Unipd research team reexamines a 1950s nuclear fusion concept
29.09.2025
A research team from the Department of Physics and Astronomy “G. Galilei” (DFA) at the University of Padua has “dusted off” and reexamined an old nuclear fusion concept dating back to the 1950s, which envisions the combustion of solid lithium-6 deuteride at room temperature using neutrons. This process, known as the Jetter cycle, named after its proponent Ulrich Jetter, offers intriguing prospects for energy production in devices not based on plasma confinement. This line of research came to a halt in the 1970s, during the Cold War, due to restrictions on publishing results regarding nuclear reactions, as they closely resembled reactions triggered in some nuclear weapon designs. Only one researcher, Rand McNally, continued this line of work, and his internal reports at the renowned Oak Ridge Laboratory were declassified only in the 1990s.
Lorenzo Fortunato, professor at DFA, after “rediscovering” these old articles and informal manuscripts, assembled a small research team made up of his undergraduate and master’s thesis students and staff from the National Institute for Nuclear Physics (INFN). The group investigated the complex network of nuclear reactions induced by a neutron beam in lithium crystals.
“Using modern compilations of nuclear data, we predicted the time evolution and isotopic composition of a network of thermonuclear reactions involving the Jetter cycle (neutrons + Lithium-6) and the Post cycle (protons + Lithium-6), a similar process triggered by protons instead of neutrons,” explains Prof. Fortunato. “In an ideal case, at the beginning there are only lithium and deuterium (purple and blue), the components of the fuel crystal, and the neutrons irradiating it. Over time, after just a few millionths of a second, the material is essentially converted into alpha particles—helium-4 nuclei, inert and harmless—plus a small amount of tritium and some secondary neutrons. The latter can be potentially harmful to health but can be contained with an external ‘jacket’ of absorbing material, such as graphite.”
The study remains at a purely academic level, but modeling is the first step toward building test devices. The technological challenges required to create a prototype—such as controlled production of intense neutron beams and the conversion of the thermal energy produced into usable electrical energy—are certainly demanding, but perhaps within reach of modern experimenters.
The simulations, easily repeatable with a code made publicly available in the University’s Data Repository, were conducted in two typical scenarios.
In an ideal scenario, which does not consider the energy losses from the motion of charged ions in matter, a huge potential energy release is obtained. More realistic calculations, which include the braking effect of charged particles, scale down this energy production but still indicate that slow and controlled nuclear combustion processes achieved by injecting neutrons could be up to a thousand times more advantageous than energy obtained, for example, from chemical combustion. All this without releasing dangerous radiation, producing harmful byproducts, or creating the risk of an uncontrolled chain reaction, as could unfortunately occur in traditional fission power plants.
The authors of the theoretical study challenge experimental colleagues to initiate an applied research program leading to new experiments on these fusion cycles, which could pave the way for new plasma-free fusion reactors—intrinsically safe and without the need for tritium as fuel. Further theoretical studies and experimental data on the nuclear reactions involved are, however, necessary to fully assess their potential.
