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Physical Review C 85 (2012) 034607
Indirect (n,γ) cross sections of thorium cycle nuclei using the surrogate method
J. N. Wilson1, F. Gunsing2, L. A. Bernstein, A. Bürger, A. Görgen, M. Guttormsen, A. C. Larsen, P. Mansouri, T. Renstrøm, S. J. Rose, A. Semchenkov, S. Siem, N. U. H. Syed, H. K. Toft, M. Wiedeking, T. Wiborg-Hagen

Indirect neutron capture (n,γ) cross sections have been extracted for the key thorium cycle nuclei 232Th, 231Pa, and 230Th using the surrogate reaction method. Final nucleus γ-decay probabilities were measured between the neutron binding energy and around 1 MeV above it using the 232Th(d,p)233Th, 232Th(3He,t)232Pa, and 232Th(3He,α)231Th reactions in experiments with the CACTUS γ-detector array and Silicon Ring charged-particle detectors at the Oslo Cyclotron Laboratory. Because the neutron capture cross section for 232Th is already well known from direct measurements a comparison with these results provides a stringent test of the applicability of the surrogate method in the actinide region for indirect (n,γ) cross-section measurements. In addition, a new technique for correcting measured γ-ray decay probabilities below the neutron emission energy threshold is proposed and used. We find good agreement between indirect and direct (n,γ) cross-section measurements in the range 500 keV-1 MeV, but large discrepancies outside this range. Explanations for the observed differences are proposed.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay
2 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
Physique/Physique Nucléaire Expérimentale