Nuclear Physics Flashcards
The mass defect of a nucleus
The difference between the total mass of the nucleus and its individual constituents
Nuclear fission
When a large unstable nucleus splits into two smaller, more stable daughter nuclei
Nuclear fusion
When two smaller nuclei fuse together to form a larger more stable nucleus
Radioactive decay
The spontaneous disintegration of the nucleus of an atom which results in the emission of particles.
Background radiation
Background radiation refers to ionizing radiation emitted from a variety of natural and artificial radiation sources.
The activity of a radioactive substance
The average number of atoms disintegrating per unit time.
The radioactive decay constant λ of a nucleus
Its probability of nucleus undergoing decay in the next second
Half-life
The time taken for half the original number of radioactive nuclei of a particular isotope to decay.
The Atomic Mass Unit
The atomic mass is defined as 1/12 the mass of Carbon-12
Binding Energy
The energy required to split up the nucleus into its individual nucleons. The greater the binding energy per nucleon the more stable the nucleus.
Chain reactions
Chain reactions occur because each fission produces 2 or 3 neutrons that can go on to induce further fission. For a chain reaction to occur, the mass of the fissile material must be greater than the critical mass.
The nature of radioactive decay
Random - Don’t know which nucleus will decay next
Spontaneous - Nucleus gives no warning that it is about to decay
Decays exponentially - Rate of decay depends on the number of nuclei
Intensity
The amount of energy per second per square metre
Atomic mass unit of electron, proton and neutron
Electron - 0.00055u
Proton - 1.00728u
Neutron - 1.00867u
Moderators
Moderators slow down neutrons so they can successfully induce fission.
Material - Water
Reason - Similar size to neutrons so lots of energy is transferred upon collisions so slows neutrons quickly and chemically/physically stable.
Coolant
Transfers heat energy away from the reactor
Material - Water
Reasons - Large specific heat capacity meaning lots of heat can be absorbed without a large increase in temperature.
Fluid - Convection currents can form meaning that it is easy to circulate.
Control Rods
Controls the rate of fission
Material - Boron
Reasons - Can absorb lots of neutrons without becoming radioactive. Can be completely lowered in an emergency to stop fission.
Critical Mass and 3 things it relies on
The minimum amount of fissile material needed for a self sustaining fission reaction to be maintained.
Relies on: The level of enrichment, higher is best. The shape, spherical is best. Add a neutron reflector to the containment vessel.
Induced fission
When a nucleon is bombarded with a neutron it splits into two smaller nuclei and neutrons are released
Critical condition
When one fission neutron per fission event on average goes on to produce further fission
