Measurements of neutron-induced fission cross sections forBi209,Pbnat,Pb208,Au197,Wnat, andTa181in the intermediate energy region

Abstract

Neutron-induced fission cross-section ratios $^{\mathrm{nat}}\mathrm{Pb}∕^{209}\mathrm{Bi},\phantom{\rule{0.2em}{0ex}}^{208}\mathrm{Pb}∕^{209}\mathrm{Bi},\phantom{\rule{0.2em}{0ex}}^{197}\mathrm{Au}∕^{209}\mathrm{Bi},\phantom{\rule{0.2em}{0ex}}^{\mathrm{nat}}\mathrm{W}∕^{209}\mathrm{Bi},\phantom{\rule{0.2em}{0ex}}^{181}\mathrm{Ta}∕^{209}\mathrm{Bi}$, and $^{209}\mathrm{Bi}∕^{238}\mathrm{U}$ have been measured in the 30--180 MeV energy range using the neutron beam facility at The Svedberg Laboratory in Uppsala. The $^{7}\mathrm{Li}(p,n)$ reaction was employed as a neutron source. The fission fragments were detected by thin-film breakdown counters. Cross sections at specific energies were determined using unfolding techniques with respect to the excitation function and the neutron spectra, the latter obtained from recent measurements and an evaluation. The absolute fission cross sections were obtained using the standard $^{238}\mathrm{U}(n,f)$ cross section. The $^{\mathrm{nat}}\mathrm{W}(n,f)$ and $^{181}\mathrm{Ta}(n,f)$ cross sections have been measured for the first time. The results for $^{209}\mathrm{Bi}(n,f),\phantom{\rule{0.2em}{0ex}}^{\mathrm{nat}}\mathrm{Pb}(n,f),\phantom{\rule{0.2em}{0ex}}^{208}\mathrm{Pb}(n,f)$, and $^{197}\mathrm{Au}(n,f)$ cross sections have been compared with available literature data. A universal easy-to-use parametrization has been suggested for all measured cross sections. The common features of subactinide neutron-induced fission cross sections are found to be similar to those of the proton-induced fission data.