HIGH ENERGY IRRADIATION: BIOELECTRIC EFFECTS 279 



T.\BLE I 

 Summary of Specifications of the 184-inch Synchrocyclotron 



Beam particles Deuterons Alpha particles 



Beam energy — maximum (Mev) 



Beam intensity — average current (ua) 



Beam intensity — peak current (ua) 



Time required for acceleration (msec) 



Number of revolutions during acceleration 



Distance traveled during acceleration (miles) 



Velocity at maximum energy (v/c) 



Mass increase at maximum energy {% of rest mass) 



Range of particles (in. of Al) 



Range of particles (gm/cm? of tissue) 



Under most experimental conditions, the dose rate received by nerves was 

 2 krad per min (1 krad = 10^ ergs absorbed per gm or 1.07 X 10^ rep 

 absorbed in tissue). High energy nuclei were generated by the 184-in. syn- 

 chrocyclotron in pulses of 500 microsec duration with 64 pulses per sec. In 

 special experiments the effect of varying the dose rate of the cyclotron's 

 beam from 0.5 to 8.0 krad per minute was tested to determine if this was 

 a significant factor in altering neural activity. The linear energy transfer 

 (also referred to as stopping power and rate of energy loss) of alpha parti- 

 cles was 15 Mev-cm- per gm (Bom et al., 1959), i.e., approximately the 

 same linear energy transfer of secondary electrons from a 250 kev x-ray 

 machine. 



Results 



Bioelectric Studies 



In exploratory experiments nerves mounted in a moist chamber were 

 placed in the horizontal path of high energy particles generated by the 

 184-in. synchrocyclotron. Irradiation of the nerve was beyond the stimulating 

 electrodes (maximum beam diameter was 44 mm). Every 10 krad, the cyclo- 

 tron's beam was interrupted, and the action potential of the nerve being 

 irradiated was recorded photographically until the electrical activity was 

 abolished. Large doses of alpha particles were required to block excitation. 

 It is now known that there is a serious difficulty with this type of procedure 

 because a greater dose than minimal was received by the nerve to eliminate 

 its electrophysiologic response. 



To determine the effect of high energy particles on neural activity, it was 

 deemed prudent to follow the time course of the survival of bioelectric activ- 



