Penning-trap mass spectrometry has reached a state that allows its application to very short-lived isotopes available from various sources of radioactive beams. Mass values with outstanding accuracy ...are achieved even far from stability. This paper illustrate the state of the art by discussing the status of the ISOLTRAP experiment at ISOLDE/CERN. In addition an overview of new ion-trap projects for nuclear mass determination will be given.
We report high-precision mass measurements of ^{50-55}Sc isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their ...uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for ^{53-55}Sc. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers N=32 and N=34 above proton-magic Z=20. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the N=32 isotone, confirming that the empirical neutron shell gap energies peak at the doubly magic ^{52}Ca. Moreover, our data, combined with other recent measurements, do not support the existence of a closed neutron shell in ^{55}Sc at N=34. The results were compared to predictions from both ab initio and phenomenological nuclear theories, which all had success describing N=32 neutron shell gap energies but were highly disparate in the description of the N=34 isotone.
Gas stoppers have been used for a long-standing successful science program at Michigan State University with stopped and rare-isotope beams produced by projectile fragmentation. The National ...Superconducting Cyclotron Laboratory’s Coupled Cyclotron Facility has recently transitioned into the Facility for Rare Isotope Beams (FRIB) laboratory to provide rare isotopes using a high-power superconducting linear accelerator and new production facilities. To allow the science program with stopped and reaccelerated beams to continue during the transition period, a stand-alone capability was added. The Batch Mode Ion Source (BMIS) was built and has been providing beams of long-lived and stable isotopes of a variety of elements for successful user experiments. The BMIS system is described and results from the production of various beams are presented.
Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. The nuclear shell structure varies as a result of changes in the nuclear mean field ...with the number of neutrons N and protons Z, and these variations can be probed by measuring the mass differences between nuclei. The N = Z = 40 self-conjugate nucleus 80Zr is of particular interest, as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. Here we provide evidence for the existence of a deformed double-shell closure in 80Zr through high-precision Penning trap mass measurements of 80–83Zr. Our mass values show that 80Zr is substantially lighter, and thus more strongly bound than predicted. This can be attributed to the deformed shell closure at N = Z = 40 and the large Wigner energy. A statistical Bayesian-model mixing analysis employing several global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory.High-precision mass measurements of exotic zirconium nuclei are reported, and reveal a double-shell closure for the deformed nucleus 80Zr, which is more strongly bound than previously thought.
Design of the Advanced Rare Isotope Separator ARIS at FRIB Hausmann, M.; Aaron, A.M.; Amthor, A.M. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2013, Letnik:
317
Journal Article
Recenzirano
The Facility for Rare Isotopes Beams (FRIB) at Michigan State University will use projectile fragmentation and induced in-flight fission of heavy-ion primary beams at energies of 200MeV/u and higher ...and at a beam power of 400kW to generate rare isotope beams for experiments in nuclear physics, nuclear astrophysics, and fundamental symmetries, as well as for societal needs. The Advanced Rare Isotope Separator (ARIS) has been designed as a three-stage fragment separator for the efficient collection and purification of the rare isotope beams of interest. A vertically bending preseparator (first stage) with production target and beam dump is fully integrated into a production target facility hot cell with remote handling. The new separator compresses the accepted momentum width of up to ±5% of the beam by a factor of three in the standard operational mode. Provisions for alternate operational modes for specific cases are included in the design. This preseparator is followed by two, horizontally-bending separator stages (second and third stages) utilizing the magnets from the existing A1900 fragment separator at the National Superconducting Cyclotron Laboratory (NSCL). These stages can alternatively be coupled to a single high-resolution separator stage, resulting in the flexibility to optimize the operation for different experiments, including momentum tagging and in-flight particle identification of rare isotope beams. The design of ARIS will be presented with an emphasis on beam physics characteristics, and anticipated operational modes will be described.
A laser ablation source for offline ion production at LEBIT Izzo, C.; Bollen, G.; Bustabad, S. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
06/2016, Letnik:
376
Journal Article
Recenzirano
Odprti dostop
A laser ablation ion source has been developed and implemented at the Low-Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory. This offline ion source ...enhances the capabilities of LEBIT by providing increased access to ions used for calibration measurements and checks of systematic effects as well as stable and long-lived ions of scientific interest. The design of the laser ablation ion source and a demonstration of its successful operation are presented.
Nuclear mass measurements of isotopes are key to improving our understanding of nuclear structure across the chart of nuclides, in particular, for the determination of the appearance or disappearance ...of nuclear shell closures. We present high-precision mass measurements of neutron-rich Ca, Ti, and V isotopes performed at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN) and the Low Energy Beam and Ion Trap (LEBIT) facilities. These measurements were made using the TITAN multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS) and the LEBIT 9.4T Penning trap mass spectrometer. In total, 13 masses were measured, 8 of which represent increases in precision over previous measurements. These measurements refine trends in the mass surface around N=32 and N=34, and support the disappearance of the N=32 shell closure with increasing proton number. Additionally, our data do not support the presence of a shell closure at N=34.
A model device to transport thermal ions in the cyclotron gas stopper, a next-generation beam thermalization device under construction at the National Superconducting Cyclotron Laboratory, is ...presented. Radioactive ions produced by projectile fragmentation will come to rest at distances as large as 45cm from the extraction orifice of the cyclotron gas stopper. The thermalized ions will be transported to the exit by RF carpets employing the recently developed “ion surfing” method. A quarter-circle prototype RF carpet was tested with potassium ions, and ion transport velocities as high as 60m/s were observed over distances greater than 10cm at a helium buffer gas pressure of 80mbar. The transport of rubidium ions from an RF carpet to an electrode below was also demonstrated. The results of this study formed the basis of the design of the RF carpets for use in the cyclotron gas stopper.
The Facility for Rare Isotope Beams (FRIB) is a major new scientific user facility under construction in the United States for nuclear science research with beams of rare isotopes. 400 kW beam ...operations with heavy ions ranging from oxygen to uranium will create a high radiation environment for many components, particularly for the beam line components located in the target hall, where approximately 100 kW of beam power are dissipated in the target and another 300 kW are dissipated in the beam dump. Detailed studies of the component activation, their remote handling, storage, and transport, have been performed to ensure safe operation levels in this environment. Levels of activation are calculated for the beam line components within the FRIB target hall.
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