sparrow: cytogenetic effects of ionizing radiations 71 



tage of the Cs 137 is' its less energetic gamma which makes shielding 

 easier. This is a potential disadvantage too, of course, wherever deep 

 penetration into tissue is desired, and more curies are required to give 

 the same output in r/hr. 



C. Accelerators and Cyclotrons 



The number of accelerators of various types available today is 

 bewildering to the average biologist and no attempt will be made to 

 enumerate all of them. The smaller accelerators for electrons cost 

 only a few thousand dollars, but those more recently developed cost 

 many millions of dollars. While the more expensive types can some- 

 times be scheduled for biological experiments, one can hardly vis- 

 ualize having such machines built at this time for our exclusive use. 



In addition to their great expense, accelerators are generally 

 difficult to use for biological experiments and are in great demand 

 by physicists. For these reasons they are used much less in biological 

 experiments than other types of radiation sources. They are a major 

 source now for biological experiments with fast electrons, protons, 

 neutrons, and stripped nuclei (44). It is possible by appropriate design 

 to obtain microbeams of a few microns in diameter from various 

 accelerators (205). Protons or deuterons usually are used in such 

 microbeams to reduce the amount of scatter which would occur with 

 X-ray or electron beams. Mesons can be produced artificially by the 

 acceleration of alpha particles or protons to energies in the Bev 

 range. As far as the author is aware no genetic experiments with 

 mesons have yet been performed owing to their elusive nature and 

 the relatively low intensity available. With the development of the 

 extremely high energy accelerators now under test or construction 

 (45), it should soon be possible to obtain enough of these energetic 

 particles to test them for their relative biological effectiveness in pro- 

 ducing breakage and mutation. 6 However, since we know that the 

 ionization density produced along their tracks varies from extremely 

 low to extremely high values, it is predictable that their effectiveness 

 will cover a broad range depending on their energy at the time they 

 traverse a oiven nucleus. 



"The Brookhaven Alternating Gradient Synchrotron will attain energies up to 30 

 billion volts. 



