OPTIMIZING LIGHT COLLECTION FROM THIN SCINTILLATORS USED IN A BETA-RAY CAMERA FOR SURGICAL USE

We are developing a 1-2 cm(2) area camera for imaging the distribution of beta-emitting radiopharmaceuticals at the surface of tissue expose d during surgery. The front end consists of a very thin continuous or segmented scintillator sensitive to betas (positrons or electrons) of a few hundred keV, yet insensitive to gamma rays. The light from the s cintillator is piped through clear fibers to the photon detector (PD). This approach requires that a sufficient number of scintillation phot ons be transported from the scintillator, through the fibers to the PD . The scintillator, reflector, surface treatments, geometry, fiber lig ht guides, and optical couplings must be optimized. We report here on efforts made to optimize the light collection from < 3 mm thick plasti c and CaF2(Eu) scintillators into clear fibers using experimental meas urements and computer simulations. We measured that with a 1.25 cm dia meter, 0.5 mm thick optimized CaF2(Eu) disk coupled to a 5 cm long bun dle of clear optical fibers, on average, similar to 250 photoelectrons are produced at a PMT photocathode for a Tl-204 beta flood source (E( max) = 763 keV). This corresponds to a sufficient number of photoelect rons for < 1 mm resolution imaging capabilities for the proposed camer a.