In this chapter, the conclusions drawn from the experiments
will be stated, and the future uses of the counter system will be
It will to obvious from the results that a .,as Čerenkov counter
system of the type described, is an extremely useful tool for the
detection of muons in the high energy range. The most useful
property of the counter is of course, its velocity dependence.
This has certain advantages over other selecting arrangements,
which select on a momentum basis, e.g. elimination of contamination
in beam experiments.
It had been shown that at 10 atmospheres pressure, the large Čerenkov counter can select particles which are 0.0009c above the
threshold velocity. This threshold is set by the least number of
photons which can be .elected by the photomultiplier (90). If
Figure (6.1) is considered the properties and limitations of the
Čerenkov counters can b e seen over a wide range of momenta.
The table shown below has been calculated from Figure (4.1),
which snows the increase in photon number with increasing momentum.
It is calculated on the basis of a 100 cm. long sensitive length.
As has been stated before, the practical threshold momentum is
displaced further from the theoretical threshold with increasing
momentum. In fact, with such a counter, it is possible that even if
the particle is travelling with the velocity of light, insufficient
photons will be produced to give a count. The only thing which can be done to rectify this situation is to increase the length of the
counters. If, for example, a particle of momentum as high as 20
Gev./c was to be selected with an atmospheric pressure counter, it
would have to be 4.8 metres long, and of such design to collect all
the photons produced in the sensitive region. Of course, such a counter should theoretically select all particles above 4.5 Gev./c and thus the spread is becoming very large. It is this effect
which puts a practical high momentum limit on the counters, and
20 Gev./c would certainly be the upper limit to any type of counter
which we would consider possible to design.
Pulse height discrimination at these higher momentum values
is also impossible, as can be seen from Figure (4.1), as the curves
flatten out after a sharp initial rise. At the higher momentum
values the increase in photon number with increasing momentum is
Tne experiments using cosmic radiation are at a great disadvantage compared to experiments using machine intensities. There
fore, the fundamental interest is in being able to select particles
in an energy range above the limits of the present accelerators.
It does not therefore, appear possible to do this with a Čerenkov
counter system alone. A combination of Čerenkov counters and
ionisation counters using the relativistic rise in the latter, is
being considered for future use. With such an arrangement, it
might be found possible to select muons with an energy greater
than those produced by accelerators.