SOURCE RANGE NUCLEAR INSTRUMENTATION
Figure 35 shows a typical source range channel in functional form.
Figure 35 Source Range Channel
B10 lined or BF3 gas-filled proportional counters are normally used as source range detectors.
Proportional counter output is in the form of one pulse for every ionizing event; therefore, there
is a series of random pulses varying in magnitude representing neutron and gamma ionizing
The pulse height may only be a few millivolts, which is too low to be directly used without
amplification. The linear amplifier amplifies the input signal by a factor of several thousand to
raise the pulse height to several volts.
The discriminator excludes passage of pulses that are less than a predetermined level. The
function of the discriminator is to exclude noise and gamma pulses that are lower in magnitude
than neutron pulses.
The pulses are then sent to the pulse integrator where they are integrated to give a signal that is
proportional to the logarithm of the count rate.
The log count rate amplifier then amplifies the signal, which varies directly as the logarithm of
the pulse rate, in the detector. The logarithmic count rate is then displayed on a meter with a
logarithmic scale in counts per second.