5.2. Radioactivity
A subsection of Physics, 5054, through 5. Nuclear physics
Listing 10 of 187 questions
A doctor has the choice of two isotopes, 131 53I and 125 53I, to inject into a patient. These isotopes emit radiation from deep inside the body. The radiation is detected outside the body and provides information to help the doctor find out what is wrong with the patient. The isotope 131 53I decays into a stable isotope of xenon by emitting a beta-particle (β) and a gamma ray (γ). State what is meant by a gamma ray. Complete the equation to show the radioactive decay of 131 53I. 53I Xe + −1β + γ When a nucleus of 125 53I decays, only a gamma ray is emitted. Suggest why it is better for the doctor to inject the isotope 125 53I into the patient.
5054_s17_qp_21
THEORY
2017
Paper 2, Variant 1
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One source of background radiation is cosmic rays. The cosmic rays that enter the Earth’s atmosphere are known as primary cosmic rays. Most of these rays are fast-moving protons or fast-moving alpha-particles. Both the Earth’s magnetic field and the Earth’s atmosphere reduce the number of primary cosmic rays that reach the Earth’s surface. Name a source of background radiation apart from cosmic rays. State one effect of background radiation. State the number of protons and the number of neutrons in an alpha-particle. number of protons number of neutrons Explain how the Earth’s atmosphere reduces the number of alpha-particles that reach the surface. shows an area where there is a uniform magnetic field into the page. On , draw a diagram to show the deflection of an alpha-particle by this magnetic field. magnetic field into page Primary cosmic rays produce carbon-14 in the atmosphere. The half-life of carbon-14 is 5700 years. Define the term half-life. A specimen of wood is found to contain 25 000 atoms of carbon-14. An otherwise identical specimen taken from a living tree is found to contain 200 000 atoms of carbon-14. Determine the age of the specimen that contains 25 000 atoms of carbon-14. age = State why it is not possible to use the amount of carbon-14 to date a specimen that is 570 000 years old. Carbon-14 is one of the isotopes of carbon. Another isotope is carbon-12. Describe how a nucleus of carbon-14 differs from a nucleus of carbon-12. Describe one similarity in the structure of the nuclei of these isotopes.
5054_s17_qp_22
THEORY
2017
Paper 2, Variant 2
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A smoke detector contains a small radioactive source of americium-241. The source emits alpha-particles. In the space below, draw a diagram of an apparatus that can be used to show that the source emits alpha-particles. Describe how this apparatus is used. Explain how the results of the test show that the source emits alpha-particles. The smoke detector works because alpha-particles from the source ionise the air. Compare the relative ionising effects and penetrating powers of alpha-particles, beta-particles and gamma rays. ionising effects penetration effects Americium-241 has a half-life of 430 years. Radium-224 is another element that emits alpha-particles. It has a half-life of 3.6 days. Explain why americium-241 is more suitable as the radioactive source in a smoke detector than radium-224. A smoke detector contains 8.0 × 1011 atoms of americium-241. Calculate the time taken for the number of atoms of americium-241 to fall to 1.0 × 1011. time = When used correctly, the radioactive source in the smoke detector is less harmful than background radiation. State one harmful effect of background radiation. A radioactive source is picked up using a long-handled tool. Explain why this is safer than using a short-handled tool.
5054_s18_qp_22
THEORY
2018
Paper 2, Variant 2
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Table 10.1 contains details of the nature and some properties of alpha, beta and gamma emissions. Table 10.1 alpha beta gamma nature 2 protons and 2 neutrons charge negative penetrating power stopped by 5 mm of aluminium Complete Table 10.1 by filling in the missing details. Surgical instruments in sealed plastic bags are placed in thin plastic boxes. A conveyor belt takes the boxes close to a cobalt-60 source which sterilises the instruments. This is shown in . cobalt-60 source thick concrete boxes of surgical instruments conveyor belt (viewed from above) The cobalt-60 source is a radioactive isotope of cobalt that emits gamma-radiation. Describe what is meant by the term isotope. Suggest a property of gamma-radiation that enables it to sterilise the instruments in the bags in the boxes. State why a source emitting only alpha-radiation cannot be used in this way. The half-life of cobalt-60 is 5.3 years. Explain why a source with a half-life of 5.3 minutes is unsuitable for use in this application. Geiger and Marsden performed an experiment in which alpha-particles were fired at a thin film of gold. shows an alpha-particle passing close to the nucleus of a gold atom. path of alpha-particle nucleus of gold atom Explain why the alpha-particle is deflected. In the experiment, most of the alpha-particles pass straight through the foil without deflection. Explain, using ideas about the structure of the atom, why this happens.
5054_s21_qp_21
THEORY
2021
Paper 2, Variant 1
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Table 9.1 shows details of seven different nuclides. Table 9.1 nuclide radiation emitted half-life hydrogen-2 none − hydrogen–3 beta 12 year francium-223 beta 22 min iridium-192 gamma 74 day phosphorus-32 beta 14 day radon−222 alpha 4 day technetium-99 gamma 6 hour Hydrogen-2 and hydrogen-3 are isotopes of the element hydrogen. Define the term isotope. The equation for the decay of phosphorus-32 (P-32) as it emits a beta particle is: 15 P → 0 –1β + 32 16 Q Explain whether the equation shows that Q is another isotope of phosphorus. Q is not the chemical symbol for the atom. One of the sources in Table 9.1 is used in a medical procedure to detect unusual bone structures. It is injected into a patient and the radiation emitted is detected outside the body. State which source in Table 9.1 is most suitable for this type of medical use. Explain two reasons for your choice Radon gas is one natural source of background radiation. Some causes of background radiation are man-made, for example, X-rays. State one other natural source of background radiation. State one other man-made source of background radiation. State one harmful effect of background radiation. One fusion reaction that occurs is: 1H + 3 1H → 4 2He + X Complete the equation to show the missing proton and nucleon numbers. Deduce the name of particle X. Suggest where this fusion reaction takes place. Compare the properties of alpha-particles and beta-particles in terms of their: • ability to penetrate through materials • ionising effects • deflection in a magnetic field.
5054_s22_qp_21
THEORY
2022
Paper 2, Variant 1
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Thorium-229 is a radioactive isotope used in several medical applications that involve alpha-particles and beta-particles. During ionisation, a helium atom becomes a helium ion. shows a diagram of a helium (He+) ion. protons neutrons electron State how the structure of a helium atom differs from the structure of the helium ion. State how the structure of an alpha-particle differs from the structure of the helium ion. A nucleus of thorium-229 (229 90 Th) decays by alpha (α) emission to a nucleus of element X. 90 Th X + 4 2α The nucleus of X then decays to a nucleus of Y by beta (β) emission. X Y + 0 –1β Complete Table 9.1 to show the number of protons and neutrons in a nucleus of X and in a nucleus of Y. Table 9.1 nucleus number of protons number of neutrons X Y Experiments can show that a sample of a material is radioactive. Describe the apparatus and the procedure used to show that a sample emits both alpha- particles and beta-particles. You may draw a diagram of the apparatus, if you wish. State what is meant by the half-life of thorium-229. A sample of pure thorium-229 contains 4.0 × 1014 atoms. After 22 000 years, the number of atoms of thorium-229 in the sample is 5.0 × 1013. Determine the half-life of thorium-229. Show your working. half-life =
5054_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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Questions Discovered
187