Internal radiation is produced by the decay of radioactive material in the body.

Isomers are nuclides with the same number of neutrons and protons of a given element in different states of excitation. Most of these unstable isomers decay very quickly (~ 10^-12 seconds).
They are characterized in the chemical formula by an m (e.g. Tc-99m).

See also Isomeric Transition.

If a nucleus still has excess energy after attempts of stabilization, it can emit energy without changing the number of protons or neutrons. This process is named isomeric transition. One way of isomeric transition is the emission of a gamma rays, the other competing way is internal conversion, where the excess energy of the nucleus must exceed the binding energy of an electron, which then will be ejected from the atom.

See also Decay, Gamma Radiation and Internal Conversion.

This elementary particle was already proposed in 1930 by Wolfgang Pauli and in 1934 by Enrico Fermi , and gets detected experimentally by Clyde Cowan and Fred Reines in 1956. In addition to the electron-, antielectron-neutrino the discovery of the muon-, antimuon-neutrino in 1962 and the tau-, antitau-neutrino in 2000 followed.
Neutrinos have no charge, a very small mass and interact rarely with matter, which make them difficult to detect. During beta decay, a neutron converts into a proton, an electron and an antineutrino, which is emitted. Some of today's Research projects try to find out the concrete mass of neutrinos or if neutrinos can change from one neutrino type to another.

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