A delta ray is a

secondary electron Secondary electrons are electrons generated as ionization products. They are called 'secondary' because they are generated by other radiation (the ''primary'' radiation). This radiation can be in the form of ions, electrons, or photons with suffici ...

with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization, and is sometimes used to describe any recoil particle caused by secondary

ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...

. The term was coined by

J. J. Thomson Sir Joseph John Thomson (18 December 1856 – 30 August 1940) was a British physicist and Nobel Laureate in Physics, credited with the discovery of the electron, the first subatomic particle to be discovered. In 1897, Thomson showed that ...

Characteristics

Nuclear particle in a diffusion cloud chamber

A delta ray is characterized by very fast

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s produced in quantity by

alpha particles Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...

or other fast energetic charged particles knocking orbiting electrons out of atoms. Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own. Delta rays appear as branches in the main track of a

cloud chamber A cloud chamber, also known as a Wilson cloud chamber, is a particle detector used for visualizing the passage of ionizing radiation. A cloud chamber consists of a sealed environment containing a supersaturated vapour of water or alcohol. An ...

(See Figs. 1,2). These branches will appear nearer the start of the track of a heavy charged particle, where more energy is imparted to the ionized electrons.

Delta rays in particle accelerators

Otherwise called a knock-on electron, the term "delta ray" is also used in high energy physics to describe single electrons in particle accelerators that are exhibiting characteristic deceleration. In a

bubble chamber A bubble chamber is a vessel filled with a superheated transparent liquid (most often liquid hydrogen) used to detect electrically charged particles moving through it. It was invented in 1952 by Donald A. Glaser, for which he was awarded the 1 ...

, electrons will lose their energy more quickly than other particles through

Bremsstrahlung ''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...

and will create a spiral track due to their small mass and the magnetic field. The Bremsstrahlung rate is proportional to the square of the acceleration of the electron.

Epsilon ray

An Epsilon ray or Epsilon radiation is a type of

tertiary radiation A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...

. Epsilon rays are a form of

particle radiation Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam. Due to the wave–par ...

and are composed of

s. The term was coined by

, but is very rarely used as of 2019.

References

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"Delta ray"
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Britannica Online

"Delta electrons"
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McGraw-Hill Encyclopedia of Science & Technology Online
Radiation Radioactivity Electron

Characteristics

Delta rays in particle accelerators

Epsilon ray

See also

References