Physics with low-energy CARIBU beams

A.J. Mitchell

University of Massachusetts Lowell, Lowell, MA 01854, USA.

The CAlifornium Rare Isotope Breeder Upgrade (CARIBU) at Argonne National Laboratory provides a unique opportunity for expanding research in nuclear structure, astrophysics and applications with neutron-rich exotic beams. CARIBU utilizes the spontaneous fission of 252Cf in generating such beams. Fission fragments are thermalized in a gas catcher, whereby a combination of high-purity He gas flow and DC/RF electric fields act to form a low- emittance beam, before purification in an isobar separator.

Major steps have been taken in developing experiments that utilise low-energy CARIBU beams. A new decay-spectroscopy station optimized for performing β-γ-t and β-γ-γ coincidence measurements has recently 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, and the “SATURN” system of plastic scintillators and moving tape collector, which offers significant removal of long-lived radiation that would otherwise contaminate the data.

The modularity of the X-Array allows for the addition of dedicated neutron detectors to be utilized in β-delayed neutron measurements. This is in addition to the dedicated Beta-decay Paul Trap (BPT) set-up, which is undergoing significant upgrades. A Total Absorption Gamma- ray Spectroscopy (TAGS) detector is also being re-commissioned to perform such measurements in 2015. The mass-measurements group continues to push further away from stability with the Canadian Penning Trap (CPT). Major efficiency and intensity upgrades to ATLAS, in addition to the acquisition of a new 1.7-Ci 252Cf source, have led to significant improvements in re-accelerated CARIBU beams.

This presentation will discuss the infrastructure that is in place and update on recent progress that has been made, with particular focus on the first decay experiments with low- energy beams from CARIBU.

This research is supported by grants from the US Department Of Energy, Office of Science.