The size of the helium nucleus: then and now

摘要

Rutherford developed his revolutionary model of the atom based on experiments using helium nuclei scattered by a thin gold foil. In this paper, we review the measurements of the size of the helium nucleus, focusing on spectroscopic techniques. We touch on the ‘proton radius puzzle’ that has incited a great deal of interest in high-resolution spectroscopy of the most fundamental atoms. We find that for an absolute value of the size of the helium nucleus, the theoretical advance that will give a new determination is just around the corner.