Single Grain Degassing

Degassing of apatite and zircon single crystals is fully automated.  Heating of samples encapsulated in flattened 1 mm Nb tubes occurs with a diode laser.  Samples may be run either spiked with a known quantity of 3He or (in the case of very young samples) run unspiked to attain 4He backgrounds < 3x10-17 mol.  Gas transfer occurs by voulume expansion with > 85% of the sample gas delivered to the mass spectrometer. A full tray (45 wells) of apatite can typically be degassed in 20 hours.  Zircons require more time (45 hours/tray) to ensure complete degassing .  Apatites can be dissolved in nitric on a hot plate.  Zircons require a hydrothermal dissolution process that takes 7 days for 90 grains.  ICP-MS analysis of U & Th is performed at UC Santa Cruz.