The Radiation Lab

The Radiation Lab 🔬

Some atoms have **unstable** nuclei. To become more stable they **decay**, firing out **nuclear radiation** — and they do it completely at **random**. In this lab you will meet the three types of radiation, learn what stops each, and crack the exam favourite: half-life.

Radioactive decay ☢️

A **radioactive** substance has unstable nuclei that break down, emitting radiation. This **decay** is a **random** process — you cannot say when any single nucleus will go. The **activity** is the rate of decay, measured in **becquerels (Bq)**; 1 Bq is one decay per second.

When will it decay?

When will one particular unstable nucleus decay?

• It is impossible to predict — decay is a random process
• Exactly one second from now
• As soon as it is heated
• The moment it is measured

Alpha, beta and gamma 🌀

There are three main types of nuclear radiation: • **Alpha (α)** — a **helium nucleus** (2 protons + 2 neutrons). The most **ionising**. • **Beta (β)** — a fast-moving **electron**. • **Gamma (γ)** — a high-energy **electromagnetic wave**. The least ionising.

Match each to what it is

What stops each one 🧱

The types differ hugely in how far they **penetrate**: • **Alpha** is stopped by a sheet of **paper** (or a few cm of air, or skin). • **Beta** passes through paper but is stopped by a few mm of **aluminium**. • **Gamma** is the most penetrating — it needs thick **lead** or concrete to reduce it.

Order by penetrating power

An interactive activity.

Balancing decay 🧮

Decay is written as a **nuclear equation**, and both the **mass number** (top) and **atomic number** (bottom) must balance on each side. In **alpha** decay the nucleus loses an alpha particle (2 protons + 2 neutrons), so its **mass number falls by 4** and its **atomic number falls by 2**. (In beta decay a neutron becomes a proton, so the atomic number rises by 1.)

Alpha decay

An interactive activity.

Half-life 🕐

Because decay is random, we describe a source by its **half-life**: the **time taken for the number of undecayed nuclei (or the activity) to HALVE**. After each half-life the amount left halves again: 800 → 400 → 200 → 100. After **n** half-lives, a fraction (½)ⁿ remains.

How much is left?

An interactive activity.

Plot the decay curve

An interactive activity.

Contamination and irradiation ⚠️

Two different hazards: • **Irradiation** — being **exposed** to radiation from an outside source. It stops the moment the source is removed, and does **not** make you radioactive. • **Contamination** — radioactive material getting **onto or into** you. It keeps emitting radiation, so it is an **ongoing** hazard.

Which hazard?

A sealed radioactive source is held near a worker for a minute, then taken away and locked up. What has the worker experienced?

• Irradiation — exposure that ends when the source is removed
• Contamination — radioactive material is now on or in them
• A half-life
• Nuclear fusion

The lab rules

Alpha radiation is the most ionising but is stopped by _____. The time for the activity of a source to halve is its _____. Radioactive material getting onto or into an object is called _____.