Recent developments in chemical characterization with MeV ion beams

A multitude of ion-atom interactions are induced with projectiles of E0.1 MeV/nucleon. Analytical techniques derived from these include particle induced X-ray emission (PIXE), charged particle activation analysis (CPAA), prompt nuclear reactions (PNR), and Rutherford backscattering spectrometry (RBS). Among their features are broad elemental coverage (PIXE), subnanogram sensitivity (PIXE, CPAA), isotopic specificity (CPAA, PNR), and depth resolution (RBS, PNR). A limiting requirement with each technique is the need for high intensity ion beams. Novel approaches seek now to obtain analytical information with very small numbers of bombarding ions. Sample integrity is then maintained; moreover, they can be delivered in a microbeam (diameter 5 mm). A phenomenon which under these conditions provides useful analytical information is the particle induced desorption of molecular fragments. Thus, microscopic chemical analysis can be achieved with a small number (<10,000) of heavy fast projectiles and identification of the species desorbed from the sample surface via time-of-flight mass spectrometry. Experimental work with 84 MeV kr ions indicates the following: (a) high desorption yields can be obtained (>50%); (b) mass spectrometry on microspots (diameter of a few m) is feasible; (c) < 10⁶ atoms can be detected. Further capabilities of ion beams for minute, detailed, and comprehensive chemical characterization remain to be explored.     

Analytical techniques with a nuclear microprobe

Nuclear microprobes have proved to be versatile tools to perform investigations in materials science with a lateral resolution of typically 1 to 10 m. Many of the commonly utilized ion beam assisted analytical techniques, like PIXE (Particle Induced X-Ray Emission), RBS (Rutherford Back Scattering), NRA (Nuclear Reaction Analysis), and Channeling can be applied with a nuclear microprobe. Additionally, there are methods typical for the nuclear microprobe, e.g. STIM (Scanning Transmission Ion Microscopy). The nuclear microprobe used here has been applied successfully to the analysis of geological and biological specimens and is currently being modified by the introduction of a superconducting solenoid as focusing element to allow higher lateral resolution. Especially the analysis and modification of electronic devices will become possible. An overview of the analytical techniques practiced with the nuclear microprobe is given with emphasis on laterally resolved trace element analysis.     

Analysis of Co and Cr dopants in epitaxial films of β-FeSi2 by ERDA, RBS, EDX and AES

Thin films of β-FeSi₂ doped with Co or Cr were grown on Si substrates by molecular beam epitaxy. The matrix components Fe and Si and the dopant were co-evaporated from three separately controlled sources. The dopant concentration was measured concurrently by ERDA, RBS, EDX and AES. Ion scattering spectrometry using heavy-ion beams of high energy (ERDA with 250 MeV ¹²⁹Xe, RBS with 15 MeV ¹⁴ N) proved to be most powerful in providing a high mass resolution (1 amu) and a low detection limit for Co and Cr (about 0.2 at %). Although the sensitivity of standard RBS (with 1.4 MeV ⁴He), EDX and AES is limited to a level of about 1 at% these methods allow to assess essential trends caused by variation of the deposition parameters.     

Possibilities of using simultaneous ion-induced nuclear and atomic activation for the characterization of hair

The possibility of a simultaneous determination of low and medium Z elements in hair in a single ion beam exposure was studied. Different ion beams, proton, deuteron,³He and¹⁸O, at velocities ranging from 2.7–6.9 MeV/amu were investigated. In this work,¹⁸ ₈O⁴⁺ beam was found to give the best experimental condition in terms of sensitivity and number of elements detected. The detection limits in a single hair ranged from 2.9·10⁻⁵ μg for Fe to 0.72 μg for H using this beam.     

Fluorine profiles in Antarctic meteorites by nuclear reaction analysis (NRA)

Terrestrial fluorine enrichment on Antarctic meteorites can be measured by detection of γ-rays from the nuclear reaction ¹⁹F(p,αγ)¹⁶O, which is induced by a scanning proton beam. The technique (Nuclear Reaction Analysis by Proton Induced Gamma Emission: PIGME-NRA) allows simultaneous measurement of distribution and concentration without any chemical sample treatment and is not destructive. By using two detectors (HPGe and NaI) and taking into account the background contribution of the main interfering elements, the detection limit is below 10 μg/g. The information obtained allows to estimate the maximum exposure duration of meteorites on the Antarctic ice surface. Received: 15 July 1997 / Accepted: 11 December 1997     

Determination of carbon impurities in epitaxial layers from semiconductor silicon by means of charged particles

The energy-dependent range of charged particles in activation analysis according to the reaction¹²C(d,n)¹³N permits the method to be applied to carbon determination in model epitaxial layers of sufficient thickness. We investigated 100 μm epitaxial layers of the n-type and undoped 50 μ layers as to p⁻ Czochralski substrates. Deuterons were slowed down with Cu and Ta foils having a limiting energy of 13.5 MeV, to 4.2 MeV and 2.9 MeV, respectively. In the resulting activation depths of 52 and 102 μm, the sensitivity of the method, which is 3·10¹⁴ at ·cm⁻³C at E_d=10 MeV in silicon, is reduced to 25% and 10%, respectively. An optimal flux of 0.9 μA·cm⁻² was maintained. After irradiation, 20 or 10 μm were etched off. The sample was inductively fused at 1500 K in a Pb₃O₄/B₂O₃ mixture.¹³N was passed with He as carrier gas into an absorption vessel kept at 77 K, and its activity was measured in γ, γ-coincidence.     

An investigation into the use of the nuclear microprobe for examining distributions of boron isotopes

A technique has been developed to permit the distribution of boron isotopes in metal samples to be measured with the nuclear microprobe. Samples are irradiated with focussed beams of α-particles, and protons from the (α, p) reactions on both¹⁰B and¹¹B are counted. Particle spectroscopy enables contributions from the two isotopes to be determined separately from the same spectrum and distributions can be followed by varying the position of the ion beam on the sample surface.     

Determination of sulfur in near-surface layers of materials by means of the32S(3He,p)34mCl nuclear reaction

The cross-sections of the³²S(³He, p)^34mCl nuclear reaction have been determined in the projectile energy region between 4.0 and 12.0 MeV with the aim of their use for the determination of sulfur in surface layers of materials by means of Charged Particle Activation Analysis (CPAA). The measured cross-sections indicate that the application of this reaction for the determination of ppm and sub-ppm concentrations of sulfur is possible depending on the matrix material (e.g. detection limit for S in GaAs is 2 ppm, whereas in Si 300 ppb).     

Non-destructive 3D-characterization of Zn 2-2x Cu x In x S 2-thin films with ion beam analysis

Thin layers of ZnS-CuInS(2) mixed crystals (called ZCIS) are promising absorber materials for thin film solar cell applications. The ZCIS-films investigated in this study were grown on (001)GaP, SiO(2) and CeO(2)/Al(2)O(3) with different elemental compositions by Pulsed Laser Deposition (PLD). In order to optimize the sample preparation process a quantitative three-dimensional (i.e. laterally and depth resolved) determination of the compositions and thicknesses of the ZCIS-films is needed. It is demonstrated how this difficult analytical task can be addressed with ion microbeam analysis. For this purpose the films have been analysed non-destructively by means of Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE) using a 2 MeV He(+) ion microbeam at the high-energy ion nanoprobe LIPSION. A large variation in film thickness caused by particulates deposited on the film was observed. The elemental compositions of the film and the particulates have been determined and compared with the target composition. The deviations found varied substantially for the individual elements. It could be concluded from these measurements, that the quality of the sintered PLD-target is of crucial importance for the roughness of the films. Furthermore concentration-depth-profiles of the individual elements have been derived non-destructively by means of RBS.     

Nuclear and atomic activation with heavy ion beams

Heavy ion activation has been studied as a method for determining hydrogen. The reactions used [e.g.¹H(⁷Li, n)⁷Be] are the “inverse” of well known reactions [e.g.⁷Li(p, n)⁷Be]. Nuclear activation parameters for the ion beams of interest (⁷Li²⁺,¹⁰B²⁺) have been studied. The analytical feasibility is demonstrated with the determination of hydrogen in titanium at the 100 and 30 ppm levels with relative precisions of 8 to 10%. Detection limits in titanium are in the 0.1 to 0.5 ppm range. Heavy ion bombardment is also accompanied by the emission of characteristic X-rays (“atomic” activation). The parameters governing X-ray emission and background production have been investigated. Experimental K and L X-ray yields from thick targets have been measured for many elements excited by Oⁿ⁺ beams of 0.5 to 7 MeV/amu and Kr⁷⁺ beams of 0.5 to 1 MeV/amu. The simultaneous determination of trace elements at levels of 10 to several 100 ppm in microsamples (∼10⁻⁵ g) is demonstrated on biological specimens. K and L X-ray yields and corresponding detection limits have also been measured with the⁷Li²⁺ and¹⁰B²⁺ beams used for the nuclear activation of hydrogen. With these beams (∼6 MeV/amu) simultaneous nuclear and atomic activation is possible, yielding an unusual multielement trace analysis capability covering hydrogen and medium and high Z elements.     

Etude des possibilites de dosage du lithium par activation au moyen de protons et de deutons de moyenne energie

The determination of lithium by measuring⁷Be, produced by proton or deuteron activation, has been studied. The extent of interference from boron or beryllium, which also form⁷Be, was measured. The calculated sensitivity limits when activating for one hour with 10μA beams of 14 MeV protons or 25 MeV deuterons are, for lithium, 1·10⁻¹ and 2.5·10⁻² ppm and for boron, 2·10⁻¹ and 1·10⁻¹ ppm, respectively.      

Production possibility of <Superscript>186</Superscript>Re via the <Superscript>192</Superscript>Os(p,α3n)<Superscript>186</Superscript>Re nuclear reaction

Experimentally measured cross-sections are presented for the first time for the ¹⁹²Os(p,α3n)¹⁸⁶Re nuclear reaction up to 67 MeV. Highly enriched thin ¹⁹²Os targets (15 pcs), prepared by electro-deposition onto Cu backings, were irradiated with an external proton beam delivered by the SSC cyclotron of iThemba LABS. The excitation function curve of the ¹⁹²Os(p,α3n)¹⁸⁶Re reaction shows a maximum cross-section of ~82 mb at about 24 MeV. According to the yield calculations based on the present results, the available cumulative no-carrier-added ¹⁸⁶Re yield is 7.76 MBq/μAh (0.21 mCi/μAh) over the energy region 13.4 → 27.3 MeV.     

Medium energy,heavy and inert ion irradiation of metallic thin films: studies of surface nano‐structuring and metal burrowing

In context to the ion induced surface nanostructuring of metals and their burrowing in the substrates, we report the influence of Xe and Kr ion‐irradiation on Pt:Si and Ag:Si thin films of ~5‐nm thickness. For the irradiation of thin films, several ion energies (275 and 350 keV of Kr; 450 and 700 keV of Xe) were chosen to maintain a constant ratio of the nuclear energy loss to the electronic energy loss (S_n/S_e) in Pt and Ag films (five in present studies). The ion‐fluence was varied from 1.0 × 10¹⁵ to 1.0 × 10¹⁷ ions/cm². The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images show ion beam induced systematic surface nano‐structuring of thin films. The surface nano‐structures evolve with the ion fluence. The RBS spectra show fluence dependent burrowing of Pt and Ag in Si upon the irradiation of both ion beams. At highest fluence, the depth of metal burrowing in Si for all irradiation conditions remains almost constant confirming the synergistic effect of energy losses by the ion beams. The RBS analysis also shows quite large sputtering of thin films bombarded with ion beams. The sputtering yield varied from 54% to 62% by irradiating the thin films with Xe and Kr ions of chosen energies at highest ion fluence. In the paper, we present the experimental results and discuss the ion induced surface nano‐structuring of Pt and Ag and their burrowing in Si. Copyright © 2016 John Wiley & Sons, Ltd.     

Trace analysis of lithium metal by PIXE

A rapid method is described for simultaneous trace determination of metallic impurities in lithium metal by Particle Induced X-ray Emission (PIXE) technique. The impurities were preconcentrated by ion-exchange separation using a weak cation exchanger, Bio Rex-70 and analyzed by 2.34 MeV protons. The reliability of the method was tested by analyzing synthetic samples having several metallic impurities at 1–5 ppm range.     

Development of [<Superscript>64</Superscript>Cu]-DOTA-anti-CD20 for targeted therapy

Copper-64 was produced as a by-product of ⁵⁵Co via ⁶⁴Ni(p,n)⁶⁴Cu by 15 MeV proton bombardment of ^natNi resulting in a thick target yield of 5.31 MBq/μAh (143.5 μCi/μAh) and a radiochemical separation yield of 95% (radionuclide purity >97% after 25 hours of bombardment). Rituximab was successively labeled with [⁶⁴Cu]-CuCl₂. N-succinimidyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-NHS) was prepared at 25 °C using DOTA and N-hydroxy succinimide (NHS) in CH₂Cl₂ followed by the addition of 1 ml of a Rituximab pharmaceutical solution. Radiolabeling was performed at 37 °C in 3 hours. Radio thin-layer chromatography showed an overall radiochemical purity of 90–95% at optimized conditions (specific activity=30 GBq/mg, labeling efficacy; 82%) using various chromatography systems. The final isotonic ⁶⁴Cu-DOTA-Rituximab complex was passed through a 0.22 μm filter and checked by gel electrophoresis for radiolysis control. Stability of the final product was checked in the formulation and in presence of human serum at 37 °C.     

Trace determination of boron,silicon and sulfur with oxygen-18 ion bombardment

In order to determine traces of boron, silicon and sulfur, B(¹⁸O, x)²⁷Mg, Si(¹⁸O, x)⁴³Sc and S(¹⁸O, x)⁴⁷V reactions have been investigated between 15 and 44MeV. At 34 MeV, only a few of the systematically identified nuclear interferences produce²⁷Mg and the detection limit is 30ng boron for a 10 minute irradiation with a 0.3μA·cm⁻² oxygen-18 beam. Silicon analysis has shown nuclear interferences from Al, P and K; interference-free detection limit is 80 ng silicon for an hour irradiation with a 0.4 μA·cm⁻² beam at 39 MeV. There is no nuclear interference for the sulfur determination and the detection limit is 5 ng sulfur for a 30 minutes irradiation with a 0.5 μA·cm⁻² beam at 39 MeV. Thus a selective and sensitive sulfur determination can be achieved.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the¹⁶O(n, p)¹⁶N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 10¹⁰ n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.     

Changes in the surface morphology induced by 1.0‐MeV Au ion bombardment of Ti and Ti‐6Al‐4V

The effects of surface sputtering by 1.0‐MeV Au ion implantation in commercially pure Ti and its alloy Ti‐6Al‐4V have been studied. These materials are associated with applications in orthopaedic implants. There are few studies that try to explain the ion implantation process of Au in these materials when considering the effects generated on the surface by sputtering, especially at energies of the order of MeV. Discs of these materials were mirror polished and then implanted with 1.0‐MeV Au ions for 4.7 × 10¹⁷ ions/cm² at 45° incident angle with respect to the surface. Part of the eroded material was deposited simultaneously on glass slides to determine their spatial distribution. These discs and the slides were analysed by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), optical microscopy and atomic force microscopy. The implanted materials show the initial production of surface ripples that evolve into banded structures. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of an ancient bronze statue by external beam pixe

A quantitative analysis of an ancient Buddha statue was performed by external beam Proton Induced X-ray Emission for the purpose of identifying its originality. It is shown how the PIXE method can be applied for archeological study. The elemental composition of the statue is compared with that of several samples with definite ages. The experiment was performed by extracting 2.4 MeV proton beam through a 2 mm diameter collimator and 7.6 m kapton foil to the He atmosphere. X-rays were measured by a Si(Li) detector. The analysed elements were Fe, Cu, Ag, Au and Hg for gold coating and Fe, Ni, Cu, Zn, As, Ag, Sn, Au, Pb and Bi for bronze body.     

Determination of boron in the thin surface layer of a silicon wafer by instrumental charged particle activation analysis

Instrumental charged particle activation analysis (CPAA) for determining boron in a thin surface layer of silicon was developed. The nuclear reaction and incident energy were selected in order to minimize any interference from surface or bulk impurities. Thin boron film was used as a standard sample and its boron content was determined by neutron induced prompt -ray analysis. As a result, we were able to determine¹¹B and¹⁰B at 10¹⁵ atoms/cm² with an accuracy of better than 3% by 4 MeV proton and 7 MeV -bombardment, respectively. Each boron isotope could be determined down to 10¹³ atoms/cm². Our CPAA was applied to determine boron in a boron implanted silicon wafer of a SIMS standard sample.