Initial Tests on First Full-size ECAL Endcap Crystals
At the end of last year the first full size ECAL endcap crystals were delivered to CERN.Thirty in number, they were produced to the final geometrical specifications; 220mm long with a rear square face of 30mm and a front square face of 28.6mm. All were delivered polished. The visual inspection , dimension, transmission, light yield and light yield uniformity tests carried out since are discussed , with particular emphasis on the light yield uniformity. The results are very encouraging. suggesting that the endcap crystals will not need uniformisation.
Low dose-rate irradiation set-up for scintillating crystals
Abstract With a 1 Ci 60 Co-source we measured the radiation damage and its recovery in PbWO 4 crystals. The method consists in measuring the anode current produced in the silicon diode of a Hybrid PhotoMultiplier Tube (HPMT) during the irradiation of the crystal. At regular time intervals, we took photon counting spectra with the same HPMT. By checking the resulting channel positions of the photoelectron peaks, we controlled the stability of our experimental set-up. Temperature control and monitoring were achieved by forced thermostatized water circulation inside the irradiation box and by using a PT100 and two AD590 temperature probes. First results on irradiations of a few PbWO 4 crystals are presented and future plans are communicated.
Further results on photoelectron counting with small diameter scintillating fibres
Abstract We measured the number of photoelectrons released from the photocathode of a newly available hybrid photomultiplier tube (HPMT) by photons from scintillating fibres. About 1600 individual 60 μm diameter fibres are contained in fused square bundles of 2.5 mm edges. The number of photoelectrons per mm fibre path changes from 10.6 at zero to 1 at 2 m bundle length. The potential difference between the HPMT photocathode and its electron detecting silicon diode amounted to 13 kV.