Atomic and Nuclear PhysicsDOE-HDBK-1019/1-93MODES OF RADIOACTIVE DECAYSummaryThe important information in this chapter is summarized below.Modes of Radioactive Decay SummaryAlpha decay is the emission of an alpha particle (2 protons and 2 neutrons) froman unstable nucleus. The daughter nuclide has an atomic number 2 less than theparent nuclide and a mass number 4 less than the parent nuclide. The daughternucleus commonly releases its excitation energy by gamma emission.Beta-minus decay effectively converts a neutron to a proton and an electron,which is immediately ejected from the nucleus. The daughter nuclide has itsatomic number increased by 1 and the same mass number compared to theparent.Beta-plus decay effectively converts a proton to a neutron and a positron, whichis immediately ejected from the nucleus. The daughter nuclide has its atomicnumber decreased by 1 and the same mass number compared to the parent.In electron capture, the nucleus absorbs an electron from the innermost orbit.This electron combines with a proton to form a neutron. Internal conversion occurs when a gamma ray, emitted by the nucleus as it goesfrom the excited state to the ground state, interacts with one of the innermostelectrons of the same atom. The electron is ejected from the atom.An isomeric transition is the decay of an excited nucleus to a lower-energy levelby the emission of a gamma ray.Decay chains can be found by tracing the steps an unstable atom goes throughas it tries to achieve stability. Many modes of radioactive decay result in a daughter nuclide that has an energylevel above the ground state. This excitation energy is usually releasedimmediately in the form of a gamma ray.The type of decay that a nuclide will typically undergo can be determined by itsrelationship to the line of stability on the Chart of the Nuclides. Nuclides thatlie below and to the right of the line of stability will typically beta minus decay.Nuclides above and to the left of the line will typically either beta plus decay orelectron capture. Most alpha emitters are found in the upper, right-hand cornerof the chart.Rev. 0Page 29NP-01
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