Which statement best describes a proportional counter?

Which statement best describes a proportional counter?

• A. A scintillation detector
• B. An ion chamber designed to operate using gas multiplication to measure ionizing radiation
• C. A semiconductor detector
• D. A cloud chamber

Answer: (B)

Gas multiplication in a detector allows the signal to be proportional to the energy deposited by radiation. In a proportional counter, the gas-filled chamber is biased so the electric field near the anode is strong enough to cause a Townsend avalanche: each primary ion pair created by the incident radiation triggers many more ionizations, amplifying the original signal. Because the number of secondary ionizations scales with the initial ionization, the pulse height is roughly proportional to the energy deposited, giving good energy discrimination for a gas detector. This distinguishes it from a plain ionization chamber, which has little or no multiplication and yields a signal proportional to total charge, and from a Geiger-Müller tube, where the avalanche is so large that the pulse height is essentially the same regardless of energy. It’s also different from scintillation detectors, which detect light, and from semiconductor detectors, which are solid-state. So the described statement correctly characterizes a proportional counter.

Gas multiplication in a detector allows the signal to be proportional to the energy deposited by radiation. In a proportional counter, the gas-filled chamber is biased so the electric field near the anode is strong enough to cause a Townsend avalanche: each primary ion pair created by the incident radiation triggers many more ionizations, amplifying the original signal. Because the number of secondary ionizations scales with the initial ionization, the pulse height is roughly proportional to the energy deposited, giving good energy discrimination for a gas detector. This distinguishes it from a plain ionization chamber, which has little or no multiplication and yields a signal proportional to total charge, and from a Geiger-Müller tube, where the avalanche is so large that the pulse height is essentially the same regardless of energy. It’s also different from scintillation detectors, which detect light, and from semiconductor detectors, which are solid-state. So the described statement correctly characterizes a proportional counter.