Mass Measurement of the Lightweight Self-Conjugate Nucleus zirconium-80 and the Development of the Single Ion Penning Trap

An atom's mass provides a unique probe to the various interactions occurring within its nucleus. Hence, precise atomic mass measurements are fundamental for nuclear physics research. Penning trap mass spectrometry (PTMS) is currently the most precise method for performing these measurements. The Low Energy Beam and Ion Trap (LEBIT) Facility at the National Superconducting Cyclotron Laboratory (NSCL) uses PTMS to measure the masses of rare isotopes produced via projectile fragmentation. In this work, mass measurements of 80-83Zr and the development of the single ion Penning trap, both performed at the LEBIT facility, are presented.Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. The nuclear shell structure varies due to changes of the nuclear mean field with the number of neutrons N and protons Z. These variations can be probed by measuring mass differences between nuclei. The N=Z=40 self-conjugate nucleus 80Zr is of particular interest as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. Here, evidence for the existence of a deformed double-shell closure in 80Zr is presented through precision mass measurements of 80-83Zr. The measurement shows that 80Zr is significantly lighter, and thus more strongly bound than predicted. This can be attributed to the deformed shell closure at N=Z=40 and the large Wigner energy. A statistical Bayesian-model mixing analysis employing several global nuclear mass models demonstrates difficulties reproducing the observed mass anomaly using current theory.To refine the deformed shell closure, high-precision mass measurements in the 80Zr region are needed, which will be made possible with next-generation radioactive ion beam facilities such as the Facility for Rare Isotope Beams (FRIB) and higher sensitivity mass measurement techniques. Current PTMS techniques used for rare isotope mass measurements are destructive. While these methods are flexible, they require a significant number of detected ions (~ 100 ions). The most exotic isotopes, however, may only be delivered at rates on the order of one ion per day, making mass measurements with the destructive techniques nearly impossible due to time restraints. To this end, LEBIT has developed a new single ion Penning trap (SIPT), which makes use of the non-destructive narrowband Fourier transform ion cyclotron resonance (FT-ICR) technique. Although FT-ICR is a widely used technique, it has never been applied to rare isotope mass measurements. SIPT’s key features, development, and commissioning are presented in this work.