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Science P2 Topic 5
Edexcel GCSE additional science physics: nuclear fission and fusion
| Question | Answer |
|---|---|
| What are nucleons? | sub-atomic particles within the nucleus i.e. neutrons and protons |
| What is the atomic number of an element? | It is the number of protons in an atom of the element, and is equal to the number of electrons |
| What is the mass number of an element? | The number of nucleons (neutrons + protons) in an atom of the element |
| How do you work out the number of neutrons in an element? | Mass number - atomic number |
| What are isotopes? | Atoms of a single element with different numbers of neutrons (making the mass number different) e.g. lithium-6 and lithium-7 |
| What is ionising radiation? | Radiation that has enough energy to make atoms lose electrons to become positively-charged ions |
| What is radioactive decay? | The random process where an unstable nucleus in a radioactive material decays by releasing ionising radiation to become more stable |
| What are the features of the 3 types of ionising radiation? | 1) alpha particles- very ionising, stopped by paper, emitted from nucleus, 2 protons + 2 neutrons 2) beta particles- electrons emitted from a nucleus, stopped by a few mm of aluminium 3) gamma rays- electromagnetic waves, stopped by lead/concrete |
| What are some dangers of ionising radiation? | Can cause skin burns (reddened skin) and can mutate DNA inside cells causing cancer |
| What is nuclear fission? | The process where a large, unstable nucleus splits into two smaller, daughter nuclei - neutrons are released as well as a lot of energy (thermal and kinetic) |
| What is the difference between a controlled and uncontrolled nuclear chain reaction? | Uncontrolled: lots of neutrons are released from each fission reaction which cause even fission and will result in an explosion. Controlled: another material is present to absorb all neutrons bar 1, so only 1 is absorbed by another nucleus |
| How does a nuclear reactor keep a controlled nuclear reaction? | Control rods are present- they contain elements that absorb extra neutrons, and they can be lowered into the core to decrease fission levels and raised out to increase the levels |
| What is the purpose of the following features of a nuclear reactor core: concrete shielding, fuel rods, moderator? | Concrete shielding- prevents stray neutrons and radiation escaping. Fuel rods- contain pellets of radioactive fuel e.g. uranium, plutonium. Moderator- slows neutrons down so they are more likely to be absorbed |
| How is the thermal energy released by nuclear fission used to generate electricity? | A coolant (water at high pressure) is pumped through the core and becomes superheated- it's pumped to a heat exchanger where it is used to produce steam, which drives a turbine and turns a generator that transfers kinetic energy into electrical energy |
| What are some advantages of using nuclear power to generate electricity? | * there is currently a large supply of radioactive fuel * no greenhouse gases are released |
| What are some disadvantages of using nuclear power to generate electricity? | * expensive to build and decomission * constant danger of radioactive materials escaping * waste has to be buried safely for a long time * energy to create fuel rods was probably produced in a way that released greenhouse gases |
| What is nuclear fusion? | the process whereby two smaller nuclei fuse to become one larger one, and lots of energy is released |
| How do stars get their energy? | Nuclear fusion |
| What conditions are needed for nuclear fusion? | * high pressures to increase densities of the nuclei, allowing them to get closer to each other and collide more easily * they need to be at a very high temperature to allow them to travel fast and overcome electrostatic repulsion |
| Why is electrostatic repulsion a problem? | • These conditions are hard to sustain on Earth so producing fusion power is very difficult |
| What is the peer-review process? | where scientists repeat the experiments done by another scientist and they must get the same results to validate the evidence e.g. this failed for the theory of 'cold fusion' |
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