sourcing electrons

In my last post I mentioned that I received two packages in the mail. What was in the other?

Tungsten SEM filaments!

I can find a bunch of references to the Cambridge S4-10 (or S-410), but very little about the unit itself. Ah, well. It's not particularly important. While I'm not building a SEM, my planned experiments will require an electron source, so these filaments are a good option. And since I purchased this unused lot of 20 for $15 shipped, it's economical too. I think this supply will outlast my needs.