Search

At Argonne we have enhanced the AMS capabilities of the Argonne Tandem Linac Accelerator System (ATLAS) to attempt to minimize crosstalk between samples and to quickly move from one (M/Q) setting to another in order to make measurements on a large number of samples provided by the MANTRA (Measurement of Actinide Neutron Transmutation Rates by Accelerator mass spectrometry) project. Those improvements include the use of a picosecond laser to ablate actinide material into the source, a new 20-sample holder that can switch samples within 1–2 min, and a number of accelerator configuration improvements that allow quick and precise switching between species. In principle, AMS can provide production yields of actinide isotopes produced during the irradiation period at a sensitivity exceeding other mass spectrometry techniques. A total of 27 irradiated samples of a variety of actinides have been provided for measurement. We discuss our experience with these facility improvements and how well we have met our performance goals. In addition, we present preliminary results on a number of the irradiated actinide samples with this approach and compare those results to Multi-Collector ICPMS measurements.

The Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory (ANL) paused production of carbon-14 ion beams with the removal of the Tandem Van de Graaff in 2013. Installation of ECR3, an Electron Cyclotron Resonance Ion Source, returned that production capability to ATLAS, with the first C-14 beam delivered in December 2020. Information is presented on C-14 beam current, gas consumption and N-14 filtering techniques using stripping foils at different sections of ATLAS. ECR3 also fulfilled the operational goal of adding flexibility to ATLAS stable beam production capabilities. Beneficial impacts to ATLAS operation, beam development and experimental programs are discussed.

The Californium Rare Isotope Breeder Upgrade (CARIBU) facility is changing the mechanism for creating neutron-rich fission products. Spontaneous fission from a 252Cf source has provided beams to support the low energy and accelerated-beams ATLAS programs. 252Cf has a 2.65-year half-life, requiring the source to be replaced every three years to maintain high beam intensities. Fabricating an appropriately thin 252Cf source to efficiently release the fission products has been challenging. The solution to these problems is nuCARIBU, a new system that provides neutron-induced fission on actinide foils. The Best Cyclotron B6P System (6-MeV proton beam at 0.5mA) is chosen, utilizing a multi-cusp negative ion source extracting into a cyclotron, which uses carbon foils to strip the H- ions to protons. These protons are delivered to a 7Li target to produce neutrons. The fast neutrons are moderated to thermal energies to induce fission in an actinide foil, providing neutron-rich fission products. These subsystems are described in detail along with comparisons between the current CARIBU facility and the presented nuCARIBU facility. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357

A laser ablation material injection system has been developed at the ATLAS electron cyclotron resonance (ECR) ion source for use in accelerator mass spectrometry experiments. Beam production with laser ablation initially suffered from instabilities due to fluctuations in laser energy and cratering on the sample surface by the laser. However, these instabilities were rectified by applying feedback correction for the laser energy and rastering the laser across the sample surface. An initial experiment successfully produced and accelerated low intensity actinide beams with up to 1000 counts per second. With continued development, laser ablation shows promise as an alternative material injection scheme for ECR ion sources and may help substantially reduce cross talk in the source.

Since 2001, the SPIRAL 1 facility has been one of the pioneering facilities in ISOL techniques for reaccelerating radioactive ion beams: the fragmentation of the heavy ion beams of GANIL on graphite targets and subsequent ionization in the Nanogan ECR ion source has permitted to deliver beams of gaseous elements (He, N, O, F, Ne, Ar, Kr) to numerous experiments. Thanks to the CIME cyclotron, energies up to 20 AMeV could be obtained. In 2014, the facility was stopped to undertake a major upgrade, with the aim to extend the production capabilities of SPIRAL 1 to a number of new elements. This upgrade, which is presently under commissioning, consists in the integration of an ECR booster in the SPIRAL 1 beam line to charge breed the beam of different 1+ sources. A FEBIAD source (the so-called VADIS from ISOLDE) was chosen to be the future workhorse for producing many metallic ion beams. The charge breeder is an upgraded version of the Phoenix booster which was previously tested in ISOLDE. The performances of the aforementioned ingredients of the upgrade (targets, 1+ source and charge breeder) have been and are still being optimized in the frame of different European projects (EMILIE, ENSAR and ENSAR2). The upgraded SPIRAL 1 facility will provide soon its first new beams for physics and further beam development are undertaken to prepare for the next AGATA campaign. The results obtained during the on-line commissioning period permit to evaluate intensities for new beams from the upgraded facility., 9 pages, 12 figures, conference proceedings of EMIS 2018, CERN, Geneva, to appear in Nuclear Instruments and Methods B

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

Despite the more than 1 order of magnitude difference between the measured dipole moments in ^{144}Ba and ^{146}Ba, the octupole correlations in ^{146}Ba are found to be as strong as those in ^{144}Ba with a similarly large value of B(E3;3^{-}→0^{+}) determined as 48(+21-29) W.u. The new results not only establish unambiguously the presence of a region of octupole deformation centered on these neutron-rich Ba isotopes, but also manifest the dependence of the electric dipole moments on the occupancy of different neutron orbitals in nuclei with enhanced octupole strength, as revealed by fully microscopic calculations.

International audience; A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich $^{110}$Ru (t$_{1/2}$= 12 s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.

This paper presents an update of an on-going collaborative INL-ANL-ISU integral reactor physics experiment whose objective is to infer the effective neutron capture cross sections for most of the actinides of importance for reactor physics and fuel cycle studies in both fast and epithermal spectra. Some fission products are also being considered. The principle of the experiment is to irradiate very pure actinide samples in the Advanced Test Reactor at INL and, after a given time, determine the amount of the different transmutation products. The determination of the nuclide densities before and after neutron irradiation together with the neutron fluence will allow inference of effective neutron capture cross-sections in different neutron spectra.

A project to measure neutron capture cross sections of a number of actinides in a reactor environment by Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory is underway. This project will require the precise and accurate measurement of produced actinide isotopes in many (>30) samples irradiated in the Advanced Test Reactor at Idaho National Laboratory with neutron fluxes having different energy distributions. The AMS technique at ATLAS is based on production of highly-charged positive ions in an electron cyclotron resonance (ECR) ion source followed by acceleration in the ATLAS linac and mass-to-charge ( m / q ) measurement at the focus of the Fragment Mass Analyzer. Laser ablation was selected as the method of feeding the actinide material into the ion source because we expect it will have higher efficiency and lower chamber contamination than either the oven or sputtering techniques, because of a much narrower angular distribution of emitted material. In addition, a new multi-sample holder/changer to allow quick change between samples and a computer-controlled routine allowing fast tuning of the accelerator for different beams, are being developed. An initial test run studying backgrounds, detector response, and accelerator scaling repeatability was conducted in December 2010. The project design, schedule, and results of the initial test run to study backgrounds are discussed.

We present here in detail the design of the future charge breeding system of the Systeme de Production d'Ions Radioactifs Acceleres en Ligne (SPIRAL) at GANIL, France. The charge breeder will be based on an optimization of an existing Phoenix ECR ion source which was formerly tested at ISOLDE, CERN. Compared to the previous prototype, the upgraded version shall include a number of modifications widely inspired from the latest results obtained with the Argonne National Laboratory CARIBU charge breeder. Those modifications are discussed here.

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of ^3He to ^4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10^(−14) level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of ^3He/^4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

The neutron-rich nucleus $^{144}$Ba ($t_{1/2}$=11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers $A$ less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced $E1$ transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a post-accelerated 650-MeV $^{144}$Ba beam on a 1.0-mg/cm$^2$ $^{208}$Pb target. The measured value of the matrix element, $\langle 3_1^- \| \mathcal{M}(E3) \| 0_1^+ \rangle=0.65(^{+17}_{-23})$ $e$b$^{3/2}$, corresponds to a reduced $B(E3)$ transition probability of 48($^{+25}_{-34}$) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation., Comment: 5 pages, 2 figures, 1 table, Physical Review Letters 2016

The first application of 39Ar Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory was to date ocean water samples relevant to oceanographic studies using the gas-filled magnet technique to separate the 39K–39Ar isobars. In particular the use of a quartz liner in the plasma chamber of the electron cyclotron resonance ion source enabled a 39K reduction of a factor ∼130 compared to previous runs without liners, and allowed us to reach a detection sensitivity of 39Ar/Ar = 4 × 10−17. In order to improve this sensitivity and allow the measurement of lower ratios, higher ion source currents and a lower overall 39K background are necessary. This paper summarizes our efforts to investigate new methods combining low level potassium cleaning techniques with the use of ultra-pure aluminum liners in the plasma chamber of the ion source. The aim of the study was to improve by 1–2 orders of magnitude the 39Ar detection sensitivity required in the selection of ultra-pure materials for detectors used in weakly interacting massive particle dark matter searches.

The Californium Rare Ion Breeder Upgrade (CARIBU) to the ATLAS superconducting linac facility is currently being commissioned. It provides low-energy and re-accelerated beams of neutron-rich isotopes obtained from 252Cf fission. The fission products from a 252Cf source are stopped in a large high-intensity gas catcher, thermalized and extracted through an RFQ cooler, accelerated to 50 kV and mass separated in a high-resolution separator before being sent to either an ECR charge breeder for post-acceleration through the ATLAS linac or to a low-energy experimental area. This approach gives access to beams of very neutron-rich isotopes, many of which have not been available at low or Coulomb barrier energies previously. These beams provide unique opportunities for measurements along the r-process path. To take advantage of these unique possibility, the reaccelerated beams from CARIBU will be made available at the experimental stations of ATLAS to serve equipment such as Gammasphere, HELIOS and the reaction spectrometers. In addition, the Canadian Penning Trap (CPT) mass spectrometer has been moved to the CARIBU low-energy experimental area and a new injection line has been built. The new injection line consists of a RFQ buncher sitting on a 50 kV high-voltage platform that will accumulate the mass separated 50 kV radioactive beams, cool and extract them as a pulsed beam of 3 keV. This beam can be sent either to a tape station for diagnostics and tuning, or a cryogenic linear trap for preparation before transfer to the high-precision Penning trap where the mass measurements will take place. Initial CARIBU commissioning is proceeding with a 2 mCi source that will be replaced by a 100 mCi source as the commissioning proceeds. Final operation will use a 1 Ci source and attain yield in excess of 107 ions/sec for the most intense beams at low energy, an order of magnitude less for reaccelerated beams.

An Electron Beam Ion Source Charge Breeder (EBIS-CB) has been developed at Argonne National Laboratory as part of the californium rare ion breeder upgrade. For the past year, the EBIS-CB has been undergoing commissioning as part of the ATLAS accelerator complex. It has delivered both stable and radioactive beams with A/Q6, breeding times30 ms, low background contamination, and charge breeding efficiencies18% into a single charge state. The operation of this device, challenges during the commissioning phase, and future improvements will be discussed.

Gas catchers allow the transformation of radioactive recoils from various sources into a good optical quality low-energy radioactive beam that is then available for experiments at low-energy or for further acceleration. The CARIBU project uses such a large gas catcher to create beams of neutron-rich isotopes from a Californium source for post-acceleration through the ATLAS superconducting linac to open new research opportunities for nuclear structure physics and astrophysics. The RF gas catcher developed at Argonne has now demonstrated operation at the high intensity required for this application.

The Californium Rare Ion Breeder Upgrade (CARIBU) for the ATLAS facility is under construction. The facility will use 252Cf fission fragments thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams an existing ATLAS ECR ion source is being reconfigured as a charge breeder source. A 1Ci 252Cf source will provide sufficient yield to deliver beams of up to ∼106 far-from-stability ions per second on target. The facility design, expected performance and the project status will be presented in this paper.

ThuM07; International audience; The present paper summarizes the results obtained from the past few years in the framework ofthe Enhanced Multi-Ionization of short-Lived Isotopes for Eurisol (EMILIE) project. The EMILIEproject aims at improving the charge breeding techniques with both Electron Cyclotron ResonanceIon Sources (ECRIS) and Electron Beam Ion Sources (EBISs) for European Radioactive Ion Beam(RIB) facilities. Within EMILIE, an original technique for debunching the beam from EBIS chargebreeders is being developed, for making an optimal use of the capabilities of CW post-acceleratorsof the future facilities. Such a debunching technique should eventually resolve duty cycle andtime structure issues which presently complicate the data-acquisition of experiments. The resultsof the first tests of this technique are reported here. In comparison with charge breeding withan EBIS, the ECRIS technique had lower performance in efficiency and attainable charge statefor metallic ion beams and also suffered from issues related to beam contamination. In recentyears, improvements have been made which significantly reduce the differences between the twotechniques, making ECRIS charge breeding more attractive especially for CW machines producingintense beams. Upgraded versions of the Phoenix charge breeder, originally developed byLPSC, will be used at SPES and GANIL/SPIRAL. These two charge breeders have benefited fromstudies undertaken within EMILIE, which are also briefly summarized here.

The r-process nuclide 244Pu (t1/2 = 80.8 Myr) was extant in the Early Solar System and is presently considered as extinct. However, fresh 244Pu produced in the Galaxy, may reach the Solar System and Earth through influx of interstellar dust or as direct ejecta from supernovae. Detection of such traces requires high sensitivity, discrimination power and efficiency. Accelerator mass spectrometry (AMS), despite low efficiency, is the method of choice. We report on the successful detection of 244Pu by AMS, using highly-charged positive ions produced in an Electron Cyclotron Resonance (ECR) ion source and accelerated with the superconducting heavy-ion linear accelerator ATLAS at Argonne National Laboratory. 244Pu34+,35+,36+ ions with a final energy of 0.7 MeV/u were dispersed in m/q using the Argonne Fragment Mass Analyzer (FMA) and are well discriminated from parasitic ions. A count rate of 0.7 244Pu counts/min was observed for a sample containing 2.7 × 108 244Pu atoms/mg. The technique described here is presently used, with improved setup and accelerator conditions, for the measurement of neutron capture cross sections in the actinide region.

Initial experiments at the ATLAS facility [Nucl. Instr. and Meth. B 92 (1994) 241] resulted in a clear detection of cosmogenic Ar-39 signal at the natural level. The present paper summarizes the recent developments of Ar-39 AMS measurements at ATLAS: the use of an electron cyclotron resonance (ECR) positive ion source equipped with a special quartz liner to reduce K-39 background, the development of a gas handling system for small volume argon samples, the acceleration of Ar-39(8+) ions to 232 MeV, and the final separation of Ar-39 from K-39 in a gas-filled spectrograph. The first successful AXIS measurements of Ar-39 in ocean water samples from the Southern Atlantic ventilation experiment (SAVE) are reported. Published by Elsevier B.V.

Among the many production and destruction nuclear reactions that bear on the net 44 Ti yield in the supernova environment, recently highlighted by γ-ray astronomy observations, the α capture on 40 Ca stands out in the α-rich freezeout phase conjectured by astrophysical models. We activate a He-gas target with a 40 Ca beam and implant recoiling 44 Ti nuclei (∼10 6 ) in a Cu catcher. The 44 Ti atoms chemicallyextracted with a nat Ti carrier are counted by accelerator mass spectrometry (AMS). The measurement of the 44 Ti/Ti ratio, together with the amount of Ti carrier added, determine the number of 44 Ti nuclei produced in the activation, independent of chemical yield or transmission efficiency. The resonance strength (7.4±2.5 eV) at E cm ∼1.1 MeV/n determined for two close-by levels of 44 Ti is in excellent agreement with previous prompt-γ measurements. We plan to extend our experiments to the lower energy range.

A new 10 GHz electron cyclotron resonance ion source (ECRIS) has been constructed and commissioned for the ATLAS accelerator. This new source replaces the original ATLAS ECRIS that has been in operations since 1987. The goal of this upgrade project was to significantly improve the source performance while maintaining maximum operational flexibility for solid material feeds. The new source design includes a large magnetic-field gradient, aluminum plasma chamber, and bias disk following modern ECRIS design concepts. Eight solenoid coils from the original source along with a new iron yoke form the magnetic mirror. Hall Probe measurements showed the axial B field to be within 1% of the POISSON design model calculated at 400 A per coil. The injection and extraction mirror ratios are approximately 4.4 and 2.9, respectively, with a minimum field of 3.0 kG. A new aluminum plasma chamber houses the NdFeB hexapole magnets, which are encased in austenitic stainless steel to allow for direct water cooling. An open he...

Two techniques for the discrete injection of material into an Electron Cyclotron Resonance ion source (ECRIS) have been developed for the purpose of measuring the ionization and confinement times of ion species. Previously only solid materials in conjunction with a pulsed laser were used in these studies due to the discrete material introduction produced by this configuration. The first method replaces the pulsed laser with a fast high voltage pulse applied to a sputter sample. The high voltage pulse has a rise time of 100 ns, fall time of 80.0 μs, and variable pulse duration. The second method utilizes a fast-pulsed gas valve capable of producing a gas pulse 160 μs in width. These pulse widths are well below the ionization times of the lower charge states and thus allows for time measurements to be made of all charge states. Both of these techniques can be employed to study the effects of rf power, coil configuration, biased disk, and gas mixing on ionization and confinement times. Rise times for neon, argon, and gold will be presented.

A new multi-sample changer has been constructed allowing rapid changes between samples. The sample changer has 20 positions and is capable of moving between samples in 1 min. The sample changer is part of a project using Accelerator Mass Spectrometry (AMS) at the Argonne Tandem Linac Accelerator System (ATLAS) facility to measure neutron capture rates on a wide range of actinides in a reactor environment. This project will require the measurement of a large number of samples previously irradiated in the Advanced Test Reactor at Idaho National Laboratory. The AMS technique at ATLAS is based on production of highly charged positive ions in an electron cyclotron resonance ion source followed by acceleration in the ATLAS linac. The sample material is introduced into the plasma via laser ablation chosen to limit the dependency of material feed rates upon the source material composition as well as minimize cross-talk between samples.

The radionuclide Ar-39 is produced in the atmosphere by cosmic rays and has an isotopic abundance of 8.1 x 10(-16). Because its half life (T-1/2 = 269 years) is well matched to the time periods involved in the oceanic currents around the Earth, the measurement of the Ar-39 isotopic ratio is an ideal tool to date ocean water from different depths. It would complement the information gained by the C-14 measurements (T-1/2 = 5730 years). However, the measurement of the isotopic ratio Ar-39/Ar-40 is a technical challenge: 1 L of modern ocean water contains similar to6500 atoms of Ar-39, and produces similar to17 decays per year. Although it has been possible to detect the Ar-39 decays in large volumes of sea water by using the low level counting technique, the possibility of measuring the number of Ar-39 atoms faster and in smaller samples using the accelerator mass spectrometry (AMS) technique would be a major breakthrough for this type of measurement. The development of a viable AMS method for Ar-39 has been underway for several years at Argonne National Laboratory, and is presently hampered by the presence of stable K-39 ions coming from the ion source. Although the intensity of this isobaric contaminant is low (similar topA extracted from the source), it has to be compared with the Ar-39 beam intensity (atoms per minutes). In order to separate, these two beams (whose mass difference is only 1.6 x 10(-5)), the intensity of the K-39 beam coming from the ion source has to be reduced by several orders of magnitude. This reduction has been investigated both at Argonne National Laboratory and at Louvain-la-Neuve. Two techniques have been tried out. In the first, a quartz liner is used to provide a clean surface, while in the second these impurities are buried in a SiO2 layer formed in situ by running the source with a mixture of silane and oxygen. The K-39 background has been reduced by a factor of 100 with these treatments. These techniques and their results obtained both at Argonne and Louvain-la-Neuve will be presented. The ion source specific requirements for this type of application will also be discussed. (C) 2004 American Institute of Physics.

An Electron Beam Ion Source Charge Breeder (EBIS-CB) has been developed at Argonne to breed radioactive beams from the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne Tandem Linac Accelerator System (ATLAS). The EBIS-CB will replace the existing ECR charge breeder to increase the intensity and significantly improve the purity of reaccelerated radioactive ion beams. The CARIBU EBIS-CB has been successfully commissioned offline with an external singly charged cesium ion source. The performance of the EBIS fully meets the specifications to breed rare isotope beams delivered from CARIBU. The EBIS is being relocated and integrated into ATLAS and CARIBU. A long electrostatic beam transport system including two 180° bends in the vertical plane has been designed. The commissioning of the EBIS and the beam transport system in their permanent location will start at the end of this year.

Current accelerator mass spectrometry experiments at the Argonne Tandem Linac Accelerator System facility at Argonne National Laboratory push us to improve the ion source performance with a large number of samples and a need to minimize cross contamination. These experiments can require the creation of ion beams from as little as a few micrograms of material. These low concentration samples push the limit of our current efficiency and stability capabilities of the electron cyclotron resonance ion source. A combination of laser ablation and sputtering techniques coupled with a newly modified multi-sample changer has been used to meet this demand. We will discuss performance, stability, and consumption rates as well as planned improvements.

The extreme sensitivity and discrimination power of accelerator mass spectrometry (AMS) allows for the search and the detection of rare nuclides either in natural samples or produced in the laboratory. At Argonne National Laboratory, we are developing an AMS setup aimed in particular at the detection of medium and heavy nuclides, relying on the high ion energy achievable with the ATLAS superconducting linear accelerator and on gas-filled magnet isobaric separation. The setup was recently used for the detection of the 146Sm p-process nuclide and for a new determination of the 146Sm half-life (68.7 My). AMS plays an important role in the measurement of stellar nuclear reaction cross sections by the activation method, extending thus the technique to the study of production of long-lived radionuclides. Preliminary measurements of the 147Sm(γ,n)146Sm are described. A measurement of the 142Nd(α,γ)146Sm and 142Nd(α,n)145Sm reactions is in preparation. A new laser-ablation method for the feeding of the Electron Cyclotron Resonance (ECR) ion source is described.

The extinct p-process nuclide 146Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its alpha-decay daughter 142Nd. Based on analyses of 146Sm/147Sm alpha-activity and atom ratios, we determined the half-life of 146Sm to be 68 \pm 7 (1sigma) million years (Ma), which is shorter than the currently used value of 103 \pm 5 Ma. This half-life value implies a higher initial 146Sm abundance in the early solar system, (146Sm/144Sm_0 = 0.0094\pm0.0005 (2sigma), than previously estimated. Terrestrial, Lunar and Martian planetary silicate mantle differentiation events dated with 146Sm-142Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)_0 values., Comment: 48 pages, 9 figures, 3 tables. Manuscript revised

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs(+) surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved ∼70% injection∕extraction efficiency and breeding efficiency into the most abundant charge state of ∼17%.

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory ATLAS facility will provide low-energy and reaccelerated neutron-rich radioactive beams for the nuclear physics program. A 70 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The final CARIBU configuration will utilize a 1 Ci (252)Cf source to produce radioactive beams with intensities up to 10(6) ions∕s for use in the ATLAS facility. The ECR charge breeder has been tested with stable beam injection and has achieved charge breeding efficiencies of 3.6% for (23)Na(8+), 15.6% for (84)Kr(17+), and 13.7% for (85)Rb(19+) with typical breeding times of 10 ms∕charge state. For the first radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The project has been commissioned with a radioactive beam of (143)Ba(27+) accelerated to 6.1 MeV∕u. In order to take advantage of its lower residual contamination, an EBIS charge breeder will replace the ECR charge breeder in the next two years. The advantages and disadvantages of the two techniques are compared taking into account the requirements of the next generation radioactive beam facilities.

A numerical toolset to help in understanding physical processes in the electron cyclotron resonance charge breeder (ECRCB) and further to help optimization and design of current and future machines is presented. The toolset consists of three modules (Monte Carlo charge breeding code, generalized electron cyclotron resonance ion source modeling, and ion extraction), each modeling different processes occurring in the ECRCB from beam injection to extraction. The toolset provides qualitative study, such as parameter studies, and scaling of the operation, and physical understanding in the ECRCB. The methodology and a sample integrated modeling are presented.

A major upgrade of the first ATLAS 10 GHz electron cyclotron resonance (ECR) ion source, which began operations in 1987, is in the planning and procurement phase. The new design will convert the old two-stage source into a single-stage source with an electron donor disk and high gradient magnetic field that preserves radial access for solid material feeds and pumping of the plasma chamber. The new magnetic-field profile allows for the possibility of a second ECR zone at a frequency of 14 GHz. An open hexapole configuration, using a high-energy-product Nd–Fe–B magnet material, having an inner diameter of 8.8 cm and pole gaps of 2.4 cm, has been adopted. Models indicate that the field strengths at the chamber wall, 4 cm in radius, will be 9.3 kG along the magnet poles and 5.6 kG along the pole gaps. The individual magnet bars will be housed in austenitic stainless steel, allowing the magnet housing within the aluminum plasma chamber to be used as a water channel for direct cooling of the magnets. Eight sole...

A conventional zero-dimensional (uniform plasma parameters with no spatial variations) fluid model will provide a good match with an experimental electron cyclotron resonance ion source (ECRIS) charge-state distribution (CSD) if provided with a judicious set of user inputs. However, this arbitrarily chosen set of inputs is not necessarily unique. To be truly predictive, an ECRIS model should rely on experimental parameters as inputs. A multi-species model for an ECRIS plasma using experimental parameters as inputs is under development. The model eliminates electron temperature as a user input by employing a 2 V(v,θ) Fokker–Planck code with an ECR heating term to calculate the non-Maxwellian anisotropic electron distribution function. Further arbitrary user inputs are eliminated in favor of controlled parameters by bounce averaging the Fokker–Planck coefficients for a one-dimensional (1D)/2 V axial model. The neutral gas modeling has been extended to 1D using axially coupled particle balance equations. The...

The isotope {sup 257}Rf was produced in the fusion-evaporation reaction {sup 208}Pb({sup 50}Ti,n){sup 257}Rf. Reaction products were separated and identified by mass. Delayed spectroscopy of {sup 257}Rf and its decay products was performed. A partial decay scheme with configuration assignments is proposed based on {alpha} hindrance factors. The excitation energy of the 1/2{sup +}[620] configuration in {sup 253}No is proposed. The energy of this 1/2{sup +} state in a series of N=151 isotones increases with nuclear charge, reflecting an increase in the N=152 gap. This gap is deduced to grow substantially from 850 to 1400 keV between Z=94 and 102. An isomeric state in {sup 257}Rf, with a half-life of 160{sub -31}{sup +42} {mu}s, was discovered by detecting internal conversion electrons followed by {alpha} decay. It is interpreted as a three-quasiparticle high-K isomer. A second group of internal conversion electrons, with a half-life of 4.1{sub -1.3}{sup +2.4} s, followed by {alpha} decay, was also observed. These events might originate from the decay of excited states in {sup 257}Lr, populated by electron-capture decay of {sup 257}Rf. Fission of {sup 257}Rf was unambiguously detected, with a branching ratio of b{sub Rf}{sup SF}=0.02{+-}0.01.

The construction of the Californium Rare Ion Breeder Upgrade, a new radioactive beam facility for the Argonne tandem linac accelerator system (ATLAS), is in progress. The facility will use fission fragments from a 1 Ci (252)Cf source, thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams, the existing ATLAS ECR1 ion source has been redesigned to function as a charge breeder source. The design features, initial results, and status of this charge breeder configuration are presented.

The Electron Beam Ion Source (EBIS), developed to breed Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beams at Argonne Tandem Linac Accelerator System (ATLAS), is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates, and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The off-line charge breeding tests are being performed using a surface ionization source that produces singly charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20% ± 0.7%) breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times, and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this paper, we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.

A 14 GHz electron-cyclotron-resonance (ECR) ion source has been designed and built at Argonne National Laboratory. The source is a modification of the AECR [D. J. Clark, C. M. Lyneis, and Z. Q. Xie, 14th Particle Accelerator Conference (PAC), IEEE Conference 91 CH3038-7, 1991 (unpublished), p. 2796 and C. M. Lyneis, Z. Q. Zie, D. J. Clark, R. S. Lam, and S. A. Lundgren, 10th International Workshop on ECR Ion Sources, Oak Ridge, ORNL CONF-9011136, 1990 (unpublished), p. 47.] at Berkeley and incorporates the latest results from electron-cyclotron-resonance (ECR) developments to produce intense beams of highly charged ions, including an improved magnetic confinement of the plasma electrons with an axial mirror ratio of 3.5. The aluminum plasma chamber and extraction electrode as well as a biased disk on axis at the microwave injection side donate additional electrons to the plasma, making use of the large secondary electron yield from aluminum oxide. The source is capable of ECR plasma heating using two diff...

The {sup 44}Ti(t{sub 1/2}=59 yr) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by {gamma}-ray astronomy from the Cas A remnant. We investigate in the laboratory the major {sup 44}Ti production reaction {sup 40}Ca({alpha},{gamma}){sup 44}Ti (E{sub c.m.}{approx}0.6-1.2 MeV/u) by direct off-line counting of {sup 44}Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova {sup 44}Ti yield by a factor {approx}2 over previous estimates and bringing it closer to Cas A observations.

The Rare Isotope Accelerator (RIA) facility utilizes the concept of simultaneous acceleration of two charge states from the ion source. We are building a prototype two charge‐state (2Q) injector of the RIA Driver Linac, which includes an ECR ion source, a LEBT and one‐segment of the prototype RFQ. Currently, the 2Q‐LEBT Facility consists of Berkeley Ion Equipment Corporation BIE‐100 ECR ion source. The rf transmitters, high voltage power supplies, turbo pumps and other related equipment were received with the source. BIE‐100 is an all‐permanent‐magnet source and has the highest magnetic field strengths for an ECR ion source of this type ever built. The magnetic field achieves a maximum strength of 11 kG at the plasma chamber surface and 13 kG on the axis. The source can operate with two‐frequency plasma heating of 12.75 and 14.5 GHz. The reassembly of the source has been completed and beam production was achieved in the June 2004. This report includes measured beam current and emittance for 16O from the s...

The excitation energy, spin and parity of the yrast superdeformed (SD) band in 152Dy have been established. The excitation energy of the lowest observed level in this band is found to be 10,644 keV with an assigned spin and parity of 24+. In addition, nine transitions of dipole character have been identified, which connect the excited superdeformed band 6 in 152Dy to the yrast SD band. The excitation energy of the lowest level in the excited SD band 6 is 14,239 keV. The spin and parity of this state has been determined to be either 29− or 31−. The measured properties of SD band 6 are consistent with an interpretation in terms of a rotational band built on an octupole vibration. A comparison with an RPA calculation by Nakatsukasa et al. suggests that the spin of the lowest SD band 6 level is 31−.

The excitation energy, spin and parity of the yrast superdeformed band 1 in 152Dy have been established. The evidence comes mainly from the measured properties of a 4011 keV single‐step transition connecting the yrast superdeformed level fed by the 693 keV transition to the 27− yrast state. Four additional, weaker, linking γ rays have been placed as well. The excitation energy of the lowest superdeformed band 1 member is 10,644 keV and its spin and parity are determined to be 24+. A further nine transitions of dipole character have been identified, which connect the excited superdeformed band 6 in 152Dy to the yrast SD band 1. The excitation energy of the lowest level in the excited SD band 1 is 14,239 keV. The lowest state in band 6 has been determined to be of negative parity and odd spin (29− or 31−). The measured properties of band 6 are consistent with an interpretation in terms of an octupole vibrational band. A comparison with an RPA calculation by Nakatsukasa et al. suggests that the spin of the lowest SD band 6 level is 31−.

A new 14 GHz ECRIS has been designed and built over the last two years. The source design incorporates the latest results from ECR developments to produce intense beams of highly charged ions. An improved magnetic electron confinement is achieved from a large mirror ratio and strong hexapole field. The aluminum plasma chamber and extraction electrode as well as a biased disk on axis at the microwave injection side donate additional electrons to the plasma, making use of the large secondary electron yield from Al/sub 2/O/sub 3/. The source will be capable of ECR plasma heating using two different frequencies simultaneously to increase the electron energy gain. To be able to deliver usable intensities of the heaviest ion beams the design will also allow axial access for metal evaporation ovens and solid material. The main design goal is to produce several e/spl mu/A of at least /sup 238/U/sup 34+/ in order to accelerate the beam to Coulomb-barrier energies without further stripping. First charge state distributions for /sup 16/O and /sup 40/Ar have been measured.

The excitation energy, spin, and parity of the yrast superdeformed band in 152Dy have been firmly established. The evidence comes mainly from the measured properties of a 4011 keV single-step transition connecting the yrast superdeformed level fed by the 693 keV transition to the 27- yrast state. Four additional, weaker, linking gamma rays have been placed as well. The excitation energy of the lowest superdeformed band member is 10 644 keV and its spin and parity are determined to be 24+.

Beams of ions from the laser ablation method of solid materials into an electron cyclotron resonance ion source (ECRIS) plasma have been used for the first time in experiments at ATLAS. Initial accelerator mass spectroscopy experiments using laser ablation for actinides and samarium have been performed. Initial results of coupling the laser system to the ECR source have guided us in making a number of changes to the original design. The point of laser impact has been moved off axis from the center of the ECR injection side. Motor control of the laser positioning mirror has been replaced with a faster and more reliable piezo-electric system, and different raster scan patterns have been tested. The use of the laser system in conjunction with a multi-sample changer has been implemented. Two major problems that are being confronted at this time are beam stability and total beam intensity. The status of the development will be presented and ideas for further improvements will be discussed.

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory Argonne Tandem Linac Accelerator System (ATLAS) facility provides low-energy and accelerated neutron-rich radioactive beams to address key nuclear physics and astrophysics questions. A 350 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The ECR charge breeder has achieved stable beam charge breeding efficiencies of 10.1% for (23)Na(7+), 17.9% for (39)K(10+), 15.6% for (84)Kr(17+), and 12.4% for (133)Cs(27+). For the radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The typical breeding times are 10 ms/charge state, but the source can be tuned such that this value increases to 100 ms/charge state with the best breeding efficiency corresponding to the longest breeding times-the variation of efficiencies with breeding time will be discussed. Efforts have been made to characterize and reduce the background contaminants present in the ion beam through judicious choice of q/m combinations. Methods of background reduction are being investigated based upon plasma chamber cleaning and vacuum practices.