An Apparatus for High-Precision Helium Diffusion Measurements from Minerals

We describe a simple and low-cost apparatus for in-vacuum helium diffusion measurements that reduces temperature gradients, set point overshoot, and ramping times compared with conventional resistance furnace techniques. The sample, suspended by a thin wire in a vacuum chamber, is heated by radiation from an Al-coated projector bulb passed through a sapphire viewport. Because the total mass of the sample package being heated is small (typically <100 mg), thermal gradients and thermal inertia are both small. In experiments with set points between 100 and 750 °C, this apparatus can achieve set point from room temperature in ∼90 s, usually with <3 °C of set point overshoot persisting for just a few seconds. Helium diffusion coefficient measurements indirectly indicate that temperatures are precise and reproducible to better than ±2 °C.