Meeting 1/27/22 - COMTRA

Eric's update cyrstals

• I am in contact with the Alpha-Spectra company which was providing BGO crystals for a local project we had in Orsay. This is a US company which provides crystals with a guaranteed 8-9% resolution. At the time we were investigating for an order they were less expensive than Saint-Gobain and turned-out to be more performant (we performed dedicated measurements to test this).

• They should be back to me shortly with information about availability of improved radiation hardness crystals as well as radiation limits of the crystals they are currently providing.

• It should be noted that litterature about radiation aging of BGO crystals indicates that after a rapid loss of about 20% of transmission, the performance is kind of stable. Some experiments chose to first irradiate crystals to operate in that regime.

• we may need tools to control the overall stability of the experimental signal... dedicated cosmic ray calibration run or light illumination... too early stage to provide a direction of answer, but this should be kept in mind.