[en] The mass excess of the superallowed β emitter ²⁶Si has been determined with the LEBIT Penning trap mass spectrometer to be -7140.4(2.9) keV, in agreement with recent measurements.

[en] A new long-lived isomeric state in ⁶⁵Fe has been discovered with Penning trap mass spectrometry and high-precision mass measurements of the neutron-rich isotopes ^63-65Fe and ^64-66Co have been performed with the Low-Energy Beam and Ion Trap Facility at the NSCL. For the new isomer in ⁶⁵Fe an excitation energy of 402(5) keV has been determined from the measured mass difference between the isomeric and ground states. The mass uncertainties of all isotopes have been reduced by a factor of 10-100 compared to previous results. In the case of ⁶⁴Co the previous mass value was found to deviate by about 5 standard deviations from the new measurement

[en] Gas stopping is becoming the method of choice for converting beams of rare isotopes obtained via projectile fragmentation and in-flight separation into low-energy beams. These beams allow ISOL-type experiments, such as mass measurements with traps or laser spectroscopy, to be performed with projectile fragmentation products. Current gas stopper systems for high-energy beams are based on linear gas cells filled with 0.1-1 bar of helium. While already used successfully for experiments, it was found that space charge effects induced by the ionization of the helium atoms during the stopping process pose a limit on the maximum beam rate that can be used. Furthermore, the extraction time of stopped ions from these devices can exceed 100 ms causing substantial decay losses for very short-lived isotopes. To avoid these limitations, a new type of gas stopper is being developed at the NSCL/MSU. The new system is based on a cyclotron-type magnet with a stopping chamber filled with Helium buffer gas at low pressure. RF-guiding techniques are used to extract the ions. The space charge effects are considerably reduced by the large volume and due to a separation between the stopping region and the region of highest ionization. Cyclotron gas stopper systems of different sizes and with different magnetic field strengths and field shapes are presently investigated.

No abstract available

[en] The Low Energy Beam and Ion Trap (LEBIT) is the only present facility to combine high precision Penning trap mass spectrometry with fast beam projectile fragmentation. Located at the National Superconducting Cyclotron Laboratory (NSCL), LEBIT is able to measure radionuclides produced in a chemically independent process with minimal decay losses. Recent exotic mass measurements include ⁶⁶As, ^63-66Fe, and ³²Si. ⁶⁶As is a new candidate to test the Conserved Vector Current (CVC) hypothesis. The masses of the neutron-rich iron isotopes provide additional information about the mass surface and the subshell closure at N = 40. ³²Si is a member of the A = 32, T = 2 quintet; its measurement permits the most stringent test of the validity of the isobaric multiplet mass equation (IMME). An overview of some recent measurements will be presented as well as advanced techniques for ion manipulation.

[en] High-precision Penning-trap mass measurements of the N≅Z≅34 nuclides ⁶⁸Se, ⁷⁰Se, ^70mBr, and ⁷¹Br were performed, reaching experimental uncertainties of 0.5-15 keV. The new and improved mass data together with theoretical Coulomb displacement energies were used as input for rp process network calculations. An increase in the effective lifetime of the waiting point nucleus ⁶⁸Se was found, and more precise information was obtained on the luminosity during a type I x-ray burst along with the final elemental abundances after the burst

[en] 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 chemistry-free 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 Isobaric Mass Multiplet Equation (IMME) with the A  =  32, T  =  2 quintet with a measurement 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.

[en] Masses of the radionuclides ^32,33Si and ³⁴P and of the stable nuclides ³²S and ³¹P have been measured with the Low Energy Beam and Ion Trap (LEBIT) Penning trap mass spectrometer. Relative mass uncertainties as low as 3x10^-9 have been achieved. The measured mass value of ³²Si differs from the literature value by four standard deviations. The precise mass determination of ³²Si and ³²S have been employed to test the validity of the quadratic form of the isobaric multiplet mass equation (IMME) for the most well known A=32, T=2 isospin quintet. The new experimental results indicate a dramatic breakdown of the model.

[en] Mass measurements of ^63,64Ga, ^64,65,66Ge, ^66,67,68As and ⁶⁹Se performed at the LEBIT facility at the NSCL by Penning trap mass spectrometry are presented. The rare isotopes were produced by fast beam fragmentation and in-flight separation, then converted to a low energy beam using a gas stopping technique. Masses of the N=Z nuclei ⁶⁶As and ⁶⁴Ge have been determined with uncertainties of δm/m=5x10^-7 and 6x10^-8, respectively, representing a more than ten-fold improvement in precision over previous measurements. For ^63,64Ga, ^65,66Ge, ^67,68As, and ⁶⁹Se relative mass uncertainties of δm/m<5x10^-8 were obtained. ⁶⁹Se is found to be 135 keV more bound than the value listed in the 2003 Atomic Mass Evaluation. Using theoretical Coulomb shift energies in combination with the experimental mass values for ^65,66Ge, ⁶⁷As, and ⁶⁹Se, masses for ⁶⁵As, ^66,67Se, and ⁶⁹Br are predicted with an estimated uncertainty of 100 keV. These mass values, in conjunction with our measurements, were used to calculate improved effective lifetimes of the rp-process waiting point nuclei ⁶⁴Ge and ⁶⁸Se. We find that ⁶⁴Ge is less of a waiting point while ⁶⁸Se poses a larger delay in the rp-process than previously thought. The improved mass values in this region were also used to investigate the neutron-proton pairing energy of odd-odd N=Z nuclei

[en] Direct mass measurements of the neutron-rich ^40-44S isotopes were performed at the Low Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. The resulting mass excesses (MEs) are ME(⁴⁰S)=-22 837.8(3.9) keV, ME(⁴¹S)=-19 008.6(4.1) keV, ME(⁴²S)=-17 637.9(2.7) keV, ME(⁴³S)=-12 195.5(4.9) keV, and ME(⁴⁴S)=-9 204.2(5.2) keV, and they represent improvements by factors of 20 to 50 in the precision of previous mass measurements of these isotopes.