Nuclear Physics Flashcards
Why is iron the most stable atom
This is because iron requires the most amount of energy to remove one nucleon. therefore has the highest binding energy per nucleon
What does u represent (1u)
the atomic mass unit (1.661*10^-27) that shows the average mass of a nucleon
What does the mass defect indicate
The energy that is being lost due to binding energy
What is meant by binding energy
It is the energy required to separate nucleons to individual protons and neutrons by overcoming the strong force
What is meant by mass difference
When the mass of sum of total constituents of protons and neutrons is higher than the mass of the nucleus
What does nuclear mass refer to
Just the mass of the nucleus
What is used as a representation of the stability of a nucleus
The binding energy per nucleon
Why is fusion and fission different
Fission - occurs in larger nuclei that are bigger than iron
Fusion - occurs in lighter nuclei that are smaller than iron
How is energy released from fission and fusion
The increase in binding energy in these reactions are the energy released.
Explain the process of fusion
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.
Explain the process of fission
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.
what is 6L in grams
6000g
What is the role of a fuel rod
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.
What is the role of a moderator in a nuclear reactor?
To slow down neutrons
How do moderators slow down neutrons
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.
What materials can a moderator be made from?
Graphite and water
What is the role of a coolant in a nuclear reactor
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
Why is the moderator normally water
Due to elastic collisions, since water has a small mass number, atoms are able to absorb more of the kinetic energy
What materials are used for coolants
carbon dioxide and water
What factors are considered when choosing coolant materials
How much heat they can store and transfer
What is the role of control rods in a nuclear reactor?
To absorb neutrons and to maintain a constant rate of nuclear fission.
What material are control rods made from?
boron and cadium
Factors affecting the choice of materials of control rods
High melting point and ability to absorb neutrons
What is shielding?
It is a safety measure where the reactor core is encased in steel which is designed to withstand high pressures and high temperatures.
What is emergency shut down
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
What can happen to control rods over time.
They can become highly radioactive and must be replaced and safely disposed of.
How is highly radioactive substances disposed off?
They’re buried and sealed in non-porous cases like glass for many years.
What happens to shielding over time due to exposure to radioactive material
Shielding absorbs radioactive neutrons, this converts nuclei into unstable isotopes.
What is the purpose of a moderator in a thermal nuclear reactor
Slows down the neutrons (reduce its kinetic energy) and allows the neutrons to be absorbed.
What is 1u in MeV
It is 931.5 Mev
What is a thermal neutron
It is a slowed down neutron
That is at thermal equilibrium with the moderator
Explain why moderator atoms must the same size at the neutrons
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
What is the most reactive waste produced by a nuclear plant
Fission fragments (left-over fuel rods, normally uranium 238)
What is the critical mass
The minimum value of mass needed to sustain a chain reaction
Why are fission fragments unstable and what type of radiation do they emit?
Fission fragments are likely to be above the line of stability
As theyre neutron rich
So they might experience beta decay
What type of radiation is emitted from an excite nucleus
Electromagnetic radiation
As energy gaps is large when it jumps from discrete energy levels to ground state.
What are the two benefits of slowing down neutrons during fission
- allows nuclei to absorb the neutrons
- increase the chance of fission occurring
