Time-dependent γ-ray emission after spontaneous fission of Cf-252 with an experimental verification

The time-dependent emission of prompt fission γ rays was measured at JRC-GEEL with the VESPA spectrometer, the versatile γ spectrometer array, coupled to a position-sensitive fission detector. Our research follows measurements performed in the 1970 years; after that, no more experimental work was performed until about the past decade. The close geometry of γ-ray detectors and the fission detector was the key to extracting the time-dependent fission γ-ray spectra. In addition to the measurements, model calculations with the Hauser-Feshbach Monte-Carlo code FIFRELIN were performed. These calculations can very well confirm the observed trend. The results show for the first time that late fission γ-ray emission occurs well beyond 5 μs after the instant of fission, as suggested by the calculations. Our new data suggests that about 1.6% of the fission γ-rays are still emitted later than those 5 μs after fission. In conclusion, for Cf-252(sf) we find a total average fission γ-ray multiplicity of Mγ,tot = 9.40 ± (0.17stat + 0.42syst), with a late multiplicity Mγ,late(t > 2.5 ns) = 0.70 ± (0.22stat + 0.57syst), corresponding to (7.4 ± 1.6stat ± 4.2syst)%.

OBERSTEDT Stephan;  PIAU V.;  CHEBBOUBI A.;  GOOK Alf;  LITAIZE O.;  OBERSTEDT Andreas;  SEROT O.;  VIDALI Marzio; 

2026-03-26

SPRINGER

JRC141721

1434-601X (online),   

https://link.springer.com/article/10.1140/epja/s10050-026-01827-2,    https://publications.jrc.ec.europa.eu/repository/handle/JRC141721,   

10.1140/epja/s10050-026-01827-2 (online),