Explain Proportional counter with neat sketch.
Answers
Proportional counters are photon counting devices, meaning that the detection of each photon (an event) results in a discrete signal in the associated electronics. A typical counter, for example as shown, consists of a gas-filled chamber fitted with one or more x-ray transparent windows.
Photons penetrate the window and pass into the gas inside where interactions with the gas atoms result in the creation of a number of ion pairs (electrons and partially ionised gas atoms). Anodes in the detector volume are held at a positive potential with respect to the rest of the detector. The anodes are usually thin metal wires, and their electric field causes the electrons to drift towards the anodes where the field strength is highest. The energy of the electrons increases, and collisions with other gas atoms cause further ionisation producing more electrons. These secondary electrons themselves drift and acquire enough energy to cause further ionisation (and electrons), and so a large cloud of electrons arrives at the anode in a process known as an avalanche. The quantity of charge produced in the avalanche is great enough to be detectable in an amplifier connected to the anode.
