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 r amping times compared with conventional resistance furnace techniques. The sample, suspended by a thin wire in a vacuum chamber, is heated by radiatio n from an Al-coated projector bulb passed through a sapphire viewport. Beca use the total mass of the sample package being heated is small (typically < 100 mg), thermal gradients and thermal inertia are both small. In experimen ts with set points between 100 and 750 degrees C, this apparatus can achiev e set point from room temperature in similar to 90 s, usually with <3 degre es C of set point overshoot persisting for just a few seconds. Helium diffu sion coefficient measurements indirectly indicate that temperatures are pre cise and reproducible to better than +/-2 degrees C.