Precision Penning trap measurements of milli-second half-life isotopes at TITAN: nuclear halo mass measurements on He, Li and Be
28 January 2009
NSCL Seminar Room
Teetering on the edge of nuclear stability, the properties of halo nuclei have long been recognized as one of the most stringent tests of our understanding of the strong force. Nuclear halos are an exotic form of nuclear matter that continues to defy the considerable scientific efforts focused upon them in the last two decades. 11Li belongs to a special category of halos called Borromean, bound as a three-body family, the two-body siblings 10Li and 2n are unbound as separate entities. Recently interest in this archetypical two-neutron halo 11Li has been renewed due to improved measurements of its halo-neutron correlation (the MAYA experiments at ISAC II), charge radius at ISAC and polarization at RIKEN. The charge-radius determination of the GSI-TOPLIS experiment (carried out at ISAC) is made through measurements of isotope shifts. It is notable because of its use of state of the art atomic physics methods, both experimental and theoretical, in order to probe the atomic nucleus. However, the charge-radius derivation is limited by the knowledge of the mass of 11Li. This is a quantity which, due to conflicting experimental results has historically been poorly understood. Recently, first mass measurement of the radioisotopes 11Li using a Penning trap spectrometer were carried out at the TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) facility at TRIUMF-ISAC. Penning traps are proved to be the most precise device to make mass measurements, but were until now not able to reach these atoms. At TRIUMF we managed, and in addition to it unprecedented accuracy, dm/m = 6x10-8, the measurement of 11Li is remarkable for the fact that with a half-life of only 8.8 ms, it is the shortest-lived nuclide ever to be weighed with this technique. Furthermore new and improved masses for 6,8He and 11Be, hence precision mass measurements on 1, 2, and 4-neutron have been performed. The new and improved mass measurements for the helium isotopes allowed for a re-evaluation of the charge radius and can also be compared to theoretical models. An overview of the TITAN mass measurements program and the ISAC facility (present and future) will be given.