Radioactive Beams Research Articles

NUCLEAR STRUCTURE STUDY OF THE HALO NUCLEI

The existence of halo nuclei is one of the major important discoveries in the field of nuclear physics. These nuclei are treated as loosely bound system in which a core of normal nuclear density is surrounded by so-called neutron (or proton) halo of diluted nuclear matter. Many theoretical investigations have attempted to understand these nuclei, which exist at light to heavy masses. The phenomenon of nuclear halo is a quantum effect that occurs in nuclei due to the presence of valence nucleons with low separation energy and I = 0, 1 (low angular momentum), and is manifested by the extraordinarily large radii of these nuclei. The core plus halo model is commonly used to describe halo nuclei. This model recognizes the need to treat the core and the halo neutrons or protons separately. By considering different model spaces for the core and the halo nucleons, we can better explain the properties of halo nuclei. This separation is justified by the fact that the valence nucleons in a halo nucleus have different properties compared to the core. Halo nuclei at rest cannot be used as target due to their short-lived species and extraordinary ratio of neutrons and protons (either neutron-rich or proton-rich). Instead, they can be studied through direct reactions with a radioactive isotope beam, employing inverse kinematics where the role of the beam and target are exchanged. In order to investigate the charge and matter densities of these nuclei, total and differential reaction cross section analyses of proton scattering on halo nuclei have been carried out using various theoretical and phenomenological methods

Study of the radionuclide deposition in the radioactive ion line of the Selective Production of Exotic Species (SPES) facility

SPES (Selective Production of Exotic Species) is a second generation facility for the production of radioactive ion beams that is going to be commissioned at the Laboratori Nazionali di Legnaro of INFN at Legnaro, Padua, Italy. Radioactive neutron-rich isotopes are expected to be produced by nuclear fission induced by a 40 MeV, 200 μA primary proton beam impinging on a 238UCx target. The expected reaction rate is about 1013 fission/s. Radioactive ion beams are produced using the isotope separation on-line technique. The production of such an amount of radioactive species raises radiological issues throughout the life cycle of the facility. A study of the radioactive contamination of the components of the radioactive ion beam line is performed with the FLUKA Monte Carlo simulation code, under realistic hypotheses for the produced isobaric beams. The present results complete previous studies focused on the radiological impact of the production target irradiation, the residual activation of the primary proton beam line and the radioactive contamination of the ion source complex. The overall ambient dose equivalent rate due to the different radiation sources is calculated at several positions inside the production bunker and at different times after a typical one-year operating period of the facility with the 238UCx target at full power. The obtained results and the developed methodology provide the guidelines and the needed tools to plan ordinary and extraordinary interventions as well as final decommissioning of the SPES facility.

Nuclear physics midterm plan at LNS

The next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-flight production of radioactive ion beams, the PANDORA plasma trap for multidisciplinary studies and a high-power laser for basic science and applied physics. The nuclear physics community has organized a workshop to discuss the new physics opportunities that will be possible in the middle term (5–7 years) by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.

Development of an optical method for temperature measurements of the ISAC targets at TRIUMF

The temperatures of isotope separator on-line targets play an important role for the overall target performance, including the yield of the radioactive ion beams and the target lifetime. At TRIUMF an optical technique is being developed to obtain accurate real-time temperature feedback from ISAC and in the future ARIEL targets during beam delivery. The light emitted from within the hot tantalum target container is captured and transmitted into a spectrometer via an ionizer opening. For accurate results an absolute irradiance calibration of the spectrometer is performed to determine the spectral power density. Then, to analyze the light spectra and calculate the maximum temperature, two mathematical methods have been applied. These methods are first evaluated using the spectrum of a light source with a known colour temperature. One method is selected and applied to a tantalum target container heated off-line at nominal temperatures and cross-checked with a thermocouple. The results of the test are in close agreement with the temperatures read by the thermocouple. This paper describes the calibration of the optical system, the methods applied, along with their results and validations. This technique will be applied to the on-line targets and correlate isotope releases with target temperatures for optimizing the delivery of short-lived radioisotopes species.

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.

Study on the performance of titanium alloy-lined thin-walled vacuum chamber

HIAF-BRing, the main synchrotron accelerator of the High Intensity Heavy-Ion Accelerator Facility, requires an average pressure lower than 1 × 10 −9 Pa and the magnetic field increase rate of no less than 12 T/s to fulfill radioactive beam physics and high energy density physics experiments. To reduce the eddy current effect and the gap size of dipoles, a titanium alloy-lined thin-walled vacuum chamber with a wall thickness of 0.3 mm is proposed by IMP, which has been developed from the initial ceramic-lined vacuum chamber. By mechanical loading testing, when the internal stress of titanium alloy rings made by 3D selective laser melting (SLM) reaches 639 MPa, it is still within the elastic deformation range, in fact, the yield strength of the 3D printed titanium alloy material is 912 MPa. In order to reduce the pressure gradient inside the thin-walled vacuum chamber caused by the surface outgassing of the rings, TiZrV thin films have been deposited on the rings by planar target magnetron sputtering. Through TiZrV deposited on the rings, the pressure at the middle of the thin-walled vacuum chamber has been dropped from 1.5 × 10−9 Pa to 1.0 × 10−9 Pa. At the same time, as the magnets are continuously energized, the actual heating state of the thin-walled vacuum chamber has been also measured.

Gamma -Ray detection with CsI(Tl) scintillators of the FARCOS array

The measurement of the response function of the CsI(Tl) scintillators of the FARCOS array, to standard sources, cosmic rays and environmental background allows the assessment of their performance. Fast–Slow analysis discriminates between gamma -rays and charged particles. The relatively good energy resolution allows the observation of well resolved escape peaks due to the interaction of the 4.44 MeV gamma -ray generated by AmBe source. Furthermore, the small noise enables to discriminate from the background the annihilation 511 keV gamma -rays of the ^{22}Na source. The energy loss of muons generated by cosmic rays has been also measured and the radioactive contaminants as ^{137}Cs, ^{40}K and ^{208}Tl have been identified. The quality of the detectors suggests the possibility to use the array also for the measurement of gamma -ray decay in reactions induced by stable and radioactive beams, once a well-defined reaction channel has been identified. Moreover, a dedicated compact detection module as a portable, high efficiency radiation detector for the control of environmental contamination will be developed.

Isospin symmetry in the T = 1,A = 62 triplet

Excited states in the Tz=0,−1 nuclei 62Ga and 62Ge were populated in direct reactions of relativistic radioactive ion beams at the RIBF. Coincident γ rays were measured with the DALI2+ array and uniquely assigned to the A=62 isobars. In addition, 62Ge was also studied independently at JYFL-ACCLAB using the 24Mg(40Ca,2n)62Ge fusion-evaporation reaction. The first excited T=1,Jπ=2+ states in 62Ga and 62Ge were identified at 979(1) and 965(1) keV, respectively, resolving discrepant interpretations in the literature. States beyond the first 2+ state in 62Ge were also identified for the first time in the present work. The results are compared with shell-model calculations in the fp model space. Mirror and triplet energy differences are analyzed in terms of individual charge-symmetry and charge-independence breaking contributions. The MED results confirm the shrinkage of the p-orbits' radii when they are occupied by at least one nucleon on average.

The St. Benedict Facility: Probing Fundamental Symmetries through Mixed Mirror β-Decays

Precise measurements of nuclear beta decays provide a unique insight into the Standard Model due to their connection to the electroweak interaction. These decays help constrain the unitarity or non-unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) quark mixing matrix, and can uniquely probe the existence of exotic scalar or tensor currents. Of these decays, superallowed mixed mirror transitions have been the least well-studied, in part due to the absence of data on their Fermi to Gamow-Teller mixing ratios (ρ). At the Nuclear Science Laboratory (NSL) at the University of Notre Dame, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is being constructed to determine the ρ for various mirror decays via a measurement of the beta–neutrino angular correlation parameter (aβν) to a relative precision of 0.5%. In this work, we present an overview of the St. Benedict facility and the impact it will have on various Beyond the Standard Model studies, including an expanded sensitivity study of ρ for various mirror nuclei accessible to the facility. A feasibility evaluation is also presented that indicates the measurement goals for many mirror nuclei, which are currently attainable in a week of radioactive beam delivery at the NSL.

Clustering states in neutron-rich nuclei

The study of clustering states in neutron-rich nuclei is an important subject of research in the field of nuclear physics, steadily growing in interest in the international scientific community. In this context, break-up reactions play an important role for the characterization of exotic states in radioactive light nuclei, like neutron halos around stable cores, α-clustering structures or exotic clusters. The CLIR (Clusters in Light Ion Reactions) experiment was performed at INFN - Laboratori Nazionali del Sud (LNS), aiming at the investigation of such states in light radioactive nuclei, by producing a radioactive beam at the FRIBs facility. Reaction products were detected by the CHIMERA multidetector, coupled with four telescopes of the FARCOS array. Calibrations of the tagging system and of the FARCOS telescopes have been performed, for which accurate procedures have been carried out. In this paper, results on the analysis will be presented. Moreover, a brief review on the new fragment separator FRAISE, currently under construction at LNS, will be given.

Recent results on the new fragment in-flight separator at INFN-LNS

A project for an upgrade of the Superconducting Cyclotron is underway at INFN-LNS. One of the goals of this project is the production of RIBs (Radioactive Ion Beams) of high intensity. To reach this purpose, a dedicated facility consisting of a new fragment separator FRAISE (FRAgment In-flight SEparator) is ongoing, exploiting primary beams with a power up to ≈ 2-3 kW. The high intensity achievable with FRAISE requires the use of appropriate diagnostics and tagging systems that can operate also in a strong radioactive environment. In this framework, a R&D program has been started to develop the FRAISE facility as well as the diagnostics and the tagging systems.

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.

Stochastic cooling notch filter developments for the high-precision spectrometer ring in the high intensity heavy-ion accelerator facility project.

Stochastic cooling of the high-precision spectrometer ring (SRing) at the High Intensity Heavy-Ion Accelerator Facility (HIAF) project in China, which is used mainly for experiments with radioactive fragment beams, is applied to speed up the cooling process of a stored ion beam. In this article, a new coaxial-type notch filter with an amplitude equalizer in the long branch and an optical-type notch filter with phase-stabilized optical fiber are discussed and evaluated for the SRing stochastic cooling system. Both prototypes of coaxial and optical notch filters are fabricated and tested. The minimum notch depth of coaxial and optical notch filters reaches to 26 and 40 dB, respectively. The performance of both coaxial notch filter and optical fiber notch filter is presented in this work. These developments will be used not only for the longitudinal stochastic cooling system but also have potential for the beam feedback system.

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.

Production and mechanical characterization of Titanium Carbide ISOL target disks fabricated by direct ink writing

Titanium carbide boasts a large variety of high-temperature applications from aerospace to electronics and is also employed as Isotope Separation On-Line target for the production of Radioactive Ion Beams, which are employed in numerous research and technological fields, ranging from nuclear physics to medical applications. High working temperature, open and tailored porosity and resistance to thermal stresses are fundamental characteristics for this kind of targets. In this work, an extrusion-based additive manufacturing technique (Direct Ink Writing) was used for the fabrication of complex three-dimensional macro-porous structures in the shape of disks with dimensions compatible for their use as targets. An ink containing a suspension of TiC powders with solid loading of 47.5 vol% was prepared and its rheological properties were investigated. Afterwards, single filaments with an average diameter of 0.36 mm were produced and characterized with four-point bending tests to determine the bulk material tensile strength and Young's modulus. TiC targets were then manufactured and their mechanical properties were characterized with the Ball on Three Balls approach, a biaxial flexural test suitable for disk-shaped samples. For both flexural tests, a Finite Element model was developed representatively reproducing the experimental results. The calculated tensile strength values for both filaments and disks were analyzed with Weibull's statistical approach to provide reference stress limit, corresponding to a survival probability of 99.9%.

Machine learning method for 12C event classification and reconstruction in the active target time-projection chamber

Active target time projection chambers are important tools in low energy radioactive ion beams or gamma rays related researches. In this work, we present the application of machine learning methods to the analysis of data obtained from an active target time projection chamber. Specifically, we investigate the effectiveness of Visual Geometry Group (VGG) and the Residual neural Network (ResNet) models for event classification and reconstruction in decays from the excited 22+ state in 12C Hoyle rotation band. The results show that machine learning methods are effective in identifying 12C events from the background noise, with ResNet-34 achieving an impressive precision of 0.99 on simulation data, and the best performing event reconstruction model ResNet-18 providing an energy resolution of σE<77 keV and an angular reconstruction deviation of σθ<0.1 rad. The promising results suggest that the ResNet model trained on Monte Carlo samples could be used for future classifying and predicting experimental data in active target time projection chambers related experiments.

Production of innovative radionuclides for medical applications at the CERN-MEDICIS facility

Since its commissioning in December 2017, the CERN-MEDICIS facility has been providing non-conventional radionuclides for research in nuclear medicine. Benefitting from decades of experience in the production of radioactive ion beams and in the mass separation process from the ISOLDE facility at CERN, MEDICIS quickly became a worldwide key player in the supply of novel medical isotopes dedicated to research in the fields of cancer imaging, diagnostics, and radiation therapy.After a few years of operation, successful collections have been performed on a large panel of radionuclides such as 128Ba, 149,152,155Tb, 153Sm, 165,167Tm, 169Er, 175Yb, 191Pt, and 225,227Ac. Several milestones have been achieved on the output of the facility, such as the collection of 0.5 GBq of 175Yb, and a total separation efficiency higher than 50% reached for 167Tm in 2020. These collections led to notable recent in-vitro and preclinical results in targeted radionuclide therapy achieved with high molar activity 175Yb and 153Sm products.Constant developments are ongoing, such as innovative target designs, molecular formation to improve the release of some specific isotopes, laser development in the dedicated MELISSA laboratory, study of new implantation foil materials, and post-collection radiochemistry.