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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.
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
The half-life of this isotope is 6.480 days, [2] which corresponds to a total decay constant of 0.1070 d −1. Then the partial decay constants, as computed from the branching fractions, are 0.1050 d −1 for ε/β + decays, and 2.14×10 −4 d −1 for β − decays. Their respective partial half-lives are 6.603 d and 347 d.
Secular equilibrium can occur in a radioactive decay chain only if the half-life of the daughter radionuclide B is much shorter than the half-life of the parent radionuclide A. In such a case, the decay rate of A and hence the production rate of B is approximately constant, because the half-life of A is very long compared to the time scales ...
The half-life of a radioisotope (usually denoted by t 1/2) is a more familiar concept than the mean-life, so although the equations above are expressed in terms of the mean-life, it is more usual to quote the value of 14 C's half-life than its mean-life. The currently accepted value for the half-life of 14 C is 5,700 ± 30 years. [21]
Not all molecules in the solution have a P-32 on the last (i.e., gamma) phosphate: the "specific activity" gives the radioactivity concentration and depends on the radionuclei's half-life. If every molecule were labelled, the maximum theoretical specific activity is obtained that for P-32 is 9131 Ci/mmol.
For example, the isotope copper-64, commonly used in medical research, has a half-life of 12.7 hours. If you inject a large group of animals at "time zero", but measure the radioactivity in their organs at two later times, the later groups must be "decay corrected" to adjust for the decay that has occurred between the two time points.
Actinium-225 has a half-life of 10 days and decays by alpha emission. It is part of the neptunium series, for it arises as a decay product of neptunium-237 and its daughters such as uranium-233 and thorium-229. It is the last nuclide in the chain with a half-life over a day until the penultimate product, bismuth-209 (half-life 2.01 × 10 19 ...