Pair production refers to the creation of an elementary particle and its antiparticle, usually when a photon ( or another neutral boson ) interacts with a nucleus.

In nuclear physics, this occurs when a high-energy photon interacts with a nucleus.

In the electroweak theory, the W also carries electric charge, and hence interacts with a photon.

This internal conversion process is also not to be confused with the similar photoelectric effect, which also may occur with gamma radiation associated electron emission, in which an incident gamma photon emitted from a nucleus interacts with an electron, expelling the electron from the atom.

Also, electrons from the gamma photoelectric effect show a spread in energy, depending on how much energy has been imparted to the ejected electron by the gamma ray which interacts with it — an amount which is variable depending on the angle of gamma photon scattering from the electron ( see Compton scattering ).

If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA / NaI and its successor DAMA / LIBRA.

If a photon interacts with an atmospheric molecule, the molecule is accelerated and its temperature increased.

Unlike an x-ray photon with a similar wavelength, which interacts with the electron cloud surrounding the nucleus, neutrons primarily interact with the nucleus itself.

In this scattering process, the incident photon interacts with matter ( gas, liquid, and solid ) and the frequency of the photon is shifted to red or blue.

# A light photon interacts with the retinal in a photoreceptor cell.

As a photon travels through a vacuum it interacts with these virtual particles, and is absorbed by them to give rise to a real electron-positron pair.

A Bohr model of the hydrogen atom, showing an electron jumping between fixed orbits and emitting a photon of energy with a specific frequency

This allows one to multiply ionize an atom with a single photon.

Bosonic particles, which include the photon as well as atoms such as helium-4, are allowed to share quantum states with each other.

Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly after of photons starting to travel freely through space rather than constantly scattering with electrons and protons in plasma is referred to as photon decoupling.

If it is " observed " ( measured with a photon ) not at a particular slit but rather at the screen, then there is no " which path " information as part of the interaction, so the electron's " observed " position on the screen is determined strictly by its probability function.

When a single photon is sent through an interferometer, it passes through both paths, interfering with itself, as waves do, yet is detected by a photomultiplier or other sensitive detector only once.

Later, Albert Einstein proposed that the quanta of light might be regarded as real particles, and ( still later ) the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton.

A photon with a wavelength of 532 nm ( green light ) would have an energy of approximately 2. 33 eV.

One consequence of this theory is a variable speed of light, where photon speed would vary with energy, and some zero-mass particles might possibly travel faster than c. However, even if this theory is accurate, it is still very unclear whether it would allow information to be communicated, and appears not in any case to allow massive particles to exceed c.

here is a generic term for photon energy with h = Planck's constant and = frequency of light.

For commonly used fluorescent compounds, typical excited state decay times for photon emissions with energies from the UV to near infrared are within the range of 0. 5 to 20 nanoseconds.

The radiation sensing element is an inert gas-filled Geiger-Muller tube ( usually containing helium, neon or argon with halogens added ) which briefly conducts electrical charge when a particle or photon of radiation makes the gas conductive by ionisation.

Efficiency is only about 1 %, due to low interaction of gamma with the tube, and the article on the Geiger-Muller tube carries an account of the technique used to detect photon radiation.

For high energy gamma, this relies on interaction of the photon radiation with the tube wall material, usually 1-2mm of chrome steel to produce electrons which can enter and ionise the fill gas.

Iodine-123 may be the preferred radionuclide in some clinics due to its more favourable radiation dosimetry ( i. e. less radiation dose to the patient per unit administered radioactivity ) and a gamma photon energy more amenable to imaging with the gamma camera.

The phase associated with the photon that is emitted is random.

A convoluted chip surface with angled facets similar to a jewel or fresnel lens can increase light output by allowing light to be emitted perpendicular to the chip surface while far to the sides of the photon emission point.

The ideal shape of a semiconductor with maximum light output would be a microsphere with the photon emission occurring at the exact center, with electrodes penetrating to the center to contact at the emission point.

* Second harmonic generation ( SHG ), or frequency doubling, generation of light with a doubled frequency ( half the wavelength ), two photons are destroyed creating a single photon at two times the frequency.

* Third harmonic generation ( THG ), generation of light with a tripled frequency ( one-third the wavelength ), three photons are destroyed creating a single photon at three times the frequency.

For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when its position is measured.

For example, if a single photon strikes the electrons, only a single electron changes states in response to the photon.

The appearance of interference built up from individual photons could seemingly be explained by assuming that a single photon has its own associated wavefront that passes through both slits, and that the single photon will show up on the detector screen according to the net probability values resulting from the co-incidence of the two probability waves coming by way of the two slits.

There are experiments in which the wave and particle natures of electromagnetic waves appear in the same experiment, such as the self-interference of a single photon.

Photosynthesis becomes possible in this range as well, for similar reasons, as a single molecule of chlorophyll is excited by a single photon.

A photon above a threshold frequency has the required energy to eject a single electron, creating the observed effect.

The base probability of a photon causing stimulated emission in a single excited atom was shown by Albert Einstein to be exactly equal to the probability of a photon being absorbed by an atom in the ground state.

A qubit is a two-state quantum-mechanical system such as the polarization of a single photon: here the two states are vertical polarization and horizontal polarization.

Low-frequency light only ejects low-energy electrons because each electron is excited by the absorption of a single photon.

So on average, a starlight photon is scattered from a single interstellar grain ; multiple scattering ( which produces circular polarization ) is much less likely.

A single photon decay is only possible if another body ( e. g. an electron ) is in the vicinity of the annihilating positronium to which some of the energy from the annihilation event may be transferred.