Isotope Separator On-Line Facility Research Articles

Recent developments in production of radioactive ion beams with the selective laser ion source at the on-line isotope separator ISOLDE

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser stepwise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS compliments the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapor lasers, ion beams of 22 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5%–30%. As part of the ongoing RILIS development, recent off-line resonance ionization spectroscopy studies have determined the optimal three-step ionization schemes for yttrium, scandium, and antimony.

Laser spectroscopy of radioactive Ti, Zr and Hf isotopes and isomers at the JYFL laser-IGISOL facility

The recent progress at the laser-ion guide isotope separator on-line facility, JYFL, is presented. At the facility new techniques for studying short-lived radioisotopes by laser spectroscopy have been developed and applied to the study of isotopes in refractory metal elements. In particular, recent results on the spectroscopy of cooled ion beams of radioactive Ti, Zr and Hf isotopes are discussed.

Beams of isotopes produced at LISOL by laser ionization after thermalization of energetic ions in a gas cell

The laser ion source (LIS) at the Leuven isotope separator on-line facility has been used to produce beams of exotic nuclei obtained in different types of nuclear reactions. The application of a gas cell filled by noble gas for thermalizing, storing and transporting trace radioactive ions and atoms, has been studied in off- and on-line conditions. Two-step laser resonance ionization has been used to produce ions of stable and radioactive isotopes inside the cell of the LIS. Results from proton-induced fission on 238U and light-/heavy-ion-induced fusion reactions are presented. The interactions of ions with impurity molecules, with noble gas atoms, with electrons and with electrical fields have been investigated in order to specify the requirements for the gas cell as a source of radioactive rare isotopes for the next generation radioactive ion beam facilities.

Intense radioactive-ion beams produced with the ISOL method

For fifty years the isotope separation on-line (ISOL) technique has been used for the production of radioactive-ion beams (RIBs). Thick-target ISOL facilities can provide very intense RIBs for a wide range of applications. The important design parameters for an ISOL facility are efficiency, rapidity and selectivity of all steps of the separation process. To achieve the anticipated beam intensities with the next-generation RIB facilities, the production rate in the ISOL target has to be increased by orders of magnitude. This is only possible by adapting the projectile beam for optimum production cross-sections and simultaneously minimizing the target heating due to the electronic stopping power of charged-particle projectiles. ISOL beams of 75 different elements have been produced up to now and further beam development is under way to produce a still greater variety of isotopes and to improve existing beams in intensity and purity.

Radioactive isotopes in solid state physics

mass separation ISOL-principle ial. Then these isotopes can be either diffused or implanted into the material under study. The most versatile procedure is ion implantation: Depending on the implantation energy, the concentration of dopants, their lateral and their depth distribution can be controlled easily. Any unwanted co-doping by other elements is only determined by the purity of the ion beam and ion implantation is a process not limited by thermal equilibrium, therefore doping is possible beyond any solubilities. But, the energies used for implantation (keV to MeV) are much higher than typical binding energies of atoms in a crystal (eV) so that high concentrations of intrinsic defects (vacancies, interstitials, antisites, dislocations, even amorphous layers) are created. A thermal annealing treatment of the implanted crystal is required in order to remove these defects. The most versatile factory is represented by an online isotope separator facility such as ISOLDE at CERN in Geneva [5]. Here, the production, the chemical separation, the mass separation and the implantation of radioactive isotopes are integrated into one device (figure 1). At ISOLDE the radioactive isotopes are produced by spallation, fragmentation or fission reactions in solid or liquid targets hit by an external high energy proton beam. More than 600 different isotopes of 70 elements can be produced. The big success of the on-line mass separation technology at ISOLDE in manyfields, and atomic physics, astrophysics and solid state physics, triggered worldwide interest in installing similar facilities for the production ofradioactive ion beams [6]. N uclear has developed a number of experimental techniques for detecting particles or y-radiation emitted during the decay of radioactive isotopes. The radioactive decay also opens the possibility to detect with high sensitivity the interaction of moments with external electromagnetic fields. Many of these techniques have successfully entered the field of condensed matter often labelled as nuclear solid state physics [1,2]. The first application of radioactive isotopes in solid-state research dates back to 1920, when radioactive Pb atoms were used by G. v. Hevesey to study self in lead [3]. Hevesey also first used radioactive atoms to study biologic systems by tracking the flow of radioactive tracers from plant roots to the leaves. The radio tracer diffusion technique was born. Nowadays it is a common method for investigating atomic processes in solids. An important advantage of employing radioactive nuclei is the ability of detecting signals from very small amounts of impurity atoms. This is particularly important for the characterization of semiconductors or surfaces where already a very low concentration of impurity atoms has a significant influence on the properties of the system. An especially useful tool represents the transmutation process caused by the ~-decayof radioactive atoms since this process effects a change of the chemical properties of the respective atoms in a solid on a well-known time scale determined by the decay constant and therefore all properties (i.e. conductivity, luminescence) connected to the chemical nature of the impurity atoms should also change. The choice ofa radioactive atom for a specific experiment is on the one hand determined by its chemical nature and on the other hand by its properties. The host system under study can be doped with these radioactive atoms either by diffusion, reaction or ion implantation. The probe atoms interact with their lattice surroundings and the information on these interactions is transmitted to the outside world by the emitted decay products and gives access to internal electric and magnetic fields in crystals, to lattice sites of the probe atoms, to processes, and to interactions between the probe atoms and other defects present in the crystal. The ongoing experiments in solid state using radioactive ion deal with a wide variety of problems involving bulk properties, surfaces and interfaces in many different systems like semiconductors, superconductors, surfaces, interfaces, magnetic systems, metals, and ceramics. This article can highlight only a few examples to illustrate the potential of the use of radiaoctive isotopes for various problems in solid state physics. For more extensive reviews of the field see [2,4].

Short-lived fission products as a diagnostics tool for studying atom and ion behavior in a gas-based laser ion source

A striking difference between gamma spectra of neutron-rich Rh isotopes obtained with the laser ion source at the Leuven Isotope Separator On-Line facility has been observed depending on the mode of operation. Although the global production rate of 112Rh g,m nuclei decreases considerably, the ratio between the productions of 112Rh g and 112Rh m increases strongly when no laser ionisation is used. This effect is caused by 112Ru atoms which decay during gas evacuation of the ion source gas cell, thereby producing 112Rh g ions. The comparison in time behaviour of reaction produced ions, β-decay produced ions and laser produced ions makes it possible to study and characterise the different processes in the gas cell. The influence of these processes has to be considered when extracting nuclear information such as the relative feeding of different short-lived isomers and isotopes and fission cross-sections in a particular mass chain.

How to produce intense and pure ISOL beams

The three key requirements for all individual parts of an ISOL (Isotope Separation On-Line) facility are efficiency, rapidity and selectivity.

Yields of products from fast neutron-induced fission of 233U measured by means of an isotope separator on-line (ISOL) system

A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission products. At a target temperature of 2250°C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields have been obtained for 203 nuclear species, among them 59 isomeric states.

The ISOLDE facility

The CERN on-line isotope separator facility ISOLDE is a unique tool for studying problems in nuclear, atomic, surface and solid state physics, nuclear medicine and astrophysics. Protons in very short high intensity pulses from the PS Booster are directed on either one of the targets of the two on-line mass separators. The 60 keV ions from them are fed into a common beam transport system to which most of the experiments are connected. The layout of the facility is presented and a detailed description of the two mass separators and the beam distribution system is given. Also the problems of radiation shielding and of the handling of radioactivity are discussed.

Performance of and possibilities at the Jyväskylä ion guide isotope separator on-line facility

At the Jyvaskyla IGISOL facility, different ion guide designs are used for different types of reactions. The performance of these ion guides is summarized. The limitations for performing nuclear decay studies and collinear laser spectroscopy due to the large beam energy spread and the presence of isobars will be removed after the installation of an ion beam cooler to reduce the energy spread and a longitudinal penning trap for performing isobaric mass separation. These new developments will bring the capabilities of the IGISOL facility to a new level.

High-efficiency-release targets for use at ISOL facilities: computational design

This report describes efforts made at the Oak Ridge National Laboratory to design high-efficiency-release targets that simultaneously incorporate the short diffusion lengths, high permeabilities, controllable temperatures, and heat-removal properties required for the generation of useful radioactive ion beam (RIB) intensities for nuclear physics and astrophysics research using the isotope separation on-line (ISOL) technique. Short diffusion lengths are achieved either by using thin fibrous target materials or by coating thin layers of selected target material onto low-density carbon fibers such as reticulated-vitreous-carbon fiber (RVCF) or carbon-bonded-carbon fiber (CBCF) to form highly permeable composite target matrices. Computational studies that simulate the generation and removal of primary beam deposited heat from target materials have been conducted to optimize the design of target/heat-sink systems for generating RIBs. The results derived from diffusion release-rate simulation studies for selected targets and thermal analyses of temperature distributions within a prototype target/heat-sink system subjected to primary ion beam irradiation are presented in this report.

β-decay study of54,55Niproduced by an element-selective laser ion source

$\ensuremath{\beta}$-decay studies of the neutron-deficient ${}^{54,55}\mathrm{Ni}$ isotopes have been performed at the Leuven isotope separator on-line facility (LISOL) at Louvain-la-Neuve. The nuclei of interest are produced using an element-selective laser ion source coupled to the on-line mass separator. The half-life of ${}^{55}\mathrm{Ni} {(T}_{1/2}= 204\ifmmode\pm\else\textpm\fi{}3$ ms) was remeasured precisely and the ${\ensuremath{\beta}}^{+}$ decay of ${}^{54}\mathrm{Ni}$ was observed for the first time. The ${\ensuremath{\beta}}^{+}$-decay Gamow-Teller strength [B(GT)] associated with the ${(J}^{\ensuremath{\pi}}{=1}^{+})$ level at 937.2 keV in the daughter nucleus ${}^{54}\mathrm{Co}$ was deduced. The ${\ensuremath{\beta}}^{+}$ GT strength of $1.09\ifmmode\pm\else\textpm\fi{}0.25$ obtained from the measured half life of ${}^{54}\mathrm{Ni}{(T}_{1/2}=106\ifmmode\pm\else\textpm\fi{}12$ ms) and branching ratio ${(I}_{\ensuremath{\beta}}=22.4\ifmmode\pm\else\textpm\fi{}4.4%)$ towards this level is in agreement with the GT strength obtained from $(p,n)$ reaction studies on ${}^{54}\mathrm{Fe}[\mathrm{B}(\mathrm{GT}\ensuremath{-})=1.172\ifmmode\pm\else\textpm\fi{}0.078].$

The Holifield Radioactive Ion Beam Facility at the Oak Ridge National Laboratory: Present status and future plans

The Holifield Radioactive Ion Beam Facility is a first-generation national user facility for nuclear physics and nuclear astrophysics research with radioactive ion beams (RIBs). The reconfiguration, construction and equipment-commissioning phases have been completed and the beam development programme is in progress. In this paper, descriptions of the facility and newly implemented experimental equipment for use in the nuclear and astrophysics programmes will be given and an outline of the initial experimental programme will be presented. Special target/ion source related problems, endemic to the production of specific short-lived RIBs will be discussed. In addition, plans, which involve either a 200 MeV or a 1 GeV proton-linac driver for a second-generation isotope separator on-line facility, will be presented.

Radioactive ion beams and techniques for solid state research

In this paper we review the most recent and new applications of solid state characterization techniques using radioactive ion beams. For such type of research, high yields of chemically clean ion beams of radioactive isotopes are needed which are provided by the on-line coupling of high resolution isotope separators to particle accelerators, such as the Isotope Separator On-line (ISOLDE) facility at CERN. These new experiments are performed by an increasing number of solid state groups. They combine nuclear spectroscopic techniques such as Mössbauer, Perturbed Angular Correlations (PAC) and Emission Channeling with the traditional non-radioactive techniques like Deep Level Transient Spectroscopy (DLTS) and Hall Effect measurements. Recently isotopes of elements, not available before, were successfully used in new PAC experiments, and the first Photoluminescence (PL) measurements, where the element transmutation plays the essential role on the PL peak identification, have been performed. The scope of applications of radioactive ion beams for research in solid state physics will be enlarged in the near future, with the installation at ISOLDE of a post-accelerator device providing radioactive beams with energies ranging from a few keV up to a few MeV.

High-resolution study of the beta decay of 41Ti

An improved high-resolution study of the beta decay of 41Ti, produced in the 40Ca( 3He, 2n) reaction at 40 MeV, has been performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility. The beta-delayed radiation was detected by a low-energy charged-particle detector and a large Ge detector for gamma rays. The experimental beta-decay strength and its distribution, extracted from delayed-proton data, are compared with results of shell-model calculations in the sdfp space. The lowest J π = 3 2 +, T = 3 2 state in 41Sc, the isobaric analogue state of the 41Ti ground state, is estimated to contain 10% isospin impurity.

Delayed Neutron Energy Spectra of 87Br, 88Br, 89Br, 90Br, 137I, 138I, 139I, and 136Te

Measurement of the energy spectra of delayed neutrons for the isotope-separated, fission product precursors 87Br, 88Br, 89Br, 90Br, 137I, 138I, 139I, and 136Te are reported for an energy range up to 1213 keV and with lower cutoff energies of 11.1, 11.1, 29.9, 48.9, 14.2, 23.3, 29.9, and 48.9 keV, respectively. These data were obtained at the TRISTAN Isotope Separation On-Line facility using H2 and CH4 gas-filled proportional counters. The data for each of the bromine, iodine, and tellurium isotopes show good qualitative agreement with the published 3He ionization chamber data at energies above ∼200 keV. In addition, they provide definitive spectral information down to their respective cutoff energies.

Methodology for the measurement of β−-decay intensity distributions from the analysis of total absorption γ-ray spectra

A total absorption γ-ray spectrometer (TAGS), based on a 25.4-cm diameter × 30.5-cm long NaI(Tl) well detector, has been developed at the INEL on-line isotope separator facility. A Si detector in the well of the NaI(Tl) detector allows one to collect β-particle-gated coincidence γ spectra in addition to singles γ spectra. From the analysis of these total absorption γ-ray spectra, β−-decay intensity distributions are obtained. The analysis methodology is based on response functions that simulate the response of the NaI(Tl) detector to the γ-rays and electrons (including external bremsstrahlung) from a radioactive source in the detector well. These response functions are computed with a Monte Carlo photon and electron transport code. This methodology has been completely upgraded since it was first developed and now provides very good simulations of both singles and coincidence spectra. As an example of the application of this methodology, the Iβ distribution for the decay of 141Cs is determined from the TAGS spectra.

Picosecond lifetime measurement systems for levels populated by electron capture and for levels decaying by E0 transitions

Two new systems, to measure lifetimes of nuclear levels in the picosecond range that decay by E0 transitions, have been developed at the UNISOR on-line isotope separator facility. These systems make use, for the first time, of fast coincidences involving characteristic X-rays. The first of the two systems involves specifically the X-rays originating from the internal conversion process, while the second involves X-rays resulting from both the internal conversion and electron capture processes.

Collinear fast atomic-beam laser spectroscopy at riken garis/igisol

We have constructed a fast atomic-beam collinear laser spectroscopy system connected to the on-line isotope separator facility GARIS/IGISOL at RIKEN. This system is potentially powerful in studying refractory elements. To test the system, an off-line collinear experiment was made on stable Hf isotopes produced by means of laser ablation technique. For production of radioactive Hf isotopes, the use of the inverse kinematics of a fusion reaction,9Be(166Er,xn)175-xHf, was investigated. The radioactive isotope169Hf was successfully extracted from GARIS/IGISOL and accelerated up to 30 keV.

Total absorption gamma-ray spectrometer for measurement of beta-decay intensity distributions for fission product radionuclides

A total absorption γ-ray spectrometer (TAGS), based on a 25.4 cm diameter × 30.5 cm long NaI(Tl) well detector, has been developed at the INEL on-line isotope separator facility. A Si detector in the well of the NaI(Tl) detector allows one to collect β-particle-gated coincidence spectra as well as singles spectra. With this system, measurements of the total absorption spectra have been made for a number of fission product nuclei. The analysis of the measured spectra is based on response functions for single γ rays that are computed with a Monte Carlo code. Routines have been written to use these response functions to simulate the response to a cascade of several γ rays and by extension to a whole decay scheme. The bremsstrahlung from a ground-state β branch can also be simulated. The quality of the simulation is demonstrated for test spectra of 137Cs, 24Na, 60Co, and 110mAg. As examples of the operation of this system, the measurements and analyses of the β-decay feeding distributions are described for the decay of 141Ba, 139Cs and 140Cs.