<P> Gamma rays ionize atoms (they are ionizing radiation), and are thus biologically hazardous . </P> <P> Natural sources of gamma rays on Earth are observed in the gamma decay of radionuclides and secondary radiation from atmospheric interactions with cosmic ray particles . There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma - ray flashes, that produce gamma rays not of a nuclear origin . Additionally, gamma rays are produced by a number of astronomical processes in which very high - energy electrons are produced, that in turn cause secondary gamma rays via bremsstrahlung, inverse Compton scattering, and synchrotron radiation . However, a large fraction of such astronomical gamma rays are screened by Earth's atmosphere and can only be detected by spacecraft . Gamma rays are produced by nuclear fusion in stars including the Sun (such as the CNO cycle), but are absorbed or inelastically scattered by the stellar material, reducing their energy, before escaping and are not observable from Earth as gamma rays . </P> <P> Gamma rays typically have energies above 100 k eV, and therefore have frequencies above 10 exahertz (or> 10 Hz) and wavelengths less than 10 picometers (10 m), which is less than the diameter of an atom . However, this is not a strict definition, but rather only a rule - of - thumb description for natural processes . Electromagnetic radiation from radioactive decay of atomic nuclei is referred to as "gamma rays" no matter its energy, so that there is no lower limit to gamma energy derived from radioactive decay . This radiation commonly has energy of a few hundred keV, and almost always less than 10 MeV . In astronomy, gamma rays are defined by their energy, and no production process needs to be specified . The energies of gamma rays from astronomical sources range to over 10 TeV, an energy far too large to result from radioactive decay . A notable example is the extremely powerful bursts of high - energy radiation referred to as long duration gamma - ray bursts, of energies higher than can be produced by radioactive decay . These bursts of gamma rays are thought to be due to the collapse of stars called hypernovae . </P> <P> Many common depictions of the Electromagnetic Spectrum show gamma rays as higher in energy (hence are higher in frequency and smaller in wave - length) than X-rays . This historically allowed a clear distinction between X-rays and gamma rays . Today, the research literature often describes photons depending on their source . While astronomers usually hold to the historical convention (often the source or production mechanism of the radiation is unknown), the physics literature often use the term historically associated with the method of production . For example, one group of scientists might describe a 1 MeV photon as a gamma ray, while another group use the term X-ray . </P>

What is the wavelength of a gamma ray