US physicists replicate forgotten nuclear fusion experiment from 1938

US physicists at Los Alamos have successfully replicated a nearly 90-year-old nuclear fusion experiment originally conducted in 1938 by University of Michigan physicist A. J. Ruhlig. Ruhlig’s experiment was the first to observe triton-deuterium (DT) fusion, a reaction now fundamental to nuclear fusion research and national security applications. Although Ruhlig overestimated the fusion reaction rate compared to modern understanding, his qualitative insight that DT fusion occurs with high probability when deuterium and tritium nuclei are brought close together has been validated. The replication helped clarify Ruhlig’s role in the early development of nuclear fuel physics and confirmed the significance of his accidental discovery. The modern experiment employed advanced neutron detection methods and introduced a novel approach to measure low-energy triton stopping powers in deuterium-containing materials. These measurements are directly relevant to ongoing fusion research, including efforts at the National Ignition Facility (NIF) and other fusion energy projects. While the replicated experiment observed secondary DT reactions