Radiation Detection, Instrumentation, and Measurement
Core concepts
Know gas-filled detectors (ionization chambers, proportional counters, Geiger-Müller), scintillation detectors (NaI(Tl), plastic), and solid-state detectors (semiconductor, TLD, OSL). Understand the gas amplification regions and which region each detector operates in. Survey meters must match the radiation type and energy: GM detectors are sensitive but energy-dependent and can saturate in high fields; ion chambers give accurate dose-rate readings. Know the purpose of calibration, energy compensation, and the difference between count rate and dose rate. Spectroscopy (gamma cameras, MCA) identifies isotopes by photopeak energy.
Traps
Questions test dead time (paralyzable vs nonparalyzable), resolving time, and the fact that GM tubes cannot measure energy. Don't confuse a survey meter reading in mR/h with absorbed dose. Watch for detector efficiency (intrinsic vs absolute) and geometry. TLD vs OSL: both integrate dose, but OSL can be re-read. A common trap is choosing a detector insensitive to the radiation present (e.g., using a thin-window detector for high-energy photons or a GM for high dose rates).
Worked example / rule of thumb
If a meter reads 2 mR/h and the calibration factor is 1.1, true rate = 2 × 1.1 = 2.2 mR/h. Rule of thumb: always apply the calibration factor and correct for background before interpreting a reading.