The value of η for 238U with neutrons of energy between 12 MeV and 19 MeV

Abstract

The number of neutrons per inelastic collision η has been measured for uranium with incident neutrons in the energy range 12–19 MeV. Over this range η was found to increase from approximately 2·6 to 4·3. The value found at 14 MeV was 3·22 ± 0·12 which agrees with previous measurements. The technique used was to measure the neutron multiplication of shells of uranium when placed around the detector. The detector employed was a gas scintillation fission counter containing 235U, 238U or 239Pu as the fissile material. At 14 MeV the multiplication measurements were obtained both with a shell around the counter and also with a shell around the neutron source in order to find the mean transport cross section for the inelastic neutrons. This was found to be 5·2 ± 0·6 barns. Values of the cross sections for the (n, 3n) and (n, 4n) reactions are deduced and compared with the predictions of statistical theory.