Accelerator Mass Spectrometry with the MONICA Detector at the Argonne Gas-Filled Analyzer and Ultra-Sensitive Detection of ^39,42Ar

As the scope of Accelerator Mass Spectrometry (AMS) expands, there is an increased need to research isobaric separation in the medium-heavy mass region. Existing AMS facilities are limited in their ability to separate medium to heavy radioactive nuclei of interest from their neighboring stable isobars, as such measurements require higher energies than available in most facilities. The Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory (ANL) can accelerate isotopes to the energies required for the separation of high mass isobars, and the Argonne Gas-Filled Analyzer (AGFA) setup at ATLAS, specifically designed to study heavy, rare isotopes, has the necessary magnetic rigidity to facilitate their measurement. A feasibility test to see if AGFA could be used to conduct AMS measurements occurred in November, 2019, and succeeded in separating the stable isobars ⁹²Zr and ⁹²Mo

. A new multi-anode ionization chamber, MONICA, was then built to enhance the ion identification for medium to heavy mass isotopes using AGFA and to aid in Noble Gas AMS (NOGAMS) measurements. MONICA underwent four commissioning runs at the Nuclear Science Laboratory at the University of Notre Dame utilizing Si, Fe, Zr, and Mn beams. Upon returning to ATLAS, MONICA was placed in the Enge split-pole spectrograph for the study of the ⁴⁰Ar(n, 2n)³⁹Ar(t_1/2=268 y) and the novel, ultra-low level detection of ⁴²Ar (33 y) using AMS, as part of a collaboration with the National Ignition Facility (NIF). MONICA was then successfully commissioned to be used with AGFA for AMS measurements through a study of ⁹²Nb utilizing a newly-developed set-up.