Fig. 11.1 shows the proton number and the nucleon number of the nuclei of five neutral atoms. [Figure 11.1]

1. (a)(i)State the two atoms in Fig. 11.1 that are different isotopes of the same element,[1]
2. (a)(ii)contain the same number of neutrons,[1]
3. (a)(iii)contain the same number of electrons.[1]
4. (b)(i)The nucleus of atom 1 is radioactive and when it decays, it emits a beta-particle. State, for the nucleus produced by this decay the proton number, proton number = [1]
5. (b)(ii)the nucleon number. nucleon number = [1]
6. (c)(i)A sample contains a large number of radioactive nuclei that emit beta-particles. The sample is placed near to a radiation detector in a laboratory and the count rate is recorded over a long period of time. Fig. 11.2 shows the count rate recorded by the detector during this period. [Figure 11.2] Suggest two major sources of background radiation. 1. 2.[2]
7. (c)(ii)1.Using Fig. 11.2, determine a value for the background count rate in the laboratory, background count rate = [1]
8. (c)(ii)2.determine the count rate, at time = 0, due to the sample on its own, count rate due to sample = [1]
9. (c)(ii)3.estimate the half-life of the radioactive atoms in the sample. half-life = [2]
10. (d)(i)A student suggests a change to the experiment in (c). He suggests completely encasing the radiation detector in lead before the sample that emits beta-particles is placed near to it. The effect on the count rate of background radiation may then be ignored. Describe and explain the effect on the background count rate recorded by the detector of completely encasing the radiation detector in lead.[2]
11. (d)(ii)State and explain whether the student's suggestion is a sensible one.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.