Nuclear fission and fusionEdexcel A-Level Physics: Mind map

Exam questions on Nuclear fission and fusion

1. The binding energy per nucleon of nuclei varies with nucleon number. It rises steeply for the lightest nuclei, reaches a maximum of about 8.8 MeV per nucleon at a nucleon number of about 56 (iron-56), and then falls slowly for heavier nuclei, to about 7.6 MeV per nucleon for uranium-235.
   Use the information about the binding energy per nucleon to explain why energy is released when two light nuclei fuse.2 marks
2. In a proposed fusion reactor, a gas of deuterium (hydrogen-2) and tritium (hydrogen-3) nuclei is heated until it forms a plasma at a temperature of about $1 \times 10^{8}$ K. The nuclei are then held together at a very high density so that they can fuse to form helium-4.
   Explain why fusion requires both a very high temperature and a very high density.2 marks
3. In a nuclear power station, one of the fission reactions of uranium-235 is ${}^{1}_{0}\text{n} + {}^{235}_{92}\text{U} \rightarrow {}^{141}_{56}\text{Ba} + {}^{92}_{36}\text{Kr} + 3\,{}^{1}_{0}\text{n}$. Binding energy per nucleon: uranium-235, 7.59 MeV; barium-141, 8.33 MeV; krypton-92, 8.51 MeV. Take $1\text{ MeV} = 1.60 \times 10^{-13}$ J, the molar mass of uranium-235 as 235 g mol⁻¹ and $N_A = 6.02 \times 10^{23}$ mol⁻¹.
   Use the binding energy per nucleon values to calculate the energy released, in MeV, when one uranium-235 nucleus undergoes this fission.3 marks