Departmental Seminar

Opportunities with CARIBU radioactive beams at Argonne National Laboratory

Dr A.J. Mitchell
University of Massachusetts Lowell (USA)

The Argonne Tandem Linac Accelerator System (ATLAS) user facility at Argonne National Laboratory, USA has been at the forefront of nuclear physics research since its first accelerated beams were delivered in the 1970’s. The more-recent CAlifornium Rare Isotope Breeder Upgrade (CARIBU) provides a unique opportunity for expanding research in nuclear structure, astrophysics and applications with neutron-rich exotic beams. CARIBU utilizes the spontaneous fission branch of 252Cf in generating such beams. Fission fragments are thermalized in a gas catcher, whereby a combination of DC fields, high-purity He gas flow and RF electric fields act to form a low-emittance beam, before purification in an isobar separator.

A new decay-spectroscopy station, optimized for performing β-γ-t and β-γ-γ coincidence measurements, has been commissioned for use with low-energy CARIBU beams. The decay station consists of the "X-Array", a highly-efficient array of five HPGe clover detectors for detection of γ rays with an absolute photo-peak efficiency at 122 keV of ~50% and ~12% at 1332 keV, and plastic scintillators for β-particle detection with efficiency >60%. The β-particle detection chamber can incorporate a tape-transport system, which offers significant removal of long-lived radiation from the subsequent decay chain that would otherwise contaminate the data. The modularity of the array will allow for the addition of dedicated neutron detectors to be utilized in β-delayed neutron measurements in the future. An extensive research program with PAC-approved β-decay measurements with CARIBU beams lies on the horizon.

Major upgrades to ATLAS have recently been completed, with measures successfully implemented to improve both efficiency and beam intensity. In addition to infrastructure upgrades, a new 1.7-Ci 252Cf has been acquired which will greatly improve CARIBU beam intensities, particularly with re-accelerated beams. This presentation will show the first γ-decay studies with low-energy ions from the CARIBU source and discuss further opportunities available with CARIBU beams.

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