Left-right and Angular Asymmetry of Fission Neutron Emission.

The prompt fission neutron spectrum N(E) plays an important role in various nuclear technologies, both in energy and non-energy applications. From a more fundamental point of view, an accurate knowledge of N(E) can shed some light on the nuclear fission process itself. At IRMM we have measured the neutron spectrum at an incident neutron energy of about 0.5 MeV. This was done on request of the OECD, Nuclear Energy Agency's (NEA) Working Party of International Nuclear Data Evaluation Co-operations (WPEC), based on a recommendation of its subgroup 9. This subgroup came to the conclusion that the present database of the neutron spectrum for 235U(n,f) at thermal incident neutron energy is insufficient and needs improvement. Modelling of this spectrum with the present Los Alamos (LA) model is not possible. First measurements at 0.5 MeV incident neutron energy have been performed, since at this energy the LA-model can perfectly describe the experimental results of Johansson and Holmquist [1]. The results achieved so far do not reproduce the measurements of Ref. [1], but are in agreement with several other literature values. Also the measurements are neither in agreement with the Los Alamos model, nor with the mean neutron energy coming from integral experiments and benchmark investigations. The present experiment is the only one utilizing several neutron detectors at different angles. Having performed three different runs, so far the conclusion is that the results at 90 degree coincide in all runs despite differences in the experimental conditions. The data at e.g. 120 degree differ between the runs. The physical reason for this behaviour is not understood at present.

KORNILOV Nikolai;  HAMBSCH Franz-Josef;  FABRY Imrich;  OBERSTEDT Stephan;  SIMAKOV S. P.; 

2009-08-11

Joint Institute for Nuclear Research

JRC44455

https://publications.jrc.ec.europa.eu/repository/handle/JRC44455,