PhysicsMicrocalorimeter Muonic Spectroscopy Sharpens Beryllium-9 RadiusA metallic magnetic calorimeter measures the muonic 2p→1s x ray at 33,391.48(34) eV, yielding a 2.5506(51) fm charge radius.nucl-exnucl-thphysicsJul 28, 20264 min2607.13690