The wave length of an probe is volubly a measure of the size of a structure that it can probe in some detail. The quark structure of protons and neutrons appear at the last minute length - scale of 10−5m or less. This structure was first probed in early 1970's using high energy electron beam produced by a linear acceleration at stanford USA. guess what might have been the order of energy of these electron beams . (Rest mass energy of electron =0.511Mev)