Prompt Neutrons from Thorium Photofission
Abstract
We have measured the distribution in angle and velocity of the prompt neutrons from the bremsstrahlung-induced photofission of Th232 in the photon energy region near threshold. Using knowledge of the fission-fragment angular distribution, the data have been interpreted in terms of the neutron distribution relative to the fragment axis. The measurement allows a quantitative estimate of the fraction of neutrons which are not emitted by fully accelerated fragments. The result for this fraction is 0.07+/-0.09. Assuming isotropic neutron emission in the fragment center-of-mass frame, the analysis also determines some characteristics of the neutron energy spectrum in this frame. The spectrum has an average energy η¯=1.14+/-0.06 MeV and a second central moment σ2(η)=(0.77+/-0.06)η¯2. If it is represented by an evaporation-type spectrum with some distribution of temperatures, there is no significant contribution from temperatures equal to or greater than η¯. We have made a similar analysis of data on prompt neutrons from the spontaneous fission of Cf252 obtained by Bowman, Thompson, Milton, and Swiatecki, and compared the results with those for Th232 photofission.
- Publication:
-
Physical Review
- Pub Date:
- January 1965
- DOI:
- 10.1103/PhysRev.137.B89
- Bibcode:
- 1965PhRv..137...89S