IMPROVEMENT IN TRANSMITTANCE AND DECAY TIME OF PBWO4 SCINTILLATING CRYSTALS BY LA-DOPING

The optical transparency of PbWO4 single crystals in the short wavelen gth region between 320 nm (cutoff) and 450 nm is significantly improve d by doping with a small amount of La. This result indicates the possi bility that the light yield detected by photomultipliers in actual det ectors could be significantly increased for the fast blue emission whi ch peaks around 420 nm. The improvement in transmittance was compared for different amounts of La doping. La-doping also shortens the decay time; the best fit of the decay spectrum is a sum of three exponential s for undoped PbWO4, while it is a sum of two exponentials for La-dope d PbWO4 with the absence of the next to the fastest component. GDMS an alysis was carried out for the grown crystals to evaluate any other im purities.