Enhancement of Fast Neutron Detection in Liquid Scintillator Detectors

Organic liquid scintillators, such as EJ-309, are capable of detecting fast neutrons and discriminating gamma rays through pulse shape. Higher detection efficiency is a common objective for detector designs and research. This paper describes two methods to enhance fast neutron detection by increasing neutron collection and reducing gamma-ray interference. Neutron collection can be increased by using strong scattering material to reflect neutrons toward scintillators. Gamma-ray interference can be reduced by using heavy material to shield gamma rays; such a material could have a minimal impact on neutron detection because neutrons and gamma rays have different interaction cross sections. In this work, both effects were investigated, experimentally and by simulation. Using a graphite reflector with simple geometry, the fast neutron detection was measured to have an increase of 9%, and simulations predicted an approximately 50% increase for optimized geometry. Using a lead shielding of 8-mm thickness, the neutron detection with a Pu source was measured to have a factor of 2 increase. These methods could be useful when cost-effective and highly efficient fast neutron detection is desired.