Impact of low-energy photons on the characteristics of prompt fissionγ-ray spectra

Abstract

In this paper we report on a new study of prompt γ-rays from the spontaneous fission of 252 Cf. Photons were measured in coincidence with fission fragments by employing four different lanthanide halide scintillation detectors. Together with results from a previous work of ours, we determined characteristic parameters with high precision, such as the average γ-ray multiplicity ν γ = (8.29 ± 0.13), the average energy per photon γ = (0.80 ± 0.02) MeV, and the total γ-ray energy release per fission E γ,tot = (6.65 ± 0.10) MeV. The excellent agreement between the individual results obtained in all six measurements proves the good repeatability of the applied experimental technique. The impact of low-energy photons, i.e., below 500 keV, on prompt fission γ-ray spectra characteristics has been investigated as well by comparing our results with those taken with the DANCE detector system, which appears to suffer from absorption effects in the low-energy region. Correction factors for this effect were estimated, giving results comparable to ours as well as to historical ones. From this we demonstrate that the different techniques of determining the average γ-ray multiplicity, either from a properly measured and normalized spectrum or a measured multiplicity distribution, give equivalent and consistent results.

Prompt particle emission in fission – news on systematics and predictions for fission induced by fast neutrons

“…Our results, also recently published [3][4][5][6]10] are shown as (red) full circles for spontaneous and (red) open circles for thermal-neutron induced fission. The good agreement between these experimental values with the modified DANCE values is obvious.…”

“…However, as discussed in detail in Ref. [6], the original prompt fission γ -ray spectra obtained with DANCE lack a considerable amount of γ -rays with energies below 500 keV, most likely due to absorption effects, leading to both lower γ -ray multiplicities and an overestimation of the average total γ -ray energy. Since this effect has been quantified, the original values could be corrected, hence modified.…”

“…Ref. [6] for details) and (red) circles represent results from our recent experiments [3][4][5][6]10]. Here, the full and open circles indicate spontaneous and thermalneutron induced fission, respectively.…”

“…(n, nf), (n, 2nf) and so on, may be open and the neutrons emitted prior to fission of the corresponding residual compound systems have to be subtracted from the total number of prompt fission neutrons. Details about the calculations will be found elsewhere [20]; here we have to restrict ourselves to presenting the results of the prediction of PFGS properties. Figure 2 shows the results as a function of incident neutron energy for n + 238 U in terms of (a) average total γ -ray energy released in fission, (b) average prompt fission γ -ray multiplicity, and (c) average γ -ray energy per fission.…”

“…Based on the latest experimental results from the reactions 235 U(n th , f) [3] and 241 Pu(n th , f) [4] as well as from the spontaneous fission of 252 Cf [5,6], we have recently presented a revised version of systematics for PFGS characteristics as function of both atomic and mass number of the compound systems undergoing fission [7,8], originally established already in 2001 [9]. In the meantime, new results have been obtained from the spontaneous fission of 240 Pu and 242 Pu [10], which now have been included in order to update the systematics.…”