Some specifications on PMTs

Light yield estimates

1. 5 mm thick scintillators
2. 10000 initial photons per tagged electron
   • assume that 2000 photons are collected (20 % light collection efficiency)
   • 400 p.e. (assuming 20% quantum efficiency)

Counter rates (according to the latest Dan's design)

• 1.1 μ A electron current, $10^{{-4}}X_{{0}}$ radiator

(corresponds to the photon flux of $5x10^{{7}}$ phot/sec in the cohrent peak region)

• Counter rate around E_gamma = 9 GeV: 1 - 1.5 MHz

(counter with ~20 MeV)

• The rate is about 4 times larger for the last counter (at 3 GeV)

Operating gain

• Assume 4 MHz counter rate, 400 p.e., 50 &m;A anode current
• The maximum anode current is typically 100 &mA. We have to operate the tubes at least 2 times smaller current.