Gamma-Radiation from Excited States of Light Nuclei

Abstract

Gamma-radiation emitted in the decay of the excited states of heavy radioactive nuclei has been the subject of experimental and theoretical investigations since the first discovery of natural radioactivity. This radiation has been found to cover the energy range from a few kev up to about 3 Mev, and in this energy range the interaction of the radiation with matter has been extensively studied. As a result, considerable information is now available on the fundamental elementary interactions, the photoelectric effect, the Compton effect, internal conversion, and pair formation. The quantum-mechanical predictions concerning these effects have been verified with a high degree of experimental accuracy. This knowledge of the fundamental interactions makes possible the use of these effects in the study of the spectroscopy of gamma-radiation which in turn leads to information concerning the excited states of the emitting nuclei. An excellent overview of this subject has recently appeared in this publication by G.D. Latyshev [1]. The situation is somewhat different in regard to the gamma-radiation emitted from the excited states of light nuclei. None of the very light nuclei have half-lives long enough to occur in natural radioactivity and, as a result, study of this radiation has been possible only since the discovery in 1919 of the artificial disintegration of light nuclei with radioactive alpha-particles. The development since 1930 of numerous devices, such as the cyclotron and the electrostatic accelerator, for the acceleration of hydrogen nuclei as well as helium nuclei to high energies for use in disintegration experiments has given considerable impetus to the experimental study of this gamma-radiation, and it is, in fact, the results of such investigations which will constitute the major portion of this discussion. Information on the gamma-radiation from light nuclei has also been obtained by the use of the neutron as a bombarding particle, although the disintegrations of light nuclei with neutrons have not been as extensively studies as have those of heavy nuclei. The major portion of this discussion will be concerned with investigations in which the proton has been employed as a bombarding agent, since it has been mainly with this particle that direct investigations of gamma-radiation have been made. We not too, at this point, that the illustrative examples are drawn mainly from experimental work dine in the Kellogg Radiation Laboratory at the California Institute. It will be clear from the discussion of the results in the last section that the full picture has been the result of experimental and theoretical work in many laboratories.

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