Some specifications on PMTs
From GlueXWiki
Light yield estimates
- 5 mm thick scintillators
- 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, radiator
- (corresponds to the photon flux of 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) =
Pulse amplitude
- Assume a triangular pulse 40 ns wide
- Umax = ( 2 / 40 ns ) x Np.e. x Gain x 1.6 10^-19 x 50 Om = 32 mV
- 64 mV for operating at two times smaller rate of 2 MHz (i.e., two times higher gain)
- We should consider to use amplifiers