276 Applied Biophysics 



patient or object, a protective barrier must be placed in front 

 of the operator. Thirdly, since all objects which are placed in 

 the path of the direct beam scatter the radiation in all directions, 

 the operator must be protected against this secondary radiation, 

 either by means of a protective barrier or by relying on remote- 

 ness from the scattering objects. 



Many papers have been published regarding the outputs of 

 X-ray tubes operating under various exciting conditions. The 

 results have been summarized by Kaye and Binks ^^ and Binks - 

 for exciting voltages up to 2 million volts. For tubes with 

 "reflection" targets, that is, where the X-radiation is emitted at 

 right angles to the electron stream, the outputs with a filtration 

 of 0.1 millimeter copper are 2T X 10"^ ( kilovolts)^-^ r per minute 

 per milliampere at 1 meter over the range 75 to 200 kilovolts, 

 while with a filtration of 0.5 millimeter copper, the outputs are 

 1.7 X 10 "* (kilovolts)--^ r per minute per milliampere at 1 meter 

 over the range 200 kilovolts to 2 million volts. For tubes with 

 "transmission" targets, i.e., tubes in which the direction of the 

 X-ray beam is a continuation of the electron stream, the X-ray 

 outputs with a filtration of 0.5 millimeter copper are 2.1 X 10^ 

 (kilovolts)--^ r per minute per milliampere at 1 meter over the 

 range 600 kilovolts to 2 million volts. 



Turning to the corresponding question of the gamma-ray 

 outputs from known quantities of radium sealed in containers 

 having a screenage equivalent of 0.5 millimeter platinum, the 

 outputs can be calculated on the basis that the quantity of radia- 

 tion received in 1 hour at 1 centimeter from a ''point source" 

 of 1 milligram radium is about 8 rontgens. For distances other 

 than 1 centimeter, the calculations are based on the inverse square 

 law of radiation. 



The preceding data on X-ray and gamma-ray outputs refer to 

 the intensities of the direct beams. Far fewer measurments have 

 been made of the intensities of scattered radiation,^ but one or 

 two examples will illustrate the magnitude and importance of the 

 intensities of scattered radiation encountered in practice. The 

 dosage rate at the side of a patient who is screened in the couch 

 position is usually of the order of 100 X 10^ r per second. The 



