EDM experiments are sensitive to electric field strength and observation time. For electrons, you can get much higher fields inside a molecule. For neutrons,

EDM experiments are sensitive to electric field strength and observation time. For electrons, you can get much higher fields inside a molecule. For neutrons, you either need a very cleverly designed crystal or a bottle with ultracold neutrons. The crystal lets you get huge fields and huge particle counts, but relatively short observation times. Ultracold neutrons let you have long observation times (100-300 seconds) but lower fields and much lower particle counts. Protons are probably the hardest of the lot. They need external fields, but they're charged so you can't just bottle them. You're stuck with a holding ring, and needing to make all those v x E corrections.