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Beryllium-10 contents in the 20-28 dpm/kg range, averaging 24.5 + or - 0.9 dpm/kg, have been obtained for 11 samples taken from along the 35-cm core AIII of the St. Severin LL chondrite. Be-10 content increases with depth in the outermost 8 cm, and there is little change in content at greater depths. Significant disagreement is noted between the measured values and the results of calculations based on the cross sections for proton-induced Be-generating reactions. Cosmogenic Be-10 in stony meteorites is better described as a medium-energy product than a high energy one.

Accelerator mass spectrometry gives the following Be-10 contents (dpm/kg) for the SNC meteorites: Shergotty, 13.0 + or - 1.5 and 17.3 + or - 2.7; Zagami, 18.6 + or - 2.5 and 20.0 + or - 3.2; ALHA 77005, 15 + or - 3; EETA 79001A, 7.8 + or - 1.1 and 6.3 + or - 0.5; EETA 79001B, 8.5 + or - 1.1; Nakhla, 19.7 + or - 3.3; Lafayette, 18.1 + or - 2.5; Governador Valadares, 25.6 + or - 3.6; Chassigny, 20.5 + or - 3.1. The Be-10 contents of the NC meteorites indicate that significant accumulation of cosmogenic nuclides occurred in decimeter rather than planetary-size bodies. The agreement of the He-3, Ne-21, and Be-10 exposure ages of the shergottites also supports small-body irradiation. A long terrestrial age for EETA 79001 appears unlikely.

A model of a small meteorite, 10 cm in diameter, made of granodiorite was rotated in a beam of 600 MeV protons to simulate 4π-irradiation conditions in space. Analysis of Al foils placed at known locations within the model give depth profiles of high energy (7Be, 10Be) and low energy (24Na, 22Na) spallation products. These isotopes were measured by means of high-resolution gamma-ray or accelerator mass spectroscopy (AMS). While the production rate profiles of the high energy products are flat within the limits of uncertainty, the profiles of the low energy products increase from the surface to the center by a factor of approximately 1.2. This increase indicates the importance of secondary neutrons and protons for the production of low energy spallation products, even within small meteorites.

Summary We report the 10Be and Be contents of 22 sediment samples of lacustrine silt from the Wilson Creek section of Mono Lake, California. The section spans about 20–35 kyr bp and contains a record of a geomagnetic excursion for which the relative palaeointensity is estimated from the ratio of natural remanent magnetization to anhysteretic remanent magnetization. The 10Be contents of the excursion samples are somewhat higher than the average of non-excursion samples (0.24 ± 0.02 versus 0.15 ± 0.02 dpm kg−1). It is clear however that geomagnetic effects are not the sole cause of the observed variations.

The Be-10 contents of 28 stony meteorites with known Ne-21 contents range from 0.97 to 23 dpm/kg and give an average Ne-21 production rate (P sub 21) of (0.28 + or - 0.02) x 10 to the -8th cu cm STP/g-My for shielding conditions corresponding to Ne-22/Ne-21 = 1.114 in an H-chondrite. This P sub 21 (Be) agrees with others' P sub 21 based on Na-22, Kr-81, and Mn-53, but not an Al-26. Temporal variations in the cosmic ray flux do not explain the disagreement satisfactorily; major errors in the radionuclide half-lives are not indicated. The discrepancy seems rooted in the data selection and the difficulties of making accurate corrections for shielding, chemical composition and other sources of variability.

Our limit of detection for 10 Be by accelerator mass spectrometry has been lowered to a few million atoms by the installation of a Wien filter which screens out co-transmitted 9 Be. Analyses of six Central American basalts gave 10 Be contents ranging from 1 × 10 6 to 60 × 10 6 atom/g. The sample richest in 10 Be has been contaminated by sediments. The other samples have 10 Be contents in the range reported in the literature by Brown and co-workers.

The ultrasensitive accelerator mass spectrometry is applied to measure as few as 106÷107 atoms of10Be, which is present in terrestrial and extraterrestrial matter, and provides a time scale for many terrestrial and solar-system events of the last few million years. Some successful results are presented.

Measurements of the Be-10 and Al-26 contents of ALHA 81005 constrain the length and conditions of its exposure to cosmic rays. Calculations based on one-step irradition models imply that the time spent by this object in space is shorter than that spent by most 'asteroidal' meteorites. On the other hand the results are readily consistent with a lunar origin for ALHA 81005.

The Be-10 contents measured in eight bulk samples of the Jilin meteorite range from 5.05 + or - 0.55 to 16.3 + or - 1.7 dpm/kg, more than threefold, and correlate with the Ne-21 contents. A least-squares fit of these data has a positive intercept on the Be-10 axis which can be explained in terms of a two-stage irradiation. The second, more recent stage lasted 0.57 + or - 0.14 Myr. Model calculations give first-stage Be-10/Ne-21 age ranging from 6.2 to 7.1 Myr.

Each of seven Australasian tektites contains about 100 micron atoms of beryllium-10 (half-life, 1.53 million years) per gram. Cosmic-ray bombardment of the australites cannot have produced the measured amounts of beryllium-10 either at the earth's surface or in space. The beryllium-10 contents of these australites are consistent with a sedimentary precursor that adsorbed from precipitation beryllium-10 produced in the atmosphere. The sediments must have spent several thousand years at the earth's surface within a few million years of the tektite-producing event.

The 10Be and Be contents of 22 samples taken from seven locations in the Maurice River-Union Lake system of southern New Jersey are reported. Bulk 10Be contents range from 0.05 to 2.7 dpm/kg and Be from