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The angular correlation of annihilation radiation and a study of high energy nuclear reactions in neon Erdman, Karl Lembit

Abstract

In the first section of this thesis the measurement of the angular correlation of annihilation radiation in various materials is described. It is found that the angular dependence of the coincidence counting rate leads to results which are not in agreement with the present theories of the mechanism of positron decay processes in crystal and metal lattices. In particular, positrons do.not appear always to reach thermal energies before annihilation with electrons takes place. A search for the photodisintegration of Ne²⁰ using the gamma rays from the Li⁷(p,ɤ )Be⁸ reaction is described. An unusually low cross-section for the photo-alpha process to the ground state of O¹⁶ is found, 8 x 10⁻³⁰cm² for the 17.6 Mev. gamma ray and 3 x 10²⁹ cm² for the 14.8 Mev. gamma ray. Cross-sections of the order of 10⁻²⁸ cm² are obtained for alpha particle transitions to the 6 and 7 Mev. Excited state of O¹⁶. These cross-sections are of the usual order of magnitude for photodisintegration reactions. Irradiation of Ne²⁰ with high energy neutrons gives rise to alpha particle transitions from the Ne²¹ compound nuclear levels so formed to several excited states of O¹⁷. The excitation energies of these states are in good agreement with those measured in other nuclear reactions.

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