---
title: "Radioactive Decay: Alpha, Beta and Gamma"
description: "An unstable nucleus throws out an alpha particle, a beta particle or a gamma ray, and each has its own range and stopping material. A nuclear equation tracks how the mass number and atomic number chan"
canonical: https://lightmysky.com/learn/science/radioactive-decay-alpha-beta-and-gamma-mt_-AmjVwkR9t
source: https://lightmysky.com/learn/science/radioactive-decay-alpha-beta-and-gamma-mt_-AmjVwkR9t.md
retrieved: 2026-09-12
---

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# Radioactive Decay: Alpha, Beta and Gamma

An unstable nucleus throws out an alpha particle, a beta particle or a gamma ray, and each has its own range and stopping material. A nuclear equation tracks how the mass number and atomic number change.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/radioactive-decay-alpha-beta-and-gamma-mt_-AmjVwkR9t

## Ready when they can

- Names what each emission is made of and what absorbs it, from paper to lead
- Completes a nuclear equation for alpha and beta decay with mass and atomic numbers balanced
- Explains why an alpha emitter is the most dangerous kind to swallow but the least dangerous at arm's length

## Lesson: Three kinds of nuclear radiation

Some nuclei are unstable and rearrange themselves with no push from outside. They throw out three families. Alpha particles are chunky helium nuclei that ionise fiercely but stop in paper or skin. Beta particles are fast electrons that cross metres of air and need aluminium. Gamma rays are pure energy waves that need thick lead or concrete.

A nuclear equation is strict bookkeeping. The top mass numbers must balance and the bottom atomic numbers must balance across the arrow. In alpha decay the mass number drops by 4 and the atomic number drops by 2. In beta decay the mass number stays put while the atomic number rises by 1. Gamma changes neither.

**Example.** Omar checks an alpha equation. He reads the parent numbers, subtracts 4 on top and 2 below, and names the daughter that is left. Then he adds both columns on each side. If either column fails to balance, he knows the equation is wrong.

**Tip.** The danger ranking flips with distance, which catches many learners out. An alpha emitter you swallow sits against living tissue and hammers it, making it the worst internal hazard. At arm's length the same source cannot cross skin, while gamma still reaches you.

**Recap.** Name each emission, balance its equation, match its stopper.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Inside the Atom: the Nuclear Model](https://lightmysky.com/learn/science/inside-the-atom-the-nuclear-model-mt_B_PtnvyRIo)

## Opens up

- [Half-Life and Activity](https://lightmysky.com/learn/science/half-life-and-activity-mt_S5snTqUjyi)
- [The Decay Constant and the Exponential Decay Law](https://lightmysky.com/learn/science/the-decay-constant-and-the-exponential-decay-law-mt_VIydSAys1W)