With experiments right to the finish, Holifield Facility user program closes
The Holifield Radioactive Ion Beam Facility user program has ended in style, with researchers scurrying to complete three exciting experiments before program’s last day of user operations on April 15. The final day was initially scheduled for April 1, but the user program received a two-week “reprieve” to finish the three experiments.
Approximately 40 people — researchers, users and Holifield veterans — showed up to count down the last minutes of beam time at midnight, Sunday, April 15.
The facility will now go into “warm standby,” says Physics Division Director David Dean.
Slightly less than a month before the user operations ended, the Holifield Facility marked its 50th anniversary. March 18, 1962, was the day operators for the Oak Ridge Isochronous Cyclotron, the “front end” of the radioactive ion beam source, circulated its first light ion beam.
The ensuing half-century has produced volumes of research through beams of, initially, heavy ions and, later, short-lived, radioactive nuclei. The Holifield Facility has been the experimental resource and training ground for researchers located all across the low-energy physics scientific community, from all corners of the world.
The three final user experiments are typical of what the facility has offered the research community for all these years.
Ricardo Orlandi, a researcher from CSIC Madrid, is leading a measurement of a unique reaction on Tin-132, an unstable isotope important to nuclear astrophysicists who investigate how the heaviest elements are created in supernova explosions. It is also important to researchers investigating the structure of the unstable, ‘doubly magic’ tin isotope, which has closed shells of both protons and neutrons.
Another experiment, led by ORNL physicist Krzysztof Rykaczewski, is using the facility’s first laser ion source and new second radioactive ion beam platform to collect data on exotic isotopes of gallium. The laser source, built by ORNL’s Yuan Liu, coupled to the facility’s isobar separator, provided completely pure beams for study of the structure of these rare isotopes. At the same time, Rykaczewski is commissioning the neutron detector 3Hen, which could see future service at another isotope facility. The HRIBF experiment hopes to yield lifetime and level information on gallium-86; previously, only the existence of this isotope had been reported.
The third project is actually four experiments to study different states of a variety of exotic tin isotopes. ORNL staff members Robert Varner and Jim Beene, working with postdoc Mitch Allmond and the University of Tennessee’s Kate Jones and Anissa Bey, blasted a beryllium-9 target with unstable tin-126, 128, 130, and 132 nuclei, and detected the resulting light particles and gamma rays to probe tin isotopes with one additional neutron to the beam. These measurements are important both to learn about the structure of heavy exotic nuclei and about supernova element creation. Two of these experiments, on tin-126 and 128, will be part of the thesis work of graduate student Brett Manning from Rutgers University.
The Holifield Facility has offered nuclear theorists and astrophysicists unique beams for studies of the forces that hold protons and neutrons together into an atomic nucleus. ORIC, which produces the initial light ion beam, was one of the first isochronous cyclotrons of its kind. Holifield is the only facility in the world that produces unique, short-lived beams of both proton-rich and neutron-rich beams such as Fluorine-17.
Besides the one-of-a-kind beams the HRIBF produced, the facility was unique in itself: For example, the massive doors that shield the staff from the cyclotron were the largest the supplying safe company had ever produced. The 100-foot-tall electrostatic tandem accelerator — the silo-shaped Lab landmark — has generated an electrostatic voltage of 32 million volts, which might still hold the record for the highest voltage ever produced by a man-made device.
The stream of researchers who came to ORNL inspired the establishment in 1982 of ORNL’s initial collaboration with state of Tennessee universities — the Joint Institute for Heavy Ion Research, located near the Holifield Facility.
The end of the Holifield Facility’s user program was announced in the February 2011 budget request for Fiscal Year 2012. The cost-saving measure was coupled with the end of another, much larger physics facility’s mission, Fermilab’s Tevatron, whose mission has been supplanted by Europe’s Large Hadron Collider.
The Holifield Facility itself more than doubled its own initial life expectancy in the early 1990s, when the late researchers Russell Robinson and Jerry Garrett led the conversion of the heavy ion facility to a radioactive ion Beam facility where beams produced from the bombardment of targets with intense light ions from ORIC were accelerated in the tall tandem.
The warm standby status conferred upon the facility may or may not be permanent. Other missions for the Holifield Facility are under consideration. The break, in fact, provides a needed two-month maintenance period for the tandem accelerator.
“We’re hoping we can get approval to run some experiments on the tandem, which is relatively cheap to run,” says the Physics Division’s Michael Smith, whose nearly two-decade ORNL tenure in astrophysics has been based at Holifield. “We hope to carry out forefront measurements as well as commission new detector and target systems for use in next-generation facilities.”
In the meantime, the last flurry of radioactive ion beam experiments recalls a half-century of science produced by a unique, at times quirky, but resilient workhorse.
“It’s been hectic and exciting,” Michael says. “We’ve had all these different groups in the facility simultaneously doing different experiments. A new laser ion source, new platform, new detector system, new reactions, and a lot of exotic beams that can’t be done anywhere else in the world. It’s an incredibly productive way to do science.”— Bill Cabage, April 17, 2012