Many materials, both fissionable and non-fissionable, become very radioactive when subjected to nuclear radiations. This radioactivity results in a high background level in X-ray diffraction studies and becomes a limiting factor in an analysis of radiation damage. A description is given of special techniques that are used to minimize this background and produce optimum diffraction conditions. The radioactive intensity of irradiated X-ray specimens varies from levels that are only mildly troublesome to levels that are extremely hazardous to personnel. The diffraction methods employed at the various levels are explained. An example of the radioactive energy spectrum of a specimen is given to show the method of selecting the best operating conditions and techniques.

The paper is based on a feasibility study to determine the suitability of various techniques for the non-destructive measurement of cladding thickness on uranium fuel elements. The techniques studied were: 1—the attentuation of the characteristic X-ray fluorescence from the uranium base metal by the cladding material, and 2—Compton scattering of X-rays from the cladding surface. The cladding materials used in the investigation were aluminum, 304 stainless steel and zirconium, providing a wide range of both atomic number and density.

The topics to be covered are X-ray projection imcroradiography, which embodies the examination of thin poly crystalline sections with the aid of a microfocus X-ray unit, and similar divergent beam examination of thin single crystals.

In X-ray projection or shadow microradiography we restrict our interest to the field of metallurgy and typical examples will be illustrated from ferrous and nonferrous alloys. No special techniques are necessary in the making of these microradiographs, which are recorded on industrial fine grain X-ray film, and which are processed and viewed like regular radiographs. A Hilger microfocus unit operated at 45 kv, 250μa, using a Cu target, 40 micron focal spot was employed.

Some preliminary results will be illustrated from our application of the divergent beam technique.to single crystals.

A detector arrangement has been developed which will give nearly 100% efficiency over the entire range of wavelengths normally used in X-ray spectroscopy, including radiation from Mg Kα. A description of this counter is given and data obtained on pulse height distribution and pulse amplitudes will be discussed. Results obtained with typical specimens will be shown.

Fluorescent x-ray speorographic studies of mineral systems were begun in the Metallurgy Division of the Denver Research Institute in 1953. These studies were concerned with several techniques but the primary research emphasis was placed on a method involving conjunctive analyses by monochromatic x-ray absorptiometry and fluorescent x-ray spectrography.

Experimental data for mineral systems with wide variations in matrix compositions exhibit departures from simple calibration curves relating intensity and concentration for an element in a series of samples analyzed by simple fluorescent x-ray spectrographic procedures.

Absorptiometric measurements are made with a thin layer of the mineral sample as an absorption filter for the monochromatic x-rays emitted by the element in question. The results of these measurements provide information for improvement of the simple correlation of intensity and concentration by manipulation of the experimental data with various operations based on Beer's law of radiation absorption.

The results of work at the Denver Research Institute indicated the feasibility of the fluorescent x-ray spectrographic-absorptiometric method and the current work is an extension of the study of basic fundamentals, mechanical factors and practical applications of the technique.

The purpose of this investigation was to develop a rapid, accurate method of analysis for small amounts of calcium in wolframite concentrates. This analysis is necessary to determine if wolframite concentrates meet the U. S. National Stockpile Specification P-57R2, which limits the calcium content to 0.2 per cent.

Because of the small depth of sample analyzed in fluorescent x-ray spectrography the calcium Kα line intensity was found to be a function of the chemical composition of the calcium-bearing particle as well as the matrix composition. This particle-conn position effect was particularly important in this analysis because the calcium may be present as a carbonate, tungstate, phosphate, etc. Three methods of sample preparation were found to eliminate the variation of calcium Kα intensity with mineralogical occurrences: (1) Reduction in particle size by extensive grinding, (2) chemical fusion wtli sodium carbonate, and (3) solution of the calcium by an add.

Determinations by all three procedures are believed to be accurate to within ± 5 per cent for more than 0.30 per cent calcium and ± 10 per cent at the 0.1-per cent level. The lower limit of detectability is in the order of 0.005-0.01 per cent.

The operating characteristics of a gas-flow proportional counter used in conjunction with a pulse-height analyzer were studied in detail. This detector was found to have a high counting efficiency for calcium Ka radiation, to have a low counting efficiency for overlapping higher order radiation and to have counting stability equivalent to Geiger tubes.

Minor amounts of rare-earth elements (0.01 to 1.0%) in high-purity rare-earth oxides may be determined by a fluorescent X-ray procedure. The analysis of high-purity yttrium, cerium, praseodymium, neodymium, and samarium is described. Basic to the method is accurate determination of spectral line intensity above background. Sample and standard preparation, choice of analytical lines, and utilization of a helium path to increase X-ray intensities are discussed. Precision and accuracy were evaluated by analyzing samples of known composition. The average of five separate determinations showed an average error of about 10 per cent.

The two basic recrystallization theories, that of oriented growth and tliat of oriented nucleation, have been reviewed in light of data obtained from growth of single grains into strained single crystals of high purity (99.99%) aluminum. It appears that a compromise of these two theories would best explain the results obtained under this investigation. Basically, the proposed theory states that a stress is developed between coherent embryo nuclei and the strained matrix crystal. The relative orientation of the embryo nucleus and the matrix coupled with the residual stress in the strained matrix crystal will determine the magnitude of the stress between the embryo arid the matrix. When this stress is of sufficient magnitude, the coherent bonds between the embryo and the matrix will rupture and the embryo will become a nucleus which can then grow and consume the matrix.

Competing with this process is the phenomenon known as polygonization. Partial relief of the residual stress in the sprained crystal takes place as polygonization occurs. This partial stress relief is often sufficient to prevent the formation of nuclei and the occurrence of subsequent recrystallization.