170 RADIATION BIOLOGY 



g^ (average) = (1 - e"") I 1 - -r: 



r 3 3e-^° ^ 3(1 

 L 4a 4q!^ 



-2a^ 



8 



a 



(19a) 



where, as for Table 2-3, oc = /xa, namely, the radius expressed in relaxa- 

 tion lengths. 



1000 



100 



°^ '0 



I 



E 

 E 



-k 



0.1 



001 



001 



10 



01 10 



(i AND ?• ENERGY, Mev 



^ PHOTONS (EXCLUOING SCATTERING COEFFICIENT) 



PARTICLES (ROSSI. 1949) 



•-— •(3 PARTICLES (LOEVINGER, 1950) 



Fig. 2-9. Relaxation lengths (1/m) in millimeters of water as a function of energy 

 of ionizing radiation. /3-ray energy refers here to the maximum energy of )3-ray 

 spectrum. 



tion of the maximum energy E^s of the /3-ray spectrum in Fig. 2-9 by the broken line 

 marked "Loevinger." The equation representing this line is m"' = 0.52£'o^, where 

 )u~' is in millimeters of H2O and Ets is in mega electron volts. 



Preliminary experiments by the Argonne Group (Brar, Clark, and Marinelli, 

 1950; Munick and Clark, 1950), on the other hand, show that, for P^^ at least, the 

 ionization function in free air could be represented approximately by 



/(r) = Kr-KR - r) 



where 72 is approximately two-thirds the theoretical range of the most energetic /3 ray 

 and K is a constant. 



