High-precision Penning trap mass measurements of ‘difficult’ elements produced via projectile fragmentation with LEBIT

摘要

Rare isotope beams of many elements can be difficult or impossible to obtain at ISOL facilities due to their high melting points or chemical reactivity, but they are easily produced by projectile fragmentation and in-flight separation, a technique that rapidly produces fragments lighter than the projectile in a chemistryfree manner. Until recently, such high-energy projectile fragments could not be reduced to the thermal energies necessary for precision mass measurements in Penning traps. The Low Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory (NSCL) has demonstrated that projectile fragment beams can be thermalized and measured in a high-precision Penning trap. Since 2005, over 30 isotopes have been measured with LEBIT, including several isotopes of elements which are difficult for ISOL facilities to produce, such as Fe, Co, Si, Br, and S. These measurements have contributed to our understanding of nuclear structure, nuclear astrophysics, and fundamental symmetries. Some recent highlights include the discovery of an isomeric state in 65Fe, testing the IsobaricMassMultiplet Equation (IMME) with theA=32, T=2 quintet with ameasurement of 32Si, probing out to the proton dripline with 70mBr, and studying the N=28 shell closure with measurements of ~(40-44)S. Results of these measurements will be discussed, along with the technical developments which made them possible.