Fission fragment angular distributions for neutron fission of Th230

Fission fragment angular distributions have been measured for the neutron fission of $^{230}\mathrm{Th}$ in the energy range 680-1100 keV with special attention to the region of the large vibrational resonance in the neutron fission cross section near 715 keV. The analysis involved the search for a set of fission barrier parameters which lead to a simultaneous description of the angular distribution data and the existing data for the fission cross section. It was found that the data for the 715 keV resonance could be reproduced only if the $K=\frac{1}{2}$ band responsible for this resonance splits into two separate bands, one of each parity, and if the decoupling parameter has a parity dependent sign. The derived moment of inertia constant $\frac{{\ensuremath{\hbar}}^{2}}{2\mathcal{I}}$ has a value of 1.85 keV which suggests that the vibrational resonance occurs within a minimum in the potential energy surface corresponding to a $\ensuremath{\beta}$ deformation of ${\ensuremath{\epsilon}}_{2}=0.85$. The derived data are all consistent with the predicted triple-humped fission barrier for the thorium nuclei.NUCLEAR REACTIONS $^{230}\mathrm{Th}(n, f)$, ${E}_{n}=0.68\ensuremath{-}1.10$ MeV, measured $W(\ensuremath{\theta})$, comprehensive statistical model analysis, barrier parameter derived, triple-humped fission barrier for thorium confirmed.