Developing Ultra Small-Scale Radiocarbon Sample Measurement at the University of Tokyo

Abstract

ABSTRACT. We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO 2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12 C 4 beam currents generated by small standards and ion beam currents (15-30 A) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14 C/ 12 C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 A, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 g of modern and 1 g of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.

Widespread collapse of the Ross Ice Shelf during the late Holocene

“…Target graphite samples were then measured at the W. M. Keck Carbon Cycle Accelerator Mass Spectrometry facility at the University of California, Irvine. Radiocarbon for total organic carbon was measured at the accelerator MS facility of the University of Tokyo (42). All radiocarbon values were corrected for the contribution of methyl carbon obtained from MeOH (Δ 14 C = −991‰) during the esterification by isotope mass balance.…”

Radiocarbon variability recorded in coral skeletons from the northwest of Luzon Island, Philippines

“…PCURIN03 was micro-sampled at 0.8-mm intervals, and the Sr/Ca ratios were measured to determine sample age using the method of Hirabayashi et al (2013). Each sample (2-5 mg) from PCURIN03 was prepared using a specially designed vacuum line for small samples (Yokoyama et al 2010;Hirabayashi et al 2017b), and 6-10 mg of each sample from PCURIN03 was prepared following the method of Yokoyama et al (2007) (Additional file 1: Table S1). We measured 55 samples with ages ranging from 1968 to 1994.…”

Carbon background and ionization yield of an AMS system during 14C measurements of microgram-size graphite samples

“…[11]). To maximize the ionization yield of microgram-size graphite targets we investigated different target geometries systematically.…”