3.5.3  Multiwire Proportional Chambers

A multiwire proportional chamber is a dispositive like the one that the Figure 9 shows. It is shown schemetized; only the essential elements are shown. Also, like the scintillator, their form, size, and sophistication depend on the experimental necessities. Basically, the multiwire proportional chamber contains two cathode planes and one or more anode planes of wires. If there is more than one plane of wires, normally they are at different angles. The multiwire proportional chamber is full of gas. The planes of wires are inside this atmosphere. The planes of wires inside the atmosphere, is the operation key for the chambers. The Figure 9 illustrates the arrangement of the wires and the physical principle of operation. When a charged particle passes through the chamber, the particle ionizes the gas, and generates ions. The generated ions are attracted by the cathode wire. The free electrons are attracted by the anode wire. The wires have some tenths of millimetre of diameter. They are coated by gold. The argon isobutane is used as the active gas in the chambers. The times of resolution of the multiwire proportional chambers are of the order of $30~ns$ and spatial resolution is of the order of $0.1~mm$.