Due to the difficulty of analyzing materials at high temperatures and in reactive atmospheres, solid-state catalysts have often been developed with little knowledge of the true chemical behavior of the catalyst, except on a bulk scale. In the field of solid-state catalysis research, a great deal of time and effort is presently being spent to better characterize the chemical and physical properties which determine a particular catalyst‘s efficiency, lifetime, and selectivity. Recently, we have undertaken a study of model copper catalysts at The Dow Chemical Company in an effort to better understand the chemical and physical properties which determine the efficiency, regenerability, and lifetime of this type of solid state catalyst.

Thermal expansion is an interesting, ubiquitous and neglected property of materials. Recently, Lenain et al. (1985) and Limaye (1986) have been investigating anisotropy in the low-expansion structures of the sodium zirconium phosphate family. In the hexagonal structure one axis expands while another contracts. In going from the calcium to the strontium analog the anisotropy actually changes sign. A change in anisotropy between CrB2 and TiB2 had been observed by R.V. Sara (1960). The results in Fig. 1 obtained by high temperature x-ray diffraction measurements indicate that for TiB2 the thermal expansion of the c-axis is greater than the expansion of the a-axis, whereas for CrB2 the reverse is true.

It is important to establish precision and accuracy of an X-ray diffraction (XRD) residual stress measurement procedure in order to compare capabilities of instrumentation and techniques, as well as to provide confidence limits for experimental data. There is no broadly acceptable method for establishment of precision and accuracy. This paper describes a proposed approach and one which is used at The Pennsylvania State University.

One impediment to the measurement of precision and accuracy is that no standard specimen with a known residual stress level is available. Proposed standard specimens have been abandoned for various reasons, including the concern for stability of the original stress condition and the existence of stress gradients, i.e., stress inhomogeneity, in the specimens. However, there is one type of specimen which has been accepted by ASTM as an alignment and zero residual stress confirmation standard. That type of specimen is a powdered sample of metal or ceramic which provides XRD peaks in the vicinity of the Bragg angle in which residual stress measurements are to be performed.

Some researchers tend to report detector counting statistics as the uncertainty of stress measurement but such statistical scatter accounts for only one part of uncertainty in precision and accuracy. The total uncertainty is best determined directly through repeated residual stress measurements performed by removal and readdressing the test specimen or through a repetition of measurements under predictably changing conditions.

This paper describes results from the use of powder specimens to establish the repeatability of measurements with a portable instrument after removal and readdressing of the specimens. Also, results showing the uncertainty of the measured stress change in specimens subjected to known loads are discussed.

Measurements of residual stress by X-ray diffraction are usually carried out with diffractometers or with one-dimensional position sensitive detectors. The stress is determined from the displacement of the peak that results from intersecting a diffraction cone at high angle with the line scanned by the detector. If a two-dimensional flat detector is used, the intersection of the diffraction cone with the detector plane is a ring, or section of a ring, which is also slightly displaced by the stress. The suggestion has been made use a two-dimensional detector to determine the surface state of stress.

This study presents a unique and novel enhancement of the double crystal diffractometer which allows topographic mapping of X-ray diffraction rocking curve half widths at about 100-150μm spatial resolution. This technique can be very effectively utilized to map micro-lattice strain fields in crystalline materials. The current focus will be on the application of a recently developed digital implementation for the rapid characterization of defect structure and distribution in various semiconductor materials.

Digital Automated Rocking Curve (DARC) topography has been successfully applied for characterizing defect structure in materials such as: GaAs, Si, AlGaAs, HgMnTe, HgCdTe, CdTe, Al, Inconnel, Steels, BaF2 PbS, PbSe, etc. The non-intrusive (non- contact & non-destructive) nature of the DARC technique allows its use in studing several phenomena such as corrosion fatigue, recrystallization, grain growth, etc., in situ. DARC topography has been used for isolating regions of non-uniform dislocation density on various materials. It is envisioned that this highly sophisticated, yet simple to operate, system will improve semiconductor-device yield significantly.

The high strain sensitivity of the technique results from combination of the highly monochromated and collimated X-ray probe beani, the State of the art linear position-sensitive detector (LPSD) and the high-precision specimen goniometer.

X-ray fractography is a new method utilizing the X-ray diffraction technique to observe the fracture surface for the analysis of the micro-mechanisms and mechanics of fracture.

In the present paper, X-ray fractography is applied to fracture surfaces of high strength aluminum alloy (JIS 7075-T6). The fracture toughness tests were conducted by using compact tension (CT) specimens with blunt notches and fatigue pre-cracks. The distribution of the residual stress near fracture surfaces was measured by the X-ray diffraction method. The effect of the notch radius on the fracture toughness value was discussed.

X-ray diffraction observation of fracture surface yields useful information to analyze the cause of failure accidents of engineering structures. This experimental technique, named X-ray fractography, has been developed especially in Japan. The relationship between X-ray parameters and fracture mechanics parameters plays a key role in determinating the mechanical condition of fracture.

While x-ray dosimetry is most definitely a "Measure of the Problem" in Analytical X-Ray Safety, there are additional factors which further enlarge the problem and are equally major considerations which must be taken into account when deciding upon the degree of action appropriate to prevent this problem.

Certainly, some idea of the nature of the typical levels of natural and man-made sources of radiation which surround us daily is useful to give us a perspective on the magnitude of radiation levels from analytical x-ray equipment. It is also important to know what levels of radiation exposure are considered unacceptable, either by regulatory limits or because of the potential for physiological damage.

The consequences of an exposure to radiation from analytical x-ray machines will often go beyond a report of an overexposure and investigation, or painful and lasting physiological damage. There are times when the matter will come before our courts in order to fix responsibility and decide compensation for injuries suffered.

Radiation-induced skin damage has been and still is the major therapeutic problem in radiation medicine. It is the well-known complication of past as well as present radiation therapy for neoplastic and related diseases even though linear accelerators and other modern teletherapy devices have reduced the unintentional incidence of skin damage remarkably. It is not well known, however, that such damage is also the most frequent presenting lesion in industrial radiation accidents even though redesigned radiography equipment as well as intensive training and radiation safety programs, are in place. In addition, state and national radiation safety officers are carrying out strict site inspections routinely. Someone once said it well when he remarked that engineers can design fool-proof radiation generating equipment, but they can't design damn fool-proof interlocks (personal communication, W. W. Burr 1986). This truism is strengthened by the not uncommon practice of constructing "cheater cords" to permit mechanical adjustments to be done while the device is operating. Numerous anecdotes abound relating how horrible destruction of parts of hands and feet has occurred year after year since radioactivity and x-rays were discovered.

After having heard about the magnitude of the problem of safety in the use of analytical x-ray equipment and then learned of the consequences of exposure to these x-rays, it is hard not to be convinced that a problem exists. Also being aware of the degree of responsibility in the event of an accident, it is clear that steps must be taken to prevent such occurrences. Controlling laboratory conditions is the key to prevention and, therefore, the solution to the problem.

Controls may be imposed administratively or with hardware. Administrative controls are easy and inexpensive to impose. Enforcement, however, is time consuming and difficult, since such controls need only be ignored to be compromised. Hardware controls are more positive and difficult to ignore. The bypassing of hardware controls is usually invasive on the equipment and leaves evidence.

When imposing controls it is necessary not to lose sight of the operational needs which brought the x-ray unit into your organization to begin with. Analytical x-ray machines are safest during massive power failures—but not very useful. Administrative and hardware controls which hobble the use of the equipment will be violated. Cooperation between the health physicist and the x-ray users can bring together the requirements of safety and Utility to create controls which will work.

In this report, we summarize over 30 years of analytical x-ray safety history at Lawrence Livermore National Laboratory (LLNL), and describe the safety procedures used in the operation of analytical x-ray equipment in the laboratories managed by the LLNL Chemistry and Materials Science Department (C&MSD). The present safety control system, which was developed by users of the equipment, has proven effective in keeping incidents at LLNL to a rate consistent with the national average.