It descends to a lower, more stable energy state by the emission of a photon called a gamma ray. The resulting gamma rays have energies of 1.173 MeV or 1.332 MeV in the majority of the Co-60 decays. Gamma rays with this energy are capable of passing through several centimeters of lead. By using a Geiger counter the number of gamma rays being emitted from a source of Co-60 can be found. Further, the shielding ability of various materials can be tested by placing different thicknesses of the material between the Co-60 source and the Geiger counter.
Shielding occurs when incident radiation is either reflected or absorbed by a material.
Linear density and composition of a material effect its ability to shield gamma radiation. The energy of the gamma ray effects the amount and the means by which it is shielded. Lower energy gamma rays undergo the photoelectric effect or Compton scattering, while higher energy photons collide with atoms to produce electron-positron pairs. The value of depends on both the material and the energy of the gamma rays in the beam. This experiment sought to investigate the shielding ability of various materials.