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), having solved the case of the missing mass of zirconium-80.
To be fair, they broke the case as well. The experimenters showed that zirconium-80 – a zirconium atom with 40 protons and 40 neutrons in its nucleus or nucleus – is lighter than expected, using NSCL’s unparalleled ability to create rare isotopes and analyze them. Then, FRIB theorists were able to explain this missing piece using advanced nuclear models and new statistical methods.
“The interaction between nuclear theorists and experimenters is like a coordinated dance,” said Alec Hamaker, FRIB graduate research assistant and first author of the study published by the team in the journal. Physics of Nature. “Each in turn leads and follows the other.”
“Sometimes the theory makes predictions ahead of time, and other times the experiments find things you didn’t expect,” said Ryan Ringle, senior scientist at the FRIB lab, who was part of the group that carried out the mass measurement of zirconium-80. Ringle is also an Assistant Associate Professor of Physics at FRIB and in the Department of Physics and Astronomy at MSU at the College of Natural Science.
“They push each other and that translates into a better understanding of the core, which is basically everything we interact with,” he said.
This story is therefore bigger than a nucleus. In a way, it’s a taste of the power of FRIB, a nuclear science user facility supported by the Office of Nuclear Physics of the US Department of Energy Office of Science.
When user operations begin next year, nuclear scientists around the world will have the chance to work with FRIB’s technology to create rare isotopes that would be impossible to study elsewhere. They will also have the opportunity to work with FRIB experts to understand the results of these studies and their implications. This knowledge has many applications, from helping scientists better understand the universe to improving cancer treatments.
“As we move forward into the FRIB era, we can perform measurements like we have done here and much more,” said Ringle. “We can go further. There is enough capacity here to allow us to learn for decades.
Having said that, zirconium-80 is a really interesting core in its own right.
For starters, it’s a difficult core to craft, but crafting rare cores is NSCL’s specialty. The facility produced enough zirconium-80 to allow Ringle, Hamaker and their colleagues to determine its mass with unprecedented precision. To do this, they used what is called a Penning trap mass spectrometer in the NSCL’s LEBIT (Low-Energy-Beam and Ion Trap) facility.
“People have measured this mass before, but never so precisely,” Hamaker said. “And it revealed some interesting physics.”
“When we take mass measurements at that precise level, we’re actually measuring how much mass is missing,” Ringle said. “The mass of a nucleus is not just the sum of the mass of its protons and neutrons. There is a missing mass which manifests as energy holding the nucleus together.
This is where one of the most famous equations in science helps explain things. In Albert Einstein’s E = mc2, the E represents energy and m the mass (c is the symbol of the speed of light). This means that the mass and energy are equivalent, although this only becomes noticeable under extreme conditions, such as those found in the heart of an atom.
When a nucleus has more binding energy, i.e. it has a tighter grip on its protons and neutrons, it will have more missing mass. This helps to explain the situation with zirconium-80. Its core is tightly bound, and this new measurement revealed that the binding was even stronger than expected.
This meant that FRIB theorists had to find an explanation and that they could look to predictions from decades ago to help provide an answer. For example, theorists suspected that the zirconium-80 core could be magical.
Every once in a while, a particular nucleus exceeds its mass expectations by having a special number of protons or neutrons. Physicists call them magic numbers. The theory postulated that zirconium-80 had a special number of protons and neutrons, which made it doubly magical.
Previous experiments have shown that zirconium-80 has the shape of a rugby ball or an American football rather than a sphere. Theorists predicted that the shape could give rise to this double magic. With the most accurate measurement of the mass of zirconium-80 to date, scientists could back up these ideas with solid data.
“Theorists predicted that zirconium-80 was a twisted doubly magical core over 30 years ago,” Hamaker said. “It took some time for the experimenters to learn the dance and provide evidence for the theorists. Now that the evidence is there, theorists can determine the next steps in the dance. “
So the dance goes on and, to extend the metaphor, NSCL, FRIB, and MSU provide one of the best ballrooms for it to take place. It has a one-of-a-kind facility, expert staff, and the nation’s top-ranked nuclear physics graduate program.
“I am able to work on-site at a national user facility on topics at the cutting edge of nuclear science,” Hamaker said. “This experience allowed me to develop relationships and learn from many laboratory staff and researchers. The project was successful due to their dedication to science and the laboratory’s world-class facilities and equipment. “
– This press release was originally published on the Michigan State University Facility for Rare Isotope Beams website