Raymond E Zirkle

Life and career

Zirkle was born in Springfield, Illinois. From 1915 to 1919 Ray attended West Plains High School, where he showed an aptitude for mathematics and took several engineering courses. After graduation he joined the Missouri National Guard and served for several years. In 1924 he married Mary Evelyn Ramsey, who spent her early years in a rural area of western Kansas and, similarly to Ray, received her primary education in a one-room country schoolhouse. They had two children, Raymond Jr. in 1927 and Thomas in 1929. Zirkle graduated from the University of Missouri with an A.B and Ph.D. in 1928 and 1932, respectively. In 1932 Zirkle joined the University of Pennsylvania in Philadelphia as a lecturer in biophysics and remained there until 1938. In 1940 Zirkle accepted a position as professor of biology at the Indiana University. During World War II Zirkle became one of the principals in the biological program of the Manhattan Project. His focus in the Manhattan Project was to study the effects on living systems from fast and slow neutrons, beta rays, and gamma rays. In 1944 Zirkle became a professor at the University of Chicago and in 1945 was appointed director of the Institute of Radiobiology and Biophysics at the university.

Zirkle died in Castle Rock, Colorado in 1988.

Research

After receiving his doctorate Zirkle joined the Johnson Foundation for Medical Physics at the University of Pennsylvania in Philadelphia. Initially he had a fellowship from the National Research Council, which had also supported his graduate studies. He remained at Penn as a Johnson Foundation fellow and a lecturer in biophysics until 1938. During this time he investigated the quantitative relationship between ionization per unit path of alpha particles and their biological effectiveness, which was not clear-cut from the data obtained up to that time. By placing fern spore (Aspergillus terreus) nuclei either near the beginning of the path (where the ionization density was low) or near the end of the path (where it was high) or in intermediate positions, he was able to calculate the number of alpha particles per nucleus that was necessary to produce a given effect, such as the inhibition of cell division. He found that the biological effectiveness is not only a function of the total number of ions formed in the nucleus but is also dependent on the variable concentration of ions formed in different portions of the path of the alpha particle. His data suggested the relationship B=kI^2.5 , where B is the biological effectiveness per alpha particle, k a proportionality constant, and I the ionization per unit path. The quantitative aspect of this work was unusual for such studies at that time and established Ray Zirkle as a leader in the field of radiation biology. A generalization of these results to other types of radiation by Zirkle and others led to his later formulation of the concept of linear energy transfer. In 1940 Zirkle was appointed professor of biology at the University of Indiana; however his academic career was interrupted during World War II when he became one of the principal investigators in the biological program of the Manhattan District. His research in this project was chiefly concerned with the comparative effects on living systems of fast and slow neutrons, beta rays, and gamma rays. A substantial part of the wartime research carried out under his direction was reported in several volumes of the National Nuclear Energy Series, of which he was the health editor. Much of the biological research in the Manhattan Project was carried out at sites where particular radiation sources were located, such as the Clinton Laboratories near Oak Ridge, Tennessee; the Radiation Laboratory at the University of California; the National Cancer Institute in Bethesda, Maryland; and the Metallurgical Laboratory at the University of Chicago, which later became the Argonne National Laboratory. Research at the latter site brought Zirkle into contact with many faculty members from the University of Chicago who shared common interests with him. Thus, it is perhaps not surprising that in 1944 he was offered and accepted a professorship there and that in 1945 he became director of the newly founded Institute of Radiobiology and Biophysics. This institute, like the Johnson Foundation, became a focal point for scientists and students with a penchant for physics and an interest in biological problems. The Zirkles purchased a home in Olympia Fields, south of Chicago, which had space for a large flower garden. In the late 1940s and early 1950s Zirkle continued his theoretical and experimental studies of the effects of radiation on living cells. As knowledge of the chemical composition of biological material began to accumulate, he attempted to relate the chemical effects caused by the absorption of radiant energy to the ultimate biological effects. He fully appreciated that an understanding of the multitude of diverse radiobiological effects—such as gene mutations, chromosome breaks, increased membrane permeability, inhibition of cell division, induction of neoplasms, and lethality of cells and organisms—would require a detailed knowledge of the intervening chemical modifications. Yet, the level of knowledge of the molecular composition and dynamics of cellular constituents was still very primitive. The relationship of DNA and proteins to genes was still uncertain. Nothing was known about the existence of DNA repair mechanisms or the molecular basis of mitosis or the mechanisms responsible for cell proliferation and cell death. At this time one had to be content with discriminating direct from indirect effects of the radiation and for establishing criteria that could sort out the relevant chemical consequences of the ionization or excitation of molecules. Zirkle’s analyses provided a rational conceptual framework for dealing with this complex problem. Until now, the link between radiation physics and biological damage is still to established.