Measurements of Resonance Neutron Self Shielding Factors for Gold and Silver Using Slowing-Down Time Spectrometer

Abstract

The resonance neutron self-shielding factors for cylindrical samples of various thicknesses of gold and silver have been measured in the narrow energy groups with a lead slowing-down time spectrometer as a neutron source.

Calculation by Wigner's rational approximation gives 10–20% smaller self shielding factors than the experimental ones except for the limiting cases of sample thickness.

The collision probability theory, on the other hand, was found to give rather good agreement with the experiments in all the measured cases.     

Measurements of Energy Dependent Doppler Factor for Uranium Dioxide Using a Lead Slowing-Down Time Spectrometer

The energy dependent Doppler factor of resonance absorption in U0₂ was measured in the region of neutron energy between 1 eV and 10 keV using a U0₂ cylindrical sample and a lead slowing-down time spectrometer.

The Doppler factor is herein defined as the ratio of neutron capture rate in the sample at the high temperatures T = 450 and 300° C to that at the low temperature T = 20°C. The Doppler factor measured at T = 450 and 300°C showed the maximum values of 1.225± 0.044 and 1.186±0.040, respectively around the resonance of 66.3 eV. In the energy region above about 200 eV, the Doppler factor decreased with increasing neutron energy. In the energy region below about 70 eV except for region around the resonance of 6.68 eV, the Doppler factor decreased with increasing neutron energy.

The energy dependent Doppler factors were calculated by the collision probability method and the resonance parameters of ENDF/B-IL In the energy region of 1~454 eV, the calculation agreed with the experiment within the error of 5A% which was not unreasonable when one considered the experimental errors of 3.1~4.7%. In the energy region of 454 eV~3 keV, the calculation was systematically 1~6.5% larger than the experiment, though the experimental errors were 2~3.6% in this energy region.