Particle physics experiments

ORNL and partners launch first experiments using new facility to make cosmic isotopes on Earth

Newswise – Two decades in the making, a new flagship facility for nuclear physics opened on May 2 and scientists from the Department of Energy’s Oak Ridge National Laboratory have participated in 10 of its first 34 experiments. ORNL researchers and their partners from other national laboratories and universities launched the first experiment on May 11.

The Facility for Rare Isotope Beams, or FRIB, a DOE Office of Science user facility at Michigan State University, will produce more than 1,000 new rare isotopes. It’s not your parents’ isotopes, like americium-241 in smoke detectors or fluorine-18 in PET scanners.

FRIB’s rare isotopes have abnormal proton/neutron ratios, so they are unstable and prone to decay. Many exist for mere fractions of a second, such as magnesium-40, calcium-55, and nickel-78. Until now, they were only made during stellar explosions and neutron star mergers. Now what is designed to be the world’s most powerful heavy ion accelerator is making them here on Earth.

“FRIB will usher in a new era of discovery,” said Witold Nazarewicz, FRIB’s chief scientist and distinguished professor of physics at MSU. “ORNL has provided long-term expertise and unique instrumentation that will help FRIB provide new insights into what holds atomic nuclei together, how elements are created, and how to use nuclei for societal benefits.”

The first standing

FRIB’s first experiment is being led by Heather Crawford of the DOE’s Lawrence Berkeley National Laboratory with partners from ORNL, the University of Tennessee, Knoxville and elsewhere. The experiment uses the FRIB Decay Station Initiator, or FDSi, a modular multi-detector system that is extremely sensitive to rare isotope decay signatures.

“The FDSi is an assembly of the best detectors available to the scientific community within an integrated infrastructure for FRIB nuclear decay studies,” said Mitch Allmond of ORNL, who manages the project. A key element of FDSi stems from pioneering work on the design of germanium detectors by David Radford of ORNL, including the CLover Array for Radioactive ION Beams, or CLARION.

FDSi allows scientists to quickly mix and match detectors to capture different types of nuclear data. “All these individual detectors existed in different groups until now,” Allmond added.

FDSi is now at FRIB and is coupled to the Versatile Array of Neutron Detectors at Low Energy, or VANDLE, a neutron spectroscopy instrument developed under Robert Grzywacz, professor of physics at UTK with a cross-appointment at ORNL. VANDLE provides energetic information about neutrons. FDSi’s CLARION-VANDLE instrument duo is the first stop on the FRIB beamline.

Its latest stop is the Modular Total Absorption Spectrometer, or MTAS, a one-ton gamma-ray detector. “It’s the big FRIB receiver’s glove,” Grzywacz said. When the beam lands in MTAS, the detector effectively measures all of its energy in one lump sum. MTAS was developed for beta decay studies of neutron- and proton-rich nuclei under the direction of Krzysztof Rykaczewski of ORNL. The instrument is installed at FRIB for experiments planned for June to probe the decay of calcium-55, an important isotope in astrophysics.

Other ORNL instruments and resources available to the international FRIB user community of nearly 1,600 researchers include:

  • GODDESS detection system. Led by Steven Pain of ORNL, GODDESS measures various reactions that cause the creation of elements in stars. At its heart is the Oak Ridge Rutgers University Barrel Array, an arrangement of position-sensitive silicon detectors to spot charged particles.
  • Jet Experiments in Nuclear Structure and Astrophysics, or JENSA. Directed by Kelly Chipps of ORNL, JENSA is a unique gas jet system for nuclear reaction studies. Chipps spearheaded its use with radioactive beams.
  • SEparator for CAPture Reactions, or SECAR. This recoil separator allows direct measurements of the reactions that fuel exploding stars. Michael Smith of ORNL conducted a proof-of-principle demonstration in 1991 that recoil separators could measure such reactions. Smith and Chipps are members of the SECAR project team.
  • Computational Infrastructure for Nuclear Astrophysics, or CINA. Developed at ORNL by Smith and Eric Lingerfelt, it is the first cloud computing system for nuclear astrophysics. CINA helps scientists understand how their FRIB results relate to cosmic events.

Electromagnetic switching stations

To accelerate stable beams of heavy ions, cryomodules containing superconducting radio frequency resonators guide positively charged atoms through segments of FRIB’s heavy ion accelerator, a 1,600-foot-long pipe bent into the shape of a paperclip. .

Inside the accelerator, the ions pick up speed. When they reach half the speed of light, they crash into the target, which breaks the nuclei into pieces, each having fewer protons and neutrons than the nuclei in the original stable beam. An array of superconducting electromagnets purifies the resulting beams of radioactive isotopes at the FRIB. “You’re basically creating a cocktail of lots of residual products,” Allmond said.

Some rare isotopes are mined for applications. Others continue through a series of magnets that filter out unwanted isotopes. Electromagnetic “switches” direct the purified beams to terminal stations which hold them for experiments.

Scientists can accelerate, stop, and reaccelerate beams for experiments in a wide range of desired energies.

ORNL DNA in the FRIB

Many FRIB experiments grew out of the pioneering work of ORNL’s Physics Division to create beams of radioactive ions.

“Oak Ridge National Laboratory is deeply rooted in the study of radioactive ions and ion beams,” ORNL Physics Division Director Marcel Demarteau said at the FRIB’s grand opening. He spoke after a ribbon cutting by Energy Secretary Jennifer Granholm.

On March 18, 1962, the first beam of light ions circulated in the isochronous cyclotron at Oak Ridge. In the 1970s, the addition of a tandem accelerator enabled heavy ion beams. In 1997, a new reconfiguration allowed the very first beams of radioactive ions. Renamed the Holifield Radioactive Ion Beam Facility, or HRIBF, it has become a resource for nuclear physicists around the world. Nazarewicz, chief scientist of FRIB, served as scientific director of HRIBF from 1999 to 2012.

“HRIBF was a key part of the global program with rare isotopes and played a crucial role in the pathway to FRIB. It was the only US facility with the capability for accelerated beams of short-lived nuclei,” Nazarewicz said.

“We did things there that just couldn’t be done anywhere else,” Grzywacz said. These feats included the first measurement with a reaccelerated unstable beam in North America and the first acceleration of neutron-rich fission fragments of tin-132 to confirm its doubly magical nature, which gives a nucleus extraordinary stability.

HRIBF users had access to high quality beams of 200 rare isotopes. They made fundamental measurements with arrays of instruments. Moving readings from detectors to electronic systems, they pioneered digitization for nuclear physics.

In 2012, HRIBF was decommissioned, but the instrumentation was still available for use. Researchers have since upgraded the instruments for installation at other facilities, such as RIKEN in Japan, ATLAS and FRIB at Argonne National Laboratory.

In 2016, the American Physical Society declared HRIBF a Historic Physics Site. Its DNA lives on in FRIB.

Chipps of ORNL, president of the FRIB users organization, also spoke at the opening of FRIB. “FRIB will position us to gain incredible new knowledge about the nature of the universe around us,” she said.

The DOE Office of Science supported the ORNL research.

UT-Battelle manages ORNL for the DOE Office of Science, the largest support of basic physical science research in the United States. The Office of Science strives to meet some of the most pressing challenges of our time. For more information, please visit energy.gov/science.