Super magnet reveals nuclear fission secrets by testing 100 exotic atomic nuclei

Nuclear fission is poised for a comeback after countries worldwide seek newer ways to fuel their energy demands. While wind and solar power plants are being readied at a frantic pace to meet net-zero targets, these technologies cannot address power requirements on demand and do not work around the clock. 

However, the technology, which offers a carbon-free means of generating large amounts of energy, also has its share of problems, such as large amounts of radioactive waste produced during the process.

Newer approaches to nuclear energy, such as small modular or microreactors, look to address these issues. However, the underlying fission reaction is still poorly understood, and researchers are working on ways to address this shortcoming. 

Asymmetry in nuclear fission

In nuclear fission, an isotope of a heavy element such as uranium is bombarded with neutrons. The nucleus of the isotope splits into fragments of elements that are much smaller in size than the original isotope.

However, the fragments formed are always asymmetric, meaning they do not have the same atomic mass or size. 

Researchers attribute this to the shell structure of the nuclei, where a certain number of protons and neutrons are more stable than the rest. Understanding this process has proven difficult since fission typically involves the study of select isotopes commercially used. 

“Fission is a process that has been investigated for a very long time, but only for a very limited number of isotopes,” said Andreas Heinz, associate professor in High Energy and Plasma Physics at Chalmers University of Technology.

“Typically, what one does is bombard the isotope of interest with, for example, neutrons, and then one observes fission. For long-lived isotopes such as uranium, this is no problem, but with much shorter-lived nuclei, it is much trickier.”

So, Hainz’s team decided to study nuclei of 100 exotic elements, such as platinum, mercury, and lead, to understand the fission process better. 

How were the nuclei studied? 

The research team deliberately chose elements whose nuclei contain a larger number of protons than neutrons. 

“What we are trying to find out is which shell effects are responsible for the nucleus splitting in one light and one heavy part. This is very difficult to predict, and also difficult to measure experimentally.” Heinz added in the press release. 

“We have measured a region of nuclei undergoing fission, which has not been investigated very thoroughly up to now.”

The team was surprised to find that the reason for the additional stability of the smaller fragment in fission reactions was due to a specific number of protons, i.e., 36. 

“This study finds evidence that it is a shell effect in the number of protons of the light fission fragments, which is responsible for a lot of the evolution [that] we have not previously seen,” Heinz concluded. 

Although it does not explain the highly complex fission reaction completely, the research sheds light on one aspect of fission research and the role of nuclear shells in the outcome. 

The research findings were published in the journal Nature.