Measurement of Doppler Effect for Metallic Fuel Alloy Material by TOF Method

In a development of the uranium-free fast reactor to reduce TRU, we have initiated the measurement of the Doppler effects for Mo sample with the KURRI-LINAC pulsed neutron source. In the experiment, neutron capture rates in Mo sample at 300 K and 600 K were obtained by prompt gamma-ray measurement with the TOF method, and the Doppler effects are defined as the ratio of neutron capture rates at 600 K and 300 K. As the results, the Doppler effects at the resonances in the energy range of 10 eV to 1 keV has been observed. The Doppler effects were clearly observed at 358.6 and 676.3 eV. However, it was hard to distinguish the Doppler effects under a mask of self-shielding effect at the 44.9, 70.9 and 131.4 eV resonances, because the self-shielding effect was so large that the counting rate around the resonance peak seems to be almost saturated. In the JSF70 group structure, it was possible to identify the Doppler effects of the almost saturated resonances such as 44.9-, 70.9-, 131.4- and 358.6-eV resonances. The numerically estimated Doppler capture rate ratios were in good agreement with the experimental ones for the energy groups including the main resonances at 44.9, 70.9 and 358.6 eV.