Physics - Recall for Chapter 26; Nuclear Physics
Flashcards
2022-04-14
What is conserved during nuclear reactions?
Mass-energy.
What is Einstein’s mass-energy equation and define each term?
What are two consequences of Einstein’s mass-energy equation?
Mass increases when energy increases and mass decreases when energy decreases.
Where does the energy of the emitted particles and photons in radioactive decay come from?
Mass is converted to energy, as the mass of the parent nucleus is greater than the mass of the products.
What happens when a particle of matter and its corresponding antimatter particle meet?
They annihilate each other, causing all their mass to be converted to energy in the form of two identical gamma photons.
What is pair production?
When a single gamma photon with sufficient produces a particle-antiparticle pair.
How does the mass of a nucleus compare to the mass of its constituent nucleons?
The mass of a nucleus is always less than the total mass of its separate nucleons
What is the binding energy of a nucleus?
The minimum energy needed to fully separate a nucleus into its constituent nucleons
What is the mass defect of a nucleus?
The difference between the mass of the completely separated nucleons and the mass of the nucleus
What equation relates binding energy and the mass defect of a nucleus?
\text{binding energy} = \text{mass defect} \times c^2
What happens to the total binding energy of a nucleus as nucleon number increases?
It increases.
How is the binding energy per nucleon calculated?
What is the stability of a nucleus affected by binding energy per nucleon?
Higher binding energy per nucleon means more tightly bound nucleons and therefore a more stable nucleus.
How does binding energy per nucleon change as nucleon number increases?
It increases with nucleon number up to iron-56 and then decreases.
Why is iron-56 the most stable nucleus?
It has the highest binding energy per nucleon and is therefore the most stable.
How does the binding energy of the products compare with the binding energy of the parent during natural radioactive decay?
Products are more stable, so must have a higher binding energy.
What are the two ways that energy released during radioactive decay can be calculated?
The difference in total binding energies between the products and the parent, or the difference in total masses multiplied by $c^2$.
What is nuclear fission?
The splitting of larger nuclei into smaller, daughter nuclei.
How can nuclear fission be induced?
By making a large nucleus absorb a neutron and making it become unstable.
Why does fission of large nuclei release energy?
The products have a higher binding energy/lower total mass than the parent nucleus as they are more stable.
What is produced during nuclear fission of a nuclei in a reactor core?
Daughter nuclei of approximately equal mass and 2 or 3 fast-moving neutrons.
What is a thermal neutron?
A neutron in a reactor with mean kinetic energy similar to the thermal energy of other particles in the reactor core.
What is a chain-reaction in a nuclear fission reaction?
When the neutrons produced from one fission reaction are absorbed by further nuclei and cause them to undergo fission.
What is the role of the moderator in a nuclear reactor?
Slows down fast-moving neutrons without absorbing them, increasing the chance of them being absorbed by other nuclei and causing fission.
What are two materials commonly used as moderators in nuclear reactors?
Water and graphite.
What is the role of the control rods in a nuclear reactor?
To absorb neutrons and can be moved into or out of the reactor core to control the rate of nuclear fission.
What is nuclear fusion?
When two high speed nuclei combine to produce a large nucleus.
Why does nuclear fusion of small nuclei lead to a release of energy?
The product has a higher binding energy/lower mass than the parent nuclei.
Why are high temperatures and pressures needed for nuclear fusion to occur?
So that nuclei can overcome electrostatic repulsion and move within $3\ \text{fm}$ of each so the strong nuclear force can bind them together.
How is energy released from stars?
Through nuclear fusion, mainly of hydrogen into helium.
What energy is required to create a particle-antiparticle pair of masses $m$?
What is the moderator typically made out of in a nuclear reactor?
Boron.