Geiger-Muller tubes and ionization chambers are both gas-filled detectors in daily use, and both pass this morning's background and constancy checks. The GM tube is the department's usual tool for low-level contamination surveys. Which statement correctly explains how each detector turns radiation into a reading?
Select an answer to reveal the explanation.
Short Explanation
You can picture each GM event triggering a gas discharge that produces one large pulse, making low-level radiation easier to count. An ionization chamber instead measures current from collected ion pairs; that difference is gas amplification.
Full Explanation
In a Geiger-Muller tube, the high operating voltage allows an initial ionization to trigger a gas discharge, producing one large output pulse. The tube counts pulses; pulse size does not indicate radiation energy. This gas amplification makes the GM tube useful for detecting low-level contamination. An ionization chamber collects ion pairs and measures the resulting current, which is generally less suitable for counting very low radiation levels, so it does not respond more strongly to weak contamination than a GM tube. Neither detector simply counts photons entering its volume: the GM tube’s higher rate alone does not establish that the field at the surface is stronger, because the detectors operate differently. A higher GM reading also need not indicate calibration drift; successful background and constancy checks provide evidence that the instrument is functioning as expected. As an exam caveat, GM-tube dead time can cause count losses at high rates, and an appropriately selected ionization chamber may be used for higher radiation levels. Before surveying, follow the instrument’s required background and constancy-check procedures.