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Half-life (symbol t½) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. The term is also used more generally to characterize any type of exponential (or, rarely ...
Geiger–Nuttall law. In nuclear physics, the Geiger–Nuttall law or Geiger–Nuttall rule relates the decay constant of a radioactive isotope with the energy of the alpha particles emitted. Roughly speaking, it states that short-lived isotopes emit more energetic alpha particles than long-lived ones. The relationship also shows that half ...
A more intuitive characteristic of exponential decay for many people is the time required for the decaying quantity to fall to one half of its initial value. (If N (t) is discrete, then this is the median life-time rather than the mean life-time.) This time is called the half-life, and often denoted by the symbol t1/2.
Caffeine. Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive substance globally. [9][10] It is mainly used for its eugeroic (wakefulness promoter), ergogenic (physical performance enhancing), or nootropic (cognition improving) properties. [11][12] Caffeine acts by ...
Half-Life (video game) Half-Life. (video game) Half-Life is a 1998 first-person shooter game developed by Valve Corporation and published by Sierra Studios for Windows. It was Valve's debut product and the first game in the Half-Life series. The player assumes the role of Gordon Freeman, a scientist who must escape from the Black Mesa Research ...
Latest release. Half-Life: Alyx. March 23, 2020. Half-Life is a series of first-person shooter (FPS) games created by Valve. The games combine shooting combat, puzzles and storytelling. The original Half-Life, Valve's first product, was released in 1998 for Windows to critical and commercial success. Players control Gordon Freeman, a scientist ...
Effective half-life. In pharmacokinetics, the effective half-life is the rate of accumulation or elimination of a biochemical or pharmacological substance in an organism; it is the analogue of biological half-life when the kinetics are governed by multiple independent mechanisms. This is seen when there are multiple mechanisms of elimination ...
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.