Kenneth Bainbridge was an early pioneer of mass spectroscopy. The Wikipedia article about him says:
He used this instrument to verify Albert Einstein's mass-energy equivalence, E = mc2
with a footnote to this paywalled paper from 1933. (Thanks, Physical Review, for making sure that I can't read a paper from almost a century ago.) The paper does not seem to be available from SciHub. WP also gives a quote from a 1933 book by Aston, which says:
By establishing accurate comparisons of the masses of the light particles concerned in nuclear disintegrations, particularly that of 7Li, discovered by Cockcroft and Walton, he achieved a noteworthy triumph in the experimental proof of the fundamental theory of Einstein of the equivalence of mass and energy.
A 1997 obituary in Physics Today says:
[...] he continued to use his mass spectrographs to measure isotopic masses and to compare nuclear mass differences with the energies measured in transitions as a check on Einstein's mass-energy equivalence.
Can anyone explain what measurement he actually did? 7Li is a stable element. One quote refers to "transitions," the other to "nuclear disintegrations." Would this be a beta decay from 7Be (half-life of 50 days) to 7Li? Or maybe disintegration of 7Li by neutrons or something?