New calculation for the neutron-induced fission cross section of ${}^{233}\mathrm{Pa}$ between 1.0 and $3.0\text{MeV}$

The ${}^{233}\mathrm{Pa}(n,f)$ cross section, a key ingredient for fast reactors and accelerators driven systems, was measured recently with relatively good accuracy [F. Tovesson et al., Phys. Rev. Lett. 88, 062502 (2002)]. The results are at strong variance with accepted evaluations and an existing indirect experiment. This circumstance led us to perform a quite detailed and complete evaluation of the ${}^{233}\mathrm{Pa}(n,f)$ cross section between 1.0 and $3.0\text{MeV}$, where use of our newly developed routines for the parametrization of the nuclear surface and the calculation of deformation parameters and level densities (including low-energy discrete levels) were made. The results show good quantitative and excellent qualitative agreement with the experimental direct data obtained by Tovesson et al. [F. Tovesson et al., Phys. Rev. Lett. 88, 062502 (2002)]. Additionally, our methodology opens new possibilities for the analysis of subthreshold fission and above threshold second-chance fission for both ${}^{233}\mathrm{Pa}$ and its decay product ${}^{233}\mathrm{U}$, as well as other strategically important fissionable nuclides.

Figure 1

Calculated potential energy topography of ${}^{234}\mathrm{Pa}$ (bottom) and the corresponding equipotentials (top), as a function of the deformation parameters $\epsilon$ and ${\alpha }_4$ (a) and $\epsilon$ and ${\alpha }_3$ (b).

Figure 2

Calculated nuclear shapes associated with the most relevant points of $V(\epsilon ,\alpha )$ along the fission path (this work).

Figure 3

Calculated (this work) and experimental numbers of cumulative levels for ${}^{234}\mathrm{Pa}$ (a) and ${}^{233}\mathrm{Pa}$ (b). Calculated total level densities in the first and the second saddle point (c).

Figure 4

Neutron-induced fission cross section of ${}^{233}\mathrm{Pa}$ meassured by Tovesson et al. (data points Refs. 1) and the result of our calculation (full curve). Also shown are two previous evaluations (Refs. 16, 17).