Maybe this is a stupid suggestion, but does all this mean that if users want the most accurate results they should keep their PicoMuon detectors in a fridge? And, if so, what would be the optimal temperature for the fridge to be set to?

Not a stupid suggestion at all. Temperature really does matter for detectors like the PicoMuon detector, especially because the silicon photomultipliers (SiPMs) inside produce thermal noise (“dark counts”) that rises…

The gain of a hydrogen horn or dish depends on its aperture which makes sense as bigger aperture means more light collected. But how does this work with a Yagi antenna tuned to hydrogen?

A Yagi works by a different mechanism from a dish or horn, but the same underlying principle still applies: For any antenna, gain and effective aperture are linked by: where:…