed systems.  During continuous i r r a d i a t i o n s  a l l three stages w i l l be i n progress.  7  D.  Radiation Induced L a t t i c e  Imperfections  An i d e a l c r y s t a l i n which the l a t t i c e has p e r f e c t p e r i o d i c i t y i n the occupation o f l a t t i c e s i t e s does not e x i s t i n r e a l i t y at temperatures above absolute zero.  In  r e a l c r y s t a l s c e r t a i n d e f e c t s can e x i s t i n thermal e q u i l i b rium w i t h i n the l a t t i c e .  These defects i n c l u d e vacant l a t t i c e  p o i n t s and i n t e r s t i t i a l atoms or i o n s .  There are two ways i n  which these l a t t i c e vacancies and i n t e r s t i t i a l atoms o r ions can a r i s e .  A vacancy and an i n t e r s t i t i a l are generated  simultaneously when a Frenkel defect i s produced. shows the formation o f t h i s type o f d e f e c t .  Figure 1(a)  The second method  of generating vacancies a r i s e s from Schottky d e f e c t s .  The  l a t t e r process i s shown i n f i g u r e 1(b). Thus a Frenkel defect c o n s i s t s o f a vacant l a t t i c e point and an atom or i o n i n an i n t e r s t i t i a l p o s i t i o n w h i l e a Schottky defect c o n s i s t s of a l a t t i c e vacancy o n l y .  The presence o f vacancies g i v e s  r i s e to e l e c t r o l y t i c conductivity i n ionic crystals.  Schottky  defects w i l l , i n g e n e r a l , be more numerous than the Frenkel type.  An i m p u r i t y atom or i o n i s another kind o f point defect.  Besides point d e f e c t s we may have other c r y s t a l imperfections such as an e x t r a row o f atoms or i o n s , a row o f vacancies, or a row o f impurity atoms o r i o n s . are known as d i s l o c a t i o n s (21).  These l i n e imperfections Line and point imperfections  probably play an important r o l e i n c o l o r center formation  (22).  The removal o f an e l e c t r o n from an atom or i o n i n the l a t t i c e r e s u l t s i n the formation o f a p o s i t i v e "hole" i n the  (o)  A  FRENKEL  TYPE  DEFECT  IN  A  SIMPLE  LATTICE  • • ••  •  •••• •  •  • •  • • •  (b)  A  SCHOTTKY  TYPE  DEFECT  IN A  • •• •  SIMPLE  LATTICE  BOROHYDRIDE ALKALI METAL  + (c)  +  -  -  +  FIGURE  ION ION  I  HYDROGEN ATOM UP  HYDROGEN ATOM DOWN TWO SUCCESIVE LAYERS IN AN ALKALI METAL BOROHYDRIDE LATTICE (fact ctnttred cubic structure)  9>  band o f e l e c t r o n i c energy l e v e l s .  The electron removed by  ionization w i l l contribute to the electronic conductivity of the material i n much the same way as "free" electrons in a metallic crystal.  The "hole" i n the valence band o f  the c r y s t a l w i l l also contribute t o the e l e c t r o n i c conductivity.  With insulators a more intimate association o f  the electron and positive hole exists i n the type of center known as an exciton ( 2 3 ) . absorption  Excitons  can be produced by  of photons o f s u f f i c i e n t energy t o t r a n s f e r the  electron from an anion to the cation.  Exciton formation  does not r e s u l t i n photoconductivity.  Ionization o f excitons  or formation o f positive holes with transfer o f electrons to a conduction band r e s u l t s i n photoconductivity. l i n e imperfections  Point and  may act as "traps" f o r electrons which  have been removed i n e x c i t a t i o n of the valence band electrons. The l a t t i c e defects a r i s i n g from the association of p o s i t i v e holes or electrons with l a t t i c e vacancies and i n t e r s t i t i a l s are c o l l e c t i v e l y known as color centers.  Their  properties have been comprehensively reviewed by S e i t z ( 2 4 ) • Figure 2 shows the structures which have been t e n t a t i v e l y assigned to explain the properties o f a number of the important radiation induced color centers.  These models  are based on r e s u l t s obtained f o r the centers i n the a l k a l i metal halides.  Centers of the type F and F  electron excessive centers.  1  are the simplest  Complexes involving these simple  10  11  centers with positive and negative ion vacancies give r i s e to R and M type centers.  V type centers are electron d e f i c i e n t .  The H-center i s the complement of the F-center, i . e . , a region of undamaged l a t t i c e i s formed when an H-center an F-center combine.  and  Some of the electron d e f i c i e n t centers  have been c l o s e l y examined by Kanzig et a l . (25) by the paramagnetic  resonance technique.  The U-center involving  the hydride ion (26,27) i s an important color center i n r a d i a t i o n induced imperfections of the a l k a l i metal borohydrides.  A model f o r the U-center i n agreement with i t s  known properties consists of a hydride ion, H-,  occupying  s u b s t i t u t i o n a l ^ the position of the normal negative ion, e.g., halide, borohydride, e t c . The various kinds of color centers have d e f i n i t e electronic structures and states.  Transitions between allowed  energy states give r i s e to the c h a r a c t e r i s t i c absorption bands, from which the name of these l a t t i c e imperfections i s derived, and also fluorescence i n the case of some of the centers. Ivey (2S) has developed empirical formulas which f i t the wavelengths of maxima o f the absorption bands f o r electron excessive centers.  For the F-center and the U-center these  are: F: Xmax • 7 0 3 d * ^ Angstroms 1  U:  Amax -  6l5d  1 # 1  ^  Angstroms  where d i s the i n t e r i o n i c distance between cation and anion i n the i o n i c c r y s t a l .  These formulas w i l l be applied i n the  12  discussion of the radiation induced absorption bands obtained with the a l k a l i metal borohydrides i n the spectroscopic studies outlined i n the experimental work of t h i s t h e s i s .  13  II.  APPARATUS AND METHODS CHARACTER1STIG OF THE RADIATION STUDIES  A.  The X-ray Generator Radiation i n the X-ray region of the electromagnetic  spectrum w i l l r e s u l t whenever s u f f i c i e n t l y energetic  electrons  interact with the strongly bound inner electrons of atoms or ions.  In practice, X-radiation i s obtained by accelerating  electrons through a high voltage i n vacuum and then allowing them to impinge on a target.  Thus two main components o f  any X-ray generator are: 1) a vacuum tube containing an "electron gun" and target, and 2) a high D.C. or r e c t i f i e d voltage t o accelerate the electrons from a filament to the target. In t h i s study two types o f high i n t e n s i t y beryllium windowed tubes were used.  Figures 3 and 4 show cutaway  diagrams o f the Machlett OEG-60 and the Machlett AEG-50 tubes, respectively.  The AEG-50 tube was used i n conjunc-  t i o n with the r a d i a t i o n vessel f o r absorption  spectra work,  while the v e r t i c a l l y mounted OEG-60 tube was used with the i r r a d i a t i o n vessel f o r chemical decomposition studies. Table 1 shows some important c h a r a c t e r i s t i c s o f the two tubes. Polar diagrams showing angular depence o f r a d i a t i o n i n t e n s i t y are given i n Figures 5 and 6.  Figure 3  Schematic View in Section of AEG-50  CATHODE  Tube.  SHOCKPROOF SHIELD  TUNGSTEN TARGET-  BERYLLIUM WINDOW -  COOLING WATER INLET  Figure 4 Schematic View in Section oj OEG-60 Tube.  TABLE 1 CHARACTERISTICS OF THE AEG-50 AND OEG-60 X-RAY TUBES AEG-50 Target Angle  20°  Focal Spot Size  5 mm  Cathode  Inherent F i l t r a t i o n X-ray Coverage  0EG-60 45°  2  Line focus with tungsten filament  6  mm  2  Line focus with tungsten filament  1,0 mm Beryllium  1.0 mm Beryllium  22° from central ray  30° from central ray  Maximum Voltage  50 Kvp  60 Kvp  Maximum Load Current (Single phase pulsating potential)  50 mamps  50 mamps  Filament C h a r a c t e r i s t i c s  6.5 v o l t s , 4*2 amps f o r 50 milliamps at 50 Kvp  6.5 v o l t s , 4#2 amps f o r 50 milliamps at 50 Kvp  Figure 5 — Angular Distribution of in Beam of Radiation from AEG-50  Intensity Tube.  17 The high tension f o r the tubes was generated by a modified General E l e c t r i c KX-8 transformer with a primary voltage and operating c i r c u i t designed by H. G. Heal, Figures 7 and 8 give the wiring o f the primary and secondary c i r c u i t s , r e s p e c t i v e l y . Tables 2 and 3 describe components of the c i r c u i t s with some notes on t h e i r operation. TABLE 2 HIGH TENSION PRIMARY OPERATING CIRCUIT COMPONENTS S  220 volt u n s t a b i l i z e d mains supply.  F,F  Two 25 ampere fuses.  S-L  D.P.S.T, main switch.  S  S.P.S.T. X-ray filament switch. located on the control panel.  2  Si and S  2  are  Filament voltage s t a b i l i z e r , consists of two transformers with t h e i r primaries i n s e r i e s . The one which supplies most o f the output voltage operates with a high f l u x density i n i t s iron core, i . e . , i t i s oversaturated. It i s also p a r t l y resonated by means of a capacitor, C ^ l O ^ a f d . The other transformer operates with a low f l u x density and i n out-of-phase r e l a t i o n s h i p to the f i r s t transformer. The p o t e n t i a l between l i n e C and the tap i n use at the s t a b i l i z e r i s 150 v o l t s . T^  Autotransformer. Only two input connections are presently i n t a c t .  S^  Multipoint switch which taps the autotransformer at various voltages to supply the primary current f o r the o i l immersed high voltage transformer. This switch i s located on the control panel with contacts l e t t e r e d A to H. When S^ i s on contact 1, contact A gives 60 v o l t s contact B gives 90 v o l t s contact C gives 110 v o l t s contact D gives 130 v o l t s contact E gives 150 volts contact F gives 165 v o l t s contact G gives I85 v o l t s contact H gives 205 v o l t s .  M  ca  20  TABLE 2 continued S/,,  Multicontact switch similar to S3. Located on control panel with contacts numbered 1 to 8. Each contact increases the voltage obtained on S3 by an increment o f approximately 2 v o l t s , e.g., contact 2 increases S3 voltage by 3 volts contact 3 increases S3 voltage by 5 v o l t s contact 4 increases S3 voltage by 7 v o l t s , etc.  T2,T3  Two 110 v.-6 v. stepdown transformers. The transformer primaries are connected i n series to the 220 v. l i n e . The transformer secondaries are connected i n p a r a l l e l . These transformers supply current at 6 v o l t s f o r the operation o f the safety relays.  T^T/j  Two ganged Powerstat  S5  Safety switch ensuring that there i s no voltage across T - T when S7 i s closed. This switch must be closed before safety relay system w i l l operate. Contacts close only when variable transformers are f u l l y counterclockwise.  S$  Water switch. Metropolitan Vickers Relay M6. This switch ensures that cooling water i s flowing through X-ray tube target before any high tension i s applied to the tube. Since t h i s switch operates on the bellows p r i n c i p l e , i t can open under excess flow of cooling water. Only when the c i r c u i t i s grounded through t h i s switch w i l l the r e l a y system operate.  Sy  "High Tension" switch located on control panel.  V  V o l t meter which i s calibrated to read k i l o v o l t s across X-ray tube. A value of 63 Kvp on t h i s meter corresponds t o 50 Kvp across the X-ray tube.  R]_  A current d i s s i p a t i n g r e s i s t a n c e .  variable transformers type 116-20.  D.P. Relay. This r e l a y switches the primary voltage on the T - T l i n e s . This voltage i s applied to the primary of the o i l immersed transformer. This relay w i l l not operate unless one of either S5 or the S.P. relay i s closed to ground. In any case, however, S^ must be closed to ground.  21 TABLE 2 continued S.P. Relay. This r e l a y ensures that the r e l a y c i r c u i t i s grounded f o r any position of the coupled variable transformers TA and T5. Se must be closed to ground before t h i s relay w i l l be actuated, .. L  Variahle inductance with i r o n core. P o t e n t i a l across l i n e between l i n e s X and C i s 130 v o l t s .  I  X-ray tube filament current meter.  R  2  Shunt f o r X-ray tube filament current meter.  T,T  Current carrying l i n e s f o r the primary c i r c u i t of the o i l immersed transformer.  C  Current carrying l i n e common to X-ray tube filament c i r c u i t and Kenotron filament c i r c u i t .  X  Current carrying l i n e used with l i n e G f o r operating X-ray tube filament transformer. Potential across l i n e s X - C i s 130 v o l t s .  K  Current carrying l i n e used with l i n e C f o r operating the Kenotron transformers. Potential across l i n e s K - C i s 145 v o l t s .  Timer  An e l e c t r i c clock has been suitably placed across r e s i s t o r R i to supply 110 v o l t s operating voltage.  22  TABLE 3 HIGH TENSION SECONDARY CIRCUIT COMPONENTS The secondary c i r c u i t r y of the high voltage supply i s o i l immersed i n a large s t e e l tank.  This container has  several terminals on i t s cover, two of which are of the large porcelain type.  One of the porcelain insulated terminals i s  grounded while the other contains a socket with two leads from the X-ray tube filament transformer T5.  These l a t t e r  two leads are at the potential o f the output from the  second-  ary c i r c u i t of the high voltage transformer, General E l e c t r i c type KX-8, Although the two high voltage wires used to operate the X-ray tube filament are of d i f f e r e n t colors, v i z . , black and white, i t i s immaterial how they are connected to the X-ray tube filament terminals.  The remaining terminals  on the tank l i d are located on a terminal board.  Terminals  K, C, X, Tj_, and T2 are connected t o the corresponding l i n e s of the primary operating c i r c u i t with the reservation that T^ and T  2  need not be distinguished and thus may be simply  connected to the l i n e s T - T o f the control c i r c u i t .  Terminal  G i s grounded while terminal P remains unconnected.  Terminal M  i s connected to the X-ray filament current meter on control panel, the other terminal on t h i s meter being connected to ground p o t e n t i a l .  23  TABLE 3 continued I,C,K,T - T l i n e s are discussed as components o f the operating primary c i r c u i t , Kenotrons KR-6 - General E l e c t r i c r e c t i f i e r tubes f o r use to a maximum of 140 k i l o v o l t s . - Kenotron transformers with primary windings i n p a r a l l e l across K - C l i n e s at a voltage o f 145 v. Secondaries of these transformers supply voltage to kenotron filaments.  TI»T2»T3ITA  Tc  I-ray tube filament transformer. Primary winding supplied with 130 v o l t s from X • C l i n e s . The secondary winding o f t h i s transformer supplies current to the tube filament. The voltage across t h i s secondary winding i s approximately 8 v. when the tube i s operating at 50 Kvp and 2 8 milliamps.  X-ray tube. Two types of tubes have been used i n the present study. Their c h a r a c t e r i s t i c s being d i s cussed i n Table 2 . The tube filament i s connected to the output o f the secondary high tension transformer which i s normally operated at 50 Krp above ground. The tube anode (target) i s grounded. High Tension Current Meter, I . This meter i s i n the secondary winding of the high voltage transformer. One o f the meter terminals has been grounded. High Tension Rectifying c i r c u i t was modified from the o r i g i n a l form i n order t o make use o f X-ray tubes with grounded anodes. This has been done by grounding the midpoint of the secondary winding of the high tension transformer along with the removal of two kenotrons. The resulting high tension i s f u l l wave with only h a l f the peak voltage.  24  B.  Radiation Vessels The radiation vessels used i n t h i s work were of a  metal evacuable type based on the p r i n c i p l e of the common Dewar f l a s k . for  The vessels had 1.0 mm beryllium f o i l windows  sample i r r a d i a t i o n .  The vessel used i n the chemical  decomposition studies i s shown i n Figure 9.  I t had a  removable top flange to which was attached a sample tray mount (copper) by means o f a glass tube (5 1/2 inches) which formed a thimble f o r coolant.  Temperatures obtainable from  that of b o i l i n g l i q u i d nitrogen to s l i g h t l y above room temperature were measured by a copper constantin thermocouple which was connected from the two insulated leads i n the  top flange to the small stud on the sample t r a y holder.  The tray holder provided f o r seven samples to be i r r a d i a t e d simultaneously, each a t a different i n t e n s i t y , by the use of suitably placed aluminum f i l t e r s .  The various samples  in an exposure were used with f i l t e r s of the following t o t a l nominal thicknesses of aluminum: Sample Sample Sample Sample Sample Sample Sample  1 2 3 4 5 6 7  Sample Sample Sample Sample Sample Sample Sample  tray tray tray tray tray tray tray  + + + + + + +  0 19 4 12 8 21 40  thousandths thousandths thousandths thousandths thousandths thousandths thousandths  inches inches inches inches inches inches inches.  Sample trays were made from aluminum f o i l (approximately 0.5 thousandths inches; 0.003 gm cm^) by punching out discs and shaping them i n a s p e c i a l l y made d i e .  It i s t o be noted  25  26  that the samples received radiation which had been "hardened" by more f i l t r a t i o n than that associated with the sample t r a y and the f i l t e r s attached t o the sample tray holder.  The  t o t a l f i l t r a t i o n i s tabulated i n figure 15, Chapter I I , Section D.  The r a d i a t i o n vessel was bolted t o the port of  the v e r t i c a l l y mounted OEG-60 tube. The r a d i a t i o n vessel f o r spectroscopic studies o f small c r y s t a l s or pressed p e l l e t s i s i l l u s t r a t e d i n figure 10. For i r r a d i a t i o n s i t was bolted t o the h o r i z o n t a l l y mounted AEG-50 tube.  It has a flange and valve to allow  evacuation  and subsequent removal from the X-ray tube so that i t can be placed i n the c e l l compartment o f the recording photometer.  spectro-  Figure 11 shows the carriage used to position  the vessel accurately i n the Cary spectrophotometer. The material examined i n the spectroscopic studies was cemented to the support on the base o f the coolant thimble. was  Provision  also made f o r thermocouples as with the vessel f o r  chemical decomposition studies.  To i r r a d i a t e the sample  the material had to face the beryllium f o i l port.  To obtain  absorption spectra the sample was then rotated through 90° by turning the whole upper coolant reservoir at the metal tapered j o i n t .  This placed the material i n a suitable p o s i -  t i o n between the quartz windows to obtain the spectra.  t RING METAL BELLQWS/fl  THERMOCOUPLE CONNECTIONS  DETAILS OF VALVE (ENLARGED)  FIGURE  10  RADIATION VESSEL FOR SPECTROSCOPIC STUDIES CONSTRUCTION BERYLLIUM WINDOW CRYSTAL MOUNT (COPPER)  -THERMOCOUPLE CONNECTION , , RADIATION VESSEL WITH ALL-METAL DEWAR  0 -J  MATERIAL:  1 2 3 I I I INCHES  BRASS  SET  SCREW  rwi  BASE SUPPORTED BY THE HORIZONTAL RODS IN CELL COMPARTMENT OF 'CARY' RADIATION VESSEL MOUNT  CARRIAGE POSITIONING ROD  FIGURE II RADIATION VESSEL CARRIAGE FOR USE WITH THE CARY RECORDING SPECTROPHOTOMETER 0  I INCHES  2  29  C.  The Vacuum System and A n c i l l a r y Equipment A vacuum system was designed and constructed to  carry out several operations connected with the studies.  radiation  I t was designed with the following operations i n  mind: 1) The use of ammonia, deutero-ammonia and hydrazine as solvents i n the p u r i f i c a t i o n of s t a r t i n g materials and the solution o f the i r r a d i a t e d borohydrides. 2) The use of boron hydrides i n attempts to study t h e i r radiation  chemistry and as intermediates i n the  preparation o f covaient and i o n i c borohydrides. This necessitated the use o f mercury f l o a t valves. 3) The c o l l e c t i o n o f gaseous decomposition  products  from the i r r a d i a t e d borohydrides upon solution i n a suitable solvent. 4) The evacuation o f radiation vessels and the c o l l e c t i o n of gases evolved during i r r a d i a t i o n s . Figure 12 shows the basic layout o f the vacuum system. Pressures were measured by the thermal conductivity method using a P i r a n i gauge (Edwards 7-2A) with s e n s i t i v i t y of ±0.05/* i n the range 0 - 5/JL .  A second range on the instrument per-  mitted pressure measurements from 0 - 500/t.  A mercury  d i f f u s i o n pump was placed i n the system f o r c i r c u l a t i n g gases through a series o f traps or f o r c o l l e c t i n g gases f o r storage i n a two l i t r e bulb.  This pump could operate up to a pressure  AMMONIA STORAGE  VACUUM AMMONIA PURIFICATION TRAIN  SYSTEM  RADIATION  USED  IN  STUDIES  FIGURE 12  [_*>_  r  TO FLOAT VALVE OPERATING SYSTEM  RADIATION VESSEL FOR CHEMICAL STUDIES  RADIATION VESSEL FOR SPECTROSCOPIC STUDIES  TO ATMOSPHERE  TO MECHANICAL . PUMP  -SILICA GEL  31  difference of approximately  100/*•  The two P i r a n i gauge  heads were placed across the d i f f u s i o n pump, i . e . , one on the high pressure side and the other on the low pressure side.  Gas c o l l e c t i o n was  considered complete when the  low pressure gauge head read l e s s than Zjx a f t e r one-half hour of pumping into the storage bulb.  The quantity of  collected gas could be determined by reference to a c a l i b r a t i o n graph obtained f o r the storage system. Several pieces of a u x i l i a r y equipment were used with the vacuum system.  These were:  1) A non-aqueous solvent metathesis vessel f o r reactions i n l i q u i d ammonia based i n p r i n c i p l e on a similar type of apparatus described by Parry et a l . (29)  who  described i t s operation.  Plate I shows the construction of the  apparatus  used i n the present work to prepare and purify some i o n i c borohydrides. 2)  A low temperature colorimeter f o r use with l i q u i d ammonia based on the " l i g h t piping" properties of l u c i t e rod.  It consists of a l i g h t source, a  U-shaped l u c i t e " l i g h t pipe," photo c e l l used i n a bridge c i r c u i t , a colorimeter c e l l with s t i r r e r , and an electromagnet  to actuate a small glass  enclosed n a i l acting as a s t i r r e r .  The  apparatus  was designed f o r estimating quantities of a l k a l i metal by measuring the o p t i c a l density of the blue coloration produced i n l i q u i d ammonia when these  metals dissolve i n t h i s solvent.  Provision was  made to prepare small amounts of the a l k a l i metals for c a l i b r a t i o n purposes by thermal decomposition of suitable compounds (e.g., a l k a l i metal azides) on a hot filament inserted into the evacuated colorimeter c e l l .  The a l k a l i metal coloration  could not be obtained with sodium i n l i q u i d ammonia unless mercury vapor from the vacuum system  was  prevented from condensing along with the ammonia as early noted by Jannis (30).  The problem  was  solved by t r a n s f e r r i n g s u f f i c i e n t ammonia to the trap at the top of the colorimeter l i n e with a l i q u i d nitrogen bath, then allowing the ammonia to be d i s t i l l e d to the colorimeter tube  (now  immersed i n l i q u i d nitrogen) from the trap at a temperature provided by a chloroform slush bath (-64° C.).  The colorimeter unit was then placed  over the colorimeter c e l l and a dry ice-alcohol bath put i n place to preserve the solution during o p t i c a l density measurements. Since no a l k a l i metal was detected i n the i r r a d i a t e d potassium borohydride t h i s method was not  further studied.  I t i s mentioned here only  because o f i t s possible value i n estimating a l k a l i metals i n i r r a d i a t e d systems where they are known to be produced (e.g., the a l k a l i metal azides).  Plate I I shows the major components of t h i s apparatus. 3) A c r y s t a l l i z a t i o n apparatus f o r use with nonaqueous solvents i n p a r t i c u l a r .  It i s a  modified version o f an apparatus used by Dreyfus and Levy ( 3 D for the growth of a l k a l i metal azides c r y s t a l s from aqueous s o l u t i o n . The apparatus used i n t h i s work i s i l l u s t r a t e d i n Plate I I I . I t was intended f o r growing c r y s t a l s of the i o n i c borohydrides from anhydrous hydrazine.  However, as t h i s work i s not complete,  no further mention w i l l be made o f t h i s apparatus i n t h i s study. D.  Radiation Dosimetry Radiation dosimetry involves the determination o f  the amount o f energy absorbed by a material on exposure to a radiation source ( 3 2 ) . This energy may be determined i n a number of ways.  For example, the i n t e n s i t y o f the trans-  mitted radiation may be deducted from* that incident on the sample of material to give the amount of energy absorbed per second.  In t h i s study use was made of semi-empirical  formulations describing the energy output of the radiation source together with attenuation factors (also calculated from semi-empirical formulas) f o r the incident r a d i a t i o n .  36  PLATE Iff  37  Thus the energy received i n the samples was estimated by c a l c u l a t i n g both the i n t e n s i t y output of the X-ray tube and the portion of t h i s incident f l u x which was attenuated by the sample. I f I (A)  i s the incident i n t e n s i t y of the radiation  0  f o r wavelengths between X and A + d X  , then the energy  dissipated per unit time i n the sample i s :  I (A)= l - e -M^-'X p 0  where e^/CJ^-Lx <j> i s the f r a c t i o n of the incident i n t e n s i t y transmitted  by the sample.  The t o t a l energy, E ( A ) , absorbed  by the sample f o r an exposure time, t , i s : E ( A ) = I ( X ) [ 1 - e-/^/jp-pxjt D  I ( A ) . t . yU/p'J>x 0  f o r small x.  The f r a c t i o n of the incident r a d i a t i o n of wavelength X which i s absorbed and which can be expressed by 1 - e~/^}C7£ a r i s e s from the various kinds o f interactions that exist between the quanta of the radiation and the electrons i n the material. Macroscopically  these interactions determine the value of^W/jp  m e ~^5^'5^whereJU/p i s the mass absorption c o e f f i c i e n t , X i s the thickness of the i r r a d i a t e d sample, and p  i s the  density of the sample. The absorption c o e f f i c i e n t ^ . , has two components such that/* = T + <y where qr i s the component due to photoelectric  38  interaction andcr'is that due to scattering.  For quanta  of fixed energy,T and <f depend upon the kinds of atoms in the i r r a d i a t e d substance because the number of electrons and t h e i r binding energies i n a particular atom depends on the atomic number, Z  .  The photoelectric factor depends  greatly on the energy of the quanta. For the dosimetry data used i n the present work, absorption c o e f f i c i e n t s have been calculated f o r various wavelengths following the method of Victoreen (33).  The  calculated values agree within 1 per cent of experimental values by the use of the following semi-empirical formula:  where C and D are constants for a particular element, 0~ i s the scattering factor per electron as determined  Q  by  the Klein-Nashina equation, - ~  i s the r a t i o of the atomic  number to atomic weight, and N  i s avagadro's number.  0  The  absorption c o e f f i c i e n t s of several elements which were used as f i l t e r s or were present in compounds used in i r r a d i a t i o n studies have been calculated for the wavelength range of 7 interest using values of C, D, and —=r— given by Victoreen (33).  The mass absorption c o e f f i c i e n t s of these elements  for several wavelengths i n the range of interest are given in Table 4.  The compton scattering factor,  , was  calculated  for several wavelengths from the Klein-Nashina formula:  39  87\e  +  3TT\C  Z  •1 4  1 + oe <  [ e(i + oL„)  0  L 1 + Zoc,  *1  j _ J _ ( L ( l + 2oc^ a  aoc  where e i s the electronic  0  l+3oc  0  (l+2ccj  i  a  charge  m i s the mass of the electron c i s the velocity of l i g h t and and  a  0  =  7TIC  ^where h i s Planck's constant  i s the frequency of the incident  radiation.  The values of (3^ for wavelengths of interest are plotted i n figure 13. To determine the mass absorption c o e f f i c i e n t of each a l k a l i metal borohydride the calculated mass absorption coefficient of each particular element in the compound was used in the r a t i o of i t s mole f r a c t i o n .  For example, the  mass absorption coefficient of KBH^ i s given by:  KBK  54.5  The mass absorption c o e f f i c i e n t s f o r the a l k a l i metal borohydrides have been tabulated f o r several i n Table 5.  wavelengths  TABLE 4 MASS ABSORPTION COEFFICIENTS OF SELECTED ELEMENTS Wavelength i n ftngstroma 0.250 0.260 0.270 0.280 0.290 0.300 0.320 0.340 0.360 0.3 SO 0.400 0.420 0.440 0.460 0.480 0.500 0.520 0.540 0.560 0.5S0 0.600 0.700 0.800 0.900 1.000 1.100 1.200 1.300 1.400 1.500  H  Li  Be  B  C  N  0  0.336 0.339 0.342 0.345 0.347 0.349 0.351 0.353 0.355 0.35S 0.360 0.361 0.362 0.364 0.365 O.366 0.367 0.368 0.369 0.371 0.373 0.379 0.335 O.389 0.393 0.400 0.407 0.415 0.424 0.434  0.14S 0.150 0.152 0.153 0.155 0.156 0.158 0.160 0.162 O.I64 0.166 0.168 0.170 0.173 0.175 0.17S 0.180 0.184 0.186 0.190 0.194 0.214 0.242 0.274 0.315 O.366 0.426 0.496 0.577 0.672  O.I56 0.157 0.159 0.161 0.163 0,166 0.169 0.172 0.176 0.179 0.184 0.188 0.192 0.197 0.202 0.209 0.214 0.221 0.228 0.236 0.245 0.293 0.356 0.434 0.533 0.653 0.799 0.969 1.17 1.39  0.167 0.170 0.172 0.174 0.177 0.179 0.184 0.189 0.194 0.200 0.206 0.213 0.220 0.228 0.236 0.246 0.255 0.267 0.27S 0.290 0.304 O.3S3 0.486 0.618 0.781 0.982 1.22 1.50 1.83 2.21  0.188 0.191 0.195 0.198 0.203 0.207 0.215 0.224 0.234 0.245 0.257 0.271 0.285 0.300 0.316 0.335 0.354 0.376 0.39S 0.432 0.44S 0.605 0.811 1.07 1.40 1.80 2.28 2.84 3.50 4.42  0.201 0.207 0.213 0.220 0.226 0.231 0.244 0.25S 0.274 0.292 0.311 0.332 0.355 O.38O 0.408 0.437 0.470 0.504 0.542 0.582 0.625 0.884 1.23 1.66 2.21 2.87 3.67 4.60 5.69 6.95  0.219 0.228 0.235 0.243 0.252 0.261 0.280 0.302 0.326 0.353 O.383 0.415 0.451 0.490 0.532 0.577 0.627 0.680 0.73S 0.799 0.865 1.26 1.79 2.56 3.30 4.33 5.56 8.66 10.6  TABLE 4 continued  Waivelength i n Angstroms 0.250 0.260 0.270 0.280 0.290 0.300 0.320 0,340 0.360 0.380 0.400 0.420 0.440 0.460 0.480 0.500 0.520 0.540 0.560 0.580 0.600 0.700 0.800 0.900 1.000 1.100 1.200 1.300 1.400 1.500  F 0.229 0.239 0.249 0.259 0.271 0.283 0.309 0.339 0.372 0.409 0.450 0.494 0.544 0.597 0.656 0.719 0.787 0.861 0.940 1.02 1.12 1.66 2.26 3.33 4.48 5.89 7.59 9.56 11.9 14.5  Na 0.294 0.312 0.331 0.351 0.372 0.395 0.444 0.500 0.562 0.632 0.709 0.793 0.886 0.987 1.10 1.22 1.34 1.49 1.64 1.80 1.97 3.02 4.40 6.16 8.35 11.0 14.2 17.9 22.2 27.2  Al 0.388 0.417 0.448 0.482 0.518 0.557 0.640 0.734 0.839 0.957 1.09 1.23 1.39 1.56 1.75 1.95 2.17 2.41 2.66 2.93 3.23 4.99 7.32 10.2 13.9 18.4 23.7 29.9 37.0 45.2  S 0.608 0.664 0.722 0.788 0.855 0.929 1.09 1.28 1.48 1.71 1.96 2.24 2.51 2.86 3.21 3.61 4.04 4.50 4.99 5.41 6.07 9.47 13.9 19.5 26.5 34.9 44.9 56.4 69.9 85.O  CI 0.675 0.741 0.810 0.886 0.966 1.05 1.24 1.45 1.69 1.95 2.24 2.57 2.92 3.31 3.73 4.18 4.67 5.20 5.77 6.38 7.03 11.0 16.1 22.6 30.6 40.4 52.0 64.9 80.5 97.5  K 0.907 1.00 1.10 1.21 1.32 1.44 1.72 2.02 2.36 2.74 3.16 3.62 4.13 4.68 5.28 5.93 6.63 7.39 8.20 9.07 10.0 15.6 22.9 32.0 43.3 56.8 72.8 91.1 112. 136.  TABLE 4 continued Wavelength i n Sngstroma 0.250 0.260 0.270 0.280  0.290 0.300 0.320 0.340  O.36O  0.380  0.400 '  0.420  0.440 O.46O  0.480  0.500 0.520 0.540 0.560 0.580 0.600 0.700 0.800 0.900 1.000 1.100 1.200  1.300 1.400  1.500  Rb 5.20  5.82 6.45  7.14 7.87 8.65 10.4 12.2 14.3 16.6 19.2 21.9 24.8 28.0 31.4 35.0  38.9  43.0 47.3 51.8 56.6 83.7 116. 22.6  30.8 40.4 52.0 65.1 80.5 98.0  Gs  Br  I  14.3 15.8 17.5 19.2 20.9 22.7  4.50  13.2 14.6 16.1 17.7 19.3 21.1 24.9 28.9 33.2 6.65 7.72 8.86 10.2 11.6 13.1 14.8 16.5 18.4 20.3 22.3 24.5 37.8 55.9 77.6 100. 130. 165. 202.  26.6 30.8  6.38 7.43 8.60 9.2 11.3 12.7 14-6  I6.4  18.2 20.2 22.4 24.8  27.2  41.9 6O.7 83.0 ill. 143. 181. 222. 268. 317.  5.02 5.58 6.18 6.80 7.48 8.72 10.6 12.5 14.5 16.7 19.1 21.7  24.6 27.6  30.8 34.2 38.0 41.7 46.0 50.2 75.0 105. 139. 20.5 27.0 34.7 43.5 53.9  65.6  245. 305.  6-6CH  — i  0.6  1  0.8  1  J.O  WAVELENGTH  (A)  1  1  1  1.2  1.4  1.6  i  1.8  TABLE 5 MASS ABSORPTION OF THE ALKALI METAL BOROHYDRIDES Wavelength i n fingstroms 0.250 0.260 0.270 0.280 0.290 0.300 0.320 0.340 0.360 0.380 0.400 0.420 0.440 0.460 0.4S0 0.500 0.520 0.540 0.560 0.5S0 0.600 0.700 0.800 0.900 1.000 1.100 1.200 1.300 1.400 1,500  LiBH  4  0.193 0.195 0.197 0.199 0.201 0.203 0.206 0.210 0.214 0.218 0.222 0.226 0.230 0.235 0.240 . .0.246 0.252 0.259 0.266 0.274 0.282 0.328 0.390 0.468 0.560 0.675 0.817 0.976 1.17 1.40  NaBH^ 0.262 0.274 0.287 0.300 0.313 0.328 0.354 0.396 0.434 0.47S 0.528 0.57S 0.639 0.703 0.774 O.850 0.924 1.02 1.12 1.21 1.32 1.9S 2.85 3.96 5.34 7.00 9.00 11.4 14.1 17.2  KBH  4  0.716 O.784 O.856 0.940 1.02 1.11 1.31 1.53 1.77 2.06 2.37 2.71 3.06 3.46 3.S9 4.37 4.S8 5.41 6.01 6.66 7.34 11.4 16.7 23.3 31.6 41.3 53.0 66.3 81.5 99.0  RbBH^ 4.47 5.02 5.54 6.13 6.77 7.43 8.88 10.48 12.3 14.2 16.4 18.7 21.2 24.0 26.9 29.9 33.2 36.8 40.4 44.2 4S.4 71.5 9S.6 19.3 26.2 34.3 44.2 55.4 68.3 83.2  CsBH^ 12.9 14.2 15.7 17.2 18.8 20.4 23.9 27.7 5.74 6.67 7.72 8.26 10.1 11.4 13.1 14.7 16.3 18.2 20.1 22.3 24.4 37.s 54.5 74.6 100. 129. 163. 200. 241. 285.  NaB(0) 0.185 0.188 0.193 0.197 0.202 0.206 0.215 0.226 0.238 0.252 0.265 0.310 0.327 0.34S 0.368 0.394 0.418 0.444 0.476 0.514 0.540 0.745 1.02 1.23 1.63 2.10 2.% 3.66 4.52 5.64  4  45  In order to determine the energy that i s absorbed i n a sample of the i r r a d i a t e d substance, one must have, besides the attenuation factors, a knowledge of the output intensity o f the source.  For a given voltage drop across  the X-ray tube a d i s t r i b u t i o n of wavelengths of varying i n t e n s i t y i s obtained with the shortest wavelength being expressed by the Duane and Hunt Law: A =^rJ p  K - 12.39  where Ap i s the minimum wavelength occurring i n the d i s t r i b u t i o n and y  i s the tube voltage i n k i l o v o l t s .  K has  been shown to be —|p where the symbols have t h e i r usual meaning. Providing the voltage drop i s not great enough to produce c h a r a c t e r i s t i c radiation from the target (69 k i l o v o l t s for the K series of tungsten), the d i s t r i b u t i o n o f i n t e n s i t y of the radiation i s continuous.  Experimental and  t h e o r e t i c a l studies of the d i s t r i b u t i o n o f t h i s continuous radiation or bremsstrahlung have recently been published by Wang (34) and by Jennings (35) f o r sources s i m i l a r to those used i n t h i s work.  The r e s u l t s of Wang show that the  d i s t r i b u t i o n f o r the Machlett OEG-60 W target tube shows considerable L series of tungsten superimposed on the bremsstrahlung.  As considerable aluminum f i l t r a t i o n has  been used i n the experimental work reported i n t h i s t h e s i s , the c h a r a c t e r i s t i c radiation was assumed t o be completely attenuated before reaching the samples of borohydride.  46  When a l t e r n a t i n g high t e n s i o n i s a p p l i e d across the X-ray tube, t h e i n t e n s i t y o f X-rays, f o r a given wavel e n g t h , v a r i e s w i t h time and thus an average i n t e n s i t y f o r each wavelength must be used i n the dosimetry c a l c u l a t i o n . De Waard (36)  has c a l c u l a t e d the i n t e n s i t y d i s t r i b u t i o n i n  continuous Xi-ray spectra corresponding t o d i f f e r e n t forms o f high t e n s i o n .  In the present work, use was made o f  de Waard s formula f o r s i n g l e phase a l t e r n a t i n g current 1  which i s :  where  i s the average i n t e n s i t y o f the r a d i a t i o n produced  at wavelength \ , L, i s the p r o p o r t i o n a l i t y constant, 2 i s the current through the X-ray tube, Ap i s the minimum wavel e n g t h corresponding t o the peak value o f the voltage ( f o r 50 k i l o v o l t s ,  A p i s 0.254 Sngstroms).  Q^*  i s a composite  f u n c t i o n defined by the f o l l o w i n g expression.  67 = £|siTlJ<-jJeOS0) where cos 0 = -^g.  A  B# as a f u n c t i o n o f cos 0 has been  p l o t t e d i n f i g u r e 14. Table 6 g i v e s the values o f cos 0 f o r various wavelengths o f r a d i a t i o n generated at 50 kilovolts.  The Sommerfeld f i n e s t r u c t u r e constant, oc , Q  used i n the Klein-Nashina formula has a l s o been i n c l u d e d in this table.  TABLE 6 COSINE 0 = - ^ e FOR 50 KVP AND THE SOMMERFELD FINE STRUCTURE CONSTANT, ©Co - —  WC  Wave Length  I  Cos 0  0.248 0.250 0.260 0.270 0.280 0.290 0.300 0.320 0.34© 0.360 0.380 0.400 0.420 0.440 0.460 0.480 0.500 0.520 0.540 0.560 0.580 0.600 0.620 0.640 0.660 0.680 0.700 0.720 0.740  1.000 0.992 0.954 0.918 0.886 0.855 0.827 0.775 0.729 0.689 0.653 0.620 0.590 0.564 0.539 0.517 0.496 0.577 0.459 0.443 0.428 0.413 0.400 O.388 0.376 0.365 0.354 0.344 0.335  Wave Length 0.097 0.096 0.093 0.089 0.086 0.083 0.080 0.075 0.071 0.067 0.063 0.060 0.057 0.055 0.052 0.050 0.048 0.046 0.044 0.043 0.041 0.040 0.039 O.O38 0.036 0.035 0.034 0.033 0.032  AT VARIOUS WAVELENGTHS 1  %  Cos 0  Ot  0.760 O.78O 0.800 0.820 0.840 0.860 0.880 0.900 0.920 0.940 O.96O 0.980 1.000 1.020 1.040 1.060 , 1.080 1.100 1.120 1.140 1.160 1.180 1.200 1.220 1.240 1.260 1.280 1.300 1.400  0.326 0.318 0.310 0.302 0.295 0.288 0.282 0.276 0.270 0.264 0.258 0.253 0.248 0.243 0.238 0.234 0.230 0.225 0.221 0.218 0.214 0.210 0.207 0.203 0.200 0.197 0.194 0.191 0.177  0.032 0.031 0.030 0,029 0.029 0.028 0.027 0.027 0.026 0.026 0.025 0.024 0.024 0.024 0.023 0.023 0.022 0.022 0.021 0.021 0.021 0.020 0.020 0.020 0.019 0.019 0.019 0.018 0.017  0  Wave Length  I  Cos 0  1.500 1.600 1.700 1.800 1.900 2.000 2.100 2.200 2.300 2.400 2.500 2.600 2.700 2.800 2.900 3.000 3.100 3.200 3.300 3.400 3.500 3.600 3.700 3.800 3.900 4.000  0.165 0.155 0.146 0.138 0.131 0.124 0.118 0.113 0.108 0.103 0.099 0.095 0.092 0.089 0.086 0.083 0.080 0.078 0.075 0.073 0.071 0.069 0.067 0.065 0.063 0.062  0.016 0.015 0.014 0.013 0.013 0.012 0.011 0.011 0.010 0.010 0.010 0.009 0.009 0.009 0.008 0.008 0.008 0.008 0.007 0.007 0.007 0.007 0.006 0.006 . 0.006 0.006  49  Figure 15 (1) shows the d i s t r i b u t i o n of  intensity  for X-rays generated by 50 k i l o v o l t single phase r e c t i f i e d alternating current at a constant current i  •  was 28 milliamps i n a l l i r r a d i a t i o n experiments.  The current Attenua-  t i o n of the source by inherent f i l t r a t i o n and by beryllium windows has been taken into account.  Measurement of the  area under t h i s curve gives a quantity proportional to the rate of energy output of the tube,  i.e.,  A calorimetric determination of the actual output of the 0EG-60 tube fixed the value of L i i n the de Waard formula and thus related the area under curve 1, figure 15, to the absolute rate of energy output of the tube. Other graphs i n figure 15 show i n t e n s i t y d i s t r i b u tions after f i l t r a t i o n by various thicknesses of aluminum used i n conjunction with the radiation vessel for chemical decomposition studies.  As the rate of energy output of  the OEG-60 tube (represented by the area under curve 1) has been determined in absolute u n i t s , the absolute intens i t y transmitted through each of the aluminum f i l t e r s d i r e c t l y proportional to the area under each of the representing a different amount of f i l t r a t i o n . were determined by mechanical i n t e g r a t i o n . c a l i b r a t i o n i s discussed i n Chapter I I I .  is  curves  These areas  The calorimetric  ENERGY DISTRIBUTION OF B R E M S S T R AHLUNG A T 5 0 KVP.,SINGLE PHASE PULSED D . C  W A V E L E N G T H (A)  51  III. The f i r s t  EXPERIMENTAL  s t e p t a k e n i n t h i s w o r k was t h e  t i o n o f the a l k a l i metal borohydrides suitable for radiation  studies.  used i n the p r e l i m i n a r y  solvent  availability  and s t a b i l i t y .  are h y d r o l i s e d  i n a pure  s t u d i e s because o f  Since a l l the  of those  state  Potassium borohydride  studied.  solvents.  The  borohydrides  The p u r i f i e d b o r o h y d r i d e s  by a periodate t i t r a t i o n method. used as a c r i t e r i o n of  its  solvents  o f r u b i d i u m and c e s i u m were p r e p a r e d b y m e t a t h e s i s in suitable  was  borohydrides  i n aqueous s o l u t i o n , non-aqueous  formed t h e m a j o r i t y  prepara-  reactions  were  assayed  I n f r a - r e d s p e c t r a were  purity.  C a l o r i m e t r i c d e t e r m i n a t i o n of the energy f l u x  from  t h e OEG-60 X - r a y t u b e was c a r r i e d o u t a s a p r e l i m i n a r y f o r more q u a n t i t a t i v e for  l a t e r work.  step  The vacuum s y s t e m u s e d  c o l l e c t i n g and m e a s u r i n g s m a l l amounts o f  products  also  gaseous  r e s u l t i n g from r a d i a t i o n induced c h e m i c a l changes  was c a l i b r a t e d .  Chapter  IV g i v e s t h e r e s u l t s  c a l i b r a t i o n work. Infra-red, spectra of  single  of  this  ' visible,  and u l t r a v i o l e t  crystals or  absorption  pressed p e l l e t s of the  h y d r i d e s were examined i n an a t t e m p t t o d e t e r m i n e t h e of products r e s u l t i n g  from X - r a y a b s o r p t i o n .  resonance s p e c t r a of potassium borohydride  borokind  Paramagnetic  were a l s o  taken.  52  The mass spectrum of gaseous products evolved during the i r r a d i a t i o n of potassium borohydride was examined.  Infra-  red spectra of solids were obtained by the K Br p e l l e t technique. A.  The Preparation of A l k a l i Metal Borohydrides 1.  Solvent Studies with Potassiuip Borohydride Although the chemical l i t e r a t u r e (37)  lists a  number of solvents f o r potassium borohydride, none mentioned was found suitable f o r producing crystals to be used i n the radiation studies.  Either the solvents reacted (e.g.,  CH^OH) or the s a l t showed i n s u f f i c i e n t s o l u b i l i t y .  HgO,  The  search f o r a good solvent f o r potassium borohydride was also expected to solve the problem of producing the p u r i f i e d rubidium and cesium s a l t s .  The solvents were tested i n most  cases by placing a small amount of the potassium s a l t i n 5 ml of the reagent grade solvent.  I f the s a l t was unaffected,  the solvent was warmed on a steam bath. the r e s u l t s .  Table 7 summarizes  Unsym.-Dimethylhydrazine was prepared by the  method of Fischer ( 3 8 ) . by Folpmer's method  Sym.-Dimethylhydrazine  was obtained  (39)•  Water made a l k a l i n e with potassium hydroxide, anhydrous l i q u i d ammonia and hydrazine hydrate (85%) to be the most promising.  proved  However, each had disadvantages:  the aqueous caustic solution and the hydrazine hydrate  53  TABLE 7 SUMMARY OF SOLVENT STUDY Solvent Water Water made basic with KOH HoO—KOH—glycerol Glycerol Ethylenediamine Isopropylamine N-butylamine N-methylformamide N,N—dimethylformamide Acetone Methyl Alcohol E t h y l Alcohol Pyridine Piperidine Dioxane Liquid ammonia 85$ hydrazine hydrate Anhydrous hydrazine Sym-dimethylhydrazine Unsym-dimethylhydrazine Liquid s u l f u r dioxide Liquid S 0 + Thionylchloride 2-aminoethanol Diethanolamine Tetrahydro furan Fur an 2  Remarks on Solvent  Suitability  Poor; considerable decomposition over a long period. Good. Poor. Insoluble. Insoluble i n cold; s l i g h t s o l u b i l i t y i n warm. Insoluble. Insoluble. Insoluble. Insoluble. Insoluble. Poor, considerable reaction. Considerable r e a c t i o n . Insoluble. Insoluble. Insoluble. Good. Soluble; slow hydrolysis. Good; 28.3 gm KBH4/IOO gm N2H/. at 18.5° C S l i g h t l y soluble. S l i g h t l y soluble. S l i g h t s o l u b i l i t y at b. pt.; only slight reaction. Vigorous reaction. Slight r e a c t i o n . Considerable r e a c t i o n . Insoluble. Insoluble.  54  showed extensive hydrolysis over the long periods required for crystallization, and liquid ammonia was found difficult to handle as a crystallizing solvent. Several attempts to grow crystals from liquid ammonia were unsuccessful. In the case of hydrazine hydrate, the solutions were evaporated over concentrated sulfuric acid in an evacuated desiccator, the insoluble hydrazine sulfate being easily recovered from the acid. As a result of the preliminary work with hydrazine hydrate, i t seemed promising to try anhydrous hydrazine because of its water-like properties and its basic character. The use of this material was delayed approximately one year during which time little progress was made in the purification and crystallization of the borohydrides. Anhydrous hydrazine was investigated as a solvent after the vacuum system and auxiliary equipment was constructed to handle this easily oxidizable material. The solubility of potassium borohydride in anhydrous hydrazine at 1S.5° C was found to be 2S.3 gm/100 gm N2R4 (solubility of KBH4 in liquid ammonia at 30° C. is 20 gm/100 gm solvent and in water at 20° G. is 19.3 gm/100 gm H 2 O ) .  No decomposi-  tion of the salt was noted even after two weeks in this solvent. The potassium salt did not appear to form a hydrazinate at the temperature studied whereas a very stable ammoniate was revealed by the infra-red spectra of material obtained from liquid ammonia. Figures 16 and 17 show the infra-red spectra of ammonia gas and hydrazine,  55  respectively, f o r reference purposes.  The i n f r a - r e d  spectra of potassium borohydride extracted w i t h l i q u i d ammonia i s shown i n figure 18.  The i n f r a - r e d spectra  of the material extracted with anhydrous hydrazine i s shown i n figure 20. of the commercial  Examination of the i n f r a - r e d spectra  s a l t (Metal Hydrides Corp., 97$ minimum  purity) revealed the presence of the ammoniate.  The i n f r a -  red spectra of t h i s material i s shown i n figure 19» 2,  Preparation of A l k a l i Metal Borohydrides The following four points were the guiding p r i n c i p l e s  used i n developing a method of preparing the i o n i c borohydrides suitable f o r the r a d i a t i o n studies: a) The borohydrides would be prepared by a simple method involving an intermediate borohydride which could be obtained e a s i l y i n high y i e l d and i n high purity from the commercial  potassium  salt. b) The cation of the intermediate borohydride must be e a s i l y exchanged f o r an a l k a l i metal cation i n a metathesis reaction. c) The p u r i f i c a t i o n of the product borohydride must be stringent yet simple. d) The synthetic method would depend to a large extent on the s o l u b i l i t y properties of the borohydrides i n various solvents p a r t i c u l a r l y non-aqueous.  AMMONIA  4000 3000  2000  gas phase  fig.  1500  0.0  j  i  i  i  1000  CM-i i  •  900  16  800  700  i  .10 £20 < £.30 O £40 <50 .60 .70 1.0 oo  7 8 9 10 WAVELENGTH (MICRONS)  HYDRAZINE 4000 3000 J " * •.' ' 0.0 null. 1  .10 £20 <  liquid film  2000  . i .i . i•  1500  i , -1 L. 1  '  ") h  V  \  1  S.30 \  CM-i  1000  J  12  900 /  \  / 1  \\  1  13  14  15  fig. 17 800 700 11 \ 11111• 1  •  /  /  /  1  1  O £.40 <50 .60 .70  11  Tf  A  /r  VJ  1.0 oo  7 8 9 10 WAVELENGTH (MICRONS)  K BH4 4000 3000  11  12  u  ' 137m  13  14  15  13  14  15  extracted with liquid N H* 2000  1500  CM-T  1000  900  7 8 9 10 11 WAVELENGTH (MICRONS)  12  |<BH4 4000 3000  commercial material 2000 1500 CM-i  O.OF  kM^l  .10t  /  I  I  1  1 \  1000  L  T  £.30i l — 1 — — O , £40f <50 .60 f •70[  J  /  1 / 1 1 1  M M / 1 1 1I I I I \ 1/  w.20  fig. 19 800  900  H 1 1 1  700  J  ^  1  1 ——  1I I I I I I I I  1  l.of WAVELENGTH (MICRONS) f<BH4 4000 3000 0.0  extracted with anhydrous N2 H4 2000 1500 CM-' 1000 • 11•. 1. 1 . • • •  .10  \ \ £.30 O  —« w  /  \\ //  /  \/  If f  2-40  .1  L-— l 1—  /  /  V  fig. 2 CD 800 700  900 111  V  <50 .60 .70 1.0 *—1 1  •i1  i<CH) X 33  4000 3000 0.0  1500  2000  .10 iu U.20  1.30  O £40 <50 .60 70  1.0  5> 10 l WAVELENGTH (MICRONS)  r  >  <  <*-  \I  1000  CM-i  /  A rJ I  /  12  11  900  \  V  13  fig. 800  2li  700  y (  f 1 y 1 V1  r—  -  \i  14  f IFESAU2E2  ~->  5S  A discussion on "onium" s a l t s by H, G. Heal (40) suggested suitable cations which could possibly be used as borohydrides f o r intermediates i n metathesis reactions to obtain the a l k a l i metal borohydrides.  Thus, the ease with  which s a l t s containing the trimethylsulfonium ion, (CR^^S*, can be decomposed when combined with anions of high p o l a r i z ing power was the b a s i s of the following attempted method: S ( C H ) 3 BH " +  3  4  130°  + RbF  •  RbBH + S ( C H ) 4  3  2  + CH3F  When a mixture of the sulfonium borohydride and rubidium f l u o r i d e ( i n s l i g h t excess) was pyrolized i n vacuum, a very fast reaction occurred at approximately 1300 C. with large quantities of (CB^^S being l i b e r a t e d . The I.R. spectrum of the product i s shown i n figure 2 3 . This spectrum shows the presence of 8 small amount of borohydride with larger quantities of an u n i d e n t i f i e d m a t e r i a l . The pyrolysis was done by heating the sample tube (connected to a vacuum l i n e ) with a small e l e c t r i c furnace controlled by a variable transformer.  Temperatures were measured with  a copper constantin thermocouple.  Pyrolysis of a s i m i l a r  mixture was done i n a i r on a sand bath.  A fast reaction  occurred at a s l i g h t l y lower temperature of approximately 90° C,  The vapor above the mixture, upon reaction,  spontaneously ignited with a b r i l l i a n t green flame i n d i c a t ing the possible presence of boron hydrides i n the gas.  ^CH )3BH4 4000 3000 2000 0.0  fig. 22 800 700  3  -A  .10  —^  / I  UJ  /  Y  £.30 O 2-40 ^50 .60 JO 1.0  1500  \  \ h  /  >  CM-i  /  f  >  1000 900  \  / i  1/  L  L u i  FTJ?JUS  WAVELENGTH (MICRONS) product from vacuum pyrolysis 4000 3000 2000 1500 CM-i . 1.1.. 0.0 uuklull. ——». pJ—L_l. 1  \ / / "20 V \  ]V/ \  /  .10  UJ  \  \  Y  £.30 O 2-40  \\ r  r \\ 1  1000 J  .  XUjJ  900 '"1  /  \ A  "~  fig. 23 800 700  • -l jJ L  \  —  \  \ J/  .50  <  .60 JO 1.0 FT17  -IF  WAVELENGTH (MICRONS) I  product from air pyrolysis 4000 3000 2000 1500 _i 1 . 1 0.0  |  CM-i  1000  fig. 24 800 700 i 1  900 1ll  .10  r  "20  \  !  £.30 O £40 <50 .60 .70 1.0  \  1 \  / \  5  ii  f  j  \  8 9 i0 11 WAiVELENC5TH (MlCRC)NS)  r  >  /  1I  H  -A j  /  1\  I2  i3  14  15  In one t r i a l t h i s flame jumped approximately two feet i g n i t i n g a large batch of mixed sulfonium borohydride and rubidium f l u o r i d e .  The I.R. spectrum of the product  from the a i r pyrolysis i s given i n figure 24. Both products showed considerable reducing power with a l k a l i n e permanganate and l i t t l e f l u o r i d e was detectable. Since the p y r o l y s i s reaction of the sulfonium borohydride was o f l i t t l e value i n the preparation of a l k a l i metal borohydrides, the possible use o f such an onium salt for metathesis reactions i n solution was considered next.  Depending on the kind of a l k a l i metal s a l t  available, two d i f f e r e n t reactions involving the sulfonium borohydride were developed.  Rubidium carbonate was  converted to the reineckate which i n turn was dissolved in a concentrated aqueous ammonia solution containing the onium borohydride.  After removing the precipitated t r i -  methylsulfonium reineckate the rubidium borohydride was i s o l a t e d by lyophilyzing the ammoniacal solution. The sequence of reactions followed i n the preparation o f rubidium borohydride i s given by the following outline of equations: 2NH [Cr (CNS) 4  4  (NH ) J 3  2  + Rb C0 2  >  3  R 0;65°C 2Rb [ Cr (CNS) 2  + NHo  + C0  o  4  (NH ) J 3  2  61  Rb[cr (CNS)  (NH ) ]  4  3  2  + S(CH ) 3  + BH " 4  where R = [cr  (CNS)  4  3  BH  4  cold, cone  + S (CH ) 3  3  NH  4 .Rb+ 0H  R  (NH ) ] 3  2  Cesium borohydride was conveniently prepared from cesium hydroxide.  The stoichiometric amount of the  sulfonium borohydride was dissolved i n a minimum amount of N,N—dimethylformamide and t h i s solution was then added to a concentrated methanol solution of the cesium hydroxide. On cooling the mixture i n dry i c e , cesium borohydride precipitated from the s o l u t i o n . Other onium borohydrides could possibly serve as a suitable intermediate such as the quaternary ammonium borohydrides reported by Banus (41).  However, these  latter  borohydrides appear to have a f a i r l y high thermal s t a b i l i t y which i s a disadvantage i n the preparation of pure a l k a l i metal borohydrides.  Heating the prepared a l k a l i metal  borohydrides from a sulfonium metathesis reaction to a temperature  of 130° C. serves to decompose any occluded  sulfonium compounds converting them to v o l a t i l e  or l i q u i d  ammonia insoluble products. Following a b r i e f heat treatment to decompose any occluded sulfonium compounds, the crude a l k a l i metal borohydride was extracted with l i q u i d ammonia i n the special metathesis vessel described i n Chapter I I , Section C.  62  With some of the extracted borohydrides i t was  necessary  to pump under vacuum f o r considerable time (approximately 24 hours) i n order to remove ammonia completely from the solid.  In some cases the extracted borohydride was  further*  treated with anhydrous hydrazine i n the metathesis v e s s e l . In contrast to the tendency to form f a i r l y stable ammoniates, the borohydrides of potassium, rubidium, and cesium did not appear to occlude hydrazine i n the l a t t i c e  at room  temperature. 2.1.  The Synthesis of Trimethylsulfonium Borohydride Trimethylsulfonium borohydride was prepared by the  following series of steps: a)  l  (CH ) S + CH r 3  2  *.S (CH ) I+  3  3  3  i£°-^S(CH ) F  b)  S ( C H ) I + AgF  c)  S ( C H ) F + KBH  a.  The Synthesis of Trimethylsulfonium Iodide Methyl  3  3  3  3  3  4  iodide (28.4 gms;  +  3  +  Agl  S(CH ) 3  3  BH  4  1/5 mole, Eastman white l a b e l )  and dimethyl s u l f i d e (12.4 gms;  1/5 mole, Eastman  white l a b e l ) were mixed i n a 50 ml volumetric flask and the r e s u l t i n g mixture cooled by packing the f l a s k i n a Dewar vessel with i c e . The Dewar vessel with the mixture was placed on a shaker set at a f a i r l y slow motion and shaken f o r 12 hours.  63  The excess reactants were then allowed to evaporate and the s o l i d onium n  of water.  n  s a l t was dissolved i n 5 0 mis  Although the heat of t h i s reaction i s  not large, i t i s advisable to cool the mixture of a l k y l sulfide and a l k y l iodide because of the v o l a t i l e and abnoxious nature of these reactants. The y i e l d was quantitative. Figure 21 shows the I.R.  spectrum of trimethylsulfonium iodide  r e c r y s t a l l i z e d from anhydrous methanol.  The  p u r i f i e d material sublimed at 213° C. (uncorrected), l i t e r a t u r e ( 4 2 ) melting point, 20$°-213° C. b.  The Preparation of Trimethylsulfonium Fluoride A s i l v e r f l u o r i d e solution was f i r s t prepared by dissolving s i l v e r n i t r a t e (170 gms;  1 mole) i n  a minimum amount of cold water (approximately 150 ml). Sodium bicarbonate (100 gms;  1.25 moles) was dissolved  i n 5 0 0 ml of water i n a 1000 ml beaker.  The  silver  n i t r a t e solution was added slowly with s t i r r i n g to the bicarbonate solution and the yellow p r e c i p i t a t e of s i l v e r carbonate washed three times by decantation using 200 ml portions of d i s t i l l e d water.  The  precipitate of s i l v e r carbonate was transferred to a 600 ml polyethylene beaker and hydrofluoric acid (k&f°) c a r e f u l l y added u n t i l the yellow precipitate was almost completely dissolved. The mixture  was  l e f t one-half hour to complete the reaction and then  f i l t e r e d to remove insoluble material.  The s i l v e r  f l u o r i d e solution was stored i n the dark. S i l v e r f l u o r i d e solution was added to the sulfonium iodide (obtained i n Section 2.1a)  until  S i l v e r iodide was just completely p r e c i p i t a t e d . The mixture was then f i l t e r e d to remove s i l v e r iodide and the f i l t r a t e saturated with hydrogen s u l f i d e to remove excess s i l v e r i o n .  The p r e c i p i -  tate of s i l v e r s u l f i d e was f i l t e r e d out. f i l t r a t e was evaporated under vacuum at 60° a volume of 30 ml.  The C. to  The concentrated solution of  sulfonium f l u o r i d e was f i l t e r e d again, the f i l t e r paper being washed with a minimum amount of water. The remaining water i n the sulfonium f l u o r i d e solution was removed by freeze-drying ( l y o p h i l i z a tion).  Because of the extreme hygroscopic nature  of t h i s f l u o r i d e , i t was necessary to store i t i n a vacuum desiccator over  P2O5 and  to handle i t i n  a dry box. The Preparation of Trimethylsulfonium Borohydride. To the trimethylsulfonium f l u o r i d e obtained i n Section 2.1b  ( i t remained s l i g h t l y damp a f t e r  l y o p h i l i z a t i o n ) was added potassium borohydride (10  gms)  and the two reactants mixed well i n the  f l a s k f o r 15 minutes.  The mixture was l e f t over-  night i n the f l a s k which was l i g h t l y covered with  a beaker.  The sulfonium borohydride was then  extracted from the mixture with four 15 ml portions of N,N—dimethylformamide.  The solvent was removed  from the extract by vacuum evaporation at room temperature.  The crude sulfonium borohydride was  f i n a l l y extracted with l i q u i d ammonia i n the metat h e s i s vessel shown i n Plate I (p. 32) to obtain a f a i r l y pure product.  The assay of two samples o f  t h i s material i s l i s t e d i n Table 8.  The y i e l d was  6.2 grams or 35 per cent of the t h e o r e t i c a l y i e l d based on the amount of dimethylsulfide used i n Section 2.1a.  The I.R. spectrum of the p u r i f i e d  material i s shown i n figure 22.  Trimethylsulfonium  borohydride i s very soluble, without reaction, i n anhydrous l i q u i d ammonia, anhydrous hydrazine, and N,N—dimethylformamide.  I t i s only s l i g h t l y soluble  i n dioxane or n-butylamine.  This borohydride i s  r a p i d l y hydolysed i n aqueous solution. 2.2.  The Preparation of Rubidium Borohydride Rubidium borohydride was prepared v i a the reineckate  by the sequence of reactions outlined above. a.  The Synthesis of Rubidium Reineckate The method o f Palmer (43) was used to prepare ammonium reineckate. To ammonium reineckate (1G gms  0.025  mole) was added rubidium carbonate  0.030  mole) i n 25 ml of water.  (5 gms;  The mixture was  TABLE 8 ASSAY OF SOME OF THE IONIC BOROHYDRIDES Material  Source  Purity  Potassium B o r o h y d r i d e  Commercial m a t e r i a l Sample #1  95.6%  Potassium Borohydride  Commercial m a t e r i a l Sample #2  93.8%  Potassium Borohydride  R e c r y s t a l l i z e d from l i q u i d NH3 Sample #1  98.2%  Potassium Borohydride  R e c r y s t a l l i z e d from l i q u i d NH  Sample #2  97.6%  Potassium Borohydride  R e c r y s t a l l i z e d from anhydrous ^ H ^ Sample #1  98.7%  Potassium Borohydride  Recrystallized  from anhydrous N H^ Sample #2  97.8%  Potassium Borohydride  R e c r y s t a l l i z e d from aqueous KOH Sample #1  88.8%  Potassium Borohydride  R e c r y s t a l l i z e d from aqueous KOH Sample #2  88.9%  T r i m e t h y l s u l f o n i u m Borohydride  Recrystallized  from l i q u i d NH3 Sample #1  100.2%  T r i m e t h y l s u l f o n i u m Borohydride  R e c r y s t a l l i z e d from l i q u i d NHj Sample #2  98.0%  3  2  ON ON  67 heated to 50° C. f o r one hour while a stream o f a i r was bubbled through i t to remove ammonia and carbon dioxide.  I t was then allowed to cool to  room, temperature and the precipitate o f rubidium reineckate f i l t e r e d out.  The r e s u l t i n g crude  rubidium reineckate was r e c r y s t a l l i z e d by d i s s o l v ing i t i n 100 ml of water at 60° C , f i l t e r i n g the hot solution, cooling the f i l t r a t e i n i c e and c o l l e c t i n g the fine c r y s t a l l i n e p r e c i p i t a t e on a Buchner funnel.  The product was f i n a l l y a i r dried  at room temperature.  The infra-red spectra o f  ammonium reineckate and rubidium reineckate are shown i n figures 25 and 26, respectively.  The I.R.  spectrum of ammonium iodide i s shown i n figure 27 for purposes of comparison.  The reineckates are  only s l i g h t l y soluble i n cold water, but are very soluble i n l i q u i d ammonia, anhydrous hydrazine and N,N—dimethylformamide. b.  The Preparation of Rubidium Borohydride by Metathesis Rubidium reineckate (4 gms; 0.01 mole) was dissolved i n concentrated aqueous ammonia (40 ml) i n a 250 ml, conical f l a s k .  To t h i s solution was  added 10 ml of concentrated aqueous ammonia containing trimethylsulfonium borohydride (0.9 gms; 0.01 mole).  The s l u r r y was then transferred to  a Buchner funnel and the f i l t r a t e used once to  NH  4  4000 3000  Cr(CNS) (NH ) 4  2000  3  1500 CMI, I I,I—h—i—i i i i—. 1  ,i i i ,i i  1  Rb Cr(CNS) (NH )2 4  4000 3000 0.0  1500  CM-i  UJ  / j V i  V  1000  fig. '26j 800 700  900  f  /  <-\  .10  1000 900 800 700 |II11J i • 111111 • 11 ••• I i i \ i i i i !• i  i  3  2000  68  fig. 25>  2  J  f/  S.30  O  £-40 <50 .60 .70 1.0 oo y  - t y  H—  J2UH  WAVELENGTH (MICRONS)  4000 3000  2000  1500 I  0.0  .  I  .  I  .  I  CM-i .  i  1000  900 Luli '"1  I  I I  fig. 2*7 I  800  I  1 1 , l,i  700  .10 £20  < S.30 <50 .60 .70 1.0 oo  \  /  O  2-40  i  /  /  u *4  II  WAVELENGTH (MICRONS)  FIB  i i,  69  wash the remaining precipitate from the f l a s k . The precipitate of the f i l t e r was washed with a further 25 ml portion of concentrated aqueous ammonia. The f i l t r a t e ( i t s t i l l had a s l i g h t pink coloration which could not be discharged by the addition of a further amount o f the sulfonium borohydride) was divided into two portions and each l y o p h i l i z e d . Only after a considerable amount o f the ammonia had been pumped o f f could the freeze-drying operation work properly. The crude rubidium borohydride from the l y o p h i l i z a t i o n was washed with  N,N—dimethyl-  formamide (approximately 10 ml) onto a f i l t e r  paper.  The residue was then allowed to a i r - d r y on the paper. This residue was then extracted with l i q u i d ammonia i n the metathesis apparatus and an I.R. spectrum of the r e s u l t i n g product taken (figure 28). The y i e l d was about 50 per cent. 2.3.  The Preparation of Cesium Borohydride  Because of the a v a i l a b i l i t y of cesium hydroxide, t h i s borohydride was prepared by the d i r e c t metathesis of the sulfonium borohydride and the a l k a l i metal hydroxide i n a methanol solution from which cesium borohydride precipitates i n the cold. Cesium hydroxide (1.5 gms; 0.01 mole) was dissolved i n methanol (25 ml, reagent grade) i n a 50 ml volumetric flask.  Trimethylsulfonium borohydride (0.9 gms; 0.01 mole)  70  71  was dissolved i n N,N—dimethylformamide (10 ml Eastman White l a b e l ) .  The dimethylformamide  solution was then  added to the methanol solution and the mixture thoroughly shaken f o r 5 minutes.  Upon cooling the mixture i n crushed  dry i c e , a fine white c r y s t a l l i n e precipitate came down. The c r y s t a l l i t e s were r a p i d l y c o l l e c t e d on a sintered glass crucible and allowed to dry i n a vacuum desiccator. The dried borohydride was placed i n a heating tube attached to a vacuum system and kept at 110° C. f o r three hours by means o f a small e l e c t r i c furnace.  The crude cesium  borohydride was f i n a l l y extracted with l i q u i d ammonia i n the metathesis v e s s e l . cent.  The y i e l d was 0.5 grams or 35 per  The I.R. spectrum o f the p u r i f i e d cesium borohydride  i s shown i n figure 29. 3«  The Assay o f the Ionic Borohydrides Some o f the i o n i c borohydrides (KBH^,  S{CE^)^  BH^) were analyzed by the volumetric method of L y t t l e et a l . (44). a)  In b r i e f , the method i s as follows: 0.5-0.6 millimoles of the borohydride i s dissolved i n 25 mis o f 0.5N NaOH.  b)  35 ml o f 0.25N (accurately known) KIO3 added immediately and the f l a s k swirled f o r 30 seconds.  c)  2 gms KI added and then 20 ml o f 4N HgSO^ added.  d)  Flask placed i n dark f o r 2-3 minutes.  72  e)  Liberated iodine t i t r a t e d with 0.10N  Na S 0 2  2  3  with starch i n d i c a t o r . Table 8 summarizes the r e s u l t s of the analyses. Only representative r e s u l t s are shown.  Liquid ammonia  and anhydrous hydrazine y i e l d a considerably purer product than any obtainable from an aqueous solvent. Trimethylsulfonium borohydride could be obtained i n very high purity by a l i q u i d ammonia extraction process.  These  r e s u l t s are confirmed by the I.R. spectra discussed i n the previous sections. B.  Calorimetric Determination of the Radiation Flux from the OEG-60 X-ray Tube The calorimetric determination was carried out by  measuring the maximum temperature of a s i l v e r disc appropr i a t e l y mounted by soldered s i l v e r wires i n the radiation vessel f o r chemical work when the disc has reached thermal equilibrium i n the X-ray beam.  The energy output of the  tube could be obtained by an experimental determination of the rate of cooling, the ambient temperature i n the absence of radiant f l u x , and the application of Newton's law of cooling. By Newton's law, the rate of energy l o s s with time, Ht'  is1 S  '  d| dt  =  _K(T-T ) 0  where T i s the temperature of the s i l v e r disc at time, t .  T  i s the ambient temperature which i n the f i r s t  Q  t r i a l was 22.3° C. Since dE = mcdT where mc i s the heat capacity of the s i l v e r disc and mounting material. Thus ^ 1 = ^1 (T-T ) at mc 0  Integrating, In (T-T ) = ~ 0  mm  or  n  T-T  0  t + Constant,  -K/lIlCt  = Ce  '  A plot of In (T-T ) as a function of time enables one to 0  calculate K from the slope of the graph (mc i s known). This plot f o r the experimental conditions used i n t h i s study i s shown i n figure 3 0 . T  h  U  S  K - -mc  = _  < - ° T  23.0 - In 8)  n c  = -mc  T  lo.p  1  »Q5° 18.5  = 0.0571 m (cal.min.~ deg.~ 1  Now the heat capacity o f the thermal radiator i s composite 1.504  gms of s i l v e r with s p e c i f i c heat of 0.0558 and 0.030  gms of solder (50/50 Sn-Pb) with s p e c i f i c heat o f 0.0451. Thus the_heat capacity = mc  =  1.504  (0.0558) + 0.030  (o.045D  = 0.0853 cal/C° Therefore  K - 0.0853 x 0.0571 = 0.00487  cal.min.^deg."  1  75  Now  at the maximum temperature of 46.3° C., when the rate  of energy absorbed from the X-ray tube i s the same as that l o s t by thermal radiation, w i l l be: dE « 0.00487 (46.3°-22.3°) dt = 0.117 cal.min." 1  A second determination gave an energy f l u x value of 0.123 cal.min." . 1  The energy output from the tube a f t e r  filtration  by 0.662 gm cm" o f beryllium and 0.081 gm cm" o f aluminum 1  1  can be taken as 0.120 ± 0.005 cal.min."  1  The mean diameter  of the s i l v e r disc used as a thermal radiator was 1.09 cm with a corresponding area of 0.933 cm . 2  Therefore, the  value of the radiant f l u x at 50 kvp and 28 milliamps f o r the  f i l t r a t i o n noted above i s 0.129 cal.min." cm" . 1  2  This  intensity corresponds to the area under curve 2 of figure 15 (p. 50). The radiant f l u x f o r the other degrees of f i l t r a t i o n can now be e a s i l y computed. i n Table 9.  The results are tabulated  TABLE 9 ENERGY FLUX FOR SAMPLES IN THE RADIATION VESSEL FOR CHEMICAL . DECOMPOSITION STUDIES (Source: OEG-60 Tube at 50 kvp and 28 milliamperes) Irradiation Sample No.  No. of Intensity Dist'n Curve o f Figure 1 5  ' ' _ Area under S p e c i f i c Energy Flux F i l t r a t i o n gm cm~ Curve of Figure 1 5 at 5 0 kvp & 28 m; (Sq. inches) (cal.min."1 cm' d  1  2  0.081A1 + 0.662 Be  2  6  0.209A1 + 0.662 Be  7.01  0.087  3  3  0.102A1 + 0 . 6 6 2 Be  9.54  0.118  4  5  0.159A1 + 0 . 6 6 2 Be  7.98  0.099  5  4  0.138A1 + 0.662 Be  8.45  0.105  6  7  0.266A1 + 0.662 Be  6.12  0.076  7  8  O.36OAI + 0.662 Be  5.02  0.062  1  0.662 Be  10.39  17.74  0.129  0.220  ON  77  C.  Spectroscopic Examination of Irradiated Borohydrides 1.  V i s i b l e and U l t r a v i o l e t Absorption Spectra Only one c r y s t a l of potassium borohydride was  obtained which was suitable f o r the spectroscopic work. Pressed p e l l e t s of potassium borohydride were used i n the majority of experiments with t h i s material.  Pressed p e l l e t s  of the other a l k a l i metal borohydrides were used e x c l u s i v e l y . P e l l e t s of the s a l t s were prepared by placing approximately 10 to 15 milligrams of the borohydride i n the die used to form KBr p e l l e t s f o r I.R. spectra studies. the die was done i n a dry box.  The loading of  The die with salt was then  placed under a 20,000 pound t o t a l load i n a small laboratory hydraulic press.  The r e s u l t i n g d i s c of borohydride was  broken into three to four small sectors each of which could be used i n a separate spectroscopic experiment.  One  of these small sectors of the pressed p e l l e t was niounted on the c r y s t a l holder of the spectroscopic radiation vessel by means of rubber cement.  The removal of the p e l l e t from the  die and the mounting operation had to be done i n the dry box. The radiation vessel and i t s operation i s discussed i n Chapter I I , Section B« In order t o determine the r a d i a t i o n induced changes i n the absorption spectra of the a l k a l i metal borohydrides i t was necessary to obtain the absorption spectra of the unirradiated materials.  After the spectrum of the  78  unirradiated borohydride was obtained with the Cary Recording Spectrophotometer, the radiation vessel was transferred to the X-radiation laboratory and there mounted on the AEG-50 tube f o r exposure.  The c r y s t a l or  p e l l e t had to be rotated through 90 degrees between the recording of the spectrum and the X-ray exposure.  Fiducial  markings located on the neck and body of the r a d i a t i o n vessel enabled the material to be aligned exactly during each exposure and spectroscopic run.  The radiation vessel  was connected to the vacuum system and pumped while mounted to the X-ray tube.  The vacuum valve and flange j o i n t  allowed the vessel to be transported while under vacuum. Samples at such low temperatures as that of b o i l i n g n i t r o gen were e a s i l y maintained with the evacuated v e s s e l . A l l spectra i n t h i s study were recorded at l i q u i d nitrogen temperature (-196° G. or 77° K).  Generally, three  exposures to X-radiation f o r varying times at 50 Kvp and 28 milliamps were taken on each sample.  When bands o f the  spectrum had formed to a s u f f i c i e n t degree, the e f f e c t on each band of prolonged exposure to wavelengths o f absorbed radiation ( i n the range of 2000 2) was studied to determine the b l e a c h a b i l i t y of the bands and the i n t e r r e l a t i o n s between bands as shown by the changes i n the o v e r - a l l spectrum r e s u l t i n g from l i g h t absorption.  F i n a l l y , the thermal  s t a b i l i t y of bands were studied i n some cases as the sample  79  was warmed to dry i c e or to room temperature.  The spectra,  however, were taken at l i q u i d nitrogen temperature a f t e r such warming experiments. The r e s u l t s of these spectroscopic studies are shown i n figures 31 to 39.  The true absorption  spectra  of unirradiated materials were obtained by subtracting from the recorded spectra o f unirradiated borohydrides, the "absorption spectrum" of the empty c r y s t a l mount The  (slit).  spectra showing only r a d i a t i o n induced changes were  obtained by subtracting from the recorded spectra at 100 2 Intervals (and at maxima and minima where p o s s i b l e ) , the recorded  spectrum o f the unirradiated material.  When the  o p t i c a l density of the material was high, as i t often was near the absorption edge of the material, the o p t i c a l density range of the instrument could be changed to higher values by placing a piece o f fine wire mesh i n the reference beam of the spectrophotometer.  The r e s u l t s of these a r i t h -  metical operations were recorded i n tables giving o p t i c a l density increments f o r various wavelengths i n ingstrom u n i t s . The values from these tables were then plotted as functions of the wavelength of absorbed r a d i a t i o n i n units of r e c i p r o c a l centimeters or electron v o l t s (both scales are included i n the spectra reported i n t h i s work).  Preliminary a r i t h -  metical work, difference tables, etc., have been omitted from t h i s report. included.  Only the f i n a l plotted spectra are  The r e s u l t s of these spectroscopic studies are  Figure 31* Curve 1.  Radiation induced changes i n LiBH^ Absorption spectra of unirradiated L1BR4 p e l l e t .  Curve 2.  Radiation induced change a f t e r 3 minutes exposure to X-rays at l i q u i d nitrogen temperature•  Curve 3»  Radiation induced change a f t e r one hour exposure to X-rays at l i q u i d nitrogen temperature.  Curve 4»  Radiation induced change a f t e r 2 1/2 hours exposure to X-rays at l i q u i d nitrogen temperature.  Curve 5«  Sample represented by Curve 4 exposed to l i g h t of 4500 &. wavelength f o r 1/2 hour at l i q u i d nitrogen temperature.  Curve 6»  Sample represented by Curve 5 exposed to bright tungsten i l l u m i n a t i o n f o r three seconds at l i q u i d nitrogen temperature.  /  81  (in Angstroms)  WAVELENGTH  0  o ro CJ 1  I-50H  o  o * CJ i  O  O r> CJ i  O  O o  O O O O o O ° ° °  o  O O O O O © to s d g i o - N i o t i n CM c j c J c J r o r o r o i o r o i p i ' 1 I i I I—I—I—I— 0  0  0  Li BH  4  0  Pressed Pellet 31 ,  4  l-00i  0-75 A  0-50  z  o  0-25  000  r0.  o  1-00  0-75 -\  0-5C-H  0-25-i  0 00—r 5-5 ELECTRON  m  o o o y  FIGURE 1-25  o o  VOLTS  o O  m  o o o o O O O o o « o >o  y y f 'r >r  $2  Figure 32. Radiation induced changed i n NaBH^ Gurve 1.  Absorption spectra of unirradiated NaBH^ pellet•  Curve 2.  Radiation induced changes a f t e r 7 minutes exposure t o X-rays at l i q u i d nitrogen temperature.  Gurve 3.  Radiation induced change a f t e r 15 minutes exposure to X-rays at l i q u i d nitrogen temperature•  Curve 4»  Radiation induced change after 30 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Curve 5»  Sample represented by Gurve 4 exposed to l i g h t of 2700 % wavelength f o r 5 minutes at l i q u i d nitrogen temperature.  Curve 6.  Sample represented by Curve 5 exposed to X-rays f o r a further one hour at l i q u i d nitrogen temperature.  The sample has now  received 1 1/2 hours exposure t o X-rays. Curve 7.  Sample represented by Curve 6 was exposed to l i g h t of 4750 % and then to l i g h t o f 5400 £ for periods o f 5 minutes at l i q u i d nitrogen temperature without any noticeable change i n the  absorption spectra.  The sample was then  exposed to bright tungsten i l l u m i n a t i o n f o r 20 seconds at l i q u i d nitrogen temperature.  83  WAVELENGTH (in Angstroms) o o  ro  O  O • CJ •  O  O  O O O O o O O O O  O O O O O O Q m to h-o)o>o — CJ 10 • in CJ CJ cjcJCMrorororprprp ' I I 1 J 1 1—I—I—I—L_ 0  I • 25 H  0  0  Na BH  0  4  o o O  I -00-  0-75 A  0-50-f  0-25 H  000  UJ  o  I -25 A 4 O  o  '-  0  0  \  0-75 A  0-50 A  0-25 -t  000  5-5  o •n  y  Pressed Pellet  FIGURE 32  </>  o  50 ELECTRON VOLTS  o  0 0 0 0 0  o o  o o o o o 10 o in o in  y  y  y y T T  Figure 33. Radiation induced changes i n KBH/,, c r y s t a l Curve 1.  Absorption spectra o f unirradiated KBH^ crystal.  Curve 2.  Radiation induced change a f t e r 15 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Curve 3*  Radiation induced change a f t e r 30 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Curve 4.  Radiation induced change a f t e r one hour exposure to X-rays at l i q u i d nitrogen temperature•  Curve 5*  A sample represented by Curve 3 exposed to bright tungsten illumination f o r one minute at l i q u i d nitrogen temperature.  Curve 6.  A sample represented by Gurve 5 warmed to dry i c e temperature ( - 77° C.) f o r two hours.  WAVELENGTH  o o o* m o CM  CJ  (in Angstroms)  O OO OoO°°° O O O O o © r~- as oi o — CJ ro * m CM CJ CJ to e o ro rp rp rp 0  0  0  O o o  0-504  0-25 H  0 00—r 5-5 ELECTRON  VOLTS  oo to  o OOO o OOO o m o m »p y y <p  j  L  Figure 3 4 »  Radiation induced changes i n KBH^  crystal  (continued) Curve 7 *  Radiation induced change a f t e r 3 0 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Curve 8 .  A sample represented by Curve 4 warmed to dry i c e temperature f o r two hours.  87  WAVELENGTH  5-5  50  45  40  (in Angstroms)  3-5  ELECTRON  VOLTS  30  2-5  20  88  Figure 3 5 . Curve 1.  Radiation induced changes i n KBH^ pressed p e l l e t Absorption spectra o f unirradiated  KBH^  sample • Curve 2 .  Radiation induced change a f t e r 3 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Curve 3 .  Radiation induced change a f t e r 7 minutes exposure to X-rays at l i q u i d nitrogen temperature.  Gurve 4 .  A sample represented by Curve 3 was exposed to l i g h t o f 2775 8 wavelength f o r 30 minutes at l i q u i d nitrogen temperature.  Curve 5»  Radiation induced change a f t e r 4 1/2 exposure to X-rays at l i q u i d nitrogen temperature.  hours  89  WAVELENGTH O o ro CJ  i  I 25  o O o o o o <• m CM  CM  I  CM  O O  r-  CM  o  o  c6 CM I  (in Angstroms) O O o  O o o o o o O o o o o o  O  — CM l O « •  to  ro ro ro ro ro ro J  I  I  I  I  L_  i  FIGURE 35  0-75  0-50H  0-25  H  000  1*25  <  o  iQ. O  i-ooH  0-75H  ® \ 0-80-^  0-25 A  0 005-5  © -1— 50  3-5 ELECTRON  *  Pressed Pellet  K BH, 100  o o m  VOLTS  o o o V  o o in m i  o o o o o o o o in o10 in o r1 i  T  Figure 36.  Radiation induced changes i n KBH^ pressed p e l l e t (continued)  Gurve 6.  Radiation induced change a f t e r 4 1/2  hours  exposure to X-rays at l i q u i d nitrogen temperature.  This curve i s the same as  Curve 5, f i g . 35. Gurve 7«  A sample represented by Curve 6 was exposed to l i g h t of 57SO A* wavelength f o r 15 minutes at l i q u i d nitrogen temperature.  91  WAVELENGTH  (in Angstroms)  o o OO OO OO OOOOO Oo oO ° ° ° O O IO * in (O K C0 0> O — N n t o C' M O' J CVJ' (MI NNNMIOniQIOIp I I I 1 1—I 1 I I 0  0  KBH  I-25 H  0  0  o o o  o o m  o O o  p  OOOOO O O O O o o » o »  w  ? y * T *•  Pressed Pellet  4  FIGURE 36 l-OOH  0-75 H  oso H  0-25 A  000 1-23-  < u  »o. o  100-  0 75-  0-50-  0-25-  0-00-L-,  55  — I —  50  —I  45  1 40  1 3-5  ELECTRON  3-0 VOLTS  I  25  -1— 20  92  Figure 37»  Radiation induced changes i n RbBH^  Curve 1.  Absorption spectra o f unirradiated RbBH^ pressed p e l l e t .  Curve 2.  Radiation induced change after 2 minutes exposure t o X-rays at l i q u i d nitrogen temperature.  Curve 3•  Radiation induced change a f t e r 8 minutes exposure to X»rays at l i q u i d nitrogen temperature•  Curve 4*  A sample represented by Curve 2 was exposed to l i g h t of 3100 % wavelength f o r 5 minutes at l i q u i d nitrogen temperature.  Curve 5.  A sample represented by Curve 3 was exposed to l i g h t o f 2400 1 wavelength f o r 3Q minutes at l i q u i d nitrogen temperature.  93 WAVELENGTH  O O O O O O O O o O O O O O O O O O O O O o O ° ° 0 ro * m 10 s s) 01 o - N r t * i n OJ  CJ CJ oj  ojcJoJrorororororO  ELECTRON  (in Angstroms)  o o  0  *  VOLTS  o o rn «•  o o o o o o O O O O O o o in O in o in m  ip  ip lp S N  Figure 38. Curve 6.  Radiation induced changes i n RbBH^ (continued) A sample represented by Curve 3 was exposed to bright tungsten i l l u m i n a t i o n f o r 2 minutes at l i q u i d nitrogen temperature.  Curve 7.  A sample represented by Curve 6 was warmed to room temperature f o r 16 hours*  95  WAVELENGTH  (in Angstroms)  >-  (A  z  0*00-•  UJ Q  _i < o  i  1-25 -  100-  0-75  5-5  50  4-5  4 0  3-5  ELECTRON  30 VOLTS  25  20  96  Figure 3 9 . Radiation induced changes i n CsBH^ Curve 1.  Absorption spectra of unirradiated CsBH^ pressed p e l l e t .  Curve 2 .  Radiation induced change a f t e r 15 seconds exposure to X-rays at l i q u i d nitrogen temperature.  Curve 3*  Radiation induced change a f t e r 30 seconds exposure to X-rays at l i q u i d nitrogen temperature.  Curve 4 .  Radiation induced change a f t e r one minute exposure t o X-rays at l i q u i d nitrogen temperature•  Curve 5*  A sample represented by Curve 4 was warmed to dry i c e temperature f o r 5 minutes.  Curve 6 .  A sample represented by Curve 5 was warmed to room temperature f o r 5 minutes.  91 WAVELENGTH o o ro CM 1  o o * CM  1  O O m CM  1  (in Angstroms) o  O O O O O o O O O O O O O O O o O O ° 0 to K a) cn o — N io t n —I 1—1—I—1—1 CM CMCMCMK)IOr)IO(OK) 1  1  1  o  o o »  o o o  1  —1  1  o  1  Cs BH  o o in 1_  o O o  o o o O O o » o »  1  1  1  L  Pressed Pellet  4  FIGURE 39  I-50H  IOOH  0-75 H  A in UJ  o  \ /  V  ' \v .  ®"* 0-25 ^  <  o »a. o  ®y  o-soH  ©  —  S 1  j  J  o-oo-  0-75H  0-50 H  0-25 H  J -  i 5-5  r=  50  1  4-5  — i 40  1  —  i  3-5  ELECTRON  30 VOLTS  1  1  2-5  20  i  discussed i n Chapter IV. Experiments were attempted i n which potassium borohydride was intimately mixed with other i o n i c s a l t s such as CaH , NBYJBr, and CaBr2, the mixture being l e f t 2  f o r several hours at room temperature under a t o t a l load of  20,000  pounds.  In a l l cases the p e l l e t s produced  were too cloudy to use i n absorption spectra and r a d i a t i o n studies. 2.  Infra-red Spectra Samples of potassium borohydride which had  received several hours exposure to X-rays were examined i n the infra-red region using the KBr p e l l e t technique both with and without the KBr matrix i n an attempt to learn something of the nature of the primary decomposit i o n products i n the i r r a d i a t e d material.  No differences  between i r r a d i a t e d and unirradiated material was detectable even when an unirradiated potassium borohydride p e l l e t was placed i n the reference beam of the i n f r a - r e d spectrophotometer• 3.  Paramagnetic Resonance Spectrum A paramagnetic resonance spectrum of a sample of  powdered potassium borohydride that had been i r r a d i a t e d for four hours at l i q u i d nitrogen temperature i s shown i n figure 40.  The spectrum was also taken at l i q u i d  ELECTRON SPIN RESONANCE SPECTRA OF IRRADIATED KBH (POWDERED). 4  FIGURE 4 0  3  H  ATOM RESONANCE ABSORPTION  H ATOM RESONANCE ABSORPTION  \  fi  »-  Q. UJ  O  <n (0  Ul  5K> gouM between H- atom re«ooonce».  >  I  or UJ  a or  MICROWAVE FREQUENCY: 9 1 KILOMEGACYCLES FIELD STRENGTH H  100  nitrogen temperature.  I r r a d i a t i o n and examination of an  empty sample tube under the same conditions as the borohydride sample showed that the hydrogen atom peaks were associated with the sample tube.  Exposure of a  potassium borohydride sample f o r several hours to a high i n t e n s i t y of u l t r a v i o l e t l i g h t from a mercury lamp f a i l e d to produce any sample coloration or paramagnetic resonance signal. D.  Examination of Irradiated KBH^ f o r Chemical Changes Although electronic processes such as color center  formation are now known to occur i n potassium borohydride on exposure to 50 Kvp X-rays, a knowledge o f possible chemical decomposition products and t h e i r y i e l d f o r a given dosage o f r a d i a t i o n would be desirable.  Therefore,  experiments were designed t o determine the kind and quantity of some of the more l i k e l y products.  These experiments were  attempts to detect and estimate the amount of m e t a l l i c potassium which may have been formed during i r r a d i a t i o n , the c o l l e c t i o n and measurement o f the quantity of gaseous material that may be evolved either during i r r a d i a t i o n s or on solution of i r r a d i a t e d samples, and the mass spectroscopic examination of the c o l l e c t e d gases.  The experiments  were only o f limited success and the conclusions to be drawn from them are f a r from d e f i n i t e . The colorimetric system shown i n Plate I I and described i n Chapter I I , Section C was applied i n the  a l k a l i metal estimation experiment.  A sample of potassium  borohydride (10 mgm) after 10 hours irradiation at room temperature was placed in a trap on the vacuum system and sufficient anhydrous ammonia to just dissolve the material was d i s t i l l e d onto the sample. detectable i n the solution.  No blue coloration was  A sample of irradiated material  with a similar dosage of X-rays, when l e f t under vacuum and away from bright light, remained deep blue for about three days.  No gas was evolved on dissolving the irradiated  samples i n anhydrous liquid ammonia. During the irradiation of samples (seven samples were irradiated simultaneously  i n the radiation vessel for  chemical studies) large quantities of gas were evolved. The rate of evolution was small at the start of the irradiation period but after several minutes i t greatly increased and finally reached a value that persisted throughout the remainder of the irradiation period.  As there were seven  samples each of which received a different dosage of X-rays, no attempt was made to analyze the results of the rate study. However, the gas collection and storage unit of the vacuum system was calibrated for small amounts of gas by generating known amounts of hydrogen i n the system.  This was done  by taking a small amount of zinc dust (about 30 milligrams) and placing i t i n the die used i n making KBr pellets for I.R. studies and pressing the dust at 20,000 pounds total  load.  Small portions of zinc metal were then broken from  the t h i n p e l l e t and weighed on the Gohn electrobalance.  A  portion o f zinc p e l l e t weighing between 6 micrograms and 0.6 milligrams was transferred t o a trap on the vacuum system and the l a t t e r pumped down.  Sufficient dilute  hydrochloric acid was then transferred ( i t had been placed i n the vacuum system previously and the dissolved a i r removed by repeated transfers through a series of traps) onto the zinc metal and allowed t o react completely. The c i r c u l a t i n g and c o l l e c t i n g d i f f u s i o n pump was then put i n operation and the vapour cycled through traps cooled i n l i q u i d nitrogen to remove water and hydrogen chloride from the vapour.  When the pressure had reached a constant low  value the evacuated storage bulb (approximately 5 l i t r e s ) was opened t o the system and the permanent gas transferred by means o f the c o l l e c t i n g d i f f u s i o n pump.  When the  pressure on the intake side of the d i f f u s i o n pump was l e s s than 1JX  the pressure i n the storage system was measured.  The r e s u l t s of t h i s c a l i b r a t i o n experiment f o r small amounts of hydrogen generated from zinc dust (analar grade) are shown i n figure 41* The gas c o l l e c t e d during i r r a d i a t i o n of potassium borohydride was examined i n a mass spectrometer.  Only  hydrogen gas was detectable. Responses i n mass regions associated with ions r e s u l t i n g from diborane or i t s f r a g ments were absent.  40  IV.  DISCUSSION  Solvent studies designed to produce the a l k a l i metal borohydrides i n a form suitable f o r the r a d i a t i o n studies showed that anhydrous hydrazine i s a very good solvent f o r the potassium, rubidium, and cesium borohydrides, although the s e n s i t i v i t y of the solvent to a i r makes the solutions d i f f i c u l t t o handle.  The use of anhydrous hydrazine as a  solvent f o r lithium and sodium borohydrides was not attempted although the l a t t e r s a l t would be expected to have a reasonable s o l u b i l i t y .  Infra-red spectra and chemical assays o f  potassium borohydride samples extracted with anhydrous hydrazine show that no detectable reaction occurs with t h i s solvent.  Although l i q u i d ammonia i s also a good solvent f o r  potassium borohydride, the p o s s i b i l i t y o f growing  crystals  that would be suitable f o r the spectroscopic studies would require more complex apparatus and closer control than the use o f hydrazine, a solvent which i s quite s i m i l a r t o water i n many of i t s physical properties (45). I t i s hoped that further work with hydrazine solutions on a larger scale may produce c r y s t a l s o f the i o n i c borohydrides that are suitable for spectroscopic and other physical studies o f radiation damage i n these s o l i d s .  105  The methods used to produce the borohydrides of rubidium and cesium are cumbersome. It is hoped that these borohydrides become commercially available as products derived directly from the pure alkali metals much as the potassium salt is obtained. The sulfonium borohydride intermediate used in the present work is not too stable and its decomposition at room temperature becomes noticeable after a few days. However, the trimethylsulfonium borohydride method has advantages when the alkali metal hydroxide is available, the hydroxides of potassium, rubidium, and cesium being much easier to handle than the pure metals. In the present work the carbonate of rubidium was used in conjunction with the sulfonium borohydride method. The carbonate was converted to the reineckate which, in a subsequent metathesis reaction with the sulfonium borohydride in an ammoniacal solution, precipitates the very slightly soluble sulfonium reineckate, the alkali metal borohydride being removed from the aqueous solution by freeze drying. Methods were not developed to prepare the alkali metal borohydrides from a boron-containing compound other than an ionic borohydride. Methods are under study which would be used to prepare borodeuterides starting with compounds other than the borohydrides. The section on radiation dosimetry has been included for reference and for the possible use of such information  106  i n a l a t e r , more quantitative study of r a d i a t i o n damage i n the borohydrides.  The radiant f l u x determination f o r the  Machlett OEG-60 X-ray tube gave the output value o f -1  min.  0.220  cal.  -2  cm. * at the port of the tube.  The v a r i a t i o n of t h i s  output with the age of the tube was not studied. Therefore, t h i s value may  change with the use of the source.  Examination of i r r a d i a t e d potassium borohydride f o r chemical changes gave few conclusive r e s u l t s . hydrogen i s d e f i n i t e l y produced.  Molecular  Elemental a l k a l i metal  was  not detected although the presence o f trapped electrons i s almost c e r t a i n .  The removal of hydrogen atoms and electrons  from borohydride ions through radiation damage can conceivably produce free molecular hydrogen, trapped electrons, and boron containing electron d e f i c i e n t molecules or molecule-ions. The absence of diborane i n the evolved gaseous r a d i a t i o n products i s not known with complete certainty.  The thermal  disproportionation of diborane i n the gas c o l l e c t i n g d i f f u s i o n pump may  explain the absence of the diborane positive ion i n  the mass spectrometric study. I f equivalent amounts of hydrogen and the electron d e f i c i e n t molecule, diborane, were formed and removed from the s o l i d l a t t i c e , one would expect that an F band would be present i n the absorption spectra o f the i r r a d i a t e d borohydride that would be as persistent as that associated with the a l k a l i halides that have been heated i n a l k a l i metal vapor.  However,  the r a d i a t i o n induced coloration i n potassium borohydride  107  bleaches slowly i n the dark at room temperature and the solution of heavily i r r a d i a t e d samples i n l i q u i d ammonia f a i l s t o produce the blue coloration associated with free electrons or the equivalent amount of free a l k a l i metal. The Ivey formulas f o r electron excessive color centers appear to be applicable to the face-centered cubic a l k a l i metal borohydrides.  The formulas f o r the F center and the  U center are given on page 1 1 , and the r e s u l t s o f t h e i r application are summarized i n Table 1 0 .  The observed  values  of the wavelength o f maximum absorption, X max, for the various bands i n the i r r a d i a t e d i o n i c borohydrides have also been included i n Table 1 0 .  The spectra shown i n f i g u r e s 3 1  to 3 7 c l e a r l y show three major band systems.  In Table 1 0  they have been denoted by I, I I , and I I I . The set denoted by I appears to be F bands.  A second c l e a r l y i d e n t i f i a b l e  band system denoted by I I I seems to be U bands associated with the hydride i o n .  The band system denoted I I has not  been assigned although the properties of the band systems as a whole with considerations of the stoichiometry of the radiation induced decomposition t o be discussed below indicate that band system I I may be associated with an electron d e f i c i e n t center of the V or H type. The spectroscopic studies show that the number of U centers exceed the number o f F centers although no quantit a t i v e estimate can be made without the knowledge o f the  TABLE 10 OBSERVED AND CALCULATED VALUES OF A^ax FOR RADIATION INDUCED ABSORPTION BANDS IN THE ALKALI METAL BOROHYDRIDES  Sample  Interionic Distance d i n A (46,47) - -  Calculated % of Fband i n a m  a  x  Calculated X of Uband i n A m  a  x  Observed Observed Observed X of X of X of Band System Band System Band System I in ft I I i n ft I I I i n A m  a  x  m  a  x  m  a  x  LiBRV. pressed p e l l e t NaBH^ pressed p e l l e t KBH^ c r y s t a l KBH pressed p e l l e t  4,170  1,740  4,300  3,000  5,150  2,020  5,350  3,050  2.95 3»36  6,530  2,330  6,900  2,950  2,350  3*36  6,530  2,330  6,400  2,850  not recorded  7,250  2,450  6,500  3,000  2,410  7,890  2,610  3,250  2,590  2.63  4  RbBH  4  pressed p e l l e t CsBH^ pressed p e l l e t  3*51  3.72  1—• ©  109  oscillator  strengths of the two kinds of centers.  I t may  be that the F centers are being developed from U centers* However, a more l i k e l y explanation i s described below.  The  results suggest that hydride ions are stable products resulting from the o v e r a l l energy dissipation of the absorbed X-ray quanta.  Hydrogen production i s probably a r e s u l t o f  dissociation of excited or ionized borohydride ions to atoms and other fragments with the subsequent atom reactions such as hydrogen abstraction during the early physicochemical stages. A possible scheme f o r the d i s s i p a t i o n o f the X-ray quanta at low temperatures i s the following:  M  +  +  BH^" + M  • M  + e"  ++  ». M *  + BH^-  +  + +  BH4- + f)V  »» BH '  + e"  4  M+*  M  +  + hi)'  However, reactions and ionizations produced through secondary electrons w i l l greatly outweigh the e f f e c t s of primary absorption noted above. BH "* • e" 4  e- + BH^"  BH^*  BHj~ • H* BH^-  ». BH  3  + H*  + 2e~  110  R a d i c a l and atom r e a c t i o n s w i l l f o l l o w .  Combination  o f two s i m i l a r r a d i c a l s i s e x p e c t e d t o be n e g l i g i b l e of t h e "cage e f f e c t .  BRj** + H  4  3  * BH - — B 2 H 6 4  BH3- + B H ^ " — B The s p e c i e s B2%"  ions.  follow:  H. + B H "  BH  view  T h e r a d i c a l s a n d h y d r o g e n atoms a r e  1 1  very l i k e l y t o react w i t h t h e nearby borohydride Possible reactions  in  2  H 6 *  2  + H" • FT  should not be taken l i t e r a l l y  molecule with an attached e x t r a e l e c t r o n .  a s a B R*6 2  Such a s p e c i e s  may p o s s i b l y b e s t a b i l i z e d t o a h i g h d e g r e e b y n e i g h b o r i n g l a t t i c e v a c a n c i e s , and b y p o l a r i z a t i o n from cations.  surrounding  Uncharged B H ^ o c c u p y i n g a n o r m a l a n i o n s i t e 2  would  be e x p e c t e d t o t r a p a n e l e c t r o n . Now e l e c t r o n s r e m o v e d i n t h e i n i t i a l e v e n t s may r e t u r n  ionization  t o a s p e c i e s s i m i l a r t o t h e one t h a t w a s  f o r m e d b y e l e c t r o n l o s s , o r t h e y may b e t r a p p e d b y v a c a n c i e s , i m p u r i t i e s , or diborane i n the l a t t i c e • P r o v i d i n g the temperature i s l o w , e l e c t r o n s are presumably trapped d u r i n g t h e i n i t i a l stages o f by t h e v a c a n c i e s present lattice.  i n thermal equilibrium with the  The s p e c t r o s c o p i c  study  shows t h a t t h e e a s e o f  formation o f F centers decreases w i t h i n c r e a s i n g time.  irradiation  exposure  V a c a n c i e s may p o s s i b l y b e p r o d u c e d b y t h e r a d i a t i o n  (22) b u t a p p a r e n t l y n o t a t t h e r a t e a t w h i c h e l e c t r o n s a r e  Ill  released.  However, as time goes on, the amount of B2H15  dispersed in the l a t t i c e may greatly a l t e r the rate of formation of F centers by the formation of B2i%" which now takes place at the expense of F-center formation. By the above scheme we would expect about twice the number of U centers as the number of F centers,  assuming  that a l l electrons removed i n primary i o n i z a t i o n s of the borohydride ions become trapped i n anion vacancies to form F centers.  Under such circumstances we would also expect  the number of centers a r i s i n g from the B^R^" be the same as the number of F centers.  species to  The number of  diborane molecules would also be the same as the number o f F centers providing there are no losses from the  lattice.  Diborane w i l l not be spectroscopically detectable  i n the  v i s i b l e range of the spectrum.  The number of major band  systems observable i n the spectroscopic studies corresponds to the number of species which are produced i n large amounts and which are expected to absorb i n the v i s i b l e region of the spectrum.  These are the F band, the U band, and a band  denoted II which can be considered as o r i g i n a t i n g from the trapped B2H6" species.  The above scheme accounts for the  kinds of absorption bands produced as well as t h e i r  intensity.  Depending on the perfection of the l a t t i c e , the r a t i o of the number of F centers to the number of centers a r i s i n g from B2H5" i s expected to vary  greatly.  112  The  o f t h e B2H6" s p e c i e s i s e x p e c t e d  to  be l o w even i n c o n s i d e r a t i o n o f t h e p o l a r i z i n g e f f e c t s  of  surrounding  stability  v a c a n c i e s and c a t i o n s .  Thus t h e i o n would be  e x p e c t e d t o be e a s i l y i o n i z e d b y l i g h t  i n the v i s i b l e  region  of the  it  that  it  will  spectrum.  At high temperatures  "decompose" w i t h r e l e a s e o f  is  charge.  expected This  latter  effect  i s i l l u s t r a t e d by c u r v e 6 o f f i g u r e 3 3 f o r t h e  of the  centers produced i n c r y s t a l l i n e  potassium  case  borohydride.  The e a s e o f f o r m a t i o n o f t h e b a n d s y s t e m d e n o t e d appears t o  i n c r e a s e from the l i t h i u m s a l t to the  With l i t h i u m borohydride Band I I  for  w i t h the potassium borohydrides The  recorded.  F band o f  than  F o r sodium b o r o h y d r i d e  i s more i n t e n s e t h a n t h e F b a n d .  salt.  cesium s a l t .  t h e F b a n d i s more i n t e n s e  a given dosage.  This l a t t e r  cesium borohydride  band  order  but not w i t h the could not  II  occurs  rubidium be  The p r o b a b i l i t y o f a s p e c i e s s u c h a s 8 2 % -  occupying a l a t t i c e s i t e w i t h l e s s e n i n g s t r a i n would greatly  II  from the l i t h i u m s a l t t o the cesium s a l t .  information of importance i n connection w i t h the of species i n l a t t i c e s i t e s i s l i s t e d  increase  Some trapping  below:  Length of the diborane molecule  2 . 9 7 ft  Diameter of the borohydride  4.06 %  Diameter of the hydride  ion  ion  Diameter o f t h e hydrogen molecule  4 . 1 6 ft 2.34 &  113  The strong peak of the paramagnetic resonance spectrum shown i n figure 40 indicates that r a d i c a l s and/or free electrons are produced i n the i r r a d i a t e d samples at low temperature. Some f i n e structure i s also noticeable but no attempt has yet been made t o analyze the spectrum.  As the sample was a  f i n e powder i t i s believed that few r e s u l t s can be obtained from i t .  I t i s hoped that single c r y s t a l s of the a l k a l i  metal borohydrides  can be obtained on which a complete study  of radiation induced changes can be studied by t h i s valuable technique.  Some suggestions f o r further work are now given.  The following points can be considered as immediate  extensions  of t h i s study: 1.  Development of methods t o produce the borodeuterides  and the growth o f single c r y s t a l s of these s a l t s and the borohydrides t o be used i n more quantitative spectroscopic work. 2.  Quantitative information on the properties of the  band systems to check t h e i r properties against the known behavior of F centers, U centers, etc.  Such properties as  t h e i r ease of formation at extremely low temperatures, t h e i r o p t i c a l b r e a c h a b i l i t y , thermal s t a b i l i t y , r e l a t i o n s between bands, and the presence o f photoconductivity during absorption i n a p a r t i c u l a r band must be studied.  Such information w i l l  establish the kinds o f color centers i n the i r r a d i a t e d borohydrides.  114  3*  Correlation of the intensity of the various centers  produced at low temperatures with the amount of molecular hydrogen formed, 4*  Electron spin resonance spectra with single c r y s t a l s  of borohydrides and borodeuterides to help elucidate the nature of the radiation induced l a t t i c e defects and chemical changes* 5*  Quantitative information on the o p t i c a l density of  the various bands produced f o r a given dosage of radiation in each of the a l k a l i metal borohydrides to determine the effects of l a t t i c e parameters on the s t a b i l i t y of the color centers produced.  115  BIBLIOGRAPHY 1.  United S t a t e s Atomic Energy Commission, Reactor HandB o o k s . V o l . 4, M a t e r i a l s . M c G r a w - H i l l , New Y o r k ,  T5557  2.  D i e n e s , G . , and G. H. V i n e y a r d , " R a d i a t i o n E f f e c t s S o l i d s , " I n t e r s c i e n c e , New Y o r k , 1957.  in  3.  S m y t h , H. D . , " A t o m i c E n e r g y f o r M i l i t a r y P u r p o s e s , " P r i n c e t o n U n i v e r s i t y P r e s s , P r i n c e t o n , 1945.  4*  F r i e d l a n d e r , G , and J . ¥ . Kennedy, " N u c l e a r and R a d i o c h e m i s t r y , " W i l e y , New Y o r k , 1955, c h a p t e r 12.  5.  Bradford, J . P. (ed.), "Radioisotopes i n R e i n h o l d , New Y o r k , 1953.  6.  United States Atomic Energy Commission, Isotopes, A F i v e - T e a r Summary o f D i s t r i b u t i o n w i t h B i b l i o g r a p h y . W a s h i n g t o n , D . C . , 1951.  7.  M u r r a y , A . , and D. L. W i l l i a m s , " O r g a n i c S y n t h e s e s w i t h I s o t o p e s , " 2 v o l u m e s , I n t e r s c i e n c e , New Y o r k , 1958.  8.  L e a , D. E . , " A c t i o n s o f R a d i a t i o n s o n L i v i n g U n i v e r s i t y P r e s s , C a m b r i d g e , 1955.  9.  B a c q , Z . M . , and P . A l e x a n d e r , "Fundamentals o f R a d i o b i o l o g y , " A c a d e m i c P r e s s , New Y o r k , 1955.  Industry,"  Cells,"  10.  C l a u s , W. D. ( e d . ) , Addison-Wesley,  " R a d i a t i o n B i o l o g y and M e d i c i n e , " R e a d i n g , M a s s . , 1958.  11.  Hollaender, A. (ed.), "Radiation Biology," M c G r a w - H i l l , New Y o r k , 1954-1956.  12.  M o h l e r , H. ( e d . ) , " C h e m i s c h e R e a k t i o n e n i o n i s i e r e n d e r Strahlen (Radiation Chemistry)," Sauerlflnder, A a r a u , 1958.  13.  L a i d l e r , K. J . , "The C h e m i c a l K i n e t i c s o f E x c i t e d S t a t e s , " O x f o r d U n i v e r s i t y P r e s s , O x f o r d , 1955.  14.  Reid, C . , "Excited S t a t e s i n Chemistry A c a d e m i c P r e s s , New Y o r k , 1957.  vols.  I-III,  and B i o l o g y , "  116  15.  Heal, H. G., unpublished observations.  16.  Rossi, B. B., "High Energy P a r t i c l e s , " Prentice-Hall, New York, 1952.  17.  H e i t l e r , W., "The Quantum Theory of Radiation," Oxford University Press, Oxford, 1954.  18.  Mott, N. F. and H. S. W. Massey, "The Theory of Atomic f  C o l l i s i o n s , " Oxford University Press, Oxford, 1949. 19.  Platzmann, R. L., i n W. D, Claus, Soc. c i t . . chapter 2.  20.  Kuppermann, A., J . Chem. Ed.. 3,6. 279 (1959).  21.  Read, W. T., "Dislocations i n Crystals," McGraw-Hill, New York, 1953.  22.  Varley, J . H. 0., J . Nuclear Energy. 1, 130 (1954).  23.  Dexter, D. L., Phys. Rev.. 108. 707 (1957).  24.  S e i t z , F., Revs. Mod. Phys.. 18, 3$4 (1946); 26, 7 (1954).  25.  Kanzig, W., and T. 0. Woodruff, J . Phys. Chem. Solids. 2» 70 (1959). Mott, N. F., and R. W. Gurney, "Electronic Processes i n  26.  Ionic Crystals," Oxford University Press, Oxford, 194S. 27.  Seitz, F., Revs. Mod. Phys.. 26, 89 (1954).  28.  Ivey, H. F., Phys. Rev.. 21* 341 (1947).  29.  Parry, R. W., et a l .  30.  Joannis.A.. Ann. Chim. Phys.. (8), 1, 53 (1906).  31.  Dreyfus, R. W., and P. W. Levy, Proc. Roy. Soc.. A, 246,  J . Am. Chem. S o c . 80, 2 (195S).  233 (1958). 32.  Hine, G. T., and G. L. Brownell (eds.), "Radiation Dosimetry," Academic Press, New York, 1956.  33.  Victoreen, J . A., J . App. Phys.. 20. 1141 (1949).  34.  Wang, P. K. S., et a l . . B r i t . J . Radiol.. 22, 70, 153 (1957).  35.  Jennings, W. A., B r i t . J . Radiol.. 26, 193, 198 (1953).  117  36.  De Waard, R. H., Proc. Acad. S c i . Amsterdam, 1011 (1946).  944,  37.  Metal Hydrides Incorporated, Technical B u l l e t i n 301-C. Beverly, Mass., U.S.A.  38.  Hatt, H. H., i n "Organic Syntheses," collected volume I I , edited by A.-H. B l a t t , Wiley, 1943, p. 211.  39.  Ibid .. p. 208.  40.  Heal, H. G., J . Chem. Ed.. 2£, 192 (195$).  41.  Banus, M. D., et a l . .  U.S. Patent 2,73$,369 (Mar. 1 3 ,  1956). 42.  Stevens, P. G., J . Am. Chem. S o c . 67. 407 (1945).  43.  Palmer, W. G., "Experimental Inorganic Chemistry," The University Press, Cambridge, 1954, p. 4©3.  44.  L y t t l e , D. A., et a l . , Anal. Chem.. 24, 1843 (1952).  45.  Audrieth, L. F., and B. A. Ogg, "The Chemistry o f Hydrazine," Wiley, New York, 1951, chapter 4 »  46.  Abrahams. S. C , and J . Kalnajs, J . Chem. Phys., 22, 434 (1954). Wells, A. F., "Structural Inorganic Chemistry," Oxford University-Press, Oxford, 1950, p. 70.  47.  

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