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action between, highly reactive species in the target system-ions, molecular fragments (free radicals), or excited molecules. Radiation has already demonstrated special value in improvement of polymers, sterilization of drugs and pharmaceuticals, and preservation of foods. The Commission's Industrial Radiation Program is designed to make use of beneficial chemical effects that already are known, and to discover new effects through continuing research.

Many millions of curies are required for high intensity radiation development. Consequently, the Commission's program also is designed to insure the continued availability of radioisotopes in massive quantities.

To be of practical value for processing, radiation must have sufficient penetrating power to irradiate target material with satisfactory uniformity, and induce no radioactivity in the target-or only a minimum of very short-lived species. High-level radiation sources should be of highly efficient design to permit maximum energy absorption in the target; be subject to reliable control and safe operation; and be available in quantity at reasonable cost.

Radiation process technology, i.e., the use of ionizing radiation as a source of energy for chemical and other processes, has not yet reached a point where engineering cost analyses such as usually precede introduction of new products and processes can be routinely performed. Indeed, there has been little basis for deciding which technologically feasible processes do merit interest.

Accordingly, the Commission has had several studies carried out to develop information which could be used as a firm basis for a carefully planned radiation development program. The studies have been aimed at delineating the present status of radiation applications and to indicate future directions for a radiation program. Concurrently, the Commission has conducted research and development work in industrial areas known to be vital to a radiation program.

Results of the studies will be published on completion and made available for public use.

PROPERTIES OF RADIATION

Radiation Interaction With Matter

The first of the Commission surveys was on the "Fundamental Considerations of Radiation Technology." It was conducted by William H. Johnston Laboratories, and defines the properties of radiation that make it a promising industrial tool.

An important feature of radiation is the great flexibility it provides for obtaining the desired reactive chemical species in a variety of surroundings and over wide ranges of temperature and pressure. A second feature is that radiation can produce pronounced changes in a single step, so that it may be possible to eliminate steps ordinarily required in conventional chemical processes. A third feature is a potential for creating chemical changes that now are difficult to achieve, or not known at all.

Molecules react chemically by coming into close proximity with one another. They form new molecules by breaking some chemical bonds between atoms which are part of the interacting molecules and by establishing new bonds. During this breaking of bonds between atoms, the geometric arrangement of atoms within the molecules also changes resulting in an arrangement characteristic of the new molecules produced. This rearrangement of chemical bonds and atomic configuration generally requires that energy be supplied to the molecules initially present. In the course of molecular transformation, a stage is reached at which it can proceed further without more energy being supplied. This configuration of atoms possessing the greatest energy and potential for further reaction is called the "activated complex."

There is a different activated complex with its own characteristic structure and energy for each reaction that a given set of molecules can undergo. In a container not subject to radiation, the relative probability of occurrence of

3 "Fundamental Considerations of Radiation Technology" Johnston Laboratories, Inc., Office of Technical Services, Department of Commerce, Washington 25, D.C., November 1959.

Rubber Vulcanization. The first tire ever vulcanized with gamma radiation is lifted from its mold during experiment at Commission's Materials Testing Reactor in Idaho. The radiation method, which does not require sulfur additives in the rubber, produces direct linkage of the carbon atomic chains in the rubber molecules. A much stronger tire is the result. these various activated complexes is a matter of statistical averages. External factors of temperature and pressure offer the principal means of directly controlling the outcome of the reactions. The principal chemical reactions resulting from a given process so controlled are reactions with those activated complexes that are formed in the highest concentration. The activated complexes formed in highest concentration will be primarily those that have the smallest energy requirement. Frequently in a system undergoing chemical reaction, only one activated complex is present in significant concentration and the resulting reaction is highly specific.

In addition to temperature and pressure chemical process technology makes use of catalysts, which can trigger formation of new and different activated complexes. Although, for each possible chemical reaction there is a dif

ferent activated complex, a number of different routes may be followed to produce the same end-product through different activated complexes.

Since radiation directly produces a variety of species such as ions, molecular fragments and excited molecules, it provides a new tool to supplement pressure, temperature, and catalysis. Among the species resulting from radiation, there may be many useful ones which require great amounts of energy to form, so that their formation in useful amounts by other chemical techniques may be difficult or even impossible. Once obtained, however, activated complexes formed by these species will lead to products in the same way, and following the same laws, as through conventional chemical techniques.

The Johnston survey indicates the need for detailed study of the products of radiation interaction with matter, and for research efforts to develop new, highly precise equipment to isolate and identify these products, many of which have exceedingly short lifetimes, some only one-one million-millionth of a second or less.

Research and Development Studies

Under its Industrial Radiation Program, the Commission supports projects aimed at improved knowledge of radiation chemistry and the development of processes efficiently utilizing ionizing radiation.

Several of the projects are designed to develop promising radiation processes in as short a time as possible. Theoretical and economic justifications have been stressed in these studies.

In one study, Technical Research Group is performing experimental work for the Commission on the synthesis of semiconductor material through radiation-induced reactions. Silane, a gas, is being irradiated to produce high purity silicon for semiconductors. Economically, this project has good prospects if successful since high quality semiconductor material is expensive and valuable throughout the electronic industry.

A second applied research effort is a study of the mechanism of radiation induced reactions of organic polymers with inorganic salts and organometallic compounds, being performed for the Commission by Radiation Applications, Inc. Some interesting films already have been prepared from polyethylene and silicon compounds. Silicon-grafted polyethylene appears to have definite high temperature stability compared to untreated polyethylene.

The Commission also is supporting a contract with Georgia Technological Research Institute on deagglomeration of kaolin by high-energy, ionizing radiation.

Kaolin, a clay mineral, is used extensively in production of high grade paper, as a filler in rubber products, ceramic ware, linoleum, medicines, and in many other applications.

Discrete particles of kaolin are flat, crystalline, and hexagonal, and it is this structure that makes kaolin a valuable mineral. About one-third of the kaolin mined, however, is found aggregated into stacks and is unsuited for most uses. It is presently discarded at considerable loss.

It is not precisely known how strongly the individual kaolin particles are bound together in the discarded aggregates, but some authorities believe hydrogen bonding to be responsible. Aggregates can be separated by the application of mechanical shearing forces, but this is extremely inefficient. Since some molecular bonds are readily broken by high energy radiation, radiation might be used to break stacks of kaolin into individual plates, thus saving up to one-third the kaolin now discarded.

Among more basic work, the Commission sponsors investigations of broad areas where radiation may offer unique advantages, and is supporting efforts to obtain information regarding the fundamental mechanisms of interaction of radiation with matter.

An experimental study of the effect of phase on the radiation-induced nitration of hydrocarbons is being performed by Battelle Memorial Institute. The effects of radiation on cy

clohexane-nitric acid systems in both liquid and vapor phases is being investigated, as suggested in the course of one of the Commission's surveys. Although it may lead directly to an industrial application in itself, it will provide results applicable in principle to a number of other systems.

At Massachusetts Institute of Technology the Commission is supporting two studies. One study is on radiation effects on polymerization at low temperatures. Very few uses of radiation to promote reactions between ions and molecules have been found or published to date. This study is directed toward expansion of knowledge in this field.

The low temperature radiation polymerization of i-butyl vinyl ether, acetaldehyde, 3,3 bis chloromethyl oxetane ("penton" of Hercules) and isoprene are being studied. The ether polymerization is being studied in the presence of different solvents and acid-clay surfaces which are ordinary catalytic for this reaction; it is planned to combine this with a study of the effect of radiation on such catalysts before and during polymerization. The work on "penton" monomer is being done in both the liquid and solid states.

Potential advantages of these studies could be the extension of radiation into the field of ion-molecule reactions where chemical means. of producing the same results are either too difficult or too expensive. The extent of possible industrial application of these techniques is difficult to gage, but it should include production of general chemicals, electrical insulation, and radiation resistant materials for space travel.

The second MIT study is on pre-irradiation of catalysts to determine how radiation may affect catalytic activity.

The mechanism of the change may be interpreted by observations of the magnitude and duration of the effect of radiation upon catalytic activity. Since changes in catalytic properties are beginning to be understood in terms of the electron theory of solids, the effects of radiation on a catalyst can be characterized and related to changes in physical

properties. The study of effects of radiation on catalysts before use for causing chemical reactions is expected to provide further insight into the mechanism of catalysis.

Commercial potential for improved catalysts is great wherever catalytic operations are carried out in the chemical and petroleum industries. Presently, iron catalysts are being studied.

A second contract on catalysis is with Engelhard Industries. It is a highly detailed experimental study of platinum catalysts and the changes in catalytic properties resulting from radiation exposure. Platinum was chosen as representative of an entire class of well known catalysts.

Finally, as a result of the completed surveys and their common conclusion that there is a lack of understanding of the fundamental mechanisms of interaction between radiation and matter, a contract has been given to William H. Johnston Laboratories for a study of the nature and distribution of ions produced by the impact of high energy radiation on gaseous molecules. This is a first step in what is expected to be a strong effort to learn to control chemical reactions induced by radiation.

SOURCES AND METHODS

Before potential radiation sources and processes utilizing them can be developed, a good deal of engineering research and development work will have to be performed. Only when this engineering information is available, and source and process economics demonstrated, can serious consideration be given to industrial installation of radioisotope or reactor radiation sources for various processes. Safe and efficient sources must be developed and demonstrated before large radiation sources can be widely used.

Types of Radiation

To be of practical value for production processes, the radiation chosen will have to satisfy a number of requirements including those of

penetration and minimum induced activity. Properties of different kinds of radiation are described in this section.

Electromagnetic radiation. Gamma rays, similar to X-rays, are a form of electromagnetic radiation just as light is, but are of higher energy. Gamma rays are emitted by radioisotopes as distinct from X-rays which may be created with electrical machines.

Gamma rays cannot be focused, bent, or scanned. However, the radioisotope source itself may be shaped to a particular geometry. The use of a simple thin slab or long rod geometry for irradiation of bulky packages, results in radiation use efficiencies generally of the order of 20 to 40 percent.

Gamma sources emit radiation in all directions and therefore require extensive shielding. For routine maintenance of radiation facilities, gamma sources must be physically removed or separated from the area of operations. With solid cobalt 60 sources this is relatively easy to accomplish-by lowering into a pool of water, for example. For more complicated fluid source materials, such as in-pile loops of a liquid gamma-emitting chemical, a more elaborate process of draining, or flushing, followed by decontamination of the loop, may be needed. Alternatively, auxiliary equipment on which maintenance work is necessary can be removed to a safe location.

Most large gamma sources need cooling because of the heat generated by self-absorption of the gamma energy and the accompanying beta radiation, and must be safely contained to prevent leakage of radioactive material. Gamma sources must be replaced, at intervals depending on the half-life of the radioisotope, to maintain uniform source strength. Subdivision of the complete source into multiple units facilitates and reduces source replenish

ment costs.

Particle radiation. Neutrons, protons, deuterons, alphas, positive ions and recoiling fission fragments are all heavy particles. Some, such as the fission fragments and alphas, lack pene