Fission and fusion



Fission, Fusion and Nuclear Energy (all questions were taken from exam papers)

Speed of light = 2.998 × 10–8 m s–1; mass of hydrogen-2 nucleus = 3.342 × 10–27 kg

Mass of hydrogen-3 nucleus = 5.004 × 10–27 kg; mass of helium nucleus = 6.644 × 10–27 kg;

Mass of neutron = 1.674 × 10–27 kg

  1. Deuterium is an isotope of hydrogen; what is an isotope?

  2. Nuclear disintegrations occur in radioactivity and in fission.
    Distinguish between radioactivity and fission.

  3. Give an application of (i) radioactivity, (ii) fission.

  4. Radioactivity causes ionisation in materials. What is ionisation?

  5. Describe an experiment to demonstrate the ionising effect of radioactivity.

  6. What is the function of a moderator in a fission reactor?

  7. How did the cadmium rods control the rate of fission?

  8. Distinguish between fission and fusion.

  9. Why are large temperatures required for fusion to occur?

  10. At present, why is a fission reactor a more viable source of energy than a fusion reactor?

  11. In one particular fusion reaction, 2 isotopes of helium, each with a mass number of 3, combine to form another isotope of helium with the release of 2 protons.

Write an equation for this nuclear reaction.

  1. What is the source of the sun’s energy?

  1. 100 MJ of energy are released in a nuclear reaction. Calculate the loss of mass during the reaction.

  2. Give one benefit of a terrestrial fusion reactor under each of the following headings:

(i) fuel; (ii) energy; (iii) pollution.

  1. Controlled nuclear fusion has been achieved on earth using the following reaction.

    (i) What condition is necessary for this reaction to take place on earth?

(ii) Calculate the energy released during this reaction.

  1. Cobalt60 is a radioactive isotope with a half-life of 5.26 years and emits beta particles.

(i) Write an equation to represent the decay of cobalt60.

(ii) Calculate the decay constant of cobalt60.

(iii) Calculate the rate of decay of a sample of cobalt60 when it has 2.5 × 1021 atoms.

  1. In 1939 Lise Meitner discovered that the uranium isotope U–238 undergoes fission when struck by a slow neutron. Barium–139 and krypton–97 nuclei are emitted along with three neutrons.

  1. Write a nuclear reaction to represent the reaction.

  2. In a nuclear fission reactor, neutrons are slowed down after being emitted. Why are the neutrons slowed down?

  3. How are they slowed down?

  4. Fission reactors are being suggested as a partial solution to Ireland’s energy needs. Give one positive and one negative environmental impact of fission reactors.