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Indirect neutron capture (n,γ) cross sections have been extracted for the key thorium cycle nuclei 232 Th, 231 Pa and 230 Th using the surrogate reaction method. Final nucleus gamma decay probabilities were measured between the neutron binding energy and around 1MeV above it using the 232 Th(d,p) 233 Th, 232 Th( 3 He,t) 232 Pa and 232 Th( 3 He,α) 231 Th reactions in experiments with the Cactus gamma-detector array and Silicon Ring charged particle detectors at the Oslo Cyclotron Laboratory. Since the neutron capture cross section for 232 Th 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 gamma 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. PACS number(s): 24.87.+y, 24.10.-i, 25.45.-z, 25.55.-e

International audienceAn IN2P3-JINR collaboration has launched a project called GABRIELA at the Flerov Laboratory for Nuclear Reactions (FLNR) within the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). The goal of the project is to perform gamma-ray and internal conversion electron spectroscopy of heavy nuclei produced in fusion-evaporation reactions and transported to the focal plane of the recoil separator VASSILISSA. During five experimental campaigns of GABRIELA, the detection system has gained in sensitivity and new spectroscopic information has been obtained for 249Fm, 251Fm, 253No and 255Lr