Cosmic ray induced

The above examples should suffice to show how ion-molecule, dissociative recombination, and neutral-neutral reactions combine to form a variety of small species. Once neutral species are produced, they are destroyed by ion-molecule and neutral-neutral reactions. Stable species such as water and ammonia are depleted only via ion-molecule reactions. The dominant reactive ions in model calculations are the species HCO+, H3, H30+, He+, C+, and H+ many of then-reactions have been studied in the laboratory.41 Radicals such as OH can also be depleted via neutral-neutral reactions with atoms (see reactions 13, 15, 16) and, according to recent measurements, by selected reactions with stable species as well.18 Another loss mechanism in interstellar clouds is adsorption onto dust particles. Still another is photodestruction caused by ultraviolet photons produced when secondary electrons from cosmic ray-induced ionization excite H2, which subsequently fluoresces.42... 

Rate constant temperature dependence Processing threshold Calculation of rate constants at different temperatures, including collision numbers and concentrations of species in steady state Calculation of the rate of photodissociation and cosmic ray-induced molecular processing from photon and particle fluxes... 

Honda M (1988) Statistical estimation of the production of cosmic-ray induced nuclides in meteorites. Meteoritics 23 3-12... 

Other than radioactive decay (Table 1.4), fission (Table 1.5), or cosmic-ray-induced spallation (Tables 5.3 and 5.4). 

Figure 2.12 Correlated isotopic variations observed in stepwise heating of lunar breccia 60019. The linear array suggests that only two components, in varying proportions, are present one is trapped solar wind, presumably near BEOC-12, the other is in situ cosmic ray-induced spallation, relatively rich in 124Xe and 126Xe.

Examinations of the same and of other lead-bearing samples for spontaneous fission events with large proportional counters in Dubna seemed to confirm these findings, but further measurements [37] of thin samples sandwiched between two plastic fission-track detectors showed that the events were background caused by cosmic-ray induced reactions of lead. Other groups [38] found no evidence for spontaneous fission activities in lead and other samples at a lower detection limit of 10" 3 g/g achieved with the sandwich technique. Even lower limits down to 10"17 g/g can be reached by etching... 

Fig. 5. Neutron counting as detection method for spontanous fission events of superheavy nuclei. The recorded neutron rates (points) were found to follow the relative cross sections of cosmic-ray induced spallation reactions (curve) and were, thus, due to background events. The numbers are rates for natural uranium and thorium. From W. Grimm, G. Herrmann and H.-D. Schiissler [40].

Tritium, which is radioactive (/T, tl/2 = 12.4 y), is made by the reaction 6Li(n,ct)3H in nuclear reactors. It is also formed in plasmas2 as 3H+ and by cosmic ray induced nuclear reactions in the upper atmosphere. The decay of 3H probably accounts for traces of 3He in the atmosphere. 

Because Ne and He are the most sensitive indicators of the presence of spallation products, it can be difficult to identify materials which can be confidently inferred to be unexposed to cosmic rays, i.e., in which we may confidently assign the abundance of these isotopes to a trapped component. Thus, the measured Ne and/or He abundances in some sample are upper limits to the trapped abundance, but it may be difficult to eliminate the possibility that some of the measured abundance was not produced in spallation. It is possible, for example, that some of the Ne in prominent components such as air or planetary trapped gases (see below) is attributable to cosmic-ray-induced spallation. 

Pu-Xe dating. Decay of Pu can be used as a chronometer of the first 100 Ma for some specific meteorite parent bodies. Both Pu and the LREE tend to be concentrated in refractory minerals like phosphates. Which LREE is the best proxy for Pu Various authors have suggested Nd (Lugmair and Marti 1977), Sm (Jones and Burnett 1987), or Pr or Ce (Boynton 1978). There are no neutron-induced reactions that produce a rare gas from any of the LREE, but all of these, particularly Nd, do produce the light xenon isotopes like Xe and Xe through cosmic-ray-induced spallation reactions (Wider 2002, this volume). In fact, in many cases, the LREE (and presumably Pu), are probably not fractionated much from each other. Hence, if the cosmic ray dose (i.e., the cosmic ray exposure age) is known, and the production rate of isotopes like " Xe and Xe is also known, then the abundance of the LREE can be calculated. Then the ratio of Xe244 (Pu-... 

Sometimes, cosmic-ray-induced isotope shifts are also a nuisance, because they may compromise the precise determinations of isotopic compositions of elements of interest. This is often a major problem in the case of trapped noble gases (Ott 2002, this volume), but may also require attention when e.g., small excesses or deficits of daughter isotopes of an extinct radionuclide present in the early solar system are to be determined (e g., Leya et al. 2000c). 

O Brien K, Sandmeier HA, Hansen GE, Campbell JE (1978) Cosmic ray induced neutron background sources and fluxes for geometries of air over water, ground, iron, and aluminum. J Geophys Res 83 114-120... 

Cosmic-ray induced 7-rays from interstellar matter. This emission has been mapped by COMPTEL in the 1 MeV - 10 MeV range, showing angular structure on scales larger than the angular resolution of COMPTEL. 

It is useful to extrapolate the cosmic ray components of the background in the deep KamLAND detector to shallower depths at which detector construction is more feasible. Most of the cosmic ray induced background comes firom neutrons with energies up to several hundred MeV produced by muon capture and spallation in materials surrounding the detector. Few experiments have been done that give detailed information on the... 

When Fritz Paneth s group in 1953 tried to determine meteorite ages by the He/U method (Paneth et al. 1953), they found much larger amounts of helium than could be accounted for by uranium decay and thus stumbled on the discovery of cosmic-ray-induced nuclear reactions in meteorites that subsequently became the subject of extensive research. Many radionuclides with half-lives ranging from days to millions of years as well as some stable spallation products have been identified in meteorites. From the amounts found, the exposure ages of meteorites in space and the average cosmic-ray flux and its time variation can be deduced (see, e.g., Schaeffer 1968). 

Be produced by cosmic-ray-induced nuclear reactions is useful for studying atmospheric transport mechanisms. Since the production of Be and other cosmogenic nuclides is directly dependent on the cosmic-ray intensity, a relationship between the production rate of these nuclides and the 11-year solar cycle has been found (Kulan et al. 2006). It is known that the galactic cosmic-ray intensity at the earth s orbit is inversely related to solar activity (Hotzl etal. 1991). 

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