Types of radiation and their properties
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Question
What is an alpha (α) particle?
Answer
A **helium nucleus** — 2 protons + 2 neutrons (⁴₂He), charge **+2**.
Question
What is a beta-minus (β⁻) particle?
Answer
A **fast electron** emitted from the nucleus, charge **−1**.
Question
What is gamma (γ) radiation?
Answer
A **high-energy photon** (electromagnetic wave), charge **0**, no mass.
Question
What does it mean to 'ionise' an atom?
Answer
To **knock an electron off it**, leaving a charged ion. More ionising = more damage but shorter range.
Question
Order the three radiations by penetrating power (lowest to highest).
Answer
**Alpha < beta < gamma** — paper, then a few mm of aluminium, then thick lead/concrete.
Question
Order the three radiations by ionising power (strongest to weakest).
Answer
**Alpha > beta > gamma** — the opposite order to penetration.
Question
What stops each type of radiation?
Answer
α: paper / a few cm of air / skin. β⁻: a few mm of aluminium. γ: thick lead or concrete.
Question
Which radiation is NOT deflected by an electric or magnetic field, and why?
Answer
**Gamma** — it is a neutral photon (charge 0), so a field cannot push it. α and β are charged and do deflect.
Question
Why does alpha penetrate the least but ionise the most?
Answer
Its **+2 charge** makes it interact strongly with atoms, so it ionises heavily and loses its energy in a short distance.
Question
Why is alpha safe outside the body but dangerous inside it?
Answer
**Outside:** the skin stops it. **Inside** (breathed in/swallowed): its strong ionising power damages tissue with no skin to shield it.
Question
In a smoke detector, why is the sealed alpha source safe?
Answer
Alpha is the least penetrating: a few cm of air, the casing and skin all stop it, and the sealed source is very weak.
Question
Given data-booklet formula for the energy released in a decay?
Answer
$E = mc^{2}$ — the lost mass (mass defect) times the speed of light squared.
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Topic 5.3 hub
Radioactive decay
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