Accelerator mass spectrometry of 10Be, 14C, 26Al, 36Cl, 41Ca, 129I

Logo for National Science Foundation

PRIME Lab is funded by the National Science Foundation.
 

Chemical and physical sample preparation


PRIME Lab has the capability to perform physical and chemical preparation for all nuclides and all types of samples that are measured by accelerator mass spectrometry at our facility. PRIME Lab prepares samples as a service to the scientific community. Samples submitted to PRIME lab that are paid for out of NSF grants are charged half price.

The main chemical facilities for geological samples are located in two refurbished laboratories in the Department of Chemistry. Both are completely equipped for routine processing of low-level samples. Radiocarbon samples and 36Cl samples with intermediate levels of radionuclide content are processed in the PRIME LAB building, and high-level biomedical samples are processed in the Physics building near PRIME Lab.

The chemistry staff consists of one faculty member, two professionals (one working only 1/4 time at PRIME Lab), one full time technician. In addition, one professional and one technician perform 14C sample preparation.

A total of 300-600 targets are prepared at PRIME Lab during a typical year. More than half of these are submitted by outside users. This clearly demonstrates the growing role of PRIME Lab as a national facility for the geoscience community. Water samples and rocks are the major sample types received for analysis, and 36Cl is the most requested nuclide.

PRIME Lab chemistry operations performs the separation of quartz from whole rock samples by density separation (2.6-2.7 g/cm3) followed by successive etching to remove any remaining feldspar, meteoric components, and weathering products. This method of quartz separation has the following advantages over purely chemical methods: other mineral phases are retained and available for additional analysis, HCl is not used making separates available for 36Cl analysis, and the processing time is shorter. For water and ice, we employ ion exchange techniques rather than evaporative methods to greatly reduce the processing time, to better separate the interfering isobars sulfur and boron. For carbon, we have developed methods for oxidizing samples to CO2 and conversion to graphite using a sealed tube technique. This has the advantages of low contamination and batch processing capability. We have developed methods to produce CaH2 from CaO using a customized evaporator. We have also developed improved techniques for separating Be, Al, and Cl from meteorites, soils, and sediments.

As important as it is to have a chemistry facility at PRIME Lab to serve the Earth science community, we realize it would be impractical for us to keep the AMS system fully supplied with targets. We provide assistance to outside users who wish to do their own processing. In several cases we have performed in-house training sessions lasting a few weeks. Some of our users qualify as "satellite chemistry labs" in that they process samples for third parties. The following PRIME Lab users process their own samples: P. Bierman, J. Fabryka-Martin, U. Fehn, R. Kay, A. Mignerey, F. Phillips, P. Santschi, and M. Zreda.