Nuclear Fission & Fusion Flashcards
What is Einstein’s theory of relativity (mass-energy equivalence)?
Matter can be considered a form of energy and vice versa.
What’s the Mass Energy equation?
E=mc^2
Examples of mass-energy equivalence?
-Fusion of hydrogen into helium in the sun’s centre.
-Fission of uranium in nuclear power plants.
-Nuclear weapons.
-High energy particle collisions on particle accelerators.
Binding energy equation.
E= Δmc^2
Where Δm is the mass defect.
What is the mass defect?
The difference between the total mass of all the nucleus’ separate nucleons and the mass of the nucleus itself.
What is annihilation?
When a particle meets its anti-particle, they are both destroyed and their mass is converted into energy in the form of 2 gamma-ray photons.
What is pair production?
The opposite of annihilation.
When a photon interacts with a nucleus or atom and the energy of the photon is used to create a particle-antiparticle pair.
What is needed for pair production and why?
The presence of a nearby neutron so the process conserves both momentum and charge. A single photon can’t do this alone.
Rest mass energy equation
ΔE = c^2 Δm
Where ΔE is rest mass energy
Δm is rest mass
What is required energy wise in order for a photon to pair produce?
Its energy carried must be twice the rest-mass energy.
2ΔE=(c^2 Δm)
Ephoton = hf = hc/λ = c^2 Δm
What is binding energy?
The energy required to break a nucleus into its constituent protons and neutrons.
Why is the sum of energies of a nucleus’ nucleons different to the sum of the nucleus’ energy.
Energy is directly proportional to mass.
The total energy of a nucleus is less than the sum of energies of its nucleons.
The formation of a musters is an exothermic reaction and also releases energy.
What does the binding energy per nucleon graph compare and show?
It compares nuclear stability.
For low values of nucleon number, there is a lower binding energy and therefore the nuclei are less stable. These are the lighter elements that have weaker electrostatic force and they are most likely to undergo fusion.
For high values of nucleon number, there is a higher binding energy and therefore the heavier elements are less stable and most likely to undergo fission.
What is the binding energy per nucleon?
The binding energy of a nucleus divided by the number of nucleons in the nucleus.
What is nuclear fission?
The splitting of a large, unstable nucleus into 2 smaller nuclei and 2/3 neutrons.
Gamma rays are also emitted.
What does nuclear fission do?
Releases energy from an atoms nucleus in nuclear reactions.
Example of nuclear fission.
Uranium and Plutonium fuel nuclear power stations and undergo fission.
Energy transfer in nuclear fission.
As the products move away quickly, the nuclear potential energy is transferred to kinetic energy.
What is spontaneous fission?
When nuclei undergo fission with no additional energy being put into the nucleus. This is very rare.
What is induced fission?
When a neutron is absorbed by the uranium-235 nucleus to make uranium-236.
This is very unstable and splits by fission almost immediately.
What are chain reactions?
When the neutrons produced in a fission reactions go on to start other fission reactions which creates more neutrons.
What is the moderator in a nuclear fission reactor?
Slows down neutrons.
Surrounds fuel and control rods inside the reactors core. Fast moving neutrons collide with the moderators molecules causing them to lose momentum.
Neutrons are slowed to be in thermal equilibrium with the moderator ad therefore neutrons can react more efficiently with the uranium fuel.
What are the control rods in a nuclear fission reactor?
Absorbs neutrons.
The number if neutrons absorbed can be varied by the depth of the control rods inside the fuel rods. Lowering rods increases no. of neutrons absorbed and therefore decreases rate if fission. Lifting rods decreases no. of neutrons absorbed and therefore increases rate of fusion.
They’re adjusted automatically so only one produced neutron can go on to start a chain reaction.
Rods nahe lowered completely to stop all reactions.
What is the coolant in a nuclear fission reactor?
Removes heat released by fission reactions.
Coolant carries heat to an external boiler to produce steam which goes onto power electricity generating turbines.
