Gamma-ray study of pion-induced reactions on the nickel isotopes

Abstract

The spectra of residual nuclides following 100-, 160-, and 220-MeV ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ bombardment of $^{58,60,62,64}\mathrm{Ni}$ have been measured by detecting prompt and, at 220 MeV, $\ensuremath{\beta}$-delayed gamma rays. A wide spectrum of residual nuclides extending along the valley of stability down to Ca, is seen. Where radioactivities were measured, the total (prompt + delayed) observed cross section amounted to \ensuremath{\approx} 900 mb. The mean number of nucleons removed increased from about 5 for the $^{58}\mathrm{Ni}$ target to about 8 for $^{64}\mathrm{Ni}$. The residual nuclide spectrum depends sensitively on the target neutron excess, but is essentially independent of pion charge or pion energy in the range observed. A Monte-Carlo cascade-evaporation calculation involving an intermediate $\ensuremath{\Delta}$ resonance reproduces the yield of residual nuclides far (more than about eight nucleons) removed from the target, but it fails to reproduce the yield of nearer nuclides which is a more sensitive measure of the early stages of the reaction.NUCLEAR REACTION $^{58,60,62,64,}\mathrm{Ni}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}, x\ensuremath{\gamma})$, ${E}_{\ensuremath{\pi}}=100, 160, 220$ MeV; measured prompt and $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ spectra; determined yields of residual nuclides and their distribution; established systematics. Enriched targets.