in a system, it is the ratio of the existing quantity of a nuclide, element, mixture, etc. to another quantity which is taken as the reference (for instance the total amount of all nuclides, elements, mixtures, etc. in the system). in particular, when referring to natural isotopes, the isotopic abundance is the proportion of all different isotopes of a chemical element in their fundamental or natural state.
number of spontaneous nuclear transitions occurring per unit of time in a given quantity of radioactive material. formally, the activity a of a given amount of radioactive material is the ratio of dn to dt where dn is the number of spontaneous nuclear transitions occurring in the interval dt. the unit of activity is the becquerel (bq) where 1 bq = 1 desintegration/s.
acronym of as low as reasonably achievable"
unit activity in the international system of units si, and amounts to 1 decays/second.
charged particle electrostatic accelerator. the high voltage that produces the acceleration is the result of the accumulation of electrostatic charge on the surface of an empty metallic sphere. the charged particles are transferred to the sphere by means of a mobile conveyor belt made of isolating (non-conducting) material. a direct current (dc) generator injects the charges on the belt through a metallic brush. a second brush, located at the other end of the conveyor, transfers the charge to the sphere surface which acts as a high voltage electrode. the tension limit depends of the characteristics of the isolator of the structure bearings and of the air that surrounds the sphere. when the system is enclosed in a steel tank filled with a dry gas at high pressure, voltages up to 5 million volts can be attained.
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