what is the difference between small and large nuclei when they are unstable?
small nuclei = radioactive decy (emit alpha, beta, gamma radiation)
large nuclei = nuclear fission
(break apart into two nuclei)
define nuclear fission
the splitting of a large parent nucleus into two smaller daughter nuclei, with the release of energy and neutrons
what causes most nuclear atoms to undergo fission
usually hit with a neutron + the unstable nucleus absorbs a neutron
why does radioactive decay not occur with large unstable nuclei?
as it would not make the nucleus stable
what does the term fissile mean?
when an atom can be made to undergo fission
how do nuclear power stations prevent a nuclear meltdown?
have control rods which absorb surplus neutrons so energy is generated at a steady rate
(so only one neutron from each fission event can produce another fission event)
what is a nuclear chain reaction?
process in which neutrons released during a fission event go on to produce further fission events
what happens during an uncontrolled chain reaction? (and give an example when that happens)
- every neutron from each fission event goes on to produce further fission events
- energy released at exponential rate
- nuclear bomb
what are fissionable isotopes of an element?
isotopes which can be made unstable, but they themselves are stable
if you add neutrons to any heavy nuclei, will it become unstable?
no, they must be fissionable isotopes (so can be made unstable)
give one example of a fissionable material
uranium-235
why must there be a material that absorbs neutrons in a nuclear reactor?
- no material to absorb neutrons = an uncontrollable reaction occurs
- energy released at exponential, increasing rate
- very dangerous, lead to an explosion
define what nuclear fusion is
the joining of two small parent nuclei into a larger daughter nucleus, with the release of energy
where does nuclear fusion occur?
and how
in stars
- 2 light nuclei (ie. hydrogen) forced together at high speeds + form heavier nuclei (ie. helium)
advantages of nuclear fusion? 4
- no radioactive waste produced (forms stable nuclei)
- fuel needed is available in water (ie. hydrogen - from electrolysis)
- fusion produces a lot more energy than fission
- no greenhouse gases produced
disadvantages of nuclear fusion?
- building reactors is very difficult/not viable
why is nuclear fusion currently not viable?
more heat energy is required to make nuclei overcome repulsive forces + fuse than is released from fusion
why are stars able to carry out fusion easily?
have very high temperatures + very high pressures
high pressure due to strong gravitational pull
why is nuclear fusion so hard?
all nuclei have the same positive charge, and so they repel each other (very hard for them to join)
why are high temperatures and pressures needed for nuclear fusion?
temp = nuclei moving at high speeds
pressure = keeps nuclei close enough to fuse
where does the energy come from in nuclear fusion?
- when two smaller nuclei fuse, the mass of the larger one is slightly smaller than the total mass of the smaller nuclei
- so the ‘missing mass’ is transformed into energy (by the equation e = mc^2)
- and released as radiation
how does nuclear fusion release so much energy?
as the speed of light is very large, and when substituted into the equation e=mc^2, it can produce a huge amount of energy
similarities of nuclear fusion and fission
- both produce more energy than fossil fuels
- both involve the use of nuclei
differences of nuclear fusion and fission
FUSION
- two small nuclei to a larger one
- more energy released than in fission
- no dangerous waste is produced
- needs high pressure + temp
FISSION
- large unstable nuclei break apart
- only needs a neutron to start reaction
- produces dangerous radioactive waste as by-product
