Neutron spectra in coincidence with gamma rays from stopped pi - capture in 165Ho.

Abstract

Neutron spectra identified by final nuclear states have been measured for stopped ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ capture in $^{165}\mathrm{Ho}$. Neutron time of flight, with a resolution of 20% at 100 MeV, was collected in coincidence with the rotational \ensuremath{\gamma}-ray transitions in the even-even Dy isotopes. The inclusive spectrum was also measured in coincidence with pionic x rays, and agrees with previous singles measurements. The neutron spectra for individual final states show sharp cutoffs at characteristic energies, and, in some cases, the structure in the high energy component of the spectra is resolved. A Monte Carlo program based on the hybrid exciton model was developed, suitable for computing the inclusive and exclusive neutron spectra. The program gives a good fit to the measured inclusive spectrum. A different set of model parameters had to be used to reproduce the features of the spectra identified by the final nuclear states, and the fit was less satisfactory, indicating the need for an improvement in the preequilibrium approach which was not apparent in the past application to the inclusive spectra.