A 500 l large liquid scintillation detector for neutron capture cross section measurements

A large liquid scintillation detector has been constructed for the purpose of measuring neutron capture cross sections. The detector is installed at a 55m time-of-flight station at the JAERI electron linear accelerator. The detector tank is filled with 500l scintillator liquid (NE224) and 20 1 tri-methylborate. The tank is optically separated into halves by thin aluminized mylar so that background counts are reduced by operating the two halves of the tank in coincidence. The gamma pulse height resolution is found to be 24% (FWHM) for 2.5MeV sum peak of Co-60 source and the overall time resolution is 4.3 ns (FWHM). The gamma-ray response function of the detector was investigated in order to determine the efficiency in either its coincidence or non-coincidence operation. Comparison was made between the observed pulse height distributions and calculations with a new Monte-Carlo code for various gamma-ray sources and neutron capture gamma-rays. This report will describe the characteristic of the detector and the preliminary experiments for demonstrating the detector performance. (author)