Inclusive neutron and charged particle spectra from the absorption of stopped negative pions in nickel isotopes

Energy spectra of neutrons and charged particles emitted after the absorption of stopped negative pions in the Ni isotopes 58Ni, 60Ni, 62Ni and 64Ni have been measured. The data are compared with model calculations for pion absorption on a peripheral nucleon pair and subsequent secondary reactions. The sum of the mean number of emitted neutrons and protons 〈n〉 + 〈p〉 is 7.2 ± 1.2, independent of the neutron number N, whereas the difference 〈n〉 — 〈p〉 increases linearly with N from 1.6 ± 0.8 for 58Ni to 5.0 ± 1.1 m for 64Ni. The experimental results are compared with measurements of residual nuclei from stopped π−- and p-induced reactions in the above-mentioned Ni isotopes.