Facilitating Precision Mass Measurements at CARIBU

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018

The Argonne Tandem Linac Accelerator System (ATLAS) is planning an upgrade to a multiuser 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 MultiUser 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-meter-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.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

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.

Nuclear Data Sheets, 2014

A new approach to β-delayed neutron spectroscopy has been demonstrated that circumvents the many limitations associated with neutron detection by instead inferring the decay branching ratios and energy spectra of the emitted neutrons by studying the nuclear recoil. Using the Beta-decay Paul Trap, fission-product ions were trapped and confined to within a 1-mm 3 volume under vacuum using only electric fields. Results from recent measurements of 137 I + and plans for development of a dedicated ion trap for future experiments using the intense fission fragment beams from the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory are summarized. The improved nuclear data that can be collected is needed in many fields of basic and applied science such as nuclear energy, nuclear astrophysics, and stockpile stewardship.

Cornell University - arXiv, 2022

Background: An ultra-low Q value β-decay can occur from a parent nuclide to an excited nuclear state in the daughter such that QUL 1 keV. These decay processes are of interest for nuclear β-decay theory and as potential candidates in neutrino mass determination experiments. To date, only one ultra-low Q value β-decay has been observed-that of 115 In with Q β = 147(10) eV. A number of other potential candidates exist, but improved mass measurements are necessary to determine if these decay channels are energetically allowed and, in fact, ultra-low. Purpose: To perform precise β-decay Q value measurements of 112,113 Ag and 115 Cd and to use them in combination with nuclear energy level data for the daughter isotopes 112,113 Cd and 115 In to determine if the potential ultra-low Q value β-decay branches of 112,113 Ag and 115 Cd are energetically allowed and 1 keV. Method: The Canadian Penning Trap at Argonne National Laboratory was used to measure the cyclotron frequency ratios of singly-charged 112,113 Ag and 115 Cd ions with respect to their daughters 112,113 Cd and 115 In. From these measurements, the ground-state to ground-state β-decay Q values were obtained. Results: The 112 Ag → 112 Cd, 113 Ag → 113 Cd, and 115 Cd → 115 In β-decay Q values were measured to be Q β (112 Ag) = 3990.16(22) keV, Q β (113 Ag) = 2085.7(4.6) keV, and Q β (115 Cd) = 1451.36(34) keV. These results were compared to energies of excited states in 112 Cd at 3997.75(14) keV, 113 Cd at 2015.6(2.5) and 2080(10) keV, and 115 In at 1448.787(9) keV, resulting in precise QUL values for the potential decay channels of-7.59(26) keV, 6(11) keV, and 2.57(34) keV, respectively. Conclusion: The potential ultra-low Q value decays of 112 Ag and 115 Cd have been ruled out. 113 Ag is still a possible candidate until a more precise measurement of the 2080(10) keV, 1/2 + state of 113 Cd is available. In the course of this work we have found the ground state mass of 113 Ag reported in the 2020 Atomic Mass Evaluation [Wang, et al., Chin. Phys. C 45, 030003 (2021)] to be lower than our measurement by 69(17) keV (a 4σ discrepancy).

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008

The research reactor Triga Mainz is an ideal facility to provide neutron-rich nuclides with production rates sufficiently large for mass spectrometric and laser spectroscopic studies. Within the Triga-Spec project, a Penning trap as well as a beam line for collinear laser spectroscopy are being installed. Several new developments will ensure high sensitivity of the trap setup enabling mass measurements even on a single ion. Besides neutron-rich fission products produced in the reactor, also heavy nuclides such as 235 U or 252 Cf can be investigated for the first time with an off-line ion source. The data provided by the mass measurements will be of interest for astrophysical calculations on the rapid neutron-capture process as well as for tests of mass models in the heavy-mass region. The laser spectroscopic measurements will yield model-independent information on nuclear ground-state properties such as nuclear moments and charge radii of neutron-rich nuclei of refractory elements far from stability. This publication describes the experimental setup as well as its present status.

2017

An Electron Beam Ion Source Charge Breeder (EBISCB) has been developed at Argonne to breed radioactive beams from the CAlifornium Rare Ion Breeder Upgrade (CARIBU) facility at ATLAS. The CARIBU EBIS-CB has been successfully commissioned offline with an external singly-charged cesium ion source [1]. The EBIS performance meets the breeding requirements to deliver CARIBU beams to ATLAS. EBIS can provide charge-tomass ratios  1/7 for all CARIBU beams with breeding times in the range of 6 ms to 30 ms. A record high breeding efficiency of up to 28% into a single charge state of Cs28+ has been demonstrated. Following the offline testing EBIS was moved to the front end of ATLAS where the alignment of EBIS was substantially improved and additional beam diagnostic tools both for electron and ion beams were installed. This paper will discuss EBIS improvements and present the results of on-line commissioning.

Nuclear Physics News, 2016

Introduction and Evolution of ATLAS ATLAS (the Argonne Tandem Linac Accelerator System) is the world's first superconducting accelerator for projectiles heavier than the electron. This unique system is a U.S. Department of Energy (DOE) national user research facility open to scientists from all over the world. It is located within the Physics Division at Argonne National Laboratory and is one of five large scientific user facilities located at the laboratory. ATLAS began as a proof-of-principle project in the early 1970s to demonstrate that a superconducting resonator's field amplitude and phase could be controlled with sufficient precision to enable the acceleration of ions. The first demonstration of such heavy-ion acceleration was accomplished in 1978 and in 1985 ATLAS [1] was identified as a U.S. national user facility for low-energy nuclear physics research. In the 30 years since, the field has moved significantly with regard to the demands for the types of beams required to address its current research topics. In order to continue to meet these evolving requirements, ATLAS has been continuously upgraded to provide the tools necessary to remain at the forefront of nuclear science.

Physical Review C, 2009

The double-beta decay Q values of 130 Te, 128 Te, and 120 Te have been determined from parentdaughter mass differences measured with the Canadian Penning Trap mass spectrometer. The 132 Xe-129 Xe mass difference, which is precisely known, was also determined to confirm the accuracy of these results. The 130 Te Q value was found to be 2527.01 ± 0.32 keV which is 3.3 keV lower than the 2003 Atomic Mass Evaluation recommended value, but in agreement with the most precise previous measurement. The uncertainty has been reduced by a factor of 6 and is now significantly smaller than the resolution achieved or foreseen in experimental searches for neutrinoless doublebeta decay. The 128 Te and 120 Te Q values were found to be 865.87 ± 1.31 keV and 1714.81 ± 1.25 keV, respectively. For 120 Te, this reduction in uncertainty of nearly a factor of 8 opens up the possibility of using this isotope for sensitive searches for neutrinoless double-electron capture and electron capture with β + emission.

2016

The ATLAS linac at Argonne National Laboratory has recently been upgraded for higher beam intensity and transport efficiency. A new 60 MHz RFQ replacing the first few cavities of the Positive Ion Injector (PII) section and a new superconducting module replaced three old cryomodules of split-ring resonators in the Booster section of the linac. Following the installation of the new RFQ, we performed a high-intensity run using a Ar beam. A beam current of 7 p A was successfully injected and accelerated in the RFQ and PII section of the linac to an energy of 1.5 MeV/u. The results of this run are presented and the limitations to reach higher currents are discussed. A second run is planned to try to push the beam current higher and farther into the Booster and ATLAS sections of the linac. Finally, a future intensity upgrade plan, motivated by the inflight production of radioactive beams using the AIRIS separator and the proposed multi-user upgrade with potential stable beam applications ...

Physical Review Special Topics - Accelerators and Beams, 2012

The front end of any modern ion accelerator includes a radio frequency quadrupole (RFQ). While many pulsed ion linacs successfully operate RFQs, several ion accelerators worldwide have significant difficulties operating continuous wave (CW) RFQs to design specifications. In this paper we describe the development and results of the beam commissioning of a CW RFQ designed and built for the National User Facility: Argonne Tandem Linac Accelerator System (ATLAS). Several innovative ideas were implemented in this CW RFQ. By selecting a multisegment split-coaxial structure, we reached moderate transverse dimensions for a 60.625-MHz resonator and provided a highly stabilized electromagnetic field distribution. The accelerating section of the RFQ occupies approximately 50% of the total length and is based on a trapezoidal vane tip modulation that increased the resonator shunt impedance by 60% in this section as compared to conventional sinusoidal modulation. To form an axially symmetric beam exiting the RFQ, a very short output radial matcher with a length of 0:75 was developed. The RFQ is designed as a 100% oxygen-free electronic (OFE) copper structure and fabricated with a two-step furnace brazing process. The radio frequency (rf) measurements show excellent rf properties for the resonator, with a measured intrinsic Q equal to 94% of the simulated value for OFE copper. An O 5þ ion beam extracted from an electron cyclotron resonance ion source was used for the RFQ commissioning. In off-line beam testing, we found excellent coincidence of the measured beam parameters with the results of beam dynamics simulations performed using the beam dynamics code TRACK, which was developed at Argonne. These results demonstrate the great success of the RFQ design and fabrication technology developed here, which can be applied to future CW RFQs.