Fig. 6.1 shows a radiation detector placed on a laboratory bench. The detector is switched on and six readings of the count rate are recorded. The table in Fig. 6.2 shows the readings obtained. [Figure 6.1] [Figure 6.2]

1. (a)Using all the readings obtained, determine an average value for the background count rate.[1]
2. (b)(i)Fig. 6.1 shows a point P which is a very short distance from the end of the radiation detector. A sample of the radioactive isotope cobalt-60 is placed at P. The average value of the count rate obtained is now 975 counts/minute. The average count rate is determined with different objects between the radiation detector and the sample. The table in Fig. 6.3 shows the results obtained. Indicate, by placing ticks (✔) in the appropriate boxes, the radiation emitted by cobalt-60. alpha-particles [ ] beta-particles [ ] gamma rays [ ][1]
3. (b)(ii)1This radiation is produced when a nucleus of cobalt-60 (⁶⁰₂₇Co) decays into a nucleus of the daughter product X. Product X is not radioactive. Determine the number of protons in a nucleus of X,[1]
4. (b)(ii)2the number of neutrons in a nucleus of X.[1]
5. (c)(i)The half-life of cobalt-60 is 5.3 years. State what is meant by half-life.[2]
6. (c)(ii)When there is a lead sheet between the detector and the sample, the average count rate is obtained from six readings taken at one-minute intervals. The six readings are given in the table in Fig. 6.4. There are reasons for suggesting that the variation in these readings is random and not because the number of cobalt-60 atoms in the sample is decreasing. State two of these reasons. 1. 2. [Figure 6.4][2]

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