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Title: A cold finger cooling system for the efficient graphitisation of microgramsized
Authors: Yang, B
Smith, AM
Hua, Q
Keywords: Cooling systems
Issue Date: 24-Mar-2011
Publisher: 12th International Conference on Accelerator Mass Spectrometry (AMS-12)
Citation: Yang, B., Smith, A., Hua, Q. (2011). A cold finger cooling system for the efficient graphitisation of microgramsized. 12th International Conference on Accelerator Mass Spectrometry (AMS 12), 20th - 25th March 2011. Museum of New Zealand: Te Papa Tongarewa, Wellington, New Zealand.
Abstract: At ANSTO we use the Bosch reaction to convert sample CO2 to graphite for production of our radiocarbon AMS targets. Key to the efficient graphitisation of ultra-small samples is the type of iron catalyst and the effective trapping of water vapour in a ‘cold finger’ during the reaction. We have developed a simple liquid nitrogen cooling system that enables us to rapidly adjust the cold finger temperature in our laser-heated ‘microfurnace’, optimised for the graphitisation of microgram-sized carbon samples. This system is used to firstly transfer the CO2 into the microfurnace, to maintain the cold finger at -80°C for ~ 5 minutes while the CO2 is converted to CO and then at -160°C for ~ 25 minutes for the remainder of the reaction as the CO is converted to graphite. It comprises a machined aluminium cylinder mounted in the insulated cap of a 600 ml Dewar. The lower end is submerged in liquid nitrogen (LN2). The upper end has a smaller diameter which is wound with an electric heating element and is provided with a thermocouple and a central hole into which the cold finger is inserted. Electrical power to the heater is adjusted by PID control, permitting the cold finger temperature to be adjusted over the range -50°C to -160°C at rates of up to 40°C/min. This simple system uses modest amounts of LN2 (typically < 0.2 L/hr during graphitisation) and is compact and reliable. We have used it to produce over 120 AMS targets containing between 5 and 20 μg of carbon, with conversion efficiencies for 5 μg targets of typically 90-100%. We are currently modifying this cooling system for use with our conventional graphitisation reactors. Copyright (c) 2011 AMS12
Gov't Doc #: 4442
Appears in Collections:Conference Publications

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