Cosmogenic nuclides in extraterrestrial materials

Abstract

The nuclides made in extraterrestrial materials by cosmic rays help reveal the histories both of the irradiated objects and of the cosmic rays. Improvements in measurement techniques, especially in accelerator mass spectrometry, have greatly reduced detection limits.Thanks to several extensive series of measurements in meteorites, a comprehensive picture has taken shape of how cosmogenic nuclide production depends on size, shape, and composition. Complementary to this work, (1) the irradiation in space of meteoroids has been simulated by means of accelerator experiments both with very thick and with spherical targets, and (2) various models for calculating production rates of cosmogenic nuclides have been developed or refined. New classes of material-meteorites recovered in Antarctica and tiny meteorites from the stratosphere and deep-sea sediments, for example--have become more widely available for analysis. From their cosmogenic nuclide contents we have learned about the exposure histories of lunar meteorites, of SNC meteorites, which may come from Mars, and of interplanetary dust particles. Cosmogenic nuclides have been put to use in unfolding increasingly complex exposure histories. Some grains in gas-rich meteorites were irradiated in at least two episodes, and others perhaps even before the solar system formed. Continuing measurements of lunar samples reveal the past behavior of energetic solar particles. We now know from cosmogenic nuclide measurements that many meteorites found in Antarctica have been there for-0.1-1 million years and that the age distributions vary from site to site.Among the more important isotopes we may list 3He, 2•Ne 10 26 (both stable), Be, A1, 36C1, 41Ca, 53Mn, and 8•Kr ("long-lived," 100,000 years to 3.7 million years, cosmogenic radionuclides), and 22Na and COCo ("short-lived," less than 10 years). Before 1969, work on cosmogenic nuclides focused on meteorites: There were no other suitable extraterrestrial materials available and, except for •4C, the concentrations of longer-lived cosmogenic nuclides in terrestrial materials were then too small to measure without heroic efforts. The emphasis switched in the 1970s to lunar samples, when a flood of samples was brought back from the Moon. During the last decade, studies of cosmogenic nuclides in extraterrestrial materials have increased in number and breadth in response to (1) the development of new sources of materials, e.g., interplanetary dust particles; (2) the identification of objects of special interest, e.g., lunar meteorites in the collections from the Antarctic ice fields; (3) the need to plan for the analysis of materials from elsewhere in the solar system, e.g., Mars and comets; and (4) the improvement of analytical methods. Among the technical advances, we would single out the pages 253-275 Paper number 90RG00850 253 ß 254 ß Vogt et al.: COSMOGENIC NUCLIDES 28,3 / REVIEWS OF GEOPHYSICS use of accelerators for high-energy mass spectrometry as having had the most profound impact to date. With accelerator mass spectrometry...

A history of solar activity over millennia

“…Moreover, possible errors of the primary observer cannot be caught or estimated. The observational uncertainties in the monthly R z can be up to 25% (e.g., Vitinsky et al 1986). The WSN series is based on observations performed at the Zürich Observatory during 1849-1981 using Annual sunspot activity for the last centuries.…”

“…In addition, earlier parts of the sunspot series were "corrected" by Wolf using geomagnetic observation (see details in Svalgaard 2012), which makes the series less homogeneous. Therefore, the WSN series is a combination of direct observations and interpolations for the period before 1849, leading to possible errors and inhomogeneities as discussed, e.g, by Vitinsky et al (1986), Wilson (1998), Letfus (1999), Svalgaard (2012), Clette et al (2014). The quality of the Wolf series before 1749 is rather poor and hardly reliable (Hoyt et al 1994;Hoyt and Schatten 1998;Hathaway and Wilson 2004).…”

“…However, the cycle varies in both amplitude and duration. The first observation of a possible regular variability in sunspot numbers was made by the Danish astronomer Christian Horrebow in the 1770s on the basis of his sunspot observations from 1761-1769 (see details in Gleissberg 1952;Vitinsky 1965), but the results were forgotten. It took over 70 years before the amateur astronomer Schwabe announced in 1844 that sunspot activity varies cyclically with a period of about 10 years.…”

A high resolution authigenic 10Be/9Be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the Portuguese margin

“…Cosmogenic production rate is thus proportional to the galactic cosmic ray flux and inversely proportional to the solar activity and the Earth's magnetic field intensity [1][2][3][4]. Measurements of cosmogenic radionuclides with different half-lives in lunar samples and in meteorites having different irradiation histories [5], and in marine sediments [6] and manganese crusts [7] yield to the conclusion that the average galactic cosmic ray flux was fairly constant on time-scales of millions of years. Solar activity varies on annual to centennial time-scales around a mean that remained roughly constant over the observed long-term (from thousands to millions of years) variations in cosmonuclide production rate.…”

Allan Hills 88019: An Antarctic H‐chondrite with a very long terrestrial age

“…Assuming mean saturation activities for IOBe, 26AI, and 36CI of 20.6 f 1.0 d p d k g , 56 2 8 d p d k g , and 22.8 f 3.1 dpm/kg Fe, respectively (Vogt et al, 1990), the measured concentrations indicate a terrestrial age >1.8 Ma. The production rates of radionuclides and, thus, also the terrestrial age can be given from the model calculations.…”