Measurement of the ratio of the232Th and235U fission cross sections in a neutron energy range 5?10 MeV

Abstract

The ratios of the /sup 232/Th and /sup 235/U fission cross sections were measured with the aid of a pulsed deuteron beam of the EGP-10M charge-exchange accelerator at the Physics and Power Engineering Institute, Obninsk. As the neutron source we used the D(d, n)/sup 3/He reaction in a gaseous deuterium target. Fissions of /sup 232/Th and /sup 235/U nuclei were recorded with a fast double ionization fission chamber filled with methane to a pressure of 1.5 x 10/sup 5/ Pa. The detection efficiency for fission fragments that entered the effective volume of the detector was 99.2 +/- 0.7%. The energy dependence of the cross-section ratio was measured with the aid of thin films of thorium and uranium oxides deposited onto aluminum substrates. The energy dependence of the ratio of fission cross sections was made absolute by using thorium targets which contained a small /sup 235/U impurity. The background of the experimental room was determined from the time spectra and had little effect on the results of the measurements.