Rapid Vaporization of Activated Lithium for Detector Testing*

A system has been developed that uses high current to rapidly and consistently vaporize activated materials which have been coated onto a tungsten ribbon filament. This system will be used to test the Short-Lived Isotope Counting System (SLICS), which is being developed to measure the quantity of short-lived radioactive fusion products created in the Laboratory for Laser Energetics (LLE) Omega facility. SLICS is tested with simulated fusion products by capturing rapidly vaporized materials after activation with a beam in the SUNY Geneseo Pelletron accelerator. Using lithium as the target material for a deuteron beam, lithium-8 is produced and decays through beta emission with a half-life of 838 milliseconds. The vaporization system uses a thyristor to quickly discharge high-voltage capacitors, delivering 500-1000 Amps of current through tungsten filaments during a 5-15 millisecond time period. The maximum temperature of the filament, and therefore the vaporization rate of the lithium, depends on the capacitor voltage, ribbon geometry, and conductance of the coating. The relationships between these parameters are reported for uncoated tungsten filaments.