Quantification of the light output anistropy in deuterated stilbene

Deuterated stilbene is an organic scintillator that is a desirable material for fast neutron spectroscopy using spectrum unfolding techniques without requiring time-of-flight information. Due to the crystal structure of the material, some anisotropy of the light output exists, which is dependent on the direction of heavy charged particle recoil relative to the crystal structure. The anisotropy of trans-stilbene (hereafter referred to as stilbene) has been well characterized in previous work, but for deuterated stilbene, the anisotropy has only been partially characterized along the a and b crystal axes, while the artificial c^′ axis, which shows the largest anisotropy in stilbene, has not been characterized until this publication. In this work, two deuterated stilbene crystals were characterized with neutron energies up to 35 MeV at the Los Alamos Neutron Science Center. For one of the crystals, the response is characterized along the a, b, and c^′ axes. This characterization shows a distinct anisotropy along the axes in deuterated stilbene, which is very similar to that found in regular stilbene, such that the a axis is the brightest, while the b and c^′ axes are approximately 3% and 20%–35% lower relative to the a axis.