Nuclear fission and fusion Flashcards
What are the two fissionable substances?
There are two fissionable substances in common use in nuclear reactors:
uranium-235 and plutonium-239
majority of reactors use uranium-235
What is fission?
splitting of an atomic nucleus
How does fission occur?
uranium-235 or plutonium-239 nucleus must first absorb a neutron
The nucleus undergoing fission splits into two smaller nuclei and two or three neutrons and energy is released
the neutrons may go on to start a chain reaction
What is nuclear fusion?
joining of two atomic nuclei to form a larger one
Where does nuclear fusion occur?
Nuclear fusion is the process by which energy is released in stars
nuclear fusion can happen because the temperatures and pressure is so high
How do stars and planets form?
Stars form when enough dust and gas from space is pulled together by gravitational attraction.
Smaller masses may also form and be attracted by a larger mass to become planets
Why did the universe once only hydrogen and how were heavier elements formed?
in a star, hydrogen nuclei fuse together to form helium nuclei
when a star runs out of hydrogen, fusion reaction take place, forming heavier elements, up to iron
elements heavier than iron are formed in supernovas
What are the beginning stages of a star?
protostar/nebula - gases are pulled together and it gets hotter
main sequence star - the star is stable because the forces are balances
What is the rest of the lifecycle for a star that is a similar size to the sun?
red giant
white dwarf
black dwarf
What is the rest of the lifecycle for a star that is larger than the sun?
red super giant star
supernova
neutron star or black hole
