Application of PIXE to study ancient Iranian silver coins

A number of ancient Iranian silver coins belonging to Khosrau II (592-626 A.D.) minted during Sasanians dynasty were analyzed using proton induced X-ray emission (PIXE) technique. The 2 MeV proton beam with a current of 2-3 nA from AEOI, Van de Graaff accelerator was used to bombard the coins. The characteristic X-rays emitted from the samples, were detected by a Si(Li) detector from ORTEC with an energy resolution of 170 eV at 5.9 keV. The detector was placed in the beam direction at 135°. The elements Cl, Ca, Ti, Mn, Fe, Cu, Au and Pb were observed in the coins along with the major component silver. The percentage of silver varied between 85.87 and 93.39%. The possible correlation between the composition of coins and the minting time or the minting location of coins was the prime goal. There was a negative correlation between copper and silver. The weight of coins varied between 4.02 and 4.30 g. Going through the results, it seems that the local mines were used to die-strike the coins. The obtained results are in good agreement with archaeological records.     

Study of the provenance of Belgian Merovingian garnets by PIXE at IPNAS cyclotron

Recent archaeological excavation in Belgium reveals one of the biggest Merovingian necropolis ever found in this country. This necropolis contains 436 tombs with a period of occupation of almost two centuries. Some of these tombs were very rich, especially two of them, and delivered an important funerary furniture. About 60 jewels inlaid with red garnets have been found, most of them of “cloisonné” style (namely about 450 garnets). The new extracted beam set-up of the IPNAS cyclotron (University of Liège, Belgium) has been improved in order to analyse by PIXE these garnets and try to determine their provenance. These analyses reveal that the garnets found in the necropolis of Grez-Doiceau are very homogeneous in composition (almandine garnets) and are coming almost from a unique source.These results have been compared to previous studies led in France during these past five years. This permits to identify the source of almandine garnet situated in India and to highlight differences in garnet supply between France and Belgium in Merovingian times.     

PIXE analysis of obsidian tools from radiocarbon dated archaeological contexts

Obsidian tools from archaeological sites in Turkey and Southern Italy, ¹⁴C-AMS dated to the Neolithic were submitted to IBA analyses at CEDAD, University of Salento, Italy. PIXE and PIGE quantitative analysis of major and trace elements allowed the separation of the samples in different compositional groups corresponding to different sources of obsidian, identified on the basis of published data.     

A DSP-based multichannel analyzer for simultaneous acquisition of coincidence and anticoincidence spectra

A digital signal processor (DSP) based multichannel analyzer (MCA) has been developed for simultaneous acquisition of coincidence and anticoincidence γ-ray spectra. The shaped pulse from the spectroscopy amplifier is digitized by a flash analog-to-digital converter and then processed by a DSP. The coincidence mode operation is implemented by an external gate signal from a coincidence module. Fundamental performance was tested using NaI(Tl) detectors and compared with that of a standard NIM module. The new MCA is currently used for in vivo neutron activation analysis. Further development is in preparation toward full digital processing, which is free from the remaining analog component, that is the spectroscopy amplifier.     

Measurements of linear attenuation coefficients of irregular shaped samples by two media method

The linear attenuation coefficient values of regular and irregular shaped flyash materials have been measured without knowing the thickness of a sample using a new technique namely “two media method”. These values have also been measured with a standard gamma ray transmission method and obtained theoretically with winXCOM computer code. From the comparison it is reported that the two media method has given accurate results of attenuation coefficients of flyash materials.     

Phantom studies of Cd, Hg and Cl by prompt gamma neutron activation analysis using a Pu-Be neutron source

Prompt gamma neutron activation analysis is a means of non-invasive monitoring for occupational exposure to toxic heavy metals such as Cd and Hg. Preliminary kidney detection limits from previous phantom studies at McMaster were 13.6 ± 0.2 ppm for Cd (125 mL phantom) and 315 ± 24 ppm for Hg (125 mL phantom) using the ²³⁸Pu-Be neutron source and 0.88 ± 0.01 ppm for Cd (125 mL phantom) and 16.91 ± 0.05 ppm for Hg (30 mL phantom) using the thermal neutron beam port at the McMaster Nuclear Reactor. The detection limits vary greatly between the two methods due to differences in experimental set-up, neutron energy spectra and a difference in dose by more than a factor of 100. The Hg detection limit from preliminary data is much higher than expected for both neutron source types. In order to explain the apparent detection limit discrepancy, measurements of Hg and Cd phantoms were performed using the ²³⁸Pu-Be neutron source. The results were compared to phantom measurements of Cl, a well-known neutron activation element.     

Compositional studies on Transylvanian gold nuggets: Advantages and limitations of PIXE-PIGE analysis

Minute fragments from nine gold nuggets from Transylvania - two belonging to placer deposits and seven to primary deposits - were analyzed by PIXE and PIGE at the AGLAE tandem accelerator of the Centre de Recherche et de Restauration des Musées de France (C2RMF) with a 3 MeV proton beam extracted into air. This study was triggered by some archaeological provenance issues for which the elemental characterization of the Transylvanian gold source, exploited from the Antiquity, was required. All analyzed Transylvanian gold nuggets are characterized by a consistently high amount of Ag (18% on average). Au and Ag add up to roughly 99%, the other elements - Cu, Fe, Te, Pb - being detected only at a trace level. The obtained results are in good agreement with the previous analyses of Transylvanian gold.     

IBA analyses and lead concentration measurements of AMS-C dated bones from two medieval sites in Italy

AMS (accelerator mass spectrometry) radiocarbon dated human bone samples recovered in the deserted medieval village of Quattro Macine, Lecce, in Southern Italy, were analyzed by PIXE (particle induced X-ray emission) and PIGE (particle induced gamma ray emission). The optimization of the PIXE-PIGE experimental set-up in term of beam energy and detection geometry resulted in the possibility to obtain information about major, minor and trace elements of the samples. Unexpectedly, all the analyzed samples showed a Pb concentration higher than 50 ppm. Two possible explanations of the measured high Pb concentration are discussed in the paper: the pre-mortem intake associated with the use of Pb-rich glazed pottery and the post-mortem intake from soil as the result of diagenetic processes.     

The limitations of associated alpha particle technique for contraband container inspections

Inspection of a shipping container for the presence of the threat materials has been investigated in the laboratory by using a 14 MeV neutron beam, a BaF₂ gamma detector and the associated alpha particle technique. The associated alpha particle technique is proposed as a part of a two sensor system for contraband container inspections. This method is effective in the reduction of background radiation with the possibility of collimating electronically the neutron beam.The intrinsic time resolution has been experimentally estimated to be 1.3 ns (FWHM), which allows inspection of a minimum voxel having 7 cm depth along the neutron flight path. The neutron beam intensity plays a crucial role as a limiting factor for the acquisition time reduction. Single counting rates of the gamma and alpha detector were investigated as a function of the neutron intensity, distance between the gamma detector and the neutron source and the type of shielding. The time and the energy spectra for different neutron intensities were evaluated.     

Characterisation of an enamelled metallic object found in Guerrero Negro (Baja California) by PIXE and RBS techniques

The coast of Guerrero Negro (Baja California) has been known for a long time by archaeologists for its shipwrecks. Archaeologists are recovering objects that come from sunken Spanish galleons in the colonial period, and reach the American coast in the frontier of the USA with Mexico.An enamelled metallic object was found next to the beach in Guerrero Negro. We have analysed the piece with proton induced X-ray emission (PIXE) and Rutherford backscattering (RBS) in an attempt to establish whether the object could come from one of the colonial shipwrecks and to valuate its cleaning process.Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) have been also performed in three samples taken from the object in order to observe the heterogeneity of the material.The materials found revealed the presence of typical lead-glass enamels from with pigments such as cuprite (red), or lead-tin yellow used in colonial times. The metallic part consisted of brass. As for the cleaning process, the average efficiency considered as the weight% of chlorine removed, was of 83.4% for brass and 100% for enamels.     

PIXE characterization of Lebanese excavated amphorae from Jiyeh archeological site

Archaeological excavations were undertaken in the Jiyeh archeological site which is located north of Sidon, identified as the Greco-Roman Porphyreon. The first investigations raised suggest a probable pottery production centre. About 40 sherds were analyzed by Proton Induce X-ray Emission technique PIXE in order to identify and characterize the elemental composition of four types of amphorae, using the 1.7 MV tandem accelerator in Beirut. The analysis protocol provided almost 24 elements in one spectrum, including majors, minors and traces. The elemental composition provided by PIXE and based on 12 most abundant elements, ranging from Mg to Zr, was used in a multivariate statistical program and consequently the studied objects were classify into well defined groups.     

Micro-SR-XRF and micro-PIXE studies for archaeological gold identification - The case of Carpathian (Transylvanian) gold and of Dacian bracelets

Trace-elements are more significant for provenancing archaeological metallic artifacts than the main components. For gold, the most promising elements are platinum group elements (PGE), Sn, Te, Sb, Hg and Pb. Several small fragments of natural Transylvanian gold - placer and primary - were studied by using micro-PIXE technique at the Legnaro National Laboratory AN2000 microbeam facility, Italy and at the AGLAE accelerator, C2RMF, Paris, France and by using micro synchrotron radiation X-ray fluorescence (micro-SR-XRF) at BESSY synchrotron, Berlin, Germany. The goal of the study was to identify the trace-elements, especially Sn, Sb and Te. A spectacular application to five Dacian gold bracelets authentication is presented (Sn and Sb traces).     

PIXE as a complement to trace metal analysis of sediments by ICP-OES

The adverse effects of metal contamination in sediments require methods that can quickly and accurately assess the extent of environmental pollution. Particle induced X-ray emission spectrometry (PIXE) is demonstrated to be a viable alternative to an established method, which consists of acid digestion and Inductively coupled plasma-optical emission spectrometry (ICP-OES) to measure trace metals in sediment. The analysis of trace metal composition by both techniques on a NIST Standard Reference Material mud gives results that are consistent with the certified values for fourteen measured metals, seven of which are common to both methods. A comparison study conducted on a sediment core from a freshwater lake with a known chromium contamination in Muskegon County, MI also shows a good correlation between the methods for transition metals of environmental interest over a wide range of metal concentrations. Total sample preparation and analysis time for the PIXE measurements is roughly one third that of acid digestion and ICP-OES. Also, the acid digestion step does not elute all the metal, while the nondestructive PIXE approach is a total metals analysis method. However the PIXE method generally has higher limits of detection for many environmental metal contaminants. By combining the two techniques, the acid digestion elution factor can be quantified by running PIXE on an original sample and on the residue resulting from acid digestion.     

Fast analytical methods for the correction of signal random time-shifts and application to segmented HPGe detectors

Detection systems rely more and more on on-line or off-line comparison of detected signals with basis signals in order to determine the characteristics of the impinging particles. Unfortunately, these comparisons are very sensitive to the random time-shifts that may alter the signal delivered by the detectors. We present two fast algebraic methods to determine the value of the time-shift and to enhance the reliability of the comparison to the basis signals.     

Differential and scanning-mode external PIXE for the analysis of the painting “Ritratto Trivulzio” by Antonello da Messina

Extensive PIXE investigations have been performed at the LABEC accelerator laboratory in Florence on the painting “Ritratto Trivulzio” by Antonello da Messina, one of the great Italian masters of XV Century and a pioneer in modern oil painting.It is well known that a complete and unambiguous characterisation of materials in paintings is often difficult, owing to their complex structure. For the “Ritratto Trivulzio”, the combination of advanced variants of PIXE, such as differential and scanning-mode analysis, provided a relevant contribution to the characterisation of paint layers, in terms of composition and structure, in a totally non-invasive and non-destructive way.Single-spot mode PIXE with external proton beams of about half millimetre diameter was first used for a general characterisation of different areas of the painting. Differential PIXE performed in many spots led to reconstruct the sequence of paints employed by the artist and to estimate in some cases the local paint layer thickness.A second run carried out with the external scanning microbeam facility, using a 3 MeV proton beam of about 80 μm size, was then crucial to clarify some issues raised by the first analysis. In particular, elemental maps from selected areas helped to understand the way some colour shades had been obtained on the red mantle of the portrayed gentleman, using different pigments irregularly distributed on the surface.     

Analysis of C, N and O in aerosol collected on an organic backing using internal blank measurements and variable beam size

A method with low MDL (minimum detection limit) was developed for analysis of carbon (C), nitrogen (N) and oxygen (O) in aerosol samples collected on an organic backing. An accelerator-produced beam of protons interacting with the sample and the detection of elastically scattered protons (PESA; particle elastic scattering analysis) and emitted X-rays (PIXE; particle-induced X-ray emission) were the basic components of the setup. The method is based on measurement of internal blank concentrations, i.e. measurement of the blank concentration outside the aerosol deposit in each sample, and the use of two sizes of the beam in order to improve the MDL of the analysis. Large beam size covering the entire aerosol deposit was used to obtain quantitative analysis with PIXE. Small beam was used to obtain relative elemental concentrations with PESA and PIXE, which were transformed to absolute values by the aid of large-beam analysis. The small-size-beam served two purposes: to make internal blank measurements feasible and to improve the signal ratio of aerosol-deposit to backing. Compared with the traditional way of analysis, using a beam that is larger than the deposit and specially prepared blank samples, the new method reduced the MDL of C, N and O by a factor of 130, 70 and 90, respectively. The new method was applied to aerosol samples collected in the upper troposphere and the lowermost stratosphere from the CARIBIC platform. As far as the authors know, these measurements are the first quantitative determinations of C, N and O in the aerosol of this part of the atmosphere. The results show that these elements together with sulfur are major components of the aerosol.     

The new Cyclone 18/9 beam transport line at the CNA (Sevilla) for high energy PIXE applications

The Cyclone 18/9 cyclotron system at the Centro Nacional de Aceleradores (Sevilla, Spain) is commonly used to create short life radioisotopes for PET applications. Besides, an external beam transport line has been recently installed in one of the target ports with two major purposes: to study the effects of 18 MeV protons irradiation on the behaviour of electronic devices for space applications and to complement the analysis of materials using our 3 MV tandem accelerator with the PIXE measurements at high energy.In this work, the main elements of our beamline will be briefly described and the first PIXE application will be presented. The usual PIXE, in the analysis of archaeological metallic objects, using around 3 MeV protons requires having a shiny area. Our purpose is to obtain a deeper determination of the bulk composition bombarding with 18 MeV protons through the corroded samples surfaces, without polishing the ancient object. To check this methodology high energy PIXE has been performed on two fibulae of the Later Bronze Age and First Iron Age, coming from the area around Sevilla.     

Comparison of the analytical sensitivities for non-1/v elements in different neutron beams

Irregular nuclides such as ¹¹³Cd, and some rare-earth isotopes show different analytical sensitivities in PGAA performed at different facilities, because the cross-sections of these nuclides have strong low-energy resonances which partly overlap the energy range of typical neutron beams used for activation. A series of systematic measurements has been performed in the spectrally different cold and thermal neutron beams of the Budapest Research Reactor, Hungary and at the research reactor of NIST, Gaithersburg, USA to quantitatively study the non-1/v behaviour of irregular nuclides. Samples were prepared that contained one of the irregular nuclides and also a regular one (¹⁰B, ³⁵Cl and ⁵⁶Fe) and their activation ratios were compared as measured in five different beams. Theoretical values of the activation ratios were calculated from estimates of the actual neutron spectra and cross-section data, and show a generally good correspondence to the experimental results, although some details are still not reproduced.     

Use of silicon drift detectors for the detection of medium-light elements in PIXE

In order to fully exploit in PIXE the superior performance of silicon drift detectors especially for the detection of low- and medium-energy X-rays, avoiding in particular the negative effects of backscattered particles, we developed a custom spectrometer based on a 10 mm² chip with a thermoelectric Peltier cooler and home-designed front-end electronics, coupled to a weakly focusing polycapillary lens.This paper briefly describes the detector + lens assembly and reports the results of first tests carried out at an external beam line of the LABEC laboratory in Florence. Excellent energy resolution is achieved under real operating conditions in a PIXE run (measured FWHM at 1 keV is 81 eV with a count-rate of 480 cps) and also the lineshapes are very good (FW1/10M over FWHM ratio is 2.1). As a whole, our preliminary tests gave encouraging results and also helped to point out some aspects which it is worthwhile to investigate further (e.g. how X-ray peak intensity ratios may be affected by inaccurate lens alignment), in order to profit fully from such a good performance of the spectrometer.     

PIXE analysis of chromium phytoaccumulation by the aquatic macrophytes Eicchornia crassipes

The uptake of hexavalent chromium in free living floating aquatic macrophytes Eicchornia crassipes cultivated in non-toxic chromium-doped hydroponic solutions is presented. A Cr-uptake bioaccumulation experiment was carried out using healthy macrophytes grown in a temperature controlled greenhouse. Six samples of nutrient media and plants were collected during the 23 day experiment. Roots and leaves were acid digested with the addition of an internal Gallium standard, for thin film sample preparation and quantitative Cr analysis by PIXE method. The Cr⁶⁺ mass uptake by the macrophytes reached up to 70% of the initial concentration, comparable to former results and literature data. The Cr-uptake data were described using a non-structural first order kinetic model. Due to low cost and high removal efficiency, living aquatic macrophytes E. crassipes are a viable biosorbent in an artificial wetland of a water effluent treatment plant.