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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.
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.
Caesium in the body has a biological half-life of about one to four months. Mercury (as methylmercury) in the body has a half-life of about 65 days. Lead in the blood has a half life of 28–36 days. [29] [30] Lead in bone has a biological half-life of about ten years. Cadmium in bone has a biological half-life of about 30 years.
A material's half-value layer (HVL), or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half. [1] HVL can also be expressed in terms of air kerma rate (AKR), rather than intensity: the half-value layer is the thickness of specified material that, "attenuates the beam of radiation to an extent such that the AKR is reduced ...
Iridium-192 (symbol 192 Ir) is a radioactive isotope of iridium, with a half-life of 73.827 days. [1] It decays by emitting beta (β) particles and gamma (γ) radiation. About 96% of 192 Ir decays occur via emission of β and γ radiation, leading to 192 Pt. Some of the β particles are captured by other 192 Ir nuclei, which are then converted ...
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.
Specific activity (symbol a) is the activity per unit mass of a radionuclide and is a physical property of that radionuclide. [1] [2] It is usually given in units of becquerel per kilogram (Bq/kg), but another commonly used unit of specific activity is the curie per gram (Ci/g).
In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182 Hf with a half-life of 8.9 × 10 6 years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation. [5] No other radioisotope has a half-life over 1.87 years. Most isotopes have half-lives under 1 ...