Short lived cosmic ray-produced

Short Lived Cosmic Ray-Produced Radionuclides as Tracers of Atmospheric Processes... 

Since the production rates of the cosmic ray radionuclides increase rapidly with increasing altitude in the lower atmosphere, the atmospheric concentrations and ratios of short lived cosmic ray radionuclides can be used to study rapid vertical air motions if the equilibrium concentrations of the radionuclides are known. For example, the concentrations of the short lived cosmic ray radionuclides in air which has moved upward recently from a lower altitude will be less than the equilibrium concentrations. The concentrations of the radionuclides will therefore increase with time until equilibrium is reached. However, the concentration of the shorter lived of two short lived radionuclides will increase more rapidly initially, causing the ratio of the two radionuclides of different half-lives to change with time until equilibrium is reached. Therefore, the time since the air moved from a lower altitude, the speed of the upward motion, and the altitude from which the air originated could be calculated from the concentrations and concentration ratios of cosmic ray radionuclides of different half-lives. Vertical motions of different speeds could be studied since several cosmic ray radionuclides of different half-lives are present in the atmosphere (Table I). Many other radionuclides are produced by cosmic rays in the atmosphere, but they have not yet been detected. Some of these with half-lives of a few minutes could serve as tracers of very short term processes such as post-nucleation scavenging. 

This method is used mainly for short-lived radioactive nuclides produced by cosmic ray spallation, such as °Be, A1, Si, C1, and Ar (Table 5-1). Because these nuclides have relatively short half-lives, if there was any initial amount of the nuclides at the beginning of Earth history, the initial amount would have completely decayed away. The small amount that can be found in... 

Finally, P also differs from other elements in that it is overwhelmingly dominated by a single isotopic form containing 15 protons and 16 neutrons. There are only two naturally occurring radioactive forms of P, P and P. Cosmic rays produce these radionuclides in the atmosphere by nuclear reactions with argon. A small amount of P is also contributed by Si decay. Because these isotopes have extremely short half-lives ( P half-life, 14.3 days P half-life,... 

Aluminum-26 is produced by stellar nucleosynthesis in a wide variety of stellar sites. Its abundance relative to other short-lived nuclides provides information about the stellar source(s) for short-lived nuclides and the environment in which the Sun formed. Aluminum-26 is also produced by interactions between heavier nuclei such as silicon atoms and cosmic rays. Aluminum-26 is one of several nuclides used to estimate the cosmic-ray exposure ages of meteorites as they traveled from their parent asteroids to the solar system. 

Another isotopic manifestation is the so-called Cosmogenic Radioactivity which is produced in meteorites owing to reactions of their stable atoms with the cosmic rays that bombard the meteorites. Owing to this, meteorites have many live short-lived radioactivities within them when they fall to ground, and measuring their amounts determines when the meteorite fell and how deep within it was the location of the sample prior to the collision that released it into space (see Extinct radioactivity and Meteorites). 

Many CAIs, together with some chondrules and samples of differentiated asteroids, contained short-lived radioactive isotopes at the time they formed. This is deduced from the abundances of the daughter isotopes seen in modern meteorites. The short-lived isotopes include " Ca, A1, °Be, e, Mn, and ° Pd, with half-lives (in units of Myr) 0.13, 0.7, 1.5, 1.5, 3.7, and 6.5, respectively. Many of these isotopes could have been produced from stable ones by absorption of neutrons in a supernova or the outer layers of a giant star. In particular, °Fe can only be produced efficiently by stellar nucleosynthesis and so must have come from an external source (Shukolyukov and Lugmair, 1993). Conversely, some isotopes such as Be almost certainly formed in the protoplanetary nebula when material was bombarded by solar cosmic rays (McKeegan et al., 2000). Multiple sources are possible for some short-lived isotopes. The abundances of the decay products of... 

Naturally occurring nuclides which have short half-lives on the geological time scale, but which are being continuously produced by cosmic-ray radiation. 

Radioactive elements are made artificially by bombarding other nuclei, either in particle accelerators or with neutrons in nuclear reactors (see Topic 12). Some short-lived radioactive isotopes (e.g. 14C) are produced naturally in small amounts on Earth by cosmic-ray bombardment in the upper atmosphere. 

Baryons refer to the class of strongly interacting particles which are made up of 3 quarks. The only long lived baryons are the neutrons and the proton. All other baryons are very short lived and produced only in accelerators (or cosmic ray collisions). 

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