Robert K. Moniot

Beryllium-10 contents of core samples from the St. Severin meteorite

Abstract Eleven samples taken from along the 35-cm core AIII of the LL-chondrite St. Severin have 10 Be contents ranging from 20 to 28 dpm/kg and averaging 24.5 ± 0.9 dpm/kg. The 10 Be contents increase with depth in the outermost 8 cm while at depths greater than 8 cm the 10 Be contents change little. Calculations based on cross sections for proton-induced reactions that make 10 Be disagree seriously with the measured values. Relatively large cross sections were constructed for neutron-induced reactions below 1 GeV. They give calculated 10 Be production rates that agree with the measured values to within 10%. Cosmogenic 10 Be in stony meteorites is better described as a medium-energy product than as a high-energy one.

Beryllium-10 in Australasian Tektites: Evidence for a Sedimentary Precursor

Each of seven Australasian tektites contains about 1 x l08 atoms of beryllium-10 (half-life, 1.53 x 106 years) per gram. Cosmic-ray bombardment of the australites cannot have produced the measured amounts of beryllium-10 either at the earths 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 earths surface within a few million years of the tektite-producing event.

Beryllium-10 contents of shergottites, nakhlites, and Chassigny

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

High-energy mass spectrometry of 10Be using a tandem van de graaff accelerator

Abstract A method of measurement of specific 10Be contents of naturally occurring materials is described. The method is based on mass spectrometry of 10Be/9Be ratios, using the Rutgers-Bell tandem van de Graaff accelerator. The detection limit is currently approximately 107 atoms 10Be, and the precision, when not limited by counting statistics, is 13%. The linear proportionality of observed 10Be/9Be ratio to actual ratio in sample has been verified within uncertainty over more than two orders of magnitude in ratio. Results are presented for the application of the method to determination of 10Be contents of six samples from various locations in the Antarctic H-chondrite ALHA 78084. No significant variations among the samples due to differences in shielding from cosmic rays were observed.

Production of 10Be in stony meteorites: Composition dependence

Abstract We measured, by accelerator mass spectrometry, the 10Be contents of 21 samples from 17 meteorites in an effort to estimate production rates of 10Be (dpm/kg) from the major elements (wt.%) present in stones. Regression analyses and other considerations yielded the equation 10Be = (0.32 ± 0.05) O + (0.30 ± 0.08) (Mg + 1.1 Al + 0.5 Si) + 0.15 S + 0.10 Ca + 0.05 (Fe + Ni) which reproduces the measured 10Be contents with an accuracy of about 10%. The high coefficient for Mg relative to O conflicts with production rates estimated from nuclear cross sections and from simulation experiments.

Accelerator mass spectrometry II: Background reduction with a Wien (velocity) filter; 10Be contents of Central American basalts

Abstract 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.

Accelerator mass spectrometry of10Be to study the fossil record of cosmic radiation

SummaryThe 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.RiassuntoSi applica la spettrometria di massa ultrasensibile con acceleratori per misurare fino a 106÷107 atomi di10Be, che è presente sia nella materia terrestre che extraterrestre e fornisce una scala temporale per molti eventi terrestri e del sistema solare degli ultimi milioni di anni. Si presentano alcuni soddisfacenti risultati.