Search results
Results from the WOW.Com Content Network
In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on. [7]
Terms "partial half-life" and "partial mean life" denote quantities derived from a decay constant as if the given decay mode were the only decay mode for the quantity. The term "partial half-life" is misleading, because it cannot be measured as a time interval for which a certain quantity is halved.
The half-life, t 1/2, is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value. The decay constant, λ "lambda", the reciprocal of the mean lifetime (in s −1), sometimes referred to as simply decay rate.
When radionuclides are used pharmacologically, for example in radiation therapy, they are eliminated through a combination of radioactive decay and biological excretion.An effective half-life of the drug will involve a decay constant that represents the sum of the biological and physical decay constants, as in the formula:
In radioactive decay the time constant is related to the decay constant (λ), and it represents both the mean lifetime of a decaying system (such as an atom) before it decays, or the time it takes for all but 36.8% of the atoms to decay. For this reason, the time constant is longer than the half-life, which is the time for only 50% of the atoms ...
The radioactive decay constant, the probability that an atom will decay per year, is the solid foundation of the common measurement of radioactivity. The accuracy and precision of the determination of an age (and a nuclide's half-life) depends on the accuracy and precision of the decay constant measurement. [11]
In practice, this means that alpha particles from all alpha-emitting isotopes across many orders of magnitude of difference in half-life, all nevertheless have about the same decay energy. Formulated in 1911 by Hans Geiger and John Mitchell Nuttall as a relation between the decay constant and the range of alpha particles in air, [ 1 ] in its ...
The partial half-life is merely an alternate way to specify the partial decay constant λ, the two being related through: / = . For example, for decays of 132 Cs, 98.13% are ε (electron capture) or β + decays, and 1.87% are β − decays. The half-life of this isotope is 6.480 days, [2] which corresponds to a total decay constant of 0.1070 ...