Radioactive half-life

The law of radioactive decay implies that the number of radioactive nuclei decreases exponentially with time with a characteristic half-life. Radioactive isotopes are used to determine the ages of objects. 

Haber, F., 357, 385 Hahn, O., 717 half-cell, 492 half-life (chemical), 543 half-life (radioactive), 712 half-reaction, 484 halide, nomenclature, 763 Hall, C., 598 Hall process, 598 haloakane, F36, 739, 756 nomenclature, 763 halogen, F20, 639... 

Half-life, Radioactive—Time required for a radioactive substance to lose 50% of its activity by decay. Each radio-nuclide has a unique physical half-life. Known also as physical half-time and symbolized as Tr or Trad. 

Most radioactive nuclides employed in radiopharmaceuticals have a short half-life. This is beneficial to the patient as the total number of radioactive atoms given to the patient to produce an image is small when the half-life of the radioactive nuelide is short, as compared to longer half-life radioactive nuclides. Fewer total atoms reduce the radiation dose to the patient and thus the risk from a nuclear medi-eine procedure. However, the short half-life of the radioactive nuclide results in a short shelf-life for the radiopharmaeeutical. As a result, most radiopharmaceuticals are eompounded on a daily basis. The most common radioactive nuclide used for this purpose is technetium-99m (Te-99m) with a half-life of 6 hr, emiting only gamma radiation with an energy almost ideal for detection. 

Half-Life (,Radioactive Element). The average time required for one-half of the atoms in a sample of radioactive element to decay The half-lite t is given by... 

In order to facilitate the purification step, organotin precursors supported on polymers were also used for the iododestannylation reaction740-742. The reaction occurred in reasonable reaction times, which are compatible with the use of short half-life radioactive elements, thus allowing the preparation of iodolisuride 32 (a dopamine D2 receptor... 

In general, proper statistical analysis of long-term stability data collected, as recommended in Section VII.E, should support at least a 1-year expiration dating period. Exceptions do exist, for example, with short half-life radioactive drug products. 

Mass, amu Atom percent in natural uranium Half-life Radioactive decay Reaction with 2200 m/s neutrons ... 

Zirconia may contain low concentrations of long half-life radioactive elements such as Th and U, which are difficult and expensive to separate out. The main concern is that they emit a-particles (He nuclei) that can destroy both soft and hard tissue. Although the activity is small, there are questions concerning the long-term effect of a radiation emission from zirconia ceramics. 

As the other source of radioactivity of FR, R D should be focused on the long-half-life fission products (FPs). Studies have been just started to transmute long-half-life radioactive fission products or to shorten half-Kves. Although further studies are necessary, it seems to be possible to solve this problem. For example, nuclide separation technology may be improved in efficiency with facilities such as lasers as well as particle accelerators. 

Radionuclide Historical name Atomic mass Half-life Radioactivity ... 

Isotope % Natural Abundance Atomic Mass Half-Life (radioactive) Radiation... 

Half-life the time any substance takes to decay by half of its original amount see also biological half-life, decay constant, effective half-life, radioactive half-life Hand antisepsis refers to either antiseptic hand wash or antiseptic hand rub Hand hygiene a general term that applies to either handwashing, antiseptic hand wash, antiseptic hand rub, or surgical hand antisepsis... 

Once a radioactive chemical is introduced into the body, little can be done to speed its removal. Some removal will eventually occur as a result of excretion (urine, feces, perspiration, or expired air) and the activity will diminish as a result of radioactive decay. The effective half-life of a radioisotope depends upon both its physical half-life (radioactive decay) and its biological half-life (biological... 

In Sprague-Dawley rats the more easily labeled derivative [3- H]isotopomer 4a showed a terminal half-life (radioactivity) of 133 h while the [7- H]isotopomer 4fe had a terminal half-life (radioactivity) of only 31 h. It turns out that the label in 4a is readily lost in metabolism and the measured half-life is most likely that of HHO, and only the 41i data actually reflect the pharmacokinetics of the target molecule itself, the label location in this isotopomer being metabolically stable. 

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