New nuclei can help shape our understanding of fundamental science on Earth and in the cosmos

By creating five new isotopes, an international research team working at Michigan State University’s Rare Isotope Beam Center (FRIB) has brought stars closer to Earth.

The isotopes, known as thulium-182, thulium-183, ytterbium-186, ytterbium-187 and lutetium-190, are reported in the journal Physical examination letters.

This is the first batch of new isotopes manufactured at FRIB, a user facility of the U.S. Department of Energy Office of Science, or DOE-SC, which supports the mission of the DOE-SC Office of Nuclear Physics. The new isotopes show that FRIB is on the verge of creating nuclear specimens that currently only exist when ultradense celestial bodies called neutron stars collide.

“That’s what’s exciting,” said Alexandra Gade, professor of physics at FRIB and the MSU Department of Physics and Astronomy and scientific director of FRIB. “We are convinced that we can get even closer to the nuclei important for astrophysics.”

Gade is also a co-spokesperson for the project, led by Oleg Tarasov, senior research physicist at FRIB.

The research team included a cohort based at FRIB and MSU, as well as collaborators from the Institute of Basic Sciences in South Korea and RIKEN in Japan, an acronym that translates to Institute of Physical and Chemical Research.

“This is probably the first time these isotopes have existed on the Earth’s surface,” said Bradley Sherrill, professor emeritus in MSU’s College of Natural Sciences and head of FRIB’s Advanced Rare Isotope Separator department.

To explain what “advanced” means in this context, Sherrill said researchers only need a few individual particles of a new isotope to confirm its existence and identity using FRIB’s cutting-edge instruments.

Because researchers now know how to make these new isotopes, they can begin producing them in larger quantities to conduct experiments that would never have been possible before. The researchers are also eager to follow the path they have blazed to produce more new isotopes that look even more like those found in stars.

“I like to make the analogy of traveling. We were looking forward to going somewhere we’ve never been before and this is the first step,” Sherrill said. “We’ve left home and we’re starting to explore.”

Almost star stuff

Our sun is a cosmic atomic factory. It is powerful enough to take the cores of two hydrogen atoms, or nuclei, and fuse them into a single helium nucleus.

Hydrogen and helium are the first and lightest entries in the periodic table. To reach the heaviest elements on the table requires even more intense environments than those found in the sun.

Scientists hypothesize that elements like gold, about 200 times more massive than hydrogen, are created when two neutron stars merge.

Neutron stars are the remaining cores of exploded stars that were originally much larger than our sun, but not so large that they could become black holes in their final acts. Although they are not black holes, neutron stars nevertheless contain an immense amount of mass in a very modest size.

“They’re about the size of Lansing with the mass of our sun,” Sherrill said. “It’s not certain, but people think that all the gold on Earth was produced in neutron star collisions.”

By manufacturing the isotopes present at the site of a neutron star collision, scientists could better explore and understand the processes involved in making these heavy elements.

The five new isotopes are not part of this environment, but they are the closest scientists have come to this special territory – and the prospects for getting there are very good.

To create the new isotopes, the team sent a beam of platinum ions toward a carbon target. The beam current divided by the state of charge was 50 nanoamps. Since these experiments were performed, FRIB has already increased its beam power to 350 nanoamps and plans to reach up to 15,000 nanoamps.

In the meantime, the new isotopes are exciting in their own right, providing the nuclear research community with new opportunities to advance into the unknown.

“It’s not a big surprise that these isotopes exist, but now that we have them, we have colleagues who will be very interested in what we can measure next,” Gade said. “I’m already starting to think about what we can do next in terms of measuring their half-lives, their masses and other properties.”

Finding these quantities in isotopes that have never been available before will help illuminate and refine our understanding of fundamental nuclear science.

“There’s so much more to learn,” Sherrill said. “And we’re on our way.”