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Instead, the half-life is defined in terms of probability: "Half-life is the time required for exactly half of the entities to decay on average". In other words, the probability of a radioactive atom decaying within its half-life is 50%. [2] For example, the accompanying image is a simulation of many identical atoms undergoing radioactive decay.
So, for example, digoxin has a half-life (or t 1 / 2 ) of 24–36 h; this means that a change in the dose will take the best part of a week to take full effect. For this reason, drugs with a long half-life (e.g., amiodarone , elimination t 1 / 2 of about 58 days) are usually started with a loading dose to achieve their desired ...
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds.
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:
Carbon (6 C) has 14 known isotopes, from 8 C to 20 C as well as 22 C, of which 12 C and 13 C are stable.The longest-lived radioisotope is 14 C, with a half-life of 5.70(3) × 10 3 years. . This is also the only carbon radioisotope found in nature, as trace quantities are formed cosmogenically by the reactio
Naturally occurring titanium (22 Ti) is composed of five stable isotopes; 46 Ti, 47 Ti, 48 Ti, 49 Ti and 50 Ti with 48 Ti being the most abundant (73.8% natural abundance).Twenty-one radioisotopes have been characterized, with the most stable being 44 Ti with a half-life of 60 years, 45 Ti with a half-life of 184.8 minutes, 51 Ti with a half-life of 5.76 minutes, and 52 Ti with a half-life of ...
with half-life 122.266(43) s and 14 O with half-life 70.621(11) s. All remaining radioisotopes have half-lives less than 27 s and most have half-lives less than 0.1 s. The four heaviest known isotopes (up to 28 O) decay by neutron emission to 24 O, whose half-life is 77.4(4.5) ms.
Forty radioisotopes have been characterized, with the most stable, besides 176 Lu, being 174 Lu with a half-life of 3.31 years, and 173 Lu with a half-life of 1.37 years. All of the remaining radioactive isotopes have half-lives that are less than 9 days, and the majority of these have half-lives that are less than half an hour.