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Nuclear physics device for ORNL accelerator due in from England

Although the Daresbury Nuclear Structure Facility in England was closed in 1993, one of its nuclear physics instruments will have a second life at the Department of Energy's Oak Ridge National Laboratory.

The large, multi-million-dollar instrument will be used with ORNL's upgraded radioactive-ion accelerator facility to study nuclear reactions predicted to occur during the life and death of stars. On October 17, the Daresbury Recoil Separator, which has been donated to the Laboratory, was delivered by ship and truck to ORNL for use in its new Holifield Radioactive Ion Beam Facility (HRIBF), now being constructed and expected to produce its first radioactive beam in 1995 and to begin routine operation in 1996. HRIBF will be the only U.S. facility dedicated to producing and accelerating intense beams of radioactive nuclei suitable for such studies.

The two accelerators that formed the heart of the Holifield Heavy Ion Research Facility from 1980 to 1992 are being reconfigured. One will be used to produce radioactive nuclei that do not occur naturally, and the second will be used to accelerate the radioactive nuclei. The products of bombarding targets with these radioactive beams, known as "recoils," will be directed to detectors, while the radioactive beam particles, or projectiles, are steered away. This job will be accomplished by the Daresbury Recoil Separator.

"The ability of the Daresbury Recoil Separator to separate recoil products from projectile particles makes it a tremendous addition to our research program," said Jim Ball, acting ORNL associate director for Physical Sciences and Advanced Materials. "Combining this instrument with ORNL's unique radioactive beams will enable pioneering advances in our understanding of the explosive events that create and destroy stars."

The recoil separator came to ORNL from the Nuclear Structure Facility of Daresbury Laboratory in Warrington, England, which was closed because of budget cutbacks. Physicists will use its capabilities to conduct nuclear astrophysics and nuclear structure research at the new Holifield Radioactive Ion Beam Facility.

"Radioactive beams at ORNL will be used to study nuclear reactions occurring in exotic stellar explosions such as novae, supernovae, and X-ray bursts," said Michael Smith of the Physics Division. "These incredibly energetic astrophysical events produce the majority of heavy elements in the universe and mark the dramatic end of the life of massive stars.

"Sophisticated computer models of these explosions," Smith continued, "require precision measurements of nuclear reactions involving radioactive nuclei like those that will be produced in our new radioactive ion beam facility. Such important measurements would not be possible without instruments such as the Daresbury Recoil Separator."

The Daresbury Recoil Separator is 13 meters long and weighs about 90 tons. Its components include two 18-ton dipole magnets surrounding vacuum chambers containing high-voltage electrostatic plates. These components form two velocity filters that separate the radioactive beam particles from the recoil products based on the differences in their direction and speed.

"The transfer of the Daresbury Recoil Separator from England to ORNL required the cooperation of researchers and technical staff from both laboratories," says Jerry Garrett, scientific director of the Holifield Radioactive Ion Beam Facility. "We anticipate that this cooperative spirit will continue through research collaborations between ORNL physicists and those from Daresbury Laboratory and sites throughout the United Kingdom. Such collaborations will greatly benefit research efforts in nuclear astrophysics, nuclear structure physics, and radioactive beam physics on both sides of the Atlantic Ocean."

ORNL, one of the Department of Energy's multiprogram research laboratories, is managed by Martin Marietta Energy Systems, which also manages the Oak Ridge K-25 Site and the Oak Ridge Y-12 Plant.