Significant increase in fast scintillation component from PbWO4 by annealing

Increase in the light yield (LY) of lead tungstate PbWO4 (PWO) more than a few times within ∼200 ns is required to utilize PWO in Positron Emission Tomography (PET) in competition with Bi4Ge3O12 (BGO). While the (Mo, Cd, Sb) co-doping increases the (LY) more than twice (Nucl. Instr. Meth. A 486 (2002) 170), much slower component (∼20 ms) accompanies. We have found that long-time annealing of non-doped PWO in low-pressure Ar gives even larger LY in the fast component with much less in the slower one than the (Mo, Cd, Sb) co-doping. This improvement could also be useful in high energy and nuclear experiments.