Gamma Spectroscopy - Gamma Ray Characteristics

Gamma Ray Characteristics

Gamma rays are the highest-energy form of electromagnetic radiation, being physically exactly like all other forms (e.g., X rays, visible light, infrared, radio) except for higher photon energy and frequency, and shorter wavelength. (Because of their high energy, gamma-ray photons are generally counted individually, whereas the lowest energy forms of EM radiation (e.g., radio to sub-millimeter) are observed as electromagnetic waves consisting of many low-energy photons.) While a Geiger counter or Gamma Probe determine only the count rate (i.e. the number of gamma rays interacting in the detector in one second), a gamma-ray spectrometer also determines the energies of the gamma-rays photons emitted by the source.

Radioactive nuclei (radionuclides) commonly emit gamma rays in the energy range from a few keV to ~10 MeV, corresponding to the typical energy levels in nuclei with reasonably long lifetimes. Such sources typically produce gamma-ray "line spectra" (i.e., many photons emitted at discrete energies), whereas much higher energies (upwards of 1 TeV) may occur in the continuum spectra observed in astrophysics and elementary particle physics. The boundary between gamma rays and X rays is somewhat blurred, as X rays typically refer to the high energy EM emission of atoms, which may extend to over 100 keV, whereas the lowest energy emissions of nuclei are typically termed gamma rays, even though their energies may be below 20 keV.