A radiation detector is placed close to a radioactive source. The detector does not surround the source. Radiation is emitted in all directions and, as a result, the activity of the source and the measured count rate are different.

1. (a)Suggest two other reasons why the activity and the measured count rate may be different.[2]
2. (b)(i)The variation with time t of the measured count rate in (a) is shown in Fig. 12.1. [Figure 12.1] State the feature of Fig. 12.1 that indicates the random nature of radioactive decay.[1]
3. (b)(ii)Use Fig. 12.1 to determine the half-life of the radioactive isotope in the source.[4]
4. (c)1The readings in (b) were obtained at room temperature. A second sample of this isotope is heated to a temperature of 500 °C. The initial count rate at time t = 0 is the same as that in (b). The variation with time t of the measured count rate from the heated source is determined. State, with a reason, the difference, if any, in the half-life,[2]
5. (c)2the measured count rate for any specific time.[1]

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