Nuclear reactions induced byπ−at rest

The experimental information on reactions induced by stopped ${\pi }^{\mathrm{-}}$ absorbed in nuclei is critically reviewed. Evidence for the presence of α-cluster absorptions is presented and arguments are given to show that ≊25% of ${\pi }^{\mathrm{-}}$ absorptions are of this kind. In the case of two-nucleon absorption, the existing experimental information concerning the ratio of n-p to p-p absorbing pairs is discussed. Calculations of particle spectra and residue spallation yield distributions that, in addition to two-nucleon absorption, include α-cluster absorption are presented, and it is shown that a satisfactory reproduction of the data is achieved.