1. 1
   Inside a nuclear power station reactor core, a slow-moving neutron is absorbed by a uranium-235 nucleus, which then splits into two smaller, roughly equal nuclei, releasing two or three new neutrons along with gamma rays and kinetic energy.

   (a)

   What is this process called?

   [1 mark]

   • ABeta emission
   • BNuclear fusion
   • CRadioactive decay
   • DNuclear fission

   (b)

   The neutrons released when a uranium-235 nucleus splits go on to be absorbed by further uranium-235 nuclei, causing them to split as well. What is this continuing process called, and how is it kept under control inside the reactor core?

   [1 mark]

   • AA chain reaction, controlled by cooling the reactor to absolute zero
   • BA fusion reaction, controlled using a strong magnetic field
   • CA chain reaction, controlled using control rods that absorb some of the released neutrons
   • DA decay chain, controlled by adding more uranium-235

   (c)

   Explain the difference between how a chain reaction is controlled inside a nuclear power station reactor and how it is allowed to proceed inside a nuclear weapon.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Deep inside the Sun's core, extreme temperature and pressure force light nuclei, such as hydrogen, close enough together to join and form heavier nuclei, such as helium, releasing energy in the process.

   (a)

   What is this process called?

   [1 mark]

   • AGamma decay
   • BNuclear fission
   • CChain reaction
   • DNuclear fusion

   (b)

   When two light nuclei join together inside the Sun to form a heavier nucleus, energy is released. Where does this released energy come from?

   [1 mark]

   • AThe nuclei absorb energy from sunlight already present in the core
   • BThe electrons surrounding the nuclei are destroyed and their charge becomes energy
   • CSome of the mass of the original nuclei is converted into the energy of radiation
   • DThe neutrons in the nuclei are converted directly into protons

   (c)

   Explain why extremely high temperature and pressure, such as those found in the Sun's core, are needed for nuclear fusion to take place.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A documentary explains that most of the elements found on Earth, including the iron in blood and the calcium in bones, were originally created inside stars.

   (a)

   Describe how fusion processes inside stars produce naturally occurring elements, and state which elements can be produced this way during a star's normal life cycle.

   [3 marks]

   (b)

   The documentary states that elements heavier than iron, such as gold and uranium, cannot be produced by the fusion processes that occur during a star's normal life. Explain how these heavier elements are created, and describe how they become spread throughout the universe.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An energy company is comparing plans to build either a new fission power station or invest in experimental fusion reactor research for future electricity generation.

   (a)

   Explain how nuclear fission is used to generate electricity in a power station, and discuss the practical challenges of controlling a fission chain reaction safely.

   [6 marks]

   (b)

   Explain why nuclear fusion could, in principle, provide a cleaner source of energy than nuclear fission, and discuss why achieving controlled fusion power generation on Earth has proved so technically difficult.

   [6 marks]

   Total for question 4: 12 marks

End of questions