A gamma quantum is a distinct photon of electromagnetic radiation with the highest energy, shortest wavelength. The energy of a single photon is above 100 keV, the wavelength is below about 10 picometers. Gamma photons are generated by processes within the atomic nuclei.

See also Quantum.

A photon is a discrete packet of electromagnetic energy. The amount of energy depends on the frequency (wavelength) of the photon. Highest frequency, most energetic photon radiations are gamma rays, up to 300 EHz - 1.24 MeV. In addition to energy, photons are also carrying momentum.
Photons have no electrical charge or rest mass and exhibit both particle and wave behavior.
Photons are traveling in vacuum (without interactions with matter) with the constant velocity of 2.9979 x 10⁸ m/s (c, speed of light).
Photons get absorbed or scattered away from their original direction of travel when interacting with matter.
High energy photons as for example x-rays cause damages to exposed tissue and cells. Radiation exposure is measured in roentgen, radiation absorption in Roentgen//min.
Photon radiation in the frequency ranges of x-rays and gamma rays are used for medical diagnostic and treatment.

See also Photon Energy and Gamma Ray.

A radiation meter is used to measure radioactivity.
Beta emitting isotopes, such as C-14, P-32, P-33, and S-35, are best detected with a Geiger-Mueller counter (GM).
Gamma emitting isotopes, such as I-125, I-123, I-131, and Tc-99m are easily detected with a gamma meter equipped with a sodium iodide (NaI) probe.
An isotope that cannot be detected with most survey meters, unless present in large activities, is tritium (H-3). Tritium emits beta particles with energies insufficient to enter the sensitive volume of most detectors.

A sample is placed into a concentrated beam of neutrons. Through neutron-capture heavier nuclei become frequently unstable. This artificial radiation decays with a characteristic half-live consisting of alpha- and beta-particles and gamma-rays.

See Neutron Activation Analysis

An accelerator uses electrostatic or electromagnetic fields to increase the kinetic energy of charged particles (see alpha particle, beta particle) in order to produce ionization or a nuclear reaction in a target.
Accelerators (see cyclotron, linear accelerator) are used for the production of radionuclides (see Fluorine-18, Molybdenum, Technetium-99m) or directly for radiation therapy. Accelerator-produced radioactive material (ARM) is any radioactive substance that is produced by a particle accelerator. The accelerators used for radiation therapy generate gamma rays (also called Bremsstrahlung) with continuous energy by collision of high energy electrons on materials with high density (also referred as 'high z' - chemical elements with a high atomic number (Z)).
Electron accelerators with energies above 10 MeV can also produce neutrons induced by photons in the accelerator head material (mainly caused by photo nuclear reaction).