Just surveyed a homemade collimator for some of our researchers. It consisted of hundreds of extremely thin, extremely closely-spaced kapton/boron sheets.
It is elegant in its sheet simplicity. Neutrons flying straight and true pass through unimpeded. Neutrons deviating even slightly from their approved flight plan get a snootful of boron.
I mentioned it was homemade, right? Staring at this marvel, I asked the scientist how long it took to assemble. He barked out a little chuckle. “Oh! A long time. A very long time.”
Science geeks are awesome. They’re the right kind of crazy.