Radiation Physics and Instrumentation
Scope of this domain
This domain covers atomic structure, radioactive decay modes, interaction of radiation with matter, and the operating principles of detection and imaging equipment. Expect questions on decay equations, half-life calculations, gamma camera components, collimator selection, and quality control of instrumentation.
Concepts to master
- Decay modes: alpha, beta minus, beta plus, electron capture, and isomeric transition.
- Parent-daughter relationships and transient versus secular equilibrium.
- Photon interactions: photoelectric effect, Compton scatter, and pair production, and how each depends on energy and atomic number.
- Detector types: scintillation crystals, photomultiplier tubes, and semiconductor detectors.
- Collimators: parallel-hole, pinhole, converging, and diverging, and their effect on resolution and sensitivity.
- Energy resolution, spatial resolution, sensitivity, and uniformity as performance measures.
Traps
Questions frequently ask which interaction dominates at a given energy, or confuse sensitivity with resolution. Remember that improving resolution usually costs sensitivity. Another common trap is misapplying the half-life formula or forgetting that activity decreases exponentially, not linearly.
Worked example
A source has a half-life of 6 hours and an initial activity of 800 MBq. After 18 hours, three half-lives have passed, so activity is 800 divided by 2 cubed, or 100 MBq. Rule of thumb: count half-lives first, then divide by 2 raised to that count.
Study approach
Build a one-page table of decay modes with their emitted particles and typical detection signatures, then practice collimator selection for common imaging tasks.