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.


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.


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.

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.

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