Measurement of neutron capture cross section of thorium-232 from 1 keV to 408 keV.

概要

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Measurement of the neutron capture reaction rate of 232Th has been made (1) in the energy range from 1 to 408 keV, and (2) with 55 and 146 keV neutrons by thick silicon filtered neutron beams, using a linac time-of-flight technique. The capture reaction rate of 232Th has been measured relative to that for the 10B(n, αγ) reaction, whose cross section values have been taken from ENDF/B-V File. The results have been normalized to the 24 keV value previously measured by the present authors. Capture r-rays were detected by a pair of C6D6 scintillators located at 12 m on the neutron flight path. Thorium samples were chemically purified in order to reduce the γ-ray background from the daughter nuclides in the thorium decay chain. The point data measured with the 55 and 146 keV neutrons have been in good agree-ment with the energy dependent cross section for the 232Th (n, γ) reaction. It has been found that the results support recent measurements and the ENDF/B-V values of the cap-ture cross section, while the discrepancies with the older measurements and the ENDF/B-IV values above 50 keV are found to be about 10 to 30%. The experimental uncertainties have been analyzed by using covariance information which combines correlation between the data.
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