Isotope Beams Research Articles

Mapping the frontiers of the nuclear mass surface

Nuclear masses play a central role in nuclear astrophysics, significantly impacting the origin of the elements and observables used to constrain ultradense matter. A variety of techniques are available to meet this need, varying in their emphasis on precision and reach from stability. Here I briefly summarize the status of and near-future for the time-of-flight magnetic-rigidity (TOF-Bρ) mass measurement technique, emphasizing the complementary and interconnectedness with higher-precision mass measurement methods. This includes of recent examples from TOF-Bρ mass measurements that map the evolution of nuclear structure across the nuclear landscape and significantly impact the results and interpretation of astrophysical model calculations. I also forecast expected expansion in the known nuclear mass surface from future measurement at the Facility for Rare Isotope Beams.

Evolution of proton single-particle states in neutron-rich Sb isotopes beyond N=82

The β decay of the semimagic Sn isotopes Sn136,137,138 has been studied at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. The first experimental information on excited states was obtained for Sb137 while, in the case of Sb136, the established excitation scheme could be extended by ten previously unidentified levels. In the decay of the most-neutron-rich isotope Sn138, two γ rays were observed for the first time. The new experimental results, in combination with state-of-the-art shell-model calculations, provide the first information with respect to the evolution of the 0g7/2 and 1d5/2 proton single-particle states with increasing neutron number beyond N=84.

Commissioning Status of the Linac for the Facility for Rare Isotope Beams

The Facility for Rare Isotope Beams will be completed in late 2021. We report here on the current efforts to commission the first stages of the 200-MeV/u superconducting, continuous wave heavy-ion linac. The statuses of the cryogenic plant and its distribution system, the accelerator cryomodule commissioning and operations, the ion source and front end transport development, the radio-frequency quadrupole commissioning, and thenbeam dynamics development to support high-power operation are reviewed. Plans for commissioning the remainder of the linac systems are presented.

Enhancement of charge breeding efficiency for rare isotope beam with the control of magnetic field profile and electron beam energy in EBIS

The magnetic field in the ion trap of electron beam ion source (EBIS) determines the current density of electron beam and thus the depth of trap potential, which affects the charge breeding efficiency to desired charge state. An EBIS charge breeder has been constructed to be used for the Rare Isotope Science Project in Korea. A 6 T superconducting solenoid is used for the trap, and uniform magnetic field is extended with correction coils at the ends. The effect of field uniformity on the electron current density is evaluated using TRAK, and it is shown sizable improvement in the charge breeding efficiency for rare isotope beams can be obtained by elaborate magnetic design. Furthermore, the electron beam energy affects the ionization efficiency. The electron energy is often reduced in the trap for optimal matching with charge striping cross section. However, virtual cathode formation can appear in the process of energy reduction. Maximum beam currents limited by electron energy are studied analytically and by TRAK simulation in the view of improving the charge breeding efficiency.

Isomeric and β -decay spectroscopy of Ho173,174

β-decay spectroscopy of Ho173,174 (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u U238 primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2+) is identified in Ho173. Moreover, a new state with a spin and parity of 9− was discovered in Er174. The experimental log ft values of 5.84(20) and 5.25(18) suggest an allowed-hindered β decay from the ground state of Ho174 to the Kπ=8− isomeric state in Er174. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.Received 11 October 2019Accepted 2 July 2020DOI:https://doi.org/10.1103/PhysRevC.102.024301©2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayElectromagnetic transitionsIsomer decaysNuclear structure & decaysProperties150 ≤ A ≤ 189TechniquesRadioactive beamsNuclear Physics

Current progress on ion driver LINAC-100 development for the new rare isotope facility DERICA at JINR

A new ambitious facility DERICA (Dubna Electron—Rare Ion Collider fAcility) was proposed recently in worldwide collaboration. A number of accelerators for various scientific applications will be built for this project and among them a driver-accelerator LINAC-100 capable of accelerating high-intensity beams of primary stable isotopes up to 100 MeV u−1. This paper contains current results on one of the LINAC-100 versions R&D: parameters of the front-end RFQ section, analysis on the stripper sections and optimal stripping energies,the layout of the superconducting part of LINAC-100 and Uranium beam dynamics simulation results.

Long term operation of the superconducting triplet quadrupoles with cryocoolers

Superconducting triplet quadrupoles (STQs) with cryocoolers characterize the BigRIPS in-flight separator and radioactive isotope (RI) beam delivery lines in the RIKEN RIBF (Radioactive Isotope Beam Factory) project. The STQ magnet is a large-aperture superferric quadrupole triplet cooled by liquid helium bath cooling method in a single cryostat. The STQ cryostat is designed to be operated continuously with a Gifford-McMahon (GM)/Joule-Thomson (JT) cryocooler and a GM cryocooler. We operate 22 STQ systems for more than twelve years without warm-up the magnets. We report operational experiences, such as degradation of cooling capacity and failures of compressors, in the long-term operation of the STQ systems. Replacement of ageing cryocooler unit is discussed to improve the cooling capacity.

Metastable States of ^{92,94}Se: Identification of an Oblate K Isomer of ^{94}Se and the Ground-State Shape Transition between N=58 and 60.

Here we present new information on the shape evolution of the very neutron-rich ^{92,94}Se nuclei from an isomer-decay spectroscopy experiment at the Radioactive Isotope Beam Factory at RIKEN. High-resolution germanium detectors were used to identify delayed γ rays emitted following the decay of their isomers. New transitions are reported extending the previously known level schemes. The isomeric levels are interpreted as originating from high-K quasineutron states with an oblate deformation of β∼0.25, with the high-K state in ^{94}Se being metastable and K hindered. Following this, ^{94}Se is the lowest-mass neutron-rich nucleus known to date with such a substantial K hindrance. Furthermore, it is the first observation of an oblate K isomer in a deformed nucleus. This opens up the possibility for a new region of K isomers at low Z and at oblate deformation, involving the same neutron orbitals as the prolate orbitals within the classic Z∼72 deformed hafnium region. From an interpretation of the level scheme guided by theoretical calculations, an oblate deformation is also suggested for the ^{94}Se_{60} ground-state band.

On the [formula omitted]-detection efficiency of a combined Si and plastic stack detector for DESPEC

A Geant4 simulation has been carried out in order to determine the β-detection efficiency of a rare isotope beam implantation setup, for decay spectroscopy experiments, comprising a number of Double Sided Silicon Strip Detectors (DSSSDs) and two plastic scintillation detectors placed upstream and downstream. The absolute efficiency for the emitted β-particle detection from radioactive fragments implanted in the DSSSDs using fast-timing plastic-scintillator detector, is calculated. The detection efficiency of the setup has been studied with two different distances between the Si layers and plastics. The requirement for the thickness of the Si detector layers and its implication on the β-detection efficiency has been investigated for 1 mm and 300μm thickness of Si layers. The combined efficiency of DSSSD and plastic detectors were also simulated for two different thicknesses of the DSSSD.

Spectroscopy of neutron-rich scandium isotopes

Within the SEASTAR III campaign at the Radioactive Isotope Beam Factory, at the RIKEN Nishina Center, neutron-rich isotopes in the vicinity of 53K were produced from the fragmentation of the primary 70Zn beam on a 9Be target. After nucleon knockout reactions on the secondary liquid hydrogen MINOS target the known γ rays of the neutron-rich 55Sc isotope were observed (shown in this proceedings) and γ rays from 57,59Sc isotopes have been identified for the first time. The evolution of the occupied nucleon orbitals of these nuclei in the ground and excited state is investigated under the prism of the tensor force.

β -decay half-lives of 55 neutron-rich isotopes beyond the N=82 shell gap

The $\beta$-decay half-lives of 55 neutron-rich nuclei $^{134-139}$Sn, $^{134-142}$Sb, $^{137-144}$Te, $^{140-146}$I, $^{142-148}$Xe, $^{145-151}$Cs, $^{148-153}$Ba, $^{151-155}$La were measured at the Radioactive Isotope Beam Factory (RIBF) employing the projectile fission fragments of $^{238}$U. The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly-measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of $r$ process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second ($A$ $\approx$ 130) peak.

Efficient continuous wave accelerating structure for ion beams

The Facility for Rare Isotope Beams driver linac was designed for acceleration of multiple-charge-state beams after the stripping at ion beam energies of 17 to $20\text{ }\text{ }\mathrm{MeV}\mathrm{/u}$ depending on the ion species. The linac includes a 180\ifmmode^\circ\else\textdegree\fi{} achromatic bend to select multiple charge states for further acceleration and to dump unwanted charge states after the first 45\ifmmode^\circ\else\textdegree\fi{} magnet. Two rf rebunchers between the stripper and the linac segment 2 (LS2) are required to minimize the effective emittance growth of the multiple-charge-state beams and provide matching to the LS2. Recent studies have shown that the best choice for these two rebunchers is a room-temperature (RT) accelerating structure capable of providing robust operation in the presence of the stripped heavy ion beam contaminants. The latter can result in uncontrolled losses of contaminant ions after the passage off the stripper. Therefore, using a superconducting (SC) rebuncher after the stripper is not rational due to possible contamination and performance degradation of SC cavities over a long period of operation. For the beam bunching in the energy range from 13 to $22\text{ }\text{ }\mathrm{MeV}\mathrm{/u}$, two 161 MHz rebunchers based on interdigital H-type (IH) structure were developed, built, installed and commissioned with beam at the FRIB linac. This is the first experimental demonstration for application of a cw RT drift tube accelerating structure in this energy range.

Development of the TIP-HOLE gas avalanche structure for nuclear physics/astrophysics applications with radioactive isotope beams: preliminary results.

We discuss the operational principle and performance of new micro-pattern gaseous detectors based on the multi-layer Thick Gaseous Electron Multiplier (M-THGEM) concept coupled to a needle-like anode. The new gas avalanche structure aims at high-gain operation in nuclear physics and nuclear astrophysics applications with radioactive isotope beams. It is thereafter named TIP-HOLE gas amplifier, and consists of a THGEM or a two-layers M-THGEM mounted in a WELL configuration. The avalanche electrodes are collected by thin conductive needles (with up to a few ten μm radius and a height of 100 μm), located at the center of the hole and acting as a point-like anode. The bottom area of the needle could be surrounded by a cylindrical cathode strip in order to increase the electron collection efficiency. The electric field lines from the drift region above the M-THGEM are focused into the holes, and then forced to converge on the needle tip. An extremely high field is reached at the top of the needle, creating a point-like avalanche process. Stable, high-gain operations in a wide range of pressures can be achieved at relatively low operational voltage, even in pure quencher gas at atmospheric pressure (e.g. pure isobutene). The TIP-HOLE structure may be produced by the innovative scalable additive manufacturing technology for large-area, multiple-layer printed circuit boards, recently developed by the UHV technology company (USA) and discussed for the first time in this work.

Development of Fast Protection System and Slow Interlock System in the RAON Accelerator

The RAON accelerator has been constructed to generate and accelerate stable and rare isotope beams for various kinds of science programs by the rare isotope science project (RISP) in Daejeon, Korea since 2011. The beam created by an ion source will be accelerated by the superconducting linear accelerator up to the experimental target in the RAON accelerator. During the acceleration and the transportation of the beam, the sudden loss of the beam with high energy and power can be occurred by a device interlock or a beam distortion, and it leads to serious damages of the accelerator equipment. Therefore, we are developing the machine protection system to protect the accelerator during the beam operation. For efficient protection, the machine protection system includes the FPGA-based fast protection system and the PLC-based slow interlock system depending on the response time to interlock signals and device types. The prototypes of both systems were successfully developed and tested at the RISP test facility, and the products are under development based on the results of the prototypes from late 2017. In this paper, we will describe the current development status of the fast protection system and the slow interlock system in the RAON accelerator and present the future plans.

Shell structure of the neutron-rich isotopes Co69,71,73

The structures of the neutron-rich Co69,71,73 isotopes were investigated via (p,2p) knockout reactions at the Radioactive Isotope Beam Factory, RIKEN. Isotopes of interest were studied using the DALI2 γ-ray detector array combined with the MINOS target and tracker system. Level schemes were reconstructed using the γ-γ coincidence technique, with tentative spin-parity assignments based on the measured inclusive and exclusive cross sections. Comparison with shell-model calculations using the Lenzi-Nowacki-Poves-Sieja LNPS and PFSDG-U interactions suggests coexistence of spherical and deformed shapes at low excitation energies in the Co69,71,73 isotopes. The distorted-wave impulse approximation (DWIA) framework was used to calculate the single-particle cross sections. These values were compared with the experimental findings.

Charged particle track reconstruction with S[formula omitted]RIT Time Projection Chamber

In this paper, we present a software framework, SπRITROOT, which is capable of track reconstruction and analysis of heavy-ion collision events recorded with the SπRIT time projection chamber. The track-fitting toolkit GENFIT and the vertex reconstruction toolkit RAVE are applied to a box-type detector system. A pattern recognition algorithm which performs helix track finding and handles overlapping pulses is described. The performance of the software is investigated using experimental data obtained at the Radioactive Isotope Beam Facility (RIBF) at RIKEN. This work focuses on data from 132Sn + 124Sn collision events with beam energy of 270 AMeV. Particle identification is established using dE∕dx and magnetic rigidity, with pions, hydrogen isotopes, and helium isotopes.

Diversifying beam species through decay and recapture ion trapping: a demonstrative experiment at TITAN-EBIT

Recapturing the recoiling daughters from radioactive decay can be a simple way to diversify beam availability at rare isotope beam facilities. In the decay and recapture ion trapping (DRIT) technique, a parent species is stored in an ion trap and left to decay, and the daughter ions are recaptured by the trap and become available for use. We successfully demonstrated the technique using the electron beam ion trap (EBIT) at the TITAN facility. A pure cloud of 30Mg ions was stored in the EBIT for about one half-life and sent to a Penning trap mass spectrometer, which confirmed the production of 30Al daughter ions. Systematic measurements and simulations suggest high recapture efficiencies of the recoil ion and little influence of the recoiling energy in the observed losses. With the secondary beam, we also performed precision mass measurements of the parent 30Mg8+ and the daughter 30Al11+ ions. Our results agree with the literature and improve its precision. The success of this experiment shows that EBITs can produce high-quality beams through the DRIT technique.

Ion-optical design of High energy FRagment Separator (HFRS) at HIAF

High Intensity heavy-ion Accelerator Facility (HIAF) project is being constructed by the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). An in-flight High energy FRagment Separator (HFRS) at HIAF was designed to study the properties of rare isotopes far away from the line of beta stability and their involved nuclear reactions of astrophysics interests. HFRS is a two-stage magnetic system which consists of Pre-Separator and Main-Separator. The maximum magnetic rigidity of 25 Tm was designed in particular for experiments with very neutron-rich rare isotopes beams and studies of hypernuclei and Δ-resonances in exotic nuclei. A dispersive mode and an achromatic mode were designed for different experimental requirements. The HFRS device can be used to separate and purify the rare isotopes produced by the projectile fragmentation of all primary beams up to Uranium or by the projectile fission of Uranium ions via Bρ-ΔE-Bρ method. The detailed HFRS ion-optical design including the first order and the higher order, and the magnet specification were presented in this paper.

Preface

The 2019 Joint Cryogenic Engineering and International Cryogenic Materials Conferences were held from July 21 through July 25 at the Connecticut Convention Center in Hartford, Connecticut. As at past conferences, the international scope of these meetings was strongly maintained with 24 countries being represented by 613 attendees who gathered to enjoy the joint technical programs, industrial exhibits, and special events.The program for the joint conferences included a total of 410 presentations in the plenary, oral, and poster sessions. Four plenary talks gave interesting in-depth overviews and discussions on the topics of the growing field of commercial application of hydrogen fuel-cells for specialized applications and large-scale semi-truck transportation, and recent 5x increase of liquid hydrogen production in the U.S.; Siemens’ perspectives on evolving hybrid-electric propulsion technologies for large commercial aircraft; the world-leading research opportunities with rare isotopes in nuclear physics, nuclear chemistry, and the application of rare isotopes for society that the Facility for Rare Isotope Beams (FIRB) at Michigan State University will soon provide; and the impressive progress designing the next-gen SPARC fusion reactor 1st-ever utilizing 2nd-generation high-temperature-superconducting (HTS) wire. The attendees also convened for two Special Joint CEC-ICMC Symposia on i) Transportation, and ii) Quantum Computing, and seven Special-or-Focus Sessions were included in the programming emphasizing high-quality invited talks. Contributed papers covered a wide range of topics including many aspects in advances in cryogenics and superconductors, along with their applications. Both CEC and ICMC boards are encouraging student participation and career growth and provided registration support for 36 student applicants. In total, 207 papers were submitted for publication of which 190 are published in these conference proceedings.Full Preface information is available in the pdf.

FRIB cryogenic system status

The Facility for Rare Isotope Beams (FRIB) cryogenic plant has been successfully commissioned, including compressor system, 4.5 K cold box system, sub-atmospheric (2 K) cold box system, and the distribution system for two of the three linear accelerator (Linacs) segments. This plant uses the Ganni-Floating pressure process, allowing the compressor discharge and 4.5 K cold box supply pressure to automatically vary from 6 to 21 bar, without introducing additional exergetic losses to reduce the capacity (e.g., throttling turbine inlet valves, load heaters, etc.). The 2 K (31 mbar) load is supported using five stages of centrifugal compressors, housed within the sub-atmospheric cold box, which recompress the helium to 1.15 bar (and around 30 K). In 2012, FRIB assumed the responsibility, in collaboration with JLab to design and procure the sub-systems after the decision to move away from an industry supplied turn-key system. FRIB was responsible for procurement of all systems, all onsite activities, including the installation and integration of all the subsystems, development of the control systems, as well as, the integration, commissioning, and testing of each sub-system. At present this has culminated in the production of the first beam through the first Linac segment. An overview of the planning and execution of the project will be presented, which allowed meeting of scheduled goals and anticipated performance, and prevented the need to store or ‘double-handle’ any equipment.