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Radiation and Radioactive Decay

• Radionuclides are atoms that spontaneously convert part of their mass into energy and emit this energy in the form of energetic particles and electromagnetic radiation.
• Radioactivity is the property of a radionuclide to emit radiation, and the actual event is referred to as radioactive decay, disintegration, or transformation.
• All radionuclides eventually decay to stable nuclides, and the process of radioactive decay is spontaneous.
• The half-life of a radionuclide is the time required for one-half of the atoms present to decay, and it is a useful measure because no two radionuclides have exactly the same half-life.
• The quantity of activity left after any time interval is given by the equation: A = Aoe-λt, where Ao is the activity of the sample at some original time, λ is the decay constant for the particular radioactive element, t is the elapsed time, and T2 is the half-life of a particular radioactive element.
• The concentration of radioactivity, or the number of curies (or mCi or μCi) per unit mass or volume, is defined by the specific activity.
• Alpha particles, beta particles, gamma rays, and x-rays are types of ionizing radiation emitted from radionuclides, and the manner in which a radionuclide emits radiation is well defined and quite characteristic.
• Alpha particles are massive charged particles, beta particles are light charged particles that come in positive and negative forms, gamma rays are electromagnetic radiation emitted from the nucleus, and x-rays are electromagnetic radiation emitted from the electron shells of an atom.
• External bremsstrahlung radiation is generated in the material surrounding the radioactive atoms rather than by the radioactive atoms themselves, and it consists of photons created by the acceleration of charged particles in the electromagnetic field of the nucleus.
• Knowledge of the characteristics of radioactive materials is helpful in establishing protective controls for the use of the material.
• The rate of emission and types of radiations emitted by radioactive materials can be used to specify the fraction of atoms that will decay in a given time span (the decay rate).
• The Curie and Becquerel are basic units used to describe the amount of activity in a sample. 1 curie (Ci) = 3.7 x 1010 disintegrations/sec. (dps), and 1 becquerel (Bq) = 1 disintegration/sec. (dps).