First simultaneous measurement of fission and gamma probabilities of $^{237}$U and $^{239}$Np via surrogate reactions

P. Marini (1) , Q. Ducasse (1, 2) , B. Jurado (1) , M. Aiche (1) , L. Mathieu (1) , G. Barreau (1) , S. Czajkowski (1) , I. Tsekhanovich (1) , A. Moro , J. Lei , F. Giacoppo , A. Gorgen , L. Audouin (3) , L. Tassan-Got (3) , J.N. Wilson (3) , F. Gunsing (4) , M. Guttormsen , A.C. Larsen , M. Lebois (3) , T. Renstrom , S. Rose , S. Siem , G.M. Tveten , M. Wiedeking , O. Serot (2) , G. Boutoux (5) , V. Méot (5) , B. Morillon (5) , D. Denis-Petit (5) , O. Roig (5) , S. Oberstedt , A. Oberstedt

1 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
2 CEA Cadarache
3 IPNO - Institut de Physique Nucléaire d'Orsay
4 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
5 DAM - Direction des Applications Militaires

Fission and gamma decay probabilities of ^237U and ^239Np have been measured, for the first time simultaneously in dedicated experiments, via the surrogate reactions ^238U(^3He, ^4He) and ^238U(^3He,d), respectively. While a good agreement between our data and neutron-induced data is found for fission probabilities, gamma decay probabilities are several times higher than the corresponding neutron-induced data for each studied nucleus. We study the role of the different spin distributions populated in the surrogate and neutron-induced reactions. The compound nucleus spin distribution populated in the surrogate reaction is extracted from the measured gamma-decay probabilities, and used as input parameter in the statistical model to predict fission probabilities to be compared to our data. A strong disagreement between our data and the prediction is obtained. Preliminary results from an additional dedicated experiment confirm the observed discrepancies, indicating the need of a better understanding of the formation and decay processes of the compound nucleus.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

P. Marini, Q. Ducasse, B. Jurado, M. Aiche, L. Mathieu, et al.. First simultaneous measurement of fission and gamma probabilities of $^{237}$U and $^{239}$Np via surrogate reactions. 5th International Workshop on Compound-Nuclear Reactions and Related Topics, Oct 2015, Tokyo, Japan. pp.12004, ⟨10.1051/epjconf/201612212004⟩. ⟨hal-01554279⟩