IB Physics SL E.3 Radioactive decay questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

For each nucleus in a sample of 500 radioactive nuclei, the probability of decay during a specified interval is 0.20. What is the expected number of nuclei that decay during the interval?

Show answer and explanation

Answer: C. The expected number of decays is the probability of decay per nucleus multiplied by the number of nuclei: $0.20 \times 500 = 100$ nuclei. Because decay is random, this is an expected number, not a guarantee of the exact number that will decay.

A: converts the probability 0.20 to 20% and reports 20 as the number of nuclei, without applying the probability to the sample of 500.
B: uses half the stated probability, 0.10, giving 50 nuclei.
D: calculates the expected number that do not decay, $0.80 \times 500 = 400$ nuclei.
Remember: probability predicts an expected fraction of a sample, not which individual nuclei decay.

Question 2

Paper 2Medium8 marks

Figure 1 shows four nuclear transformations. In the first sequence, the nucleus formed after alpha decay becomes the parent nucleus in the following beta-minus decay. The symbol * denotes an excited nucleus.

(a)

Write the complete nuclear equation for the alpha decay in the first sequence.

[3]

(b)

Using your answer to (a), write the complete nuclear equation for the beta-minus decay in the first sequence. Include all emitted particles.

[2]

(c)

Write the complete nuclear equation for the beta-plus decay shown in Figure 1. Include all emitted particles.

[2]

(d)

Write the complete nuclear equation for the gamma emission shown in Figure 1.

[1]

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