Exposure age

Origin. Typical meteorites have formation ages of 4.55 Gyr and exposure ages of only 10 years, duting which time they existed as meter-sized bodies unshielded to the effects of cosmic rays. With the exception of the SNC (Martian) and lunar meteorites it is widely befleved that most conventional... 

Dose-response assessment is the process of characterizing the relationship between the dose of an agent administered or received and the incidence of an adverse health effect in e.xposed populations, and estimating the incidence of the effect as a function of e.xposure to the agent. This process considers such important factors as intensity of exposure, age pattern of exposure, and possibly other variables that might affect response, such as sex, lifestyle, and other modifying factors. 

As discussed earlier, the production ratio Pgi/P83 cani in general, reliably be obtained from equation (1) and, therefore, the 81Kr-Kr method avoids much of the uncertainty arising from unknown production rates or production ratios. The method derives exposure ages from Kr isotopic ratios as obtained from mass spectrometry and does not require a knowledge of the concentration of spallation Kr, which makes the method inherently more precise. 

Nishiizumi, K., Regnier, S., and Marti, K., "Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past, 1980, Earth Planet. Sci. Lett., 50, 156-170. 

Morgan, C. J., "Cosmic ray exposure ages of features and events at the Apollo landing sites", 1975, The Moon, 1 3,... 

Wetheril 1, G. W., Multiple Cosmic Ray Exposure Ages, paper presented at 43rd meeting of Meteoritical Society, La Jolla, Calif., 1980, Meteoritics (in press). 

Brown, E. T., Edmond, J. M., Raisbeck, G. M., Yiou, F., Kurz, M. D. Brook, E. J. (1991). Examination of surface exposure ages of Antarctica moraines using in situ produced 10Be and 26Al. Geochim. Cosmochim. Acta, 55, 2269-83. 

Schwarzmiiller, J. Stettler, A. (1970). Trapped solar wind noble gases, exposure age and K/Ar-age in Apollo 11 lunar fine material. Proc. Apollo 11 Lunar Sci. Conf, 2,1037-70. 

Large numbers of farm workers reported symptoms. Of 760 workers and nearby residents surveyed, five required medical attention and 72X reported one or more symptoms. The five workers, evaluated more extensively, experienced lacrlmatlon, vertigo, headache, fatigue, and orthostatic hypotension for several hours after exposure to PS. The other persons surveyed had lacrlmatlon, headache, coughing, nausea, and anorexia for 1-3 d after exposure and 30 had symptoms for over 1 mo after exposure. Age and symptoms were positively correlated. 

Analysis of dose-incidence relationships for chemical carcinogenesis is further complicated by the fact that the dose of a chemical at its biological site of action depends on a number of metabolic and pharmacokinetic factors which can vary with route of exposure, age,... 

ICHIMARU, M., ISHIMARU, T., AND Belskv J.L. (1978). Incidence of leukemia in atomic bomb survivors belonging to a fixed cohort in Hiroshima and Nagasaki, 1950-71. Radiation dose, years after exposure, age at exposure, and type of leukemia, Japan J. Radiat. Res. 19,262. 

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. 

Turner, G., Huneke, J. C., Podosek, F. A. and Wasserburg, G. J. (1971) 40Ar-39Ar ages and cosmic-ray exposure ages of Apollo 14 samples. Earth and Planetary Science Letters, 12,... 

Table 9.1 Nuclides used for cosmic-ray exposure ages ...

The fraction of incoming cosmic rays that generate nuclear reactions is quite low. In a meteorite traveling in space, about one in 108 of the target atoms undergoes a nuclear reaction in a 10-Myr period. However, the cosmogenic nuclides that they produce can be measured to estimate the time that an object has been exposed to cosmic rays. Table 9.1 shows some of the nuclides that are used to estimate cosmic-ray exposure ages in meteorites and in materials from planetary surfaces. 

Cosmic-ray exposure ages of Cl and CM chondrites. Modified from Eugster et al. (2006). 

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