PIXE Results Research Articles

Emulation of the Curiosity rover alpha particle X-ray spectrometer with accelerator-based PIXE: Implications for calibration

Abstract A 2.5 MeV broad-beam PIXE system was designed to emulate the alpha particle X-ray spectrometer (APXS) of the Curiosity rover. APXS measurements of the light elements (sodium, magnesium and aluminum) in powdered rock standards showed systematic deviations arising from the rock’s violation of the assumption of atomic scale sample homogeneity. These deviations, which are dependent on the iron concentration of the sample, were confirmed with high-accuracy accelerator-based PIXE measurements. Systematically low iron concentrations, not seen in APXS measurements, were present in the PIXE results. These are unlikely to arise due to violation of the homogeneity assumption. Measured particle-size distributions suggest that they are more likely due to the grain size distribution of iron-bearing minerals in the powdered standards. Terrestrial analogs to recently discovered Martian rock types were used to extend the calibration to include high iron and high-alkali samples.

Heterogeneous intratumoral distribution of gadolinium nanoparticles within U87 human glioblastoma xenografts unveiled by micro-PIXE imaging

Metallic nanoparticles have great potential in cancer radiotherapy as theranostic drugs since, they serve simultaneously as contrast agents for medical imaging and as radio-therapy sensitizers. As with other anticancer drugs, intratumoral diffusion is one of the main limiting factors for therapeutic efficiency. To date, a few reports have investigated the intratumoral distribution of metallic nanoparticles. The aim of this study was to determine the quantitative distribution of gadolinium (Gd) nanoparticles after direct intratumoral injection within U87 human glioblastoma tumors grafted in mice, using micro-PIXE (Particle Induced X-ray Emission) imaging. AGuIX (Activation and Guiding of Irradiation by X-ray) 3 nm particles composed of a polysiloxane network surrounded by gadolinium chelates were used. PIXE results indicate that the direct injection of Gd nanoparticles in tumors results in their heterogeneous diffusion, probably related to variations in tumor density. All tumor regions contain Gd, but with markedly different concentrations, with a more than 250-fold difference. Also Gd can diffuse to the healthy adjacent tissue. This study highlights the usefulness of mapping the distribution of metallic nanoparticles at the intratumoral level, and proposes PIXE as an imaging modality to probe the quantitative distribution of metallic nanoparticles in tumors from experimental animal models with micrometer resolution.

Prehispanic goldwork technology study by PIXE analysis

Technological characterization of pre-Hispanic gold metallurgy has still a wide deficit of analytical data. A set of 103 pieces from the so called “Quimbaya’s treasure” (QT) and the “Costa Rica collection” (CRC) of the Museo de America of Madrid were submitted to IBA analysis (PIXE and RBS) at the CMAM in three phases and the metal composition was determined. Only in a limited number of cases, due to the dramatic erosion of the gilded layer, produced by abrasive cleaning methods applied after the discovery and before the seventies, it was possible to determine also the sequence of layers, which gives information on the manufacture technology and the type and purity of the metals. PIXE results are reported and discussed. Data show that the CRC objects have very high gold levels (>80% in weight) while the QT have a more variable composition with significant Cu levels associated to the so called Tumbaga-alloy. In the cases where polishing had a tolerable effect, PIXE (and RBS), point to depletion gilding as a standard finishing process in the Costa Rica production, resulting in a gold rich surface alloy, while the variable composition of the QT objects may well be linked to deliberate colour choice.

Possibilities of LA-ICP-MS technique for the spatial elemental analysis of the recent fish scales: Line scan vs. depth profiling

LA-ICP-MS and solution based ICP-MS in combination with electron microprobe are presented as a method for the determination of the elemental spatial distribution in fish scales which represent an example of a heterogeneous layered bone structure. Two different LA-ICP-MS techniques were tested on recent common carp ( Cyprinus carpio) scales: (a) A line scan through the whole fish scale perpendicular to the growth rings. The ablation crater of 55 μm width and 50 μm depth allowed analysis of the elemental distribution in the external layer. Suitable ablation conditions providing a deeper ablation crater gave average values from the external HAP layer and the collagen basal plate. (b) Depth profiling using spot analysis was tested in fish scales for the first time. Spot analysis allows information to be obtained about the depth profile of the elements at the selected position on the sample. The combination of all mentioned laser ablation techniques provides complete information about the elemental distribution in the fish scale samples. The results were compared with the solution based ICP-MS and EMP analyses. The fact that the results of depth profiling are in a good agreement both with EMP and PIXE results and, with the assumed ways of incorporation of the studied elements in the HAP structure, suggests a very good potential for this method.

Experimental characterization and Monte Carlo simulation of Si(Li) detector efficiency by radioactive sources and PIXE

This work relates to the study and characterization of the response function of an X-ray spectrometry system. The intrinsic efficiency of a Si(Li) detector has been simulated with the Monte Carlo codes MCNP and GEANT4 in the photon energy range of 2.6–59.5 keV. After finding it necessary to take a radiograph of the detector inside its cryostat to learn the correct dimensions, agreement within 10% between the simulations and experimental measurements with several point-like sources and PIXE results was obtained.

Atmospheric inorganic contaminants and their distribution inside stem tissues of Fraxinus excelsior L.

The elements present on and in 4-year-old stem of Fraxinus excelsior L. were analysed and estimated quantitatively. The superficial deposit on the bark is a complex mixture mainly composed of organic matter, mineral nutrients, clay and anthropogenic elements coming from the atmosphere. The elements present inside the stem tissues represent a total amount which is generally much higher than the superficial deposit. The distribution of elements such as Ca, K, Fe, Mn, Zn, Cu and Pb was shown by PIXE analysis in stem transversal cuttings, showing the presence of solid multimineral particles only inside the suber. A new strategy of mechanical tissues isolation on fresh stems was carried out in order to obtain high amounts of each tissue allowing an accurate ICP-MS analysis and estimation of >20 elements in each tissue. A concentration decreasing gradient was measured for each element from suber to wood and pith in good agreement with the PIXE results. In the dividing cells of the vascular cambium, elements concentrations were very high since the cell wall weight was minimal. When expressing the amounts of each element per bark area unit, the whole bark content was only twice the wood+pith content for the studied elements. All these results suggest that, in Fraxinus stems, the root uptake and xylem transport of elements are generally not intense enough to hide the atmospheric flux of mineral contaminants.

Investigation of doppler broadening of Compton line by PIXE

We have investigated the possibility to highlight the Compton broadening effect using proton-induced X-ray emission. A special configuration of the irradiated sample has been chosen: a very thin rhodium layer deposited on a glassy carbon substrate. The X-rays photons are generated in the thin layer of rhodium owing to the ionisation by the proton irradiation. The substrate is in glassy carbon to prevent it to fluoresce. The PIXE results are compared with Monte-Carlo simulation (MCNPX) and with the theoretical model of DuMond et al. A very good agreement is observed.

Nigerian coal analysis by PIXE and RBS techniques

PIXE and RBS techniques were employed for the measurement of the concentrations of the major, minor and trace elements in Nigerian coal samples from a major deposit. The samples were irradiated with 2.55 MeV protons from the 3 MeV tandem accelerator (NEC 3 UDH) in Lund. The PIXE results are reported and compared with an earlier work on Nigerian coal using FNAA and INAA analytical techniques while the RBS results are compared with ASTM previous results. The results show that Nigerian coals have a low (0.82–0.99)% sulfur content. This is quite important for pollution control reasons.

PIXE measurements of Kr-sputtered TiN coatings

Titanium nitride films of 30–300 nm thickness deposited via dc magnetron sputtering were irradiated with 150–700 keV Kr ions at fluences up to 2.1 × 10 17 cm −2. These films were then scanned with a well-collimated 400 keV proton beam and the X-ray yield of Ti was measured both in and outside the Kr beam spot. This procedure results in a precision determination of the average film thickness (± 1% in the case of tens of nm films). The PIXE results are found to be consistent with RBS data of the same specimens. Sputtering yields were determined from the variation of X-ray yields assuming unchanged Ti/N stoichiometry in the implanted area. For thick TiN films ( d 0 > 100 nm) the sputtering yields are in good agreement with predictions of the collisional cascade model by Sigmund. In contrast, sputtering of thin layers ( d 0 = 30 nm) depended sensitively on the ion energy, being a factor of 2 higher at 150 keV than at 500 keV.

Aerosols in the exhaust gas in traffic: Re-emission analyzed by PIXE

Particle characteristics were investigated by performing measurements, i.e. among traffic. The necessary instrumentation was carried on a trailer behind the test vehicle. Particle emission, re-emission and deposition were determined in high and low traffic density areas and in winter as well as in summer. For scientific analysis particle characteristics were investigated also under laboratory conditions at temperatures of + 20°C and − 20°C. The average mass concentration at the lower temperature as detected by the filter technique was 1.5 times higher in diesel exhaust and 2 times higher in gasoline exhaust. The samples were analyzed by the internal PIXE method. Lead concentrations as analyzed by the AAS method were in good agreement with the PIXE results. The particle size was determined by SEM classification. Condensed particles collected during the first seconds of travel were observed to be below 0.5 μm mean size and re-emitted particles larger than 1 μm. The elemental results were analyzed by the statistical cluster method. The exhaust cluster (Pb, Br, Cl) can most easily be used to calculate e.g. particle mass re-emission. The re-emission fraction was found to be over 78% in high traffic density areas (in summer) and about 50% in low density areas (in summer). In winter the re-emission fraction is greatly dependent on the road surface condition.

A PIXE system for routine longitudinal scanning of single hair strands

This article describes a PIXE system designed and constructed for routine longitudinal scanning of single hair strands. In constructing a PIXE system for trace elemental scans of single hair strands on a routine basis, a fairly intense beam has to be used but the heating damage must be kept to a minimum. The experimental conditions (charge integration, beam homogeneity etc.) have to be carefully controlled in order to give accurate PIXE results. The geometrical thickness of the hair at each point of the scan has to be determined and a qualitative knowledge of the elemental distribution over the cross section of the hair has to be provided for a proper interpretation of the PIXE results. In the present PIXE system the geometrical thickness of a hair strand at each point along the scan is determined by counting the number of backscattered protons simultaneously with the PIXE analysis, and a qualitative knowledge of the elemental distribution over the cross section of the hair is obtained through bombarding the hair at particular points with different proton energies.