A multi-institutional team of nuclear science researchers has published the results of the first experiment at the Facility for Rare Isotope Beams (FRIB). The experiment studied the decay of isotopes so unstable that they only exist for fractions of a second. These measurements involve half-life, how long it takes the radioactivity of an isotope to drop to half its original value. These measurements are among the most fundamental properties that researchers can observe about short-lived particles. The measurement focused on unstable isotopes near the “drip line,” the spot where neutrons can no longer bind to a nucleus. Instead, any additional neutrons drip off, like water from a saturated kitchen sponge.
FRIB will provide access to thousands of nuclei far from stability, many for the first time. These rare isotope beams will enable scientists to make the measurements they need to understand the properties of exotic nuclei and how the elements are synthesized. The first experiment reached some of the most neutron-rich isotopes studied to date of phosphorus, silicon, aluminum, and magnesium. This despite operating at only 1/400th of FRIB’s full power. This demonstrates the advanced capabilities and new science opportunities to come in the future.
The Facility for Rare Isotope Beams at Michigan State University has recently begun operations and will provide access to thousands of nuclei far from stability. In the first experiment at FRIB, researchers smashed a beam of stable calcium-48 nuclei traveling at about 60 percent of the speed of light into a beryllium target. The calcium fragmented, producing a slew of isotopes that were separated in the FRIB separator to select the isotopes of interest near the neutron drip line.
Researchers implanted these isotopes into the center of a sensitive detector known as the FRIB Decay Station initiator (FDSi). The FDSi, a community-built device, provided sensitivity to detect all the sub-atomic particles emitted in the decay of the radioactive isotopes, including the beta particle (electrons), gamma-rays, and neutrons. The research involved more than 50 participants from ten universities and national laboratories, including co-principal investigators from Lawrence Berkeley National Laboratory, Florida State University, Mississippi State University, Oak Ridge National Laboratory, and the University of Tennessee at Knoxville.
Lawrence Berkeley National Laboratory
Funding for this work was provided by the Department of Energy (DOE) Office of Science, Office of Nuclear Physics, the DOE National Nuclear Security Administration, and the Stewardship Science Academic Alliances Program. Support was also provided by the U.S. National Science Foundation (NSF) and the NSF Major Research Instrumentation Program.
Crawford, H. L., et al., Crossing N=28 Toward the Neutron Drip Line: First Measurement of Half-Lives at FRIB. Physical Review Letters 129, 212501 (2022). [DOI: 10.1103/PhysRevLett.129.212501]
FRIB Experiment Pushes Elements to the Limit, Berkeley Lab news