Effect of preequilibrium spin distribution onTi48+ncross sections

Abstract

Nuclear model calculations of discrete γ -ray production cross sections produced in 48 Ti(n, n γ i ) 48 Ti and 48 Ti(n, 2nγ i ) 47 Ti 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 FeshbachKerman-Koonin (FKK) quantum-mechanical preequilibrium theory, was used to calculate partial γ -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 48 Ti 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 γ -ray decay cascades feed this transition. In addition, the FKK calculation has a significant impact on the partial γ -ray transition cross sections for the (n, 2n) reaction above E n = 15 MeV. The calculated cross sections for high-spin states in 47 Ti are reduced, and those from the low-spin states are enhanced, in agreement with the experimental cross section data.

Neutron inelastic cross section measurements fornatTi

“…The same contribution can be also observed in panel d) where we can see an increase in the value of the cross section around 9 MeV. This is also the main difference between our experimental results and the results of Dashdorj et al [8] and it comes from the fact that they used an enriched 48 Ti sample. All the cross sections reported here have maximum values above 1.2 b and total relative uncertainties around 5% except the one for 49 Ti where the cross section is around 0.2 b.…”

“…Looking in the experimental nuclear reaction database EXFOR [7] we observe that most of the neutron inelastic scattering experiments on the titanium isotopes were performed between 1960 and 1980 in a limited energy range. The energy range was extended by Dashdorj et al [8] in 2007 when they determined the γ -production cross sections of the transitions observed from the inelastic scattering of the neutrons on 48 Ti up to E n = 200 MeV. Our goal was to measure the γ -production cross sections for the most important transitions in all of the stable Ti isotopes.…”

Monte Carlo simulation for statistical Hauser-Feshbach theory

“…The Monte Carlo technique also facilitates new insights into the nuclear reaction, as correlations between different processes can be studied by gating on a particular γ-ray so as to provide useful information on spin and parity distributions in the continuum state [3]. Coincidence experiments, i.e.…”

Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections

“…Recent results of γ-ray production cross section measurements at LANSCE performed with the GEANIE detector array [1] demonstrated that the spin distribution of the pre-equilibrium reaction has a large impact on the γ-ray transition probability when incident energies are above E n = 10 MeV [2,3]. Since it was previously assumed that the spin distribution in the preequilibrium process had a limited impact on nuclear reaction cross sections, classical theories such as the exciton model [4,5] are still widely used to analyze particle emission data at high incident energies.…”