Investigation of the ${}^{241}\mathrm{Am}\left(n,2n\right){}^{240}\mathrm{Am}$ cross section

The ${}^{241}\mathrm{Am}\left(n,2n\right){}^{240}\mathrm{Am}$ reaction cross section has been measured at four energies, 10.0, 10.4, 10.8, and 17.1 MeV, by means of the activation technique, relative to the ${}^{27}\mathrm{Al}\left(n,\alpha \right){}^{24}\mathrm{Na}$ reaction reference cross section. Quasi-monoenergetic neutron beams were produced via the ${}^2\mathrm{H}\left(d,n\right){}^3\mathrm{He}$ and the ${}^3\mathrm{H}\left(d,n\right){}^4\mathrm{He}$ reactions at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR “Demokritos”. The high purity ${}^{241}\mathrm{Am}$ targets were provided by JRC-IRMM, Geel, Belgium. The induced $\gamma$-ray activity of ${}^{240}\mathrm{Am}$ was measured with high-resolution high-purity germanium (HPGe) detectors. Auxiliary Monte Carlo simulations were performed with the mcnp code. The present results are in agreement with data obtained earlier and predictions obtained with the empire code.

Figure 1

Schematic diagram of the Am target assembly.

Figure 2

Neutron energy spectra calculated with neusdesc and mcnp5 at the distance of interest either from the gas or from the tritium target for each irradiation: (a) $10.0\pm 0.1$ MeV, (b) $10.4\pm 0.1$ MeV, (c) $10.8\pm 0.1$ MeV, (d) $17.1\pm 0.3$ MeV.

Figure 3

High-energy part of the $\gamma$-ray spectra of an Am sample, before and after irradiation with 10.4 MeV neutrons.

Figure 4

Plot of the quantity $R$ of Eq. (6), as a function of $\gamma$-ray energy taken at 10.4 MeV. The $R$ value at 987.8 keV was determined by extrapolation. mcnp5 simulation results which indicate the dependence of ratio $R$ from energy are also presented. The dotted curves denote the confidence bands.

Figure 5

The experimental ${}^{241}\mathrm{Am}\left(n,2n\right){}^{240}\mathrm{Am}$ cross section values obtained at NCSR “Demokritos” compared with previous data and evaluations.

Figure 6

Cross section of four reaction channels for the $n+{}^{241}\mathrm{Am}$ interaction. Theoretical calculations results obtained with the empire code are presented along with the existing experimental data for each reaction: (a) ${}^{241}\mathrm{Am}\left(n,2n\right)$, (b) ${}^{241}\mathrm{Am}\left(n,f\right)$, (c) ${}^{241}\mathrm{Am}\left(n,3n\right)$, (d) ${}^{241}\mathrm{Am}(n$,tot).