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.     

The new Melbourne nuclear microprobe system

The spatial resolution in a nuclear microprobe system has been stalled at around 1 μm for many years. In Melbourne we are presently constructing a new facility which aims to break this barrier. The key ingredients of the new facility are: (i) a novel magnetic quadrupole lens quintuplet probe forming system that is a further optimised version of the CSIRO/MARC system presently in operation in Sydney, (ii) high solid angle detectors for particles, X-rays and secondary electrons and (iii) a fast data acquisition system able to cope with greater than 20 kHz count rates from up to four detectors with full deadtime correction. This paper describes the optimised probe forming lens system which is comprised of four thin lenses and one thick lens to produce an orthomorphic probe forming lens system with a demagnification of 150.     

Applications to cultural heritage diagnostics at the new nuclear microprobe beam line at CEDAD

A nuclear microprobe beam line has been installed at CEDAD (Centre for Dating and Diagnostics), University of Salento, Lecce, Italy. The beam line is connected to the ?30° port of the high energy switching magnet of a 3 MV HVEE 4130HC Tandetron accelerator. It is based on an Oxford Microbeam magnetic quadrupole triplet and its general features are presented. The results of functional tests are presented showing how a lateral spatial resolution as low as ～2 μm has been achieved in vacuum by analysing standard reference material. The results obtained in the analysis of ancient radiocarbon dated biological tissues are presented for the identification and distribution of toxic elements such as Pb.     

The nuclear microprobe determination of the spatial distribution of stable isotope tracers

The use of the nuclear microprobe for the measurement of the spatial distribution of stable isotope tracers has been critically appraised. Prospective areas of application are suggested.     

The effects of surface topography in nuclear microprobe Rutherford backscattering analysis

The influence of two geometric surface topographies on Rutherford backscattering spectra in nuclear microprobe analysis has been investigated through computer simulation. Periodic triangular surfaces are shown to give structureless spectra of reduced yield in perpendicular incidence, but oscillatory features develop as the target is tilted. Steps on the surface give less structured spectra, though the total backscattering yield can vary dramatically, depending on geometry.The quantitative effects of topographical amplitude, finite beam width, target tilt and target atomic number, in the two detector geometries available at Harwell, θ = 170° and 135°, on the distortion of flat target spectra, for two basic types of surface topography, are presented. The influence of energy straggling is shown to be small and multiple scattering is considered. The consequences of surface topography in practical nuclear microprobe analysis are discussed.     

The nuclear microprobe: An insight of applications in cell biology

During the last five years, the evolution of biomedical research based upon nuclear microprobe analysis has followed the development of experimental models of cultured or isolated cells. Fundamental studies of cellular mechanisms have been approached by means of in vitro assays associated with single cell analysis. Within those groups which are involved in such programs, special emphasis has been placed on cell culture and processing techniques which fulfill the methodological requirements for intracellular ion beam analysis. Great efforts have been orientated towards the improvement of normalization procedures. It is now possible to provide reliable quantitative results expressed in such units that they can be easily cross-checked using conventional methods. Imaging techniques have been also developed for the identification of the analyzed structures. In this paper, different domains of cell biology which have been addressed during the last years are reviewed. Studies dealing with cellular physiology and pharmacology are briefly presented as are also those related to the role of trace elements. Topics under development in our group as well as ongoing investigations will be also evoked.     

Ion source brightness and nuclear microprobe applications

The ion source used to provide beams for nuclear microprobe systems must ideally satisfy several demands. Of primary importance is the beam brightness. It is clearly desirable to employ the brightest possible source in order to focus the smallest possible probe size on the specimen, with the highest possible beam current. Also important is the need for minimal maintenance, particularly for ion sources used inside single ended accelerators.

We report here on measurements conducted on the beam from the RF ion source in our 5U Pelletron accelerator. We have found that the beam brightness is highly heterogenous, with the paraxial rays about an order of magnitude brighter than the surrounding rays. This is desirable for nuclear microprobe operation because probe forming lens systems optimised for large demagnification magnitude can exploit the high brightness of the paraxial region. We find several other accelerators around the world also exhibit this characteristic.     

Applications of nuclear microprobe analysis to dermatological research

The elemental distributions over epidermal skin cross sections as revealed by nuclear microprobe analysis on cryo-sections from human skin provides new insight into the physiology of skin. Recently interest has been focused on the end stage of epidermal differentiation, the programmed cell death, occurring in the uppermost layer of the viable epidermis, the stratum granulosum. Calcium is one of the important messengers that controls the events of this programmed cell death, which shares a number of characteristics with apoptosis. We have previously shown that the Ca-gradient over normal skin cross sections is compatible with the finding from cell culture of epidermal cells which need a minimum level of 0.1 mM (Ca²⁺) to develop a normal stratum corneum. To gain more information from the large number of data assessed during the actual analysis we have applied multivariate statistical analysis to the complete dataset obtained at NMP analyses. This statistical method reveals covariation of several elements and in addition provides a means to interpret the quantitative data in a meaningful biological context.     

Novel method of nuclear microprobe beam profile determination

A simple method to directly determine the nuclear microprobe beam profile is described. Whereas the accuracy of the method can be drastically reduced by the alignment of the test specimen, secondary electron emission was used to determine the precise specimen orientation. The resulting technique was used for both accurate beam size and profile determinations.     

Recent applications of nuclear microprobe techniques to microelectronics

Applications of nuclear microprobe techniques to microelectronics, in particular, two- or three-dimensional analysis of integrated circuit structures using micro RBS (Rutherford Backscattering) and IBIC (Ion Beam Induced Current) measurements are discussed. SEU (Single Event Upset) mapping and IBIC measurements in SRAMs (Static Random Access Memories) and DRAMs (Dynamic Random Access Memories) are reviewed together with charge carrier collection simulation and transient IBIC measurements. Importance of applications of microprobes to new microelectronic structures such as SOI (Silicon-on-Insulator) devices for future hand-held information systems are also discussed. Possible applications of SEU measurement as alternative experimental procedures to cosmic ray neutron strikes are discribed.     

Nonlinear processes of probe formation of a beam with inhomogeneous phase density at nuclear microprobe

The work describes nonlinear processes of probe formation on the target with allowance for an inhomogeneous density of ion distribution in phase space in the object collimator plane taken from experimental data. The chromatic aberrations, intrinsic aberrations of the 3rd order and parasitic aberrations caused by sextupole and octupole components of the magnetic quadrupole lens field have been taken into account in the object-target phase coordinate transformation. The criterion of obtaining the optimal resolution was defined as the minimum spot size (FWHM) for a fixed ratio I_FWHM/I₀ of beam current in this spot to the total beam current. The conditions for which the initial density of ion distribution in phase space is matched with the ion-optical characteristics of the probe-forming system were considered. The influence of axial brightness and parasitic sextupole and octupole field components on the beam current distribution at the target has been determined.     

The use of maximum entropy and Bayesian techniques in nuclear microprobe applications

This paper presents an overview of the Bayesian Formalism (BF) and Maximum Entropy (ME), as well as applications of the theory to various ion-beam and nuclear microprobe (NMP) related work. The Bayesian formalism is an efficient and theoretically sound technique of information recovery, with special applications in ill-posed inverse problems, such as detector function deconvolution. Results are presented showing the promise of Bayesian Statistics and Maximum Entropy in PIXE spectrum deconvolution, deconvolution of the beam profile from one-dimensional scans and the recovery of depth profiles in RBS.     

Performance of the Sumy nuclear microprobe with the integrated probe-forming system

The integrated probe-forming system for the Sumy nuclear microprobe comprises two doublets of magnetic quadrupole lenses of new design. Each doublet has been made from a single piece of soft iron by electro-discharge machining. This paper describes the performance tests of the microprobe including the beam scanning control and data acquisition systems. In the first runs a spot size of about 2 μm (FWHM) was obtained for the high beam current mode (up to 200 pA) by scanning a conventional copper grid with 1000 meshes per inch. Simulated beam optics parameters are compared with the experimental data.     

Mapping of hydrogen isotopes with a scanning nuclear microprobe

Elastic recoil detection analysis using heavy ions with a scanning nuclear microprobe was applied to determine the content of hydrogen isotopes in carbon material facing fusion plasma in the JET fusion reactor. The hydrogen and deuterium concentrations in re-deposited material were obtained by mapping a cross sectional cut of a wall sample. De-trapping and hydrogen release caused by the primary ion beam were investigated. For both the deuterium and hydrogen concentration a drop of ∼75% was observed from an extrapolated initial value to a final steady state region. A procedure was used to determine the initial concentration. In this way a mapping of the initial deuterium concentration could be obtained.     

Study of white lead paint layers by the Debrecen nuclear microprobe

The white colours of cross-section samples taken from 10 paintings and 3 different kinds of modern white lead pigments were examined by PIXE using the Debrecen nuclear microprobe. Elemental concentrations of impurities relative to Pb were determined. A comparison with EDAX on the same samples is made.     

Early works on the nuclear microprobe for microelectronics irradiation tests at the CEICI (Sevilla, Spain)

Particle radiation effects are a fundamental problem in the use of numerous electronic devices for space applications, which is aggravated with the technology shrinking towards smaller and smaller scales. The suitability of low-energy accelerators for irradiation testing is being considered nowadays. Moreover, the possibility to use a nuclear microprobe, with a lateral resolution of a few microns, allows us to evaluate the behavior under ion irradiation of specific elements in an electronic device. The CEICI is the new CEnter for Integrated Circuits Irradiation tests, created into the facilities at the Centro Nacional de Aceleradores (CNA) in Sevilla-Spain. We have verified that our 3 MV Tandem accelerator, typically used for ion beam characterization of materials, is also a valuable tool to perform irradiation experiments in the low LET (Linear Energy Transfer) region.     

Optical dot gain on newsprint determined with the Lund nuclear microprobe

A technique for measuring optical dot gain, i.e. the relative difference between the actual screen dot and the optically perceived one, is presented. By combining measurements from the non-optical nuclear microprobe with data from image analyzing technique the optical dot gain can be determined. The procedure to reach pixel by pixel correlation on a micrometer scale is discussed. In the newsprint sample studied in this investigation a typical optical dot gain between 15 and 20% was deduced. The variation in the optical dot gain was correlated with other characteristic parameters of the print and newsprint and especially a positive correlation to the mass density of the newsprint was observed.     

Stained glasses under the nuclear microprobe: A window into history

Stained glass fragments from the 15th, 16th and 20th centuries, belonging to Mosteiro de Santa Maria da Vitória, Batalha (Portugal), were characterised non-destructively in a nuclear microprobe. The work aimed at finding the composition of the glasses and glass paintings and relating these with the corresponding production periods.The elemental compositions of the glass fragments were obtained by means of scanning micro-beam Particle Induced X-ray Emission (μ-PIXE) spectrometry in selected cross-sections. These were complemented by micro X-Ray fluorescence spectrometry. Characterisation of colour was performed by optical absorption spectroscopy in the UV–vis range, while the corrosion products were identified by optical microscopy and μ-FTIR (Fourier Transform Infra Red) spectroscopy in combination with the data generated by μ-PIXE.Nuclear microprobe analysis allowed unveiling the compositions and structures, in particular of glass paintings and corrosion products. While it is not surprising that Fe, Cu and Pb were the main elements identified in the grisaille paintings of all studied periods, as well as Ag and Cu found in the glasses decorated with yellow silver painting, their distribution gave important clues on the materials and techniques used to manufacture these stained glasses. Furthermore, it allowed establishing a definite relation between the compositions found and the periods of production, with the added bonus of correctly reassigning the manufacturing period of some samples.     

Deuteron induced gamma-ray emission method applied at a nuclear microprobe for carbon and oxygen content measurements

The deuteron induced gamma-ray emission (DIGE) method is not usually used for analytical purposes at nuclear microprobes; therefore we show here its capabilities at the microprobe facility of the Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI). In this paper the compositional analysis of magnetic spherules carried out earlier [Nucl. Instr. and Meth B 181 (2001) 557] is combined with the determination of their carbon and oxygen contents, elements which (beside nitrogen and hydrogen) play a relevant role in the study of planetary evolution and in the elucidation of the composition of cosmic parent bodies.     

Quantitative elemental imaging of octopus stylets using PIXE and the nuclear microprobe

By utilising targeted microprobe technology, the analysis of elements incorporated within the hard bio-mineralised structures of marine organisms has provided unique insights into the population biology of many species. As hard structures grow, elements from surrounding waters are incorporated effectively providing a natural ‘tag’ that is often unique to the animal’s particular location or habitat. The spatial distribution of elements within octopus stylets was investigated, using the nuclear microprobe, to assess their potential for determining dispersal and population structure in octopus populations. Proton Induced X-ray Emission (PIXE) was conducted using the Dynamic Analysis method and GeoPIXE software package, which produced high resolution, quantitative elemental maps of whole stylet cross-sections. Ten elements were detected within the stylets which were heterogeneously distributed throughout the microstructure. Although Ca decreased towards the section edge, this trend was consistent between individuals and remained homogeneous in the inner region of the stylet, and thus appears a suitable internal standard for future microprobe analyses. Additional analyses used to investigate the general composition of the stylet structure suggested that they are amorphous and largely organic, however, there was some evidence of phosphatic mineralisation. In conclusion, this study indicates that stylets are suitable for targeted elemental analysis, although this is currently limited to the inner hatch region of the microstructure.