Progress in the Development of a Lead Slowing-Down Spectrometer at LANSCE

Lead Slowing-Down Spectrometers (LSDS) have been used for many years to measure neutron-induced fission cross sections of very small samples of actinides. We are extending the range to ultra-small samples by driving a 20-ton LSDS with short, intense pulses of 800-MeV protons from the Proton Storage Ring at the Los Alamos Neutron Science Center. Neutrons are produced by the pulsed proton beam from the LANSCE Proton Storage Ring striking a tungsten target in the center of the lead. Fission reactions are detected as a function of time, and therefore neutron energy, after the beam pulse. Initial experiments have confirmed the calculated performance of the LSDS and have demonstrated the capability of measuring the neutron-induced fission cross section of Pu-239 with a sample mass of less than 10 nanograms. Progress in the development of this new capability and plans for a program of measurements will be described.