Argonne Tandem Linac Accelerator System Research Articles

Status update of the ATLAS ECR ion sources at Argonne National Laboratory

The Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory (ANL) typically operates 24/7 with weekly ion beam changes and an annual 1 month maintenance period. Due to recent installations and upgrades at ATLAS, user demands for new beams and higher intensities have expanded an already diverse operational envelope of both electron cyclotron resonance ion sources (ECRIS), ECR2 and ECR3. A variety of material introduction techniques including sputter, oven, reduction and gas feed were used to meet the challenge of an intense run schedule. With two ECRIS available to feed the accelerator, beam development and preparation were able to occur concurrently with ATLAS programmatic activities. Highlights of operational experiences and improvements with ECR2 and ECR3 over the last 2 years are presented.

RF Frequency Combining for the ATLAS ECR Ion Sources

The ECR2 and ECR3 ion sources at the Argonne Tandem Linac Accelerator System (ATLAS) operate with two microwave frequencies, improving their performance over single frequency operation. A typical method for transmitting both microwave frequencies is by having two separate frequency generators with their own corresponding amplifiers. These amplifiers transmit their microwaves into the ion source using separate waveguides. Another method that is investigated is to combine the low power microwave frequencies with a splitter/combiner and input the combined signals into the high-power amplifier, where the combined signal is amplified and transmitted down a single waveguide into the ion source. These different methods for delivering microwave power with multiple frequencies are compared, focusing on the average charge state and the intensities of each of the charge states for an oxygen plasma produced by the ECR2 ion source.This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.

Sputter sample preparation for ion beam delivery of radium-223 at ATLAS.

A radium-223 ion beam was delivered to an experiment from the electron cyclotron resonance ion source, ECR2, at the Argonne Tandem Linac Accelerator System (ATLAS). The radium-223 material was in a nitrate salt form within a vial, prior to being converted to a usable sputter sample. The sputter sample was produced using a new sample preparation method, where the radium nitrate was dissolved into a solution and pipetted onto pressed aluminum powder. This sample was then allowed to dry, distributing the radium-223 material throughout the sputter sample. Ion source operation using the radium sputter sample is described with the operating parameters listed. The intensity and energy requirements for this ion beam were 1 × 106 particles/s and 1.07 GeV, respectively. Because the intensity is relatively low compared to most experiments at ATLAS, previously developed accelerator mass spectrometry methods were used Scott etal. [Rev. Sci. Instrum. 87, 02A732 (2016)] to avoid the need for tuning of the low-intensity beam of interest. Handling of the radium material, as well as loading and unloading of the sputter sample from ECR2, required collaboration with Health Physics. Procedures were used and dry runs were carried out before, during, and after the experiment to ensure the safety of the workers. The processes used and lessons learned are described within.

Zirconium nanoparticle coating development for FCCI diffusion barrier in nuclear cladding

Fuel clad chemical interaction (FCCI) is a pervasive issue for metallic nuclear fuels. FCCI can damage cladding, reduce thermal efficiency, and compromise the structural integrity of the fuel rod. In this study, we evaluated the FCCI mitigation capabilities of electrophoretically-deposited Zr nanoparticle coatings on ferritic-martensitic stainless-steel cladding (HT9). Zr was deposited on the internal surface of 6 mm outer diameter cladding using electrophoretic deposition (EPD). Thickness varied among samples with similar EPD conditions. A uniformly coated sample was selected and sent to the Argonne Tandem Linac Accelerator System (ATLAS) to simulate the coating's behavior under irradiation conditions. The coating prevented FCCI in diffusion couple studies. Results of this study confirm that Zr could potentially make an effective FCCI barrier in metallic fuel rods but the deposition process needs improvement.

Experimental study of the isomeric state in N16 using the Ng,m16(d,He3) reaction

The isomeric state of $^{16}\mathrm{N}$ was studied using the $^{16}\mathrm{N}{}^{g,m}(d,^{3}\mathrm{He})$ proton-removal reactions at 11.8 MeV/u in inverse kinematics. The $^{16}\mathrm{N}$ beam, of which 24% was in the isomeric state, was produced using the Argonne Tandem-Linac Accelerator System (ATLAS) in-flight system and delivered to the Helical Orbit Spectrometer (HELIOS), which was used to analyze the $^{3}\mathrm{He}$ ions from the $(d,^{3}\mathrm{He})$ reactions. The simultaneous measurement of reactions on both the ground state and the isomeric states, reduced the systematic uncertainties from the experiment and in the analysis. A direct and reliable extraction of the relative spectroscopic factors was made based on a distorted-wave Born approximation approach. The experimental results suggest that the isomeric state of $^{16}\mathrm{N}$ is an excited neutron-halo state. The results can be understood through calculations using a Woods-Saxon potential model, which captures the effects of weak binding.

Measurement of the Mo100(α,xn) cross section at weak r -process energies

The weak $r$ process in neutrino-driven winds following a core-collapse supernova is thought to contribute to the cosmic abundances of the first $r$-process peak elements between Se and Ag. Sensitivity studies have found that the early nucleosynthesis in the weak $r$ process is primarily driven by $(\ensuremath{\alpha},xn)$ reactions due to the high temperatures, and that current nuclear physics uncertainties in the $(\ensuremath{\alpha},xn)$ rates result in significant uncertainties of the calculated abundances. The weak $r$-process path proceeds several nuclei away from stability where $(\ensuremath{\alpha},xn)$ reaction cross sections have not yet been measured. In this paper we report the $^{100}\mathrm{Mo}(\ensuremath{\alpha},xn)$ cross section (between 8.9 and 13.2 MeV in the center of mass, corresponding to 3.5--6.8 GK) in inverse kinematics using the Multi-Sampling Ionization Chamber (MUSIC) detector at the Argonne Tandem Linac Accelerator System (ATLAS) facility. With this first measurement of the $^{100}\mathrm{Mo}(\ensuremath{\alpha},xn)$ cross section, we have demonstrated the ability of MUSIC to measure $(\ensuremath{\alpha},xn)$ cross sections for $A$ up to 100, therefore paving the way for further measurements with radioactive beams at ATLAS or the Facility for Rare Isotope Beams.

How to approach the island of stability: Reactions using multinucleon transfer or radioactive neutron-rich beams?

The multinucleon transfer (MNT) process and radioactive beam induced fusion-evaporation (FE) reactions are the considered routines to explore the island of stability. We make the first direct comparison of the two approaches for producing neutron-rich superheavy nuclei, especially the predicted double magic isotope 298Fl. The radioactive beams 49−59Ca induced hot FE reactions with actinide targets and the MNT reaction 238U + 252Cf are investigated within the framework of the dinuclear system model. Based on the beam intensities proposed by Argonne Tandem Linac Accelerator System, we find that the MNT and FE processes are comparable for producing 298Fl. The influence of the shell structures uncertainties on the production cross section of 298Fl is evaluated. It is found that the shell structures weakly influence the production cross sections of 298Fl around the optimal incident energy, although, the double shell closures could strongly enhance the stability of 298Fl. We also quantitatively estimated the relative proportion of shell effects on cross sections in the transfer stage of the MNT reaction 238U + 252Cf. It is demonstrated that the shell effects on production cross section of 298Fl are mainly from de-excitation process. The general conclusion of this work is that the radioactive beam induced FE reactions show advantages for the excursion toward N=184 from current status.

Production of C-14 and stable ion beams at the Argonne Tandem Linac Accelerator System with the ECR3 ion source

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.

NuCARIBU : An upgrade for the CARIBU facility at the Argonne Tandem Linac Accelerator System

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

Search for the 1/2+ intruder state in P35

The excitation energy of deformed intruder states (specifically the 2p2h bandhead) as a function of proton number $Z$ along $N=20$ is of interest both in terms of better understanding the evolution of nuclear structure between spherical $^{40}$Ca and the Island of Inversion nuclei, and for benchmarking theoretical descriptions in this region. At the center of the $N=20$ Island of Inversion, the npnh (where n=2,4,6) neutron excitations across a diminished $N=20$ gap result in deformed and collective ground states, as observed in $^{32}$Mg. In heavier isotones, npnh excitations do not dominate in the ground states, but are present in the relatively low-lying level schemes. With the aim of identifying the expected 2p2h$\otimes\mathrm{s}_{1/2^+}$ state in $^{35}$P, the only $N=20$ isotone for which the neutron 2p2h excitation bandhead has not yet been identified, the $^{36}$S(d,$^3$He)$^{35}$P reaction has been revisited in inverse kinematics with the HELical Orbit Spectrometer (HELIOS) at the Argonne Tandem Linac Accelerator System (ATLAS). While a candidate state has not been located, an upper limit for the transfer reaction cross-section to populate such a configuration within a 2.5 to 3.6\,MeV energy range, provides a stringent constraint on the wavefunction compositions in both $^{36}$S and $^{35}$P.

Design of Stand-Alone Cryomodule Based on Superconducting Quarter-Wave Resonator

Present superconducting accelerators require a central refrigeration system and piping to distribute liquid helium and nitrogen. Stand-alone cryocooler-based systems are of significant interest both to scientific and industrial customers, as they allow applications at facilities where no cryogenic equipment and expertise exists, where it is undesirable to develop additional cryogenic systems, or where a mobile system that can be transported between beamlines or facilities is required. The technical challenge of this approach is to minimize the heat losses to the liquid helium so that commercially available, self-contained cryocoolers are able to handle the thermal load. This article presents an improved design for a stand-alone quarter-wave resonator (QWR) cryomodule based on commercially available cryocoolers. This cryomodule has a particular application in the Argonne Tandem Linac Accelerator System intensity upgrade project, where it will house a 72.75 MHz QWR for beam energy adjustments to experimental areas, where no helium cryogenic systems exist. The described cryomodule may also be the critical part of a turnkey system with application to material processing, semiconductor manufacturing, food irradiation, and homeland security. The development of low-heat loss peripheral components reduces the cost and widens applicability of the system. We will discuss the cryomodule and RF coupler designs, including numerical thermal and structural analyses.

Development of 211At Production via Continuous Extraction of 211Rn

Critically needed radionuclides for cancer therapy include the alpha-emitter 211At [1] and therapeutically useful Auger-electron emitters. The ATLAS (Argonne Tandem Linac Accelerator System) superconducting linac at Argonne National Laboratory is suitable for production of these radionuclides. Our work is initially focusing on demonstrating production capabilities for 211At (7.2 h half-life) using the 209Bi(7Li,5n)211Rn reaction. Cross sections for these reactions peak at 600 mbarn [2,3] making production of 10’s of mCi per batch feasible using only a very small percentage of the accelerator beam time. Presently, in the U.S. 211At is primarily produced at 3 university facilities using the 209Bi(α,2n)211At reaction at in-house cyclotrons. Hence, clinical use of 211At nation-wide is limited due to its short half-life. By using the lithium induced reaction, the 211At daughter is extracted from the parent 211Rn, which has a half-life of 14 h, significantly extending the time-frame for effective distribution and use of this important radionuclide. ATLAS is an appropriate and flexible accelerator for production of medical isotopes because it can provide beams of any ion including protons, helium, lithium, and heavier ions with energies adjustable over a wide range. An upgrade of the accelerator to produce more intense lithium beams and the construction of improved neutron shielding is in progress. Following the completion of this work, currents of lithium beams of 1-10 particle microamps will be available to support the development of a 211Rn/211At generator. These combined upgrades will enable yields of ∼100 mCi of 211Rn per batch. As part of this development, an option for the continuous collection of 211Rn from a bismuth oxide target followed by separation of the 211At daughter product is being investigated. Porous bismuth oxide targets have been developed by Innosense, LLC under a DOE Small Business Grant. [4] In two test runs to date, 211Rn released from the targets was collected in charcoal traps. In the first run a metallic bismuth target was used and in the second the recently developed bismuth oxide target was used. In both runs only a low fraction of the 211Rn was released and collected on line. The first case was limited by the melting point of the metal target, and the second was limited by the target being heated only to 60 °C. The release and capture were quantified by off-line gamma counting of the long lived 207Bi daughter remaining in the production target and in the charcoal. In upcoming test runs target heating up to 600 oC will be implemented to increase release and collection efficiency.1.Vaidyanathan. G. and Zalutsky, M.R., Curr Radiopharm. 2011 October ; 4(4): 283–294.2.Meyer, G.J., Lambrecht, R.M., Inter. J. of App. Rad. and Isotopes, 31(1980)351-355.3.Washiyama, K., et al., 16th International Workshop on Targetry and Target Chemistry, Santa Fe, NM, 20164.Sampathkumaran, U. and Winter, R., Innosense, LLC, Torrance, CA, U.S. DOE SBIR project

Four-harmonic buncher for radioactive and stable beams switching at the ATLAS facility

The Argonne Tandem Linac Accelerator System (ATLAS) is planning an upgrade to a multi-user facility to simultaneously accelerate both stable beams from an ECR ion source and radioactive beams from an Electron Beam Ion Source charge breeder. The ATLAS Multi-User Upgrade will need to provide high transmission of ion beams with a mass-to-charge ratio up to 7 as it enables more options to alternate radioactive and stable beams. Currently, the bunching is provided with a lumped circuit multi-harmonic buncher, which cannot effectively operate at the required amplitude of the saw-tooth voltage for ions with mass-to-charge ratio of 7 due to thermal issues.RadiaBeam Systems in collaboration with Argonne National Laboratory has designed a four-harmonic coaxial resonator buncher with the ATLAS fundamental frequency of 12.125 MHz, and a compact, less than 2-m-long, footprint, capable of providing the required voltage of 6.2 kV. This device allows fast and reliable pre-bunching of DC ion beams with the capability of fast switching of heavy-ion radioactive and stable beams for delivery to multiple users. In this paper, we will discuss the RF and engineering design considerations of this buncher.

Synthesis of neutron-rich superheavy nuclei with radioactive beams within the dinuclear system model

The production of neutron-rich superheavy nuclei with Z=105–118 in neutron evaporation channels is investigated within the dinuclear system model. The different stable and radioactive beam-induced hot fusion reactions are studied systematically. The prospect for synthesizing neutron-rich superheavy nuclei using radioactive beams is evaluated quantitatively based on the beam intensities proposed by Argonne Tandem Linac Accelerator System [B. B. Back and C. L. Jiang, Argonne National Laboratory Report No. ANL-06/55, 2006 (unpublished)]. All possible combinations (with projectiles of Z=16–22 and half-lives longer than 1 ms; with targets of half-lives longer than 30 days), which can be performed in available experimental equipment, for producing several unknown neutron-rich superheavy nuclei in neutron evaporation channels are investigated and the most promising reactions are predicted. It is found that the stable beams still show great advantages for producing most of superheavy nuclei. The calculated results are also compared with production cross sections in the pxn and αxn evaporation channels [Hong et al., Phys. Lett. B 764, 42 (2017)PYLBAJ0370-269310.1016/j.physletb.2016.11.002]. We find that the radioactive beam-induced reactions are comparable to the stable beam-induced reactions in charged particle evaporation channels. To obtain more experimental achievements, the beam intensities of modern radioactive beam facilities need to be further improved in the future.

Laser ablation positive-ion AMS of neutron activated actinides

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.

Microstructure investigations of U3Si2 implanted by high-energy Xe ions at 600 °C

The microstructure investigations on a high-energy Xe-implanted U3Si2 pellet were performed. The promising accident tolerant fuel (ATF) candidate, U3Si2, was irradiated by 84 MeV Xe ions at 600 °C at Argonne Tandem Linac Accelerator System (ATLAS). The characterizations of the Xe implanted sample were conducted using advanced transmission electron microscopy (TEM) techniques. An oxidation layer was observed on the sample surface after irradiation under the ∼10-5 Pa vacuum. The study on the oxidation layer not only unveils the readily oxidation behavior of U3Si2 under high-temperature irradiation conditions, but also develops an understanding of its oxidation mechanism. Intragranular Xe bubbles with bimodal size distribution were observed within the Xe deposition region of the sample induced by 84 MeV Xe ion implantation. At the irradiation temperature of 600 °C, the gaseous swelling strain contributed by intragranular bubbles was found to be insignificant, indicating an acceptable fission gas behavior of U3Si2 as a light water reactor (LWR) fuel operating at such a temperature.

Bubble morphology in U3Si2 implanted by high-energy Xe ions at 300 °C

The microstructure modifications of a high-energy Xe implanted U3Si2, a promising accident tolerant fuel candidate, were characterized and are reported upon. The U3Si2 pellet was irradiated at Argonne Tandem Linac Accelerator System (ATLAS) by an 84 MeV Xe ion beam at 300 °C. The irradiated specimen was then investigated using a series of transmission electron microscopy (TEM) techniques. A dense distribution of bubbles were observed near the range of the 84 MeV Xe ions. Xe gas was also found to accumulate at multiple types of sinks, such as dislocations and grain boundaries. Bubbles aggregated at those sinks are slightly larger than intragranular bubbles in lattice. At 300 °C, the gaseous swelling strain is limited as all the bubbles are below 10 nm, implying the promising fission gas behavior of U3Si2 under normal operating conditions in light water reactors (LWRs).

SRF acceleration for heavy ions: ATLAS decadal operation and evolution

This review paper presents the history and status of superconducting RF at the Argonne Tandem Linac Accelerator System (ATLAS) which is a Department of Energy (DOE) National User Facility for research in nuclear physics with accelerated stable and radioactive ion beams.

Towards laser spectroscopy of the proton-halo candidate boron-8

We propose to determine the nuclear charge radius of 8B by high-resolution laser spectroscopy. 8B (t 1/2 = 770 ms) is perhaps the best candidate of a nucleus exhibiting an extended proton wave-function or “one-proton-halo” in a more descriptive picture. Laser spectroscopic measurements of the isotope shift will be used to probe the change in nuclear charge radius along the three boron isotopes 8B, 10B and 11B. The change in nuclear charge radius directly correlates with the extent of the proton wave function. In-flight production and preparation of sufficient yields of 8B ions at low energies is provided by the Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory (ANL) in Chicago, IL, USA. Subsequently, the ions will be guided through a charge exchange cell for neutralization and the fluorescence signal of the atoms which interact with the resonant laser light will be detected. The charge radius can then be extracted from the measured isotope shift by employing highly accurate atomic theory calculations of this five-electron system which are carried out presently.

Investigation of High-Energy Ion-Irradiated MA957 Using Synchrotron Radiation under In-Situ Tension.

In this study, an MA957 oxide dispersion-strengthened (ODS) alloy was irradiated with high-energy ions in the Argonne Tandem Linac Accelerator System. Fe ions at an energy of 84 MeV bombarded MA957 tensile specimens, creating a damage region ~7.5 μm in depth; the peak damage (~40 dpa) was estimated to be at ~7 μm from the surface. Following the irradiation, in-situ high-energy X-ray diffraction measurements were performed at the Advanced Photon Source in order to study the dynamic deformation behavior of the specimens after ion irradiation damage. In-situ X-ray measurements taken during tensile testing of the ion-irradiated MA957 revealed a difference in loading behavior between the irradiated and un-irradiated regions of the specimen. At equivalent applied stresses, lower lattice strains were found in the radiation-damaged region than those in the un-irradiated region. This might be associated with a higher level of Type II stresses as a result of radiation hardening. The study has demonstrated the feasibility of combining high-energy ion radiation and high-energy synchrotron X-ray diffraction to study materials’ radiation damage in a dynamic manner.