Study of Anomalous Subbarrier Fission of Np-237 Using an SVZ-100 Lead Slowing-Down Neutron Spectrometer

In addition to the well studied complex resonance of subbarrier fission of Np-237 at the neutron energy of 39 eV, intense anomalous fission resonances are detected at the SVZ-100 spectrometer. The energy of the first resonance is lower than 0.3 eV. The second resonance creates an energy dependence of the cross section according to the law 1/v, extrapolation of which to the thermal energy yielded the value of 17 barn. The third resonance at short times of neutron slowing down is characterized by a cross section no lower than 1.4 barn. The fission cross sections in these anomalous resonances exceed available data by two orders of magnitude and larger.