Shuji Yamamoto, Katsuhei Kobayashi and Yoshiaki Fujita

Research Reactor Institute, Kyoto University
Kumatori-cho, Sennan-gun, Osaka 590-04, Japan

A total absorption gamma-ray detector has been made using twelve BGO scintillator bricks of 5 × 5 × 7.5 cm3, with an incentive to study the possibility of BGO for neutron capture cross section measurements of higher precision.

In this report, a study of the detection efficiency of the BGO for thermal neutron capture is presented. The efficiency has been measured at a neutron time-of-flight spectrometer at KURRI electron linear accelerator. Cd, In, Au and Fe were employed for capture samples as they have different types of capture gamma rays. The efficiency have been found between 80 to 100 %.

A study has been made on a technique to estimate the efficiency for a sample of unknown cross section and cascade gamma-ray spectrum using the information of the pulse height spectrum obtained with the BGO. At present, the estimation is only partly succeeded. For a sample of high multiplicity cascade gamma-rays, the BGO is satisfactorily used for capture cross section measurements. Further studies are needed before the BGO is used for samples of low gamma-ray multiplicity.

KEYWORDS: bithmuth germanium oxide scintillator, neutron capture cross section, total absorption detector