Neutron induced fission of 235sub(U)

In order to achieve a better understanding of the fision process it is essential to get experimental data on the details of the mass, energy and angular distributions, and the mass versus energy and mass versus angular distribution correlations as function of excitation energy. The present work describes the result of such a measurement for 235U(n,f) with thermal <Esub(n)<6.0 MeV. Experimental problems as well as difficulties in the data analysis are considered. The working principle and electronic setup of the double Frisch gridded ionization chamber is discussed in detail. Since the present work also involed developments of the detector it was important that the 235U(n,f) reaction has a rather high cross section, especially for thermal neutrons. The changes in the average total kinetic energy relative to the thermal value have been measured at several neutron energies above thermal, and the angular anisotropy of the fission fragments averaged over all fragment masses has been determined in several measurements. Many of the thermal values, the average kinetic energy and average angular anisotropy values at higher neutron energies were compared with measurements using other techniques. Good agreement is found. It indicates that the chamber works as intended and it gives confidence to the data measured for the first time with the present setup. It furthermore allows to use the chamber with confidence in future measurements on less known fission reactions and at less explored excitation energies of the compound nucleus. (author)