Correlations of neutron multiplicity andγ-ray multiplicity with fragment mass and total kinetic energy in spontaneous fission ofCf252

Abstract

The dependence of correlations of neutron multiplicity ν and gamma-ray multiplicity Mγ in spontaneous fission of 252 Cf on fragment mass A* and total kinetic energy TKE has been investigated employing the ratio of M γ /ν and the form of Mγ(ν). We show for the first time that Mγ and ν have a complex correlation for heavy fragment masses, while there is a positive dependence of Mγ(ν) for light fragment masses and for near-symmetric mass splits. The ratio Mγ/ν exhibits strong shell effects for the neutron magic number N = 50 and near the doubly magic number shell closure at Z = 50 and N = 82. The gamma-ray multiplicity Mγ has a maximum for TKE = 165-170 MeV. Above 170 MeV Mγ(TKE) is approximately linear, while it deviates significantly from a linear dependence at lower TKE. The correlation between the average neutron and gamma-ray multiplicities can be partly reproduced by model calculations.

Statistical study of the prompt-fission γ -ray spectrum for U238(n, f ) in the fast-neutron region

“…This suggests that (76 ± 13)% of the excess energy is evacuated by neutron evaporation and (24 ± 18)% for the photon emission, which means that the majority of the extra available TXE is dissipated by prompt-fission neutron (PFN) emission. Despite the weaker increase of PFG emission relative to PFN emission, our results suggest that the assumption that neutron emission entirely precedes γ emission, is not valid and that competition of both play a considerable role during the deexcitation of fission fragments [4][5][6]. Figure 11 contains-as a function of incident neutron energy-the average values for each quantity from this work, together with results from various fission models, including PbP [42], GEF [41], and FREYA [43], as well as calculations based on systematics [44].…”

“…Measurements, namely, allow further insight into angular momentum generation at scission [2,3]. In addition, they are expected to lead to a better understanding of the competition between neutron and γ emission [4][5][6], and thereby possibly contribute to investigate the mechanism of excitation energy sorting between the two fission partners [7][8][9].…”

Neutron-neutron and neutron-photon correlations withFREYA

“…The FREYA calculation, not including the discrete cascade, has structure similar to the data from Ref. [16] but differs in magnitude. There is a peak in both results near the doubly-closed shell at A = 132, the location of the minimum of the sawtooth in ν(A).…”

“…[16] is not as good, the results are promising. Since they were obtained before the RIPL-3 lines were added to FREYA, perhaps further improvement is possible.…”

“…In Ref. [16], the photon multiplicity was also plotted against neutron multiplicity in three different fragment mass regions representing the light fragment, the region around symmetric splits, and the heavy fragment. Given the A region, the data were binned in TKE.…”