UNM Assistant Professor of Chemical and Nuclear Engineering Adam Hecht and his research group of graduates and undergraduates have received a $400,000 grant from the Department of Energy. The infusion of funding will allow the group to continue work that the Los Alamos National Laboratory is now using as a foundation for experiments into how nuclear fission actually works.
Knowledge of the details of nuclear fission is important for building new concept nuclear reactors, to figure out how to detect and identify smuggled nuclear materials or for nuclear forensics to understand where nuclear materials may have come from.
In fission, a large nucleus primarily breaks apart into two smaller parts, releasing a lot of energy. Before the parts separate, in the intermediate preformed state, the nucleus stretches like a peanut before popping apart. Theory tells researchers how the nucleus stretches and separates, but to develop the theory, more data is needed. Researchers can’t measure the peanut itself, but they can measure the parts it breaks into when they reconstruct the peanut, the fission fragments. Surprisingly, there is very little data on the separated parts, the fission fragment distributions, and this is where Hecht’s group enters the picture.
“We’re working to do very delicate measurements, atom by atom, to measure the particles coming out of fission," Hecht said. "Our part of the work with Los Alamos is to come up with ideas on how to measure with greater sensitivity than anyone before, and build the equipment to test them out. Its basic scientific research at the moment, but it is likely to be useful when weapons inspectors try to detect nuclear material. The research tells them exactly what daughter nuclei and radiation signatures to expect when plutonium or uranium – 235 is present."
When weapons inspectors search for special nuclear material, it isn’t easily found. Uranium and plutonium do emit low energy photons and alpha and beta particles as they decay, but it’s fairly easy to shield this decay activity in a container.
A possible solution is to excite the material enough internally to cause a small amount of fission activity that can be detected with instruments. If a beam of neutrons or gamma rays could be fired at a suspect container holding special nuclear materials it might produce a strong enough radioactive signal to tell inspectors what is inside. Of course, the process is not as easy as it sounds. The beta decaying daughter products must be understood and characterized and inspectors would have to know how long it takes to “see” a reaction.
Another application of these data is for advanced concepts in nuclear power reactors. There is a good understanding of uranium – 235, the workhorse of modern reactors, as it’s currently used. For reactors using faster neutrons, or other fuels, understanding reaction rates and the heat produced from all the processes following fission requires the type of data Hecht and LANL are pursuing.
Hecht has two Ph.D. candidates on the project, Rick Blakeley and Lena Heffern, who lead the design and testing. Four undergraduate students are also on the project and have independent and complementary research on this project.
The group is now building the UNM Fission Fragment Spectrometer, instrumentation to gather the initial data, and the new grant will allow them to expand them to expand and continue that and perform measurements at LANL.