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 μA anode current
• The maximum anode current is typically 100 μ A. We have to operate tubes at at least 2 times smaller current.
• Gain = A / (Rate x Np.e. x 1.6 10^-19) = $2x10^{{5}}$

Pulse amplitude

• Assume a triangular pulse 20 ns wide
• Umax = ( 2 / 20 ns ) x Np.e. x Gain x 1.6 10^-19 x 50 Om = 64 mV
• 128 mV for operating at two times smaller rate of 2 MHz (i.e., two times higher gain)
• The signal pulse has to be splitted (FADC250 and LE/F1TDC)
• We should consider to use amplifiers