PIXE System Research Articles

Comparison of analogue and digital silicon drift detectors in PIXE analysis

The AXAS-A silicon drift detector that has been a part of the University of Guelph PIXE system for over a decade has recently been replaced by an AXAS-D unit. The calibration process previously performed on the AXAS-A, which uses a suite of high purity, “thick-target” single element and simple compound standards, was repeated for the AXAS-D. This allows for comparison between the analogue and digital approach to measuring PIXE spectra. The similarities between the results of the two detectors and the high accuracy found in geological applications affirm the validity of the use of an energy-dependent calibration factor within the GUPIX software. The upgrade to a digital detector offers multiple advantages. Unlike the AXAS-A, the AXAS-D contains a pre-amplifier and digital pulse processing circuitry and therefore requires significantly less supporting equipment. The improved count rate of the AXAS-D decreases the time required to complete projects.

Quantification of major and trace elements contained in aircraft JET A-1 fuel by in-vacuum PIXE analysis

To characterize the chemical composition of aircraft exhaust particles, we developed a treatment method of jet fuel for an elemental analysis by an in-vacuum PIXE system. Eleven elements (Si, S, Cl, K, Ca, Cr, Fe, Ni, Cu, Zn, and Pb) were identified from each sample. The concentrations of S from five JET A-1 fuel samples collected on different days ranged from 30.4 to 440 wt.-ppm. The concentration level of S agreed well with the measurement results obtained by an in-air PIXE analysis, which we have previously performed to determine the major content elements and their concentration levels. Nine elements out of the identified 11 elements (Si, Cl, K, Ca, Cr, Ni, Cu, Zn, and Pb), which were not detected by the in-air PIXE analysis, were detected in all the JET A-1 fuel samples measured. Among these elements, Si, Ni, Cu, Zn, and Pb were found to be the major components. It is suggested that particles emitted from aircraft jet engines, which are generally in the size range smaller than 100 nm (ultrafine particles: UFPs), may contain Si, Ni, Cu, Zn, and Pb. These findings provide useful insights into the source apportionment of UFPs in and around airports.

Elemental analysis of jet engine lubrication oil and jet fuel using in-air PIXE

To understand the elemental characteristics of the exhaust particles from a jet aircraft, we performed an element analysis using an in-air PIXE system of the different lubrication oils of a jet engine (Mobil Jet Oil II, Mobil Jet Oil 254 and Eastman Turbo Oil 2380) and the jet fuel (JET A-1) to determine the effects on the exhaust particles. A high concentration (1,400–2,500 wt.-ppm) of P was detected from the analyzed three oil samples. The high concentration of P is probably due to the tricresyl phosphate (TCP: C[Formula: see text]H[Formula: see text]O4P) contained in the oil samples. The S concentrations of the JET A-1 fuel samples with different collection dates were in the range of [Formula: see text]10 to 530 wt.-ppm. These results aid in determining the component features of nanoparticles emitted from an aircraft.

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.

Role of the mass attenuation coefficient database in standardization of a silicon drift X‐ray detector for PIXE analysis

A simple, inexpensive procedure is described for calibrating a silicon drift detector‐based PIXE system for the analysis of geological and other “thick‐target” materials. It rests on the use of single element, chemical compound, and National Institute for Standards and Technology multielement standards. Much less effort has been focussed on the impact of mass attenuation coefficients on PIXE's analytical accuracy than on ionization cross sections and fluorescence yields. The calibrated system enables us to investigate the effects of inserting different mass attenuation coefficient datasets into the GUPIX database. For the K X‐rays of light elements, accuracy is significantly improved by replacing the formerly used XCOM self‐attenuation coefficients by the corresponding FFAST values; this effect decreases rapidly with increasing atomic number. Similar improvement was found for L X‐rays of medium‐Z, but not for high‐Z atoms.

Preliminary Study on the Elemental Quantification of in Ambient Liquid Samples of Microliter Volume Using the In-air Micro-PIXE Technique

Quantifying the trace elements in infinitesimal ambient liquid samples (e.g., single raindrop, cloud/ fog water, and the soluble fraction extracted from the particles collected for a short time) is an important task for understanding formation processes, heating/cooling rates, and their health hazards. The purpose of this study is to employ an in-air micro PIXE system for quantitative analysis of the trace elements in a thimbleful of reference liquid sample. The bag type liquid sample holder originally designed with 10 μm thick Mylar ® film retained the original shape without any film perforation and apparent peaks of film blank by the end of the analysis. As one of tasks to be solved, the homogeneity of the elemental distribution in liquid reference species was verified by the X-ray line profiles for several references. It was possible to resolve the significant peaks for whole target elements corresponding to the channel number of micro-PIXE spectrum. The calibration curves for the six target elements (Si, S, Cl, Fe, Ni, and Zn) in standard solutions were successfully plotted by concentration (ppm) and ROI of interest net counts/dose (nC).

Setting up of in-vacuum PIXE system for direct elemental analysis of thick solid environmental samples

Experimental set-up, development, characterization, and calibration of an in-vacuum PIXE system at the tandem accelerator facility of the Atomic Energy Commission of Syria (AECS) is described. The PIXE system calibration involved experimental characterization of the X-ray detector parameters and careful determination of the H-values that control dependence of the detector solid angle with the X-ray energies and correct imperfect values of the detector efficiency. Setting up of an electron flood gun to compensate charge built up and utilization of a beam profile monitor to perform indirect measurement of the beam charge, provide a direct PIXE measurement of thick insulating samples in-vacuum. The PIXE system has been subsequently examined to verify its ability to perform direct PIXE measurements on geological materials. A combination of minimum sample preparation procedures and specific experimental conditions applied enables simple and accurate elemental analysis. Elemental concentrations of several elements heavier than sodium in different reference geological samples, at about 5–10% absolute accuracy for most elements, have been determined. Comprehensive discussion of the obtained elemental concentration values, for most elements of visible X-ray peaks in the PIXE spectra, has been considered.

Improvement of Low-Energy PIXE System for Precise Surface Analysis

Improvement of Low-Energy PIXE System for Precise Surface Analysis

Development of a WDX-μ-PIXE system for chemical state mapping

In this paper, we have developed a wavelength dispersive X-ray spectrometer microparticle-induced X-ray emission (WDX-[Formula: see text]-PIXE) system combining a microbeam system with high spatial resolution and wavelength dispersive X-ray (WDX) spectrometry with high-energy resolution for chemical state mapping. A Von Hamos geometry was used for the WDX system to achieve higher detection efficiency and energy resolution. The system consists of a curved crystal and a CCD camera. The WDX system was installed in a newly developed microbeam system. The energy resolution of the WDX system was 0.67 eV for [Formula: see text] (1740 eV). [Formula: see text] and [Formula: see text] X-ray spectra from various Si compounds were measured and chemical shifts related to chemical states were clearly observed. The system was applied to the chemical state analysis of clay particles. After elemental mapping of the clay particles using a conventional [Formula: see text]-PIXE system with a Si(Li) detector, particles to be analyzed were selected and analyzed sequentially with the WDX system. [Formula: see text] spectra from clay particles were obtained. The microscopic spatial distribution of elements and chemical state of the clay particles were sequentially measured with high energy and spatial resolution using a microbeam.

Development of a high-current microbeam system

We report on the development of a high-current microbeam system for wavelength-dispersive X-ray micro particle-induced X-ray emission (WDX-[Formula: see text]-PIXE) for chemical state mapping. The microbeam system is composed of two slits and a quadrupole doublet lens mounted on a heavy rigid support. The microbeam system is installed immediately after a switching magnet. A beam brightness of [Formula: see text] is obtained at a half-divergence of 0.1 mrad. A beam current of more than 300 pA is obtained for object sizes of [Formula: see text] with a half-divergence of 0.2 mrad, which corresponds to a beam spot size of [Formula: see text]. The calculated spot size of the beam was [Formula: see text] and the measured spot size was [Formula: see text]. The WDX-[Formula: see text]-PIXE system with the microbeam system is now operational.

Quantitative analysis with a two-detector measuring system in in-air PIXE-design to improve detection sensitivity at low energies

In this paper, a two-detector measuring system in in-air PIXE system composed of two Si(Li) detectors has been developed for simultaneous measurement of low- and high-Z elements. In order to improve detection sensitivity of the detector for low energy region, a new device which is attached at the tip of the detector has been designed. It is made of acryl and has a thin end on which a 1.5 μm-thick Mylar film is stuck. As a result, it exhibited a miraculous effect in improving detection sensitivity at low energies and it became possible to detect K X-rays of aluminium. In order to perform quantitative analysis in in-air system, we have measured detection efficiencies for the two Si(Li) detectors including the effect of X-ray absorption in air on the basis of the method that we developed. Concerning the beam energy at the target and corresponding X-ray production cross-sections, the same values as were reported in the previous paper were applicable since conditions of irradiating system were unchanged. It was confirmed that the new method allows us to quantitatively analyze all the elements heavier than aluminum and to obtain mostly the same results as those by in-vacuum PIXE for various kinds of samples. Accuracy of analysis was also confirmed by using a standard material.

Compositions of Xylem Fluid of Arsenic-Stressed Barley Seedlings: A Measurement with PIXE System and HPLC

Compositions of the xylem fluid of arsenic (As)-stressed hydroponic barley (Hordeum vulgare L. cv. Minorimugi) were investigated. The seedlings were treated with 0, 6.7, 33.5, and 67 μM As in the form of arsenite. The xylem fluids were collected from the cut surface of plants 14 days after treatments and analyzed. Arsenic toxicity reduced the flow rate of xylem fluid. Mineral concentrations of the xylem fluid were measured with particle-induced X-ray emission system, but organic solutes were measured with high-performance liquid chromatography. Arsenic did not influence the concentrations of phosphorus (P), potassium (K), magnesium (Mg), and iron (Fe) very much. However, the concentrations of manganese (Mn), zinc (Zn), and copper (Cu) increased resulting in fairly stable translocation of the elements. The concentration and translocation of Ca decreased in the xylem fluid with increasing As concentrations in the medium. Arsenic concentration increased with increasing As in the nutrient solution, but its translocation decreased. Arsenic treatments did not affect phytosiderophore concentration very much, but their translocation decreased. The concentration of citrate increased but that of malate and succinate decreased in 33.5 μM As-treated plants.

PIXE STUDY ON THE GROWTH ENVIRONMENT OF PLANTS

Growth environment of plants was investigated by analyzing the elemental concentration in leaves of the plants. Camellia was selected as the sample and the leaves of the camellias were collected from Miyagi and Chiba prefectures. The species of elements and their concentrations in the leaves were measured by the in-air PIXE system at Tohoku University. More than 10 elements were detected from the leaves. The concentrations of Mn , Fe , and Rb in the leaves were strongly affected by the place where the tree grew. On the other hand, the concentration of P, S, K, and Ca were less affected by the place of the tree. The determination of the place of the tree was also performed by evaluating the similarity of the elemental concentration in the leaves quantitatively. The difference due to the place was clearly identified and the sampling place was successfully determined by using the elemental concentrations in the leaves.

PIXE ANALYSIS OF DYES USED IN TRADITIONAL JAPANESE CARPETS (NABESHIMA-DANTSU)

NABESHIMA-DANTSU is the name of the first Japanese-made carpets which have been produced in the Nabeshima domain (Saga Prefecture) since the later Edo period. The NABESHIMA-DANTSU carpets have been woven from one kind of cotton, and have been dyed with various dyes and color fixatives. We analyzed pieces of the NABESHIMA-DANTSU carpets stored in the Saga Prefectural Museum and the Saga Prefectural Art Museum, by using PIXE method in order to detect dyeing methods used in them. We also analyzed dyes, color fixatives and cotton used in the traditional Japanese dyeing method. From the NABESHIMA-DANTSU carpets, small amounts of dyed and non-dyed samples were picked up and were analyzed by in-air PIXE system at Tohoku University. It was found that Fe and Cu are related to the parts dyed orange, and Al is related to the parts dyed green. The analysis of cotton dyed by the traditional Japanese method shows the similar results. It means that both colors in the NABESHIMA-DANTSU carpets were dyed by the traditional Japanese method which uses natural dyes. From literature documentation, it is considered that synthetic dyes were mainly used during the Taisho era. The present result shows that natural dyes might have been used in the Taisho era. In this research the PIXE method has proved to be very effective for the analysis of dyeing methods.

Construction of a confocal PIXE set-up at the Jožef Stefan Institute and first results

A new confocal PIXE set-up at the Jožef Stefan Institute in Ljubljana was recently designed and built. It consists of a silicon-drift detector, a specially designed polycapillary lens and a snout-alignment interface for precise positioning. It allows detector movement in all directions and therefore precise alignment during the creation of the probing volume and the possibility of simultaneous use of other complementary techniques, including standard μ-PIXE measurements with another X-ray detector. A description of the new set-up is given, as well as a short presentation of the method itself. Two custom-designed types of X-ray lenses were tailored and manufactured for this application, a standard semi-lens and a polycapillary conic collimator; both were characterized and compared within the scope of development of the confocal PIXE system. First results of depth profiling with the beam scanning mode are shown.

MEASUREMENT OF CHEMICAL STATE CHANGE OF PHOSPHORUS DURING MEV-PROTON IRRADIATION BY A HIGH-RESOLUTION WAVELENGTH-DISPERSIVE PIXE SYSTEM

Chemical state changes of phosphorus induced by proton irradiation were measured by a high-resolution wavelength-dispersive (WD) PIXE system. Six standard samples of phosphorus with different chemical states ( Ca ( H 2 PO 4)2• H 2 O ( P 5+), CaHPO 4•2 H 2 O ( P 5+), NaH 2 PO 4 ( P 5+), CaHPO 3• H 2 O ( P 3+), Ca ( H 2 PO 2)2 ( P 1+), and NaH 2 PO 2• H 2 O ( P 1+)) were prepared for the measurements. The P - K α1 peak energy for the sample of P 3+ increased after the irradiation. The peak energy of the P 3+ sample became nearly same as that of P 5+ after irradiation with more than 2 ×107 Gy . This result indicates that P 3+ in the sample has changed to P 5+ due to proton irradiation. On the other hand, the P - K α X-ray spectra for the samples of P 5+ didn't show any interesting changes even for much higher proton dose (3.4 × 108 Gy ). Also, P - K α peaks which correspond to chemical states ( P 5+ and P 3-) other than original state were observed for the sample of P 1+ in the region of more than 107 Gy .

Chemical shift measurements of chlorine K X-ray spectra using a high-resolution PIXE system

A high-efficiency high-resolution wavelength-dispersive spectrograph with a von-Hamos configuration was developed for chemical state identification of elements in environmental samples using PIXE analysis. To evaluate the performance of this system, chlorine K X-ray spectra for NaCl, NH4Cl and polyvinylchloride (PVC) targets were measured and compared. Also, to study the applicability to environmental mixed samples, mixtures of NaCl and NH4Cl with different mixing ratios were measured. Through observation of Cl Kα1 X-ray from NaCl, the energy resolution of the system was determined to be 1.1eV. For the NaCl sample, a Kβx line was observed at an energy, which is higher than that of the Kβ main peak by 2eV, whereas no Kβx emission was observed for the NH4Cl sample. The chemical shift of the Kβ main peak for PVC relative to that for NaCl was about 1.2eV. For NaCl–NH4Cl mixture targets, the relative intensity of Kβx satellite to the Kβ main line provided an indication of mixing ratio. Energies and relative intensity of Cl Kβ X-ray satellites for NaCl and NH4Cl samples calculated by a simple molecular-orbital method agreed only qualitatively with the experimental results.

PIXE ANALYSIS OF UMEBOSHI (DRIED PLUM)

In recent years, the self-sufficiency ratio of food in Japan has gradually decreased and 60% of foods are now imported from abroad. Japanese people rely strongly upon imported food and should take care of their safety, but what is happening now is that soil pollution in country of origin grows into a serious problem and can affect imported food. Umeboshi is one of the traditional pickled food in Japan and very popular. In the case of umeboshi, more than 65% of it is imported. We analyzed imported umeboshi and domestic ones by using in-air PIXE system and submili-PIXE camera at Tohoku University. In this experiment, the concentrations of toxic heavy metals such as As, Cd, Hg and Pb were lower than standard values given by a food hygiene law. Concentrations of elements heavier than Ca show similar trend among each sample. On the other hand, lighter elements than Ca show large differences, which is related to food coloring or processing technique.

SIMULTANEOUS MEASUREMENT OF TWO DIFFERENT TARGETS BY MEANS OF VACUUM AND IN-AIR PIXE

A simultaneous measuring system of two different targets by in-vacuum and in-air PIXE has been developed in order to improve efficiency of analyses in the limited machine time. The proton beam passes through a thin target in vacuum and it allows us to perform in-vacuum PIXE, and the beam is further transported to the in-air PIXE system for analyzing another target. The beam intensity for in-air PIXE while performing in-vacuum PIXE is 1.5 nA, which is almost sufficient. The effect of slight changes in the beam transport parameters on the background X-rays for both in-vacuum and in-air PIXE has been found to be negligible. As a result, it is confirmed that accuracy and sensitivity of analysis for many kinds of sample, such as various samples in earth, environmental sciences and in bio-medicine, are almost unchanged for the both systems, and a four-detector-simultaneous measuring system has been completed. It is expected that the system will work miracle for solving the problem of deficient machine time in our laboratory.

PIXE ANALYSIS OF ATMOSPHERIC AEROSOLS FROM ASIAN CONTINENT

A large amount of yellow sand dust from Asian continent transported to Japan by air, affecting traffic, climate and human health. The yellow sand is known as a natural phenomenon, but it is mixed with anthropogenic aerosols over the industrial area in East Asia and causes environmental pollution. In addition, atmospheric turbid phenomena are occasionally observed in spring of recent years over western part of Japan. This phenomenon is caused by the increase in the amounts of fine particles. For a better comprehension of such turbid phenomena, we collected aerosols at Nagasaki. At the same time, particle number concentrations were observed by OPC. The samples were analyzed by an in-air PIXE system at Tohoku University. Time series of elemental concentrations and particle number concentration were obtained. It found that the yellow sand dust phenomenon occurred when coarse particles reached high concentrations, and elemental concentrations of Si, Ca, Fe, Pb and Hg showed similar variations along with that of coarse particles. On the other hand, when fumes or mists were observed, concentrations of fine particles were also correlated with concentrations of S and Zn.