Shown in the diagram is a He3 nucleus consisting of a proton-neutron pair and a second proton.  Other nuclei in the helium target can consist of a proton-proton pair and the neutron.  Bonded pairs exist like this in the nucleus about 25% of the time.  When electrons are fired into the target, some of them knock out the single proton or neutron, momentarily leaving behind the bonded proton-neutron or proton-proton pair. The bonded pair then disintegrates almost immediately, the two particles repelling each other identically, whether the pair was proton-neutron or proton-proton.  Theoretical physicists have long thought that bonded pairs existed and are responsible for holding the atom's nucleus together.  Dr. Weinstein's experiment provided direct experimental evidence that they were correct.