John Connellan
Valued Senior Member
I've been following this pretty close since about 1986 and have never heard of the method. I do know that some physicists thought a nucleon was necessary to get the energy mass conversion. Now we know that a nucleon need not be present.
I am not sure if the following paper is where I have read about it but it is helping me recall alright. I think it had to do with single-photon pair production.
http://www.astea.ch/physik/pdfs/pairprod.pdf