Year 10 Science · Unit 2 · Lesson 23

Radioactive Decay, Alpha and Beta Reactions

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Learning Goals

Identify the odd one out in groups about radiation and decay.
Apply the balancing rules to a uranium decay-chain scenario.
Write and balance alpha and beta nuclear equations, checking mass and atomic numbers.

Warm Up

Odd one out

Circle the item that does not belong in each group. Then explain why it doesn't fit in the answer column.

#	Group	Odd one out + reason
1	Alpha particle Beta particle Gamma ray Proton
2	Mass number drops by 4 Atomic number drops by 2 Emits ⁴₂He A neutron becomes a proton
3	Stopped by paper Stopped by aluminium Stopped by lead Stopped by a magnet
4	U-238 Ra-226 Po-210 C-14
5	Gamma radiation No change to mass number No change to atomic number Changes the element

Your Turn

Scenario: the uranium-238 decay chain

Uranium-238 ( ²³⁸₉₂U ) does not become stable lead in one jump. It decays in a long chain of alpha and beta steps, balancing at every stage. The first three steps are: U-238 emits an alpha particle to form thorium-234; thorium-234 emits a beta particle to form protactinium-234; protactinium-234 emits a beta particle to form uranium-234. Remember the rules: an alpha particle is ⁴₂He, a beta-minus particle is ⁰_-1e, and the total mass number and total atomic number must be equal on both sides.

Step 1, alpha decay Complete: ²³⁸₉₂U → ___ + ⁴₂He. Give the daughter nuclide and show your check.
Step 2, beta decay Complete: ²³⁴₉₀Th → ___ + ⁰_-1e. Give the daughter nuclide and show your check.
Step 3, identify the type ²³⁴₉₁Pa → ²³⁴₉₂U + ___. Name the missing particle and the type of decay.
Balance a new equation Radium-226 ( ²²⁶₈₈Ra ) undergoes alpha decay. Write the full balanced equation, then check both rows.
Why it matters Explain why the atomic number changes at every step, and what that means for the element produced.

Wrap Up

In one sentence, explain how you can always check that a nuclear equation you have written is balanced.