Visual inspection of lead glass modules

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  Fig. 1 Broken glass.

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  Fig. 2 Wrapping issue: teared Aluminized mylar, can be fixed without disassembling module.

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  Fig. 3 Wrapping issue: Al layer peeled off.

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  Fig. 4 Wrapping issue: Al layer peeled off, wrapping foil is teared. A newly wrapped module is shown on the top.

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  Fig. 5 Damaged PMT.

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  Fig. 6 Colored lead glass module, possible radiation damage issue.

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  Fig. 7 Colored lead glass module.

Possible issues with lead glass module

1. Broken lead glass, see Fig. 1 (module taken from the FCAL prototype)
   • some problems can be seen by looking on the lead glass block from the side opposite to the PMT
   • lead glass module has to be disassembled; the glass block has to be replaced.
2. Issues with wrapping:
   • small damages (holes) in the Aluminized mylar, see Fig. 2. This can be fixed by using Al sticky tape, thickness < 20 um
   • Aluminum layer in the wrapping foil peels off or adheres to the glass block (penetrates into the block):
     • Fig. 3 and Fig. 4: Aluminum layer peeled off resulting in some transparent holes in wrapping.
     • recommend to disassemble and re-wrap the lead glass block
3. Issues with Silicon cookies
   • Inspect optical coupling of the glass block and the PMT by looking inside the crystal from the side opposite to the PMT
4. Possible damages of PMTs during deinstallation (see Fig. 5)
5. Glass blocks with discoloration signs (due to radiation)
   • some glass blocks may have a brown tint (see Fig. 6 and Fig. 7). Can be checked without removing steel flange.
   • recommend to replace this module

• Estimated time to refurbish FCAL module - 40 min