Deexcitation gamma rays from the interaction of 70-MeV pions withs−dshell nuclei

The interaction of 70-MeV positive and negative pions with $s-d$ shell nuclei was studied via measurements of the deexcitation $\gamma$ rays from residual nuclei produced in the reactions. Cross sections for producing specific levels in the residual nuclei were measured. The results are compared with Monte Carlo calculations of intranuclear cascades, followed by evaporation processes. In order to take into account the special features of the prompt $\gamma$-ray technique, the probability for leaving the residual nuclei at different regions of excitation, together with measured $\gamma$-ray branching ratios, are incorporated into the calculated cross sections. Good agreement is found between measured and calculated cross sections for reactions involving the removal of four or more nucleons. For such reactions, the calculations are dominated by pion absorption processes. The cross sections for the removal of an $\alpha$-equivalent cluster from T = 0 nuclei have about the same strength as those corresponding to the removal of a triton cluster from the neighboring $T=\frac{1}{2}$ nuclei. This suggests that the final nucleus, rather than the removed particle, is mainly responsible for the observed strength. The cross sections for single-nucleon-removal reactions do not agree with the calculations.