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The energies of the delayed gamma rays are used to determine which elements are present in the sample, and the number of gamma rays of a specific energy is used to determine the amount of an element in the sample. For example, when a sample that contains silver is irradiated, a fraction of the 109Ag atoms in the sample will capture a neutron and become 110Ag. The 110Ag atoms are radioactive and have a half-life of 24.6 seconds. When the 110Ag atoms beta decay to 110Cd, a 658 keV gamma ray is emitted 4.5 % of the time. The amount of silver in the original sample can be determined by measuring the number of 658 keV gamma-rays emitted from the sample in a given time interval after the sample has been exposed to a flux of neutrons.