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Simulation of rare isotope release from ISOL target
Abstract
Releases of short-lived species from ISOL targets are simulated with computer codes. Analytic solutions to the diffusion equation are compared with those obtained from a finite-difference code for radioactive isotope diffusion release from simple geometry targets. The Monte Carlo technique as a practical means for vapor transport system design is demonstrated by simulating the effusive-flow of neutral particles through complex target–vapor transport systems. Particle release curves involving decay losses in both diffusion and effusive-flow are computed; and a numerical procedure is proposed to measure the diffusion coefficients and the characteristic effusion times of rare isotopes in target–ion source systems.
... At the site of Korea Multi-purpose Accelerator Complex (KOMAC), which was established and is being operated since 2013 as one of branches in the Korea Atomic Energy Research Institute (KAERI), we initiated a research project to develop a radioactive ion (RI) beam facility dedicated for a β -NMR facility based on a 100-MeV proton linear accelerator. Several nuclides, 8 Li, 11 Be, 12 B, 15 O, and 19 O, are known for RI probes for the β -NMR studies [1], and 8 Li is the most widely used β -NMR probe among them. In this endeavour, we developed the prototype of a targetion-source (TIS), which is basically an isotope separation on-line (ISOL) target system for RI beam productions, for the development of a 8 Li beam and demonstrated the production of the 8 Li beam through on-line experiments at KOMAC. ...
... For evaluating the performance of the TIS with an arbitrary design including all the physical processes, a Monte Carlo simulation code was developed. A new physics model, which is called ISOLPhysics, has been implemented [8] based on the Geant4 10.03 release because no simulation tool for such simulations is readily accessible these days, while a few papers have reported the development of simulation tools for ISOL targets [9,10,11]. The ISOLPhysics incorporates generation, radioactive decay, diffusion, and effusion of radioactive isotopes in arbitrary geometry. ...
The beta-detected nuclear magnetic resonance (β -NMR) technique is a novel method that obtains depth-resolved information on samples by observing the asymmetric beta decay of nuclear probes. Although the beta-detected NMR has several advantages over the conventional NMR techniques, the number of user facilities in the world is severely limited. At the site of Korea Multi-purpose Accelerator Complex (KOMAC), we initiated a research project to develop a radioactive ion (RI) beam facility dedicated for the future beta-detected NMR facility at KOMAC based on a 100-MeV proton linear accelerator. In this endeavour, we developed a prototype of a target-ion-source (TIS) composed of low-Z production targets, target container, target heater, high-current feed through, and hot surface ion source. In recent on-line experiments, we have demonstrated that a Li-8 beam of the order of 10⁶ pps could be extracted with the prototype design of the TIS. Here, we present the recent progress of the RI beam development study.
The SPES (Selective Production of Exotic Species) facility, currently under development at Legnaro National Laboratories of INFN, aims at the production of intense RIB (Radioactive Ion Beams) employing the Isotope Separation On-Line (ISOL) technique for interdisciplinary research. The radioactive isotopes of interest are produced by the interaction of a multi-foil uranium carbide target with a 40 MeV 200 μA proton beam generated by a cyclotron proton driver. The Target Ion Source (TIS) is the core of the SPES project, here the radioactive nuclei, mainly neutron-rich isotopes, are stopped, extracted, ionized, separated, accelerated and delivered to specific experimental areas. Due to efficiency reasons, the TIS unit needs to be replaced periodically during operation. In this highly radioactive environment, the employment of autonomous systems allows the manipulation, transport, and storage of the TIS unit without the need for human intervention. A dedicated remote handling infrastructure is therefore under development to fulfill the functional and safety requirement of the project. This contribution describes the layout of the SPES target area, where all the remote handling systems operate to grant the smooth operation of the facility avoiding personnel exposure to a high dose rate or contamination issues.
Research in the field of radiopharmaceuticals is increasingly promoted by the widespread and growing interest in applying nuclear medicine procedures in both disease diagnosis and treatment. The production of radionuclides of medical interest is however a challenging issue. Along with the conventional techniques other innovative approaches are being investigated and, among those, the ISOLPHARM project is being developed at INFN-LNL (Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Legnaro). Such technique foresees the employment of the SPES ISOL facility to produce isobarically pure Radioactive Ion Beams (RIBs), obtained thanks to electromagnetic mass separation and collected on appropriate substrates. The latter are successively recovered and dissolved, allowing thus the chemical separation and harvesting of the nuclides of interest, free from any isotopic contaminant. Although ISOLPHARM can be potentially employed for most of the routinely used medical radioisotopes, its innovation potential is better expressed considering its capability to provide carrier free unconventional nuclides, difficult to produce with state-of-art techniques, such as ¹¹¹Ag, a β— emitter potentially interesting for therapeutic applications. Thus, in the framework of ISOLPHARM, INFN supported a two-years experiment, called ISOLPHARM_Ag, aimed at evaluating the feasibility of the production of a¹¹¹Ag labelled radiopharmaceutical. The ISOL production yields are estimated by computing intensive Monte Carlo codes, that require an appropriate custom Information Technology infrastructure. The presented work is focused on the first part of the production chain including the capability to extract, ionize, and collect stable Ag beams with SPES technologies. MC calculations were used to estimate the expected ¹¹¹Ag in-target yields, whereas experiments with stable Ag were performed to test the ionization, transport and collection of Ag beams.
The upgrade of the Système de Production d’Ions Radioactifs Accélérés en Ligne (SPIRAL1) facility will deliver its new Radioactive Ion Beams (RIB) by summer 2017. The goal of the upgrade is an improvement of the performances of the installation in terms of isotopes species and ion charge states [1]. Ion beams are produced using the Isotope Separator On Line Method, consisting in an association of a primary beam of stable ions, a hot target and an ion source. The primary beam impinges on the material of the target. Radioactive isotopes are produced by nuclear reactions and propagate up to the source, where they are ionized and accelerated to create a RIB. One advantage of SPIRAL1 driver is the variety of its available primary beams, from carbon to uranium with energies up to 95 MeV/A. Within the SPIRAL1 upgrade, they will be combined with targets made of a large choice of materials, extending in this way the number of possible nuclear reactions (fusion-evaporation, transfer, fragmentation) for producing a wider range of isotopes, up to regions of the nuclide chart still scarcely explored. Depending on the reaction process, on the collision energy and on the primary beam power, thin and thick targets are used. As their functions can be different, their design must cope with specific constraints which will be described. After a presentation of the goals of present and future SPIRAL1 Target Ion Source System, the main target features, studies and designs under progress are presented.
Emittance of short-lived nuclide beams produced in hot cavity ion sources is calculated. Influence of half-life period as well as the average sticking time on beam emittance is under investigation. Two different shapes of ionizer cavity are considered: almost fully spherical and hemispherical ones. Changes of beam emittance due to the extraction channel geometry (its diameter and length) are studied. A new concept of scaled efficiency (ion source brightness analogon) is introduced in order to compare the two-ion source configurations. Phase space portraits of the extracted beams are presented.
An extended Monte Carlo method based numerical model of the hot cavity ion source is presented. Not only the radioactive decay and delays due to the sticking of atoms to hot walls are taken into account, but also (i) delays due to the diffusion of nuclides, (ii) contributions from electron impact ionization, (iii) calculations of ion release curves and (iv) the case of hemispherical cavities are implemented. The code enables calculations of ionization efficiency for a broader range of parameters including ionizer material, size, geometry and temperature; extraction voltage; timescales characterizing radioactive decay, particle sticking, out-diffusion; and electron impact ionization cross-sections. The dependences of ion source efficiency on decay half-life, sticking time and diffusion timescale are shown and discussed. Two different schemes of radioactive nuclide generation are introduced and compared. Influence of ionizer length and extraction voltage is extensively studied. The importance of the electron ionization for short-lived isotope ion production is for the first time demonstrated. Two new analytical models of ionization in the case short-lived nuclides are introduced and compared to simulation results. Good agreement of experimental and simulated data (efficiency vs. temperature) is shown. New features enabling simulations of ion release curves are demonstrated.
Nanodendritic Ir@Pt core-shell bifunctional electrocatalysts were synthesized by a one-pot synthesis method for the first time. Besides good dispersion and uniform composition distribution, Ir@Pt bifunctional electrocatalysts have exhibited outstanding catalytic activity for both oxygen reduction and oxygen evolution reactions in comparison with the mixture of commercial Ir and Pt blacks. Keywords: Unitized regenerative fuel cell, Bifunctional electrocatalyst, Nanodendrite, Core-shell, Iridium, Platinum
A Monte-Carlo code has been developed that can be used to optimally
design vapor transport systems for isotope-separator-on-line-based
radioactive ion beam facilities in lieu of costly iterative trial and
error design methods. The code provides a powerful means for delineating
diffusion-release and effusive-flow (molecular-flow) processes, in
combination, the delay times of which are principal intensity limiters
of short-lived radioactive species at such facilities. The code provides
time dependent particle evacuation, average distance traveled per
particle, and particle/wall interaction information during particle
transit through a given vapor-transport system under molecular-flow
conditions, independent of the chemistry between particles of interest
and the materials of which the transport system are constructed. In
addition, the code provides powerful graphical insight via particle
trajectories that serve as strong assets in arriving at a final design
by identifying regions within the transport system where hold-up times
are problematical. In this article, we compare simulation and
experimental measurement results for transport of noble gases through
selected vapor-transport systems using both cosine and isotropic
particle re-emission distributions about the normal to the surface
following adsorption (isotropic re-emission distributions are found to
be in close agreement with experimental measurements) and describe a
concept vapor-transport system that reduces transport times over those
of conventional systems by >two orders of magnitude.
Decay losses, associated with the times required for particles to diffuse from ISOL production targets and to effusively-flow to an ion source, must be reduced to as low as practically achievable levels in order to deliver useful beam intensities of short-lived isotopes for research at ISOL based Radioactive Ion Beam (RIB) facilities. We have developed a fast-valve system and complementary 3-D Monte-Carlo code which can be used separately or in combination to assess the effusive-flow properties of vapor-transport systems, independent of size, geometry and chemical properties of the transport species. In this report, we describe the fast valve and present time spectra and characteristic time data for noble gases flowing through serial- and parallel-coupled vapor-transport systems similar in geometry but longer than those used for RIB generation at the HRIBF with and without target coating matrices.
Monte Carlo simulations of the low- and high-conductivity Target/Ion Source systems used at Oak Ridge National Laboratory for effusion measurements are performed. Comparisons with the corresponding experimental data for the different geometries are presented and discussed. Independent checks of the simulation using data for simple geometries and using the conductance approach well known in vacuum technology are performed. A simulation-based comparison between the low- and high-conductivity systems is also presented.
We summarize the formula for the diffusion of a radioactive product from a solid target or catcher material in the form of foils, fibers and particles for the case of vanishing surface density of the diffusing isotopes, in which the analytical expression for the diffusion yield, i.e., the probability for radioisotope to escape before decaying is newly obtained for diffusion from a solid in the form of a fiber.
In the framework of the SPES project at LNL [A. Bracco, A. Pisent (Ed.), REP 181/02, LNL-INFN, 2002], the realization of a direct ISOL Target for a mid-term radioactive ion beam facility is in progress. Using a primary proton beam of energy 40 MeV and intensity 0.2 mA, a high number of fission products will be obtained in the SPES multi-foil uranium carbide target, keeping a low power density deposition in the refractory matrix [A. Andrighetto, S. Cevolani, C. Petrovich, Eur. Phys J. A 25 (2005) 41]. The exotic species produced by Uranium fission in the target are collected in the ion source after the diffusion and the effusion processes. When short lived isotopes are produced it is very important to optimize the release properties of the target. To this purpose the RIBO code (radioactive ion beam optimiser) [M. Santana Leitner, A Monte Carlo Code to Optimize the Production of Radioactive Ion Beams by the ISOL Technique, PhD. Thesis, UPC-ETSEIB/CERN] has been used in order to estimate the target release efficiency for some neutron-rich nuclei. A SiC prototype of the target was recently produced at LNL and tested at ORNL using a 42 MeV proton beam. The yield of some aluminum isotopes was measured as a function of the target temperature. Some preliminary results of the data analysis will be presented.
The 2.4 μs proton pulses from the PS Booster are delivered to the ISOLDE targets at a low repetition rate (typically 0.4 Hz). However, the synchronously produced radioisotopes have partially lost this time structure due to the delay incurred by the mass transfer processes used in their conversion into an ion beam. Since the pulse shape of the ion bunches is a vital information for the target development and the experiments, new techniques have been developed to measure it. These methods as well as the mathematics used for calculating the production yield will be described in detail. The limits of the techniques are discussed and a set of examples are presented.
In order to generate useful beam intensities of short-lived radioactive isotopes for nuclear and nuclear-astrophysics research at ISOL-based radioactive ion beam facilities, delay times associated with diffusion release from target materials and effusive-flow transport from production targets to ion sources must be reduced to as low as practically achievable levels. A fast vapor-transport system has been conceived that reduces effusive-flow times from target to ion source by>2 orders of magnitude over those of conventional transport systems used at CERN-ISOLDE and the Holifield Radioactive Ion Beam Facility. For target material thicknesses of ∼1 μm, the new system permits the generation of useful RIB intensities of species with lifetimes of a few tens of milliseconds to a few seconds and target/species combinations with diffusion coefficients in the range, 10−8⩾D(cm2/s)⩾10−10.
The Rare Isotope Accelerator (RIA) facility, planned to be built in the USA, will be capable of delivering diverse beams, from protons to uranium ions, with energies from 1 GeV to at least 400 MeV per nucleon to rare isotope-producing targets. High beam power—400 kW—will allow RIA to become the most powerful rare isotope beam facility in the world; however, it also creates challenges for the design of the isotope-production targets. This paper focuses on the isotope-separator-on-line (ISOL) target work, particularly the radiation transport aspects of the two-step fission target design. Simulations were performed with the PHITS, MCNPX, and MARS15 computer codes. A two-step ISOL target considered here consists of a mercury or tungsten primary target in which primary beam interactions release neutrons, which in turn induce fissions—and produce rare isotopes—in the secondary target filled with fissionable material. Three primary beams were considered: 1-GeV protons, 622-MeV/u deuterons, and 777-MeV/u 3He ions. The proton and deuterium beams were found to be about equivalent in terms of induced fission rates and heating rates in the target, while the 3He beam, without optimizing the target geometry, was less favorable, producing about 15% fewer fissions and about 50% higher heating rates than the proton beam at the same beam power.
Recently, a series of dedicated inverse-kinematics experiments performed at GSI, Darmstadt, has brought an important progress in our understanding of proton and heavy-ion induced reactions at relativistic energies. The nuclear reaction code ABRABLA that has been developed and benchmarked against the results of these experiments has been used to calculate nuclide production cross-sections at different energies and with different targets and beams. These calculations are used to estimate nuclide production rates by protons in thick targets, taking into account the energy loss and the attenuation of the proton beam in the target, as well as the low-energy fission induced by the secondary neutrons. The results are compared to the yields of isotopes of various elements obtained from different targets at CERN-ISOLDE with 600 MeV protons, and the overall extraction efficiencies are deduced. The dependence of these extraction efficiencies on the nuclide half-life follows a simple pattern in many different cases. A universal function is proposed to parameterize this behavior in a way that quantifies the essential properties of the extraction efficiency for the element and the target–ion-source system in question.
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