Los Alamos National Laboratory physicists are paying tribute to a Manhattan Project scientist who discovered a significant effect that occurs during a certain type of nuclear fusion. The unique type of resonance that arises during deuterium-tritium (DT) fusion contributed to the beginning of life on Earth.
You see, something special happens when deuterium and tritium—both isotopes of hydrogen—get together, or fuse. Fusing deuterium (an atomic nucleus that consists of a proton and a neutron) and tritium (a proton and two neutrons) forms, for a very short time, a relatively stable arrangement of two protons and three neutrons called a compound system.
After an extremely short interval (think fractions of fractions of fractions of a second), the system falls apart to produce a neutron and a helium nucleus, also called an alpha particle. This reaction produces energy. In fact, it produces a huge amount of energy.
Now, sometimes, not always (you have to get lucky), these types of energy-producing reactions happen really quickly, with extremely high reaction rates. This “luck” is due to an effect called “resonance.”
Resonance is familiar in the everyday world—think of a soprano breaking a wine glass by hitting and sustaining the perfect ear-piercing note. When the frequency of the note is just right, the energy in the sound waves is absorbed by the wine glass, causing the glass to vibrate. If the soprano sustains the high-pitched musical note for too long—crash! The vibrations of the glass will get too big, and the wine glass will shatter.
Resonance also operates in the submicroscopic world of hydrogen nuclei. When deuterium and tritium come together and react, they form a system that resonates with its own natural frequencies. This resonance greatly increases the intensity of the DT interaction, which leads to greatly increased production of neutrons and alpha particles. In fact, the reaction is about 100 times faster than it would be without the resonance. The resonance enhancement of the reaction means more energy can be created more easily. That’s why deuterium and tritium are so often used to fuel fusion energy experiments.
Physicists now understand that nuclear resonance was a factor in the Big Bang—the DT reaction that created the universe. “That DT reaction and the unique resonance of fusing nuclei that took place during the Big Bang created most of the helium in our universe,” says Mark Chadwick, interim deputy director for Science, Technology, and Engineering at Los Alamos. Helium, enhanced by the unique DT resonance, became the source for about a quarter of the carbon and other heavier elements in the human body. “Without this resonance, not only would fusion energy be beyond reach, but the universe itself might look very different, perhaps unable to support life,” Chadwick says. “Basically, about one fourth of the human body is made up of the products of DT fusion.”
Although DT resonance has been essential to life for nearly 14 billion years, it wasn’t recognized as such until 1945. That year, Egon Bretscher, a Manhattan Project physicist working at Los Alamos, was the first person to identify and measure the particular DT resonance essential to the formation of helium.
“This resonant enhancement was a game changer, opening up the potential for nuclear fusion technologies,” Chadwick says.
Despite the significance of this discovery, Chadwick says Bretscher did not receive recognition for his discovery. So, in honor of Bretscher’s role in identifying, characterizing, and measuring the DT reaction resonance, Chadwick and his colleague Mark Paris have proposed naming the resonant state created during the DT reaction after the Manhattan Project scientist. “We propose that the nuclear science community refer to it as the ‘Bretscher state,’” Chadwick says, adding that he hopes that others in nuclear astrophysics adopt the term. “Naming this state after him acknowledges his work and Los Alamos National Laboratory’s rich history in nuclear physics.”
To learn more, read Chadwick’s paper, “Big Bang fusion 13.8 billion years ago and its importance today,” in the August 2023 edition of the American Nuclear Society’s Nuclear News. ★
Mark Paris contributed to this article.