Physics Colloquium - Revisiting Fusion’s Beginnings: A 1938 Mystery Meets a Modern Duke-Los Alamos Experiment

In 1938, Arthur Ruhlig at the University of Michigan reported an unexpected result while studying deuterium-deuterium fusion: evidence that tritium produced in one nuclear reaction could fuse with deuterium in a second. His brief Physical Review letter, now associated with the earliest observation of deuterium-tritium fusion, went unrecognized in the published literature for decades. Its rediscovery raised a question that could be tested experimentally: what would a modern recreation reveal?

This colloquium connects fusion's early history with a recent experiment by Duke's Triangle Universities Nuclear Laboratory and Los Alamos National Laboratory. Using modern neutron detection and complementary measurements, the team recreated the fusion reaction sequence, in agreement with modern calculations. The result illustrates both the power of revisiting historical experiments and the difficulty of interpreting observations from incomplete records. I will place this investigation within the broader development of fusion physics, including the discovery of the remarkably favorable nuclear resonance that makes deuterium-tritium fusion so attractive. The talk will conclude with connections to present-day NIF fusion diagnostics and the challenges of fusion energy, emphasizing the interplay of curiosity, experiment,
theory, and scientific surprise.