Elemental analysis of agricultural soil samples by particle induced X-ray emission (PIXE) technique

In agriculture, elements essential to vital processes are also called nutrients. A suitable and reliable particle induced X-ray emission (PIXE) methodology for content determination of essential nutrients in soil samples was developed and its effectiveness proved. The PIXE method is applied to intermediate thickness samples, whose mass per area unit are smaller than 1 μg/cm². Precision and accuracy of the method was estimated after repeated measurements of a single reference material: CRM PACS-2 (estuarine sediment) with a matrix quite similar to the soil samples measured. This paper reports the results of elemental measurements in soil samples. A discussion of agricultural soil sample preparation for PIXE analysis is also presented.     

Air quality work at Guelph: GAViM and a traffic tunnel study

The Guelph Aerosol and Visibility Monitoring (GAViM) program presently runs three monitoring sites: two rural sites compatible with the IMPROVE protocol and one urban site mostly for special comparison studies. Fine aerosol is analyzed by the Laser Integrated Plate Method (LIPM), Proton Elastic Scattering Analysis (PESA), Proton Induced X-ray Emission (PIXE) and gravimetric analysis. Air quality data from the presently running sites and from two rural sites operated in the past are available through the WWW. The Guelph Scanning Proton Laboratory also participates in other aerosol programs: PIXE was employed to determine the composition of the ambient aerosol in a Vancouver traffic tunnel, to identify the main emission sources and to make estimates of vehicle emission factors. The PIXE facility was also modified for analysis of size-fractionated samples from the PIXE International Cascade Impactor (PCI) sampler. Significant improvement in detection limits for light elements due to the two-detector PIXE system used in Guelph, was justified particularly because of low air particulate loadings in case of PCI.     

Research of Si and GaAs diode structures by Ion Beam Induced Charge (IBIC) collection

A Si pn junction diode and a GaAs Schottky diode were prepared for studying the basic mechanism of charge collection followed by high energy charged particle incidence in order to improve the resistance against single event upset. A 2 μm wide and 20 μm long rectangular Al electrode attached to a circular Al electrode with a 50 μm diameter was made on a 2.5 μm thick epilayer (minority carrier density 2 × 10¹⁵ /cm³). Both a Schottky electrode of Al (5 μm × 110 μm) and two ohmic electrodes of AuGe/Ni (110 μm × 110 μm) were made on a 2 μm thick epilayer (7.3 × 10¹⁵ /cm³) grown on a semi insulator GaAs substrate (1 × 10⁷ Ω cm). The internal device structure was examined by the IBIC (Ion Beam Induced Charge) method using a 2 MeV He⁺ ion microbeam. IBIC images clearly show an Al electrode, the SiO₂, and an epilayer. These results were then used to improve the qualities of the test diodes.     

Extraction efficiency of N(T1/2 = 9.96 min) atoms from a graphite target: comparison between off- and on-line obtained results

An off-line release study ¹³N(T1/2 = 9.96 min) produced by proton induced reaction on a graphite target (POCO-graphite EDM3, density = 1.84 g/cm³, grain size /t 3 μm) has been performed. The activation energy for the diffusion process is determined to be 6.15(16)×10⁵ J/mol. With this activation energy, extraction efficiencies for ¹³N are obtained at different temperatures and are compared to on-line measured extraction efficiencies.     

气溶胶样品氢含量的质子弹性散射分析

利用单个标准样品比较法质子弹性散射分析（PESA）对一组采集在核孔膜上的气溶胶样品的氢含量进行定量分析。在质子束能量为2.5MeV、散射角为40°时，PESA测量10μm厚核孔膜上气溶胶中H含量的探测限为0.36μg/cm²。几个样品H含量的测量结果在3.2~37.5μg/cm²之间，显著高于探测限。质子能量在1.0~2.5MeV范围内，3.5μmMylar膜的束流归一化H峰面积随入射质子能量的变化在±3%以内。所以，不同厚度的气溶胶样品可采用同一个标准样品来进行PESA测量。     

Microbeam line with 1.5 MeV helium ions and protons at Osaka

A microprobe for Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) measurements has been realized by focusing 1.5 MeV helium-ion or proton beams with a demagnification system consisting of piezo-driven objective slits and a magnetic quadrupole doublet. Minimum beam spot sizes of 1.3 × 2.2 μm² for helium ions and 2.2 × 4.0 μm² for protons have been achieved. The factors which may limit the minimum spot size are discussed using a Monte Carlo simulation procedure. Rutherford backscattering image mapping of 3-dimensional structures is demonstrated.     

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl₂, K₂Cr₂O₇, and NaAsO₂. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.     

Low energy nitrogen ion doping into GaAs using combined ion-beam and molecular-beam epitaxy method

Low energy nitrogen (N) ions were irradiated during the epitaxial growth of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) method as a function of N⁺ ion acceleration energy (E_a) and N⁺ ion beam current density (I_N). E_a was varied from 70 to 170 eV I_N from 900 pA/cm² to 75 nA/cm². GaAs growth rate was fixed to 1 μm/h. In 2 K photoluminescence (PL) spectra of the samples with I_N = 3 nA/cm² and E_a = 70–100 eV, two sharp emissions at 1.508 eV (X₁) and 1.495 eV (X₂), which have been attributed to the emissions of excitons bound to isolated N atoms, and another one at 1.443 eV (X₅) were observed. These results show that nitrogen (N) atom in GaAs becomes optically active as an isoelectronic impurity at least in as-grown condition. For N⁺ ion-irradiated samples with rather high I_N, e.g., with I_N = 75 nA/cm² and E_a = 100 eV, a broad emission together with multiple sharp ones were observed after furnace annealing at 750°C which were ascribed to emissions of excitons bound to nitrogen-nitrogen (N---N) pairs.     

The performance of the Ljubljana ion microprobe

In August 2000 the setup of the Ljubljana ion microprobe, based on OM 150 triplet, has been completed. The beam line is installed at the 10° exit port of the 2 MeV Tandetron accelerator. It is equipped with motor driven slits, a precise five-axis goniometer and a spherically shaped measuring chamber with detectors for PIXE, PIGE, PESA, SE and RBS. In order to understand the beam optics along the complete system, consisting of the tandem accelerator and the beam line optical elements, an interactive computer code, based on a linear approximation, has been developed. The program is used both to determine the optimal parameters of the tandem focusing system in its daily use and to develop new beam line configurations. Test measurements performed on a copper grid yielded a spatial resolution of 1.0×1.5 μm² in the high current mode (30–100 pA) and 0.5×0.9 μm² in low current mode (10⁴ counts/s). First analytical results confirmed excellent performance of the new Ljubljana ion microprobe.     

High energy resolution PIXE with high efficiency using the heavy ion microbeam

An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E < 6 MeV) with reasonable detection efficiency. The design of the spectrometer, such as detection geometry, detectable energy range and energy resolution, are described. This system was applied to high energy resolution PIXE analysis of Ti, SUS and Si with 2 MeV proton and 5 MeV Si³⁺ focused or collimated beams. The best energy resolution was 2 eV for the Si K line.     

Heavy-ion-induced luminescence of amorphous SiO2 during nanoparticle formation

Silica glass was implanted with negative 60 keV Cu ions at an ion flux from 5 to 75 μA/cm² up to a fluence of 1 × 10¹⁷ ions/cm² at initial sample temperatures of 300, 573 and 773 K. Spectra of ion-induced photon emission (IIPE) were collected in situ in the range from 250 to 850 nm. Optical absorption spectra of implanted specimens were ex situ measured in the range from 190 to 2500 nm.

IIPE spectra showed a broad band centered around 560 nm (2.2 eV) that was assigned to Cu⁺ solutes. The band appeared at the onset of irradiation, increased in intensity up to a fluence of about 5 × 10¹⁵ ions/cm² and then gradually decreased indicating three stage of the ion beam synthesis of nanoclusters: accumulation of implants, nucleation and growth nanoclusters. The IIPE intensity normalized on the ion flux is independent on the ion flux below 20 μA/cm²at higher fluences. The intensity of the band increased with increasing samples temperature, when optical absorption spectra reveal the increase of Cu nanoparticles size.     

On the accuracy of element concentrations and masses of micron sized samples determined with the Heidelberg proton microprobe

We have already tested the reliability of element-normalized PIXE (Proton Induced X-ray Emission) data on small (10–100 μm) particles that we routinely obtain with the Heidelberg proton microprobe. Thus, we here discuss the accuracy of quantitative results, i.e., absolute concentrations inferred from PIXE analyses of such particles. We investigated and reduced the effects of mechanical vibrations and of the instability of the electronic devices on the achievable minimum beam spot. We implemented into our computer code a mapping software for qualitative element distributions (PIXE) and quantitative mass images using STIM (Scanning Transmission Ion Microscopy). The STIM images determine the area density required to calculate from PIXE spectra the absolute element concentrations in thin samples. The accuracy of absolute PIXE concentrations is tested by measurements on 15 μm soda lime glass microspheres. Finally, the complete results of PIXE and STIM analyses of an interplanetary dust particle (IDP) are described.     

Effect of Foil Target Thickness in Proton Acceleration Driven by an Ultra-Short Laser

Proton acceleration experiments were carried out by a 1.2 x 101s W/cm2 ultra-short laser interaction with solid foil targets.The peak proton energy observed from an optimum target thickness of 7μm in our experiments was 2.1 MeV.Peak proton energy and proton yield were investigated for different foil target thicknesses.It was shown that proton energy and conversion efficiency increased as the target became thinner,on one condition that the preplasma generated by the laser prepulse did not have enough shock energy and time to influence or destroy the target rear-surface.The existence of optimum foil thickness is due to the effect of the prepulse and hot electron transportation behavior on the foil target.     

Study of basic mechanisms of semiconductor devices using ion beam induced charge (IBIC) collection

A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 μm width and 10 μm length as a function of the ion incident position. Three pn junctions were made on a 3 μm thick Si epilayer (1 × 10¹⁶/cm³) grown on Si substrate and were in a line along an aluminum electrode with 10 μm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a 1 μm diameter 15 MeV C⁺ heavy ion microbeam spacing steps by 3 μm. At a bias voltage of − 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 μm and 4 μm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He⁺ ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.     

Beam heating and cooling of thick targets for on-line production of exotic nuclei

Calculations have been made of energy deposition distributions for “thick” targets (1 mole/cm²) employed in on-line production of exotic nuclei using the Monte Carlo based LAHET code system for high-energy charged particle transport. A variety of target materials and incident proton beam energies have been examined. For 600 MeV protons, the results are compared to those from a similar study reported in the literature. The agreement between the two studies for total energy deposition is reasonably good for monatomic targets, but the results differ in some details of the energy deposition distributions. Target cooling, both radiative and conductive, is examined to assess the suitability of existing target concepts exposed to bombardment by intense (up to 100 μA), energetic (500 MeV to 1.2 GeV) proton beams to produce exotic nuclei. Implications of cooling requirements to target material selection and design are discussed.     

Characterisation of ferromagnetic magnetic storage media surfaces by complementary particle induced X-ray analysis and time of flight-energy dispersive elastic recoil detection analysis

Thin (10 nm–1 μm) films of ferromagnetic material constitute an important class of materials that are difficult to analyse by conventional ion beam analytical (IBA) techniques because they are based on the ferromagnetic elements (Co, Fe, Mn, Ni, and Cr). The similar or overlapping isotope masses makes it difficult to separate the elemental signals using time of flight and energy dispersive elastic recoil detection (ToF-E ERD). In this exploratory study we have investigated the use of Particle Induced X-ray Emission (PIXE) measurements to refine the mass dispersive depth profile information from ToF-E ERD. The surfaces of two commercial magnetic media were investigated. One sample was a double density diskette with a coating of ferrite particles in an organic binder. The other sample was a complex C/Co/Cr/Ni–P/Al multilayer structure taken from a standard hard disc. The Lund nuclear microprobe with a 2.55 MeV proton beam was used for PIXE analysis. ToF-ERD measurements were carried out using a 55 MeV ¹²⁷I¹⁰⁺ ion beam incident at 67.5° to the surface normal. The time of flight and kinetic energy of recoils ejected at 45° to the ion beam direction was measured in a detector telescope. The findings demonstrate that by detailed analysis of the PIXE spectra it is possible to remove the ambiguities in mass assignment of the ToF-ERD data associated with the ferromagnetic elements.     

Electron microscopy and Rutherford backscattering spectrometry characterisation of 6H SiC samples implanted with He

6H SiC single crystals were implanted at room temperature with 1 MeV He⁺ up to a fluence of 2 × 10¹⁷ at./cm². RBS-channeling analysis with a 2 MeV He⁺ beam indicated the formation of extended defects or the generation of point defects at a constant concentration over a depth of about 1 μm. Electron microscopy characterisation revealed the presence of two amorphous buried layers at depths of about 1.75 and 4.8 μm. They are due to the implantation and to the analysing RBS beam, respectively. No extended planar or linear faults were found in the region between the surface and the first amorphous layer. However, at the surface, a 50 nm thick amorphous layer was observed in which crystalline inclusions were embedded. Electron diffraction and HREM data of the inclusions were typical for diamond. These inclusions were even found in the crystalline SiC material below this layer, however at a reduced density.     

Quadrupole-doublet with permanent magnets for proton beam focussing

For PIXE studies on inhomogeneous samples with medium spatial resolution of about 50 μm two quadrupole doublets with Co₅Sm pole pieces for focussing 2.0 and 2.5 MeV proton beams, respectively, have been designed and tested. Technical data and first results are presented.     

Analysis of metallic pigments by ion microbeam

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm² at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al K map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree.     

Charge state distribution and its equilibration of 2 MeV/u sulfur ions passing through carbon foils

Charge state distributions of 2.0 MeV/u sulfur ions of various initial charge states (6, 10, 11, 13+) after passing through 0.9, 1.5, 2.0, 3.0, 4.7, 6.9 and 10 μg/cm² carbon foils have been studied. It is observed that the processes involving the L-shell electrons are equilibrated within the target thickness of 5 μg/cm² and the charge equilibration over this thickness is ruled by the K-shell processes. Measured charge state distributions do not flat off to establish equilibrium within the measured thicknesses, but the mean charge states almost saturate to 12.4 for all initial charge states examined. Calculation with ETACHA code, developed by Rozet et al. [Nucl. Instr. and Meth. B 107 (1996) 67], is employed, although the present impact energy is lower than the assumed region for the code.