First Penning-trap mass measurement in the millisecond half-life range: The exotic halo nucleus Li-11

Perched precariously on the brink of nuclear stability, 11Li has the lowest two-neutron binding energy of all nuclei. This gives rise to the exotic phenomena of a nuclear halo that has a wavefunction extending beyond the range normally allowed for by the strong interaction. The most accurate mass measurements are achieved using Penning traps. In this letter, we report a new mass for 11Li using the TITAN trapping experiment at TRIUMF's ISAC facility where 'designer atomic nuclei' can be produced and studied in detail. This is by far the shortest-lived nuclide, t1/2 = 8.8 ms, for which a mass measurement has ever been performed with a Penning trap. We derive a new two-neutron separation energy of 369.15(65) keV: seven times more precise than the best previous value. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11Li from recent isotope shift measurements