Analysis of prompt fission neutrons in²³⁵U(n_th,f) and fission fragment distributions for the thermal neutron induced fission of²³⁴U

Abstract

Abstract. This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of 235 U(n,f). The second, on the fission fragment properties in the thermal fission of 234 U(n,f). The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on 235 U(n th ,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called sawtooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results. In addition, the analysis of thermal neutron induced fission of 234 U(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235 U(n th ,f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

Neutron-multiplicity experiments for enhanced fission modelling

“…This was discussed in Refs. [4,5]. Particularly in the 2-E data this assumption has been shown to have significant effect on the measured mass yields [6].…”

Prompt fission neutron investigation in 235U(nth,f) reaction

“…The studies of PFN emission in fission induced by neutrons from energies extending from resonances up to a few MeV would contribute to better understanding the mechanism of PFN emission from the excited FF. The experiments on sub-barrier fission, induced by thermal neutrons are of particular interest because of no measurements was done so far on mass and energy distributions for this systems [2]. In this work we report preliminary results of PFN investigation thermal neutron-induced fission of 235 U.…”

Prompt Fission Neutron Investigation in 235U(nth,f) and 252Cf(sf) Reactions

“…[11]. Dependence of average PFN multiplicities on mass and TKE were evaluated using formulae (1,2) and plotted in Fig. 3.…”

“…The studies of PFN emission in fission induced by neutrons from energies extending from resonances up to a few MeV could possibly contribute to better understanding the mechanism of PFN emission from the excited FF. The experiments on sub-barrier fission, induced by thermal neutrons are of particular interest because no measurements were done so far on mass and energy distributions for this systems [2]. In this work we report results of PFN investigation in thermal neutron-induced fission of 235 U and spontaneous fission of 252 Cf.…”