Effect of preequilibrium spin distribution on 48Ti+n cross sections

Nuclear model calculations of discrete gamma-ray production cross sections produced in Ti-48(n,n(')gamma(i))Ti-48 and Ti-48(n,2n gamma(i))Ti-47 reactions were made as a function of incident neutron energy from E-n=1 MeV to 35 MeV and compared with new experimental results using the large-scale Compton-suppressed germanium array for neutron induced excitations (GEANIE) at LANSCE. The Hauser-Feshbach reaction code GNASH, incorporating the spin distribution for the preequilibrium process calculated with the Feshbach-Kerman-Koonin (FKK) quantum-mechanical preequilibrium theory, was used to calculate partial gamma-ray transition cross sections. The comparisons of calculated and experimental data demonstrate that, the FKK model for preequilibrium leads a better overall reproduction of the experimental data above E-n=10 MeV, where preequilibrium processes are important. The FKK calculation predicts a strong reduction in the high-spin state population in Ti-48 by inelastic scattering. Population of low-spin states was also affected, however the change in the low-lying 983.5-keV (2(+)) state production is small because almost all gamma-ray decay cascades feed this transition. In addition, the FKK calculation has a significant impact on the partial gamma-ray transition cross sections for the (n,2n) reaction above E-n=15 MeV. The calculated cross sections for high-spin states in Ti-47 are reduced, and those from the low-spin states are enhanced, in agreement with the experimental cross section data.