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Beta and gamma ray spectroscopic analysis of the radiations emitted in the decay of selenium 75

University of British Columbia

The nuclear energy levels of As⁷⁵ have been investigated through the study of the Se⁷⁵ decay scheme. The internal conversion spectrum as well as the photoelectron spectra (using bismuth and lead radiators) were measured with a modified thin lens magnetic spectrometer. A technique was developed for accurate determination of the transmission of the spectrometer in order to obtain the absolute conversion electron transition intensities. The gamma ray intensities were determined from the spectrum measured with a NaI(T1) scintillation spectrometer in conjunction with the results from the photoelectron spectra. From these measurements the absolute conversion coefficients for eight transitions were obtained. In addition coincidence techniques employing a slow- fast coincidence system (resolving time 10⁻⁷ sec) were used to measure gamma-gamma coincidences, conversion electron-gamma coincidences and gamma-gamma directional correlations. A one hundred channel kicksorter was used to facilitate accumulation of the data at the relatively low coincidence counting rates. Multipolarities of the following transitions were determined, (energies in kev), 97(E2); 121(El); 136(El); 199(M1+E2); 265(Ml,-0.12<δ(E2)<+0.07); 279(M1+E2, δ =-0.46 ±0.16); 304(E3) and 401(El). Also detected but for which multipolarities could not be determined was a 66 kev transition and a very weak 572 kev gamma transition. In addition the existence of a 24 kev and a 77 kev transition was inferred from the intensity measurements. An energy level diagram for As⁷⁵ has been constructed with the following energy levels and spin assignments, (energies in kev), 572 (7/2 +), 477 (?), 401 (5/2 +), 304 (9/2 +), 279 (5/2 -), 265 (3/2 -), 199 (1/2 -), 0 (3/2 -). It was concluded that the ground state of Se⁷⁵ has even parity.

Text

2011-11-23

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http://hdl.handle.net/2429/39246

Physics

University of British Columbia

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