A new study led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has measured how long it takes for different types of exotic nuclei to decay. The paper published today in Physical Verification Lettersmarks the first experimental result from the Facility for Rare Isotope Beams (FRIB), a DOE Office of Science user facility operated by Michigan State University.
Scientists used the unique facility to better understand nuclei, the collection of protons and neutrons at the heart of atoms. Understanding these fundamental building blocks allows scientists to refine their best models and has applications in medicine, national security, and industry.
“The breadth of the facility and the programs that are being pursued are really exciting to watch,” said Heather Crawford, a physicist at the Berkeley Lab and senior spokesperson for the first FRIB experiment. “Research will come out in different areas that will affect things that we haven’t even thought about. There is so much potential for discovery.”
The first experiment is just a small foretaste of the future of the plant, which will become 400 times more powerful in the coming years. “It’s going to be really exciting – frankly overwhelming,” Crawford said.
The first experiment involved more than 50 participants from ten universities and national laboratories. The study looked at isotopes of several elements. Isotopes are variations of a particular element; They have the same number of protons but can have different numbers of neutrons.
Researchers focused on unstable isotopes near the “drip line,” the point where neutrons can no longer bind to a nucleus. Instead, additional neutrons roll off like water from a saturated kitchen sponge.
The researchers slammed a beam of stable calcium-48 nuclei, traveling at about 60% the speed of light, onto a beryllium target. The calcium fragmented, producing a series of isotopes that were separated, individually identified, and delivered to a sensitive detector that measured how long they took to decay. The result? The first reported measurements of half-lives for five exotic, neutron-loaded isotopes of phosphorus, silicon, aluminum and magnesium.
Half-life measurements (perhaps best known from applications in carbon dating) are one of the first things researchers can observe about these short-lived particles. The basic information about nuclei at the limits of their existence provides a useful test for different models of the atomic world.
“This is a fundamental scientific question, but it ties into the bigger picture of the field,” Crawford said. “Our goal is to not only describe these nuclei, but all types of nuclei. These models help us fill in the gaps, which helps us more reliably predict things we haven’t been able to measure yet.”
More complete theories help advance research in areas like astrophysics and nuclear physics – for example, to understand how elements form in exploding stars or how processes work in nuclear reactors.
Crawford and the team plan to repeat the half-life experiment again next year, taking advantage of the extra beam intensity, which increases the number of isotopes produced, including rare isotopes near the neutron drip line. In the meantime, other groups will make use of the facility’s many beamlines and instruments.
“Bringing the facility online has been a huge effort by many people and something the community has been looking forward to for a long time,” Crawford said. “I’m happy that I’m young enough to benefit from it in the coming decades.”
In the first experiment, multiple institutions collaborated with researchers from Argonne National Laboratory (ANL), Berkeley Lab, Brookhaven National Laboratory, Florida State University, FRIB, Lawrence Livermore National Laboratory, Louisiana State University, Los Alamos National Laboratory, Mississippi State University, Oak, together with Ridge National Laboratory (ORNL) and the University of Tennessee Knoxville (UTK).
Scientists from ORNL, UTK, ANL and FRIB led the collaboration to provide the instruments used in the FRIB decay station’s initiator, the sensitive detector system that measured the isotopes.
Michigan State University (MSU) operates the Facility for Rare Isotope Beams (FRIB) as a user facility for the US Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics. Home to the most powerful heavy ion accelerator, FRIB allows scientists to make discoveries about the properties of rare isotopes to better understand the physics of nuclei, nuclear astrophysics, fundamental interactions and applications to society including medicine, homeland security and industry.
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