Abstract-The HF/HCl-resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, C03.4 Lance, C03.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed-system stepped etching (CSSE) in order to better characterise the noble gases in "phase Q", a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (20NeP2Ne)Q. As already suggested by precise earlier measurements (Schelhaas et ul., 1990;Wieler et al., 1991Wieler et al., , 1992, (20NePzNe)Q is the least uniform isotopic ratio of the Q noble gases. The data cluster -10.1 for Cold Bokkeveld and Lance and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (20NeP2Ne)q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar-Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne-Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases "Ql" and "42" with slightly distinct chemical properties. Ratios (Ar/Xe)Q and (Kr/Xe)Q reflect both thermal metamorphism and aqueous alteration. These parent-body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)Q and (Ne/Ar)Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than 4 2 . Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q1 and 4 2 must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q1 may be related to presolar graphite. Phases Q1 and 4 2 might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the 20NeP2Ne ratios cannot be attributed to the carriers Q1 and Q2. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne-E(L), and the data confirm the suggestion of Huss (1997) that the 22Ne-E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.

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~~ ~~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 semiempirical 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.

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