SMS(S) Radioactivity WS 2 Qn

1 St. Margaret’s School (Secondary) Department of Science Physics Name: …………………………………………… Class: …………. Date: …………. 1 Fig. 1.1 shows the main parts of a nuclear reactor. Fig. 1.1 (a) The fuel rod contains uranium-235, which can undergo nuclear fission. Describe the process of nuclear fission that occurs in the fuel rod. Your description should include the role of neutrons in the process.

2 (b) Explain what happens as a control rod is moved out of the reactor core. (c) The nuclear reactor releases energy at a steady rate. By referring to neutrons, describe what is happening to achieve this steady rate. (d) Explain the purpose of the moderator in the nuclear reactor.

3 2 Protactiniu-234 ( 𝑃𝑃𝑃𝑃91 234 ) is a radioactive isotope of protactinium that decays to uranium-234 ( 𝑈𝑈92 234 ). (a) Compare the nuclide notation 𝑃𝑃𝑃𝑃91 234 with the nuclide 𝑈𝑈92 234 and deduce what this shows about what is emitted from a nucleus of protactinium-234 as it decays to uranium-234. Place a tick () in the appropriate boxes of Table 2.1 to show what is deduced from comparing the nuclide notations. Table 2.1 yes no it is not possible to tell An alpha-particle is emitted A beta-particle is emitted A gamma-ray is emitted (b) The most abundant isotope of protactinium is protactinium-231. (i) Explain, by referring to their nuclear compositions, why protactinium-231 and protactinium-234 are both isotopes of the same element. (ii) Explain, by referring to their nuclear compositions, why protactinium-231 and protactinium-234 are different isotopes of that element. (c) A teacher places a radiation detector on a bench in a school laboratory and switches it on. (i) The teacher measures and records the background radiation count rate. Describe what is meant by ‘background radiation’ and state two significant sources of the count rate recorded by the teacher. Background radiation Source 1 Source 2

4 (ii) The teacher moves a sample of protactinium-234 so that it is next to the detector. Suggest one precaution that ensures that the sample is moved in a safe way. (iii) The count rate is measured every 20 s with the sample present, and then corrected for background radiation. Fig. 2.1 shows a graph of the corrected countrrate against time for the protactinium-234 sample. Fig. 2.1 The curve is the best-fit line. Explain why many of the crosses do not lie on the curve.

5 (iv) Using Fig. 2.1, determine the half-life of protactinium-234. Show your working. Half-life = (v) The uranium-234 formed from the protactinium-234 is also radioactive. Its half- life is many thousands of years. Explain why the radiation from uranium-234 does not affect the count rates measured in this experiment.

6 3 Isotope X is radioactive. IT decays