Radioactive Ion Beam Facility Research Articles

First ion source at ISOL@MYRRHA with an improved thermal profile - Theoretical considerations

ISOL@MYRRHA will be a new Radioactive Ion Beam (RIB) facility in Belgium based on the Isotope Separation On-Line (ISOL) technique, and established within the framework of MYRRHA, the world’s first large-scale accelerator driven system project at power levels scalable to industrial systems. The surface ion source, or hot cavity, is chosen as initial source for its reliability and simple design. To account for the higher flux of atoms through this cavity, a theoretical study of the processes within the ion source is discussed here, based on theoretical equations and thermal-electric simulations. In the past, the temperature was clearly identified as a key element to this source, but with the assumption that it remains constant throughout the cavity. Nonetheless, more recent thermal-electric simulations have revealed that the source Ohmic heating leads to temperature gradients along the cavity tube. The temperature profile impact on ionisation in the hot cavity will be reviewed here.

BlueSTEAl: A pair of silicon arrays and a zero-degree phoswich detector for studies of scattering and reactions in inverse kinematics

BlueSTEAl, the Blue (aluminum chamber of) Silicon TElescope Arrays for light nuclei, has been developed to study direct reactions in inverse kinematics, as well as scattering and breakup reactions using radioactive ion beams. It is a detector system consisting of a pair of annular silicon detector arrays and a zero-degree phoswich plastic scintillator. For typical binary reaction studies in inverse kinematics, light ions are detected by the Si array in coincidence with heavy recoils detected by the phoswich placed at the focal-plane of a zero-degree magnetic spectrometer. The Si array can also be used to detect light nuclei such as beryllium and carbon with clear isotope separation, while the phoswich can also be placed at zero degrees without a spectrometer and used as a high-efficiency beam counting monitor with particle identification capability at the rate of up to ∼5 × 104 particles per second. This paper reports on the capabilities of BlueSTEAl as determined by recent experiments performed at the Texas A&M Cyclotron Institute. The device is also anticipated to be used in future experiments at other radioactive ion beam facilities.

Ion-source development at the off-line LERIB test-facility at iThemba LABS

The Low Energy Radioactive Ion Beam (LERIB) facility [1] will be used to produce low-energy radioactive-ion beams (RIBs) with energies up to 60 keV. Radioactive reaction products will be created by a 66 MeV proton-beam impinging on a target made of carbide disks, such as SiC [2]. These reaction products will then be ionized in a target-ion-source (TIS) and extracted as beam. The TIS design allows three ion-sources: a surface ion-source [3], a forced electron-beam induced arc-discharge (FEBIAD) ion-source [4], and a resonance-ionization laser ion-source, or RILIS. The surface-ionization source was commissioned with stable beams in October 2021. The production of ions from Group-1 elements was accomplished with beams of 39K+, 41K+ and 23Na+ where currents were measured in the μA range. This source may be advantageous for producing stable pilot-beams for future radioactive-beam experiments. The FEBIAD is still in development at present.

β-decay studies across N = 126

With the advent of the first Radioactive Ion Beam facilities of new generation, the investigation of the neutron-rich side of the nuclear chart has experienced an impressive progress. However, the discovery and study of new nuclear species in the region around the heaviest known neutron shell closure, N = 126, is still one of the most coveted experimental challenges. At a slower pace, the exploitation of alternative reaction mechanisms and/or advanced instrumentation has opened the possibility to investigate the isomeric and β decay of new, moderately neutron-rich N ∼ 126 nuclei. These are of relevance for the understanding of the nuclear structure below the doubly-magic 208Pb and for their role in the synthesis of the trans-bismuth fissile elements in the r process. In this contribution, a general overview of the β-decay experiments performed at both sides of N = 126 is provided, with a main focus on the experiments carried out at the fragmentation facilities GSI and RIBF.

Shape Coexistence in Even–Even Nuclei: A Theoretical Overview

The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can occur have been identified, and the different microscopic particle–hole excitation mechanisms leading to neutron-induced or proton-induced shape coexistence have been clarified. The relation of shape coexistence to the islands of inversion, appearing in light nuclei, to the new spin-aligned phase appearing in N=Z nuclei, as well as to shape/phase transitions occurring in medium mass and heavy nuclei, has been understood. In the present review, these developments are considered within the shell-model and mean-field approaches, as well as by symmetry methods. In addition, based on systematics of data, as well as on symmetry considerations, quantitative rules are developed, predicting regions in which shape coexistence can appear, as a possible guide for further experimental efforts that can help in improving our understanding of the details of the nucleon–nucleon interaction, as well as of its modifications occurring far from stability.

Nuclear physics midterm plan at Legnaro National Laboratories (LNL)

The next years will see the completion of the radioactive ion beam facility SPES (Selective Production of Exotic Species) and the upgrade of the accelerators complex at Istituto Nazionale di Fisica Nucleare – Legnaro National Laboratories (LNL) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics, and applications. The nuclear physics community has organised a workshop to discuss the new physics opportunities that will be possible in the near future by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.

Increased beam energy as a pathway towards a highly selective and high-flux MR-ToF mass separator

Many experiments at radioactive ion beam (RIB) facilities suffer from isobaric contamination, i.e. unwanted ions of similar mass. During the last decade, Multi-Reflection Time-of-Flight (MR-ToF) devices have gained remarkable attention for mass separation of short-lived, low-intensity beams of radionuclides at RIB facilities throughout the world. They exceed mass resolving powers m/Δm of 105 within a processing time of some (tens of) milliseconds. Due to space-charge effects, however, the mass separation remains an experimental challenge when many ions are simultaneously confined in the MR-ToF device. This limits the wider application of MR-ToF mass separators at RIB facilities. By performing ion-optical simulations including space-charge effects, we investigate different schemes of ion preparation in a Paul trap upstream of the MR-ToF device as well as MR-ToF operation and study their influence on mass separation and maximal ion flux. The validity of these simulations are benchmarked by time-of-flight and collision-induced fluorescence measurements with a 1.5 keV MR-ToF device. More advanced ion-beam preparation techniques such as the use of laser cooling, buffer-gas cooling at cryogenic temperatures or specific electric-field parameters for ion trapping and ejection from the Paul trap can significantly reduce the processing time needed to reach a given mass resolving power. However, the simulations of these methods also indicate that space-charge effects in the MR-ToF device become relevant at lower ion numbers compared to ’standard’ ion preparation. Thus, the overall amount of mass separated ions per unit of time remains essentially the same. In contrast, the simulations suggest that increasing the kinetic energy of typically just a few kiloelectronvolts in present MR-ToF instruments to 30 keV results in a significant increase of the attainable maximal ion flux.

Targets and ion sources at CERN-ISOLDE — Facilities and developments

At the CERN-ISOLDE radioactive ion beam facility, thick targets are irradiated using a beam of 1.4-GeV protons. One of ISOLDE’s key features is the large choice of ion source types and target materials available, enabling us to select the ideal combination for optimal intensity and purity of the isotopes requested by ISOLDE users. The ever-increasing demands in terms of isotope production yield, beam purity, and overall reliability of the employed systems are driving the continuous development efforts.Over the past few years, CERN has invested heavily in facilities and infrastructure that facilitate ongoing developments required for ISOLDE. A dedicated offline laboratory (Offline 2) has been recently equipped with high repetition rate nanosecond tunable lasers required for scheme development and developments of specialized laser ion source types such as VADLIS, LIST and PI-LIST. Moreover, it hosts a twin setup of the ISOLDE RFQ cooler and buncher (ISCOOL), which is envisaged to be used for studies of molecular beam creation and breakup, as well as the development of improved RFQ services and operational modes. For material development, particularly for nanostructured materials, the new nano laboratory has just been commissioned and will enable the production and development of nano actinide targets for ISOLDE. In this contribution we describe the infrastructure required for target and ion source developments, highlight recent efforts and experimental results on both target material development and ion source development, and provide an outlook on what to expect in the near future.

Investigating radioactive negative ion production via double electron capture

The relative cross sections for radioactive negative ion production via double electron capture have been measured for collisions between a 40 keV projectile beam of uranium-238 and potassium vapor. This was performed at the collinear resonance ionization spectroscopy (CRIS) experiment at CERN-ISOLDE and is a step towards measuring the electron affinities (EAs) of elements that cannot be efficiently produced in negative ion sources at radioactive ion beam (RIB) facilities. This includes short-lived radioactive isotopes that have low production quantities and heavy and superheavy elements that systematically have smaller EAs than work functions of available ion source materials. Negative ions are particularly sensitive to electron–electron correlation effects, which make such studies ideal for benchmarking atomic structure models that go beyond the independent particle model. While the EAs of most light elements have been measured, experimental investigations on heavier elements, namely the actinides, remain scarce due to their radioactive nature and production difficulty. By developing negative ion production by charge exchange, we aim to make these studies feasible at RIB facilities.

Mass tagging: Verification and calibration of particle identification by high-resolution mass measurements

The access to exotic nuclei at radioactive ion beam facilities is crucial for the state of the art research across several fields of physics such as in nuclear structure, the understanding of fundamental interactions and nuclear astrophysics. The particle identification is of high importance, besides the challenging production of these rare and short-lived nuclei. At in-flight facilities, the particle identification is based on measuring the time-of-flight, energy-deposition and magnetic rigidity. These quantities are calibrated to convert them into A/Q and Z of the ions. To ensure a correct calibration, the unambiguous identification, also called tagging, of one species is necessary. Here, we present a novel tagging method by high-resolution mass measurements using an MR-TOF-MS after thermalization of the ions in a cryogenic stopping cell. The method was successfully established and tested at the fragment separator FRS at GSI with the FRS Ion Catcher in experiments using different FRS operation modes.

Status of LAMPS at RAON

A new radioactive ion-beam accelerator facility, RAON, is under construction in Korea. Among the seven experimental systems being built, the Large Acceptance Multi-Purpose Spectrometer (LAMPS) in the high-energy experimental hall is the versatile detector system for nuclear physics. Its primary goal is to study the nuclear equation of state (EoS) and the symmetry energy of the compressed nuclear matter, which should be essential to understand the effective nuclear interactions and structure of the astrophysical objects like neutron stars. The basic LAMPS system consists of the beam diagnostic elements such as the starting counters and beam drift chambers, the time-projection chamber, the barrel and forward time-of-flight systems, the forward neutron detector array, and the superconducting solenoid magnet. In this paper the overview of the present status of each detector component for LAMPS will be given with some prospects.

The CERN-ISOLDE fast tape station

The employment of a suitable radioactive decay spectroscopy setup is essential for the operation of radioactive ion beam (RIB) facilities. CERN-ISOLDE recently developed a new fast tape station (FTS) setup to replace its more than 40 years old predecessor. The new FTS is equipped with several β-detectors, a HPGe-detector, provisions for an α-detector, and constitutes a significant improvement in terms of transport times and detector noise characteristics. Since 2021 it is routinely used as the primary asset for yield determination and quality control of produced RIBs at ISOLDE. We address in this work its technical features and introduce the utilized control system.

Development and characterization of new position-sensitive silicon strip detectors

Direct reaction experiments in inverse kinematics are one of the best experimental tools to study a wide range of nuclear properties, providing a great probe into the nuclear structure of exotic nuclei and enabling the measurement of reactions relevant to many astrophysical scenarios. In order to fully exploit the next generation of radioactive ion beam facilities, a large amount of effort was devoted to developing nuclear detectors specially designed for direct reaction experiments. An instrumental part of these detector devices is the Micron X6 position-sensitive double sided silicon strip detector. This custom-made detector is segmented in 4 strips on its ohmic side and 8 resistive charge-splitting strips on its junction side, providing excellent position measurement of charged particles with a much smaller number of signals than traditional DSSSD with similar position resolution.

First on-line application of the high-resolution spectroscopy laser ion source PI-LIST at ISOLDE

We report on the development, characterization, and first application of a specialized resonance ionization laser ion source for high-resolution spectroscopy applications below usual hot cavity Doppler broadening limitations, for on-line experiments at CERN-ISOLDE. The new PI-LIST ion source comprises perpendicular laser/atom beam interaction in a radio-frequency quadrupole unit directly downstream the hot atomizer cavity. A spectral linewidth of 200–300MHz is demonstrated, with the potential to achieve below 100MHz. Compared to standard in-source laser ionization, the efficiency reduction factor ranges from a few 100 to above 1000. The implementation of this ion source concept at thick target radioactive ion beam facilities will greatly enhance capabilities for nuclear structure investigations without demanding dedicated experimental beam line setups, and will facilitate the delivery of isomer-pure beams to experimental stations.

Radioactive decays of stored highly charged ions

Decay properties known in neutral atoms can be altered significantly if all or most bound electrons are removed. Straightforwardly, in fully-ionised nuclei, the decay channels involving electrons are simply disabled. Also decay modes, that are hindered or completely blocked in neutral atoms, may, respectively, become dominant or open up in highly charged ions. Few-electron ions are by themselves clean systems with well-defined quantum numbers, in which the interactions within the remaining electrons can either be excluded or treated precisely, thereby allowing for investigations of the influence of atomic shell on nuclear decay properties. Violent stellar environments characterised by high temperatures and densities lead to high ionisation degrees of nuclides involved in nucleosynthesis processes. In spite of the rich motivation for studying radioactive decays of highly charged ions, intensive measurements became possible only after heavy-ion storage rings coupled to radioactive-ion beam facilities became available. Presented here is a compact review of the relevant experimental techniques and experiments.

Elastic scattering measurements of 7Be+natZr at sub- and near – barrier energies

We will present a recent experiment for elastic scattering of 7Be+natZr at five sub – and near- barrier energies, namely at 21.5, 22.5, 24, 27 and 28 MeV, for determining the optical potential. The experiment was performed at the TriSol radioactive beam facility of Notre Dame University, simultaneously with elastic scattering and breakup measurements of 8B+90Zr , the last performed at 28MeV. This optical potential will be used as one of the coupling potentials in our CDCC calculations for 8B. Further more we will look for the energy dependence of the potential and its resemblance to either the one exhibited by 7Li or the one by 6Li, extracting useful conclusions about their structure. Preliminary data are presented and discussed.

Nuclear structure aspects of the heaviest N∼Z nuclei south of 100Sn

Ever-lasting interest in the structure of 100Sn and neighbouring nuclei is still well justified by the fact that it is the heaviest doubly-magic nucleus with N=Z. State-of-the-art experimental techniques involving stable and radioactive beam facilities have enabled access to these exotic nuclei. In particular, the analysis of experimental data obtained in two DESPEC experiments at GSI Darmstadt extends the information on the shell structure and its evolution towards N = Z = 50, and allows the study of seniority conservation and proton-neutron interaction in the g9/2 orbit. Several theoretical approaches for shell-model investigations are discussed and their predictive power assessed. The calculated systematics of the reduced transition probabilities for high- to medium-spin states in N∼Z isotopes with active g9/2 orbit is presented for the first time.

Experimental setup for Weak Interaction Studies with Radioactive ion-beams WISArD

The article describes the commissioning and technical development of the Weak Interaction Studies with 32Ar Decay (WISArD) experiment, installed at the radioactive ion-beam facility ISOLDE/CERN. The experiment aims to extend the present limits on scalar and tensor currents in the weak interaction and hence search for physics beyond the Standard Model. The evaluation of these limits relies on measuring the proton energy in beta-delayed proton emission, sensitive to both the beta-neutrino angular correlation coefficient aβν and the Fierz interference term b. The method tries to improve previous studies by considering the positron-proton coincidences when determining the kinematic shift in the energy of the emitted protons. Using this coincidence technique, the aβν and b coefficients will be measured at the per mil level. Simulations were employed to optimize the ion beam transport efficiency and validate proof-of-principle results obtained in November 2018 (Nov2018). Upgrades are ongoing, and we are looking into improvements to the overall performance of the setup.

TriSol: A major upgrade of the TwinSol RNB facility

We report here on the recent upgrade of the TwinSol radioactive nuclear beam (RNB) facility at the University of Notre Dame. The new TriSol system includes a magnetic dipole to provide a second beamline and a third solenoid which acts to reduce the size of the radioactive beam on target.

Outlook on software framework in low and intermediate energy nuclear physics

Over the past decades nuclear physics experiments have seen a drastic increase in complexity. With the arrival of second generation radioactive ion beam facilities all over the world, the run for exploring more and more exotic nuclei is raging. The low intensity of RI-beams requires more complex setup, larger solid angle coverage and detection of a wider variety of charged and neutral particles. Design, construction and operation of a variety of complex instruments used in such experiments require many software developments. The short lifetime of experimental setups and multiple combinations of instruments demand a strong methodology. As the community is shifting to this new paradigm, the quest for the optimum framework is becoming central in the field. In this outlook we will introduce the specificity of the nuclear physics community, technical needs of such frameworks, and give an overview of the existing ones, with an emphasize on the difficult balance between computing performances, versatility and integration with other frameworks.