Off-line studies of the laser ionization of yttrium at the IGISOL facility

A laser ion source is under development at the IGISOL facility, Jyväskylä, in order to address deficiencies in the ion guide technique. The key elements of interest are those of a refractory nature, whose isotopes and isomers are widely studied using both laser spectroscopic and high precision mass measurement techniques. Yttrium has been the first element of choice for the new laser ion source. In this work, we present a new coupled dye-Ti:Sapphire laser scheme and give a detailed discussion of the results obtained from laser ionization of yttrium atoms produced in an ion guide via resistive heating of a filament. The importance of not only gas purity, but indeed the baseline vacuum pressure in the environment outside the ion guide is discussed in light of the fast gas phase chemistry seen in the yttrium system. A single laser shot model is introduced and is compared to the experimental data in order to extract the level of impurities within the gas cell.     

Release of Al from SiC targets used for radioactive ion beam production

On-line targets of silicon carbide have been used to produce radioactive ion beams (RIB) at TRIUMF’s ISAC facility. Surface ionized beams of Li, Na and Al from SiC targets have been delivered to a variety of experiments. While yields of Li and Na radionuclide beams have been high enough to meet experimental requirements, the yields of radio-aluminums have been very low in comparison to in-target production estimates. The properties of SiC relevant to radioactive Al ion beam production are reviewed and on-line measurements of radiogenic Li, Na and Al from SiC are presented. Diffusion, effusion and formation of stable phases are found to strongly affect the release of radio-aluminum from SiC, greatly reducing overall Al RIB production efficiency. In comparison, the production of radio-sodium beams from SiC is found to be relatively efficient.     

Development of a high intensity Al beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of ^26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced ^26gAl beam intensities of 5.1 × 10¹⁰ s⁻¹.     

Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector

An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel-decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now.     

Pulsed extraction of ionization from helium buffer gas

The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a particle-in-cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.     

A tunable collimator for precision irradiation with ion microbeams

We describe a cheap yet effective beam collimation system capable of providing square apertures from 1 mm down to about 10 μm. The tunable part is driven by two manual micrometers, one controlling the shape the other the size, which could be immediately replaced by high precision stepping motors should remote control be needed. The aperture was calibrated by means of a simple home-made laser diffraction system which allows a considerable precision. The collimation system was used to produce low-divergence beams of oxygen and protons, in order to test the position sensitivity of a silicon microstrip telescope detector.     

A high charge state all-permanent magnet ECR ion source for the IMP 320 kV HV platform

A 320 kV high voltage (HV) platform has been constructed at Institute of Modern Physics (IMP) to satisfy the increasing requirements of experimental studies in some heavy ion associated directions. A high charge state all-permanent magnet ECRIS-LAPECR2 has been designed and fabricated to provide intense multiple charge state ion beams (such as 1000 eμA O⁶⁺, 16.7 eμA Ar¹⁴⁺, 24 eμA Xe²⁷⁺, etc.) for the HV platform. LAPECR2 has a dimension of ∅ 650 mm × 560 mm. The powerful 3D magnetic confinement to the ECR plasma and the optimum designed magnetic field for the operation at 14.5 GHz makes it possible to obtain very good performances from this source. After a brief introduction of the ECRIS and accelerator development at IMP, the conceptual design of LAPECR2 source is presented. The first test results of this all-permanent magnet ECRIS are given in this paper.     

A low-cost, accurate and non-intercepting continuous method for beam current measurements in a high-current ion implanter

The development of a low-cost, accurate, non-intercepting continuous method for measuring the beam current in a high-current ion implanter is described. The method, named a differential current monitor, is based on the electric charge conservation principle, applied to the currents that flow in the implanter electrical system, due to the acceleration voltage applied to the ion beam and the leakage currents to ground. This method allows for continuous measurement of the ion beam current without intercepting it. Since its installation, it is possible to accurate measure ion beam currents from tens of μA to mA, which is the normal range for this type of system.     

A beam optics study of the biomedical beam line at a proton therapy facility

A biomedical beam line has been designed for the experimental area of a proton therapy facility to deliver mm to sub-mm size beams in the energy range of 20-50 MeV using the TRANSPORT/TURTLE beam optics codes and a newly-written program. The proton therapy facility is equipped with a 230 MeV fixed-energy cyclotron and an energy selection system based on a degrader and slits, so that beam currents available for therapy decrease at lower energies in the therapeutic beam energy range of 70-230 MeV. The new beam line system is composed of an energy-degrader, two slits, and three quadrupole magnets. The minimum beam sizes achievable at the focal point are estimated for the two energies of 50 and 20 MeV. The focused FWHM beam size is approximately 0.3 mm with an expected beam current of 20 pA when the beam energy is reduced to 50 MeV from 100 MeV, and roughly 0.8 mm with a current of 10 pA for a 20 MeV beam.     

Development of a silver ion source using nanosecond pulses of a Nd:YAG laser at different wavelengths

A silver ion source was designed by focusing the fundamental and harmonics of Q-switched Nd:YAG laser pulses onto a silver target and simultaneously applying an electric potential in an argon environment. The silver ions were detected at a distance of 2 cm from the target surface using a Faraday cup ion probe after letting them pass through a retarding mesh grid (copper electrode). We aim to produce and characterize the silver ions generated by the laser radiation of different wavelengths and pulse energy, ambient gas pressure and the electrode spacing under applied electric field. In addition to this, the effect of laser radiation on plasma under vacuum and at different argon gas pressures was investigated. The velocity distribution function of the plasma emitted from the silver target was investigated under argon discharge. These measurements demonstrated clearly that the velocity distribution function and current signals depend on laser power, laser wavelength and argon pressure. We observed a ten fold increase in the plume current with increase in the applied voltage and ion velocity in the presence of a laser field. The surface morphology of the laser irradiated samples was investigated using reflection optical microscopy.     

On-line control of crystal deflector quality

An on-line control method of crystal deflector quality based on parametric X-ray radiation is proposed. The technique considered will allow information to be received about the state of the deflector crystal structure directly in the local interaction area of the beam and the crystal.     

Study of low work function materials for hot cavity resonance ionization laser ion sources

The selectivity of a hot cavity resonance ionization laser ion source (RILIS) is most often limited by contributions from competing surface ionization of the hot walls of the ionization cavity. In this article we present investigations on the properties of designated high temperature, low work function materials regarding their performance and suitability as cavity material for RILIS. Tungsten test cavities, impregnated with a mixture of barium oxide and strontium oxide (BaOSrO on W), or alternatively gadolinium hexaboride (GdB₆) were studied in comparison to a standard tungsten RILIS cavity as being routinely used for hot cavity laser ionization at ISOLDE. Measurement campaigns took place at the off-line mass separators at ISOLDE/CERN, Geneva and RISIKO/University of Mainz.     

Study of a new cusp field for an 18 GHz ECR ion source

A feasibility study was performed to generate new sufficient mirror cusp magnetic field (CMF) by using the coils of the existing room temperature traditional 18 GHz electron cyclotron resonance ion source (ECRIS) at RIKEN. The CMF configuration was chosen because it contains plasma superbly and no multipole magnet is needed to make the contained plasma quiescent with no magneto-hydrodynamic (MHD) instability and to make the system cost-effective. The least magnetic field, 13 kG is achieved at the interior wall of the plasma chamber including the point cusps (PC) on the central axis and the ring cusp (RC) on the mid-plane. The mirror ratio calculation and electron simulation were done in the computed CMF. It was found to contain the electrons for longer time than in traditional field. It is proposed that a powerful CMF ECRIS can be constructed, which is capable of producing intense highly charged ion (HCI) beam for light and heavy elements.     

Proton beam writing of microstructures at the ion nanoprobe LIPSION

Proton beam writing (PBW) is a direct writing technique which allows the creation of three-dimensional structures with a high aspect ratio in the micrometer and nanometer range in photoresist materials without the use of templates. At the high-energy ion nanoprobe LIPSION of the University of Leipzig this technique was established recently. In this article the latest results concerning this topic are presented. PBW was successfully performed with the positive resist polymethyl methacrylate (PMMA) which is now used at LIPSION in addition to the negative resist SU-8. With the new data acquisition system MICRODAS being commissioned, a new scan program was developed and tested which is dedicated to the creation of arbitrarily shaped structures. Squares with dimensions down to 1.2 μm were created in SU-8 at LIPSION. Furthermore, Ni grids were produced by electroplating, using templates written in PMMA resist. In addition, first structures for studying the growing behavior of Bragg reflectors and the optical characterisation of ZnO nanowhiskers were produced by PBW.     

Fabrication of microfluidic devices using MeV ion beam Programmable Proximity Aperture Lithography (PPAL)

MeV ion beam lithography is a direct writing technique capable of producing microfluidic patterns and lab-on-chip devices with straight walls in thick resist films. In this technique a small beam spot of MeV ions is scanned over the resist surface to generate a latent image of the pattern. The microstructures in resist polymer can be then revealed using a chemical developer that removes exposed resist, while leaving unexposed resist unaffected. In our system the size of the rectangular beam spot is programmably defined by two L-shaped tantalum blades with well-polished edges. This allows rapid exposure of entire rectangular pattern elements up to 500 × 500 μm in one step. By combining different dimensions of the defining aperture with the sample movements relative to the beam spot, entire fluidic patterns with large reservoirs and narrow flow channels can be written over large areas in short time. Fluidic patterns were written in PMMA using 56 MeV ¹⁴N³⁺ and a 3 MeV ⁴He²⁺ beams from K130 cyclotron and a 1.7 MV Pelletron accelerators, respectively, at the University of Jyväskylä Accelerator Laboratory. The patterns were characterized using SEM, and the factors affecting patterns quality are discussed.     

Feasibility of BNCT radiobiological experiments at the HYTHOR facility

HYTHOR (HYbrid Thermal spectrum sHifter tapirO Reactor) is a new thermal-neutron irradiation facility, which was installed and became operative in mid 2005 at the TAPIRO (TAratura PIla Rapida potenza 0) fast reactor, in the Casaccia research centre (near Rome) of ENEA (Ente per le Nuove tecnologie Energia ed Ambiente). The facility has been designed for in vivo radiobiological studies. In HYTHOR irradiation cavity, 1-6 mice can be simultaneously irradiated to study skin melanoma treatments with the BNCT (boron neutron capture therapy). The therapeutic effects of HYTHOR radiation field on mouse melanoma has been studied as a preliminary investigation before studying the tumour local control due to boron neutron capture effect after boronated molecule injection. The method to properly irradiate small animals has been precisely defined. Results show that HYTHOR radiation field is by itself effective in reducing the tumour-growth rate. This finding has to be taken into account in studying the effectiveness of new ¹⁰B carriers. A method to properly measure the reduction of the tumour-growth rate is reported and discussed.     

A review of ion beam induced charge microscopy

Since its development in the early 1990’s, ion beam induced charge (IBIC) microscopy has found widespread applications in many microprobe laboratories for the analysis of microelectronic devices, dislocations, semiconductor radiation detectors, semi-insulating materials, high power transistors, charge-coupled arrays, solar cells, light emitting diodes, and in conjunction with Single Event Upset imaging. Several modalities of the techniques have been developed, such as lateral IBIC and time-resolved IBIC. The theoretical model of IBIC generation and collection has developed from a one-dimensional model of charge drift and diffusion to a detailed model of the motion of ion charge carriers in semiconductors and insulators. This paper reviews the current state-of-the-art of IBIC theory and applications.     

Neutronic design of a sub-critical, source driven reactor at the RA-8 facility

We present a LEU-ADS design based on an existing Argentine experimental facility, the RA-8 pool type zero power reactor. The versatility of this reactor allows measurement of different core configurations using different fuel enrichment, burnable poison rods, water perturbations, different control rods types in critical or subcritical configurations with an external source.To assess the feasibility of the LEU-ADS, multiplication factors, kinetic parameters, spectra, and time flux evolution were computed. Two external sources were considered: an isotopic source, and a D-D pulsed neutron source.Parameters for different core configurations were calculated, and the feasibility of using continuous and pulsed neutron sources was verified.     

Correlation between ion beam parameters and physical characteristics of nanostructures fabricated by focused ion beam

We report a study of the physical characteristics of the pillars of C, Pt and W grown by 10-30 keV Ga focused ion beam (FIB) as a function of Ga ion flux, and present a quantitative analysis of the elements using energy-dispersive analysis of X-rays (EDAX). All the FIB grown pillars exhibit a rough morphology with whisker like protrusions on the cylindrical surface and broadening of the base as compared to the nominal size. For a constant fluence, the height of the pillar initially increases and then reduces after going through a maximum as a function of ion flux in all the cases. The compositional analysis shows good metallic quality for Pt structures but reveals significant contamination of Ga in C and Ga and C in W structures at higher ion fluxes. Explanation to all these observations has been sought in the light of secondary ion and electron effects and the different processes involved which lead to the FIB induced deposition.     

Stability and delayed fragmentation of highly charged C60 trapped in a conic-electrode electrostatic ion resonator (ConeTrap)

We employed a conic-electrode electrostatic ion resonator (ConeTrap) to store the recoil ions resulting from collision between 56 keV Ar⁸⁺ ions and C₆₀ in order to study their stability over a long time range (several milliseconds). The originality of our method, based on the trapping of a single ion to preserve the detection in coincidence of all the products of the collision, is presented in detail. Our results show that C₆₀ ions produced in such collisions are stable in the considered observation time. By employing the ConeTrap as a secondary mass spectrometer in order to let the ions oscillate only for a single period, we have been able to observe delayed evaporation of cold ions 20 μs after the collision. We interpret quantitatively the relative yields of daughter ions with a cascade model in which the transition rates are estimated via the commonly used Arrhenius law, taking into account the contribution of the radiative decay.