A Gas Ion Source for Radiocarbon Measurements at 200 kV

Abstract

ABSTRACT. The novel tabletop miniaturized radiocarbon dating system (MICADAS) at ETH Zurich features a hybrid Cs sputter negative ion source for the measurement of solid graphite and gaseous CO 2 samples. The source produces stable currents of up to 6 µA C -out of gaseous samples with an efficiency of 3-6%. A gas feeding system has been set up that enables constant dosing of CO 2 into the Cs sputter ion source and ensures stable measuring conditions. The system is based on a syringe in which CO 2 gas is mixed with He and then pressed continuously into the ion source at a constant flow rate. Minimized volumes allow feeding samples of 3-30 µg carbon quantitatively into the ion source. In order to test the performance of the system, several standards and blanks have successfully been measured. The ratios of 14 C/ 12 C could be repeated within statistical errors to better than 1.0% and the 13 C/ 12 C ratios to better than 0.2%. The blank was <1 pMC.

A novel approach for construction of radiocarbon-based chronologies for speleothems

“…For this, the top 176 1mm of NIED08-05 was milled at an extremely high resolution (100μm per 177 sample) over four different tracks. Approximately 0.8 mg of carbonate were 178 dissolved in 85% H3PO4, and the CO2 produced was measured directly on the 179 MICADAS using a Gas Ion Source (GIS) system (Ruff et al, 2007), again at LIP. A 180 series of laboratory standards (Oxalic acid II, IAEA C1 and C2, and a modern 181 coral standard) were used to ensure high precision: Oxalic acid II was measured 182 to a precision of better than 2‰ for graphite and 10‰ for GIS analyses.…”

Radiocarbon Analysis of Carbonaceous Aerosols: Recent Developments

“…[24] These problems were solved with the implementation of a gas ion source [26] in the next generation of small AMS machines: the mini radiocarbon dating system MI-CADAS [27] became operational in 2005 for 14 C measurements in the 1 + charge state. It is a prototype of AMS spectrometers, which achieve the terminal voltage for 14 C measurement of 195 kV with a vacuuminsulated high-voltage platform in contrast to previous systems based on conventional particle accelerators.…”

“…The self-constructed ion source of MICADAS was modified in order to insert gases to the focal point of the sputtering caesium beam. [26] CO 2 is released from the sealed ampoules in a cracker, transferred to a syringe, mixed with helium, and fed to the ion source via a glass capillary (Fig. 3).…”

“…In combination with the uncertain success of solid target production mentioned above, the substantially lower carbon blank contribution (on average 55 ng per analysis compared to 750 ng for gaseous and solid targets, respectively) indicates the superiority of the gaseous 14 C measurements. [29] Another advantage of a gas ion source is the potential of on-line coupled systems of separation or combustion of organic compounds. Coupling an elemental analyzer (EA) with AMS generates a multifunctional system, because it provides automated on- 2.…”

Applications of Radiocarbon Dating Method

“…Because of the small amount of carbon required (down to 2.5 μg; Ruff et al 2007), dating of specific cell types and molecules is now possible. A clinical study by Robertson et al (2001) determined the formation of senile plaques (SP) and neurofibrillary tangles (NFT).…”