First Penning trap mass measurement of Calcium-38

The LEBIT (Low Energy Beam and Ion Trap) project converts high-energy beams of nuclei produced in fragmentation reactions into low-energy beams. LEBIT uses a high-pressure gas stopping cell and a gas-filled ion cooler and buncher to form a slow, pulsed beam. The high quality of the extracted beam allows trap-type and other high-precision nuclear and atomic physics experiments to explore the exotic beams in a way that had up to now been restricted to ISOL-facilities like ISOLDE or TRIUMF.

For the mass measurement (38Ca-H2O)++ molecules that had been formed in the extraction process from the gas stopping cell were transferred into LEBIT's cooler/buncher system where the water was stripped off in collisions with Neon buffer gas. The doubly-charged 38Ca ions were then transferred to the Penning trap located in LEBIT's 9.4T superconducting magnet, where the mass of the ions was measured.

The figure shows the time-of-flight of Ca-ions having travelled from the Penning trap to a particle detector as a function of the frequency of a radiofrequency field applied in the Penning trap. The dip occurs at the ions' cyclotron frequency which is a direct measure of the ions' mass.

Figure 1: Time-of-flight resonance of doubly-charged Ca-38 ions. more

This measurement marks not only LEBIT's first resonance of an instable nucleus, it is the first Penning trap mass measurement of the 38Ca nuclide and it is the first Penning trap mass measurement of any nucleus at a fragmentation facility. The successful demonstration of the deceleration process is not not only a milestone in the LEBIT project at the NSCL but an important part of future facilities like the Rare Isotope Accelerator RIA.

This work was supported by the National Science Foundation through grant PHY 0110253 and by Michigan State University.

Georg Bollen
bollen at, 517-333-6435