AQA GCSE Physics (8463), Higher tier · Atomic structure › Hazards and uses of radiation
Practise Different half-lives of radioactive isotopes. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Which isotope's activity falls to a very low level more quickly?
P
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy2 marks
Isotope P has a half-life of 2 hours. Isotope Q has a half-life of 20 years.
(a) Which isotope's activity falls to a very low level more quickly?[1]
(b) Which isotope would need to be stored safely for longer?[1]
Show the answer and mark scheme
(a)Answer: P
P
(b)Answer: Q
Q (it stays radioactive for much longer)
Question 2Medium6 marks
Two samples, A and B, contain the same number of radioactive nuclei. The isotope in sample A has a half-life of 2 hours. The isotope in sample B has a half-life of 5000 years.
(a) Which sample has the higher activity at the start? Give a reason for your answer.[2]
(b) Explain why sample A is less hazardous than sample B one week later.[2]
(c) Explain why the hazard from a radioactive material depends on the half-life of the isotope it contains.[2]
Show the answer and mark scheme
(a)Answer: A: its nuclei decay much more quickly, so there are more decays per second.
A
with a shorter half-life, a larger proportion of its nuclei decay each second
(b)Answer: After 84 half-lives A has almost completely decayed, but B's activity is practically unchanged.
one week is 84 half-lives of A, so almost all of A has decayed / its activity is negligible
the activity of B has hardly changed (because its half-life is so long), so it is still hazardous
(c)Answer: Short half-life: intense but short-lived hazard. Long half-life: weaker but very long-lasting hazard.
a short half-life gives a high activity, but only for a short time
a long half-life means the material stays radioactive (hazardous) for a very long time, although its activity is lower
Question 3Hard8 marks
After a nuclear accident, two of the most important radioactive isotopes released into the environment were iodine-131 and caesium-137. half-life of iodine-131 = 8 days half-life of caesium-137 = 30 years
(a) Calculate the fraction of the iodine-131 that remained 80 days after the accident.[2]
(b) Calculate the fraction of the caesium-137 that remained 90 years after the accident.[2]
(c) Evaluate which isotope was the greater hazard to people living near the accident in the first few weeks, and which is the greater hazard in the long term.[4]
Show the answer and mark scheme
(a)Answer: 1/1024
80 ÷ 8 = 10 half-lives
1/1024
(b)Answer: 1/8
90 ÷ 30 = 3 half-lives
1/8
(c)Answer: Iodine-131 in the first weeks (short half-life, high activity); caesium-137 in the long term (30-year half-life keeps it active for decades, while iodine-131 is gone within months).
in the first few weeks iodine-131 was the greater hazard
because its short half-life means a high activity / it was decaying rapidly and emitting a lot of radiation
in the long term caesium-137 is the greater hazard
because its long half-life means it stays radioactive in the environment (soil, food) for many decades, while the iodine-131 has almost all decayed within a few months