The BLM calibration is performed with a ¹³⁷Cs source. The source emits a single gamma at 661.7 keV. The source activity was 323.2 kBq as of 11.01.2019. Its serial number is AB-9020, 370 kBq when purchased.

I have used 10 s integration time and set all BLM to count 30 k. (3 kHz)

Note on the light yield. Reference Glenn Knoll 3rd edition p.235 and p226 NE102A 10 k photons per MeV. BC400 light output 0.65 of NE102A (anthrscene). Hence one can expect: 6500 photons / keV

Bellow is a spectrum taken with the HDO6104A scope when for a BLM set to count 3 kHz (in this case XP2972 34391)

CBS - Cathode Blue sensitivity ABS - For a anode blue sensitivity Id - Dark current

Reason for the service: The detector counts more than 10 times compare to the detectors above, left and right of it. Will examine it if:

• The detector is light tight
• If the AVD is damaged
• If there is radiation damage to the scintillator (not related to the above problem)

1. LED check with multimeter:
   • Forward bias 1.75 V
   • Backward bias, open
2. Dark counts, trigger 30 mV :

• Visual inspection of the SCI
  • No yellowing, signs of mechanical damage on the surface.
  • Under UV, no spots

The Standard operating voltage is 1100 V, I_l = 739 uA, counting rate bellow 5 Hz