Position sensitivity of large volume LaBr3:Ce detectors

The position sensitivity of two large volume (1¿ × 1¿ and 3¿ × 3¿) LaBr
₃
:Ce crystals has been measured using collimated beams of 662 keV ¿-rays. The crystals have been coupled to a Position Sensitive Photo Multiplier Tube (PSPMT) and/or shielded phototube. The results indicate that, in the case of 662 keV ¿ -rays, both crystals should allow identification of the the position of the ¿-ray first interaction with a 1-2 cm resolution. Similar tests have been done in the past using 140 keV ¿-rays and no sensitivity was found. Using GEANT4 simulations we confirmed these results.