Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing Samples of faceplate glass are irradiated to approximately 20 kGy gamma ray dose in our facility at Brunel. At least 3 faceplate samples per glass batch are tested. Samples are irradiated in the dark, at a temperature around 20C, at a dose rate of abour 300 Gy per hour. Induced absorption is measured within two hours of irradiation. Irradiated samples are stored in the dark at 201C. Spectrophotometer is recalibrated every 12 months. Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing We use the latest measured PbWO 4 emission spectrum appropriate for end-cap crystals This is convolved with the induced absorption over the wavelength range 350 nm to 610 nm The integrated transmission after irradiation must be > 90% of the unirradiated transmission for all sample in one batch. Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing Irradiated causes the growth of an absorption band centred around 330 nm. This band is well known in the literature for borosilicate glasses. Even after 20 kGy dose there is no induced absorption at 800 nm. This allows a measurement consistency check. The induced absorption shape is very similar in different batches, peak height does however vary. Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing Recent faceplates (June 2003) were generally very good quality, but note batch Glass Post irradiation internal transmission (%) after 20.0 kGy Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing One sample from batch showed very poor radiation tolerance. Peter Hobson - Brunel University, UK3 July 2003 VPT faceplate testing Long term annealing (in dark at 20C) shows increase in absorption in the band centres at 330 nm. Peter Hobson - Brunel University, UK3 July 2003 Summary Pre-testing of faceplate glass is an essential part of ensuring that production tubes will be able to operate over the full lifetime of CMS. We have a standard protocol for determining which glass batches can be used. A new Hitachi U4100 spectrophotometer, used for all glass batches in the production run, has improved our measurement accuracy repeatability. Recent glass batches have been very good. The anomalous result for one sample of a batch (29992) is unique all other batches have shown very little variation between samples.