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 by alpha-particle emission to a stable isotope. (a) State how a nucleus of X changes when it emits an alpha-particle. (b) There is a radiation detector in a laboratory where there are no radioactive samples. The detector is switched on and shows an average count rate of 22 counts / minute. (i) State why the radiation detector shows a count rate. (ii) A sample of isotope C is placed 2 cm from the detector and the reading displayed is 8000 counts / minute. The sample is moved a distance of 10 cm from the detector. The reading returns to an average value of 22 counts / minute. Explain why the reading returns to the original value.

7 (c) An alpha-particle passes into a region where here is a magnetic field. In the magnetic field, a force acts on the alpha-particle so that it follows a circular path. Fig. 3.1 shows that the particle passes through point J. Fig. 3.1 (i) On Fig. 3.1, draw an arrow through point J to show the direction of the force on the alpha-particle at J. (ii) Determine the direction of the magnetic field and mark a tick in the box () that indicates this direction. To the left To the right Towards the top of the page Towards the bottom of the page Into the page Out of the page (iii) Explain whether this force does work on the alpha-particle as the particle moves along the circular path.

8 4 Phosphorous-32 ( 𝑃𝑃15 32 ) is an isotope of phosphorus that undergoes radioactive decay. (a) The most common isotope of phosphorus is phosphorus-31. (i) Describe the structure and composition of a neutral atom of phosphorus-31. (ii) State how an atom of phosphorus-32 differs from an atom of phosphorus-31. (b) Phosphorus-32 decays by beta-particle emission to a stable isotope of sulfur. The half-life for this decay is 2.0 weeks. (i) State how a nucleus of this isotope of sulfur is different to a nucleus of phosphorus-32. (ii) At time t = 0, a radioactive sample contains 3.2  1011 atoms of phosphorus- 32. At the same moment, the sample contains no atoms of sulfur. This is shown by the cross on Fig. 4.1. On Fig. 4.1, plot a graph, to show how the total number of sulfur atoms in the sample changes with t and draw a suitable curve. Fig. 4.1

9 (c) State two precautions taken when storing or moving radioactive materials. 1. 2.

10 5 All the isotopes of the gas radon are radioactive. (a) State one similarity and one difference between the nuclei of two different isotopes of radon. similarity difference (b) The isotope radon-222 decays by alpha-particle emission to an isotope of polonium (Po). The proton number (atomic number) of polonium is 84. (i) Determine the number of neutrons in an atom of the polonium isotope. number of neutrons = (ii) Determine the number of protons in an atom of radon-222. number of protons = (iii) Describe how a neutral atom of helium ( 𝐻𝐻𝐻𝐻2 4 ) differs from an alpha-particle.