The energy of a photon is direct proportional to its frequency.
E = h * v
E = Energy (J joule)
h = Planck's constant, 6.626 x 10^-34 J-s (Joule-seconds)
v = Frequency (Hz)
This relation between energy and frequency of a photon is known as Planck's relation.

See also Photon.

The attenuation of radiation is a decrease in intensity as a result of interactions by transmission through matter. X-ray beams attenuate due to photon absorption by the material or scattering. Both effects are energy dependent. The probability of absorption or scattering is a function of the photon energy. The photoelectric absorption is much more energy dependent than the Compton scatter effect.

See also Attenuation Correction, Linear Energy Transfer, Broad Beam and Ion Beam.

The effective energy (related to bremsstrahlung radiation from an x-ray machine) is the monoenergetic photon energy which produces the same first half value layer in a given material as the x-ray beam.

In physics, energy is described as the ability to do work by a force, measured in joules (J).
Several different forms of energy exist to describe various natural phenomena.

See also Photon Energy, Rest Energy, Binding Energy, Kinetic Energy and Effective Energy.

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.