P2- Energy from the nucleus Flashcards
What is nuclear fission?
Nuclear fission is the splitting of an atomic nucleus into equal fragments and the release of two or three neutrons.
A fission occurs when an unstable nucleus breaks apart, and can be spontaneous although in most cases requires the absorbtion of a stray neutron.
When does nuclear fission occur?
When a neutron hits a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits.
What is ‘enriched’ uranium?
Naturally occurring uranium is mostly uranium-238, which is non fissionable.
Most nuclear reactors use ‘enriched’ uranium contains 2-3% uranium-235.
What is chain reaction?
A chain reaction occurs when each fission event causes further fission events. In a nuclear reactor the process is controlled.
How is a chain reacion controlled in a nuclear reactor?
Control rods absorb fission neutrons to ensure that, on average, only one neutron per fission goes on to produce further fission.
How is nuclear fission used in a controlled way and in an uncontrolled way?
Controlled: Nuclear power.
Uncontrolled: Atom bomb.
What is nuclear fusion?
Nuclear fusion is the process of forcing two nuclei close enough together so they form a single larger nucleus.
By what process is energy released in stars?
Nuclear fusion.
Why is it hard to produce energy from nuclear fusion?
Nuclei approaching one another repel each other, so need to be heated to very high temperatures to give them enough energy to overcome the repulsion and fuse.
How are nuclei contained in a fusion reactor?
By a magnetic field.
What is radon gas?
Radon gas is a major source of background radiation. It is an 𝛼-emitting isotope that seeps into houses in certain areas through the ground.
How can workers in nuclear power stations reduce exposure?
- Keep as far as possible from sources of radiation.
- Spend as little time exposed as possible.
- Shield themselves with materials such as concrete and lead.
What is a galaxy?
A galaxy is a collection of billions of stars held together by their own gravity.
What was the universe like before galaxies and stars formed?
The universe was a dark patchy cloud of hydrogen and helium.
How did stars and galaxies form?
Dust and gas were pulled together by gravitational attraction to form stars.
The resulting intense heat started off nucleur fusion reactions in the stars, so they began to emit visible light and other radiation.
What is the life cycle of a low mass star?
Protostar➡️Main sequence➡️Red giant➡️White dwarf➡️Black dwarf.
What is the life cycle of a high mass star?
Protostar➡️Main sequence➡️Red supergiant➡️Supernova➡️Neutron star (Black hole if sufficient mass).
