D. Davies

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 9.4 T Penning trap mass spectrometer. Examples include 66As, which has a half-live of only 96 ms, and the super-allowed Fermi-emitter 38Ca, for which a mass accuracy of 8 ppb (280 eV) has been achieved. The high accuracy of this new mass value makes 38Ca a new candidate for the test of the conserved vector current hypothesis.

A high-power laser ablation ion source for Penning trap studies of nuclear reaction products

A state of the art Penning trap is being developed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University to make precision mass measurements of rare isotopes. The system relies on thermalizing nuclear reaction products in a helium-filled cell and then extracting them from the gas through ion-manipulation and differential pumping. Atomic ions and clusters are needed to calibrate various aspects of the entire system such as transport efficiency and the main magnetic field. High-power laser ablation has proven to be a successful method for producing a wide range of ions under various conditions, including atmospheric pressure. We have developed a laser ablation system to explore the production of test beams using a variety of targets. Laser ablation studies of C, Al, Au, Ag, Cu, Fe, and Zn were carried out in a test chamber with the second harmonic, 532 nm, from a Q-switched Nd:YAG laser. Many studies were carried out under vacuum using an ion-drift system and mass analysis in a quadrupole mass filter. The ablation target and laser optics were moved to the gas cell used to collect the nuclear reaction products and several ablation studies were performed. An overview of the laser-ablation system as well as some of the results of this work will be presented.

Production Yields of Neutron‐Rich Fluorine Isotopes

Two experiments were performed at the NSCL to investigate the momentum distributions from projectile fragmentation. An 40Ar beam reacted with three N/Z targets in order to determine the effects of the N/Z of the target on the production yields of neutron‐rich fluorine isotopes. A 48Ca beam was then used with a Ta target to re‐measure the production cross‐sections and to determine the neutron drip‐line of fluorine. The cross‐sections are compared to the predictions from a deep inelastic transfer model and a semi‐empirical model, EPAX 2.15.

LEBIT — a low‐energy beam and ion trap facility at NSCL/MSU

The Low Energy Beam and Ion Trap (LEBIT) Project aims to convert the high‐energy exotic beams produced at NSCL/MSU into low‐energy low‐emittance beams. A combination of a high‐pressure gas stopping cell and a radiofrequency quadrupole (RFQ) ion accumulator and buncher will be used to manipulate the beam accordingly. High‐accuracy mass measurements on very short‐lived isotopes with a 9.4 T Penning trap system will be the first experimental program to profit from the low‐energy beams. The status of the project is presented with a focus on recent stopping tests of 100–140 MeV/A Ar18+ ions in a gas cell.