Changing the mass spectrometer filament in the argon lab

Mass spectrometers allow the precise measurement of ratios of isotopes. In our New Mexico Geochronology Laboratory, our noble gas spectrometers measure isotopes of argon (Ar). We use the ⁴⁰Ar/³⁹Ar ratio to calculate the age of rocks and minerals.

The tungsten filament in the spectrometer ionizes the argon gas molecules, which are then accelerated past a large magnet. The magnet deflects the ions variably depending on their mass/charge ratio and separates them for measurement.

These filaments last for many years before they need replacement and require precise alignment to work properly. This particular filament was last replaced in 2016. Changing the filament is a relatively big deal because it can take up to a year for the instrument to recover to optimal working conditions. Also, following filament change, the entire mass spectrometer has to be covered with an oven and baked at 300°C for a couple of days to achieve ultra-high vacuum. This baking process is hard on delicate components and increases the possibility of a vacuum seal failing, so changing a filament is a big event for any noble gas lab.

The New Mexico Geochronology Laboratory is one of the most sophisticated facilities of its kind anywhere. The laboratory has dated materials from all over New Mexico and the rest of the world.