nuclear physics prt 2

Question 1

what is Einsteins equation for particles?

Answer 1

E = mc^2

E = energy
m = mass
c = speed of light in a vacuum

Question 2

what is Nuclear Fission?

Answer 2

• 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

Question 3

what is mass energy equivalence

Answer 3

• mass can be converted into energy
• energy can be converted to mass

Question 4

what is the famous Einstein equation

Answer 4

E = mc^2

Question 5

what are some examples of mass energy equivalence?

Answer 5

• fusion of hydrogen into helium in centre of sun
• nuclear weapons
• fission of uranium in nuclear power plants

Question 6

what is mass defect?

Answer 6

• difference between an atoms mass and the sum of the masses of its protons and neutrons

Question 7

what is binding energy?

Answer 7

• amount of energy required to seperate a nucleus into its constituent protons and neutrons

Question 8

what is nuclear fusion?

Answer 8

• fusing together of two small nuclei to produce a larger nucleus

Question 9

what are conditions for nuclei to fuse?

Answer 9

• they must have high kinetic energies
• must be able to go close enough to fuse, whilst overcoming preventions

Question 10

what are the two preventions for nuclear fusion?

Answer 10

• protons electrostatically repel one another
• nuclei must get very close together for the strong nuclear force to take effect

Question 11

what is nuclear fission?

Answer 11

• splitting of a large atomic nucleus into smaller nuclei

Question 12

how does nuclear fission work?

Answer 12

• 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

Question 13

what is the binding energy per nucleon defined as?

Answer 13

• the binding energy of a nucleus divided by the number of nucleons in the nucleus

Question 14

what does a higher binding energy represent?

Answer 14

• a higher stability

Question 15

what are the key features of the binding energy graph for low values of A?

Answer 15

• 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

Question 16

what are the key features of the binding energy graph at high values of A?

Answer 16

• 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

Question 17

why is iron the most stable element

Answer 17

• highest binding energy per nucleon

Question 18

what are similarities between fission and fusion?

Answer 18

• total mass of products is slightly less than mass of reactants
• mass defect is equivalent to binding energy released
• both release energy

Question 19

what are differences between fusion and fission?

Answer 19

• fusion occurs between A<56 (light nuclei)
• fission occurs in heavy nuclei A>56
• in light nuclei attractive nuclear forces dominate

Question 20

when does induced nuclear fission occur?

Answer 20

• a stable nucleus splits into small nuclei due to the absorption of a slow moving neutron

Question 21

what are thermal neutrons?

Answer 21

• neutrons involved in induced fission
• they have low KE
• slow moving

Question 22

what is a thermal neutron defined as?

Answer 22

• a neutron which is in thermal equilibrium with its surroundings

Question 23

what happens in chain reactions?

Answer 23

• products of fission are two daughter nuclei and two or three neutrons
• these neutrons can cause more fission leading to chain reactions

Question 24

what are the two things that need to be controlled in a nuclear reactor?

Answer 24

• number of free neutrons in the reactor
• the energy of the free neutrons

Question 25

what are the main components of a nuclear reactor?

Answer 25

- moderator - control rods - coolant

Question 26

what is the purpose of the moderator?

Answer 26

- slows down neutrons

Question 27

what is the purpose of the control rods?

Answer 27

- they absorb neutrons

Question 28

what is the purpose of the coolant?

Answer 28

- to transfer thermal energy efficiently between the water systems of a nuclear power plant

Question 29

recap, what is the purpose of the moderator?

Answer 29

- slow down neutrons to maintain the chain reaction

Question 30

how does moderation of fission reactors generally work?

Answer 30

- 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

Question 31

what must moderators be made from?

Answer 31

- light nuclei which are not fissionable and will not absorb neutrons

Question 32

what must control rods be made of?

Answer 32

- non fissionable materials

Question 33

why is water used as both coolant and moderator

Answer 33

- high specific heat capacity, transfers large amounts of energy

Question 34

what must the shielding be made out of and why?

Answer 34

- lead / concreete to prevent radiation leakage

Question 35

what are the common materials used for moderators

Answer 35

water and graphite

Question 36

what are the common materials used for controlling?

Answer 36

- boron and cadmium

Question 37

what are the common substances for cooling?

Answer 37

- water heloum and molten salts

Question 38

how do moderators work?

Answer 38

- fast moving neutrons collide with the moderators molecules, causing loss of momentum - neutrons slowed down are in thermal equilibrium with the moderator

Question 39

how is the number of neutrons absorbed controlled by varying depth?

Answer 39

- 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

Question 40

what is the critical mass?

Answer 40

- minimum amount of fissile material needed for a sustained chain reaction to occur

Question 41

what does low level waste include, and how is it dealth with?

Answer 41

- gloves, labcoats and tools - stored in secured landfills with concrete barriers

Question 42

what is intermediate level waste, and how is it dealth with?

Answer 42

- more radioactive than LLW, often including reactor components -stored deep underground in specially designed containers

Question 43

what is high level waste, and how is it dealt with?

Answer 43

- 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