The LEBIT facility at MSU. High-precision mass measurements at a fragmentation facility

The low-energy beam and ion trap facility LEBIT at the NSCL at MSU has demonstrated that rare isotopes produced by fast-beam fragmentation can be slowed down and prepared such that precision experiments with low-energy beams are possible. For this purpose high-pressure gas-stopping is employed combined with advanced ion manipulation techniques. Penning trap mass measurements on short-lived rare isotopes have been performed with a 9.4T Penning trap mass spectrometer. Examples indude 66 As, which has a half-live of only 96ms, and the super-allowed Fermi-emitter 38 Ca, for which a mass accuracy of 8 ppb (280 eV) has been achieved. The high accuracy of this new mass value makes 38 Ca a new candidate for the test of the conserved vector current hypothesis.