Measurement of (n,α) reactions on 147Sm and 149Sm using a lead slowing-down spectrometer

The lead slowing-down spectrometer (LSDS) at Rensselaer Polytechnic Institute (RPI) was used to extend previous measurements of the (n,α) cross section on 147Sm and perform measurements on 149Sm over the energy range 0.1 eV-10 keV. A compensated detector based on passivated implanted planar silicon (PIPS) detectors was constructed. Signals from two detectors were combined in opposite polarity and digitized providing a single detector capable of discriminating against capture γ's and “γ-flash” while preserving the discrete signals produced by α events and providing a simultaneous background measurement. Extrapolating the results predicts a 0.3±0.3 mbarn and 11.5±1.1 mbarn thermal neutron (n,α) cross section for 147Sm and 149Sm, respectively. This measurement provides new information on (n,α) reaction cross sections. The method of measuring neutron induced charged particle emission cross sections presented here can be expanded to more isotopes of interest to reactor engineers or astrophysicists, as well as to (n,p) reactions.