The degree of crystallinity and unit cell parameters have been determined using WAXS on a number of compression molded high-density polyethylene (HDPE) plaques processed at widely varying conditions of crystallization and annealing times and temperatures. Changes in unit cell parameters with variations in processing conditions can be explained in terms of increases in lamellar thickness of polyethylene crystals with increasing thermal treatments. Concomitant increases in the degree of crystallinity of these samples can also be explained in terms of lamellar thickening and other changes in polyethylene morphology. Crystallinity determinations using XRD data are also compared with values determined by differential scanning calorimetry (DSC) and solid-state 13C nuclear magnetic resonance (NMR). Comparisons of crystallinity values obtained by these three different techniques can reveal details of the morphology of HDPE including the presence of an interfacial zone in addition to the crystalline and amorphous components of the system.

We describe a new X-ray fibre diffractometer, consisting of a commercial X-ray sensitive video camera coupled to a conventional 3-circle goniometer in place of a more traditional single-point detector. The active element of the video camera is a charge-coupled device (CCD). Diffraction images, obtained at various goniometer settings, are transformed into reciprocal space, and combined to give a complete section through the origin and parallel to the symmetry axis of cyiindrically averaged reciprocal space. A greater density of measurements is needed in the vicinity of the reciprocal fibre axis in order to avoid information loss due to the curvature of the Ewald sphere. The pros and cons of using CCD's as X-ray detectors are discussed and sample results from polymer fibres are shown.

With the increased use of composite materials, it has become increasingly important to perform analysis that quantifies the amount of crystal lographic orientation. In polymers fibers and films the orientation is used to predict the physical properties, such as strength. To determine the orientation it is first necessary to collect a pole figure on a specific reflection. With the conventional powder diffiactometer equipped with an Eulerian cradle, the data collection procedure often lakes a few hours. Additional time is involved for separate background measurements, which are collected at 2θ positions away from the peak. Also, the intensity from these samples is usually weak, requiring increased data collection time to improve counting statistics.

Using an area detector decreases the data collection time significantly, because the background experiments are performed simultaneously. We can collect the entire pole figure on both polymer fibers and films in less than one hour using a series of “frames.” The pole figure is determined by integrating over 2θ regions in each frame. For fibers the rules developed by Stein are used to calculate the Hermans orientation factors. For films, the rules are generalized to make them more suitable for biaxial orientation, and the White-Spniieli biaxial orientation factors are reported.

A normal coordinate approach was used to generate ciystallographic packing candidates of a multitorsional polyimide synthesized from 3,3′,4,4′-benzophenonetetracarboxylic acid (BTDA) and 2,2-dimethyl-l,3-(4-aminophenoxy)propane (DMDA) (PI-2). Candidates were obtained under conditions of fixed axial advance of 24.6 Å per monomer, and imposed 2/1 helical or 1/0 transiational symmetry, consistent with the observed WAXD meridional layer line spacing [1]. The ability of comb in atori ally generated torsional states to adopt the desired geometry was examined. Necessary corrections to die conformational parameter equations originally derived by Kusanagi, et al. [2|, have been made. The procedure described allowed crystallographic conformations satisfying explicit geometric and MM3 intramolecular energy criteria to be generated for a linear multitorsional polyimide prior to the application of crystallographic screening or refinement procedures.

The ability to prcbe the structure of a polymer during deformation is of considerable technological interest as it lends an insight into the mechanisms involved in polymer processing. The behaviour of Liquid Crystalline Polymers (LCP's) during shear flow has generated much experimental interest by virtue of their unusual behaviour compared to that of simpler polymeric melts. The theory developed by Doi attempts to explain the observed phenomena in terms of considering interactions of rigid-rods Exact solutions to the Doi theory have been compared to experimental procedures using lyotropic LCP systems. Although much of the available data relates to mechanical measurements, the comparisons with quantitative structural data can provide useful insight.

The development of a new charge coupled device (CCD)-based detector for the scanning electron microscope (SEM) has allowed high quality backscattered electron Kikuchi patterns (BEKP) suitable for crystallographic analysis to be collected. These BEKPs can be used for crystallographic texture, phase and microstress analysis. This CCD detector system, can also be equipped with a special filter for removing backscattered electrons, which allows us to image low intensity, highly divergent x-ray diffraction (Kossel) patterns. The Kossel patterns are utilized for the accurate measurement of d-spacings suitable foe residual stress and lattice parameter measurements.

For a complete description of a material's microstructure the morphology as well as the distributions of chemical elements and of crystal lattice orientations must be known. While morphology is a standard issue of electron microscopy, and element distributions can be mapped readily using an EDX appliance, crystal lattice orientations in the bulk surface are accessible in routine work only recently [1, 2]. Backscatter Kikuchi patterns (BKP), also termed electron backscattering patterns (EBSP), are widely used for the determination of individual grain orientations in the surface of bulk polycrystals.

Microdiffraction is defined as the x-ray diffraction analysis performed on small samples or small areas of large samples. Since smallness is a relative term, micro diffraction is considered the technique of choice when samples are too small for the optics and precision of conventional instrumentation.

The chemistry of heterogeneous materials can be understood only after determining the elements composing the material, the ways in which those elements combine, and the distribution of the resulting phases. The techniques of photon-induced x-ray microfluorescence (XRMF) and x-ray microdiffraction (XRMD) offer several advantages over conventional electron- beam methods for determinations of element and phase distributions. Those advantages include minimal specimen preparation, good element sensitivity, air operation, the capability of wide area coverage, and the availability of sophisticated search/match routines for phase identification.

The first in vivo x-ray fluorescence measurements of lead in bone used y-rays from a 57Co source to excite Pb K x-rays. Later systems used γ-rays from 109Cd to excite Pb K x-rays or polarized x-rays to excite Pb L x-rays. All three approaches involve an extremely low effective dose to the subject. Of the two K x-ray techniques, 109Cd is more precise and more flexible in choice of measurement site. Pb L x-ray fluorescence (L-XRF) effectively samples lead at bone surfaces, whereas Pb K x-ray fluorescence (K-XRF) samples through the bulk of a bone. Both the polarized L-XRF and 109Cd K-XRF achieve similar precision.

Renal mercury has recently been determined using a polarized x-ray source. Both renal and hepatic cadmium can be measured using polarized x-rays in conjunction with a Si(Li) detector. Platinum and gold have been measured both by radioisotopic source excitation and by using polarized x-rays, but the latter is to be preferred.

Applications of Pb K-XRF have shown that measured bone lead relates strongly to cumulative lead exposure. Secondly, biological half lives of lead in different bone types have been estimated from limited longitudinal data sets and from some cross sectional surveys. Thirdly, the effect of hone lead as an endogenous source of lead has been demonstrated and it has been shown that a majority of circulating blood lead can be mobilized from bone, rather than deriving from new exposure, in some retired lead workers.

Initially, Wielopolski (Wielopolski et al. 1981) used x-rays from either a 125I or a 105Cd source to estimate lead (Pb) in tibial cortical bone in intact legs, post-mortem. This system utilized the Lα and Lβ x-rays of Pb with energies of 10.5 and 12.6 keV, respectively. The minimum detection limit (MDL) was considered to be comparable with existing K-line x-ray fluorescence (KXRF) instruments, namely, 20-30 ppm. The feasibility of partially polarized radiation (Barkla, 1906) was assessed from a 125I source on Pb (No3)2 (10,000 ppm) dissolved in wa:er. Reduction of the detector total count rate was observed by a factor of two; and reduction in background by the same factor was appaent. This preliminary study suggested that, with improved design, tlie MDL might be lowered by a factor of five (Wielopolski et al., 1981).

X-ray fluorescence (XRF) has become a well established technique for the measurement of trace levels of toxic heavy metals in vivo, including cadmium, platinum, mercury and lead (Mattsson et al.. 1987). The clinical motivation for the measurement of platinum (Pt) is the need to investigate the kinetics of Pt-based cancer chemotherapy drugs such as cisplatin and paraplatin. Currently the main research interest in Swansea lies in the study of the uptake and distribution of Pt administered during chemotherapy of patients with tumours in the head and neck region.

In this study we present the results of in vivo measurements of the mercury concentration in organs of occupationally exposed persons by the use of X-ray fluorescence analysis (XRF). The mercury concentration in the right kidney was measured in 20 occupationally exposed workers and 12 referents. The detection limit for the individual persons varied with the kidney depth (mean 26 μg/g, range 12-45 μg/g), was exceeded in nine of the exposed workers but in none of the referents. The mean kidney mercury concentration (including estimated concentration values below the detection limit) was 24 μg/g in the group of exposed workers (group MDC 5 μg/g) and for the group of referents no detectable concentration (mean 1 μg/g) was found (group MDC 6 μg/g). The mean urinary mercury excretions for the two groups were 34 and 1.7 μg per g creatinine. X-ray fluorescence measurements made on liver (n = 10) and thyroid (n = 8), in some of the exposed workers, revealed no measurable mercury concentrations.

The occupational exposure to uranium associated with milling and fabrication of depleted uranium is presently assessed from bioassay of urine samples. The evaluation of the body-burden of uraninm from urine analysis has many difficulties and uncertainties associated with accounting for the bio-transport of inhaled uranium psrticles from the lungs, to absorption in the blood and excretion through the kidneys. The chemical toxicity of uranium and other transuranic elements is not fully understood, partially because of the difficulty of assessing the body burden of these metals in-situ. The transuranic elements are known to be deposited and retained in bone. A non-invasive X-ray fluorescence technique has been developed to assay the depleted uranium in bones in-situ. The K-shell electrons in uranium, which have a binding energy of 115.6 key are excited by the 122 and 136 keV gamma rays from a Co-57 source. A liquid N2 cooled intrinsic Ge-detector is employed to measure the characteristic K fluorescence from the uranium as well as the coherently scattered gamma raj's from the Co-57 source. The quantity of uranium in the bone is determined from the number of K fluorescence events extracted from the measured scattered photon spectrum. In addition, the bone mineral mass is determined from the number of coherently scattered gamma rays, permitting the assay of uranium to be expressed in terms of micrograms per unit mass bone. Using this system it was possible to measure molar concentrations of uranium with high precision and reproducibility.

Traditionally, clinical studies of lead's effect on health have relied on blood lead levels to indicate lead exposure. However, this is unsatisfactory because blood lead levels have a half-life of approximately 5 weeks (Rabinowitz et al., 1976), and thus reflect recent exposure. Over 90% of the lead body burden is in bone, and it is thought to have a long residence time, thus implying that measurements of bone lead reflect cumulative exposure (Barry, 1975). So, measurements of bone lead are useful m understanding the long-term health effects of lead.

The analysis of lead concentration in bone utilizing LXRF can be adversely effected by overlymg tissue. A quantitative measure of the attenuation of the 10.5 keV Pb L a x-ray signal by skin and skin equivalent plastic has been conducted. Concentration ranges in plaster of Paris and doped goat bone from 7 to 90 ppm with attenuators of Lucite® and pig skin were examined. It is concluded that no quantitative or semi quantitative analysis can be achieved if overlying tissue thickness exceeds 3 mm for Pb concentrations of less than 30 ppm Pb in bone.

A nineteen element mercuric iodide (HgI2) detector array has been developed in order to investigate the potential of using this technology for in-vivo x-ray and gamma-ray imaging. A prototype cross-grid detector array was constructed with hexagonal pixels of 1.9 mm diameter (active area = 3.28 mm2) and 0.2 mm thick septa. The overall detector active area is roughly 65 mm2. A detector thickness of 1.2 mm was used to achieve about 100% efficiency at 60 keV and 67% efficiency at 140 keV The detector fabrication, geometry and structure were optimized for charge collection and to minimize crosstalk between elements. A section of a standard high resolution cast-lead gamma-camera collimator was incorporated into the detector to provide collimation matching the discrete pixel geometry. Measurements of spectral and spatial performance of the array were made using 241-Am and 99m-Tc sources. These measurements were compared with similar measurements made using an optimized single HgI2 x-ray detector with active area of about 3 mm2 and thickness of 500 μm.

A number of biological reference materials (RM) have been prepared in our laboratory specifically for validating analytical methods for the determination of Pb in biological matrices (e.g. blood, urine, liver, and bone). The RM's were developed using animal (goats and cows) that are routinely dosed with lead acetate to produce proficiency test samples for blood lead (and erythrocyte protoporphyrin). In cases where an animal becomes injured or infirm, the veterinarian in charge may recommend that the animal be euthanized. In such cases, samples of bone, brain, liver, and other tissues containing lead are removed at autopsy.

Currently, we have collected bone samples from nine goats and one cow that were dosed with lead over periods ranging from 1 to 10 years, During the autopsy, the epiphyses (bone joints) are separated from each long bone. Skin, muscle, and other adhering tissues are dissected or scraped from each bone. Bone marrow is also removed. All bare bones are currently stored at -70°C until analyses for Pb are conducted.

The only certified reference materials for bone Pb are those available from the National Institute for Standards and Technology (NIST), Gaithersburg, MD. Standard Reference Material (SRM) 1486 Bone Meal has a certified Pb concentration of only 1.335 μg/g. This is close to normal for humans, but is too low to be of practical use for in vivo X-Ray Fluorescence (XRF) equipment, SRM 1400 Bone Ash has a certified Pb concentration of 9.07 μg/g. Neither SRM is optimal for validating in vivo XRF equipment, but they are both very useful in validating other analytical methods for bone Pb such as Graphite Furnace Atomic Absorption Spectrometry (GFAAS).

We have developed an accurate, precise, and sensitive method for determining Pb in bone using GFAAS with Zeeman background correction. Using this method, we have analyzed the animal bones for Pb. Bone samples were divided into smaller pieces using a diamond-disc saw, freeze dried, and homogenized in a tantalum ball mill. Samples of bone powder were digested in nitric acid using a closed vessel microwave digestion system. Lead was determined using aqueous Pb standards in a chemical modifier optimized for the bone matrix. The method was validated using NIST SRM Bone Meal and Bone Ash. The detection limit is 0.6 μg/g based on 3 SD. Results for Pb in our animal bone range from approximately 5 to 50 μg/g dry weight. The results indicate that the intact bare bones would be excellent candidates for interlaboratory studies of in vivo XRF measurements of bone Pb. They are stable, well-characterized, easily transported between sites, and cover the clinically relevant range of bone lead concentrations likely to be encountered in the field. It is proposed that these materials be circulated as part of an interlaboratory comparison to interested centers using in vivo XRF After the XRF analyses, the bone samples will be analyzed for Pb by GFAAS for comparison purposes.

Human exposure to lead may induce a variety of adverse effects on health including haematological, neurobehavioural, cardiovascular and renal changes and therefore continues to be a public health concern (Needleman 1989). Lead is dispersed in the environment from where it may be inhaled or ingested by man. Environmental exposure may arise from a number of potential sources: typically industrial emissions, exhaust from petrol engines, drinking water, foodstuffs, paint, soldered cans, lead glazed earthenware, dust and soil. A further source is tobacco smoke.

This is a brief summary of the first workshop of “In Vivo XRF Measurements of Heavy Elements,” at the Denver Conference on Applications of X-Ray Analysis. In vivo x-ray fluorescence has been applied to medical applications since the 1960's, with much of the pioneering work being done in Sweden (1). First measurements were of iodine in the thyroid. Elements from iron to uranium have now been measured, at natural and elevated levels. Elevated levels occur either unintentionally through occupational or environmental exposure, or intentionally through medical administration. Examples of measurements are cadmium in kidney and liver, platinum in kidneys and tumors, mercury in the wrists and skulls of dentists, lead in various near-surface bones, copper in the eye and iron in skin. Nearly all measurements make use of either silicon or germanium detectors; radioisotopes and less frequently x-ray tubes are used for excitation.