keV-neutron capture in cesium-133, gold-197 and tantalum-181.

概要

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The keV-neutron capture in 133Cs, 197Au and 181Ta was studied by measuring the cross section and the emitted gamma-ray spectrum. The neutron was produced with the KUR linear accelerator and a photoneutron target, and the samples were placed at 11.7 m from the neutron source. The gamma-rays following the keV-neutron capture were detected with a pair of C6D6 scintillators. The relative capture cross section between 3.2 and 270 keV was normalized to the absolute cross section at 24 keV obtained with an iron-filtered neutron beam. The results of 133Cs and 197Au are in good agreement with the recently measured and evaluated capture cross sections. The capture gamma-ray spectrum was obtained by unfolding the observed spectrum with the response functions of the detector. The gamma-ray strength function, which represents the average gamma-ray transition probability, was derived with the spectrum fitting method. The level density distributions used in the calculation of spectrum fitting were investigated and it is found that the constant temperature level density is preferable. The gamma-ray strength functions for 198Au and 134Cs show the 5.5-MeV bump and the deficiency of strength compared with the tail of giant dipole resonance, and that for 182Ta does not give the bump but shows the similarity to the tail of giant resonance. The results were compared with other data.
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