ISOLDE Research Articles

Resonant Converter Topology With Losses Compensation for the ISOLDE/CERN Modulator

This paper describes a solid-state asymmetric bridge resonant topology to increase the energy efficiency of switching pulse modulators. The solid-state resonant topology will replace an existing pulse transformer and thyratron-based resonant modulator to supply the 60-kV target potential for the ion acceleration of the On-Line Isotope Mass Separator ISOLDE accelerator. An experimental prototype is tested in order to validate the proposed concept, including a low auxiliary voltage power supply to compensate the losses in the circuit. The design of the circuit components and the experimental results for a 6-kV prototype are presented and discussed, as well as the design procedure and parameters for the 60-kV modulator, including a high-voltage gapped coil core.

In-gas laser ionization and spectroscopy of actinium isotopes near the N=126 closed shell

The in-gas laser ionization and spectroscopy (IGLIS) technique was applied on the $^{212--215}\mathrm{Ac}$ isotopes, produced at the Leuven Isotope Separator On-Line (LISOL) facility by using the in-gas-cell and the in-gas-jet methods. The first application under on-line conditions of the in-gas-jet laser spectroscopy method showed a superior performance in terms of selectivity, spectral resolution, and efficiency in comparison with the in-gas-cell method. Following the analysis of both experiments, the magnetic-dipole moments for the $^{212--215}\mathrm{Ac}$ isotopes, electric-quadrupole moments and nuclear spins for the $^{214,215}\mathrm{Ac}$ isotopes are presented and discussed. A good agreement is obtained with large-scale nuclear shell-model calculations by using a $^{208}\mathrm{Pb}$ core.

Effect of sacrificial fiber length on gas permeability of lanthanum carbide

Lanthanum carbide is considered as a potential target for generation of radioactive ion beams by means of the ISOL (Isotope Separation On Line) technique. This method requires the use of porous refractories as targets, in order to work in extreme conditions (more than 2000°C in high vacuum) to enhance the release of the generated isotopes. Several techniques can be used to generate open interconnected porosity in lanthanum carbide. The use of polymeric (nylon and polypropylene) fibers as sacrificial fillers was successfully tested in a previous work. Here, the effect of the fibers length is reported and discussed in terms of porosity and permeability.

Design for simultaneous acceleration of stable and unstable beams in a superconducting heavy-ion linear accelerator for RISP

The post-accelerator of isotope separation on-line (ISOL) system for rare isotope science project (RISP) is a superconducting linear accelerator (SC-linac) with a DC equivalent voltage of around 160 MV. An isotope beam extracted from the ISOL is in a charge state of [Formula: see text] and its charge state is increased to [Formula: see text] by charge breeding with an electron beam ion source (EBIS). The charge breeding takes tens of ms and the pulse width of extracted beam from the EBIS is tens of [Formula: see text]s, which operates at up to 30 Hz. Consequently a large portion of radio frequency (rf) time of the post SC-linac is unused. The post-linac is equipped also with an electron cyclotron resonance (ECR) ion source for stable ion acceleration. Thanks to the large phase acceptance of SC-linac, it is possible to accelerate simultaneously both stable and radioisotope ions with a similar charge to mass ratio by sharing rf time. This operation scheme is implemented for RISP with the addition of an electric chopper and magnetic kickers. The facility will be capable of providing the users of the ISOL and in-flight fragmentation (IF) systems with different beams simultaneously, which would help nuclear science users in obtaining a beam time as high-precision measurements often need long hours.

Lattice design and beam dynamics simulation for the simultaneous operation of stable ion beam and rare isotope beam in the RAON accelerator

The Rare Isotope Accelerator of Newness (RAON) accelerator is under construction to generate and accelerate the stable ion beams and the rare isotope beams for various kinds of experiment programs. Especially, the post accelerator section was designed to be able to separately accelerate and transport the stable ion beams created by the superconducting electron cyclotron resonance ion source (ECR-IS) and the rare isotope beams created by the Isotope Separation On-Line (ISOL) system. However, recently, the research of the simultaneous operation of the stable ion beams and the rare isotope beams has been conducted to more efficiently satisfy the a wide range of beam requirements of the experimental halls. For the operation, we has modified the lattice of the post low energy beam transport (LEBT) section for the injection of the rare isotope beam and the next lattice after the low energy superconducting linac (SCL3) section for the extraction of the accelerated beam in the post accelerator section of the RAON accelerator. In this paper, the new lattice designs of the injection and extraction parts will be presented and we will describe the results of the beam dynamics simulations for the simultaneous operation of the two kinds of beams.

Quadrupole moment of Fr203

The spectroscopic electric quadrupole moment of the neutron-deficient francium isotope 203 Fr was measured by using high-resolution collinear resonance ionization spectroscopy (CRIS) at the CERN Isotope Separation On-Line Device (ISOLDE) facility. A remeasurement of the 207 Fr quadrupole moment was also performed, resulting in a departure from the established literature value. A sudden increase in magnitude of the 203 Fr quadrupole moment, with respect to the general trend in the region, points to an onset of static deformation at N = 116 in the 87 Fr isotopic chain. Calculation of the static and total deformation parameters show that the increase in static deformation only cannot account for the observed departure of its relative charge radius from the 82 Pb chain.

Doughnut-shaped gas cell for KEK Isotope Separation System

Abstract We have developed a doughnut-shaped argon gas cell with a rotating target for the KEK Isotope Separation System (KISS). The new gas cell increased extraction yields for target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions. KISS is an on-line isotope separator, which makes use of a laser ion source combined with an argon gas cell as a gas catcher for TLFs. This system has been implemented for nuclear spectroscopy of neutron-rich isotopes in the region of N = 126 . A gas flow simulation was performed to optimize the design of the gas cell for efficient and fast transport of TLFs. To confirm the performance expected at the design stage, we performed off- and on-line experiments by using iridium atoms evaporated from a filament in the gas cell and TLFs produced by a 136 Xe beam and 198 Pt target system respectively. We could increase the extraction yield by more than an order of magnitude by applying a doughnut-shaped gas cell with a rotating target. Thus, we could perform nuclear spectroscopy in this heavy region with the use of KISS.

A preliminary study for the production of high specific activity radionuclides for nuclear medicine obtained with the isotope separation on line technique

Radiopharmaceuticals represent a fundamental tool for nuclear medicine procedures, both for diagnostic and therapeutic purposes. The present work aims to explore the Isotope Separation On-Line (ISOL) technique for the production of carrier-free radionuclides for nuclear medicine at SPES, a nuclear physics facility under construction at INFN-LNL. Stable ion beams of strontium, yttrium and iodine were produced using the SPES test bench (Front-End) to simulate the production of 89Sr, 90Y, 125I and 131I and collected with good efficiency on suitable targets.

Influence of the injected beam parameters on the capture efficiency of an electron cyclotron resonance based charge breeder

Electron cyclotron resonance ion sources based charge breeders (ECR-CB) are fundamental devices for Isotope Separation On Line (ISOL) facilities aiming at postaccelerating radioactive ion beams (RIBs). Presently, low intensity RIBs do not allow a conventional tuning of the ECR-CB: as a consequence, it has to be set with a stable 1+ pilot beam first, switching then to the radioactive one without changing any parameter; this procedure is usually called ``blind tuning.'' Besides having different masses, pilot and radioactive beams can also differ in terms of the rms transverse emittance ${\ensuremath{\epsilon}}_{\mathrm{rms}}$ and/or longitudinal energy spread $\mathrm{\ensuremath{\Delta}}E$, so the choice of a given pilot beam can determine the overall performances of the final breeding stage. This paper shows a numerical study of how the capture efficiency of the PHOENIX charge breeder is affected by the aforementioned beam paramaters: the analysis reveals the two-step nature of the process, highlighting the role of the injection optics and the plasma capture capability in the overall performances of this device. The simulations predict highest efficiency for ${\ensuremath{\epsilon}}_{\mathrm{rms}}l5\ensuremath{\pi}\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ and $\mathrm{\ensuremath{\Delta}}El5\text{ }\text{ }\mathrm{eV}$ in a optimum energy range between 2 and 6 eV, thus giving important information on the possibility of blindly tuning an ECR-CB. No isotopical effects were observed, while it clearly came out the necessity to improve the $1+$ beam characteristics with a rf beam cooler prior to the injection into an ECR-CB.

Shape coexistence studied in Hg via the β decay of Tl

The /EC decay of Tl to excited states in the daughter nuclei Hg has been investigated at the CERN on-line isotope mass separator facility. In both Tl nuclei two β-decaying states were observed. In the case of 184Tl, narrow-band laser spectroscopy could be used to disentangle the decay of both isomers. In 182Hg a precise energy of 335 (1) keV for the state was measured together with its feeding from a tentatively proposed state at 973 keV. Large conversion coefficients for the transition in Hg were measured to be 7.2 (13) and 14.2 (36), respectively, evidencing a strong E0 component.

Development of an EBIS charge breeder for the Rare Isotope Science Project

In Korea, a heavy ion accelerator facility called RAON is being designed to produce various rare isotopes for the Rare Isotope Science Project (RISP) (Jeong, 2016) [1], (Moon, 2014) [2]. This facility is designed to use both In-flight Fragment (IF) and Isotope Separation On-Line (ISOL) techniques in order to produce a wide variety of RI beams for nuclear physics experiments. An Electron Beam Ion Source (EBIS) will be used for charge breeding of Rare Isotope (RI) beams in the ISOL system. The charge-to-mass ratio (q/A) of the RI beams after charge breeding is ≥1/4. The highly charged RI beams will be accelerated by a linac post-accelerator and delivered to a low energy (∼18MeV/u) experimental hall or the IF system. The RAON EBIS will use a 3A electron gun and a 6T superconducting solenoid for high capacity, high efficiency, and short breeding time. In front of the charge breeder, an RFQ cooler-buncher will be used to deliver a bunched beam with small emittance to the EBIS charge breeder. The main design of the RAON EBIS has been carried out on the basis of several beam analyses and technical reviews. In this paper, current progress of the development of the RAON EBIS charge breeder will be presented.

Penning-trap-assisted study of excitations in Br88 populated in β decay of Se88

Excited levels of $^{88}\mathrm{Br}$ populated in the $\ensuremath{\beta}$ decay of $^{88}\mathrm{Se}$ have been studied by means of $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectroscopy methods. Neutron-rich parent $^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of $^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyv\askyl\a. The level scheme of $^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin of $^{88}\mathrm{Br}$ is now firmly determined to be ${1}^{\ensuremath{-}}$. Low-energy levels in $^{88}\mathrm{Br}$ were interpreted as members of the $\ensuremath{\pi}{p}_{3/2}{(\ensuremath{\nu}{d}_{5/2})}^{3}, \ensuremath{\pi}{p}_{3/2}^{\ensuremath{-}1}{(\ensuremath{\nu}{d}_{5/2})}^{3}, \ensuremath{\pi}{f}_{5/2}^{\ensuremath{-}1}{(\ensuremath{\nu}{d}_{5/2})}^{3}$, and $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{g}_{7/2}$ multiplets. The shell-model calculations performed in this work reproduce well the experimental results.

Identification of the crossing point at N=21 between normal and intruder configurations

The β− decay of Mg34 was used to study the Al34 nucleus through γ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two β-decaying states in Al34 having spin-parity assignments Jπ=4− dominated by the normal configuration π(d5/2)−1⊗ν(f7/2) and Jπ=1+ by the intruder configuration π(d5/2)−1⊗ν(d3/2)−1(f7/2)2. Their unknown ordering and relative energy have been the subject of debate for the placement of Al34 inside or outside the N=20 “island of inversion.” We report here that the 1+ intruder lies only 46.6 keV above the 4− ground state. In addition, a new half-life of T1/2=44.9(4)ms, that is twice as long as the previously measured 20(10) ms, has been determined for Mg34. Large-scale shell-model calculations with the recently developed sdpf-u-mix interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the N=20 island of inversion.

The current status of the MASHA setup

The MASHA setup designed as the mass-separator with the resolving power of about 1700, which allows mass identification of superheavy nuclides is described. The setup uses solid ISOL (Isotope Separation On-Line) method. In the present article the upgrade of some parts of MASHA are described: target box (rotating target + hot catcher), ion source based on electron cyclotron resonance, data acquisition, beam diagnostics and control systems. The upgrade is undertaken in order to increase the total separation efficiency, reduce the separation time, of the installation and working stability and make possible continuous measurements at high beam currents. Ion source efficiency was measured in autonomous regime with using calibrated gas leaks of Kr and Xe injected directly to ion source. Some results of the first experiments for production of radon isotopes using the multi-nucleon transfer reaction 48Ca+242Pu are described in the present article. The using of TIMEPIX detector with MASHA setup for neutron-rich Rn isotopes identification is also described.

Simulations of the stopping efficiencies of fission ion guides

With the Ion Guide Isotope Separator On-Line (IGISOL) facility, located at the University of Jyvaskyla, products of nuclear reactions are separated by mass. The high resolving power of the JYFLTRAP Penning trap, with full separation of individual nuclides, capacitates the study of nuclides far from the line of stability. For the production of neutron-rich medium-heavy nuclides, fissioning of actinides is a feasible reaction. This can be achieved with protons from an in-house accelerator or, alternatively, with neutrons through the addition of a newly developed Be(p,xn)-converter. The hereby-obtained fission products are used in nuclear data measurements, for example fission yields, nuclear masses, Q-values and decay spectroscopy. Prior to separation, the ionized reaction products are stopped in a helium-filled gas cell, referred to as the ion-guide. In this work we present simulations of the stopping of fission products in an ion guide developed for neutron-induced fission. The production and extraction rates are evaluated and compared against experimental values.

Decay of theN=126, Fr213nucleus

gamma rays following the EC/beta(+) and alpha decay of the N = 126, Fr-213 nucleus have been observed at the CERN isotope separator on-line (ISOLDE) facility with the help of gamma-ray and conversion-electron spectroscopy. These gamma rays establish several hitherto unknown excited states in Rn-213. Also, five new a-decay branches from the Fr-213 ground state have been discovered. Shell model calculations have been performed to understand the newly observed states in Rn-213.

β-delayed fission andαdecay ofAt196

A nuclear-decay spectroscopy study of the neutron-deficient isotope $^{196}\mathrm{At}$ is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure $\ensuremath{\alpha}$ decay of $^{196}\mathrm{At}$ allowed the low-energy excited states in the daughter nucleus $^{192}\mathrm{Bi}$ to be investigated. A $\ensuremath{\beta}$-delayed fission study of $^{196}\mathrm{At}$ was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope $^{196}\mathrm{Po}$ (populated by $\ensuremath{\beta}$ decay of $^{196}\mathrm{At}$) was deduced based on the measured fission-fragment energies. A $\ensuremath{\beta}\text{DF}$ probability ${P}_{\ensuremath{\beta}\mathrm{DF}}(^{196}\mathrm{At})=9(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ was determined.

Design of an EBIS charge breeder system for rare-isotope beams

Rare-isotope beams will be produced by using the isotope separation on-line (ISOL) system at the Rare Isotope Science Project (RISP). A proton cyclotron is the driver accelerator for ISOL targets, and uranium carbide (UCx) will be a major target material. An isotope beam of interest extracted from the target will be ionized and selected by using a mass separator. The beam emittance will then be reduced by using a radio-frequency quadrupole (RFQ) cooler before the beam is injected into the electron-beam ion-source (EBIS) charge breeder (CB). The maximum electron beam current of the EBIS is 3 A from a cathode made of IrCe in an applied magnetic field of 0.2 T. The size of the electron beam is compressed by magnetic fields of up to 6 T caused in the charge-breeding region by a superconducting solenoid. The design of EBIS-CB was performed by using mechanics as well as beam optics. A test stand for the electron gun and its collector, which can take an electron-beam power of 20 kW, are under construction. The gun assembly was first tested by using a high-voltage pulse so as to measure its perveance. The design of the EBIS, along with its test stand, is described.

Start-to-end simulation with rare isotope beam for post accelerator of the RAON accelerator

The RAON accelerator of the Rare Isotope Science Project (RISP) has been developed to create and accelerate various kinds of stable heavy ion beams and rare isotope beams for a wide range of the science applications. In the RAON accelerator, the rare isotope beams generated by the Isotope Separation On-Line (ISOL) system will be transported through the post accelerator, namely, from the post Low Energy Beam Transport (LEBT) system and the post Radio Frequency Quadrupole (RFQ) to the superconducting linac (SCL3). The accelerated beams will be put to use in the low energy experimental hall or accelerated again by the superconducting linac (SCL2) in order to be used in the high energy experimental hall. In this paper, we will describe the results of the start-to-end simulations with the rare isotope beams generated by the ISOL system in the post accelerator of the RAON accelerator. In addition, the error analysis and correction at the superconducting linac SCL3 will be presented.

The SPES High Power ISOL production target

SPES (Selective Production of Exotic Species) is a facility under construction at INFN-LNL (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Legnaro), aimed to produce intense neutron-rich radioactive ion beams (RIBs). These will be obtained using the ISOL (Isotope Separation On-Line) method, bombarding a uranium carbide target with a proton beam of 40MeV energy and currents up to 200 μA. The target configuration was designed to obtain a high number of fissions, up to 1013 per second, low power deposition and fast release of the produced isotopes. The exotic isotopes generated in the target are ionized, mass separated and re-accelerated by the ALPI superconducting LINAC at energies of 10AMeV and higher, for masses in the region of A = 130amu, with an expected rate on the secondary target up to 109 particles per second. In this work, recent results on the R&D activities regarding the SPES RIB production target-ion source system are reported.