Non-uniformity measurements of $PbWO_{4}$ crystals

Two independent methods have been used to measure the longitudinal non - uniformity scintillation response of 3 different ( 23-cm long) PbWO4 crystals. The first one is the classical Co60 source method.The source is collimated along the crystal, each 1,5-cm, and the scintillation signal is measured with a photomultiplier ( a hybrid photomultiplier in our case). The second one is the use of cosmic particles ( Minimum Ionizing Particles). A cosmic bench allows reconstructing the track of the MIP's and thus the energy deposit with the help of a full GEANT simulation of the setup. Variations of E along the crystal artificially cut in 1,5-cm divisions, leads to determine the non-uniformity. The conclusion is that both methods agree quite well. Furthermore, a good estimation of crystal light yield can be obtained.