Measurements of energy dependent doppler factor for uranium dioxide using a lead slowing-down time spectrometer.

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The energy dependent Doppler factor of resonance absorption in UO2 was measured in the region of neutron energy between 1 eV and 10 keV using a UO2 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-III. In the energy region of 1454 eV, the calculation agreed with the experiment within the error of 5.4% which was not unreasonable when one considered the experimental errors of 3.14.7%. In the energy region of 454 eV3 keV, the calculation was systematically 16.5% larger than the experiment, though the experimental errors were 23.6% in this energy region.
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