Atomic StructureAQA GCSE Physics (8463)

Atoms and Nuclear Radiation

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)

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Master the topic

Worked examples8 Key formulae3 Definitions11 Common mistakes8

Step-by-step worked examples

01.Identify radiation by penetration
Foundation
Question
A source emits radiation that is blocked by paper but not by aluminium. What type is it likely to be?
Solution
1. 1
  Reason.
  $\text{Paper-stoppable radiation is alpha. Beta passes through paper but not 5 mm Al. Gamma passes through both.}$
Answer
Alpha (α).
02.Why α is dangerous if ingested
Higher
Question
Explain why alpha radiation is the most hazardous if inhaled, even though it cannot pass through skin.
Solution
1. 1
  Inside the body.
  $\text{Once inside, there is no skin barrier; α reaches body cells directly.}$
2. 2
  Ionising power.
  $\text{α is highly ionising — it knocks many electrons out of cell molecules.}$
3. 3
  Damage.
  $\text{This damages DNA and other cell structures, increasing cancer risk significantly.}$
Answer
Inside the body, α has no barrier and its high ionising power causes lots of cell damage per particle — particularly to DNA — raising cancer risk.
03.Alpha decay of polonium
Higher
Question
Polonium-210 (Z = 84) decays by alpha emission. Write the balanced equation.
Solution
1. 1
  Apply α rules.
  $\text{New A = 210 − 4 = 206; new Z = 84 − 2 = 82 (lead, Pb).}$
2. 2
  Write equation.
  ${}^{210}_{84}\text{Po} \to {}^{206}_{82}\text{Pb} + {}^4_2\text{He}$
Answer
²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He.
04.Beta decay of caesium
Higher
Question
Caesium-137 (Z = 55) undergoes β⁻ decay. Write the equation.
Solution
1. 1
  Apply β⁻ rules.
  $\text{A stays 137; Z rises to 56 (barium, Ba).}$
2. 2
  Write.
  ${}^{137}_{55}\text{Cs} \to {}^{137}_{56}\text{Ba} + {}^0_{-1}\text{e}$
Answer
¹³⁷₅₅Cs → ¹³⁷₅₆Ba + ⁰₋₁e.
05.Read half-life from graph
Foundation
Question
A decay curve shows count rate dropping from 800 cpm at t = 0 to 400 cpm at t = 12 hours. Find the half-life.
Solution
1. 1
  Definition.
  $\text{Count rate halved (800 → 400) in 12 hours.}$
2. 2
  Half-life.
  $t_{1/2} = 12\,\text{hours}$
Answer
12 hours.
06.Net decline after n half-lives
Higher
Question
A sample of Sr-90 (half-life 29 years) initially contains 8000 unstable nuclei. How many remain after 87 years? Express the net decline as a ratio.
Solution
1. 1
  n half-lives.
  $n = 87 / 29 = 3$
2. 2
  Fraction remaining.
  $(1/2)^3 = 1/8$
3. 3
  Nuclei left.
  $8000 \times 1/8 = 1000$
4. 4
  Ratio of decline.
  $8000 : 1000 = 8 : 1$
Answer
1000 nuclei remain. Net decline ratio = 8 : 1.
07.Distinguish irradiation from contamination
Foundation
Question
A lab worker is briefly exposed to a sealed gamma source. Later, a colleague spills a beaker of radioactive iodine onto their lab coat. Identify which person experiences irradiation and which experiences contamination.
Solution
1. 1
  Worker 1.
  $\text{Sealed gamma source from outside → irradiation. Exposure stops when they leave the room.}$
2. 2
  Worker 2.
  $\text{Radioactive iodine on lab coat → contamination. Source travels with the person until removed.}$
Answer
Worker 1 is irradiated (external, transient). Worker 2 is contaminated (source on body until removed/decayed).
08.Two precautions for working with a beta source
Higher
Question
Describe TWO precautions a school physics technician should take when storing and handling a beta source.
Solution
1. 1
  Shielding.
  $\text{Store inside an aluminium-lined container (β stops in ~5 mm Al).}$
2. 2
  Distance/handling.
  $\text{Use tongs to keep the source far from the body when in use (intensity falls with distance).}$
Answer
(1) Store inside an aluminium container; (2) handle with tongs, keeping distance.

Key formulae

Alpha decay (general)
${}^A_Z X \to {}^{A-4}_{Z-2} Y + {}^4_2 \text{He}$
- $A, Z$
  — Parent mass and atomic numbers
When to use
α decay (mostly heavy nuclei, A > 200).
Beta-minus decay (general)
${}^A_Z X \to {}^A_{Z+1} Y + {}^0_{-1} \text{e}$
- $A, Z$
  — Parent values
When to use
β⁻ decay — neutron-rich nuclei.
Half-life ratio (HT)
$\text{remaining fraction} = (1/2)^n$
- $n$
  — Number of half-lives elapsed = total time / t½
When to use
HT: after n complete half-lives.

Practice with flashcards

Card 1 of 110 known · 0 to review

Key definitions and keywords

Alpha (α) particleExaminer keyword: A helium-4 nucleus (2 protons + 2 neutrons), emitted from heavy unstable nuclei.
Beta (β) particleExaminer keyword: A high-speed electron emitted from the nucleus when a neutron decays into a proton.
Gamma (γ) rayExaminer keyword: High-energy electromagnetic radiation emitted from an unstable nucleus.
Ionising power: The ability of radiation to knock electrons off atoms it passes through.
Alpha decayExaminer keyword: A nuclear decay in which an alpha particle (²₂He nucleus) is emitted; A decreases by 4 and Z by 2.
Beta-minus decayExaminer keyword: A nuclear decay in which a neutron becomes a proton, emitting an electron; A unchanged, Z increases by 1.
Half-life (t½)Examiner keyword: The time taken for HALF the unstable nuclei in a sample to decay (or equivalently for the count rate to halve).
ActivityExaminer keyword: The number of decays per second in a radioactive sample. Unit: becquerel (Bq) = 1 decay/s.
IrradiationExaminer keyword: Exposure to radiation from an external source. Stops when the source is removed.
ContaminationExaminer keyword: The unwanted presence of a radioactive substance on or inside an object or person. Continues to irradiate until removed or decayed.
Peer reviewExaminer keyword: The independent scrutiny of a scientist's work by experts before publication, to check methodology, data, and conclusions.

Common mistakes and misconceptions

Mistake
Saying beta is an orbital electron.
Why it happens
Both are electrons.
How to avoid it
Beta comes from the NUCLEUS (when a neutron decays), not from the electron shell.
Mistake
Thinking penetration and ionising power are the same.
Why it happens
Both 'how dangerous'.
How to avoid it
They're INVERSELY related. α = most ionising, least penetrating. γ = least ionising, most penetrating.
Mistake
Writing beta as charge +1 instead of −1.
Why it happens
Confused with positron.
How to avoid it
Beta-minus is an electron: charge −1.
Mistake
Failing to balance A and Z.
Why it happens
Quick substitution.
How to avoid it
Total A on left = total A on right; same for Z. Check both.
Mistake
Saying 'half the mass' has gone.
Why it happens
Confusing 'undecayed nuclei' with 'mass'.
How to avoid it
Half the UNDECAYED nuclei have decayed — but the total mass is almost unchanged (daughter nuclei are similar mass).
Mistake
Saying you can change half-life by heating.
Why it happens
Analogy with chemical reactions.
How to avoid it
Nuclear processes are unaffected by external conditions (chemistry, T, P).
Mistake
Swapping irradiation and contamination.
Why it happens
Both involve radiation.
How to avoid it
Irradiation = irradiated by RAYS from outside. Contamination = contaminated WITH the source itself.
Mistake
Shielding gamma with aluminium.
Why it happens
Confusing β and γ shielding.
How to avoid it
γ needs LEAD (or thick concrete); aluminium is only enough for β.

Atomic StructureAQA GCSE Physics (8463)

Atoms and Nuclear Radiation

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)

Previous Next

Master the topic

Worked examples8 Key formulae3 Definitions11 Common mistakes8

Step-by-step worked examples

01.Identify radiation by penetration
Foundation
Question
A source emits radiation that is blocked by paper but not by aluminium. What type is it likely to be?
Solution
1. 1
  Reason.
  $\text{Paper-stoppable radiation is alpha. Beta passes through paper but not 5 mm Al. Gamma passes through both.}$
Answer
Alpha (α).
02.Why α is dangerous if ingested
Higher
Question
Explain why alpha radiation is the most hazardous if inhaled, even though it cannot pass through skin.
Solution
1. 1
  Inside the body.
  $\text{Once inside, there is no skin barrier; α reaches body cells directly.}$
2. 2
  Ionising power.
  $\text{α is highly ionising — it knocks many electrons out of cell molecules.}$
3. 3
  Damage.
  $\text{This damages DNA and other cell structures, increasing cancer risk significantly.}$
Answer
Inside the body, α has no barrier and its high ionising power causes lots of cell damage per particle — particularly to DNA — raising cancer risk.
03.Alpha decay of polonium
Higher
Question
Polonium-210 (Z = 84) decays by alpha emission. Write the balanced equation.
Solution
1. 1
  Apply α rules.
  $\text{New A = 210 − 4 = 206; new Z = 84 − 2 = 82 (lead, Pb).}$
2. 2
  Write equation.
  ${}^{210}_{84}\text{Po} \to {}^{206}_{82}\text{Pb} + {}^4_2\text{He}$
Answer
²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He.
04.Beta decay of caesium
Higher
Question
Caesium-137 (Z = 55) undergoes β⁻ decay. Write the equation.
Solution
1. 1
  Apply β⁻ rules.
  $\text{A stays 137; Z rises to 56 (barium, Ba).}$
2. 2
  Write.
  ${}^{137}_{55}\text{Cs} \to {}^{137}_{56}\text{Ba} + {}^0_{-1}\text{e}$
Answer
¹³⁷₅₅Cs → ¹³⁷₅₆Ba + ⁰₋₁e.
05.Read half-life from graph
Foundation
Question
A decay curve shows count rate dropping from 800 cpm at t = 0 to 400 cpm at t = 12 hours. Find the half-life.
Solution
1. 1
  Definition.
  $\text{Count rate halved (800 → 400) in 12 hours.}$
2. 2
  Half-life.
  $t_{1/2} = 12\,\text{hours}$
Answer
12 hours.
06.Net decline after n half-lives
Higher
Question
A sample of Sr-90 (half-life 29 years) initially contains 8000 unstable nuclei. How many remain after 87 years? Express the net decline as a ratio.
Solution
1. 1
  n half-lives.
  $n = 87 / 29 = 3$
2. 2
  Fraction remaining.
  $(1/2)^3 = 1/8$
3. 3
  Nuclei left.
  $8000 \times 1/8 = 1000$
4. 4
  Ratio of decline.
  $8000 : 1000 = 8 : 1$
Answer
1000 nuclei remain. Net decline ratio = 8 : 1.
07.Distinguish irradiation from contamination
Foundation
Question
A lab worker is briefly exposed to a sealed gamma source. Later, a colleague spills a beaker of radioactive iodine onto their lab coat. Identify which person experiences irradiation and which experiences contamination.
Solution
1. 1
  Worker 1.
  $\text{Sealed gamma source from outside → irradiation. Exposure stops when they leave the room.}$
2. 2
  Worker 2.
  $\text{Radioactive iodine on lab coat → contamination. Source travels with the person until removed.}$
Answer
Worker 1 is irradiated (external, transient). Worker 2 is contaminated (source on body until removed/decayed).
08.Two precautions for working with a beta source
Higher
Question
Describe TWO precautions a school physics technician should take when storing and handling a beta source.
Solution
1. 1
  Shielding.
  $\text{Store inside an aluminium-lined container (β stops in ~5 mm Al).}$
2. 2
  Distance/handling.
  $\text{Use tongs to keep the source far from the body when in use (intensity falls with distance).}$
Answer
(1) Store inside an aluminium container; (2) handle with tongs, keeping distance.

Key formulae

Alpha decay (general)
${}^A_Z X \to {}^{A-4}_{Z-2} Y + {}^4_2 \text{He}$
- $A, Z$
  — Parent mass and atomic numbers
When to use
α decay (mostly heavy nuclei, A > 200).
Beta-minus decay (general)
${}^A_Z X \to {}^A_{Z+1} Y + {}^0_{-1} \text{e}$
- $A, Z$
  — Parent values
When to use
β⁻ decay — neutron-rich nuclei.
Half-life ratio (HT)
$\text{remaining fraction} = (1/2)^n$
- $n$
  — Number of half-lives elapsed = total time / t½
When to use
HT: after n complete half-lives.

Practice with flashcards

Card 1 of 110 known · 0 to review

Key definitions and keywords

Alpha (α) particleExaminer keyword: A helium-4 nucleus (2 protons + 2 neutrons), emitted from heavy unstable nuclei.
Beta (β) particleExaminer keyword: A high-speed electron emitted from the nucleus when a neutron decays into a proton.
Gamma (γ) rayExaminer keyword: High-energy electromagnetic radiation emitted from an unstable nucleus.
Ionising power: The ability of radiation to knock electrons off atoms it passes through.
Alpha decayExaminer keyword: A nuclear decay in which an alpha particle (²₂He nucleus) is emitted; A decreases by 4 and Z by 2.
Beta-minus decayExaminer keyword: A nuclear decay in which a neutron becomes a proton, emitting an electron; A unchanged, Z increases by 1.
Half-life (t½)Examiner keyword: The time taken for HALF the unstable nuclei in a sample to decay (or equivalently for the count rate to halve).
ActivityExaminer keyword: The number of decays per second in a radioactive sample. Unit: becquerel (Bq) = 1 decay/s.
IrradiationExaminer keyword: Exposure to radiation from an external source. Stops when the source is removed.
ContaminationExaminer keyword: The unwanted presence of a radioactive substance on or inside an object or person. Continues to irradiate until removed or decayed.
Peer reviewExaminer keyword: The independent scrutiny of a scientist's work by experts before publication, to check methodology, data, and conclusions.

Common mistakes and misconceptions

Mistake
Saying beta is an orbital electron.
Why it happens
Both are electrons.
How to avoid it
Beta comes from the NUCLEUS (when a neutron decays), not from the electron shell.
Mistake
Thinking penetration and ionising power are the same.
Why it happens
Both 'how dangerous'.
How to avoid it
They're INVERSELY related. α = most ionising, least penetrating. γ = least ionising, most penetrating.
Mistake
Writing beta as charge +1 instead of −1.
Why it happens
Confused with positron.
How to avoid it
Beta-minus is an electron: charge −1.
Mistake
Failing to balance A and Z.
Why it happens
Quick substitution.
How to avoid it
Total A on left = total A on right; same for Z. Check both.
Mistake
Saying 'half the mass' has gone.
Why it happens
Confusing 'undecayed nuclei' with 'mass'.
How to avoid it
Half the UNDECAYED nuclei have decayed — but the total mass is almost unchanged (daughter nuclei are similar mass).
Mistake
Saying you can change half-life by heating.
Why it happens
Analogy with chemical reactions.
How to avoid it
Nuclear processes are unaffected by external conditions (chemistry, T, P).
Mistake
Swapping irradiation and contamination.
Why it happens
Both involve radiation.
How to avoid it
Irradiation = irradiated by RAYS from outside. Contamination = contaminated WITH the source itself.
Mistake
Shielding gamma with aluminium.
Why it happens
Confusing β and γ shielding.
How to avoid it
γ needs LEAD (or thick concrete); aluminium is only enough for β.

Atoms and Nuclear Radiation

Master the topic

Step-by-step worked examples

01.Identify radiation by penetration

02.Why α is dangerous if ingested

03.Alpha decay of polonium

04.Beta decay of caesium

05.Read half-life from graph

06.Net decline after n half-lives

07.Distinguish irradiation from contamination

08.Two precautions for working with a beta source

Key formulae

Practice with flashcards

Key definitions and keywords

Common mistakes and misconceptions

Atoms and Nuclear Radiation

Master the topic

Step-by-step worked examples

01.Identify radiation by penetration

02.Why α is dangerous if ingested

03.Alpha decay of polonium

04.Beta decay of caesium

05.Read half-life from graph

06.Net decline after n half-lives

07.Distinguish irradiation from contamination

08.Two precautions for working with a beta source

Key formulae

Practice with flashcards

Key definitions and keywords

Common mistakes and misconceptions