Spring 2003 — vol. 21, no. 1 logos home page Contact the logos editor Argonne home page Feature articles Ice smoothie gives heart attacks the 'Big Chill,' may save lives Cadmium causes calcium loss in bones within hours of exposure X-rays penetrate secrets of diesel engine Argonne Update Insect breathing mechanism discovered Surface disorder is more than skin deep Portable detector finds concealed nuclear weapons Gammasphere returns to Argonne

Gammasphere returns to Argonne

Gammasphere, the world's most sensitive gamma-ray detector for nuclear physics research, has returned to Argonne after a two-year stay at Lawrence Berkeley National Laboratory.

Gammasphere is a high-resolution gamma-ray "microscope" with unparalleled detection sensitivity to nuclear electromagnetic radiation due to its high resolution, granularity and efficiency. This powerful combination of features makes it the ideal device for studying rare and exotic nuclear processes. Gammasphere is a national facility funded by the Department of Energy.

GAMMA-RAY MICROSCOPE — Gammasphere, the world’s most sensitive gamma-ray detector for nuclear physics research, has returned to Argonne after a two-year stay at Lawrence Berkeley National Laboratory. Gammasphere is a high-resolution gamma-ray “microscope” designed to help answer fundamental questions about the structure and behavior of atomic nuclei, and study rare and exotic nuclear processes. The 10-foot-tall, 14-ton device has 110 germanium detectors that are cooled with liquid nitrogen.

The 10-foot-tall device is a silvery machined aluminum sphere about seven feet in diameter pierced by 110 holes. Yard-long gamma-ray detectors fit through the holes, with their blunted tips converging near the center of the sphere. The detectors are cooled to 320 F (minus 196 C) with liquid nitrogen — 200 gallons a day — to increase their sensitivity. Beams of ions from the Argonne Tandem-Linac Accelerator System (ATLAS) will strike a target in the center of Gammasphere. Some of the nuclei from the beam fuse with nuclei in the target. The gamma rays produced by these interactions provide information about nuclear structure and dynamics.

Going mobile

Researchers at Argonne's Physics Division are devising a method to increase Gammasphere's flexibility by making it mobile — by summer 2003 it should be able to move from one beamline to another, a first for the 14-ton, $25 million instrument. Until then, it will be used in conjunction with another instrument called the Fragment Mass Analyzer,or FMA.

Since its last visit to Argonne, Gammasphere's trigger electronics have been modified to work better with the FMA. For some experiments, this should increase the amount of data the detector can record during a typical experiment by a factor of 10. This is particularly critical when measuring nuclear systems produced with very low cross-sections.

"The FMA is the Cadillac of fragment detection systems," said Mike Carpenter, who leads the Gammasphere project at Argonne. "But many experiments don't require that kind of exquisite sensitivity. Moving Gammasphere to its own beamline frees up the FMA for other work."

Tests of the roving-detector idea were conducted in December 2002. Two 5,000-lb. concrete shielding blocks were placed on a steel frame in the ATLAS detector area to simulate the weight of the detectors. When roller bearings were placed under the frame, the assembly could be pushed across the floor by team of six. — Dave Jacqué

For more information, please contact Dave Jacqué (630-252-5582 or info@anl.gov) at Argonne.