9.2 Problems 495
ionizing potential for Argon is 15.7 V, calculate the maximum voltage which
must be applied to produce the avalanche.9.48 An electrometer with a capacitance 0.4 PF and 5.0 PF chamber are both
charged to a potential of 600 V. Calculate the potential of the combined system
after 8× 109 ions have been collected in the chamber.
9.2.6 Scintillation Counter...............................
9.49 Pions and protons, both with momentum 4 GeV/c, travel between two scintil-
lation counters distanceLm apart. What is the minimum value ofLnecessary
to differentiate between the particles if the time of flight can be measured with
an accuracy of 100 ps?
9.50 In the historical discovery of antiproton, negatively charged particles of pro-
tonic mass had to be isolated from a heavy background ofK−,π−andμ−.
The negatively charged particles which originated from the bombardment of a
target with 5.3 GeV protons, were subject to momentum analysis in a magnetic
field which permitted only those particles with momentump= 1 .19 GeV/c
to pass through a telescope system comprising two scintillation counters in
coincidence with a separation of d =12 metres between the detectors. Identify
the particles whose time of flight in the telescope arrangement was determined
ast= 51 ±1 ns. What would have been the time of flight ofπmesons?
9.51 A scintillation spectrometer consists of an anthracene crystal and a 10-stage
photomultiplier tube. The crystal yields about 15 photons for each 1 keV of
energy dissipated. The photo-cathode of the photomultiplier tube generates
one photo-electron for every 10 photons striking it, and each dynode produces
3 secondary electrons. Estimate the pulse height observed at the output of
the spectrometer if a 1 MeV electron deposits its energy in the crystal. The
capacitance of the output circuit is 1. 2 × 10 −^10 F.
9.52 A sodium iodide crystal is used with a ten-stage photomultiplier to observe
protons of energy 5 MeV. The phosphor gives one photon per 100 eV of energy
loss. If the optical collection efficiency is 60% and the conversion efficiency of
the photo-cathode is 5%, calculate the average size and the standard deviation
of the output voltage pulses when the mean gain per stage of the multiplier is
3 and the collector capacity is 12 PF.
[University of Manchester]
9.53 A 400-channel pulse-height analyzer has a dead timeτ =(17+ 0. 5 K)μs
when it registers counts in channelK. How large may the pulse frequencies
become if in channel 100 the dead time correction is not to exceed 10%?
Repeat the calculations for the channel 400.
9.54 An anthracene crystal and a 12-stage photomultiplier tube are to be used as
a scintillation spectrometer forβ-rays. The phototube output circuit has a