C.P. Swann

An exploratory study with the proton microprobe of the ontogenetic distribution of 16 elements in the shell of living oysters (Crassostrea virginica)

Study of the chemical composition of shell of exoskeletonous organisms in the past has required the sacrifice of the organism. Because the beam of the proton microprobe is relatively nondestructive and analyzes the surface layer of the shell, organisms do not have to be killed. The present paper presents results of a preliminary experiment in which distribution of elements (Na to Sr) in shell of living juvenile oysters, Crassostrea virginica (Gmelin), was studied in situ with a proton microprobe at monthly intervals for four months. The relative concentration of 16 elements was measured in the newly deposited prismatic edge of the right valve of three oysters reared in controlled laboratory conditions. Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Br, and Sr were detected in concentrations as low as a few parts per million relative to the concentration of standards added to pure CaCO3. Concentration of elements varied nominally among shells of the three individual oysters and in their successive ontogenetic stages. Fluctuations in concentration of Na, Mg, S, Cl, Ca, Mn, Fe, Cu, and Zn were generally similar in the two normally growing oysters, but differed from those in the oyster that stopped growing. Trends in concentration of Al, Si, and Sr were similar in the three oysters: those of Br were variable. Relative concentrations of Na, Cl, S, Mn, Fe, and Zn increased slightly with age of oysters, that of the other elements stayed relatively constant. Concentration of most elements was higher in shell than in seawater. Variable concentrations, especially of Na, Cl, and Si in valve edges, tend to support the hypothesis of earlier workers that separate mineral phases are present as impurities entrapped within the shell during calcification.

Chemical elements in the aragonitic and calcitic microstructural groups of shell of the oysterCrassostrea virginica: A proton probe study

We report the results of a study with proton-induced X-ray emissions (PIXE) of the distribution and concentration of 15 chemical elements (Na to Sr in periodic chart) in four microstructural and two mineralogical regions of shell of rapidly growing adult oysters [Crassostrea virginica (Gmelin)]. Hatchery-raised oysters were grown in Broadkill Estuary, Delaware, USA, for 16 wk in summer 1978. Their valve edges were filed as a marker, and the oysters were replaced in the estuary, where they grew rapidly. Shell deposited after marking had a normal microstructure and mineralogy after a narrow zone of disturbance. After 17 d oysters were sacrificed, and different mineralogical and microstructural regions of valves of three oysters, and parts of valves of two oysters, were analyzed for the elements Na to Sr. Quadrats (2.5 × 0.45 mm) included three calcitic groups (prismatic, foliated, chalky) and one aragonitic (myostracal) microstructural group; four quadrats were on the exterior and five on the interior of right and left valves. Inhalant and exhalant margins of valves and ground right and left valves of one oyster were also analyzed. Elemental chemistry of different regions of shell varied among the three microstructural groups within the single calcitic polymorph, between aragonitic and calcitic regions, and between exhalant and inhalant margins of the valves. Elements were most concentrated in the prismatic region of the right valve. Element concentrations were similar in ground right and left valves, except for higher levels of Si, Fe, and Zn in the right valve (corresponding to their high contents in prismatic shell) and of Cl in the left valve (reflecting high concentration in chalky shell, abundant in this valve). Na, Mg, Cl, Cr, Cu, Zn and Br were more concentrated in prismatic than in foliated shell. Chalky shell contained higher concentrations of Na than did prismatic shell, and high concentrations (but lower than in prismatic shell) of Mg, Cl, Ti, Mn, Fe, Zn and Br. Element concentration in myostracum was approximately the same as, or lower than, in foliated shell, except for Sr, which was higher than that in any other shell group. In the right valve most elements were concentrated in inhalant margins, and on the left valve, in exhalant margins. With increased weathering of the exterior surface of prismatic shell, Mg, Si, and Mn increased in concentration and Na, Al, Cl, Ti, Cr, Fe, Br, and Sr decreased.

Effect of composition on thermal stability and electrical resistivity of Ta-Si-N films

The role of composition on the resistivity and thermal stability of sputtered Ta–Si–N films have been studied using X-ray diffraction, Rutherford backscattering spectrometry, and sheet resistance measurement. Films with higher silicon to tantalum ratio were found to be more thermally stable and have higher sheet resistance than films with lower Si to Ta ratio. While Ta0.28Si0.07N0.65 starts to crystallize at about 900°C, Ta0.24Si0.10N0.66 and Ta0.24Si0.12N0.64 were thermal for heat treatment below 1100°C. In-situ sheet resistance measurement also showed that the sheet resistance for the alloys varies with composition and decreases with temperature. Our results indicate that Ta–Si–N films would find other applications in semiconductor devices, beside being used as a diffusion barrier.

Selective filtering in PIXE spectrometry

Abstract The Bartol Research Institutes PIXE facility has made extensive use of selective filters in the study of compositional patterns in archaeological artifacts. The purpose of such filtering is to reduce the intensity of the primary X-rays by up to two orders of magnitude. This allows for an equivalent increase in the beam current and a corresponding reduction in the detection limits for the higher Z trace elements. In this report we bring together all the filter combinations we currently use and discuss their purpose and effectiveness.

Ontogenetic trends of elements (Na to Sr) in prismatic shell of living Crassostrea virginica (Gmelin) grown in three ecologically dissimilar habitats for 28 weeks: a proton probe study

Abstract Distribution of 16 trace and minor chemical elements was examined ontogenetically with PIXE in the calcitic-prismatic margin of the shell of genetically close individuals of Crassostrea virginica (Gmelin) growing in three different marine habitats. Concentration of elements was also related to that in ostreid soft tissues and in suspended sedimentary particles in the ambient seawater. Distribution of the elements (Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Br and Sr) was analyzed every 4 weeks (from May to November) with a non-destructive probe (PIXE) in newly deposited shell of the left valve, and in pigmented, non-pigmented and the right valve of 30 living C. virginica grown for 28 weeks in three dissimilar environments (10 oysters in each habitat): closed laboratory mariculture (HI), closed laboratory mariculture plus suspended sediment (HII) and natural flowing estuary (HIII). The same elements were analyzed weekly in suspended particles (on 0.4 μm Millipore filters) in the culture seawater in HI and HII and in ambient seawater in HIII; and at the end of the study in gills, adductor muscles, gonads and tissues of whole oysters. Elements in suspended sediment were concentrated primarily on the particles; not in the seawater filtrate. Barite crystals were present in some of the plankton samples. Growth rate was slowest in HI oysters, that of HII and HIII was similar and greater than that of HI. Seasonal trends in concentration of elements in valves in the different habitats varied. Ti remained relatively constant in HI valves during culture, but tended to decrease in HII, and increased in HIII. Other elements in HI tended to remain constant (Cu), or to increase (Fe); in HII some elements decreased conspicuously; in HIII some increases were prominent (Mg, Zn). A temporal change in level of many elements in shell paralleled that of the same element in suspended particles (Fe in HI, Mg, Cu, Zn in HIII); levels decreased in HII (Al, Ti, Fe). Parallelism of elemental concentration in shell and suspended particles was expressed as major peaks in both, mostly in HIII, the natural estuarine setting. For Ni, Cu, Zn and Br, especially in HII, peaks were out of phase. Comparison of concentration of elements in old (4th week of culture) and new (28th week) shell showed some trends among the three habitats; consistent association was evident in 10 elements in HIII. Maximal concentration of most elements occurred in the right valve. Pigmented shell contained slightly higher levels of most elements, but differences were only suggestive. After 28 weeks of culture, soft tissues contained several times the concentration of elements, and greater variability, than shell. Maximal concentration (biomagnification) of 13 elements took place in gills, gonads and adductor muscles, but not in whole oysters. There were clear differences in concentration of many of the elements among gills, gonads and adductor muscles in HI, HII and HIII, decreasing or increasing incrementally from HI to HII. Concentration of a few elements was associated in shell and tissues: in shell in HI, Fe, and in HIII, Zn increased during the 28 weeks and was also maximal in the three organs at the end of the study. All other elements (less Ca, Mn and Sr) were more concentrated in tissues than in shell, Zn, Cl and Br to a high degree. The relationship between biomagnification in different organs and the different microstructures of the shell is still unclear. The investigation focused on ecological aspects of biomineralization in living bivalves, an aspect little studied in the past. It was made possible by the use of the non-destructive PIXE probe and suggests a model from which to initiate further comparative studies.

The study of archaeological artifacts using proton induced X-rays

Abstract The Bartol-Delaware proton probe has been used extensively in the study of archaeological artifacts. An AN 2000 Van de Graaff accelerator provides the energetic protons which are brought out into the atmosphere through a small hole in a graphite tip. The induced characteristic X-rays are observed in a Si(Li) detector. For the elements from Na up to Fe or Cu a helium atmosphere and a proton energy of 1.3 MeV are used. For the observation of elements from Fe or Cu upward the proton energy is raised to 2.0 MeV, with air or nitrogen as the atmosphere, and selective filters are placed between the sample under study and the Si(Li) diode. The data displaying the capabilities of this technique were taken from selected samples from India (bronze), Jordan (glass beads) and Crete (potsherds). The importance of proper data analysis is also referred to with specific examples.

PIXE spectrometry in Archaeometry: The development of a system with high spatial resolution

Abstract A new PIXE facility has been constructed at the Bartol Foundation with a tightly-focused proton beam (typically 50 μm across) that allows a variety of inhomogeneous archaeological artifacts to be studied in spatial detail. This paper discusses the practical need for micro-PIXE research in archaeology — applications could include the analysis of metal residues in smelting slag, the solder joins of Classical jewelry, sound metal in corroded bronzes and individual color bands on core-formed glass vessels — and summarizes the role of the various components that comprise the facility itself.

Recent applications of PIXE spectrometry in archaeology I. Characterization of bronzes with special consideration of the influence of corrosion processes on data reliability

Abstract Long-term burial of bronze invariably results in a number of complex chemical processes through which the superficial layers of the metal are converted into cuprite and various kinds of copper chlorides and/or carbonates. Dependent upon the environmental conditions under which such conversions are achieved, minor and trace elements in the bronze are leached out of the bulk metal with varying degrees of efficiency, thereafter tending to accumulate among the corrosion products. We discuss the practicalities and problems involved in the PIXE analysis of ancient bronzes in a nondestructive way, with particular reference to artifacts from ancient Mesopotamia.

Roman mosaic glass: a study of production processes, using PIXE spectrometry

The most attractive Roman glass produced during the early part of the 1st century A.D. was mosaic ware ‐ bowls and dishes molded from arrays of multi-colored canes that created abstract floral and geometric designs. Yet ancient literature tells us little about the organization of the glassworking industry in which such wares were produced. We have focused upon two kinds of mosaic decoration that include a component of white glass in their cane construction and have purple glass as their matrix. A consistent pattern in the minor levels of lead in each kind of glass suggests that they were the products of two separate workshops, each with separate sources of supply for their glass stock. ” 1999 Elsevier Science B.V. All rights reserved.

Color additives and trace elements in ancient glasses: Specialized studies using PIXE spectrometry

Abstract This paper discusses the physical processes of proton induced X-ray emission (PIXE) spectrometry that underlie its general advantages as an analytical tool in the study of ancient glasses, and reviews the practical limitations met in the routine determination of certain elements (e.g., titanium in a calcium-rich matrix, arsenic and tin in an lead-rich matrix). Detection limits are given for 19 elements (minor and trace) that might characterize the source of raw materials used in the making of an ancient glass. Emphasis is laid upon how a controlled variation of the proton beams energy, together with the use of a wide variety of selective filters, allows certain background effects from the X-ray output of dominant matrix elements to be appreciably reduced. Applications include the study of brown and blue decorated glass vessels from the ancient Greek settlement site of Cyrene, in Libya.