Year 13 - Nuclear Physics Flashcards
Activity
The average number of atoms disintegrating per unit time.
Alpha Decay
The emission of an alpha particle (Helium Nuclei) from an unstable nucleus (usually one with too much mass) to make it more stable. Alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper.
Alpha Particle
A Helium Nucleus.
Atomic Mass Unit
Defined as one-twelfth the mass of an atom of carbon-12 (Do Not Write Nucleus of Carbon-12).
Background Radiation
The ionising radiation emitted from a variety of natural and artificial radiation sources e.g. Radon Gas, Cosmic Rays, Hospital X-Rays etc.
Beta Particle
A fast moving electron.
Binding Energy
Energy required/work done to separate the nucleus into its individual nucleons/protons and neutrons.
Chain Reaction
When the neutrons released by a fission reaction are absorbed by the nucleus of fissile material, causing further fission.
Contamination
The introduction of radioactive material to another object. The object is consequently radioactive. This is often confused with Irradiation.
Control Rods (Boron)
Absorbs Neutrons.
Coolant
A substance that passes through nuclear reactors and is responsible for removing heat from the core. This heat is then used to generate electrical energy. Common coolants include: Water, Heavy Water, Liquid Sodium, Carbon Dioxide.
Corrected Count Rate
Count rate with the measured background count (rate) deducted.
Count Rate
The number of decays recorded each second by a detector.
Critical Mass
The smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained. This is the mass required for 1 of the emitted neutrons to be absorbed by another fissile nucleus.
Daughter Nuclei
Smaller nuclei produced during nuclear fission when a fissile nucleus (U-235) splits.
Decay Constant
The constant of proportionality which links rate of decay to the number of undecayed nuclei. It is the probability of a decay per unit time.
Excited Nucleus
One or more of the protons or neutrons in a nucleus occupy a nuclear orbital of higher energy, this happens when they absorb energy.
Gamma Decay
The emission of gamma rays from an unstable nucleus that has too much energy, caused by an excited nucleus. Gamma radiation is only very weakly ionising but requires several centimetres of lead to be stopped.
Gamma Ray
EM Wave (Photon). It is more penetrating than alpha or beta radiation of the same energy through the same material.
Half Life
The time taken for half the original number of radioactive nuclei to decay or the time taken for the original activity to half.
High Level Nuclear Waste Disposal
• Very hot and radioactive so has to be placed in cooling ponds (to absorb the radiation)
• the waste also needs to be remotely handled
• In liquid form the waste may leak, so need to vitrify
• storage needs to be stable in a container deep underground
Inverse Square Law
EM (Gamma) intensity is inversely proportional to the square of the distance from its source.
Irradiation
The exposure of an object to radiation. Importantly the exposed object does not become radioactive. This is often confused with Contamination.
Mass Defect or Difference
Δmis difference between mass of nucleus and total mass of separate nucleons.
