${}^{233}\mathrm{Pa}(n,\gamma )$ cross section extraction using the surrogate reaction ${}^{232}\mathrm{Th}({}^3\mathrm{He},p){}^{234}\mathrm{Pa}^{*}$ involving spin-parity distribution

The neutronic properties of ${}^{233}\mathrm{Pa}$ play a crucial role in the thorium fuel cycle since it directly impacts the inventory of the fissile isotope ${}^{233}\mathrm{U}$. Currently, the experimental data of the ${}^{233}\mathrm{Pa}(n,\gamma )$ cross section are rather scanty with poor accuracy and significant discrepancy exists in the experimental and evaluated data. In this work, the ${}^{233}\mathrm{Pa}(n,\gamma )$ cross section is studied through the surrogate reaction ${}^{232}\mathrm{Th}({}^3\mathrm{He},p){}^{234}\mathrm{Pa}^{*}$. The spin-parity (SP) distribution of the ${}^{232}\mathrm{Th}({}^3\mathrm{He},p){}^{234}\mathrm{Pa}^{*}$ is calculated with the distorted wave Born approximation and then the ${}^{233}\mathrm{Pa}(n,\gamma )$ cross section is extracted using the statistical Hauser-Feshbach model. It is found that the extracted ${}^{233}\mathrm{Pa}(n,\gamma )$ data considering the SP distribution have a tendency to agree with the evaluated nuclear data files, ENDF/B-VIII.0 and JENDL-5, whereas the experimental ones without considering the SP distribution are visibly higher than the evaluated data. This suggests that the SP distribution should be considered reasonably when employing the surrogate-reaction method to extract the ${}^{233}\mathrm{Pa}(n,\gamma )$ cross section.

Figure 1

Schematic representation of the desired reaction ${}^{233}\mathrm{Pa}(n,\gamma ){}^{234}\mathrm{Pa}^{*}$ and surrogate reaction ${}^{232}\mathrm{Th}({}^3\mathrm{He},p){}^{234}\mathrm{Pa}^{*}$. Generally, the ${}^{234}\mathrm{Pa}$ decays through the following pathways: nuclear fission, $\gamma$ decay, and neutron emission with certain probabilities.

Figure 2

The calculated ${\sigma }_n^{\mathcal{C}N}(E^{*},J,\pi )$ as a function of neutron energy in the cases of negative (a) and positive (b) parities.

Figure 3

The calculated $F_{\delta }^{CN}(E^{*},J,\pi )$ for ${}^{234}\mathrm{Pa}^{*}$ populated by the reaction ${}^{232}\mathrm{Th}({}^3\mathrm{He},p)$ at 5.72 MeV.

Figure 4

The calculated and experimental $P_{\delta \gamma }\left(E^{*}\right)$ at $=5.32$, 5.52, 5.72, 5.92, and 6.12 MeV. The calculated data are obtained when $\chi$${}^2$ is minimized to be 3.38. The experimental data are taken from Ref. [10].

Figure 5

The ${}^{233}\mathrm{Pa}(n,\gamma )$ cross section depending on neutron energy. The calculated data are obtained when $G_{\mathrm{norm}}=3.2$. The experimental data is taken from Ref. [10] and the evaluated ones are taken from ENDF/B-VIII.0, JENDL-5, and ROSFOND-2010.