| Gamma ray photon radiation: High-energy electromagnetic radiation emitted from the nucleus of an atom. Gamma rays have no charge, are very penetrating and are best shielded by lead or steel. Gamma rays can cause internal and external damage. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays penetrate tissue farther than do beta or alpha particles but leave a lower concentration of ions in their path to potentially cause cell damage. Very similar to x-rays except that x-rays originate from the outer shell of the atom. The gauge uses gamma ray photons to help measure density. Geiger-Mueller Detector Tube (G-M tube): A gas filled tube that measures voltage pulses created by ionizing gamma radiation. Used in a gauge to determine density. Geiger counter: A device that utilizes Geiger-Mueller tubes for detecting and measuring ionizing radiation. Gauges use GM tubes to help measure density. Genetic effects: Effects from radiation exposure that are seen in the offspring of the individual. Gray (Gy): This SI unit is used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material and is used for any type of radiation and any material. It does not describe the biological effects of the different radiations. On gray is equivalent to 100 rads. | 
