Cross sections and isomeric cross-section ratios in the interactions of fast neutrons with isotopes of mercury

Abstract

Excitation functions were measured for the reactions $^{196}\mathrm{Hg}$($n$, $2n)$$^{195}\mathrm{Hg}$${}^{m,g},$$^{198}\mathrm{Hg}$($n$, $2n)$$^{197}\mathrm{Hg}$${}^{m,g},$$^{204}\mathrm{Hg}$($n$, $2n)$$^{203}\mathrm{Hg}$,$^{198}\mathrm{Hg}$($n,p)$$^{198}\mathrm{Au}$${}^{g}$, and $^{199}\mathrm{Hg}$($n,p)$$^{199}\mathrm{Au}$ over the neutron energy range of 7.6--12.5 MeV. Quasimonoenergetic neutrons were produced via the $^{2}\mathrm{H}$($d,n)$$^{3}\mathrm{He}$ reaction using a deuterium gas target at the J\"ulich variable energy compact cyclotron CV 28. Use was made of the activation technique in combination with high-resolution, high-purity Ge detector $\ensuremath{\gamma}$-ray spectroscopy. All the data were measured for the first time over the investigated energy range. The transition from the present low-energy data to the literature data around 14 MeV is generally good. Nuclear model calculations using the codes STAPRE and EMPIRE-2.19, which employ the statistical and precompound model formalisms, were undertaken to describe the formation of both the isomeric and ground states of the products. The total reaction cross section of a particular channel is reproduced fairly well by the model calculations, with STAPRE giving slightly better results. Regarding the isomeric cross sections, the agreement between the experiment and theory is only in approximate terms. A description of the isomeric cross-section ratio by the model was possible only with a very low value of \ensuremath{\eta}, i.e., the ${\ensuremath{\Theta}}_{\text{eff}}$/${\ensuremath{\Theta}}_{\text{rig}}$ ratio.