Resolution of the nature of the coupling in subthreshold fission in 238U+n.

Abstract

The analysis of a recent high-resolution neutron capture measurement at 152 m has provided the first evidence that the strong fission resonance at 721 eV is a class-II resonance. This conclusion is based on the measured capture width of 4.7\ifmmode\pm\else\textpm\fi{}0.6 meV, which is considerably smaller than the average capture width of 23.5 meV for the neighboring resonances. Furthermore, after analyzing the fission widths for the 721- and 1211-eV clusters, we conclude for the ${J}^{\ensuremath{\pi}}={\frac{1}{2}}^{+}$ fission barrier in $^{239}\mathrm{U}$ that the inner barrier is lower than the outer barrier by \ensuremath{\sim} 1.5 MeV.