Direct Mass Measurement of the Four-Neutron Halo Nuclide He-8
Abstract
A high-precision Penning trap mass measurement of the exotic (8)He nuclide (T(1/2)=119 ms) has been carried out resulting in a reduction of the uncertainty of the halo binding energy by over an order of magnitude. The new mass, determined with a relative uncertainty of 9.2x10(-8) (delta m=690 eV) is 13 keV less bound than the previously accepted value. The mass measurement is of great relevance for the recent charge-radius measurement of (8)He [P. Mueller , Phys. Rev. Lett. 99, 252501 (2007).]. The (8)He mass is the first result from the newly-commissioned Penning trap: TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) at the ISAC (Isotope Separator and Accelerator) radioactive beam facility at TRIUMF.