Spatial pulse shape discrimination response of an organic-liquid scintillator using a collimated source

The separation of neutron and gamma-ray events in organic-liquid scintillators is of significant importance for nonproliferation applications. Typically pulse shape discrimination (PSD) technique is used to differentiate neutron distribution from gamma-ray distribution. However, one of the challenges remains whether the scintillator´s PSD is affected with respect to the particle interaction position. This can be studied by mapping the detector´s PSD performance by discriminating neutron from gamma-rays as a function of the particle interaction position within its active volume. This is useful for developing procedures for improved data analysis and simulations. This paper presents the PSD response of an organic-liquid scintillator with respect to the position of neutron and gamma-ray interactions. A ²⁵²Cf source was used to collect neutron and gamma-ray pulses in 25 × 25 × 8.2 cm³ BC-501A liquid scintillator. The detector´s spatial PSD responses are analyzed with Pb and polyethylene collimators having 6-mm aperture. Figure-of-merits are then computed from their respective PSDs to quantify the detector´s PSD response with respect to the particle interaction position. Based on the findings, the spatial PSD response for all positions are within 5% to the PSD response at the detector´s center position.