TUNL Researchers Recreate Historic Fusion Measurement

Modern version of the 1938 experiment that first observed DT fusion performed at TUNL

Werner Tornow and Sean Finch with setup to measure DT fusion
Photo of TUNL researchers Werner Tornow and Sean Finch along with the experiment setup used to recreate the historic first measurement of DT fusion.

The promise of fusion energy rides on the unusually large deuterium-tritium (DT) reaction rate. Deuterium and tritium—heavy isotopes of hydrogen—fuse to release energy, and DT fusion is not only the basis of the hydrogen bomb, but has also been the leading candidate for practical reactors like Tokamaks, for example. In 1955, Edward Teller credited Emil Konopinski with first recognizing this at Oppenheimer’s 1942 Berkeley conference. A team of researchers from Los Alamos and TUNL have traced the origins of this insight even earlier to a pioneering 1938 experiment performed by A.J. Ruhlig at the University of Michigan.   Following a suggestion of the Director of Los Alamos National Laboratory to redo Ruhlig’s experiment with modern equipment., measurements were repeated at TUNL.

A 1938 Physical Review paper by Arthur Ruhlig reported detecting >14 MeV neutrons in DD experiments. Ruhlig hypothesized these as secondary DT(n,a) reactions from recoiling tritons following D(D,p)T, concluding that DT fusion must be “exceedingly probable.” His prescient insight was overlooked for eight decades. Until recently, Ruhlig’s paper had never been cited for its first DT observation, though circumstantial evidence indicates that Konopinski had read it. The TUNL-Los Alamos team performed the first experiment to duplicate with modern detector technology the seminal 1938 DT fusion experiment of Ruhlig. The DT/DD ratio depends on the triton stopping power. As accurate triton stopping powers are important for DT fusion research facilities, such as NIF and OMEGA, this opens the possibility of using the present experimental technique to measure triton stopping powers in various deuterated targets. In contrast to NIF and OMEGA, the research team has performed for the first time DT secondary reaction experiments at a low-energy nuclear physics facility.

This research has been published as an "Editor's Suggestion" in Physical Review C:

W. Tornow, S.W. Finch, J.B. Wilhelmy, M.B. Chadwick, G.M. Hale, J.P. Lestone, and M.W. Paris, Phys. Rev. C 111, 064618 (2025), “Modern version of the uncited 1938 experiment that first observed DT fusion”.  DOI: 10.1103/PhysRevC.111.064618

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