Does temperature change a half-life?

No. Nuclear decay is unaffected by temperature, pressure or chemical state; the half-life is a property of the isotope.

Does activity decay the same way?

Yes. Activity is proportional to the number of undecayed nuclei, so it halves every half-life too.

S6 Physics: Radioactivity and Half-life, Paper 4 (Error redo)

2026-11-09

Ten redo items on miscounting half-lives, confusing activity with mass, and applying a statistical law to a single nucleus.

Where do half-life questions usually go wrong?　Most errors come from miscounting how many half-lives have passed and forgetting that activity decays by the same factor. Count the divisions by two first, then multiply or divide.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S6 Physics: Radioactivity and Half-life
Level	Level: Error redo

02　Questions (10 items)

FoundationA radioisotope has a half-life of 5 days. A 160 g sample is left for 15 days. What mass remains?
FoundationA sample has an activity of 4 800 Bq. What is its activity after four half-lives?
FoundationA sample starts with 24 000 undecayed nuclei. How many remain after three half-lives?
FoundationOnly one eighth of a sample remains. How many half-lives have passed?
IntermediateA 32 g sample decays to 2 g. If the half-life is 8 years, how much time has passed?
IntermediateAn isotope has a half-life of 12 years. What percentage remains after 36 years?
IntermediateAfter two half-lives a sample has 120 g left. What was the original mass?
ChallengeActivity falls from 9 600 Bq to 600 Bq. How many half-lives is that?
ChallengeAn 800 g sample falls to 100 g in 10 days. Find the half-life.
Error redoA student says that after one half-life every atom has decayed by half. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	20 g remains	15 days is three half-lives, so divide by 8.
2	Activity = 300 Bq	Activity halves each half-life, so four half-lives mean dividing by 16.
3	3000 nuclei remain	Half remain after each half-life, so three half-lives mean dividing by 8.
4	3 half-lives	One eighth is (1/2)³.
5	32 years	32 g to 2 g is a factor of 16, i.e. four half-lives, so 4 × 8 = 32 years.
6	12.5% remains	36 years is three half-lives, leaving one eighth.
7	480 g originally	After two half-lives one quarter remains, so the original was 120 × 4.
8	4 half-lives	9 600 ÷ 600 = 16 = 2⁴, so four half-lives.
9	About 3.3 days (10 ÷ 3)	800 to 100 is a factor of 8, i.e. three half-lives, so divide 10 days by 3.
10	It treats a statistical result as an individual one: each nucleus either decays completely or not at all. A half-life is the expected time for half a large sample to decay.	Radioactive decay is random; the half-life describes the expected behaviour of a large number of nuclei, not a single atom.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Book a senior secondary physics tutor Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.