extent on the direction of the movement. In a parallel study on self-diffusion along grain boundaries in bicrystals of the body-centered cubic lattice (i. e., iron containing about 3 percent silicon), it was shown that there is a good correlation between the density of dislocations in grain boundaries and the depth of diffusion penetration. This aspect of the program is continuing to clarify the role of atomic size in grain-boundary diffusion and also the diffusion behavior along grain boundaries made out of various types and combinations of dislocations.

Anisotropy. It is well known that many metal crystals exhibit different diffusion rates in the various lattice directions. This problem of anisotropy of diffusion is being vigorously investigated at the Rensselaer Polytechnic Institute. Measurements of the diffusion coefficients (numbers indicating the rate of diffusion) and energies required for diffusion in different lattice directions in zinc, cadmium, and thallium have been completed. Similar studies on antimony, arsenic, and bismuth-members of a different crystal system-are in progress.

Moreover, it is intended to study the anisotropy of diffusion in iridium and uranium. Knowledge of the diffusion rates in uranium in the different lattice directions is of vital importance in understanding many of its peculiar characteristics.

Liquids. Besides atom movements in solids, the diffusion of atoms in the liquid state is also of great interest and concern. Not only does a study of diffusion in liquids contribute to an understanding of the liquid state, but such data are useful in dealing with problems associated with heat-transfer liquids, mass transfer, and corrosion in nuclear reactors.

A study has been completed at the Carnegie Institute of Technology on the diffusion of atoms in liquid lead-bismuth alloys. The program for investigating various diffusion phenomena in liquid metals is now being expanded to include other academic institutions.

Sintering of Metals and Oxides

The process of bonding metal or other powders by heating below the melting temperature to form a strong cohesive body is called sintering. In this process the powders are usually first pressed into the desired shape when cold. Metal-cutting tools, bearings, machine parts, insulators, and many other items can be fabricated by using the sintering process. The technique is often employed in making special materials required in the atomic energy program.

It was shown that atoms move within metals—especially at higher temperatures and that bonding of metals can result from this process. Thus, diffusion is generally acknowledged to take place during the sintering process. Sintering in certain cases is believed to be partly due to the flow of the powdered material under the processing conditions-a phenomenon known as plastic flow. New cohesive bonds are thus formed both by diffusion and by plastic flow. Other mechanisms are also thought to contribute to the bonding of powders. In the hot pressing of powder formed into a compact, or briquette by compression in a die, elevated temperature and pressure are used to increase the surface contacts through deformation of the powder particles. Diffusion can then proceed at a more rapid pace. The resulting metal is polycrystalline and resembles that obtained by conventional fabrication methods-melting, casting, and forming. Plastic flow during sintering is related to the surface forces of the particles. Just as two drops of water will join together to form a larger droplet with a resulting decrease in surface area, solid particles will combine with a decrease in the area of exposed metal surface. The decrease in surface is accompanied by a decrease in surface energy, and a more stable condition is thus reached. The fact that temperature increases the reaction is directly related to the increase in surface energy attending the rise in temperature. When bonding is accomplished, surface energies are reduced, and only a grain boundary may remain as a reminder of the previous status.

To clarify the mechanism of sintering in metals and ceramic powders, AEC-financed experimental and theoretical studies are under way at various laboratories, including work at the Massachusetts Institute of Technology and the University of Utah.

At MIT, sintering studies were made for sodium chloride, glass, copper, aluminum oxide, zirconium dioxide, sodium fluoride, and calcium fluoride. It was shown that sodium chloride, glass, and copper sinter by a distinctly different mechanism. Investigations are planned for systems which have a limited quantity of material present in the liquid state. Surface energies will also be studied. Metals rolled when cold, or otherwise cold worked, possess stressed and distorted grains. When the metal is heated to a sufficiently high temperature, which varies with the conditions, and then slowly cooled, the grains are rendered free of stress. This process is known as recrystallization. In a similar fashion, recrystallization is observed as a part of the sintering process.

At the University of Utah, research is being performed on the sintering characteristics of alumina (Al2O3), with special attention to recrystallization and the influence of impurities.

Since the sintering process is often accompanied by an increase in the grain size of the material (grain growth), relationships will be

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sought that link recrystallization, grain growth, and impurities. The Utah investigators have already found that impurities can increase or decrease the temperature at which recrystallization will occur and that the observed effect depends upon the particular impurity present. Measurements of plastic deformation under load are also being made in order to determine the effect of crystal structure on this property of materials.

RESULTS OF UNIVERSITY RESEARCH

The ingenuity of university researchers led to the design and construction of a variety of particle accelerators that impart energies up to billions of electron volts in nuclear particles. In addition, North Carolina State University now owns and operates a nuclear reactor and many others are being planned by educational institutions. All of these are tools useful for basic studies of the structure of matter and forces at work in the nucleus. They are also useful in finding practical answers relating to the nature and properties of materials produced in production and power reactors, to the effects of irradiation in changing the character of materials, and to methods of separating the mixtures of radioactive materials that are the products of nuclear bombardment.

University research in sintering of metal powders and in the diffusion of atoms in metals proved useful in the fabrication and cladding of reactor elements and in fuel recovery studies. Such studies have shed light on the peculiar characteristics of uranium-the most important source of nuclear energy.

University studies of the age of minerals and of mineral deposits are making easier the location of thorium and uranium ores and their extraction from these ores. New nuclides are being prepared and identified, and novel uses for these are surely forthcoming. Research at educational institutions advanced the discovery and use of nuclides for isotopic tracing, and this technique can now be used with all of the 101 known chemical elements.

Studies of high-temperature corrosion of metals and alloys help in the selection of satisfactory materials for reactors and chemicalprocessing equipment.

Advances made in isotope separation methods, as in the isolation of nitrogen 15 by chemical exchange, have served the atomic energy program in many ways.

Only a few of the university accomplishments in the Commission's research program could be outlined here. Contributions from our educational institutions have accounted for major breakthroughs in science and technology, resulting in the investment of substantial

sums of money in successful processes used in reactor and weapons programs.

Biology and Medicine

The biology and medicine program of the Commission includes research relating to the establishment of control measures against harmful exposure to radiation for the protection of atomic energy workers and the public. Laboratory and field investigations continued in the past 6 months to be projected toward studies of the effects of radiation on living things, understanding the mechanisms by which these effects are produced, and developing controls for and methods of protection against damaging effects. Current progress is reported here on research projects indicative of the broad scope of this program. Funds allocated for the 1955 fiscal year for the biology and medicine research program totaled $27 million and financed investigations in such fields as cancer, medicine, biology, and biophysics. The budget for the work done at the national laboratories and major research installations represented $19,570,000 of this total. Approximately 415 separate "off-site" studies at colleges, universities, hospitals and other research centers throughout the Nation received support in the amount of $7,430,000. The results of these studies are published and disseminated widely to research groups under the unclassified technical information program of the AEC. Illustrative of the many ways in which experimental data can be put to use are the techniques used by the Commission in the application of radioactive isotopes in research, some of which are described in the following.

A report on the biological and medical phases of the 1955 atomic test scries held at the Nevada Test Site is given in this report.

WEAPONS TEST ACTIVITIES

Various safeguards were in effect during Operation TEAPOT to hold to a minimum the exposure of the public to fall-out radioactivity. The Commission also maintained an extensive monitoring system to detect and measure levels of radioactivity near the test site and also at points throughout the Nation. In general, the radiological safeguards and the monitoring system were similar to those for previous Nevada test series, but past experience made it possible to improve controls and procedures in several respects. As a result, fall-out outside the controlled area was less than that resulting from the preceding Nevada test series in the spring of 1953. Off-site

levels of radioactivity were well below those which would impair the health of human beings or animals or cause damage to crops.

Improved Controls and Procedures

Improved weather prediction techniques and methods of forecasting fall-out intensity and location were utilized. For the first time, towers as high as 500 feet were built, and their use aided in keeping fall-out to a minimum. As in the past, all factors relating to health and safety were carefully considered by an Advisory Panel before the detonation of each device.

The system of radiological monitoring around the test site was strengthened by reorganization of procedures and the addition of two additional monitoring programs. The area within 150 miles of the test site was divided into 12 zones, each of which was staffed by a joint AEC-Public Health Service team. These personnel lived in communities within their zones during the test series, and acted both as monitors and as liaison between the residents and the test organization. There were also six mobile teams which moved to areas where additional monitoring was desired.

In addition to the monitoring teams, about 30 automatic recording instruments and the same number of telemetering units were in operation in localities within about 350 miles of the test site. The telemetering units were part of a unique system which made it possible for an operator at a control point to place a long distance telephone call to each unit, and to receive signals which could be translated into radiation readings in a few seconds.

As in the past, aerial surveys were conducted to provide for monitoring over large areas in a relatively short time.

National Monitoring System

The monitoring systems described above were used to obtain information on radiation levels within a few hundred miles of the test site, where more fall-out would be expected. To provide a continuous record of the lower level fall-out in more distant areas, samples were collected at 89 U. S. Weather Bureau Stations across the Nation as part of the Commission's National Monitoring System. This system has operated during previous Nevada series, and is maintained on a partial basis between testing periods.

Weather Bureau personnel at the stations cooperate with the Commission by serving as fall-out collection agents. A one-foot square gummed film, spread on a three-foot high stand, provides a simple but excellent device for catching and retaining fall-out particles. The films are changed each day. After being exposed, the