326 CORNELIUS A. TOBIAS 



Acceleration of Atomic Nuclei 



The original reason for artificially accelerating nuclei of light atoms was 

 the realization that such particles might penetrate the atomic nucleus. About 

 the same time that Ernest Lawrence built the first cyclotron (see Lawrence 

 and Livingston, 1932) for acceleration of deuterons, protons, and alpha 

 particles, it was realized by Zirkle (1932) that atomic nuclei, particularly 

 alpha particles, were more efHcient in killing cells than x- or gamma rays, 

 and that the major effect of alpha particles was on cell nuclei. Acceleration 

 of heavier nuclei (e.g., lithium, mercury) was attempted in the early 1930's 

 (Sloan, 1935), but did not become practical until about 1940 (Alvarez, 1940; 

 Tobias and Segre, 1946), when the nuclei of carbon were accelerated in the 

 Berkeley 60 in. cyclotron to about 120 Mev kinetic energy. In about the 

 same year, the Swedish scientist Edlen (1941, 1942) discovered that multiply 

 charged atoms of various elements, including carbon, calcium, and iron, 

 were constantly present in the solar corona. These elements are either a result 

 of emissions of solar plasma into surrounding space, or come about by inter- 

 action of the interplanetary dust with solar radiations. In 1948, Freier et al. 

 discovered in observations taken on photographic emulsions in high altitude 

 balloons, that primary cosmic rays reaching the earth at the top of the 

 atmosphere were protons, alphas, and heavier nuclei, many of them with 

 billions of electron-volts kinetic energy. It was demonstrated that at least 

 part of the heavy nucleons arriving at the earth originate in the sun or solar 

 corona. 



For 30 or 40 years physicians concerned with tumor therapy realized the 

 desirability of concentrating radiations in limited regions in the body. High 

 energy x-rays, gamma rays, and neutrons were tried in succession. In 1946, 

 Robert Wilson, then at the University of California, realized that high 

 energy protons, due to their particular ionizing properties, might be useful 

 for irradiation of deep seated tumors in the body. In 1948, with completion 

 of the first large cyclotron, the Berkeley group undertook systematic investi- 

 gation of the usefulness of protons and deutrons in biological research. 

 Tobias et al. (1952) demonstrated that high energy particles (190 Mev 

 deuterons) are useful for production of localized radiolesions in the body, 

 and that the Bragg ionization peak for tumors in mice does indeed possess 

 some advantages. A technique was developed for hypophyseal radiation of 

 the rat (Tobias et al., 1954; Van Dyke et al., 1959) and monkey (Simpson 

 et al., 1959), which led to a well-defined, chronic hypophysectomized state 

 in the animals. In 1955, encouraged by the mounting evidence for hormone 

 dependence of many human cancers and by the initial successes of surgical 

 hypophysectomy (Luft and Olivecrona, 1953), and following initial studies 

 of hypophyseal radiation of dogs with advanced mammary carcinoma (un- 



