for analysis of raw materials, and for aluminum, calcium, manganese, and sodium.

Tracers in Process Control

Although the importance of radiotracers to industrial research and development is recognized by most major companies, the potential of radiotracers for large scale in situ industrial process control in manufacturing is less widely known. In this application, an intermediary material in the manufacturing process is labeled with a small amount of radioisotopes and traced at appropriate stations in the process. By using low-level counting and appropriate kinds and quantities of isotopes, the process tracer may be used with complete safety.

Existing instrumentation and associated technology are inadequate for immediate industrial application, and there is a shortage of trained radiochemists who can find and establish each economically attractive application. The Commission is sponsoring a study by W. H. Johnston Laboratories on research and development of such large-scale, low-level in situ tracer applications for in-plant research, development, manufacturing and on-stream process control.

The study is directed toward developing both new instrumentation and exploratory applications.

In some applications, industrial in situ tracers may make possible process controls that cannot be accomplished by any other means; in others, controls may be more economical or more accurate than present techniques. Initially, many applications undoubtedly will be on the basis of research on a process in order to disclose new information on process control.

A related study undertaken by Battelle Memorial Institute is development of chemical process control by use of intrinsic radioactive tracers. In principle, this work under Commission contract would involve introducing a radioisotope into a process stream, either with raw materials at the first stage, or in inter

mediate stages; the radioisotope then would be used to control important parameters of the process. Types of parameters which might be controlled include mixing rate, kinetics of material transfer, and location and quantitative determination of impurity or major constituent concentration.

In conventional techniques, control frequently is based on the measurement of a property of the system which may be influenced by operating parameters other than the one to be controlled. In radioisotopic control, the measured quantity (radioactivity) is not influenced by extraneous physical or chemical changes in the system. Thus, a fixed correspondence between the radioactivity level and the process variable is obtained. Also, the presence of the radioisotope does not alter system performance, as may be the case in a conventional procedure when measuring elements are introduced in the system.

The direct introduction of radioisotopes in process streams, however, presents the problem of contamination of the final products. Two approaches to circumvent this problem are possible: The use of radioisotopes with a short half-life which will quickly lose their radioactivity or the use of very low concentrations of radioisotopes.

Accurate evaluation of the economics of any specific application can be made only after the technical problems are solved, the equipment requirements defined, and benefits of the application established. This study will provide this information for selected processes.

Activation Analysis

Activation analysis, accomplished by exposing a sample to neutron irradiation, is used to identify and measure an unknown element in a sample, or to determine the concentration of a substance known to be in a sample. Neutron irradiation makes radioactive some atoms of each element present, and each then can be identified or measured by its radiation characteristics. The technique is particularly useful when the concentration of an unknown

element is too low to be identified by chemical or spectroscopic methods, or where standard analysis is balked by contaminants.

Nuclear reactors and particle accelerators have been used in activation analysis but for industrial purposes a weaker source of neutrons such as a polonium-beryllium sealed source is entirely adequate. With use of sensitive radiation measuring instruments, the amount of induced radioactivity necessary to accomplish an activation analysis may be well below maximum allowable concentrations in consumer items.

Special Techniques for Activation Analyses

Special nuclear and computer techniques are being developed so that activation analysis may be used for process and quality control of liquids and solids in production systems. A largely theoretical investigation is being carried out for the Commission by Engineering Experiment Station, Texas Agricultural and Mechanical College. The necessary experimental verification for this theoretical study is being performed using a nuclear reactor, multichannel analyzer and digital computer.

The electronic radiation-counting devices used in activation analysis have reached a high level of development. However, it is not possible at present to analyze a sample simultaneously for a large number of elements without chemically separating the components of the sample. This investigation is intended to develop computer techniques to permit simultaneous activation analyses of multiple elements on a continuous basis.

Activation analysis of solids and liquids for a few constituents can be performed on a continuous, sensitive and nondestructive basis with present techniques with advantages over alternate analytical procedures. For example, in using conventional methods to analyze the composition of a bar of metal to be fabricated, samples would be chipped from the bar and analyzed with a spectrometer. With a continuous industrial activation analyzer, the bar could be passed through a source of neutrons and the resultant radiations measured to de

termine the distribution of elements within the bar.

Since all textile fibers contain some trace impurities, activation analysis may assist fiber identification. This is accomplished under present conditions by using 5 or 6 chemical and physical tests; the process is usually timeconsuming and may not give accurate results.

In applying activation analysis to fiber differentiation and identification, the assumption is that each fiber contains one or more unique and characteristic impurities. The gamma energy spectra for each fiber are sought. A specific example involves identification of nylon. For example, nylon type 6 is manufactured in the United States by three fiber producers using the same process. Present physical and chemical methods of fiber analysis may not permit differentiation among these products, and neither producer nor consumer can definitely identify the origin of a fiber.

Differences do exist, however, in process waters used during production at different. sites. Trace impurities in the water can be rendered radioactive with neutrons. In such cases where gamma energy spectra do not enable differentiation, minute quantities of a preselected nonradioactive impurity can be incorporated in one material, or each supplier's nylon can be tagged with a different impurity. After irradiation, each material then could be identified readily.

Identification is by no means the only possible use of activation analysis in the textile and allied industries. Many processes involve the addition or removal of chemicals, lubricants, and finishing agents. Activation analysis may be used to measure accurately the efficiency of each operation—a factor important in quality-control and for economic reasons.

The contract study of the Textile Research Center includes other specific tasks described elsewhere in this report. Research into uses of activation analysis in textiles is a companion task being supported by the textile industry. The work is summarized here to indicate the total scope of related work at the Center.

Inspection of Pressure Tubes

The reliable and efficient construction and operation of any heat exchanger, superheater, boiler, or other heat transfer equipment depend to a great extent on the effectiveness with which the tubing of the unit can be examined during fabrication and service for breaks, cracks, pits, variations in thickness, or foreign deposits. Simple, accurate, and convenient methods for tube inspection can improve plant efficiency.

To seek ways to facilitate inspections, the Commission has sponsored a study by Nuclear Products Branch, Lockheed Corp., on development of a gamma-ray backscatter instrument to measure steel tubing corrosion or erosion in high and low pressure steam generators.

Tube-inspections now are made by visual, eddy current, and ultrasonic methods. In the eddy-current method, eddy currents are induced in the test specimen by electromagnetic induction; variations in the current reflect irregularities in the test specimens. In the ultrasonic method, changes in a high-frequency sound pulse passed through the test object indicate imperfections. Both methods are highly sensitive to temperature changes and extraneous properties of the test material.

Ultrasonic test equipment responds to variations in microstructure and minor variations in the processing of a material. Because there must be a positive contact between the sound source and the test material, these tests usually are conducted under water in large tanks and require skilled technicians working under closely controlled laboratory conditions.

The eddy-current test responds to differences that would be within manufacturing tolerances for the material tested, and is not generally feasible except on a production line. The most reliable technique for detecting tubing flaws involves visual inspection, but this is time-consuming during fabrication and not feasible after installation.

The gamma-backscatter tube being developed to detect flaws may provide a simply operated device that can accurately detect, locate, and

evaluate defects in the walls of boiler and heat exchanger tubing during fabrication and service without requiring a major shutdown.

Measuring Levels in Special Tanks

The measurement of liquid levels in sealed tanks is difficult, especially in tanks with heavy walls, or those used for bulk storage of chemicals and foods which are sterilized, sealed and then aseptically filled. For tanks with walls less than 1/4-inch thick, back-scattering gages can be used from outside the tank wall. For thick or insulated walls, this technique will not work. The Commission has undertaken, through a contract with Nuclear Science and Engineering Corp., a study on development of a battery-operated variable height liquid-level measuring device for use in large sealed pressurized tanks with heavy-gage walls.

The backscattering technique has shown promise for this type of liquid level measurement. A probe containing both the source and detector is lowered into a tube sealed into the top of the tank. Since the built-in tube is of small diameter, it may have thin walls and still withstand considerable pressure. A radiation source with a strength of 10 microcuries or less is feasible and minimizes radiation hazards. This design can be used when normal methods of liquid level measurement are infeasible.

Some companies have used a transmission type of radioactivity gage in one built-in tube and measured radioactivity through another built-in tube a foot or so away. A source is raised and lowered in one tube while simultaneously a detector is raised and lowered in the opposite tube. Aside from the cost of installation of two tubes rather than one, the two units must be raised or lowered simultaneously to measured depths.

In the present study, a battery-operated portable liquid level device to operate in a single tube has been constructed and has demonstrated its ability to measure the level of liquids to +1% inch regardless of depth of liquid or diameter of the tank. The probe

itself is 134 inch in diameter, enabling the built-in tube to be kept to an inside diameter of 2 inches.

With hand operation, one such instrument could be used to measure the liquid level in any number of sealed tanks, since the complete unit is external to the tank. The only installation required is the 2 inch diameter tube welded into the tank.

Measuring Changes in Materials

Quantitative measurement of physical changes in materials is an important area of industrial research. The development of new materials, equipment and processes is directly related to the ease and accuracy by which physical characteristics of the materials may be determined and evaluated. Through a contract with Aerojet General Nucleonics, the Commission has under study the development of a radioactive, independent transducer-receiver system for measuring temperature, pressure, and strain.

A small capsule containing a radioactive source-target is being constructed which will be coupled with a sample to be tested in such a manner that physical changes in the sample will alter the secondary neutron or gammaray emission. Such a device has a potentially high sensitivity. The project includes evaluation of prototype transducers, design of receiver or detection systems for both neutron and gamma measurements, development and fabrication of complete prototype systems, and experimental testing and evaluation.

Two methods for quantitatively measuring physical changes may be categorized generally as: those which are self-contained and permit local reading; and those which permit remote reading. Methods in the latter group have a local sensing element (or transducer), and a remote receiving (or reading) element.

With the exception of a few specialized optical systems, all remote reading gages depend either upon thermoelectric effects, or upon the conversion of mechanical distortion into electrical energy, and direct transmission of the electrical signal by wires. Limitations arise.

from use of the wires, which become a third component. Industry has many requirements for making measurements without a physical connection between the transducer and its receiver.

For example, attempts have been made to measure the effects of environment on strains in cast, solid-propellant rocket motors. The problem of casting into the motor the strain gages and their associated wire connections, and accomplishing this without distorting the system, has appeared to be insurmountable. The use of a transducer completely independent of physical connections to its receiving element should help solve this problem.

Eliminating physical connections between a transducer and its receiver also will permit the measurement of temperatures and strains under exact operating conditions of rotating machinery. Another area in which gage technology requires improvement involves measurements at extreme temperatures; these measurements now are limited by temperature effects on conventional gage materials.

The new device could be used for measuring pressures and strains in rolling-mill billets, in high-pressure systems such as boiler tubes, stress-testing in formed structures, measurements in operating centrifuges, measurements in combustion chambers, and temperature and depth measurements in liquid metals.

The examples cited involve applications to problems as diverse as metal working, plastics, power generation, chemical production, automatic controls, and aircraft and missile production. Further, since the device will permit accurate measurements previously impossible, it undoubtedly will have a considerable impact on future research and development.

Measurement of Particle Size

Methods used to measure particle size fall into two categories: those that give information only about average particle sizes and those that give data on particle size distribution. Commonly used methods require considerable expenditure of manpower, are imprecise, severely