1. 1
   A teacher shows a class a sample containing billions of nuclei of a radioactive isotope, explaining that decay events happen unpredictably over time, and uses a detector to demonstrate the changing count rate as time passes.

   (a)

   A teacher explains that a sample of a radioactive isotope contains billions of unstable nuclei, and that it is impossible to predict exactly when any particular nucleus will decay. What term describes this unpredictable nature of radioactive decay?

   [1 mark]

   • ARandom and spontaneous
   • BFixed and predictable
   • CControlled by an external switch
   • DDependent on the surrounding temperature

   (b)

   The teacher explains that during beta decay, a neutron in the nucleus changes into a proton and an electron, and the electron is emitted. What happens to the proton number of the nucleus as a result of this process?

   [1 mark]

   • AThe proton number doubles
   • BThe proton number decreases by 1
   • CThe proton number stays exactly the same
   • DThe proton number increases by 1

   (c)

   State what happens to the nucleon number of a nucleus during beta decay, and explain why the nucleus becomes a different element after beta decay has occurred.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A radiographer explains to trainee staff that a sample of radium-226 undergoes alpha decay to form radon-222, releasing an alpha particle in the process, as part of training on radioactive decay equations.

   (a)

   A radiographer explains that a sample of radium-226 undergoes alpha decay to form radon-222. During this decay, an alpha particle is emitted from the nucleus. What effect does emitting an alpha particle have on the nucleon number of the nucleus?

   [1 mark]

   • AIt leaves the nucleon number unchanged
   • BIt increases the nucleon number by 4
   • CIt decreases the nucleon number by 4
   • DIt decreases the nucleon number by 2

   (b)

   What is the effect of emitting an alpha particle on the proton number of the nucleus?

   [1 mark]

   • AIt increases the proton number by 2
   • BIt decreases the proton number by 2
   • CIt leaves the proton number unchanged
   • DIt decreases the proton number by 4

   (c)

   Write a nuclide equation for the alpha decay of radium-226 (proton number 88) to form radon-222, including the alpha particle emitted, and state the proton number of the radon-222 nucleus produced.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A physics student is studying carbon-14, a radioactive isotope with a proton number of 6 that decays by beta emission to form nitrogen-14, as part of coursework on radioactive dating methods.

   (a)

   A physics student is studying carbon-14, which decays by beta emission to form nitrogen-14. Carbon-14 has a proton number of 6. Write a full nuclide equation for this beta decay, clearly showing the nucleon number and proton number of each particle involved, and explain how you determined the proton number of the beta particle.

   [3 marks]

   (b)

   The student then investigates a third isotope, cobalt-60, which decays by beta emission to form nickel-60, and this decay is also accompanied by the emission of gamma radiation from the resulting nickel nucleus. Cobalt-60 has a proton number of 27. Write a nuclide equation for this decay, including the beta particle and the gamma ray, and explain why the emission of a gamma ray does not change the proton number or nucleon number of the nucleus, unlike alpha or beta decay.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A geologist is dating an ancient rock sample using the radioactive decay of uranium-238, which undergoes a series of decays, including alpha and beta emissions, eventually forming a stable isotope of lead.

   (a)

   Explain what is meant by radioactive decay, describing the roles of alpha, beta and gamma emission in changing (or not changing) the identity of a nucleus, and explain why radioactive decay is described as both random and spontaneous, and what this means for predicting the behaviour of an individual unstable nucleus versus a large sample of nuclei.

   [6 marks]

   (b)

   The geologist explains to a colleague that, before uranium-238 became stable as lead, it passed through several intermediate isotopes, some of which decayed by alpha emission and others by beta emission. Explain, using the changes in proton number and nucleon number caused by alpha and beta decay, how a nucleus could pass through a sequence of two alpha decays followed by one beta decay, describing the overall change in proton number and nucleon number of the nucleus after these three decays, starting from a nucleus with proton number 92 and nucleon number 238.

   [6 marks]

   Total for question 4: 12 marks

End of questions