Rare Isotope Production Research Articles

LISE[formula omitted], the latest generation of the LISE[formula omitted] package, to simulate rare isotope production with fragment-separators

The LISE++ software for fragment separator simulations has undergone a major update. The package, widely used at rare isotope beam facilities, can be used to predict intensities and purities of rare isotope beams and for planning and running of experiments using in-flight separators. It is especially useful for radioactive beam production as its results can be quickly compared to on-line data. The LISE++ package has been ported to the Qt-framework in order to support modern compilers and computing methods. The benefits include 64-bit operation and LISE++ availability on three different platforms: Windows, MacOS and Linux. In addition, the porting provides the ability to take advantage of future computational improvements. The updated package is named LISEcute++ to indicate a major step forward from the previous Borland-based versions. In addition to porting to the new platform, new main features and modifications have been added, mostly devoted to improving models and implementing other codes involved in rare isotope production at FRIB. A summary of modifications completed to improve the functionality of the code are discussed in this work, as well as future plans.

Recent Progress in the Study of the Reaction 70Zn (15 MeV/nucleon) + 64Ni with the MAGNEX Spectrometer

The present paper is focused on our recent efforts to study the production and identification of neutron-rich medium-mass rare isotopes from peripheral reactions at beam energies around and below the Fermi energy. We obtained high-quality experimental data from a recent experiment with the MAGNEX spectrometer at the INFN-LNS in Catania, Italy. The main aim of this experiment was to check the feasibility of ejectile identification in this energy regime with the use of a large acceptance magnetic spectrometer. Our developed technique for particle identification depends mainly on a reconstruction of both the atomic number Z and the ionic charge q of the ions, followed by the identification of the mass. Our method was successfully applied to identify neutron-rich ejectiles from multinucleon transfer from the reaction of 70Zn (15 MeV/nucleon) + 64Ni. Preliminary results indicate that the extracted experimental distributions, along with comparisons with the theoretical models could help us to shed light to the complex reaction mechanism of multinucleon transfer in this energy regime.

Study of Multinucleon Transfer Mechanisms in 86Kr-Induced Peripheral Reactions at 15 and 25 MeV/nucleon

This paper presents our recent studies of the multinucleon transfer in peripheral collisions in reactions near the Fermi regime. Specifically, the reactions of a 86Kr beam at 15 MeV/nucleon with targets of 124Sn ,112Sn, 64Ni and 58Ni and reactions of a 86Kr beam at 25 MeV/nucleon with targets of 124Sn and 112Sn. The experimental data were obtained from the previous work of our group with the MARS spectrometer at the Cyclotron Institute of Texas A&M University. Our current focus is the thorough study of the experimental mass and momentum distributions of the projectile-like fragments. The momentum distributions are characterised by a narrow quasi-elastic peak and a broader deep-inelastic peak. We employed two-body kinematics to characterize the excitation energies of these reactions. We also compared the data with model calculations. The dynamical stage is described with either the Deep-Inelastic Transfer Model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot projectile-like fragments is performed with the Gemini model. Studying these reactions will provide us with a better understanding as to how the energy of the beam and the different targets affect the mechanism of the multinucleon transfer reactions. With the recent work, our continued efforts in the study of peripheral reactions in the Fermi energy regime delineate new opportunities to elucidate the reaction mechanism(s) of rare isotope production and may effectively contribute to the study of unexplored regions of the nuclear chart toward the r-process and the neutron drip line.

Heavy ion beam physics at Facility for Rare Isotope Beams

The Facility for Rare Isotope Beams (FRIB) will be the world's premier rare-isotope beam facility. Experiments with the majority (∼80%) of the isotope predicted to exist will become available. The FRIB facility is based on a superconducting (SC) heavy ion linac with output energy above 200 MeV/u for any ions at beam power of 400 kW. FRIB includes a target facility for in-flight production of rare isotopes. A three-stage fragment separator will be used to prepare fast rare isotope beams with high-purity for nuclear physics experiments. The installation work of the accelerator and experimental systems is approaching completion and multi-stage beam commissioning activities started in summer 2017 with expected project completion in early 2022. The commencement of operation for users' experiments is planned immediately following the project completion.

Rare Isotope Production in peripheral heavy-ion collisions at beam energy of 15 MeV/nucleon

This paper presents our recent study on the production of neutron-rich rare isotopes with heavy-ion beams in the energy region of 15 MeV/nucleon. We present calculated production cross sections of neutron-rich nuclides from collisions of a 86Kr (15 MeV/nucleon) beam with 238U targets. Our calculations are based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot heavy projectile fragments is performed with the Statistical Multifragmentation Model (SMM). We also performed calculations with a radioactive beam of 92Kr (15 MeV/nucleon) with a target of 238U and observed that the multinucleon transfer mechanism leads to very neutron-rich nuclides toward and beyond the astrophysical r-process path. In the future, we plan to experimentally investigate such reactions in the KOBRA spectrometer at the RISP facility in Korea. We conclude that the reaction mechanism at beam energies below the Fermi energy involving periph- eral nucleon exchange, constitutes a novel and effective route to access extremely neutron-rich isotopes toward the r-process path and the neutron drip-line.

Rare Isotope Production in peripheral heavy-ion collisions in the energy range 15-25 MeV/nucleon

In this contribution we summarize recent efforts to describe the production of rare isotopes with beams of 15–25 MeV/nucleon expected from low-energy facilities. We first present calculated production cross sections of proton-rich nuclides from collisions of stable beams of mass A∼60–80. Our calculations are performed with the phenomenological deep-inelastic transfer (DIT) model and the microscopic con- strained molecular dynamics model (CoMD). De-excitation of the excited quasipro- jectiles from the dynamical stage of the reaction is performed with the statistical multifragmentation model (SMM). In addition to the efforts on proton-rich nuclides, we investigated the possibility of producing neutron-rich rare isotopes in the mass range A∼180–200, i.e. near the third r-process peak of A=195. We performed calcu- lations for a 208Pb (15MeV/nucleon) beam and find that the multinucleon transfer mechanism leads to very neutron-rich nuclides in this mass range. We believe that our continued progress on the study of multinucleon transfer reactions using heavy- ion beams of 15–25 MeV/nucleon, can provide new opportunities in rare isotope research in the near future, as planned at the KOBRA facility of RISP in Korea.

Neutron-rich rare isotope production with stable and radioactive beams in the mass range A~40-60 at 15 MeV/u

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Heating factors of gas targets for radioactive ion beam production

At low-energy nuclear physics facilities, the in-flight fragmentation method is often employed to produce radioactive ion beams. This technique often involves a stable ion beam at high intensity and a gas cell target. Since the parameters for the production reaction are usually chosen to take advantage of a large cross section of the resonance reaction, a slight change in the center-of-mass energy due to the reduced target density may significantly affect the rare isotope production rate. Therefore, to estimate the heating effect due to beam particles on the target thickness, a new and more comprehensive semi-empirical model is developed by employing a heating factor function. The estimated heating factors were consistent with experimental data, which were obtained from various reaction measurements at wide ranges of heat densities.

Prototype HTS Quadrupole Magnet for the In-Flight Fragment Separator of RISP

The Rare Isotope Science Project (RISP) for constructing a heavy ion accelerator complex was launched in 2011 in Korea. As one of the rare isotope production systems, an in-flight fragment (IF) separator system will be installed for the RISP. We plan to use high-temperature superconducting (HTS) quadrupole magnets in the forepart of the IF separator to cool efficiently the magnets from large radiation heat load at around 40 K. The HTS quadrupole magnet should withstand a high radiation dose (~10 MGy/year). A prototype HTS quadrupole magnet was designed and fabricated taking into account the radiation damage and heating. The magnet employs two kinds of HTS wires, and the HTS wire is cowound with a stainless steel tape for electrical insulation. The magnet is cooled by circulation of cold helium gas through the cooling channels. Various tests were performed under normal and abnormal operating conditions. The test results show that the HTS quadrupole magnet can operate in the required field gradient stably. The magnet can also be self-protected by metal insulation under the abnormal operating conditions.

Neutron-rich rare isotope production with stable and radioactive beams in the mass range A ∼ 40–60 at beam energy around 15 MeV/nucleon

We studied the production of neutron-rich nuclides in multinucleon transfer collisions of stable and radioactive beams (RIB) in the mass range A ∼ 40–60. We first presented our experimental cross section data of projectile fragments from the reaction of 40Ar(15 MeV/nucleon) with 64Ni, 58Ni and 27Al. We then compared them with calculations based on either the deep-inelastic transfer model or the constrained molecular dynamics model, followed by the statistical multifragmentation model. An overall good agreement of the calculations with the experimental data is obtained. We continued with calculations of the reaction of 40Ar (15 MeV/nucleon) with 238U target and then with reactions of 48Ca (15 MeV/nucleon) with 64Ni and 238U targets. In these reactions, very neutron-rich rare isotopes are produced with large cross sections. These nuclides, in turn, can be assumed to form RIB and interact with a subsequent target (preferably 238U), leading to the production of extremely neutron-rich and even new isotopes (e.g. 60Ca) in this mass range. We conclude that multinucleon transfer reactions with stable or RIB at energy around 15 MeV/nucleon offer an effective route to access extremely neutron-rich rare isotopes for nuclear structure or reaction studies.

Estimation of dose delivered to accelerator devices from stripping of 18.5 MeV/n 238U ions using the FLUKA code

In Korea, a heavy ion accelerator facility (RAON) has been designed for production of rare isotopes. The 90° bending section of this accelerator includes a 1.3-μm-carbon stripper followed by two dipole magnets and other devices. An incident beam is 18.5 MeV/n 238U33+,34+ ions passing through the carbon stripper at the beginning of the section. The two dipoles are tuned to transport 238U ions with specific charge states of 77+, 78+, 79+, 80+ and 81+. Then other ions will be deflected at the bends and cause beam losses. These beam losses are a concern to the devices of transport/beam line. The absorbed dose in devices and prompt dose in the tunnel were calculated using the FLUKA code in order to estimate radiation damage of such devices located at the 90° bending section and for the radiation protection. A novel method to transport multi-charged 238U ions beam was applied in the FLUKA code by using charge distribution of 238U ions after the stripper obtained from LISE++ code. The calculated results showed that the absorbed dose in the devices is influenced by the geometrical arrangement. The maximum dose was observed at the coils of first, second, fourth and fifth quadruples placed after first dipole magnet. The integrated doses for 30 years of operation with 9.5 pμA 238U ions were about 2 MGy for those quadrupoles. In conclusion, the protection of devices particularly, quadruples would be necessary to reduce the damage to devices. Moreover, results showed that the prompt radiation penetrated within the first 60 - 120 cm of concrete.

Neutron-rich rare-isotope production from projectile fission of heavy nuclei near 20 MeV/nucleon beam energy

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The deexcitation/fission of the hot heavy projectile fragments is performed with the Statistical Mul- tifragmentation Model (SMM). We compared our model calculations with our previous experimental projectile-fission data of 238U (20 MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall reasonable agreement. Our study suggests that projectile fission following periph- eral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path.

Construction and simulation of a multi-reflection time-of-flight mass spectrometer at the University of Notre Dame

One of the most significant problems in the production of rare isotopes is the simultaneous production of contaminants, often time isobaric. Thus, a high-resolution beam purification method is required which needs to be compatible with both the low yield and short half-life of the desired radionuclide. A multi-reflection time-of-flight mass spectrometer meets all these criteria, in addition to boasting a smaller footprint relative to traditional separator dipole magnets. Such a device is currently under construction at the University of Notre Dame and is intended to be coupled to the IG-ISOL source of the planned cyclotron facility. The motivation and conceptual design are presented, as well as the status of simulations to determine the feasibility of using a Bradbury–Nielsen gate for bunching ion beams during initial system testing.

Thermal, mechanical and fluid flow aspects of the high power beam dump for FRIB

The Facility for Rare Isotope Beams (FRIB) under construction at Michigan State University is based on a 400kW heavy ion accelerator and uses in-flight production and separation to generate rare isotope beams. The first section of the fragment separator houses the rare isotope production target, and the primary beam dump to stop the unreacted primary beam. The experimental program will use 400kW ion beams from 16O to 238U. After interaction with the production target, over 300kW in remaining beam power must be absorbed by the beam dump. A rotating water-cooled thin-shell metal drum was chosen as the basic concept for the beam dump. Extensive thermal, mechanical and fluid flow analyses were performed to evaluate the effects of the high power density in the beam dump shell and in the water. Many properties were optimized simultaneously, such as shell temperature, mechanical strength, fatigue strength, and radiation resistance. Results of the analyses of the beam dump performance with different design options will be discussed. For example, it was found that a design modification to the initial water flow pattern resulted in a substantial increase in the wall heat transfer coefficient. A detailed evaluation of materials for the shell is in progress. The widely used titanium alloy, Ti–6Al–4V (wt%), is presently considered as the best candidate, and is the subject of specific tests, such as studies of performance under heavy ion irradiation.

Recent progress of in-flight separators and rare isotope beam production

New-generation in-flight separators are being developed worldwide, including the Super-FRS separator at the GSI Facility for Antiproton and Ion Research (FAIR), the ARIS separator at the Michigan State University (MSU) Facility for Rare Isotopes Beams (FRIB), and the BigRIPS separator at the RIKEN RI Beam Factory (RIBF), each of which is aimed at expanding the frontiers of rare isotope (RI) production and advancing experimental studies on exotic nuclei far from stability. Here, the recent progress of in-flight separators is reviewed, focusing on the advanced features of these three representative separators. The RI beam production that we have conducted using the BigRIPS separator at RIKEN RIBF is also outlined.

Design status of KOBRA for rare isotope production and direct measurements of radiative capture cross sections

KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility being designed at Rare Isotope Science Project in Korea will be utilized to produce rare isotope beams by employing multi-nucleon transfer reactions at about 20MeV/nucleon for studies of nuclear structure. KOBRA will also provide high suppression of beam induced background for direct measurements of radiative-capture cross sections in the astrophysical energy range. The present design status of the KOBRA facility is reported along with a brief introduction to the facility. We have studied the feasibility of production of 44Ti based on the present design of KOBRA as an example, and calculated the intensity of 44Ti secondary beam, to be about 105 particles per second, for 1 pnA 46Ti primary beam with a carbon target for a beam energy of 25MeV/nucleon. A Monte Carlo simulation with a ray-tracing code has been performed to show that recoil products 66Se are well separated from a 65As beam by KOBRA for the 65As(p,γ)66Se reaction at a beam energy of 1MeV/nucleon.

A 50-kW prototype of the high-power production target for the FRIB

For the rare isotope production the Facility for Rare Isotope Beams (FRIB) will use the thin target that comprises a rotating carbon disk with multiple slices and heat dissipation via radiative cooling. A prototype of such a target was designed, built and successfully tested with an intense electron beam simulating the thermal and mechanical conditions for target operation at FRIB. The experimental data and the results of extensive numeric simulations validate the thermal and mechanical aspects of the multi-slice target design and confirm the chosen concept.

Systematic study of neutron-rich rare isotope production in peripheral heavy-ion collisions below the Fermi energy

Detailed calculations of the yields of projectilelike fragments (with focus on the neutron-rich isotopes) are presented for the interaction of $^{86}\mathrm{Kr}$ (15 MeV/nucleon) with $^{64}\mathrm{Ni}$, $^{58}\mathrm{Ni}$, and $^{124}\mathrm{Sn}$, $^{112}\mathrm{Sn}$, as well as $^{86}\mathrm{Kr}$ (25 MeV/nucleon) with $^{124}\mathrm{Sn}$ and compared with our recently published experimental data for these reactions. The calculations are based on a two-step approach: the dynamical stage of the collision was described with the microscopic constrained molecular dynamics (CoMD) model, as well as the phenomenological deep-inelastic transfer (DIT) model and its modified (DITm) version. The deexcitation of the hot projectile fragments was performed with the statistical multifragmentation model (SMM) and the binary-decay model gemini, which provided nearly similar results for the neutron-rich products from the reactions studied. An overall good agreement of the calculations with the experimental results, especially for near-projectile isotopes was observed using both the CoMD model and the DITm model for the dynamical stage. The successful description of the production of neutron-rich isotopes with the CoMD model is of particular importance, due to the predictive power of the microscopic approach that essentially does not depend on the reaction dynamics. Our studies to date suggest that peripheral heavy-ion collisions at this energy range (i.e., well above the Coulomb barrier, but below the Fermi energy), if induced by neutron-rich rare-isotope beams of adequate intensity may offer a unique route to access extremely neutron-rich rare isotopes toward the astrophysical $r$-process path and the presently uncharted neutron drip line.

ISOL facility for rare isotope beams at RAON

The Rare Isotope Science Project (RISP) in Korea is developing the Rare Isotope (RI) Accelerator, RAON. The RAON is planned to be an advanced RI beam using isotope separation on-line (ISOL) with a high-power target. The main goal of the ISOL facility is to deliver high-quality, intense, neutron-rich (n-rich) beams to the experimental hall; for example 108 atoms per second of the 132Sn n-rich reference isotope. The RAON ISOL facility consists of mainly two systems. One is the RI production system of a high-power uranium fission target combined with the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source, Surface Ionization (SI) ion source and Resonance Ionization Laser Ion Source (RILIS), in which system the final goal for the RI production rate is 1014 fission per second. The other is the RI beam purification system, which is comprised of an RF beam cooler, a high resolution mass separator (HRMS), a charge breeder and a charge state separator, and the design goal is to deliver the RI beam with a mass resolving power up to 45,000 and with a limit of 6 × 105 background counts per second. The current status of the ISOL facility of the RISP is reported.

Possible evolutions of rare isotope production methods and the associated instrumentation

In recent decades, an impressive progress was made in high intensity light and heavy ion accelerators, reaching now several hundreds kilowatts to megawatt average beam power. Simultaneously, large solid angle spectrometers were developed, preserving good resolution properties by the introduction of sophisticated high order corrections. For further progress in the study of the properties of nuclei far from stability, it will be important to optimize the global layout of the accelerator-experimental devices. It will be more and more important to take radiation safety concerns into account since the very conception of the devices. The global efficiency to obtain a result concerning the properties of a given nucleus depends not only on the detection efficiencies but also on the resolution of the measurement device. Another new frontier may open now, this is the optimization of the use of primary and secondary beams to avoid dumping of possibly useful beams, and utilize them for multiple purposes. Different aspects of this optimization will be discussed.