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Gamma rays are produced in many processes of particle physics. Typically, gamma rays are the products of neutral systems which decay through electromagnetic interactions (rather than a weak or strong interaction). For example, in an electron–positron annihilation, the usual products are two gamma ray photons
Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear ...
This is unlike cosmic rays which have their direction of travel scrambled by magnetic fields. Sources that produce cosmic rays will almost certainly produce gamma rays as well, as the cosmic ray particles interact with nuclei or electrons to produce photons or neutral pions which in turn decay to ultra-high-energy photons. [8]
An FM radio station transmitting at 100 MHz emits photons with an energy of about 4.1357 × 10 −7 eV. This minuscule amount of energy is approximately 8 × 10 −13 times the electron's mass (via mass–energy equivalence). Very-high-energy gamma rays have photon energies of 100 GeV to over 1 PeV (10 11 to 10 15 electronvolts) or 16 nJ to 160 ...
The reverse process, pair production, is the dominant mechanism by which high-energy photons such as gamma rays lose energy while passing through matter. [32] That process is the reverse of "annihilation to one photon" allowed in the electric field of an atomic nucleus.
Gamma rays, at the high-frequency end of the spectrum, have the highest photon energies and the shortest wavelengths—much smaller than an atomic nucleus. Gamma rays, X-rays, and extreme ultraviolet rays are called ionizing radiation because their high photon energy is able to ionize atoms, causing chemical reactions. Longer-wavelength ...
These annihilation photons are emitted in opposite directions, 180˚ apart. This is the basis for PET scanners in a process called coincidence counting. A Germanium detector spectrum showing the annihilation radiation peak (under the arrow). Note the width of the peak compared to the gamma ray peaks from radioactive decay visible in the spectrum.
The high-energy particles then go on to produce more lower energy photons that can suffer the same fate. This effect creates a beam of several 10 17 eV gamma ray photons heading in the same direction as the original UHE photon. This beam is less than 0.1 m wide when it strikes the atmosphere. These gamma rays are too low-energy to show the ...