216 Chapter 3. Gas Filled Detectors
12.A GM counter records a rate of 2× 103 counts per second when placed in a
radiation field. Compute the efficiency of the detector if its dead time is 90μs.
Also compute the GM count rate you would expect if the detector was 100%
efficient.
13.A gas filled ionization chamber is bombarded with a steady beam of photons
having intensity of 10^10 cm−^3 s−^1. The photons produce electron ion pairs in
the active volume of the detector. If the number density of electrons (or ions) is
found to be in a steady state with a value of approximately 10^9 cm−^3 , estimate
the recombination coefficient of the filling gas.14.Estimate the decrease in quantum efficiency of a photon detector if the entrance
window absorbs 10% of incident photons instead of 1%. Assume that the
absorption in the active volume remains 60% of the available photons in both
cases.15.An ionization chamber having an active depth of 5cmis exposed to a photon
flux of 1. 5 × 105 cm^2 s−^1. The entrance window of the detector has an area
of 6cm^2 and the detector is filled withCO 2 under standard conditions of
temperature and pressure. Compute the quantum efficiency of the detector.
You can assume that the absorption in the window material is negligible.16.For the detector in the previous problem, calculate the detective quantum ef-
ficiency if the standard deviation of the measurements turns out to be 400
photons within the integration time of 1 second. What should be the stan-
dard deviation of the measurement be if the detective quantum efficiency is to
increase by 10%.17.Derive expression for the detective quantum efficiency of an integrating detector
(equation 3.8.8).18.A quantum detector is exposed to a photon beam delivering 10^4 photons per
second. Assume that the quantum efficiency of the detector is 0.6 and its dead
time is 100μs. Compute the detective quantum efficiency for a measurement
time of 1s. What will be the detective quantum efficiency if the measurement
time is decreased by half?19.A detector having a quantum efficiency of 0.4 sees a photon flux of 10^6 s−^1 .The
detector’s window has an area of 5cm^2. Assuming that the readout noise for
the integration time of 100msis 350, compute the detective quantum efficiency
of the system.