Experimental inspection of the (n, gamman') reaction in heavy nuclei

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The present research aims at the experimental inspection of (n, gamman, ) reaction using a Bi sample and TOF and/or correlation methods.1.Detector preparation :We supplemented electronics circuits necessary to do experiments, and prepared a BaF_2 gamma-ray detector having a good energy resolution (<9% for Cs-137 gamma-ray) and a timing resolution (<600ps). For TOF experiments, we optimized the performance of an existing NE213 (5"-diam x2"thick) detector for pulse-height, TOF,and pulse-shape properties, and developed a data processing method based on a dynamic-biasing technique using three-parameter data. It enabled measurements of neutrons lower than 20 ke V.2.Measurement and AnalysisWe carried out TOF experiment for 1-2 MeV neutrons first because problem were foreseen in the correlation methods because of the uncertainty in the overall gamma-ray detection efficiency and the gamma-ray contamination ratio into the neutron detector. The TOF experiments employed a quasi-monoenergetic ^7Li (p, n) source because the updated detector system proved that the monoenergetic T(p, n) source with a Ti-T target have backgrounds neutrons. Up to now, we could not confirm any significant difference between the spectra for Bi and C,Al which have no appreciable (n, gamman, ) cross sections. Thus we have not confirmed yet the evidence of the (n, gamman, ) process. Nevertheless, further experiments will be worthwhile using an updated experimental system and method established in this study because the signal-to-noise ratio is good enough to observe reactions with cross section<1mb/(Sr MeV). The experimental system developed in the present study is useful for other research works too.