Rare Ion Beams Research Articles

Characteristics of rare isotope beams in the KoRIA facility

The Korea Rare Isotope Accelerator (KoRIA) facility plans to provide neutron-rich rare isotopes (RIs) and stable heavy ion beams for research in the fields of basic and applied sciences. In the facility, both the isotope separator on-line (ISOL) and the in-flight fragmentation (IFF) methods are employed for RI production by 238U fission, which is effective for producing neutron-rich RI beams. These ISOL and IFF systems are designed to obtain world-class RI beam intensity, which allows exotic nuclei near the neutron drip line in the nuclear chart, which have not yet been explored, to be studied. In this paper, the uniqueness of the KoRIA facility under consideration, compared to other facilities, is described, and we present the characteristics of the RI beams that will be available at KoRIA.

BRIF and CARIF progress

China Institute of Atomic Energy (CIAE) is currently constructing Beijing rare ion beam facility (BRIF) and is proposing China advanced rare ion beam facility (CARIF). This paper is aiming at introducing the progress of BRIF project and the conceptual design CARIF. The ISOL type facility BRIF under construction is composed of a 100 MeV 300 μA proton cyclotron, an ISOL with mass resolution of 20000, and a super-conducting LINAC of 2 MeV/q, and will be commissioned in 2013. CARIF facility proposed is planned to use both ISOL and PF techniques. It is based on a China advanced research reactor CARR that was critical, with ISOL separation of fission fragment, post acceleration to 150 MeV/u, and fragmentation of neutron-rich fission fragment beam like 132Sn. Such unique combination will allow CARIF to deliver beam intensity better than the best world facilities by more than one order of magnitude.

Measurements of charge state breeding efficiency at BNL test EBIS

Charge breeding of singly charged ions is required to efficiently accelerate rare isotope ion beams for nuclear and astrophysics experiments, and to enhance the accuracy of low-energy Penning trap-assisted spectroscopy. An efficient charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) to the ANL Tandem Linear Accelerator System (ATLAS) facility is being developed using the BNL Test Electron Beam Ion Source (Test EBIS) as a prototype. Parameters of the CARIBU EBIS charge breeder are similar to those of the BNL Test EBIS except the electron beam current will be adjustable in the range from 1 to 2 A. The electron beam current density in the CARIBU EBIS trap will be significantly higher than in existing operational charge state breeders based on the EBIS concept. The charge state breeding efficiency is expected to be about 25% for the isotope ions extracted from the CARIBU. For the success of our EBIS project, it is essential to demonstrate high breeding efficiency at the BNL Test EBIS tuned to the regime close to the parameters of the CARIBU EBIS at ANL. The breeding efficiency optimization and measurements have been successfully carried out using a Cs + surface ionization ion source for externally pulsed injection into the BNL Test EBIS. A Cs + ion beam with a total number of ions of 5×10 8 and optimized pulse length of 70 μs has been injected into the Test EBIS and charge-bred for 5.3 ms for two different electron beam currents – 1 and 1.5 A. In these experiments we have achieved 70% injection/extraction efficiency and breeding efficiency into the most abundant charge state ∼17%.

Design of the Medium Energy Beam Transport (MEBT) line for the Rare Ion Beam (RIB) project at VECC

The design of a 19m long MEBT line connecting the accelerator LINAC 2 with LINAC 3 of the VECC-RIB project is presented. The design goal is to achieve a robust solution for the transport of heavy ion beams, emerging from LINAC 2 with a fairly large momentum width and transverse emittance with the mean energy of 289keV/u and q/A≥1/14 so that the beam is well matched both in transverse and longitudinal directions at the entry of the LINAC 3. The limitations of the site necessitate a 90° bending of the beam a few metres downstream of LINAC 2 that adds to the further requirement and complication of dispersion suppression. The skewed position of the RFQ (before LINAC 1) vanes with respect to conventional horizontal and vertical planes complicates the design by requiring the decoupling of the X (horizontal) and Y (vertical) motion before the beam is bent in the 90° dipole after LINAC 2. In the design presented, step-by-step all the requirements, viz, decoupling of X–Y motion, dispersion suppression and transverse and longitudinal beam matching could be effectively met. The robustness of the design with respect to orientation of the initial beam ellipses has also been checked.

Expansion of the radioactive ion beam program at Argonne

The Argonne Tandem Linear Accelerator System (ATLAS) at Argonne National Laboratory (ANL) provides a wide range of stable ion beams and radioactive beams which have contributed to our understanding of nuclear structure and reactions. Until now, most radioactive ion beams at ATLAS were produced in flight using light-ion reactions such as (p, n), (d, n), (d, p), (d,3He), and (3He,n). Within the next few months, the radioactive ion beam program at ATLAS will acquire much extended, new capabilities with the commissioning of a new facility: the CAlifornium Rare Isotope Breeder Upgrade (CARIBU). CARIBU will supply ion beams of 252Cf fission fragments, which are thermalized in a gas catcher. The singly- and doubly-charged ions extracted from the gas catcher will be mass-separated and either delivered to a low-energy experimental area, or charge bred with a modified ECR source and subsequently reaccelerated by the ATLAS facility. Properties of hundreds of these neutron-rich nuclides will be investigated using ion traps, decay stations, the newly commissioned HELical Orbit Spectrometer (HELIOS), and other available experimental equipment such as Gammasphere and the FMA. HELIOS was constructed to take advantage of rare ion beams, such as those provided by CARIBU, through light-ion transfer reactions in inverse kinematics, and represents a new approach to the study of direct reactions in inverse kinematics which avoids kinematic broadening. Experiments are currently being conducted with HELIOS, and first results with the d(28Si,p) and d(12B,p) reactions have shown excellent energy resolution.

Design and development of a radio frequency quadrupole linac postaccelerator for the Variable Energy Cyclotron Center rare ion beam project

A four-rod type heavy-ion radio frequency quadrupole (RFQ) linac has been designed, constructed, and tested for the rare ion beam (RIB) facility project at VECC. Designed for cw operation, this RFQ is the first postaccelerator in the RIB beam line. It will accelerate A/q < or = 14 heavy ions coming from the ion source to the energy of around 100 keV/u for subsequent acceleration in a number of Interdigital H-Linac. Operating at a resonance frequency of 37.83 MHz, maximum intervane voltage of around 54 kV will be needed to achieve the final energy over a vane length of 3.12 m for a power loss of 35 kW. In the first beam tests, transmission efficiency of about 90% was measured at the QQ focus after the RFQ for O(5+) beam. In this article the design of the RFQ including the effect of vane modulation on the rf characteristics and results of beam tests will be presented.

Development of Zn and Eu beams by plasma sputtering

Accelerated ion beams of various species are important tools to engineer the materials. The low energy ion beam facility (LEIBF) at Nuclear Science Centre (NSC) provides the ion beams of energy in the range of a few keV to a few MeV. The LEIBF is fully operational since 2001 and its performance has been tested very well with ion beams from noble gases. Metallic and rare earth ion beams have important role in the field of nano-technology and enhancement of optical properties of semiconducting nano-particles inside various matrices. During the last few years, an effort was made to extract ion beams of various metal and rare earth elements using different techniques. Here we describe the successful development of Zn and Eu ion beams using sputtering technique in electron cyclotron resonance (ECR) ion source. Operational experience to produce such kind of beams and results on beam analysis are described in the paper.

Amorphisation of GaN during processing with rare earth ion beams

GaN epilayers grown by metal organic chemical vapor deposition (MOCVD) were implanted with Tm and Eu ions with different energies and fluences and at different temperatures in order to optimize the implantation conditions. The recovery of the implantation damage was studied using both rapid thermal annealing and furnace annealing with nitrogen overpressure of 4×10 5 Pa. Rutherford backscattering spectrometry in the channeling mode (RBS/C) was used to monitor the evolution of damage introduction and recovery in the Ga-sublattice and transmission electron microscopy (TEM) was carried out for further structural analysis. The RBS/C spectra as well as TEM images show two different damage regions, one at the surface arising from an amorphous surface layer and another one deeper in the crystal coinciding with the end of range of the implanted ions. For implantation with 150 keV at room temperature, even for fluences as low as 3×10 14 at/cm 2, a thin amorphous surface layer, which becomes thicker with increasing implantation fluence, was observed by TEM. High temperature annealing of these highly damaged layers often results in loss of the amorphous layer and accumulation of the implanted species at the surface rather than a regrowth of the crystal. It was possible to prevent the formation of an amorphous layer by implanting at 500 ∘C. In those samples a large part of the lattice damage was removed during annealing at 1000 ∘C and the recovery of the lattice is similar for both applied annealing methods.

Isoscaling studies of fission: A sensitive probe into the dynamics of scission

The fragment yield ratios were investigated in the fission of 238,233U targets induced by 14 MeV neutrons. The isoscaling behavior was typically observed for the isotopic chains of fragments ranging from the proton-rich to the most neutron-rich ones. The observed high sensitivity of neutron-rich heavy fragments to the target neutron content suggests fission as a source of neutron-rich heavy nuclei for present and future rare ion beam facilities, allowing studies of nuclear properties towards the neutron drip-line and investigations of the conditions for nucleosynthesis of heavy nuclei. The breakdowns of the isoscaling behavior around N=62 and N=80 manifest the effect of two shell closures on the dynamics of scission. The shell closure around N=64 can be explained by the deformed shell. The investigation of isoscaling in the spontaneous fission of 248,244Cm further supports such conclusion. The Z-dependence of the isoscaling parameter exhibits a structure which can be possibly related to details of scission dynamics. The fission isoscaling studies can be a suitable tool for the investigation of possible new pathways to synthesize still heavier nuclei.

The BIE100 ECR ion source

BIE100, an all-permanent-magnet-based electron cyclotron resonance (ECR) ion source, has been under development at Berkeley Ion Equipment (BIE). With a relatively small but optimized source magnet volume, the maximum peak magnetic field strengths of the BIE100 reach 13 kG on axis and 11 kG at the plasma chamber walls, respectively. Microwaves of frequencies of 12.75 and 14 GHz are to simultaneously heat the plasma electrons. The development goal of this ECR ion source is to further explore the capabilities of ECR ion source in the efficient production of the intermediate and high charge state rare ion beams needed for the generation of rare ion beams and industrial applications. This article will present the design features of the BIE100 ion source and its current status.

Scattering and recoiling imaging spectrometry (SARIS) study of chlorine chemisorption on Ni(1 1 0)

The clean and chlorine chemisorbed Ni(1 1 0) surface has been investigated by scattering and recoiling imaging spectrometry (SARIS). Rare gas ion beams at 4 keV were scattered at different incident ( α) and exit ( β) angles along different azimuthal directions of the surface. The LEED pattern changed from a sharp (1 × 1) to a weak (3 × 1) after exposure to Cl 2. The He + images from the Cl/Ni surface exhibited very little differences compared to those of the clean surface. This is due to the high penetration depth of the He + ions, which results in low surface sensitivity. The images obtained from the Cl/Ni surface with the heavier ions exhibited obvious changes due to their low penetration depths, which facilitates high surface sensitivity. Scattering and Recoiling Imaging Code (SARIC) simulations were carried out in order to interpret the perturbations induced by the chlorine adatoms. Different chemisorption sites for chlorine were tested. The results of the experiments and simulations agree that Cl atoms are chemisorbed in the short-bridge sites above the [1 1 0] rows.

Ion beam amorphization of muscovite mica

The microstructure of a muscovite mica exposed to a rare gas ion beam has been studied by transmission electron microscopy. The investigation of damage without implantation was carried out using argon and helium ions of sufficient energy to traverse the 100–150 nm mica specimens. For 340 keV Ar++ irradiation, amorphization of mica occurred at a fluence as low as 3.5 × 1014 ions · cm−2, which corresponds to 0.29 dpa. Muscovite can be amorphized using 80 keV helium ions, but this requires a much higher fluence and damage production of 4.6 × 10−6 ions · cm−2 and 0.60 dpa, respectively. Since helium irradiation results principally in ionization energy loss, it indicates that amorphization of muscovite results mainly from nuclear interactions. Complete amorphization of muscovite mica is found to take place for all ions at approximately the same amount of nuclear energy transfer to energetic primary knock-on atoms, assuming a recoil energy greater than 500 eV. This suggests that amorphization occurs directly in dense displacement cascades. A significant amount of helium, 100 ppm, can be implanted into muscovite mica without destroying the crystal structure.

Coaxial scattering as a probe of surface structure: (1 × 2)- and (1 × 3)-Pt(110)

The technique of coaxial scattering is described and its capabilities are demonstrated on (1 × 2)- and (1 × 3)-Pt{110} reconstructed surfaces. The apparatus consists of a pulsed rare gas ion beam line with time-of-flight analysis of backscattered neutrals and ions at a scattering angle of ∼ 180° using a microchannel plate detector. Both azimuthal δ and incident α angle scans versus backscattering intensity are presented and analyzed in terms of shadowing and blocking cones and classical trajectory simulations. Coaxial scattering, as compared to non-coaxial scattering ( θ < 180°), has the advantages of extremely high counting rates, requires only a single port for mounting on the vacuum chamber, effectively delineates scattering from subsurface layers, and can probe down to at least six atomic layers.

The efficiency of consuming rare isotopes in a PIG ion source

The efficiency of consuming a working substance in the cyclotron arc ion source during operation at the LNR JINR cyclotrons is analyzed in comparison with the results obtained for the ECR ion source of GANIL and the Berkeley cyclotrons. The experimental results described have been obtained during the acceleration of rare isotopes ion beams (Mg-Ge) at the U-400 and U-300 cyclotrons. Some features of solid working substances fed into the cyclotron ion source are described. The optimal conditions for the efficient use of working substances in the arc discharge are discussed. The results of producing and accelerating rare gas isotopes ion beams, including the radioactive isotope carbon-14, are presented. Prospects for the future development of efficient ion sources for the LNR cyclotron complex consisting of the U-400 and the U-400M are also discussed.