ARRT category · 10% of exam
Radiation Physics and Radiobiology
Tests photon production (bremsstrahlung, characteristic), photon interactions (photoelectric, Compton, coherent), and the cellular and systemic effects of ionizing radiation. Approximately 10% of the ARRT exam.
Sample question
One free question from the 79-question Radiation Physics bank. Read it, pick your answer, then expand the rationale.
Which of the following photon interactions is the primary source of radiographic contrast between bone and soft tissue?
Show answer and full rationale
Correct answer: C. Photoelectric effect
A, Incorrect: Compton scatter is the source of patient and operator dose, not contrast. It produces uniform fog that reduces contrast.
B, Incorrect: Pair production requires photon energies above 1.022 MeV, far above diagnostic range.
C, Correct: Correct. The photoelectric effect is highly dependent on atomic number (Z³) and photon energy (1/E³). Bone (high Z) absorbs photoelectrically far more than soft tissue, producing the contrast difference between them.
D, Incorrect: Coherent scatter is a minor interaction at diagnostic energies and contributes negligibly to contrast.
Topics tested in this category
- Bremsstrahlung radiation
- Characteristic radiation and the K-shell
- Photoelectric effect (diagnostic contrast)
- Compton scatter (operator dose)
- Coherent (classical) scatter
- Direct and indirect cellular effects
- Single- and double-strand DNA breaks
- Stochastic vs. deterministic effects
- LD50/30 and acute radiation syndrome
Drill the full 79-question bank.
Free tier includes 50 mixed-category questions. Premium unlocks all 1,814 ARRT-style questions, 3 timed mock exams, and adaptive drill sessions in this category.
Frequently asked questions
How many Radiation Physics questions are on the ARRT Radiography Boards?
The Radiation Physics and Radiobiology category accounts for approximately 10% of the ARRT Radiography Boards exam, that's roughly 20 of the 200 scored questions on each administration. The full Radtechprepper practice bank contains 79 questions in this category, giving you ample room to drill until the patterns are second nature.
What topics are tested in the Radiation Physics category?
The Radiation Physics category tests: Bremsstrahlung radiation; Characteristic radiation and the K-shell; Photoelectric effect (diagnostic contrast); Compton scatter (operator dose); Coherent (classical) scatter. The full topic list is in the ARRT Radiography Content Specifications 2025.
How should I study for the Radiation Physics category?
Start with the chapter overviews in this curriculum that map to Radiation Physics, they cover the core concepts in plain English. Then drill questions in the practice bank, pause on every miss, read the rationale, and re-drill the same topic the next day. The ARRT exam rewards spaced repetition more than cram studying.