Dyson, Freeman J. "Electromagnetic Shift of Energy Levels" in The Physical Review, second series, vol 73, no 6, March 15, 1948. The paperbound issue offered in the original wrappers. Very nice copy, with the original owner's name in (small) pen at top center of the front wrapper. Scarce. $150
The fine description of the young Dyson is from the superior History of Math website of St. Andrews (found here):
"Dyson worked closely with Bethe and became deeply impressed by him (as all Bethe's students were.) In 1948 Dyson published a paper on Lamb shift in Physical Review called The Electromagnetic Shift of Energy Levels. This was the first paper he had published on physics, and it showed his remarkable ability at calculation as well as a deep physical understanding. It is clear that at this time Dyson was considered to be an extraordinarily gifted and able student. Bethe persuaded Oppenheimer to take Dyson on at the Institute for Advanced Study at Princeton. He wrote in his letter of recommendation:-
Mr Dyson is absolutely unusual in his ability and accomplishments. I can say without reservation that he is the best I have ever had or observed."