The sensitivity of the PIGE analytical technique

The aim of this work is to provide a basis for the estimation of fluorine and lithium contributions to the background of gamma-ray spectra and of their influence on PIGE (Proton-Induced Gamma-Ray Emission) detection limits of lithium, boron, fluorine and sodium. Results for yields and background contributions of lithium and fluorine were obtained from measurements using samples of known composition. Detection limits were determined by extrapolation of those measurements and by calculations based on the inferred background values. Yields were converted in concentrations using the ERYA (Emitted Radiation Yield Analysis) code. This code divides the sample in sublayers parallel to its surface for the integration of the partial gamma-ray yields along the depth of the target.     

PIXE characterization of CsI(Tl) scintillators used for particle detection in nuclear reactions

Particle-Induced X-ray Emission has been used to measure Thallium concentration in several CsI(Tl) scintillators from different manufacturers, in order to check their nominal declared values and correlate their behaviour with actual Tl concentration. Indeed, both Tl doping level and its uniformity affect light emission of these detectors, which are largely employed in nuclear physics experiments.In some of the examined crystals Tl concentration values from PIXE measurements came out to be quite different from those declared. This allowed us to explain apparent anomalies in the trend of their α/γ-induced light yield ratio versus Tl content. In some cases, the presence of unexpected contaminants was also pointed out.     

Measurement of nitrogen depth profile in steel

The characterization of nitridated steel samples, in special the depth profile of nitrogen, aims to help improving the quality of the surface and to increase the durability of the steel pieces. In this work we used ERDA and NRA to determinate the profile of nitrogen in different sets of stainless steel samples. An incident beam of ³⁵Cl of 56 MeV was used for ERDA analysis of a first set of samples. Results indicated an homogeneous distribution for most of the identified elements, with atomic nitrogen concentrations around 2% in the analyzed depth range (0.2 μm) and the presence of thin films on the surface (about 50 × 10¹⁵ at/cm²), one of C and the other of iron oxide. In a second set of samples, 4.43 MeV gamma rays produced from ¹⁵N(H,αγ)¹²C reaction, using an external proton beam of 1.3 MeV, were used to quantify nitrogen concentration. N concentrations of about 0.47% were obtained comparing the gamma production rate of the samples with a referenced material (Stainless steel CRM298 - 0.236% of N in mass) irradiated in the same conditions. Also PIXE analyses were done on both sets of samples in order to identify main elements in the matrix.     

PIGE analysis and profiling of aluminium

In this work we present an alternative method for PIGE analysis of aluminium in thick samples. This method is based on the ERYA - emitted radiation yield analysis - code, which integrates the nuclear reaction excitation function along the depth of the sample. For this purpose, the excitations functions of the ²⁷Al(p,p′γ_1,2)²⁷Al reaction (with gamma-ray energies of 844 and 1014 keV) were employed. Calculated gamma-ray yields were compared, at several proton energy values, with experimental yields for thick samples made of inorganic compounds containing aluminium. The agreement is better than 5%.The 1684 keV resonance of the same reaction, with a natural width of 100 eV, was used to profile samples of Ti implanted with several doses of Al. We show that this resonance, stronger than the 992 keV resonance of the ²⁷Al(p,γ)²⁸Si usually employed for aluminium profiling, leads to similar depth resolution in shorter collection time.     

Quantification of sodium in ancient Roman glasses with ion beam analysis

Concentrations of light elements (Na, Al, Si) in glass have been profiled by comparing the PIGE yields as a function of beam energy to those of a glass standard in combination with PIXE measurements which are used to determine the specific energy loss of protons in the unknown glasses. The technique has been tested on a known sample and applied to a few Roman natron glasses giving results compatible with the morphology of the archaeological samples, as deduced from microscopy. The results have suggested some considerations on the systematic use of the PIGE technique in the determination of bulk sodium concentration in ancient materials.     

Estimating particle size effects in X-ray fluorescence spectrometry

The influence of size of particles on the X-ray fluorescence intensity for powdered substances with different sized particles is estimated, based on a simple modification of the Berry-Furuta-Rhodes formulae. Analytical expressions are obtained for the model of a powder substance consisting of particles of various sizes distributed randomly in the sample volume. The results of calculations by these expressions agree fairly well with experimental data for binary powder mixtures. The particle size effect on X-ray fluorescence for the powders presented is considerably more than one could be predicted by the models proposed earlier.     

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.     

PIXE and RBS analysis of Tl-1223 superconducting phase substituted by scandium

Ion beam analysis techniques (IBA) were performed to determine the elemental stoichiometry of superconducting samples of type TlBa₂Ca_2−xSc_xCu₃O_9−δ, with 0 ? x ? 0.6, prepared via solid-state reaction technique. By combining particle induced X-ray emission (PIXE) with Rutherford backscattering spectrometry (RBS), the stoichiometry of the samples is determined. However, the oxygen content is obtained by using non-Rutherford backscattering cross-section at 3 MeV proton beam. Furthermore, the prepared samples were also characterized using X-ray powder diffraction (XRD) and electrical resistivity measurements. The X-ray data indicate that the partial substitution of Ca²⁺ by Sc³⁺ ions does not affect the tetragonal structure of Tl-1223 superconducting phase. The superconducting transition temperatures T_c, determined from electrical resistivity measurements, was found to be highly correlated to the Sc-content.     

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.     

The application of LA-ICP-MS in the examination of the thin plating layers found in late Roman coins

During the late Roman period the production of complex copper alloy (Cu-Sn-Pb-Ag) coins with a silvered surface, became common practice. Previous analyses of these coins did not solve key technological issues and in particular, the silvering process. Two methods have been suggested for the production of the thin plating layers in late Roman coins the dipping in molten silver chloride and the use of silvering pastes. However, there are questions about their use. More recent research showed that hot-dipping methods, such as the dipping in molten silver chloride, were not really suitable for mass production. Also, the earliest references to the use of silvering pastes dated to 17th century AD. A review of ancient sources and historic literature indicated silver amalgam plating as the possible method for the production of the plating in late Roman coins. Results derived from non-destructive LA-ICP-MS analysis have demonstrated, for the first time, the presence of Hg in the surface layers of these coins. The optimization of the method and the factors influenced the analyses results, are discussed. The examination of the coins by means of EPMA confirmed the ICP-MS results. The introduction of a new technique for the examination of plating layers, helped in the identification of amalgam silvering as the method used in the production of the coins.     

Elemental analysis of light constituents in thin plastic films

Experiments with 1-3 MeV ⁴He beams and 2.2-3.2 MeV proton beams have been performed in order to develop a precise and highly sensitive method for the detection and analysis of light elements in threat or drug materials using simultaneously the RBS and ERDA techniques. Commercially available plastic films have been used as samples. The 1 MeV ⁴He beam has been found to be inadequate owing to the rapid destruction of the targets. Best results have been obtained using proton beams with energies higher than 3 MeV. For 3.2 MeV proton beams, ERDA has been used for the analysis of the hydrogen constituent.     

Methodologies for hydrogen determination in metal oxides by prompt gamma activation analysis

Prompt gamma activation analysis (PGAA), available at The University of Texas at Austin (UT), has been employed for the direct determination of hydrogen content in a series of metal oxide materials typically used as cathodes in lithium ion battery systems. Special attention was given to the experimental setup including potential sources of error and system calibration for the detection of hydrogen. Spectral interference with hydrogen arising from cobalt was identified and corrected for. Limits of detection as a function of cobalt mass present in a given sample are also discussed. PGAA has proven to be a novel and precise technique for the determination of hydrogen in metal oxides. This type of investigation could provide valuable insight regarding the factors that limit the practical capacities of lithium ion oxide cathodes.     

3D Micro-PIXE at atmospheric pressure: A new tool for the investigation of art and archaeological objects

The paper describes a novel experiment characterized by the development of a confocal geometry in an external Micro-PIXE set-up. The position of X-ray optics in front of the X-ray detector and its proper alignment with respect to the proton micro-beam focus provided the possibility of carrying out 3D Micro-PIXE analysis. As a first application, depth intensity profiles of the major elements that compose the patina layer of a quaternary bronze alloy were measured. A simulation approach of the 3D Micro-PIXE data deduced elemental concentration profiles in rather good agreement with corresponding results obtained by electron probe micro-analysis from a cross-sectioned patina sample. With its non-destructive and depth-resolving properties, as well as its feasibility in atmospheric pressure, 3D Micro-PIXE seems especially suited for investigations in the field of cultural heritage.     

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.     

Measurement of neutron total cross-section and resonance parameters of xenon

We measured the neutron total cross-sections of natural xenon in the neutron energy region from 0.1 to 40 eV by using the time-of-flight method at the Pohang neutron facility, which consists of an electron linear accelerator, a water-cooled tantalum target with a water moderator, and a 12-m long time-of-flight path. A ⁶Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.6 cm was used as a neutron detector. Notch filters composed of Co, In, Cd were used to estimate the background level and to calculate the neutron flight path length. The present measurement was compared with the existing experimental and the evaluated data. The resonance parameters of Xe isotopes were obtained from the transmission ratio by using the SAMMY code and were compared with other previous results.     

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.     

Optical appearance of alpha particle tracks in CR-39 SSNTD

A ray tracing method based on geometrical optics was used to study the tracks from alpha particles with different energies and with an incident angle of 50°. The transmission operation mode of the microscope is simulated. Considering the distribution of light intensities from the tracks, the mean and the 80% percentile gray levels from real experiments are proposed as quantitative variables to differentiate among tracks. The gray level properties for the same track for different exposures can vary to large extents. We introduce three variables, κ, λ and ε, to make empirical corrections. It is interesting to see that these coefficients are very consistent for the same alpha particle track despite the very different gray level properties. Gray level results have been obtained for tracks from alpha particles with 50° incident angle and different incident energies. However, the track depths cannot be predicted by any one of the coefficients κ, λ and ε. Multivariate analyses can help separate the tracks corresponding to different alpha energies. By using discriminant analysis with κ, λ and ε as independents, effectively all alpha energies can be determined with an accuracy of ±0.5 MeV.     

Silver surface enrichment controlled by simultaneous RBS for reliable PIXE analysis of ancient coins

Evidence of silver surface enrichment of ancient silver-copper coins has been pointed out in the past years. Surface enrichment can be fortuitous or intentional. In this paper, we have investigated the cleaning procedures usually performed after excavation or in museums. We have shown that chemicals or commercial products routinely used dissolve preferentially the copper phase and consequently contribute to the silver surface enrichment. As a result, surface analyses such as PIXE or XRF can be strongly affected by this effect. By using simultaneously RBS and PIXE, it is possible to check through the silver surface enrichment and then select the reliable measurements, characteristic of the bulk composition. Results on coins recently discovered and mechanically or chemically cleaned are presented.     

Plating of archaeological metallic objects - studies by differential PIXE

The differential PIXE method using an external proton beam up to 3 MeV energy was applied to examine plated layers of tin, silver and gold on bronze, brass, iron and silver objects from Roman and Early Medieval period. The concentration profiles were deduced from the measurements by the method of virtual slicing the target into layers, and minimizing the differences between the measured and calculated X-ray yields. The tinned layers were usually thin (about 1 μm), but the thickness of silver and gold layers was in several cases thicker and exceeded the proton range. The plating techniques were identified as application of the molten metal for tinning, and as fire gilding for the gilded objects.     

EDXRF and micro-EDXRF studies of Late Bronze Age metallurgical productions from Canedotes (Portugal)

Metallurgical production in Central Portugal during the Late Bronze Age was primarily based on copper-tin alloys, despite influences from the Atlantic area where copper-tin-lead alloys are common. Metallic artefacts from archaeological site of Canedotes (Central Portugal) were analysed by EDXRF to establish the type of alloys present. Polished spots in selected artefacts were also analysed by micro-EDXRF to determine the major and minor elemental composition of the original alloys. The collection constitutes 18 copper-tin artefacts and one unalloyed copper artefact with tin and arsenic as minor constituents. Artefacts that require a thermomechanical finishing process, such as tools and weapons, seem to have improved control over the tin content. The composition of two buttons, one cramp and one metallic droplet suggest that some of the copper sources were rich in arsenic. Finally, the low iron content of the artefacts seems to agree well with the smelting of copper ores in crucible furnaces, a smelting process used in certain areas of the Iberian Peninsula until pre-Roman times.