Discriminator:

Proportional counters could also count neutrons through introducing boron into the chamber. The most general means of introducing boron is through merging it along with tri-fluoride gas to form Boron Tri-Fluoride (BF₃). When a neutron interacts with a boron atom, an alpha particle is emitted. The BF₃ counter could be made sensitive to neutrons and not to gamma rays.

Gamma rays could be eliminated since the neutron-induced alpha particles generate more ionizations than gamma rays generates. This is because mainly to the fact in which gamma ray-induced electrons have a much longer range than the dimensions of the chamber; the alpha particle energy is, in many cases, greater than gamma rays generate within a reactor. Thus, neutron pulses are much larger than gamma ray-generates pulses.

Through using a discriminator, the scaler could be set to read only the larger pulses generated through the neutron.  A discriminator is classically a single channel analyzer along with only one setting. above figure described the operation of a discriminator.

Any  input  pulse  >  2 volts causes an output pulse if  the  discriminator  is  set  at  2 volts.

Below Figure display a classical circuit used to measure neutrons with a BF₃ proportional counter.

Figure: Discriminator