nuclear physics prt 2 Flashcards
what is Einsteins equation for particles?
E = mc^2
E = energy
m = mass
c = speed of light in a vacuum
what is Nuclear Fission?
- heavy nucleus splits into smaller nuclei, releasing a tremendous amount of energy
- mass of resulting product is slightly smaller than original mass of nucleus
- missing mass converted into energy
what is mass energy equivalence
- mass can be converted into energy
- energy can be converted to mass
what is the famous Einstein equation
E = mc^2
what are some examples of mass energy equivalence?
- fusion of hydrogen into helium in centre of sun
- nuclear weapons
- fission of uranium in nuclear power plants
what is mass defect?
- difference between an atoms mass and the sum of the masses of its protons and neutrons
what is binding energy?
- amount of energy required to seperate a nucleus into its constituent protons and neutrons
what is nuclear fusion?
- fusing together of two small nuclei to produce a larger nucleus
what are conditions for nuclei to fuse?
- they must have high kinetic energies
- must be able to go close enough to fuse, whilst overcoming preventions
what are the two preventions for nuclear fusion?
- protons electrostatically repel one another
- nuclei must get very close together for the strong nuclear force to take effect
what is nuclear fission?
- splitting of a large atomic nucleus into smaller nuclei
how does nuclear fission work?
- neutrons are fired at the nucleus
- when the nucleus is struck it splits into two or more nuclei
- during fission, neutrons are ejected from the nucleus which can collide with other nuclei
- chain reaction which lasts until stopped
what is the binding energy per nucleon defined as?
- the binding energy of a nucleus divided by the number of nucleons in the nucleus
what does a higher binding energy represent?
- a higher stability
what are the key features of the binding energy graph for low values of A?
- nuclei have lower binding energies per nucleon
- light nuclei have weaker electrostatic forces and will undergo fusion
- gradient is much steeper
- fusion release a greater binding energy than fission
what are the key features of the binding energy graph at high values of A?
- nuclei have higher binding energies per nucleon, grad decreases
- heaviest elements are most unstable and will undergo fission
- gradient less steep
- fission reactions release less binding energy than fusion
why is iron the most stable element
- highest binding energy per nucleon
what are similarities between fission and fusion?
- total mass of products is slightly less than mass of reactants
- mass defect is equivalent to binding energy released
- both release energy
what are differences between fusion and fission?
- fusion occurs between A<56 (light nuclei)
- fission occurs in heavy nuclei A>56
- in light nuclei attractive nuclear forces dominate
when does induced nuclear fission occur?
- a stable nucleus splits into small nuclei due to the absorption of a slow moving neutron
what are thermal neutrons?
- neutrons involved in induced fission
- they have low KE
- slow moving
what is a thermal neutron defined as?
- a neutron which is in thermal equilibrium with its surroundings
what happens in chain reactions?
- products of fission are two daughter nuclei and two or three neutrons
- these neutrons can cause more fission leading to chain reactions
what are the two things that need to be controlled in a nuclear reactor?
- number of free neutrons in the reactor
- the energy of the free neutrons
what are the main components of a nuclear reactor?
- moderator
- control rods
- coolant
what is the purpose of the moderator?
- slows down neutrons
what is the purpose of the control rods?
- they absorb neutrons
what is the purpose of the coolant?
- to transfer thermal energy efficiently between the water systems of a nuclear power plant
recap, what is the purpose of the moderator?
- slow down neutrons to maintain the chain reaction
how does moderation of fission reactors generally work?
- when fast neutrons collide with moderator nuclei they lose energy through elastic collisions
- after several collisions, neutrons slow down to thermal speeds making them more likely to induce further fission
what must moderators be made from?
- light nuclei which are not fissionable and will not absorb neutrons
what must control rods be made of?
- non fissionable materials
why is water used as both coolant and moderator
- high specific heat capacity, transfers large amounts of energy
what must the shielding be made out of and why?
- lead / concreete to prevent radiation leakage
what are the common materials used for moderators
water and graphite
what are the common materials used for controlling?
- boron and cadmium
what are the common substances for cooling?
- water heloum and molten salts
how do moderators work?
- fast moving neutrons collide with the moderators molecules, causing loss of momentum
- neutrons slowed down are in thermal equilibrium with the moderator
how is the number of neutrons absorbed controlled by varying depth?
- lowering the rod decreases rate of fission, as more neutrons absorbed
- raising the rod increases rate of fission as fewer neutrons absorbed
- adjusted so exactly one fission neutron produced by each fission goes to cause another fission
what is the critical mass?
- minimum amount of fissile material needed for a sustained chain reaction to occur
what does low level waste include, and how is it dealth with?
- gloves, labcoats and tools
- stored in secured landfills with concrete barriers
what is intermediate level waste, and how is it dealth with?
- more radioactive than LLW, often including reactor components
-stored deep underground in specially designed containers
what is high level waste, and how is it dealt with?
- exteemely radioactive waste, udually nuclear fuel and waste frok nuclear processing, produces a lot of heat
- oftenstored in cooling ponds for several of years to allow heat radiaton levels to decrease
- deep geological strage
