The Nucleus, Nuclear Decay, Energy, Fission + Fusion

Alpha Radiation

Particles consisting of 2 protons and 2 neutrons - identical to a helium nucleus.

Beta Radiation

Energetic electrons emitted from the unstable nucleus of an atom.

Gamma Radiation

High energy electromagnetic radiation emitted from the nucleus.

Exponential Decay

The rate of decay is directly proportional to the number remaining.

Radioactive Decay

The random, spontaneous emission of radiation from an unstable nucleus (an example of exponential decay).

Law of Radioactive Decay

The rate of decay of a nuclide is directly proportional to the number of unstable nuclei present.

Decay Constant

The fraction of the nuclei decaying per second.

Activity

Number of radioactive disintegrations per unit time.

Half Life

The time taken for the activity of the material (or number of nuclei remaining) to fall to half its original value.

Electron Volt

The kinetic energy possessed by an electron accelerated from rest through a potential difference of 1 V.

Unified Atomic Mass Unit

1/12 of the mass of the carbon-12 atom (= 1.66 x 10-27 kg). On data sheet.

Mass Defect

The difference between the mass of the nucleus and the sum of the masses of its constituent nucleons.

Binding Energy

The amount of energy that must b e supplied to separate the nucleons completely i.e. to an infinite distance apart.

Nuclear Fission

The deep division of a massive nucleus into two less massive nuclei, each with a higher binding energy per nucleon.

Nuclear Fusion

The joining of lighter nuclei to produce a heavier and more stable nucleus.

Chain Reaction

When fission neutrons go on to cause a series of further fission reactions.

Critical Size

The minimum amount of fuel which is capable of sustaining a chain reaction.

Moderators

Slow down fission neutrons - usually graphite, water or heavy water.

Control Rods

Boron-coated steel rods which are lowered to absorb excessive neutrons.

Reactor Shielding

Very thick concrete shield to absorb excess radiation.

D-T Reaction

Deuterium + Tritium → Helium + neutron + energy

Fuels: Deuterium from water, tritium from lithium

150 x 106 °C temp achieved through ohmic (electrical) heating, neutral beam injection and high frequency e/m radiation.

Plasma

Gas-like fluid consisting of electrons, positive ions and free nuclei.

Gravitational Confinement

Using a gravitational force to contain the plasma (requires sufficient mass e.g. works in stars but not on Earth).

Inertial Confinement

Using intense ion or laser beams directed at a fuel pellet (e.g. lithium hydride).

Magnetic Confinement

Using a toroidal magnetic field (magnetic bottle) to confine plasma.