Types of Ionizing Radiation and Their 

 Cytogenetic Effects 1 



ARNOLD H. SPARROW 2 

 Brookhaven National Laboratory, Upton, New York 



cc T)HYSiciSTS now comprehend not only the structure of stars, the 

 XT motion of our own and other galaxies, the curvature of space, 

 the possible ways in which our universe has evolved, but also matter 

 on a finer and finer scale: from familiar objects to molecules; then to 

 the atoms of which the molecules are composed; the internal struc- 

 ture of the atom with its electrons orbiting around nuclei; the nucleus 

 itself, made up of protons and neutrons and the mesons which bind 

 them together; and lately even something of a picture of the inside of 

 the proton itself, complex and containing yet other particles. We are 

 peeling an onion layer by layer, each layer uncovering in a sense 

 another universe; unexpected, complicated, and — as we understand 

 more — strangely beautiful." 



So begins a memorandum prepared for former President Eisen- 

 hower by a Special Advisory Panel on High Energy Accelerator 

 Physics (120). 3 In a similar manner, geneticists are probing at the ulti- 

 mate secrets of life or the fine structure of the chromosome, the gene, 

 and of their nucleoprotein components. It is of considerable interest 

 that the use by geneticists of the knowledge and tools of the atomic 

 and nuclear physicists is making a significant contribution to our new 

 knowledge of genetic fine structure and also, we hope, to the useful 

 application of radiobiological techniques in plant breeding. 



It is my assignment to try to outline the physical nature of the 

 ionizing radiations of most interest to the geneticist, to explain some- 

 thing of their interaction with matter, i.e., the process of energy 

 transfer from the radiation into the atoms or molecules, and to survey 

 briefly some of the biological effects produced by the complex series 



Research carried out at Brookhaven National Laboratory, Upton, N. Y., under the 

 auspices of the U. S. Atomic Energy Commission. 



2 The author gratefully acknowledges the many helpful suggestions regarding the 

 manuscript offered by Doctors H. J. Evans and Rae P. Mericle and by Miss Virginia 

 Pond and Mrs. Rhoda Sparrow. 



3 See References, page 105. 



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