  We report on the results of the positional-dependent pulse shape
discrimination (PSD) parameter observed within a monolithic CLLB scintillation
crystal. CLLB, a relatively novel inorganic scintillation crystal, is capable
of PSD between gamma rays, neutrons, and alpha particles. In this work, we
observed distinguishable differences in the pulse shapes for gamma-ray-induced
events. The CLLB crystals used for this experiment are 5 cm (diameter) by 10 cm
(length). By using monoenergetic 2.614 MeV photons from a set of thoriated
welding rods and performing collimated scans along the length of the crystal,
we found that the centroid of the PSD distribution shifted as a function of
position. With positional-dependent PSD, one can obtain more accurate knowledge
of the interaction location within a monolithic scintillation crystal. These
results could lead to improved angular resolution in imaging systems employing
scintillation crystals that exhibit this behavior. Lastly, an understanding of
the dependence of the PSD as a function of position could give manufacturers a
better understanding of the crystal properties and provide insight to the
distribution of internal contaminants and dopants within the crystal.
