Nonmetallic crystals with a variety of structures and chemical compositions have been exposed to fission spectrum neutrons in a core position of the Low Intensity Test Reactor (LITR), Oak Ridge, and examined by X-ray diffraction techniques. Wherever possible, single crystals were employed, and the neutron dosages ranged between 1019 and 1021 neutrons/cm2 at a temperature of approximately 85°C. In no case was a special technique used for examining radioactive materials because the problem of heavy induced radioactivity was greatly reduced by working withcrystals weighing a milligram or less. Both film and counter measurements were employed.

Two methods are described for the detection of lattice imperfections of different kinds.

• 1. Imperfections in Solid Solutions. Normal diffraction methods with monochromatized X-rays are applied to single crystals of supersaturated solid solutions, where preprecipitation states occur. The calculated intensity distribution for a one-dimensional model of clustering shows the influence of atomic distribution and lattice distortion. Results are given on the structure of clusters in aluminum-rich alloys.

• 2. Detection of Dislocations in Nearly Ideal Crystals. A method first given by Barth and Hosemann is improved and used for the detection of dislocations in crystals of germanium. Use is made of the anomalously low absorption coefficient existing for X-rays which make the Bragg angle with a certain set of lattice planes going through a perfect crystal. The absorption is increased at points where the lattice planes are distorted by a dislocation line, and shadows from these lines can be seen on a photographic plate behind the crystal. The method gives information on the spatial distribution of dislocation lines and the direction of the Burgers vectors,

By means of cristallographie (inverse) pole figures for extruded uranium rods and tubes, the effect of extrusion variables on the texture can be examined. The principal variables are: prior texture, billet and liner temperatures, reduction in area, and ram speed. The final texture can be deeply affected by the prior texture, since two extrusions made under the same conditions but with different prior textures can be markedly different.

In general, an increase in extrusion temperature has an effect similar to an increase in reduction ratio. Ram speed has no important effect between 13 and 100 in./min except that a slow ram speed allows more time for recrystallization to occur.

The effect of temperature on texture is the development of a strong 110 axial texture for relatively high temperature (above about 525°C), a strong 010 axial texture for relatively low temperatures (below 400°C), and a mixture of 110 and 010 axial textures at intermediate temperatures, although these textures may be somewhat complicated by 130 axial recrystallization textures.

The variation of axial texture along the extrusion length and parallel to the radius of extruded tubes may be large.

A 900°C gamma-phase extrusion is shown to have a mild 100, 010, 021, 001 texture.

The feasibility of using X-ray diffraction methods to measure residual stresses in uranium and zirconium (Zircaloy-2) was investigated. A precision method was developed for the determination of diffraction peak positions and the precision associated therewith. The statistical tables of Fisher and Yates were used to determine what order polynomial provided the best least squares fit within the known precision of the observed data. It was found that a second-order polynomial provided an adequate regression. With the aid of a desk calculator less than 5 min calculation time is required to determine the peak position to a precision of ±0.01°.

The stress constant for uranium was determined to be 1308 ± 110 psi/0.01° shift in Δ2θ for copper radiation on the (116) planes at 2θ = 158.3°. The stress constant for Zircaloy-2 was determined to be 430 ± 1 psi/0.01° shift in Δ2θ for chromium radiation on the (10,4) planes at 2θ = 156.4°.

A theoretical approach of some factors influencing the intensity diffracted by a polycrystalline material at a definite Bragg angle has been confirmed by experimental data obtained with a high-angle Norelco diffractometer. The factors mainly considered are the focusing arrangement of the goniometer which delineates the geometric shape of the volume fraction of the sample being irradiated and the absorption of the latter.

Tests have been performed (a) with quartz mixed in samples covering a large range of absorption coefficients, (b) with two different K radiations using copper and molybdenum targets, (c) with three different angles of beam divergence of 1, ½, and ¼°, respectively, and (d) with the sample packed and leveled in a copper grid with openings of about 350 μ. As this test with copper grids was to demonstrate that each opening was acting like a volume of sample irradiated by a beam of extremely small divergence (0.1°), it also shows that more accuracy in the measurement of the exact Bragg angle can be reached in these conditions as compared to that obtained with conventional sample holders.

A general equation, suitable for qualitative and quantitative analysis when these factors have to be taken into consideration, is proposed.

The use of the X-ray diffraction Debye-Scherrer powder technique for the identification of crystalline material often found in pathologic tissue is discussed. Cases cited include: heart calcification, lung silicosis, thorium dioxide in liver and spleen, and granulomas of the skin and pericardium. The routine analysis of kidney stones using powder cameras as well as an X-ray diffractometer will be described.

Many of the iron- and nickel-base superalloys exhibit brittle properties on heat treatment, welding, or other fabrication processes at temperatures of about 2000°F or higher. Studies have been carried out by means of electron microscopy, electron diffraction, and X-ray diffraction and fluorescence analysis of the precipitation in the metal and in an isolated form.

Results of the electron microscope study of the surface of the metal show a grain boundary constituent to be present which increases in amount as the temperature is increased. Studies on the isolated residue of such samples show a very thin “featherlike” film to be located at the grain boundaries and enclosing the grains. Electron diffraction, X-ray diffraction, and X-ray fluorescence analysis studies of the thin films indicate that they are a TiC phase with very little alloying elements in solution.

At temperatures above 2000°F the thin film becomes quite thick and tends to force the grains apart. It is believed that this form of the TiC phase promotes the severe embrittling nature of these alloys at high temperatures. Suitable heat treatment at lower temperatures causes the TiC film to agglomerate and the grain boundaries become “tight,” and a more ductile condition results.