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That there are problems in soil mechanics need hardly be emphasized to soil engineers and not the least of these problems is the proper evaluation of new techniques and methods. Nuclear physics has already established a beachhead in the field of soil mechanics, and now it is ready to widen its invasion of that domain. The question is “How shall it be received?” and the answer to that question should be, “According to its merits for each particular problem.” It is the purpose of this discussion to present the merits of some techniques of nuclear physics in the solution of some problems of soil mechanics. For the purpose of discussion, the field of application of nuclear physics to soils engineering problems may be divided into two broad categories: tracer techniques and techniques depending upon the inter-reaction of radiations with matter. Neither of these techniques is new nor even restricted to the use of radioactive materials. Radioactive isotopes of lead were used as early as 1920 by Hevesy to determine the rate of exchange of lead atoms between lead nitrate and lead chloride in solution, but even before this fluorescent dyes were used to trace the movement of water, and if it is desired to go back into antiquity, the practice of tying a bell on a wandering cow to aid in locating it in a forest can be cited as a tracer technique. Similarly considering the interaction of radiations with matter, in 1895 Roentgen using X-rays produced shadowgrams showing the difference in density between bone and flesh. Earlier than this, the absorption of light by certain chemicals in solution was used to measure the concentration of those chemicals. Indeed, as early as 1873, the laws governing the absorption of light (visible electromagnetic radiation) by solutions were well enough understood to allow the establishment of quantitative methods of analysis based on this effect. What is new is the greatly increased availability of a wide variety of radioactive materials at reasonable cost, the easy availability of a wide selection of commercial instruments for the detection of radioactivity, and the general dissemination of pertinent information on their use.
Hosticka, Harold E.
Formerly Physicist, U. S. Bureau of Reclamation, Denver Federal CenterIdeal Cement Co., DenverFort Collins, Col.Col.