Physics and Engineering of Radiation Detection

7.2. Position Sensitive Detection 443

Anode Wires

Cathode Plane

Wire Holder

Cathode Plane

−HV

−HV

Signal Out

Signal Out

(a)

Signal Out

Cathode Plane

Cathode Plane

Anode Wires

d

~3d

−HV

−HV

(b)

Figure 7.2.2: Top (a) and cross sectional (b) views of a simple mul-

tiwire proportional chamber. The spacing between a cathode plane

and the plane of anode wires is approximately three times the anode-

to-anode distance or pitch, which is typically 2mmto 3mm.

proportional counter, avalanche spreading is not of much concern. The best way
to deal with this problem is to use a quenching gas. The basic idea behind this is
to suppress the electron population through absorption by the quencher molecules.
Again, the quenching mechanisms and quenching gases have already been discussed
in the chapter on gas filled detectors.
The output of a multiwire proportional chamber depends on the associated elec-
tronics, which in turn depends on its mode of operation. In digital mode, in which
only counting is performed and the information is binary, the electronics might con-
sist of simple level crossing discriminators and counters. However if the pulse height
is also to be measured then the circuitry would become more complicated and in-
volved. Since a multiwire proportional counter can be thought of as a combination