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Date November 2012 Marks available 2 Reference code 12N.2.SL.TZ0.3
Level Standard level Paper Paper 2 Time zone Time zone 0
Command term Explain Question number 3 Adapted from N/A

Question

This question is about radioactivity.

Caesium-137 \(\left( {{}_{55}^{137}{\rm{Cs}}} \right)\) is a radioactive waste product with a half-life of 30 years that is formed during the fission of uranium. Caesium-137 decays by the emission of a beta-minus (β) particle to form a nuclide of barium (Ba).

State the nuclear equation for this reaction.

[2]
a.

Determine the fraction of caesium-137 that will have decayed after 120 years.

[2]
b.

Explain, with reference to the biological effects of ionizing radiation, why it is important that humans should be shielded from the radiation emitted by caesium-137.

[2]
c.

Markscheme

\({}_{56}^{137}{\rm{Ba}}\);
anti-neutrino / \(\bar v\);

a.

evidence of use of 4 half-lives;
so 0.938 or 93.8% or \(\frac{{15}}{{16}}\) decays;

b.

reference to a short-term effect e.g. skin reddening / burning;
reference to a long-term effect e.g. genetic damage / cancer;
reference to relative penetrative power of beta/ionizing power compared to alpha or gamma;

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 7: Atomic, nuclear and particle physics » 7.1 – Discrete energy and radioactivity
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