Proton-induced X-rays Research Articles

Low-radiation dose XRF excited by MeV protons for cultural heritage samples

In this work, we tested a setup of X-ray fluorescence (XRF) excited by proton-induced quasi-monochromatic X-rays (proton-induced XRF (PIXRF)) as a low-radiation dose analytical technique for precious cultural heritage samples. The low-dose performance of the PIXRF is experimentally assessed in comparison with the performance of a conventional XRF. For this assessment, we prepared test samples, which simulated original Japanese paintings with copper-bearing pigments. By introducing a figure-of-merit, the PIXRF is found to potentially give a better performance in terms of the radiation dose to the sample and the limit of detection, albeit the degraded multi-elemental analytical capability. PIXRF can be a cost-effective method to perform low dose measurements of precious samples, if introduced in an existing PIXE facility.

New parallel beam wavelength dispersive X-ray emission spectrometer at Ljubljana microprobe

A new parallel beam wavelength dispersive X-ray emission spectrometer for high energy resolution PIXE analysis using focused proton microbeam has been constructed and installed at the microprobe of the J. Stefan Institute. Polycapillary X-ray optics is used to enhance the solid angle of X-ray collection and to transform collected proton-induced X-rays into quasi parallel beam which is analyzed using diffraction on a flat crystal. The spectrometer is installed in a vacuum chamber and operates in the 2–10keV energy range. The main characteristics and operational properties are presented together with the results of first characterization measurements. Finally, two selected experimental examples are given illustrating the capabilities of the spectrometer in PIXE analysis and fundamental research in atomic physics.

Design of a Proton-induced Quasimonochromatic Micro-XRF Setup for Wet Biological Samples

Abstract We designed and constructed a proton-induced quasimonochromatic micro-XRF system for wet biological samples. A horizontal beam of MeV protons delivered by a 1.6 MV tandem accelerator was bent downward by 45° using a dipole magnet. A copper (Cu) foil target was placed perpendicular to the incident proton beam. The thickness of the foil was 30 μm, which is slightly larger the proton range. This Cu foil was used also as a vacuum window for the X-rays. The proton-induced quasimonochromatic X-rays (QMXRs) emitted to the atmosphere through the foil were focused by a polycapillary X-ray half lens. The monochromaticity and intensity of the QMXR microbeam as a function of the incident proton energy were investigated. The QMXR microbeam impinged on the horizontal sample surface with an incident angle of 45°, and emitted fluorescent X-rays from the sample were collected by a Si-PIN X-ray detector positioned at 90° with respect to the incident microbeam. The size of the X-ray beam was 250 μm × 350 μm. To demonstrate the capability of the micro-XRF setup for in-vivo measurement of trace elements in biological samples, we measured cobalt (Co) accumulated in leaves of duckweed floating on a Co solution surface. By using standard samples which simulated the duckweed leaf, the Co concentration in the leaf in the order of 100 ppm could be quantitatively determined.

Selective internal radiotherapy using proton-induced monochromatic X-rays and cancer-targeting nanoparticle sensitizers

In this paper, we propose a highly-selective radiotherapy based on monochromatic X-rays and cancer-targeting gold nanoparticle (GNP) sensitizer. In order to deliver the low-energy monochromatic X-rays which selectively ionize the Au L-shell into the cancerous tissue deep inside the patient’s body, we employ a syringe-needle type X-ray source driven by an MeV proton beam. From a simple numerical evaluation, we found that optimization of the primary X-ray energy was essential to enhance the dose around the nanoparticle. In order to confirm the above idea qualitatively, we performed a simulation experiment in the atmosphere, where 100 nm Au foils were used instead of the GNPs. The experimental result showed that the dose around the Au foils was much higher than that at positions away from the foils, owing to short-range secondary electrons from the foils.

Development of a micro-XRF system for biological samples based on proton-induced quasimonochromatic X-rays

We have developed a micro-XRF system based on a proton-induced quasimonochromatic X-ray (QMXR) microbeam for in vivo measurement of biological samples. A 2.5-MeV proton beam impinged normally on a Cu foil target that was slightly thicker than the proton range. The emitted QMXR behind the Cu target was focused with a polycapillary X-ray half lens. For application to analysis of wet or aquatic samples, we prepared a QMXR beam with an incident angle of 45° with respect to the horizontal plane by using a dipole magnet in order to bend the primary proton beam downward by 45°. The focal spot size of the QMXR microbeam on a horizontal sample surface was evaluated to be 250×350μm by a wire scanning method. A microscope camera with a long working distance was installed perpendicular to the sample surface to identify the analyzed position on the sample. The fluorescent radiation from the sample was collected by a Si-PIN photodiode X-ray detector. Using the setup above, we were able to successfully measure the accumulation and distribution of Co in the leaves of a free-floating aquatic plant on a dilute Co solution surface.

The origin of emeralds embedded in archaeological artefacts in Slovenia

Roman gold jewellery, which was excavated in Ptuj (Poetovio) and consists of a necklace, earrings and a bracelet with embedded emeralds, is part of the Slovenian archaeological artefacts collections. Crystallographic characteristics, inclusions, luminous phenomena and geological characteristics were determined in order to establish the origin of the emeralds. Chemical composition of the emeralds was determined non-destructively using the methods of proton-induced X-rays and gamma rays (PIXE/PIGE). The results were compared with reference emeralds from Habachtal in Austria and with green beryls from the Ural Mts. Literature data for emeralds from Egypt and modern-day Afghanistan area were used to interpret the results. Specifically, these sites were known for emeralds being mined for jewellery in Roman times. It was assumed that emeralds from archaeological artefacts originated from Habachtal in Austria, given that this site was the nearest to the place where found. But the emeralds from the necklace and earrings in fact came from Egyptian deposits. The origin of emeralds from the bracelet could not have been determined absolutely reliably due to the lack of comparative materials; they may originate from a site in modern-day Afghanistan or from Egypt, but certainly not from the same site as the previously mentioned emeralds in the necklace and earrings.

Digital subtraction cineangiography using proton-induced quasi-monochromatic pulsed X-rays

Two different kinds of metallic plates on a rotating disk target were irradiated with a MeV proton beam, and quasi-monochromatic pulsed X-rays with different energies around the absorption edge of the contrast medium were alternately produced. By using these dual-energy X-rays and a high-sensitivity X-ray movie camera, we took a motion picture of the transmission image of a periodically moving phantom, which simulated a rat heart as a test animal. We found that the enhanced movie imaging of the contrast agent is available by subtraction between adjacent picture frames.

The Columbia University proton-induced soft X-ray microbeam

A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium ( K α 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/ e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments.

Analysis of a chondrite meteorite from Slovenia

AbstractThe chondrite meteorite that exploded above the city of Jesenice in north‐west Slovenia on April 2009, and was partly recovered during the subsequent summer months, was investigated by the in‐air method of proton‐induced X‐rays and gamma rays (PIXE‐PIGE) and by microbeam mapping in a vacuum. The chondrules composed of olivine/pyroxene and pyroxenes were identified and the composition of the minerals determined. Different pyroxene types were found in the chondrule core and in the enveloping material. Copyright © 2011 John Wiley & Sons, Ltd.

A compact micro-beam system using a tapered glass capillary for proton-induced X-ray radiography

A compact micro-beam system, containing a tapered glass capillary tube with a tip diameter on the order of 10μm, was constructed to examine the applicability of capillary-generated micro-beams to high-contrast radiography based on proton-induced quasi-monochromatic X-rays. The transport efficiency of swift protons (2–3MeV) through the capillary was examined as a function of the capillary tilt angle and the capillary tip diameter. We obtained transport efficiencies of approximately three times larger than would be expected from the geometrical shape of the capillary. This enhancement indicates that a focusing effect occurred in the capillary. A metallic thin foil was irradiated with the micro-beam and quasi-monochromatic X-rays were produced. By calculating the X-ray yields induced by proton bombardment in the foil and comparing them with the X-ray counts observed at the detector, the throughput efficiency of the X-ray imaging system was evaluated. We demonstrated magnification radiography of a small object to show that a spatial resolution on the order of 10μm was achievable in our system.

COMPOSITION AND OPTICAL CHARACTERISTICS OF ELECTROCHEMICALLY-SYNTHESIZED GaAs NANOCRYSTALS

The synthesis of the GaAs nanoparticles, having sizes 7 nm to 15 nm, by a low cost electrochemical technique has been reported. The absence of any foreign impurity has been confirmed by the Proton-Induced X-rays Emission analysis. Rutherford Backscattering measurement has been performed in order to estimate the thickness of the nanoparticle-generated thin film as a function of the electrolysis current density. The X-ray Photoelectron Spectroscopic study confirms the formation of GaAs and exhibits the binding energy shift of the core shell electrons as an implication of the nanostructure effect. Very weak infrared luminescence due to the radiative recombination of the impurity bound exciton has been detected from yttrium-doped GaAs nanocrystals, even at room temperature.

Comparison of grazing-exit particle-induced X-ray emission with other related methods

Particle-induced X-ray emission (PIXE) is recognized as a trace analysis method; the Bremsstrahlung background, however, still limits the detection power in the low-energy region of spectrum. The grazing-incidence or grazing-exit arrangements are considered to be useful in order to reduce the background intensity. We measure grazing-incidence PIXE (GI-PIXE) and grazing-exit PIXE (GE-PIXE) using an identical sample vacuum chamber to evaluate the performance of both methods. The sample used is a standard sample (Ca, Fe, Ni and Zn) prepared on Si wafer by the spin-coating method. In GI-PIXE mode, a collimated 2.5 MeV proton beam irradiates the surface of the sample at grazing incident angles. However, it was difficult to reduce sufficiently the background intensity in the GI-PIXE spectra because of the Bremsstrahlung background induced by secondary electrons. In the GE-PIXE mode, proton-induced X-rays are measured at grazing-exit angles. The background intensity is reduced, because only the X-rays emitted from the near-surface layer can be detected in the grazing-exit arrangement. Furthermore, the result obtained for an Au–Cu thin film sample by GE-PIXE method was compared with the result obtained by other related methods: grazing-exit X-ray fluorescence and grazing-exit electron probe microanalysis. Similar results were obtained by different methods, indicating that the same phenomena occur in all grazing-exit X-rays measurements. One of the merits of the grazing-exit microprobe analysis method is in microanalysis using a small diameter electron probe; however, the damage by electron irradiation is more severe than that in GE-PIXE.

Kα x-ray emission induced by 1—100 MeV protons

In the course of a feasibility study of high-intensity sources of monochromatic x-rays to be used for XRF, extensive numerical calculations were conducted on the production of characteristic x-rays by proton bombardment of pure element targets. This paper presents the analytical model used for the computer simulations and compares the x-ray production by protons and alpha particles. The K x-ray production cross-section was calculated by the ECPSSR theoretical model and by Paul's analytical formula. The dependence of the x-ray yield on projectile energy, target atomic number, target thickness and irradiation geometry is discussed. The thick target Kα x-ray yields produced by 1—100 MeV proton bombardment were calculated for 66 elements from Na to Pb. From these results, a number of scaling laws and fitting procedures are given for proton-induced Kα x-rays.

Lattice location of B atoms in Ni0.75Al0.15Ti0.10 intermetallic compounds as observed by the channeling method

The lattice location of B atoms doped in Ll2-type Ni0.75Al0.15Ti0.10 intermetallic compounds was investigated by the ion channeling method with a 720 keV proton beam. Backscattered protons, α-particles generated by the 11B(p, α)8Be nuclear reaction and proton-induced X-rays were measured under channeling conditions. The channeling angular profiles for the α-particle yields exhibited a dip for the 〈100〉 and 〈111〉 channels, while a central peak for the 〈110〉 channel was observed, indicating octahedral (O) site occupancy of B atoms. There are two types of O-sites in a Ni2Al-type compound: body-centered positions surrounded by six Ni atoms (site I), and edge-centered positions surrounded by four Ni atoms and two Al atoms (site II). For the 〈111〉 channel, the half-width of the channeling dip for the a yields agreed well to that for the Al Kα X-rays rather than that for the Ni Kα X-rays. Hence, it is concluded that most of the B atoms occupy O-sites of type-I (site-I).

Compton scattering contribution to response function of Si(Li) X-ray detectors

Peaks in the 20–40 keV region of Si(Li) X-ray spectra exhibit pronounced low-energy tailing due to Compton scattering of X-rays en route to the detector. An analytic description of this tailing is proposed and tested using proton-induced X-rays from thick targets. In the PIXE context this provides more accurate extraction of peak intensity and a better description of the matrix background.

Foil thickness measurement via the [formula omitted] intensity ratio of proton-induced X-Rays

A differential method for measuring the thickness of aluminum foils used as X-ray absorbers in thick-target PIXE analysis is described. It involves the change in K β K α X-ray intensity resulting from transmission through the foil and provides better acc than direct X-ray attenuation measurements.

Deviation of the Kβ /Kα intensity ratio from theory observed in proton-induced X-ray spectra in the 22⩽Z⩽32 region

Measurements of I(K beta )/I(K alpha ) for proton-induced X-rays from thin targets in the 22<or=Z<or=32 region confirm a previously suspected systematic discrepancy between experimental data and the theoretical predictions for de-excitation of a single K vacancy in a neutral atom. The present paper is the first proton work to pay specific attention to the KMM radiative Auger satellite and to use a measured resolution function in unfolding K alpha -K beta peak overlaps. A discrepancy is common to electron-, photon- and proton-induced ionisation but sufficient precision is not yet available to reveal any small differences among the three processes, which might arise from differing multiple ionisation.

Proton induced X-ray fluorescence analysis and its application to the measurement of trace elements in hair

This paper describes the use of proton-induced X-rays as the exciting source in X-ray fluorescence analysis. The possible advantages arising from the virtually mono-energetic nature of this radiation are discussed. A system has been developed using this approach for measuring trace element levels in biological samples and the performance characteristics have been evaluated. The system has been used to analyse a range of specimens and the results of analysis of a set of hair samples are presented as an illustration.

Proton-induced characteristic x-rays: a versatile source of ultrasoft x-rays for biological and biochemical investigations

Very low energy (ultrasoft) x-rays of 0.3-5 keV have provided a unique tool for investigation of mechanisms of radiation action, especially with respect to the energy and spatial properties of critical radiation damage in mammalian cells. Experimental investigations to data have been partially limited by the availability and characteristics of suitable ultrasoft x-ray sources. The suitability of small electrostatic proton accelerators, such as exist in many laboratories, have been investigated as a means of producing a secondary beam of ultrasoft x-rays suitable for irradiation of biological and biochemical systems. Results are presented on the physical characteristic of carbon K (0.28 keV) and aluminium K (1.5 keV) ultrasoft x-ray beams produced by bombardment of solid targets of carbon and aluminium with protons of energies up to 750 kV and currents up to 500 mu A. These characteristics are compared with those of a cold cathode discharge ultrasoft x-ray tube previously used for mammalian cell investigations. It is seen that the proton accelerator produces much more versatile beams of characteristic ultrasoft x-rays which greatly extend the scope for future experiments on mammalian cells, micro-organisms and biochemical systems. Nevertheless there are situations in which the cold-cathode discharge tube will remain the source of choice and there are other situations, requiring for example energies between characteristic lines, where the greatly more complex synchrotron radiation sources are required.

Desert varnish in Antarctica: A nuclear microprobe and backscattered 57Fe Mössbauer spectroscopic study

Nuclear microprobe analysis and backscattered 57Fe Mössbauer spectroscopic methods have been used to study the desert varnish surface coatings on samples of dolerite and sandstone from the Taylor Valley area of the McMurdo Dry Valley region, South Victoria Land, Antarctica. With the nuclear microprobe method the oxygen content of the varnish coating and underlying bulk rock was measured directly using the emitted protons from the 16O(d,p 1) 17O nuclear reaction, and also the 871-keV gamma rays emitted from the excited oxygen nucleus. In addition, the iron, calcium and sulphur contents were measured using their characteristic proton-induced fluorescent X-rays. The concentration profiles of these elements are presented in three- and two-dimensional diagrammatic representations. These show that in the Fe-containing dolerites, the desert varnish is formed by subsurface leaching of the Fe from the bulk rock. This is transported to the surface and deposited as a coating of hydrous ferric oxide, probably ferrihydrite, by subsequent oxidation and evaporation. In the essentially Fe-deficient sandstone, the Fe is derived externally from the overlying dolerite sills and is similarly transported and deposited as a varnish coating on the upper surfaces of the sandstone. Windblown inorganic salts, notably thenardite (Na 2SO 4) may be incorporated in the outer layers of the varnish. The backscattered 57Fe Mössbauer spectra recorded using both the conversion electrons and X-rays show that at a depth of ∼ 0.1 μm from the surface the predominant oxidation state of the Fe in the dolerite is Fe 3+, whereas at depths of 10 μm or more it is Fe 2+. For the sandstone it is present only as Fe 3+.