The deformed nucleus of zirconium-80 is lighter than the sum of the masses of its 40 protons and 40 neutrons. Through E=mc2, the missing mass can be converted to binding energy. The binding energy holds the nucleus together. Credit: Facility for Rare Isotope Beams
A team of researchers, including scientists from the National Superconducting Cyclotron Laboratory (NSCL) and the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU), have solved the case of zirconium-80’s missing mass.
To be fair, they also broke the case. Experimentalists showed that zirconium-80–a zirconium atom with 40 protons and 40 neutrons in its core or nucleus–is lighter than expected, using NSCL’s unparalleled ability to create rare isotopes and analyze them. Then FRIB’s theorists were able to account for that missing piece using advanced nuclear models and novel statistical methods.
“The interaction between nuclear theorists and experimentalists is like a coordinated dance,” said Alec Hamaker, a graduate research assistant at FRIB and first author of the study the team published 25 November in the journal Nature Physics. “Each takes turns leading and following each other. “
“Sometimes theory makes predictions ahead of time, and other times experiments find things that weren’t expected,” said Ryan Ringle, FRIB Laboratory senior scientist, who was in the group that made the zirconium-80 mass measurement. Ringle is an adjunct associate professor of Physics at FRIB and MSU, in the College of Natural Science’s Department of Physics and Astronomy.
” They push each other, and that leads to a better understanding the nucleus which basically makes up all that we interact with,” he stated.
This story goes beyond one nucleus. It’s also a glimpse of FRIB’s power, which is a user facility for nuclear science supported by the Office of Nuclear Physics at the U.S. Department of Energy Office of Science.
When user operations start next year, nuclear scientists around the world will have the opportunity to use FRIB’s technology for rare isotopes. FRIB experts will be available to help them understand the implications of the studies. This knowledge can be used to improve cancer treatment and science.
” As we move into the FRIB age, we can perform measurements like what we did here and many more,” Ringle stated. Ringle said, “We can push even further.” We have enough potential to continue learning for many decades. “
That said, zirconium-80 is a really interesting nucleus in its own right.
For starters, it is a difficult nucleus to create, but NSCL’s specialty is making rare nuclei. The facility produced enough zirconium-80 to enable Ringle, Hamaker, and their colleagues to determine its mass with unprecedented precision. They used what is known as a Penning trap mass spectrometer at NSCL’s Low Energy-Beam (LEBIT) Facility.
” People have measured this mass before but not this accurately,” Hamaker stated. That revealed some fascinating physics. “
” When we measure mass at such a precise level, we are actually measuring the amount that is missing,” Ringle stated. Ringle stated that the nucleus’ mass is not just the sum of its protons or neutrons. The nucleus is held together by missing mass. “
This is where one the most well-known equations in science helps to explain things. In Albert Einstein’s E = mc2, the E stands for energy and m stands for mass (c is the symbol for the speed of light). This implies that energy and mass are equal, but this is only noticeable under extreme conditions such as those at the core an atom.
When a nucleus has more binding energy–meaning it’s got a tighter hold of its protons and neutrons–it’ll have more missing mass. That helps explain the zirconium-80 situation. The nucleus of the zirconium is tightly bound and the new measurement showed that this binding was stronger than expected.
This meant that FRIB’s theory-makers had to come up with a solution. They could look back to decades-old predictions to provide the answer. For example, theorists suspected that the zirconium-80 nucleus could be magic.
Every so often, a nucleus surprises its mass expectations with a unique number of neutrons or protons. These are known as magic numbers by physicists. Theory posited that zirconium-80 had a special number of protons and neutrons, making it doubly magic.
Earlier experiments have shown that zirconium-80 is shaped more like a rugby ball or American football than sphere. This shape may give rise to double magicity, according to theorists. With the most precise measurement of zirconium-80’s mass to date, the scientists could support these ideas with solid data.
“Theorists had predicted that zirconium-80 was a deformed doubly-magic nucleus over 30 years ago,” Hamaker said. It took the experimentalists some time to learn the dance and give evidence to the theorists. Theorists now have the data to help them figure out the next steps. “
The dance goes on and, to expand the metaphor, NSCL and FRIB offer the best ballrooms in which to perform. It is home to a unique facility, highly qualified staff, and the nation’s highest-ranked graduate program in nuclear physics.
” I am able work onsite at a National User Facility on topics at The forefront of Nuclear Science,” Hamaker stated. “This has given me the opportunity to build relationships with many of the laboratory’s researchers and staff. Their dedication to science and world-leading equipment made the project a success.
Alec Hamaker, Precision mass measurement of lightweight self-conjugate nucleus 80Zr, Nature Physics (2021). DOI: 10.1038/s41567-021-01395-w. www.nature.com/articles/s41567-021-01395-w
A doubly magic discovery (2021, November 25)
retrieved 25 November 2021
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