Quickal Meeting Dave's office 3-Oct-1997 Present Paul Flower Bruce Kennedy Mark Osborne (Brunel) Bob Brown Derek Imrie Ken Bell Peter Hobson (Brunel) Dave Cockerill Paul Flower Last week worked at Sheffield Discuss ICP results with Graham Glossop, All samples gave Similar impurities at the ppm level except the "bad" Russian sample. This had higher concentrations of ZrF4, at the 0.4% level. Carried out test to see if moisture affecting transmission by adding 0.3 g of H2O to HfF4, used small crucible P354 Made new big block using the latest Russ HfF4 and carried out tests on contamination from the crucible. It was suggested that Paul pursue the analysis of the different HfF4 samples to identify what is causing the differences in transmission. Peter Hobson said that JM had used mass spectrometry techniques to identify parts per billion levels of contamination in HfF4 samples and said he would be interested in looking at Paul's results in more detail. Next week Paul will be working on data and measuring glass samples. Bruce Kennedy Has de-bugged Dave Barney's program. It now runs at RAL but results on beam position resolution are still not fully understood. Bruce, Glenn Patrick and Helen Heath are now exchanging software to run simulations of the crystal and pre-shower interactions. Has been working on a PPARC document and calculations of the back plate spacer dimensions with Len Next week will be working on End cap simulation, especially critical areas near the end cap / barrel interface. Dave reported that the present dimensions of the crystals are determined by a projection from a position 1.3m beyond the interaction region and an outer end face of the crystal 25.9mm square. Mark Osborne Last week worked on simulation of radiation damage in APD's using computer models. He considered radiation doses of up to 2.4E14 neutrons. The models were tentative and geometry specific but investigated the effect of radiation dose on gain at different bias voltages. The results indicated that there may be a peak in this curve and a plateau region. The effect on leakage current was not modelled. It was felt that this data should be compared with Roger Rusak's data. It was noted that calibration was a problem between groups and that neutron spectra and energy would differ for exposures at ISIS, Oak Ridge and Rome. Bob Brown Reported that he had been working on work for the PPESP. He also reported that the barrel calorimeter had modules of 5 by 5, whereas the end cap has modules 6 by 6. This mismatch must be appreciated in decisions where common architecture is proposed. Next week working on chapter 6 of the TDR. Bob highlighted the need for thought to be given to methods for calibration of the end cap. Derek Imrie Derek has now modified his VPT simulation model so that he can simulate illumination by a small spot. He noted that it was very difficult to study different data sets if one did not have consistent illumination. It was considered whether it would be possible to use a laser excite a lead tungstate sample. Peter Hobson said that Brunel had a dye laser that could provide a 5 ns pulse. Derek has improved his model to take account of electrons that go back through the grid with sufficient energy to cause limited (25%) re-emission from the photocathode. This increased the final gain of the VPT by 25%. It was noted that the predicted electron noise from the system was now expected to be nearer to 4000 electrons rather than the hoped for 1500. It is proposed that an FET is incorporated into the input of the amplifier chain to reduce this. However, this means that we need to work to get the biggest signal. It was suggested that Electron Tubes be approached to see if they could use a more red enhanced material, better matched the PWO emission spectrum, for the photocathode. Bob noted that when he worked on Opal, the group had been offered red enhanced tubes but this was inappropriate for a Cerenkov generated signal. The Hamamatsu tube has not yet arrived. Ken Bell Working on INTAS document on glass Next week in CERN Peter Hobson Outlined facilities at Brunel for VPT work They now have a Nd Yag laser which can deliver a 5 ns pulse at 355,532 and 1064nm and can be used as a dye laser to give wavelengths between 200 and 800nm. This facility can be used to test and calibrate photodetectors. Peter would like to attend quickal meetings regularly but has lecturing commitments on Fridays. Dave Cockerill Dave proposed that the Next UK ECAL meeting be on the 16 Oct. at RAL from 10.00 - 17.00 Dave has copies of the Madison meeting transparencies He said that the latest management proposals were that there be one End cap regional centre and that be in the UK. It is no longer proposed that there should be end cap assembly at Protvino. This means that Imperial will no longer be investing in an ACOS system but will take on some end cap production work. The present arrangement of crystals and amplifiers envisages the preamplifiers being separated from the crystals in a polyethylene cocoon coupled by about 50cm cable of about 40 pf estimated capacity. This greatly rationalised the design of the end cap assembly and reduced the heat load on the crystal temperature stabilisation system There will be beam at CERN for tests from the 24 Oct to 15 Nov. It is hoped to test 9 channels of Russian VPT's and PWO. The Lyon type pre amps may not be ready in time so initial tests may have to take place with Stephenson type pre amps. Some concern was expressed that the tubes may exhibit a nuclear counter effect. This should be tested at CERN using a masked crystal. Next week Dave at CERN.