General Meeting Summary 2/13/14

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  • Negotiations about acceptable light yield loss for the PbWO4 (10) crystals order from SICCAS ongoing with the company. Expect the negotiations to be finalized soon.
  • Several types of blue and IR LEDs have been delivered - trying to determine the best one for the prototype tests
  • Received quotes from Hamamatsu for photodiodes, one of them (S2281) has a wide wavelength range in the IR region
  • Placed order for 10 high voltage divider boards with the same company that we used last year. Expect delivery of these in next few months.
  • The original prototype design allowed for 3 x 3 PbWO4 crystals. Work is in progress to make the design more flexible to allow for a hybrid prototype, which would include both PbWO4 and PbF2 crystals. Expect this to be ready in the next month.
  • Preparing a PWO sample for a radiation test at JLab with the RadCon group. Idea is to measure transmission of the crystal before and after radiation. Two (different) facilities are available: one at JLab (used for measuring transmittance of the lead glass crystals used in the SHMS calorimeter) and one at CUA (Perkin/Elmer UV/vis/IR photospectrometer). To compare the methods one could measure the transmittance with both instruments. If the results are the same this could also minimize transportation of the crystals.
  • Discussion about how much radiation is needed for the transmittance tests. It would be good to make the transmittance measurements without too much time delay between irradiation and measurement. Both measurement facilities available require the irradiated crystals to be transported from the irradiation to the measurement facility. Previous irradiation tests on PbF2 crystals for DVCS/HA were done with electron beam at Idaho and measurements were done right away with a special setup. Lower doses of 10-20 krad may be beneficial to avoid residual radiation and allow for using one of the two facilities we have available. Previous tests for Hall A calorimeter lead glass crystals irradiated with doses of about 14 krad resulted in no residual radiation. This has to be checked for PbWO4, but perhaps a level of 10-20 krad would be a good starting point.
  • Discussion about radiation from one or all sides of the crystal. Practically, RadCon setup only allows radiation from the front unless the sample is very small. Irradiation is done with a Cs source whose energy spectrum is ~200keV. For the PbF2 crystals used in DVCS/HA there was concern that using such small energy from the front would never irradiate the center of the crystal were the shower develops. For PbWO4 this could also be a concern, but one also has to take into account that the mechanism of radiation damage is different. For instance, measurements with PbWO4 at CMS have shown that radiation damage is due to low energy events and mostly damages the front (the first few cm) of the crystal while there is only a small effect on the energy resolution. This damage mechanism for PbWO4 is also what the current NPS curing system is built on, e.g., in-situ curing from the front of the calorimeter crystals.
  • Discussion about including C. Zorn in the NPS collaboration officially.


  • Optimize the introduction together with Hamlet's NPS talk to reduce overlap
  • Specify more details about the tests to be done and what the goals are of each test. It may also be good to include a timeline.


  • Very comprehensive talk, which includes all major points
  • Please send any comments to Hamlet


  • Will circulate draft soon. Talk will include ideas for both RCS and pi0 photoproduction experiments
  • Idea is to submit RCS and pi0 photoproduction experiments as different proposal, but as the same run group, i.e., sharing beam time.


  • Carlos was contacted by R. Novotny about the conference where discussions on PWO are planned.
  • We will submit an abstract about NPS and decide later who will give the talk


  • NPS design and prototype