P2.7 Energy From The Nucleus Flashcards
When does nuclear fission occur?
When a stable isotope is struck by a neutron. The isotope absorbs the neutron, becomes unstable and splits apart, releasing large amounts of energy.
What isotopes undergo nuclear fission?
Uranium-235
Plutonium-239
What do you need for a chain reaction?
Neutrons
When fission occurs, what does it split into?
Daughter nuclei
Draw a chain reaction.
Look it up
What the danger with chain reactions?
They release a lot of energy very quickly and if it’s uncontrolled heat builds up and could explode.
How are neutrons controlled?
The reactors graphite core slows down released neutrons so chain reaction can keep going.
Control rods made of boron absorb excess neutrons to prevent chain reactions getting out of control.
Draw a reactor for nuclear fission.
Look it up
How does nuclear fission start?
A uranium-235 atom absorbs a low speed neutron
What are pros of nuclear fission?
Reduces use of fossil fuels
No greenhouse gases produced
Cheap to run once built
What are cons of nuclear fission?
Expensive to build new power stations
Produces long lasting nuclear waste
Risk of uncontrolled chain reactions.
What’s nuclear fusion?
Powers the sun and other stars.
Small nuclei join together to form larger nuclei and energy is released.
What are deuterium and tritium?
Isotopes of hydrogen
Deuterium + tritium ->
Fusion -> helium + neutron
What conditions does nuclear fusion happen in?
In stars
High temp
High pressure
What’s a life cycle for a star about the same size as our sun?
Protostar Main sequence star Red giant White dwarf Black dwarf
What’s the life cycle for a star bigger than our sun?
Protostar Main sequence star Red super giant Supernova Then either neutron star or a black hole
How do all stars start?
Nebula
Large clouds of dust and gas (mainly hydrogen)
Give details of a protostar
Over millions of years gravity will cause dust&gas in the nebulae to come together. As it does this the temperature increases until hydrogen can fuse. When this happens a protostar is born. This is a star nursery.
Give details of a main sequence star
Next stage after protostar. Hydrogen fusion has been happening and the star is much hotter and brighter than the protostar.
Give details of a red giant star
When a star runs out of hydrogen it begins to fuse other heavier elements. This releases more energy causing the star to expand. It also gives off red light, hence the name.
Give details of a white dwarf.
When the red giant runs out of fuel and can fuse nothing more it will lose its outer layers. This leaves just the core which is still extremely hot. It’s so hot it glows white hot giving its name.
Give details of a black dwarf.
After a long enough time the white dwarf will cool down enough so that it stops glowing white hot. Now called black dwarf.
Give details of a red super giant star
Following the main sequence the star begins to fuse together heavier elements. However, as it has far more fuel, it expands to a much larger size and gives off much more energy.
