149Sm(n,α)146Nd cross sections in the MeV region.

We have measured the (149)Sm(n,α)(146)Nd cross section at 4.5, 5.0, 5.5, 6.0, and 6.5 MeV. Measurements were performed at the 4.5 MV Van de Graaff accelerator of Peking University with monoenergetic neutrons produced via the (2)H(d,n)(3)He reaction using a deuterium gas target. Alpha particles were detected with a double-section gridded ionization chamber having two back-to-back (149)Sm(2)O(3) samples attached to the common cathode. Absolute neutron flux was measured using a small (238)U fission chamber and monitored by a BF(3) long counter. These are the first reported cross sections for this reaction at these energies, except at 6.0 eV, where our new data are in good agreement with our earlier result. The present results help to much better constrain the (149)Sm(n,α)(146)Nd cross section in a region where its energy dependence is changing fairly rapidly and there are large differences between evaluated nuclear data libraries.