Parameter Tree:  Gamma Rays (or gamma radiation) is
electromagnetic radiation originating from transitions between
energy levels of atomic nuclei.  A nucleus formed as a
consequence of beta or alpha emission sometimes exists briefly
in an excited energy level and makes a transition to a lower
energy level accompanied by emission of a gamma ray photon with
energy equal to the difference between the energies of the
initial and final levels. Gamma ray energies from radioactive
decay lie in the approximate range 10 keV6 MeV. Gamma rays are
also emitted in nuclear reactions. The boundary between x-rays
and gamma rays is fuzzy, the latter term being most often used
for electromagnetic radiation of nuclear origin.  American
Meteorological Society Glossary of Meteorology Online  Boorse,
H. A., and L. Motz, 1966: The World of the Atom, Vol. I, 446448.