Energetic particles of the galactic cosmic radiation (GCR) have a mean penetration depth in rock of about 50 cm, comparable to the typical size of a meteorite. GCR-induced effects therefore provide a means to study the history of meteorites as small objects in space or in the top few meters of their parent body. These effects include cosmic ray tracks, i.e., the radiation damage trails in a crystal lattice produced by heavy ions in the GCR (Fleischer et al. 1975), and thermoluminescence, i.e., the light emitted by a heated sample which had been irradiated by energetic particles (Benoit and Sears 1997). By far most important, however, are “cosmogenic” nuclides, produced by interactions of primary and secondary cosmic ray particles with target atoms.

This chapter concentrates on the cosmogenic noble gas nuclides in meteorites. A separate chapter in this book by Niedermann (2002) discusses cosmogenic noble gases in terrestrial rocks, which are by now a major tool in quantitative geomorphology. Cosmogenic noble gases in lunar samples are briefly presented in the chapter by Wieler (2002) on noble gases in the solar system. Here and in the other chapters mentioned, cosmogenic radionuclides such as 10Be, 26Al, or 36Cl are often also considered, as comprehensive studies usually require combining noble gas and radionuclide analyses. Not further discussed here are cosmic-ray-induced shifts of the abundances of stable isotopes of a few elements besides noble gases. The most important of these are Gd, Sm, and Cd, which have isotopes with extremely high cross sections for the capture of slow (thermal or epithermal) neutrons produced as secondary cosmic ray particles by interactions of the primary GCR protons with target atoms (Eugster et al. 1970; Hidaka et al. 1999; Sands et al. 2001). Because the flux of thermal and epithermal neutrons peaks …

Cosmic-Ray-Produced Noble Gases in Meteorites

(Received 1999 April 5; accepted in revised form 1999 October 12) ~~ ~~ Abstract-We present a purely physical model for the calculation of depth- and size-dependent production rates of cosmogenic nuclides by galactic cosmic-ray (GCR) particles. Besides the spectra of primary and secondary particles and the excitation hnctions of the underlying nuclear reactions, the model is based on only one free parameter-the integral number of GCR particles in the meteoroid orbits. We derived this value from analysis of radionuclide data in Knyahinya. We also show that the mean GCR proton spectrum in the meteoroid orbits has been constant over about the last 10 Ma. For the major target elements in stony meteoroids, we present depth- and size-dependent production rates for loBe, 14C, 26A1, 36Cl, and 53Mn as well as for the rare gas isotopes 3He, ZoNe, 21Ne, 22Ne, 36Ar, and 38Ar. The new data differ from semi- empirical estimates by up to a factor of 4 but agree within -20% with results obtained by earlier parametric or physical approaches. The depth and size dependence of the shielding parameter 22Ne/21Ne and the correlations 26AI vs. loge, 26AI vs. 53Mn, loBe/zlNe vs. 22Ne/21Ne, and 36Ar vs. 36Cl for deciphering preatmospheric sizes, shielding depths, terrestrial residence times, and exposure histories are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.2000.tb01775.x

The production of cosmogenic nuclides in stony meteoroids by galactic cosmic‐ray particles

Noble gas contents of shergottites and implications for the Martian origin of SNC meteorites

The concept of a cosmic-ray exposure (CRE) age for a meteorite is based on a simple but useful picture of meteorite evolution, the one-stage irradiation model. CRE ages have implications for several interrelated questions. From how many different parent bodies do meteorites come? How well do meteorites represent the population of their source region? How many distinct collisions on each parent body have created the known meteorites of each type? How often do parent bodies collide? How big and how energetic were the collisions that produced meteoroids? What factors control the CRE age of a meteorite and how do meteoroid orbits evolve through time? This chapter touches on these questions as it examines the data. In recent years, CRE ages also have become important for interpreting small variations in the abundances of stable isotopes.

Cosmic-Ray Exposure Ages of Meteorites

On the calculation of cosmic-ray exposure ages of stone meteorites

Cosmic ray spallation produced He-3, Ne-21, Ne-22 and Ar-38 have been measured as a function of depth in three mutually perpendicular cores (56, 51, and 21 cm) taken from the 120-kg L chondrite found near Keyes, Oklahoma. The data obtained represent the first experimental determination of the depth variation in the production rates of these cosmogenic nuclides in a single stone meteorite. Fifteen samples across the 56-cm core showed maximum concentration changes of 14% He-3, 28% Ne-21, 19% He-3/Ne-21, and 5% Ne-22/Ne-21. The 51-cm core showed somewhat smaller concentration changes.

Depth variation of cosmogenic noble gases in the ∼120-kg Keyes chondrite

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Depth variation of cosmogenic noble gases in the ∼120-kg Keyes chondrite