Mass Measurements of Neutron-Deficient Yb Isotopes and Nuclear Structure at the Extreme Proton-Rich Side of the N=82 Shell

International audienceHigh-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN’s multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of Yb150,153 and the excitation energy of Ybm151 were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h11/2-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculation

Resurrecting the N = 20 shell closure and upgrades to the TITAN measurement Penning trap

Experimental investigations of nuclear structure provide a probe to study the strong nuclear force, many properties of which still remain unknown. One powerful way to experimentally investigate nuclear structure is through the mass of the atomic nucleus, as it reveals the binding energy of the nucleus. In this work, mass measurements of Mg and Na isotopes are carried out and the results indicate, for the first time, a gradual re-emergence of magicity or closed shell behavior for Z ≤ 11 nuclei at the N = 20 island of inversion. The results also discover a previously unknown low-lying isomer, hence a long-lived excited state in ³²Na. In addition, complementary work at higher mass numbers which combines mass measurements and decay energies allows us to trace the two-proton dripline between iridium and lead, thus determining the limits of existence for elements with proton numbers Z = 77−82 on the proton-rich side of the Segrè chart. Comparisons with some theoretical calculations for this work show agreement while others, such as ab initio theory calculations, are currently unable to reproduce effects of the N = 20 island of inversion, and will require further developments. Yet the mass measurements serve as important benchmarks. Beyond studies of nuclear structure via direct mass measurements, this thesis describes the technical developments and improvements to the Measurement Penning Trap (MPET). The Penning trap, an experimental apparatus that uses electric and magnetic fields to determine the atomic mass through the ion’s cyclotron frequency, has been upgraded to operate at cryogenic temperatures with the goal to reach storage times on the order of seconds for highly-charged Ions. The aim for this upgrade is an improvement of the achievable precision by an order of magnitude. In addition, simulations and further technical upgrades towards the implementation of the Phase-Imaging Ion-Cyclotron measurement technique are carried out. With its new capabilities, the TITAN MPET is now able to perform mass measurements of short-lived radioactive isotopes in singly and highly charged states with an unprecedented precision.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Construction and Ion-Beam Characterization of Nuclear Targets

A poster presented at HNPS2016, NCSR "Demokritos", Greece<div>03-04.06.2016</div

High-precision mass measurement of neutron-rich 96Kr

International audienceWhile the nuclear deformation in the region around Z = 40 and N = 60 has been studied in great detail, the possible onset of nuclear deformation in the isotopic chain of krypton (Z = 36) is still a subject of controversy. Here, we present a high-precision mass measurement of the neutron-rich nuclide $^{96}$Kr, as measured by the Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) at TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN). A statistical method, based on a hyper-exponentially modified Gaussian, has been employed to model the data. As such, the uncertainty introduced by overlapping peaks from beam contaminants was reduced and the mass excess of $^{96}$Kr determined to be -53097(57)keV. The capability of the method has been confirmed with measurements of the stable isotopic pair $^{40}$Ar/$^{40}$Ca, in which a relative accuracy Δm/m of 3.5 ⋅ 10$^{− 8}$ and a mass resolving power of more than 400000 were achieved