360 ENERGY LOSS AND BIOLOGICAL EFFECTS 



Experimental Facilities 



During the past two years the Berkeley 184-in. cyclotron (2) was 

 available part of the time for biological investigations, through the 

 courtesy of E. O. Lawrence and R. L. Thornton. The successful pro- 

 duction of an ion beam deflected away from the magnet (3) made it 

 possible to use this instrument for biological treatments on animals in 

 a manner suggested by Wilson (4). In the paper by Wilson at this sym- 

 posium the properties of high-energy ion beams were presented. The 

 initial biological application of the cyclotron beam to mammals and the 

 demonstration of effective depth doses in mouse-tumor therapy have 

 been described (5, 6, 7). The same ion beam of protons, deuterons, and 

 alphas may be used to advantage for biological tests in the region of 

 REL 3 mev/cm tissue to 300 mev/cm tissue. Pollard (8) has recently 

 used the deuteron beam of a small cyclotron. The Berkeley linear 

 accelerator (9) has also become available for biological experimentation. 

 It delivers protons at 32 mev or, if the attached Van de Graaf generator 

 is used by itself, monoenergetic protons up to 4 mev. In the high specific 

 ionization range, it is convenient to use polonium alpha particles, as 

 was done in some of the experiments described below. With micro- 

 organisms of small dimensions, data may be secured up to 2 bev/cm 

 REL. There are radiations available even at higher rates of energy loss. 

 High-energy multiple ionized beams have been produced in cyclotrons 

 (10). Slow neutron induced fission recoils (11) are also available, having 

 a mean REL of 3 X lO'* mev/cm tissue. 



Method of Irradiation 



The method of irradiation as used in the present work will now briefly 

 be described. At the cyclotron a collimated beam of 190-mev deuterons, 

 380-mev helium ions, or 340-mev protons was brought out to air. The 

 deuteron beam had intensities up to 2000 rep/min, and extended as a 

 beam of parallel particles over a cross-sectional area somewhat larger 

 than 1 in. diameter. This beam could be monitored in various ways. 

 The total beam intensity (number of ions per second) was measured in 

 a Faraday cage. The total ionization and the ionization per unit volume 

 in air or other gases were measured in specially constructed ionization 

 chambers. To evaluate energy absorption in tissue, experimentally 

 measured stopping-power determinations were used (12). Several other 

 methods are available for beam monitoring, for example measurement of 

 the neutron flux close to the beam, fluorescent counters, and measure- 

 ment of the formation of radioactive isotopes with known cross sections. 



