First Penning-Trap Mass Measurement of the Exotic Halo NucleusLi11

Abstract

In this Letter, we report a new mass for 11Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, t_{1/2}=8.8 ms, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of ;{8,9}Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of 7 more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11Li. This result is a remarkable confluence of nuclear and atomic physics.

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

“…This imposes a boundary condition on the excitation time and, therefore, limits the achievable resolving power. For some gases and alkaline elements, the limit may be on the order of 10 ms [32]. On the other hand, exotic nuclei far from stability often have millisecond half-lives and minute production rates.…”

“…This is possible especially for some very special cases such as 11 Li (T 1/2 = 8.75 ms). To achieve a mass resolving power of about ∆m = 86 000 and an excitation time of 18 ms, the total number of 11 Li ions has to approach N = 10000 [32]. Note, however, that the number of ions N ion is limited by the RIB production yield as well as the efficiency of the spectrometer.…”

The trap design of PENTATRAP

“…With a destructive time-of-flight cyclotron frequency detection method, the most precise mass values reached so far for stable atoms have a relative accuracy of δm/m ∼ 6 · 10 −10 [3,4]. Even for extremely short-lived species (down to t 1/2 = 8.8 ms) or very low production rates of less than one atom per second in the case of heavy and superheavy ions, relative accuracies down to 5·10 −8 have been shown [5,6]. For light and stable atoms and with a non-destructive image current detection method, results with an even more striking accuracy below the 10 −11 barrier have been achieved, allowing, e.g., for the most stringent direct test of Einstein's energy-mass-relation E = mc 2 [7] and the most precise mass measurement of 4 He [8].…”

Precision Penning trap mass measurements on exotic ions: status and perspectives

“…Mass measurements also play a crucial role for the identification of halo nuclei such as 11 Li whose mass has been recently determined with the TITAN system [7]. The superb resolving power of Penning trap mass spectrometers of 10 6 and above allows in addition the resolution [8] and even discovery of low-lying isomeric states [9].…”

“…The limited resolving power as discussed above favors measurements on light ions. Recently, the mass of the halo nucleus 11 Li with a half-life of only T 1/2 = 8.8 ms has been determined with the TITAN system [7] making it the shortest-lived nuclide studied in a Penning trap.…”