T04_P26

Production of radiocarbon micro-samples at ANSTO

Hua Q¹, Levchenko V¹, Smith A¹, Varley S¹, Williams A², Yang B¹, Zoppi U³

¹Australian Nuclear Science & Technology Organization (ansto), Lucas Heights, Australia, ²Deceased, 9th February 2021., , , ³Deceased, 27the March 2016., ,

ANSTO’s Centre for Accelerator Science has been providing radiocarbon analyses for nearly three decades using our solid sample ion sources. From the beginning, there was a need to refine capability for ever smaller samples. This paper summarises the various approaches we have developed to deal with samples containing just a few micrograms of carbon (µgC). Initially we began optimising our ‘conventional’ graphitisation furnaces. We decreased the reaction volume to ~ 3.5 mL and investigated various catalysts and means of activating them. Today, we operate a bank of 24 conventional furnaces for samples containing >10 µgC. In 2003 we developed novel, Laser Heated Furnaces using a focused infrared laser to directly heat the Fe catalyst in a quartz crucible, with temperature measured indirectly by infrared thermometry. These units have a reaction volume of ~0.25 mL. Smaller volumes allow a higher initial pressure for small amounts of CO₂, improving the graphite yield. Efficient trapping of by-product H₂O and careful selection of the catalyst are also key to optimising graphitisation of micro-samples. By localising the heated region within the reaction volume, the addition of extraneous carbon is minimised and samples containing just 1-2 µgC are routinely prepared.

The fabrication approach developed for the LHF was adapted to a new type of miniaturised furnace, namely micro-conventional furnaces (MCF). These furnaces have a minimum reaction volume of 0.9 mL with a small tube furnace for catalyst heating. Variable temperature cold traps have been developed to optimise sample processing with samples containing 5 µgC routinely prepared.