A recent and significant addition to the
Nuclear Science Laboratory facilities is the Radioactive Nuclear Beam
facility, designed for the study of nuclear reactions using radioactive
beams. The facility is the result of a collaborative effort between
the University of Notre Dame and the University of Michigan, and it
consists of a pair of in-line superconducting solenoid magnets, with
each solenoid comprised of thousands of meters of Niobium-Titanium wire
wound into a cylindrical coil. Each coil is housed in a thermally insulating
vessel, known as a cryostat, and when in operation, each superconducting
coil is surrounded by liquid helium (boiling temperature -268oC).
Each of the superconducting solenoids produces a maximum magnetic field
of about 6 Tesla (by comparison, the earth's magnetic field is about
0.00005 Tesla).
In a standard configuraton, the use of radioactive nuclear beams for experimentation is very difficult, since by definition the ions in the beam are unstable and therefore decay into more stable forms. The lifetime of a radioactive nuclear beam varies depending upon the ion involved, but is often so short that traditional methods of beam production cannot be used, as the ions in the beam decay in flight on their way to the target. It is often simply not possible to produce a radioactive ion beam with a traditional ion source, accelerate it to the energy needed for experimentation, and deliver it to the target in the extremely short lifetime of the radioactive ion.
Our RNB facility circumvents these problems by producing the radioactive ion beam at the target station. A stable ion beam, such as7Li, is produced using the SNICS II Sputter Ion Source, and accelerated to the appropriate energy by the FN Tandem Van de Graaff accelerator. This primary beam is focussed and steered into the RNB beamline, where it impinges upon a target located just upstream of the first superconducting solenoid magnet. The nuclear reactions that take place when the energetic primary beam strikes the target produce a wide variety of particles exiting the target region, many of which are quite exotic and very short lived. By proper choice of the target material, primary beam, and the primary beam energy, the production of a particular radioactive ion, such as 6He, can be maximized.
The superconducting solenoid magnets are used to selectively
collect and focus the appropriate radioactive ions emerging
from the primary target area, producing a secondary radioactive
nuclear beam which can then be used for experimentation
by transporting this beam to a secondary target within the
RNB facility. To date, several experiments have been performed,
producing and studying radioactive nuclear beams such as
3H, 6He, 7Be, 8Li, 8B, 11C, 12N, and 18Ne with a typical beam intensity of 5 x 105
per microA of primary beam.
Also, please visit the site maintained by the University of Michigan about this collaborative dual solenoid project.
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