A teacher carries out an experiment on radioactivity using the apparatus shown in Fig. 11.1. [Figure 11.1] The count rate is a measurement of the count during one minute.

1. (a)(i)State the name of one type of radiation detector.[1]
2. (a)(ii)State one safety precaution the teacher must take when using a radioactive source.[1]
3. (b)(i)The teacher states that the emissions from the radioactive source are random in time. State what is meant by random in time.[1]
4. (b)(ii)Describe how the apparatus is used to show that the emissions are random in time.[2]
5. (c)(i)State what is meant by background radiation.[1]
6. (c)(ii)The teacher measures the count rate due to the source. Describe how the count rate is corrected for the background radiation.[2]
7. (d)(i)The corrected count rate is recorded for various distances d between the source and the detector. Fig. 11.2 shows a graph of the results obtained. [Figure 11.2] Determine the maximum distance that the radiation travels in air.[1]
8. (d)(ii)State the name of the radiation emitted by the radioactive source and give a reason for your answer.[2]
9. (d)(iii)As the radiation from the source travels in the air it causes ionisation. Describe what is meant by ionisation of the air.[1]
10. (e)The half-life of another radioactive source is 40 minutes. Initially, the corrected count rate from this source is 300 counts/minute. On Fig. 11.3, plot suitable points and draw a graph of the corrected count rate as it changes with time. [Figure 11.3][3]

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