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Nuclear Chemistry

Half-lives of rare isotopes revealed

New isotope accelerator lets scientists explore the limits of atomic structure

by Neil Savage, special to C&EN
November 25, 2022 | A version of this story appeared in Volume 100, Issue 42


A large detector at the Facility for Rare Isotope Beams.
Credit: Facility for Rare Isotope Beams
A device at the Facility for Rare Isotope Beams sets up ion collisions that create rare isotopes.

Scientists have measured the half-lives of five never-before-seen isotopes in a first demonstration of a research facility that will help probe the nuclear structures of elements (Phys. Rev. Lett. 2022, DOI: 10.1103/PhysRevLett.129.212501).

The Facility for Rare Isotope Beams (FRIB) at Michigan State University allows scientists to study the so-called drip line, the point at which no more neutrons can be added to an atomic nucleus. “In trying to understand what kind of combinations of protons and neutrons can form isotopes, understanding the limit beyond which they can’t is important and really tests our theories to see if we’re getting things right,” says Heather L. Crawford, a staff scientist at Lawrence Berkeley National Laboratory and part of the team that did the work.

The team fired a beam of calcium-48, accelerated by electrical fields within the machine, into a beryllium target at roughly 60% of the speed of light. The collision caused the beam to break into several exotic isotopes of lighter elements, including five never before measured—phosphorus-45, silicon-42, aluminum-40, aluminum-41, and magnesium-38—which then struck a detector. The time to reach the detector and the amount of energy absorbed identified the isotopes. The time it took for the isotopes to lose an electron provided the half-life, measured in milliseconds.

The $730 million facility is currently operating at 1 kW but will eventually reach 400 kW, which will allow it to accelerate many more ions, increasing the number of isotopes it can produce. The FRIB is advancing basic science but, Crawford says, could lead to greater understanding that may one day improve medical applications or nuclear reactors.

“We can also learn about reactions that happen in stars, stellar explosions, and collisions,” says Katherine Grzywacz-Jones, a physicist at the University of Tennessee, Knoxville, who is scheduled to run an experiment at FRIB next month. “This can answer questions about how the elements that exist on Earth came to be.”



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