Nuclear Physics Flashcards
What are the two conclusions that can be drawn from E=mc^2?
1) Mass is a store of energy.
2) Energy has mass.
What is pair production?
When a photon’s energy is converted into a particle-antiparticle pair, which sometimes annihilate each other to produce another photon.
What is mass defect?
The difference in mass between a nucleus and its completely separated nucleons.
What is the binding energy of a nucleus?
The minimum energy required to completely separate a nucleus into its constituent nucleons.
From a graph of binding energy per nucleon against nucleon number, what is the most stable isotope in nature?
Iron-56
What is induced nuclear fission?
When a heavy atomic nucleus absorbs slow neutrons, becoming unstable and splitting into smaller nuclei and several fast moving neutrons.
What is neutron capture?
When a nucleus absorbs a slow moving neutron.
What happens when a sample has subcritical mass?
Each fission event causes an average of less than one subsequent fission event as most neutrons are lost through the surface. Fission stops.
What happens when a sample has critical mass?
Each fission event causes one other fission event. Fission happens at a constant rate.
What happens when a sample has supercritical mass?
Each fission event causes more than one fission event. The rate of fission increases.
What is the purpose of a moderator in a nuclear reactor?
To slow down fast moving neutrons to allow more fission events to take place.
What is the purpose of control rods in a nuclear reactor?
To absorb excess neutrons so that the rate of fission can be controlled.
Why does nuclear waste need to be disposed of by burying it deep underground?
The isotopes produced in fission reactions have very long half lives and so need to be secure for hundreds or thousands of years.
How does nuclear fusion happen?
Nuclei need to be close enough together so that the the strong nuclear force can overcome the electrostatic force between them.
What are the conditions needed for fusion?
High temperatures or high pressures.
