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Special Topics

EPJ A Highlight - Prompt x-rays emitted in neutron-induced fission help unveil the evolution of fission fragment charge yields as a function of incident neutron energy

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Charge distribution determined from the x-ray yield measurements (symbols) for different incident neutron intervals: threshold to 6MeV ~3MeV, from 6 to 11MeV ~8MeV, from 11 to 20MeV ~14MeV, from 20 to 50MeV ~32MeV and from 50to 400MeV ~180MeV. For more detail see text.

Nuclear fission is accompanied by the prompt emission of neutrons, gamma rays and x-rays. It has been known since the sixties that fission prompt x-rays originate essentially as a consequence of the internal conversions occurring in the prompt gamma deexcitation cascades of fission fragments.

This work presents for the first time a measurement of the prompt fission x-ray yields in 238U(n,f) for average incident neutron energies ranging from 3 to 200 MeV. These results provide new information on fission fragment deexcitation and allow testing the current knowledge of fission fragment nuclear structure. These results provide also a means to investigate the evolution, as a function of incident neutron energy, of fission fragment charge yields and elemental prompt x-ray emission probabilities.

Fission fragment charge distributions are derived from the measured x-ray yields using x-ray emission probabilities per fragment obtained in an earlier work on low energy fission. The results are found to be in a remarkable agreement with the Wahl phenomenological systematics for fission product yields, as well as with the more sophisticated GEF fission model. This agreement shows that the variation of x-ray emission probabilities remains moderate over a wide range of incident neutron energies. More detailed comparisons demonstrate that x-ray emission evolution with increasing incident neutron energy tends to be dominated by the transition towards lighter fragments which on average are closer to closed-shell nuclei and are thus less subject to internal conversion.

Measurement of prompt x-rays in 238U(n,f) from threshold to 400 MeV, T. Granier, R.O. Nelson, T. Ethvignot, M. Devlin, N. Fotiades, P.E. Garrett, and W. Younes (2013), European Physical Journal A 49:114, DOI 10.1140/epja/i2013-13114-8

Managing Editors
Anne Ruimy (EDP Sciences) and Sabine Lehr (Springer-Verlag)
Dear Isabelle,
Many thanks for the hard work indeed! The entire volume and the cover look really very good, thanks again.

George Kampis, Collegium Budapest, Hungary
Editor EPJ Special Topics 222/6, 2013

ISSN: 1951-6355 (Print Edition)
ISSN: 1951-6401 (Electronic Edition)

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