Yields of Photonuclear Reactions with 320-Mev X-Rays. II. Interpretation of Results

It is convenient to separate the yields of radio-nuclides obtained in the work described in the preceding paper into two groups. The first group consists of the yields of nuclides which are only one or two mass units lighter than the target. All of the yields in this group, and especially those corresponding to (γ, n) reactions, are relatively large. They are due mainly to photons in the giant resonance region (hν~20 Mev) of the x-ray spectrum, and account for most of the nuclear events produced in mediumweight targets by 320-Mev x-rays. The yields of those radio-nuclides which are more than a few mass units lighter than the target are in many ways more interesting than the ones in the first group. They are found to exhibit a simple pattern very similar to those obtained in particle-induced high-energy reactions. It is shown that such patterns are at least qualitatively consistent with models of high-energy nuclear reactions in which the last few particles emitted from a struck nucleus, leave by "evaporation." Indeed the evaporation of these last particles exerts so strong an influence on the form of the observed yield pattern, that it becomes very difficult to say anything about either the nature of the original nuclear events or the emission of the first few particles on the basis of a study of yield patterns. Finally, a rough quantitative comparison is made of the yields of radio-nuclides and the reported yields of neutrons and other particles emitted from medium-weight nuclei irradiated with 320-Mev x-rays.