What is a disadvantage of a Geiger counter?

• A. It cannot detect alpha particles
• B. It is immune to saturation
• C. It can saturate at high levels and not indicate true level
• D. It provides precise energy spectra

Answer: (C)

The main idea here is that Geiger counters have a limited ability to handle very high radiation rates because of a brief recovery period after each detected event. When a particle ionizes the gas in the Geiger-Müller tube, a pulse is produced, and the tube needs a short dead time to reset before it can register another event. If radiation levels are high, many events occur during this recovery window, so the counter misses some, causing the displayed count to be lower than the true activity. In other words, the instrument can saturate at high levels and not indicate the real level of radiation.

Extra context: Geiger counters are great for detecting presence and estimating activity, but they don’t provide energy information about the radiation. The device responds to ionizing events with similar pulses regardless of the particle’s energy, so you don’t get an energy spectrum from this instrument.

Why the other ideas aren’t the best fit: a Geiger counter can detect alpha particles under suitable conditions (with a thin window), so the statement that it cannot detect alpha isn’t universally true. It is not immune to saturation, since dead time makes high rates misleading. And it does not provide precise energy spectra, which is a separate limitation from the saturation issue.