Nuclear Physics

Question 1

Why is iron the most stable atom

Answer 1

This is because iron requires the most amount of energy to remove one nucleon. therefore has the highest binding energy per nucleon

Question 2

What does u represent (1u)

Answer 2

the atomic mass unit (1.661*10^-27) that shows the average mass of a nucleon

Question 3

What does the mass defect indicate

Answer 3

The energy that is being lost due to binding energy

Question 4

What is meant by binding energy

Answer 4

It is the energy required to separate nucleons to individual protons and neutrons by overcoming the strong force

Question 5

What is meant by mass difference

Answer 5

When the mass of sum of total constituents of protons and neutrons is higher than the mass of the nucleus

Question 6

What does nuclear mass refer to

Answer 6

Just the mass of the nucleus

Question 7

What is used as a representation of the stability of a nucleus

Answer 7

The binding energy per nucleon

Question 8

Why is fusion and fission different

Answer 8

Fission - occurs in larger nuclei that are bigger than iron
Fusion - occurs in lighter nuclei that are smaller than iron

Question 9

How is energy released from fission and fusion

Answer 9

The increase in binding energy in these reactions are the energy released.

Question 10

Explain the process of fusion

Answer 10

This is when two light nuclei overcome the electrostatic force of repulsion and fuse together to form a larger nuclei. This larger nuclei had a great increase in binding energy which is the energy released.

Question 11

Explain the process of fission

Answer 11

This is when a nucleus is absorbed by a large nuclei which then splits into daughter nuclei, 2 or 3 neutrons and gamma radiation. Overall the binding energy has increased which is the energy we harness.

Question 12

what is 6L in grams

Answer 12

6000g

Question 13

What is the role of a fuel rod

Answer 13

To be made out of uranium (mostly 235 isotope) because fission occurs more easily. When this is the case the fuel rod is neutron enriched.

Question 14

What is the role of a moderator in a nuclear reactor?

Answer 14

To slow down neutrons

Question 15

How do moderators slow down neutrons

Answer 15

When they’re collided by high speed neutrons, atoms of the moderator turns the kinetic energy into heat. The slow neutrons produced are called thermal neutron because they have the same speed as the atoms in moderators.

Question 16

What materials can a moderator be made from?

Answer 16

Graphite and water

Question 17

What is the role of a coolant in a nuclear reactor

Answer 17

Heat is carried from the moderator to the coolant where now the hot coolant touches the cold coolant in turn creating the steam to turn turbines

Question 18

Why is the moderator normally water

Answer 18

Due to elastic collisions, since water has a small mass number, atoms are able to absorb more of the kinetic energy

Question 19

What materials are used for coolants

Answer 19

carbon dioxide and water

Question 20

What factors are considered when choosing coolant materials

Answer 20

How much heat they can store and transfer

Question 21

What is the role of control rods in a nuclear reactor?

Answer 21

To absorb neutrons and to maintain a constant rate of nuclear fission.

Question 22

What material are control rods made from?

Answer 22

boron and cadium

Question 23

Factors affecting the choice of materials of control rods

Answer 23

High melting point and ability to absorb neutrons

Question 24

What is shielding?

Answer 24

It is a safety measure where the reactor core is encased in steel which is designed to withstand high pressures and high temperatures.

Question 25

What is emergency shut down

Answer 25

When the reactor must be stopped, all control rods will be inserted fully, in case of a power cut, secondary rods held by electromagnets will be released.

In case there is no coolants, nitrogen is released to cool or absorb any spare neutrons

Question 26

What can happen to control rods over time.

Answer 26

They can become highly radioactive and must be replaced and safely disposed of.

Question 27

How is highly radioactive substances disposed off?

Answer 27

They’re buried and sealed in non-porous cases like glass for many years.

Question 28

What happens to shielding over time due to exposure to radioactive material

Answer 28

Shielding absorbs radioactive neutrons, this converts nuclei into unstable isotopes.

Question 29

What is the purpose of a moderator in a thermal nuclear reactor

Answer 29

Slows down the neutrons (reduce its kinetic energy) and allows the neutrons to be absorbed.

Question 30

What is 1u in MeV

Answer 30

It is 931.5 Mev

Question 31

What is a thermal neutron

Answer 31

It is a slowed down neutron
That is at thermal equilibrium with the moderator

Question 32

Explain why moderator atoms must the same size at the neutrons

Answer 32

As when they collide, momentum is transferred from the neutron to the moderator atom more evenly allowing for the neutron to be slowed so it can be readily absorbed

Question 33

What is the most reactive waste produced by a nuclear plant

Answer 33

Fission fragments (left-over fuel rods, normally uranium 238)

Question 34

What is the critical mass

Answer 34

The minimum value of mass needed to sustain a chain reaction

Question 35

Why are fission fragments unstable and what type of radiation do they emit?

Answer 35

Fission fragments are likely to be above the line of stability
As theyre neutron rich
So they might experience beta decay

Question 36

What type of radiation is emitted from an excite nucleus

Answer 36

Electromagnetic radiation
As energy gaps is large when it jumps from discrete energy levels to ground state.

Question 38

What are the two benefits of slowing down neutrons during fission

Answer 38

• allows nuclei to absorb the neutrons
• increase the chance of fission occurring