Study of anomalous subbarrier fission of Th-232 in the lead body of the SVZ-100 lead slowing-down neutron spectrometer

Anomalous fission of Th-232 was twice studied at the SVZ-100, in 2003 and after the formation of hydroxide films on the surface of lead blocks, in 2005. After the formation of these films, the Th-232 fission cross section in the region of short slowing down times decreased by a factor of 140 to 0.3 mbarn which is 200 times larger than the values determined using neutron time-of-flight spectrometers (TFSs) to energies of 700 keV. The explanation of previously unknown features of neutron properties in Lead Slowing-down Spectrometers, previously published by A. A. Bergman, is presented.