Absorption, Charge-Exchange, and Double-Charge-Exchange Reactions ofπMesons with Complex Nuclei: Comparison of Theoretical Predictions with Experimental Results

Abstract

The two-step intranuclear-cascade evaporation model is used in the calculation of nucleon spectra, particle multiplicities, and radiochemical cross sections following stopped-${\pi }^{-}$ absorptions by complex nuclei. The nucleon spectra and particle multiplicities from the pion absorption by light elements are, in general, predicted quite well. The theoretical particle yields from the heavy elements are overestimated and the particle spectra are too soft. These discrepancies are attributed to an insufficient number of pion absorptions near the edge of the nucleus for the heavy elements in the theoretical model. The magnitudes of the theoretical radiochemical cross sections from slow-${\pi }^{-}$ absorption by iodine are in fair agreement with those from experiments, but the peak in the cross-section distribution versus isotope mass for some of the isotopes appears at lower mass values than the measured ones. This discrepancy is consistent with those above. The model does well in predicting the change-exchange cross section, but does poorly in estimating the double-charge-exchange cross section for pions with energies below 200 MeV. These cross sections represent about 1% or less of the total interaction cross section, and the theoretical model does not accurately reproduce such events, in general.