Photoneutron reaction cross-section data for ${}^{75}\mathrm{As}$: Experiments and evaluation

The problems of reliability of partial photoneutron cross-section data for ${}^{75}\mathrm{As}$ obtained using beams of quasimonoenergetic photons produced by annihilation in flight of relativistic positrons and the method of neutron multiplicity sorting at Lawrence Livermore National Laboratory (USA) and Centre d’Etudes Nucleaires of Saclay (France) were discussed using the objective physical data reliability criteria. New data for photoneutron reaction cross sections for ${}^{75}\mathrm{As}$, satisfying those criteria, were obtained using the experimental-theoretical method for partial reaction cross-section evaluating. Evaluated data for ${}^{75}\mathrm{As}$ were compared with experimental data and the problems of significant disagreements between Livermore and Saclay data were discussed in detail. It was shown that experimental data for the $(\gamma ,1n)$ and $(\gamma ,2n)$ reactions’ cross sections obtained at Livermore are not reliable because of significant systematic uncertainties of different nature.

Figure 1

Comparison of the experimental ([22], triangles; [23], squares) neutron yield cross sections $\sigma (\gamma ,Sn)$ with the cross sections calculated before (dotted line) and after (solid line) correction (see further) in the CMPNR ([11, 12].

Figure 2

$F_1^{exp}$ (a) and $F_2^{exp}$ (b) data obtained for ${}^{75}\mathrm{As}$ using experimental data of Livermore ([22], triangles) and Saclay ([23], squares) in comparison with results of calculated $F_{1,2}^{\mathrm{theor}}$ (model from [11, 12], lines).

Figure 3

The comparison of the evaluated (circles) and the experimental ([22], triangles; [23], squares) cross sections of the reactions on ${}^{75}\mathrm{As}$: (a) $\sigma (\gamma ,\mathrm{tot})$, (b) $\sigma (\gamma ,1n)$, and (c) $\sigma (\gamma ,2n)$.

Figure 4

Comparison of the differences $\mathrm{\Delta }\sigma$ [Eq. (6)] between the evaluated and the experimental cross sections for ${}^{75}\mathrm{As}$: (a) for data from [23] [squares for reaction $(\gamma ,1n)$; circles for $\left(\gamma ,2n\right)]$ and (b) for data from [22] [triangles for reaction $(\gamma ,1n)$; circles for $\left(\gamma ,2n\right)]$.

Figure 5

Comparison of the experimental ([22], triangles; [23], squares) neutron yield cross sections $\sigma (\gamma ,Sn)$ with the corrected (open triangles) cross section [22].

Figure 6

Comparison of the specially evaluated using normalized data [22] cross sections (open circles) and the normalized experimental [22] (open triangles) cross sections of the reactions on ${}^{75}\mathrm{As}$: (a) $\sigma (\gamma ,\mathrm{tot})$, (b) $\sigma (\gamma ,1n)$, and (c) $\sigma (\gamma ,2n)$.

Figure 7

Comparison of the differences Δσ [Eq. (6)] between the cross sections specially evaluated using normalized [22] data and the normalized experimental [22] cross sections for ${}^{75}\mathrm{As}$ [open triangles for reaction $(\gamma ,1n)$; open circles for $\left(\gamma ,2n\right)]$.