Cosmic ray spallation

Marti, K. and Lugmair, G. W., "81Kr-Kr and K-40Ar ages, cosmic-ray spallation products and neutron effects in lunar samples from Oceanus Procell arum", Proc. Second Lunar Sci. Conf., 1971, 2, 1591-1605. 

Curiously, there are some nearby interstellar diffuse clouds displaying anomalously low isotope ratios for 7Li/6Li, with a ratio apparently as small as 2 in one case (Lemoine et at. 1994 Knauth, Federman Lambert 2003), compared to the Solar-System (and more usual interstellar) ratio of 12 the anomaly here is that the low ratio in such clouds is consistent with cosmic-ray spallation whereas that in the Solar-System is not. 

The above models are all rather unsatisfactory, because they involve somewhat arbitrary assumptions about the time-dependence of the cosmic-ray flux and spectrum and because they predict a secondary-like behaviour for Be and B abundances, whereas the overall trend indicated by the data is more like a primary one and there are the energetic difficulties pointed out above. In the case of nB, there is a possible primary mechanism for stellar production in supemovae by neutrino spallation processes (Woosley et al. 1990 Woosley Weaver 1995), but the primary-like behaviour of beryllium in metal-poor stars, combined with a constant B/Be ratio of about 20 fully consistent with cosmic-ray spallation (Garcia Lopez et al. 1998) in the absence of any known similar process for Be, indicates that this does not solve the problem unless a primary process can be found for Be as well. Indeed,... 

The discussion of the GCE of light elements formed by cosmic-ray spallation is based on Pagel (1994) and has a somewhat different outlook from many other treatments in the literature, e.g. Fields, Olive and Schramm (1995), which should be consulted to get another viewpoint. A numerical treatment of the Simple model by Vangioni-Flam et al. (1990) gave similar results to the ones derived more simply here, as did the discussion of inflow models by Prantzos (1994). 

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... 

In addition to cosmic ray spallation also produces many other radioactive nuclides. °Be is another example. Once cosmogenically produced, atoms of °Be are rapidly removed from the atmosphere by meteoric precipitation, and are absorbed onto surfaces of solid particles such as clay minerals. Hence, newly formed marine sediment contains some initial concentration of °Be. After removal from the atmosphere, the concentration of °Be in sediment decays away by p-decay to °B with a half-life of 1.51 million years (and a decay constant of 4.59 X 10 yr ). 

With these circulation features in mind, the apparent stratospheric residence times deduced from the tungsten tracer data (9), the cosmic ray spallation product distribution (2), and the 90Sr concentration variations displayed by recent balloon samples (23) can be placed in better perspective. 

Using sulfur-35. Sulfur-35 ( S) is a naturally produced radioactive tracer (half-life = 87 d) that can be used to trace the movement of atmospherically derived sulfate in the environment. It is formed in the atmosphere from cosmic ray spallation of " °Ar (Peters, 1959), and deposits on the Earth s surface in precipitation or as dryfall. It can be used both to trace the timescales for movement of atmospheric sulfate through the hydrosphere and, in ideal cases, to trace the movement of young (<1 yr) water. It is an especially useful tracer in regions away from the ocean where sulfate concentrations are relatively low. 

Tritium is produced in the atmosphere by cosmic-ray spallation of nitrogen (Lai and Peters, 1967). Tritium decays to He with a half-life of... 

Iodine-129 has major sources in both surface and subsurface environments. It is produced in the atmosphere by cosmic-ray spallation of xenon and in the subsurface by the spontaneous fission of uranium. Iodine-129 of subsurface origin is released to the surface environment through volcanic emissions, groundwater discharge, and other fluxes. Due to its very long half-life, 15.7 Ma, these sources are well mixed in the oceans and surface environment, producing a specific activity of 5 xBq (g I) (equivalent to a I/I ratio of 10 ). Due to its low activity, the preferred detection method of I is AMS (Elmore et al., 1980). 

The distributions of both natural and bomb-produced radiocarbon in the ocean have been used to determine the mean global gas exchange mass transfer coefficient. The calculation based on natural radiocarbon assumes a steady-state mass balance between the production of in the atmosphere by cosmic ray spallation (see Chapter 5) and... 

Marti K, Lugmair GW, Urey HC (1970) Solar wind gases, cosmic-ray spallation products and the irradiation history of Apollo 11 samples. Proc Apollo 11 Ltmar Sci Conf 1357-1367 Marti K, Lightner BD, Osbom TW (1973) Krypton and xenon in some ltmar samples and the age of North Ray Crater. Proc Ltmar Sci Conf 4th 2037-2048... 

Marti K, Lugmair GW (1971) Kr -Kr and K-Ar" ° ages, cosmic ray spallation products, and neutron effects in lunar samples from Oceanus Procellaram. Proc Lunar Sci Conf 2nd 1591-1605 Marti K, Graf T (1992) Cosmic ray exposure history of ordinary chondrites. Ann Rev Earth Planet Sci 20 221-243... 

Lead-210 formed in the atmosphere via Rn which diffuses from the earth s surface is adsorbed to aerosols or dust particles, and gradually deposits on to the earth s surface. It is not in radioequilibrium with Ra, and is referred to as unsupported Pb . Thus, after being deposited, atmospherically derived Pb can be distinguished as an excess of associated Ra, and can be used as a radioactive tracer. An extensive discussion of the origin and the scientific applications of radioactive lead has been provided by Wise (1980). Beryllium-7 is formed by cosmic ray spallation of... 

Regional laboratories that conform to national standards practices perform external QA measures of the network of RASA systems. An international testing procedure assures that the laboratories remain proficient. Randomly selected filters from the network of monitoring stations, automatic and manual, are sent to regional laboratories to determine if the station results are in control. This can be partially accomplished by measuring the level of 7Be (fi/2 = 53.28d), a cosmic-ray spallation product of atmospheric nitrogen and oxygen that is always in the atmosphere and is easily measurable on air filters. 

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