Characteristics of the Kyoto University Lead Slowing-down Spectrometer (KULS) coupled to an electron linac

Abstract A lead slowing-down spectrometer coupled to a 46 MeV electron linear accelerator (linac) was installed at Research Reactor Institute, Kyoto University (KURRI). The size of this Kyoto University Lead Slowing-down Spectrometer (KULS) is 1.5 × 1.5 × 1.5 m 3 , and it is covered with Cd sheets 0.5 mm thick. One of the eleven experimental holes in the KULS is covered with 10 to 15 cm thick bismuth layers to suppress high energy capture gamma-rays from lead. The characteristics of this KULS have been experimentally obtained and the results are compared with the predicted values by Monte Carlo calculations using the MCNP code. 1) The slowing-down constant K in the relation E = K t 2 between the neutron slowing-down time t and energy E is 190±2 (keV μ s 2 ) for the bismuth hole and 156±2 (keV μ s 2 ) for an ordinary lead hole, respectively. The K values agree with the calculated ones. 2) The measured energy resolution ΔE E at full-width-at-half-maximum (FWHM) was about 40% for both holes, while the calculated values were lower by about 10% than the measured ones in the relevant energy region. 3) The neutron energy spectrum from 0.01 eV to 20 MeV and the spatial distribution of neutrons in the KULS were measured by the foil activation method. The angular neutron spectrum perpendicular to the linac electron beam was also obtained experimentally in the energy range from a few eV to about 10 MeV by the neutron time-of-flight (TOF) method. The measured results are compared with the calculated ones in which we have used the three evaluated nuclear data JENDL-3, ENDL-85 and ENDF/B-IV for lead. Through the comparison a check on the nuclear data has been performed.