[Moltke]

Don’t think it’s necessary to be a clean room environment - the experiments are carried out in high vacuum apparatus anyway.

[null and void]

If you've ever worked with high vacuum equipment you know that to get to 10^-11 torr or higher vacuum you need to keep things scrupulously clean. Not only can bits of crud keep seals from mating properly, they can also deposit out in some of the most amazing places, and they outgas 'sorbed water and organics.