The isotope yttrium-90 (⁹⁰₃₉Y) is radioactive. It is a beta-particle emitter that decays to product Q. Product Q is stable.

1. (a)State one feature that is common to all isotopes of yttrium.[1]
2. (b)Describe how a neutral atom of Q differs from a neutral atom of yttrium-90.[3]
3. (c)(i)A sample of yttrium-90 is placed close to a radiation detector in a laboratory. There are no other radioactive samples in the laboratory. A counter records the count rate. Fig. 10.1 is a graph of the count rate plotted against time. [Figure 10.1] Using Fig. 10.1, determine the average background count rate. average background count rate =[1]
4. (c)(ii)Suggest two different origins for the background count. 1. 2.[2]
5. (c)(iii)Using Fig. 10.1, determine the half-life of yttrium-90. Show how the answer is obtained. half-life =[4]
6. (c)(iv)Many of the points plotted in Fig. 10.1 do not lie on the best-fit line. Explain why.[2]
7. (d)A beam of beta-particles, travelling in a vacuum, enters the region between two parallel, metal plates. One plate is negatively charged and the other is positively charged. Fig. 10.2 shows the arrangement. [Figure 10.2] On Fig. 10.2, draw the path taken by the beta-particles as they travel between the two plates.[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.