P2.7 Flashcards
What is nuclear fission?
Splitting of a nucleus into two equal fragments and the release of two or three neutrons.
Which radioactive isotopes undergo fission?
Uranium or plutonium.
What is a chain reaction?
Occurs in a nuclear reactor when each fission event causes further fission events.
How is a chain reaction in a nuclear reactor controlled?
Control rods absorb fission neutrons to ensure that only one neutron per fission goes on to produce further fission.
What does water act as and why?
Moderator because it slows down the fission neutrons.
What happens during nuclear fission?
A late nucleus breaks up into two smaller nuclei.
What is nuclear fusion?
When two small nuclei release energy when they are fused together to form a single larger nucleus.
How can nuclei be made to fuse together?
By making two light nuclei collide at very high speed.
Where does the Sun’s energy come from?
Released when two light nuclei are fused together. Nuclear fusion in the Sun’s core releases energy.
Why is it difficult to make nuclear fusion reactor?
It needs to be at a high temperature before nuclear fusion can take place.
What is formed when two protons fuse?
A ‘heavy hydrogen’ nucleus.
What happens in a fusion reactor?
- plasma is heated by passing a very large electric current through it
- plasma is contained by a magnetic field so it doesn’t touch the reactor walls
What would happen if the plasma touched the reactor walls?
It would go cold and fusion would stop.
What is radon gas and why is it dangerous?
It’s an emitting isotope that seeps into houses in certain areas through the ground.
What happens to nuclear waste?
It’s stored in safe and secure conditions for many years after unused uranium and plutonium is removed from it.
What is a galaxy?
Collection of billions of stars held together by their own gravity.
What was the universe like in the billions of years before stars and galaxies were formed?
The universe was a dark patchy cloud of hydrogen and helium.
What is the force responsible for the formation of stars and galaxies?
The force of gravity pulled matter into galaxies and stars.
What is a protostar?
A gas and dust cloud in space that can go on to form a star.
What are the stages in the life of a star?
Low mass star:protostar-main sequence star-red giant-white dwarf-black dwarf
High mass star:protostar-main sequence star-red supergiant-supernova-neutron star-black hole if sufficient mass
What will eventually happen to the Sun?
Will eventually become a black dwarf.
What is a supernova?
Explosion of a supergiant after it collapses.
What chemical elements are formed inside stars?
Elements as heavy as iron are formed as a result of nuclear fusion.
What chemical weapons formed in supernovas?
Elements heavier than iron as well as light elements.
Why does the Earth contain heavy elements?
Because it was formed from the debris of a supernova.
