Air gap effect on the properties of a long liquid scintillation detector

Light attenuation, n-γ pulse shape discrimination and timing properties of a long liquid scintillation detector (LLSD) were examined by means of Monte Carlo simulations and experiments. LLSD is a long rectangular shaped NE213 scintillator (80 × 6.5 × 10 cm3) coupled with two photomultipliers and has been developed for neutron scattering experiments. We found that an air gap between a photomultiplier and a scintillator cell worked as a filter and reduced position dependencies of pulse height and of n-γ pulse shape discrimination which were disadvantages on the use of LLSD, whereas it deteriorated n-γ separation. This paper discusses the advantages and disadvantages of the air gap to the detector properties.