Gamma-ray spectra from thermal neutron capture on gadolinium-155 and natural gadolinium

Natural gadolinium is widely used for its excellent thermal neutron capture cross section, because of its two major isotopes: $^{\rm 155}$Gd and $^{\rm 157}$Gd. We measured the $\gamma$-ray spectra produced from the thermal neutron capture on targets comprising a natural gadolinium film and enriched $^{\rm 155}$Gd (in Gd$_{2}$O$_{3}$ powder) in the energy range from 0.11 MeV to 8.0 MeV, using the ANNRI germanium spectrometer at MLF, J-PARC. The freshly analyzed data of the $^{\rm 155}$Gd($n, \gamma$) reaction are used to improve our previously developed model (ANNRI-Gd model) for the $^{\rm 157}$Gd($n, \gamma$) reaction [K. Hagiwara et al. [ANNRI-Gd Collaboration], Prog. Theor. Exp. Phys. 2019, 023D01 (2019)], and its performance confirmed with the independent data from the $^{\rm nat}$Gd($n, \gamma$) reaction. This article completes the development of an efficient Monte Carlo model required to simulate and analyze particle interactions involving the thermal neutron captures on gadolinium in any relevant future experiments.

Covariance analysis on the thermal neutron capture cross sections using an Am-Be neutron source

We measured the thermal cross sections of 71Ga(n, γ)72Ga using an Am-Be neutron source having strength of 4 × 107 neutrons/sec using the two monitor reactions 197Au(n, γ)198Au and 55Mn(n, γ)56Mn, and obtained 4.07±0.27 b and 3.97±0.31 b as the values measured relative to Au and Mn neutron captures, respectively. We constructed their covariance matrix by taking into account the correlation of parameters which are not independent in derivation of these two thermal cross sections (e.g., Ga sample weight, decay data of 72Ga, detector efficiency of γ -ray emitted from 72Ga). The off-diagonal weighted mean of the two cross sections 4.04±0.27 b was derived from the two thermal cross sections and their covariance matrix.