Determination of theCe142(γ,n)cross section using quasi-monoenergetic Compton backscatteredγrays

Abstract

Background: Knowing the energy dependence of the $(\ensuremath{\gamma},n)$ cross section is mandatory to predict the abundances of heavy elements using astrophysical models. The data can be applied directly or used to constrain the cross section of the inverse ($n$,$\ensuremath{\gamma}$) reaction.Purpose: The measurement of the reaction $^{142}\mathrm{Ce}$${(\ensuremath{\gamma},n)}^{141}$Ce just above the reaction threshold amends the existing experimental database in that mass region for $p$-process nucleosynthesis and helps to understand the $s$-process branching at the isotope $^{141}\mathrm{Ce}$.Method: The quasi-monoenergetic photon beam of the High Intensity $\ensuremath{\gamma}$-ray Source (HI$\ensuremath{\gamma}$S), TUNL, USA, is used to irradiate naturally composed Ce targets. The reaction yield is determined afterwards with high-resolution $\ensuremath{\gamma}$-ray spectroscopy.Results: The experimental data are in agreement with previous measurements at higher energies. Since the cross-section prediction of the $^{142}\mathrm{Ce}$$(\ensuremath{\gamma},n)$ reaction is exclusively sensitive to the $\ensuremath{\gamma}$-ray strength function, the resulting cross-section values were compared to Hauser-Feshbach calculations using different $\ensuremath{\gamma}$-ray strength functions. A microscopic description within the framework of the Hartree-Fock-BCS model describes the experimental values well within the measured energy range.Conclusions: The measured data show that the predicted $(\ensuremath{\gamma},n)$ reaction rate is correct within a factor of 2 even though the closed neutron shell $N=82$ is approached. This agreement allows us to constrain the ($n$,$\ensuremath{\gamma}$) cross section and to improve the understanding of the $s$-process branching at $^{141}\mathrm{Ce}$.