Radioactive Ion Beam Facility Research Articles

Cross-section prediction for isotopes near neutron drip line in 70, 80Zn projectile fragmentation reactions * * Supported by the National Natural Science Foundation of China (U1732135) and Natural Science Foundation of Henan Province (162300410179)

The cross sections for 59, 60Ca, recently measured in the 345 A MeV reaction, were estimated using the FRACS parametrization and an empirical formula, which are in good agreement. The FRACS parametrization and the empirical formula are combined to predict the cross sections for extreme calcium isotopes in the reactions at the incident energies of 60, 80, and 345 A MeV. The dependence of emperical formula parameters on the reaction system, as well as the incident energy, are discussed. The results indicate that can be discovered in reactions of 60, 80 A MeV . The predicted binding energy for extreme neutron-rich isotopes by the spherical relativistic continuum Hartree-Bogoliubov theory was adopted in the calculation. Hence, the planned Beijing Isotope-Separation-On Line Neutron-Rich Beam Facility (BISOL), which is a third generation radioactive ion beam facility, could provide the opportunity to discover and neighboring neutron-drip line nuclei.

Production of a 15C radioactive ion beam based on 18O(n,alpha)

.In the context of the SPIRAL2 radioactive beam facility the production rate of the neutron-rich 15C nucleus by 18O(n,alpha) has been investigated. In a water target of 20 cm3, enriched in 18O and placed behind the neutron converter, a rate of a few 1010 nuclei per second can be reached with 1mA of 40MeV deuterons. A 18O(n,alpha) cross-section based on the activation method is proposed. It is intermediate between the highest and lowest evaluations available to date.

Measurement of the laser resonance ionization efficiency for lutetium

Abstract The development of a highly efficient resonance ionization scheme for lutetium is presented. A laser ion source, based on the all-solid-state Titanium:sapphire laser system, was used at the 30 keV RISIKO off-line mass separator to characterize different possible optical excitation schemes in respect to their ionization efficiency. The developed laser resonance ionization scheme can be directly applied to the use at radioactive ion beam facilities, e. g. at the CERN-MEDICIS facility, for large-scale production of medical radioisotopes.

Formula omitted]-ray tracking with AGATA: A new perspective for spectroscopy at radioactive ion beam facilities

The Advanced GAmma Tracking Array (AGATA) is a next generation high-resolution γ-ray spectrometer for nuclear structure studies based on the principle of γ-ray tracking. It is built from high-fold segmented germanium detectors which will operate in position-sensitive mode by employing digital electronics and pulse-shape decomposition algorithms. The unique combination of highest detection efficiency and position sensitivity allows spectroscopic studies with instable ion beams of lowest intensity. The first implementation of the array consisted of five AGATA modules; it was operated at INFN Legnaro. A larger array of AGATA modules was used at GSI for experiments with unstable ion beams at relativistic energies. At the moment the spectrometer is hosted by GANIL. In the near future AGATA will be employed at the leading infrastructures for nuclear structure studies in Europe. The presentation will illustrate the potential of the novel gamma-ray tracking method by physics cases from the different exploitation sites. Perspectives and opportunities for γ-ray spectroscopy at future radioactive ion beam facilities are presented and discussed.

MELISSA: Laser ion source setup at CERN-MEDICIS facility. Blueprint

The Resonance Ionization Laser Ion Source (RILIS) has become an essential feature of many radioactive ion beam facilities worldwide since it offers an unmatched combination of efficiency and selectivity in the production of ion beams of many different chemical elements. In 2019, the laser ion source setup MELISSA is going to be established at the CERN-MEDICIS facility, based on the experience of the workgroup LARISSA of the University Mainz and CERN ISOLDE RILIS team. The purpose is to enhance the capability of the radioactive ion beam supply for end users by optimizing the yield and the purity of the final product. In this article, the blueprint of the laser ion source, as well as the key aspects of its development and operation are presented.

Improved beam diagnostics and optimization at ISAC via TITAN’s MR-TOF-MS

Determination of the constituents of the radioactive ion beam (RIB) is crucial for successful experiments at low-energy RIB facilities and as such decides the fate of many experiments. Here we present the role of TITAN’s Multiple-Reflection Time-Of-Flight Mass Separator (MR-TOF-MS) and how it complements the present capabilities at ISAC-TRIUMF for yield determinations and beam delivery. This non-scanning, broadband, high-resolution mass spectrometer allows for real-time identification and quantification of all species, ranging from radionuclides with half-lives as low as a few ms to stable isotopes and molecules. In this manner it can be efficiently used to optimize RIB delivery through the ISAC mass separator for rate of the species of interest or its ratio to contamination. We present an example of this optimization approach, where the purity of secondary beams of neutron-rich titanium was improved by more than one order of magnitude based on the diagnostics capabilities of the new MR-TOF-MS and thus, allowed for high-precision mass measurements at TITAN.

New mass measurements with trapped (radioactive) ions and related fundamental physics

Mass measurements give us the nuclear binding energy, a fundamental property that is indispensable for the study of nuclear structure, stellar nucleosynthesis and neutron-star composition, as well as atomic and weak-interaction physics. The dedicated experimental programs at all major nuclear-physics installations on the planet is excellent testimony to their relevance. The use of stored ions (in rings and traps) has made an enormous impact on the field of mass spectrometry. While Penning traps contribute particularly with their hallmark precision, another type of ion trap has now come into play: the multi-reflection time-of-flight mass spectrometer (MR-TOF MS). Read on for a tour of mass-measurement installations at radioactive-beam facilities worldwide with the physics highlights achieved since the last TCP conference.

First steps in the development of the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy

Collinear laser spectroscopy (CLS) has been combined with the multi-reflection time-of-flight (MR-ToF) technique. To this end, a photodetection system has been implemented at the drift region of a MR-ToF apparatus and a laser beam has been sent along the path of the ions that are stored between the two ion-optical mirrors. The main goal of the present proof-of-principle (PoP) experiments, is the confirmation of the expected increase in sensitivity compared to conventional fluorescence-based CLS due to the repeated probing of the trapped ion bunches. The novel method will be used for the precise measurement of nuclear ground- and isomeric-state properties of exotic nuclei with low production yields at radioactive ion-beam facilities. A significant sensitivity improvement of CLS is expected, depending on the half-life and mass of the nuclide of interest. The status of the PoP setup and future improvements are discussed.

S -wave scattering lengths for the Be7+p system from an R -matrix analysis

The astrophysical $S$-factor for the radiative proton capture reaction on $^7$Be ($S_{17}$) at low energies is affected by the $s$-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the $^7$Be+p system in the center-of-mass energy range 0.474 - 2.740 MeV and center-of-mass angular range of 70$^\circ$- 150$^\circ$. A radioactive $^7$Be beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH$_{2}$)$_\text n$ target. Scattered ions were detected in the segmented Silicon Detector Array. Using an $\textit{R}$-matrix analysis of ORNL and Louvain-la-Neuve cross section data, the $s$-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34$^{+1.11}_{-1.33}$ and -3.18$^{+0.55}_{-0.50}$ fm, respectively. The uncertainty in the $s$-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in $S_{17}$ at zero energy. The level structure of $^8$B is discussed based upon the results from this work. Evidence for the existence of 0$^+$ and 2$^+$ levels in $^8$B at 1.9 and 2.21 MeV, respectively, is observed.

Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

Neutron-deficient $^{177-185}$Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility, in an experiment combining different detection methods tailored to the studied isotopes. These include either alpha-decay tagging or Multi-reflection Time-of-Flight gating to identify the isotopes of interest. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of $^{177-180}$Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole and electric quadrupole moments of the odd-A isotopes and arguments in favor of $I = 7/2$ spin assignment for $^{177,179}$Hg were deduced. Experimental results are compared with Density Functional Theory (DFT) and Monte-Carlo Shell Model (MCSM) calculations. DFT calculations with several Skyrme parameterizations predict a large jump in the charge radius around the neutron $N = 104$ mid shell, with an odd-even staggering pattern related to the coexistence of nearly-degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiment out of reach for current functionals. Despite this inherent diffculty, the SLy5s1 and a modified UNEDF1^{SO} parameterization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton $\pi h_{9/2}$ and neutron $\nu i_{13/2}$ orbitals.

Opportunities for nuclear reaction studies at future facilities

Opportunities for investigations of nuclear reactions at the future nuclear physics facilities such as radioactive ion beam facilities and high-power laser facilities are considered. Post-accelerated radioactive ion beams offer possibilities for study of the role of isospin asymmetry in the reaction mechanisms at various beam energies. Fission barrier heights of neutron-deficient nuclei can be directly determined at low energies. Post-accelerated radioactive ion beams, specifically at the future facilities such as HIE-ISOLDE, SPIRAL-2 or RAON-RISP can be also considered as a candidate for production of very neutron-rich nuclei via mechanism of multi-nucleon transfer. High-power laser facilities such as ELI-NP offer possibilities for nuclear reaction studies with beams of unprecedented properties. Specific cases such as ternary reactions or even production of super-heavy elements are considered.

Comparison of Reactor Production of 229Th vs. Accelerator Production of 229Th at Oak Ridge National Laboratory

Actinium-225 (t1/2 = 10.0 ± 0.1 d) is one of the more effective radioisotopes used in alpha radioimmunotherapy. It has been used to treat many forms of cancer including glioblastoma, acute myeloid leukemia, prostate cancer, and breast cancer. Actinium-225 can be directly applied in vivo or used as a generator of the short-lived daughter product 213Bi (t1/2 = 45.59 ± 0.06 minutes). Actinium-225 can be produced directly via cyclotron through the 226Ra(p,2n)225Ac reaction or by high energy proton spallation (Ep > 90 MeV) of thorium targets. However, because of its ten-day half-life, it is more efficient to create its precursor, 229Th (t1/2 = 7932 ± 28 years). Current supplies of 229Th originate from the decay of 233U [t1/2 = (1.592 ± 0.002) x 105 y], but that supply is insufficient to support the demand for 225Ac and access to 233U is limited. In order to close the gap between supply and demand of 225Ac, work has been initiated at Oak Ridge National Lab to produce 229Th through the irradiation of 226Ra targets in the High Flux Isotope Reactor. This method to produce 229Th will be presented and compared to previous studies performed at ORNL to produce 229Th through the low energy proton bombardment (Ep < 40 MeV) of 232Th at the Holifield Radioactive Ion Beam Facilities Tandem Accelerator.

The TRAPSENSOR facility: an open-ring 7 tesla Penning trap for laser-based precision experiments

A Penning-trap facility for high-precision mass spectrometry based on a novel detection method has been built. This method consists in measuring motional frequencies of singly-charged ions trapped in strong magnetic fields through the fluorescence photons from laser-cooled 40Ca+ ions, to overcome limitations faced in electronic single-ion detection techniques. The key element of this facility is an open-ring Penning trap coupled upstream to a preparation Penning trap similar to those used at Radioactive Ion Beam facilities. Here we present a full characterization of the trap and demonstrate motional frequency measurements of trapped ions stored by applying external radiofrequency fields in resonance with the ions’ eigenmotions, in combination with time-of-flight identification. The infrastructure developed to observe the fluorescence photons from 40Ca+, comprising the 12 laser beams and the optical system to register the image in a high-sensitive CCD sensor, has been proved by taking images of the trapped and cooled 40Ca+ ions. This demonstrates the functionality of the proposed laser-based mass-spectrometry technique, providing a unique platform for precision experiments with implications in different fields of physics.

Challenges and prospects of electron cyclotron resonance charge breeders applied to radioactive ion beam facilities

Electron cyclotron resonance charge breeder (ECR CB) is one of the instruments used to boost the radioactive ion beam (RIB) charge state (from 1+ to N+) in isotope separator on-line (ISOL) facilities. While existing ECR CB can manage intense incoming 1+ RIB without difficulty, significant amounts of background impurities are extracted with the N+ RIB signal. When the N+ RIB signal is very low, the dominant background can be detrimental to the study of the RIB in today facilities, if no downstream high mass resolution separation is available. This work investigates the improvements achievable with a new generation 18 GHz ECR CB applicable to future facility like EURISOL. The study shows that with a modified ion source geometry, an optimized magnetic confinement, a careful wall metal choice like beryllium, a UHV technology, the charge breeder performance will improve as follows: +20% higher capture efficiency, −40% charge breeding time, charge state ion production with mass over charge of 3 up to xenon and over 6 up to uranium, co-extracted contaminant density reduction by a factor 60 to 600. An 18 GHz ECR CB ion source layout is finally proposed for EURISOL.

Masses and Beta-decay Studies of Neutron-rich Nuclei using the X-array and Gammasphere

Properties of neutron-rich nuclei in the A˜160 region are important for achieving a better understanding of the nuclear structure in this region where little is known owing to diffculties in the production of these nuclei at the present nuclear physics facilities. These properties are essential ingredients in the interpretation of the rareearth peak at A˜160 in the r process abundance distribution, since theoretical models are sensitive to nuclear structure input. Predicated on these ideas, we have initiated a new experimental program at Argonne National Laboratory. During the first experiment, beams from the Californium Rare Isotope Breeder Upgrade radioactive beam facility were used in conjunction with the SATURN decay station and the X-array. We focused initially on several odd-odd nuclei, where β decays of both the ground state and an excited isomer were investigated. Because of the spin difference, a variety of structures in the daughter nuclei were selectively populated and characterized based on their decay properties. Mass measurements using the Canadian Penning Trap aimed at establishing the excitation energy of the β-decaying isomers were also carried out. Evidence was found for a change in the single-particle structure, which in turn results in the formation of a sizable N=98 sub-shell gap at large deformation. Results from the first experimental campaign using the newly-commissioned β-decay station at Gammasphere are also presented.

Redesign of the GANIL GTS ECRIS for 1+/n+ studies

More than half of the beams produced at GANIL are metallic elements, underlining the importance of their continuing development. Compared to the conventional techniques (oven, sputtering, MIVOC), the 1+/n+ method has demonstrated superior ionization efficiencies, suggesting the potential for improved metal beam production. Dedicated studies are required to assess the feasibility of this approach. The SPIRAL1 Charge Breeder is now in operation at the GANIL radioactive beam facility SPIRAL1. Operation in high radiation area poses challenges for its future development. A separate test stand supporting charge breeder and metal ion beam R&D is thus desirable.The GTS 14.5 GHz ECRIS has been chosen as a platform for 1+/n+ studies. After the upgrade program of 2017–2018, the GTS provides good performance and versatility, making it well-suited for ion source R&D. A new injection module has been designed for 1+ injection into the GTS plasma to be used in the 1+/n+ studies. It can be easily replaced with the conventional system for normal ion source operation. The design of the new injection system will be presented in detail with ion optical simulations of the 1+ beam injection.

Radium ionization scheme development: The first observed autoionizing states and optical pumping effects in the hot cavity environment

This paper reports on resonance ionization scheme development for the production of exotic radium ion beams with the Resonance Ionization Laser Ion Source (RILIS) of the CERN-ISOLDE radioactive ion beam facility. During the study, autoionizing states of atomic radium were observed for the first time. Three ionization schemes were identified, originating from the 7s2 1S0 atomic ground state. The optimal of the identified ionization schemes involves five atomic transitions, four of which are induced by three resonantly tuned lasers. This is the first hot cavity RILIS ionization scheme to employ optical pumping effects. The details of the spectroscopic studies are described and the new ionization schemes are summarized.

Systematic study of high-K isomers in the midshell Gd and Dy nuclei

High-K isomers are well known in the rare-earth region and provide unique access to the high spin structures of the nuclei. With the current interest in the study of neutron-rich rare-earth nuclei at Radioactive Ion Beam (RIB) facilities, we present here theoretical results of the band structures of neutron-rich Gd and Dy nuclei, including the high K-isomers. Apart from the already known K-isomers, we predict some more K-isomers and these are suggested for future studies at RIB facilities. Self-consistent Deformed Hartree-Fock and Angular Momentum Projection theories are used to get the intrinsic structures, band-spectra and electromagnetic transitions probabilities of the ground band as well as bands based on isomers.

Study of the 2H(7Be,p+3He+4He)n Reaction for Resonances in 8B

The solar neutrino is a good probe for understanding the internal structure and the energy production mechanism of stars with masses of about that of the sun because it does not interact with other materials of the star. The production rate of the solar neutrino is largely uncertain due to the lack of nuclear structure information on the 8B nucleus. In the search for resonances in the highly unstable nucleus 8B, which affect the production of solar neutrino, the 2H(7Be, p+3He+4He)n reaction was studied by using a radioactive 7Be beam produced at the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory. Two layers of annular silicon strip detectors were used for particle identification, and the excitation energy of 8B was reconstructed by requiring triple coincidence for p, 3He, and 4He.

Determination of the first ionization energy of polonium by resonance ionization spectroscopy – Part II: Measurement of odd-parity Rydberg states at CERN–ISOLDE

Polonium (Po) is one of the rarest elements in Earth's crust. None of its isotopes are stable and sufficient amounts for systematic experimental studies of its most fundamental properties are only available by artificial production. At the radioactive ion beam facility ISOLDE at CERN, 208Po was produced by proton-induced spallation of uranium. Using the technique of in-source Resonance Ionization Spectroscopy the ionization threshold was probed with a tunable dye laser. A spectrum of 110 previously undocumented odd-parity Rydberg states was observed. Applying the Rydberg formalism to the data enabled the determination of the first ionization energy of polonium as 67896.310(14)(30) cm−1 or 8.4180700(18)(37) eV. This is a precision improvement of more than 600 over the existing literature value. A comparison with the homologous elements sulfur, selenium and tellurium enabled the assignment of the electron configuration of the resonances found in the spectrum.