Abstract
Vulcanization is the industrial process which transforms rubber from a soft, sticky, readily molded plastic to the highly elastic material familiar to everyone from innumerable uses. It was discovered by Charles Goodyear in 1839 and was one of the series of crucial inventions which started the United States on its industrial revolution in the nineteenth century. The automotive direction of this industrial development has accentuated the importance of rubber in succeeding years. This year the worldwide product volume to which vulcanization will be applied will exceed two and a half million tons. It is readily understood that vulcanization is now a highly developed process, the resultant of many improvements and developments over the course of a century of competitive use. Goodyear's original conception involved simply the heating of rubber with sulfur. The recognition of the chemical nature of the process was followed by the discovery of materials which, when added to the system, accelerated the reaction tremendously, allowed it to be carried out at lower temperatures, and improved profoundly the physical properties, uniformity, and aging resistance of the rubber. Such chemical vulcanizing systems are now applied in great variety. Many ways are known for vulcanizing rubber without using any sulfur, but they are of relatively minor commerical importance. Some of the synthetic rubbers require rather unique systems for vulcanization. There is continuous, intensive chemical research activity to find still better ways of vulcanizing rubber. So with gamma-ray vulcanization, it will be necessary to show some very tangible advantages to find even a few specialized applications. The idea of vulcanizing rubber by exposure to energetic radiation is not new. A patent issued to E. B. Newton in 1933 claimed the vulcanization of rubber by short exposures to 250-kV cathode rays. Effects of pile irradiation on uncured elastomers were studied by Davidson and Geib. Numerous investigations of the effects of radiation on the physical properties of plastics are listed in the bibliography prepared by Sun. Gehman and Hobbs observed the vulcanization of rubber by intense gamma radiation. Jackson and Hale measured the physical properties of rubber-filler mixtures as a function of the radiation dose from a strong Co60 source for a variety of elastomers. Cross-linking of rubber by pile irradiation was studied in a quantitative way by Charlesby. He emphasized the usefulness of radiation crosslinking as a means for studying the average molecular weight, variation of the gel fraction, and the changes in properties of rubber as the degree of crosslinking is varied.
Crystal gamma-ray detectors for high-energy physics