Search

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.

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.

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 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.

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.

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.

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.

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 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 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...

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 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.

A Monte Carlo charge breeding code (MCBC) is being developed by FAR-TECH, Inc. to model the capture and charge breeding of 1+ ion beam in an electron cyclotron resonance ion source (ECRIS) device. The ECRIS plasma is simulated using the generalized ECRIS model which has two choices of boundary settings, free boundary condition and Bohm condition. The charge state distribution of the extracted beam ions is calculated by solving the steady state ion continuity equations where the profiles of the captured ions are used as source terms. MCBC simulations of the charge breeding of Rb+ showed good agreement with recent charge breeding experiments at Argonne National Laboratory (ANL). MCBC correctly predicted the peak of highly charged ion state outputs under free boundary condition and similar charge state distribution width but a lower peak charge state under the Bohm condition. The comparisons between the simulation results and ANL experimental measurements are presented and discussed.

The 10.5GHz electron cyclotron resonance ion source (ECRIS) at Argonne National Laboratory has been utilizing a 10.5GHz klystron and an 11–13GHz traveling wave tube amplifier (TWTA) for beam production in two-frequency heating mode. The beam intensities obtained from the source with two-frequency heating have shown a factor of 2 improvement over single-frequency heating for the higher charge states. Following a simple logic that an increased number of resonance zones leads to enhanced source performance, a 14GHz klystron was added to the source configuration enabling the plasma to be simultaneously excited with three discrete frequencies. In studies with three-frequency heating when compared to two-frequency heating, the beam intensity for O7+ increased from 70.4to84.2eμA, Kr23+ (mass 86, 99.9% enriched) increased from 3.5to7.2eμA, and Xe28+ (mass 136, 60% enriched) increased from 7.9to12.2eμA. A rf power combiner was added to the TWTA so that it could be driven simultaneously with two frequencies. With t...

The 10 GHz ECR-I ion source at ATLAS is being modified to create a small inner volume within the main plasma chamber to reduce the residual helium background gas load. This effort is part of an experiment to measure the residual concentration of 3He in highly isotopically enriched 4He samples. The modification consists of a new extractor electrode on which is integrally mounted a 2.5-cm-diam quartz tube of approximately 8 cm length. Energizing just the extraction coil produces an ECR only inside the quartz volume. The quartz tube is pumped only through the 1-mm-diam extraction hole. rf power is provided by propagation through the main plasma tank acting as a multimode waveguide. The source must operate in the pressure regime of 10–200 mTorr in order to achieve sufficient sensitivity to measure a 3He/4He ratio of approximately 1×10−15. Results of these tests and the operation of the source in this highly unusual mode will be presented.