Neutron Multiplicity in the Fission ofU238andU235with Neutrons up to 200 MeV

Abstract

Prompt-fission-neutron multiplicities were measured for 238U(n,f) and 235U(n,f) from 0.4 to 200 MeV. The data are of great importance in connection with accelerator-coupled nuclear reactor systems incinerating actinides. We report that fission induced by 200 MeV neutrons produces approximately 10 more prompt neutrons than fission induced by reactor neutrons. Most neutrons are evaporated from the fission fragments and the prefission compound nucleus, as the preequilibrium emission of energetic neutrons accounts for a maximum of 15% of the prompt neutrons at 200 MeV.

235mU and 235U neutron-induced fission

“…The effect of (n,nf) neutrons is the strongest for 232 Th(n,F) reaction. It was shown in [6] that similar discrepancies are observed at E n = 14.7 MeV when compared to recent 235 U(n,F) PFNS data [34,35]. Modelling of the spectra of neutrons, emitted from the fission fragments [36], appears to be rather crude, however it nicely reproduces measured PFNS for 232 Th(n,F) and 238 U(n,F) [27], 235 U(n,F) [6] and might be used for PFNS prediction for the nuclides with various fissilities [37][38][39][40].…”

Measurement of the average energy and multiplicity of prompt-fission neutrons from 238U(n,f) and 237Np(n,f) from 1 to 200 MeV

“…[3,4]) recent experimental results concerning prompt fission neutron spectra (PFNS) emerging from the neutron induced fission of 238 U and 235 U. Those results have been obtained taking advantage of a similar experimental set-up.…”

“…In the previously reported experiment (refs. [3] and [4]), only 3 neutron detectors were available. This improvement made possible a better angular coverage and allowed for higher statistics.…”

Spatial Distribution of Induced Fission from the Pixilated Alpha Detector in a DT Generator

“…Multiplicity coincidence measurements are based on the assumption that two or more prompt fission particles (neutrons and gamma rays) are emitted nearly simultaneously and instantaneously after absorption of the incident neutron and occur on a timescale ten orders of magnitude faster than detector capabilities. In the case of 238 U fission initiated by 14.1 MeV neutrons, there are on average 4.4 prompt fission neutrons 4 . Fission neutrons that leave the interrogated object can then be detected in neutron detectors placed around the interrogated object.…”