Nuclear 2

Question 1

What type of nuclei undergo alpha decay?

Answer 1

large nuclei

Question 2

What type of nuclei undergo beta minus decay?

Answer 2

neutron-rich nuclei

Question 3

What type of nuclei undergo beta plus decay?

Answer 3

proton-rich nuclei

Question 4

What type of nuclei undergo electron capture?

Answer 4

proton-rich nuclei

Question 5

Where does the electron come from for electron capture?

Answer 5

the electron from one of the inner orbitals

Question 6

For the plot of number of neutrons against number of protons, for what region does Z = N?

Answer 6

for Z (or N) is less than 20

Question 7

What is the N value when Z = 80 on a plot of number of neutrons against number of protons?

Answer 7

A = 120

Question 8

Define binding energy

Answer 8

the energy required to separate a nucleus into its component parts

Question 9

Define mass defect

Answer 9

the difference between the mass of the component parts and the nuclear mass

Question 10

Explain why a nucleus has a lower mass per nucleon compared to free nucleons

Answer 10

• more stable when in a nucleus
• due to being in a lower energy state (less PE) (SNF)
• energy is proportional to mass (ΔE = Δmc²)
• therefore it has a lower mass per nucleon

Question 11

What does ΔE/A measure?

Answer 11

measures stability, the greater ΔE/A, the more stable

Question 12

What is ΔE/A for Iron-56?

Answer 12

≈9 MeV

Question 13

What is ΔE/A for U-235?

Answer 13

≈7

Question 14

What is ΔE/A for He-4?

Answer 14

≈7.5

Question 15

Define nuclear fission?

Answer 15

the splitting of a large nucleus into two smaller, daughter nuclei (plus several neutrons and a release of energy)

Question 16

Why are 2/3/4 neutrons released during nuclear fission?

Answer 16

as the ratio of neutrons to protons is greater for heavier nuclei

Question 17

What is meant by a controlled chain reaction?

Answer 17

only one neutron from each fission causes another fission, on average

Question 18

What do the control rods do, and what is their function?

Answer 18

• control rods absorb neutrons

- so they control the chain reaction by limiting the number of neutrons in the reactor

Question 19

What type of material are control rods made out of, and why?

Answer 19

• a material that can absorb a neutron to create a stable product
• e.g. boron steel

Question 20

What are fuel rods?

Answer 20

contain enriched uranium as fuel

Question 21

What does the moderator do, and why?

Answer 21

• scatters neutrons through a series of elastic collisions, in order to slow neutrons down to thermal speeds
• it does this so that there is a greater period of time for the SNF to act

Question 22

What type of materials are used for a moderator, and why?

Answer 22

• a material with relatively light nuclei so they can exchange energy effectively with the neutrons
• e.g. graphite or water

Question 23

What is the optimal mass for the moderator?

Answer 23

a moderator with similar mass to the neutrons is more efficient as slowing the neutrons down

Question 24

What does the coolant do?

Answer 24

is sent around the reactor to remove the heat produced by fission

Question 25

What type of material should be used as a coolant?

Answer 25

the material should be a liquid or gas at room temperature, and should be efficient at transferring heat

Question 26

What is meant by enriched uranium?

Answer 26

• the ratio or U-235 to U-238 is high (higher than natural uranium)
• (as U-235 is needed for fission)

Question 27

Why do both nuclear fission and nuclear fusion result in a release of energy?

Answer 27

BOTH increase ΔE/A, increase stability, reduce PE, work out / energy released

Question 28

Why is nuclear fusion considered ‘clean’?

Answer 28

• no long half lives

- very little radiation

Question 29

What conditions are required for fusion?

Answer 29

• very hot

- very high pressure

Question 30

List and explain 3 things that increase the likelihood of further fission occurring?

Answer 30

• spherical shape, lowest SA to volume ratio so fewer neutrons escape
• a critical mass (enough U-235)
• high level of enrichment (high ratio of U-235 to U-238)