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2 marksHalf-life

CSEC Physics · 1988 · Paper 2 · Question 3(b)(iii)

A thorium decay series is given: ²³²₉₀Th -> ²²⁸₈₈Ra -> ²²⁸₈₉Ac -> ²²⁸₉₀Th.

Calculate the half-life of a radioactive substance whose activity falls to 25% in 10 hours.

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Other parts of this question

  1. 3(a)(i)Identify the components X, Y and Z labelled in the diagram.[3 marks]
  2. 3(a)(ii)State whether or not the atom is neutral and explain your answer. Then record the mass (nucleon) number of the atom.[3 marks]
  3. 3(a)(iii)Draw a similar diagram to represent an isotope of the atom in (ii), and record its mass (nucleon) number.[3 marks]
  4. 3(b)(i)Enter, above each arrow, the symbols for the radiations that are likely to be emitted.[4 marks]
  5. 3(b)(ii)If someone is exposed to all three radiations from the thorium source, which one do you think is most likely to cause the greatest harm? Explain your answer.[3 marks]
  6. 3(b)(iv)The activity of a substance falls from 3 000 Bq to 750 Bq in 10 hours. What is its activity after a further fifteen hours?[2 marks]

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