Here’s what you’ll learn when you read this story:

• Today, many fusion reactors rely on deuterium and tritium—heavy isotopes of hydrogen—to power fusion reactions. But where did this idea come from?
• Although the Manhattan Project makes mention of the advantages of deuterium-tritium reactions, they only vaguely source pre-war research.
• After some sleuthing, scientists at Los Alamos National Laboratory discovered the work of little-known physicist Arthur Ruhlig, and recreated his 1938 experiment to better understand his unknown-yet-groundbreaking contribution to fusion physics.

This story is a collaboration with Biography.com.

Around the world, scientists are working diligently to perfect ways to fuse deuterium and tritium—two heavy isotopes of hydrogen—through nuclear fusion. This DT fuel will be at the heart of the International Thermonuclear Experimental Reactor (ITER) in southern France, which will be the world’s most advanced nuclear reactor once it’s up and running in the 2030s.

The energy-producing magic of these two isotopes has been known for more than 80 years. One of the earliest mentions of the advantages of DT interactions came from Emil Konopinski—an American scientist who worked on the Manhattan project during World War II—who famously mentioned at a July, 1942 Berkeley physics conference that deuterium and tritium would be good components for a future thermonuclear bomb. There was just one question: Where did this idea to use deuterium and tritium even come from?

That’s the question that Los Alamos Laboratory’s Mark Chadwick and Mark Paris wondered as they searched for the original mind behind using DT fuel for fusion reactions in an attempt to to compile a compendium on the early history of fusion research. After a little bit of sleuthing, Chadwick and Paris found a 1986 audio recording of Konopinski, who mentions being inspired by “pre-war” research.

Scouring physics literature between 1934 (the year tritium was discovered) and the start of the war, Paris stumbled across a 1938 paper written by little-known physicist Arthur Ruhlig titled “Search for Gamma-Rays from the Deuteron-Deuteron Reaction.”

Ruhlig was studying the interactions between deuterium and deuterons—the nuclei of deuterium atoms—and mentioned observing protons with very high energies that were likely produced by secondary deuterium-tritium fusion neutrons. According to Chadwick and Paris, Ruhlig noted that a DT reaction “must be an exceedingly probable one,” but the paper received few citations. The plot thickened when the researchers realized that Ruhlig and Konopinski overlapped at the University of Michigan, and even shared the mentor George Uhlenbeck, who helped discover the electron’s spin.

With serious evidence pointing to Ruhlig being the initial mind behind deuterium-tritium fusion, Chadwick, Paris, and a team of physicists from Duke University decided to recreate Ruhlig’s experiment to understand the physicists’ insights and role in fusion history.

“Replicating his experiment helped us interpret his work and better understand his role, and what proved to be his essentially correct conclusions,” Chadwick said in a press statement. “The course of nuclear fuel physics has borne out the profound consequences of Arthur Ruhlig’s clever insight.”

The team used the Tandem accelerator at Duke University to essentially recreate Ruhlig’s original experiment step-by-step, publishing the results in the journal Physical Review C. The team found the expected secondary DT reactions, and though the ratio of these interactions was smaller than Ruhlig’s original estimate, the experiment nonetheless provided extremely strong evidence that Ruhlig’s initial tests likely mark the beginning of humanity’s investigation into deuterium-tritium fusion.

“Regardless of the inconsistency of Ruhlig’s rate of fusion against our modern understanding, our replication leaves no doubt that he was at least qualitatively correct when he said that DT fusion was ‘exceedingly probable,’” Chadwick said in a press statement. “I think we’re all proud to lift Arthur Ruhlig up again out of history as an important contributor to ongoing, vital research.”