# physics

## duoplasmatron

Another great physics word.

A duoplasmatron is a type of ion source. It operates as follows: a cathode filament emits electrons into a vacuum chamber. A gas such as argon is introduced in very small quantities into the chamber, where it becomes charged or ionized through interactions with the free electrons from the cathode, forming a plasma. The plasma is then accelerated through a series of at least two highly charged grids, and becomes an ion beam, moving at fairly high speed from the aperture of the device.

## electron

A stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids.

Electrons belong to a class of particles called leptons.

## elementary particle

Another term for fundamental particle. "Fundamental particle" is preferable – there is nothing elementary about the complex interactions of subatomic particles.

## event

An "event" is what happens after a collision: particles decay, form tracks and are detected.

## femtobarn

A unit of area, equal to 10−43 square metres. See barn and inverse femtobarn.

"Femto" means a factor of 10-15, a thousandth of a millionth of a millionth. So a femtobarn is a barn (10-28 square metres) multiplied by 10-15, which equals 10-43 square metres.

When writing pages for the general public, always give an approximate number of collisions as well as the figure in inverse femtobarns.

## fermion

A subatomic particle, such as a nucleon, which has half-integral spin and follows a statistical description given by Fermi and Dirac.

## g (lower case)

Denotes gravity in mathematical notation.

Specifically, g is the acceleration due to the local gravitational field - the force exerted by the Earth on a sky diver in free fall, for example.

The sky diver experienced a force of 5 g. (not "5 g's")

g is measured in metres per second per second (m/s2) and has a value of 9.81 m/s2 on Earth.

Not to be confused with G.

## G (upper case)

Denotes the gravitational constant in mathematical notation.

G is the constant term in Newton's law of universal gravitation, which states: "The attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them."

## GEM detector

The Gas Electron Multiplier (GEM) is a gaseous-ionization detector – a type of detector used in nuclear physics, particle physics and radiation detection.

## gluon

Plural: gluons

A hypothetical massless subatomic particle believed to transmit the force binding quarks together in a hadron.