C. M. Folden

New isotope {sup 44}Si and systematics of the production cross sections of the most neutron-rich nuclei

The results of measurements of the production of neutron-rich nuclei by the fragmentation of a {sup 48}Ca beam at 142 MeV/nucleon are presented. Evidence was found for the production of a new isotope that is the most neutron-rich silicon nuclide, {sup 44}Si, in a net neutron pickup process. A simple systematic framework was found to describe the production cross sections based on thermal evaporation from excited prefragments that allows extrapolation to other weak reaction products.

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.

First observation of new neutron-rich magnesium, aluminum, and silicon isotopes

The investigation of the limits of nuclear existence is fundamental to the understanding of nuclear forces and structure. The limits of binding for very neutron‐rich nuclei and the location of the neutron dripline are established experimentally only for the lightest elements. We report on the discovery of the new neutron‐rich isotopes 40Mg, 42,43Al, and 44Si. These rare isotopes were produced at the National Superconducting Cyclotron Laboratory by fragmentation of a 141 MeV/u 48Ca beam on a tungsten target. The combination of the A1900 fragment separator together with the analysis beam line of the S800 spectrograph provided a two‐stage fragment separation with exceptional selectivity. The observation of the odd‐odd nucleus 42Al, which was predicted to be unbound by FRDM [1] and HFB‐8 [2] models, is the first indication that the neutron drip line may be located significantly further towards heavier isotopes in this mass region than it is currently believed.