Ultra small mass AMS C-14 sample preparation and analyses at NIES-TERRA AMS facility

We have made substantial improvements to the NEC 5 MV tandem Pelletron AMS system, such as installing a new type of MC-SNICS ionizer, reconstructing beam lines with the development of the graphite preparation method using an online elemental analyzer for small mass samples down to 1 & mu;gC. To obtain an adequately stable and strong beam current intensity for reliable measurement of small mass samples, we examined graphite position depths (0.35-2.0 mm) related to the optimal geometric conditions to enhance the efficiency of the iron catalyst. Our AMS system generated the most stable and intense beam current at a graphite depth of 1.5-2.0 mm and 2 mg of the iron catalyst, with ionization efficiency of 18-22 %. Under these conditions, the current produced with the 1-10 & mu;gC samples showed a more stable beam current (10-20 & mu;A) and a fivefold increase in beam output duration (greater than 30 min compared to 5 min at 1 & mu;gC). Effects of small carbon graphite-induced isotopic fractionation and higher background was corrected by measuring samples relative to standards of similar mass and a blank. The pMC results were obtained for ultra-small samples ranging from 1 to 50 & mu;gC, calculated relative to adjacent HOxII (NIST SRM 4990C) and IAEA-C1 standards of similar amounts for corrected 14C contents, were approximately in agreement with consensus values overall. By using the method developed in this study, we confirmed the 14C content of ultra-small carbon samples of (1-10 & mu;gC) of IAEA-C8 standards can be measured with precision and accuracy of a few percent.

Automated summary

We have made significant improvements to the NEC 5 MV tandem Pelletron AMS system, including the installation of a new MC-SNICS ionizer and the reconstruction of beam lines. These enhancements have allowed for the reliable measurement of small mass samples and the generation of stable and intense beam currents. By measuring samples relative to standards and correcting for isotopic fractionation and background effects, we have obtained accurate results for ultra-small carbon samples.