Speaker
Rodney Orford
(McGill University)
Description
Roughly half of the elements heavier than iron are thought to be produced through the astrophysical rapid-neutron capture process of nucleosynthesis. Despite its large influence in explaining the observed abundance of heavy elements, much of the *r* process is still poorly understood. A more thorough library of nuclear data, particularly masses, of neutron-rich nuclei is needed to improve the accuracy and progression of r-process calculations. The Canadian Penning trap mass spectrometer (CPT) is currently located in the CARIBU facility at Argonne National Laboratory where intense radioactive beams of neutron-rich nuclei are produced from the spontaneous fission of $^{252}$Cf. Since its move to CARIBU in 2010, the CPT has successfully measured the masses of more than 110 isotopes to a typical precision of 15 keV/c$^2$ by measuring the cyclotron frequency of ions through a time-of-flight (TOF) technique. An upgrade to a position-sensitive microchannel plate detector at the CPT has facilitated a contemporary technique in the determination of masses by measuring the phases of orbital motion of trapped ions. This phase-imaging method is intrinsically more efficient than the TOF technique, and provides an order of magnitude improvement in mass-resolving power without loss in precision, allowing access to more weakly produced isotopes with shorter half-lives than was previously achievable at CARIBU. The low-energy beamline at CARIBU was recently fitted with a multi-reflection time-of-flight mass separator (MR-TOF) which improved beam purity by more than an order of magnitude. In a preliminary measurement campaign the phase-imaging technique, buoyed by the MR-TOF, has yielded the masses of eight previously unmeasured ground-state rare-earth isotopes, and another three nuclear isomers whose masses were directly measured for the first time. These results and future plans to probe another 1-3 neutrons from stability will be discussed.
Primary author
Rodney Orford
(McGill University)
