IRVINE: INITIAL OPERATION AND A BACKGROUND SURPRISE

A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported 14C AMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator. THE KCCAMS FACILITY The Keck Carbon Cycle accelerator mass spectrometry (KCCAMS) facility was established in 2001-2002 with a $2M grant from the W M Keck Foundation and matching funds from University of California, Irvine (UC Irvine), and was set up to use carbon isotopic techniques, primarily AMS, to advance understanding of the carbon cycle and its linkages with climate. The facility consists of 3 major elements: 1. A National Electrostatics (NEC) 0.5MV 1.5SDH-1 accelerator mass spectrometry (AMS) sys- tem with a 40-sample MC-SNICS ion source; 2. A Finnegan MAT Delta Plus Isotope Ratio Mass Spectrometer equipped with Gas Bench and Elemental Analyzer (Fisons 1500NC) inputs for gas and solid organic samples, respectively; 3. A new sample preparation laboratory with two 12-head graphitizer lines to supplement existing UC Irvine sample preparation facilities.