--- title: "Radiation hazards, protection and shielding" subject: "Energy Resources" chapter: 7 key: "semester_6/energy_resources:radiation-hazards-protection-shielding" source: https://www.bctengineer.com/q/semester_6/energy_resources/radiation-hazards-protection-shielding site: BCT Engineering --- # Radiation hazards, protection and shielding Energy Resources · Chapter 7: Nuclear energy - Asked in: year not given, 4+4 marks - Video: [Radiation Protection](https://www.youtube.com/watch?v=cFRj9jc18ac) — Zainab Alkurmanji - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/energy_resources/radiation-hazards-protection-shielding - Whole chapter: https://www.bctengineer.com/md/semester_6/energy_resources/chapter-7 ## Question (a) Explain the health hazards of nuclear radiation and the three principles of radiation protection. (b) Gamma rays of 1 MeV pass through lead for which the linear attenuation coefficient is 0.806 cm⁻¹. Find the half-value layer and the thickness of lead needed to reduce the intensity to 1 % of its original value. If the dose rate is 4 mSv/h at 1 m from a small source, what is it at 4 m, neglecting absorption? ## Short answer Nuclear radiation can cause acute effects like radiation sickness and death at high doses, and delayed effects like cancer and genetic mutations. Protection principles: minimize time, maximize distance (inverse-square law), and use shielding. Half-value layer for 1 MeV gamma in lead is 0.86 cm; thickness for 1% transmission is 5.7 cm; dose rate at 4 m is 0.25 mSv/h. ## Answer #### (a) Health hazards Ionising radiation (alpha, beta, gamma, X-rays, neutrons) breaks chemical bonds and damages cells. - **Acute (deterministic) effects** from a high dose in a short time: radiation sickness (nausea, hair loss, burns), and death above about 4–5 Sv whole-body. - **Stochastic (delayed) effects:** cancer (leukaemia, thyroid, lung) and shortening of life, which appear after years; their probability rises with dose. - **Genetic effects:** mutations in reproductive cells that are passed on to children. - **Internal exposure** by inhaling or swallowing radioactive material (e.g. iodine-131 in the thyroid, radon, strontium-90 in bones) is especially dangerous for alpha emitters. Units: activity in becquerel (Bq); absorbed dose in gray (Gy); equivalent dose in sievert (Sv). The public limit is about 1 mSv per year and the limit for radiation workers is about 20 mSv per year (averaged, ICRP). #### Principles of protection 1. **Time:** reduce the time of exposure; dose is proportional to time. 2. **Distance:** dose falls with the square of the distance from a point source, $I \propto 1/r^2$. 3. **Shielding:** place absorbers between the source and the person: lead and concrete for gamma and X-rays, plastic or perspex for beta, water or polythene (hydrogen-rich) and boron/cadmium for neutrons, and paper or skin for alpha. Other measures are containment, ventilation, personal monitoring badges (TLD) and the ALARA principle (as low as reasonably achievable). #### (b) Shielding calculation Attenuation law: $I = I_0 e^{-\mu x}$. Half-value layer: $$ x_{1/2} = \frac{\ln 2}{\mu} = \frac{0.693}{0.806} = 0.860\ \text{cm} $$ For 1 % transmission, $I/I_0 = 0.01$: $$ x = \frac{\ln 100}{\mu} = \frac{4.605}{0.806} = 5.71\ \text{cm} $$ Distance effect: $$ D_4 = D_1\left(\frac{1}{4}\right)^2 = \frac{4}{16} = 0.25\ \text{mSv/h} $$ **Answer:** HVL = 0.86 cm; thickness for 1 % = 5.7 cm of lead; dose rate at 4 m = 0.25 mSv/h. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What are stochastic effects of radiation? A. Radiation sickness within hours B. Delayed effects such as cancer whose probability rises with dose C. Burns only D. Effects that occur only above 4 Sv Answer: B. Stochastic effects appear after years; the probability, not severity, increases with dose. (Key point: Stochastic effects) 2. What are the three principles of radiation protection? A. Time, distance and shielding B. Heat, light and sound C. Dose, mass and volume D. Containment, cost and speed Answer: A. Reduce exposure time, increase distance and place shielding. (Key point: Three principles) 3. How is the HVL found for mu = 0.806 cm^-1? A. ln 100 / mu B. 1 / mu^2 C. ln 2 / mu = 0.86 cm D. mu / ln 2 Answer: C. At HVL, I/I0 = 0.5, so x = ln2/mu. (Key point: Half-value layer) 4. What thickness of lead reduces intensity to 1 %? A. 0.86 cm B. 5.71 cm using x = ln 100 / mu C. 0.01/0.806 cm D. 57 cm Answer: B. From I = I0 e^(-mu x), x = ln(100)/0.806 = 5.71 cm. (Key point: Thickness for 1 %) 5. A source gives 4 mSv/h at 1 m. What is the rate at 4 m? A. 1 mSv/h B. 16 mSv/h C. 0.25 mSv/h D. 2 mSv/h Answer: C. Dose falls with the square of distance: 4 / 16 = 0.25 mSv/h. 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