MEASUREMENT OF IONIZING RADIATIONS 



155 



of these functions are shown in Fig. 2-4 as calculated by Laurence (1937) 

 for monochromatic radiations; Fig. 2-5 shows the relation between B and 

 photon energy for a few wall elements; and Table 2-1 gives the values of 

 2 log Zn,/Za and (2 log Zu,/Za)' for several materials of radiological inter- 

 est. If the radiation consists of a number of monochromatic hues of 



I 15 



PHOTON ENERGY, Mev 

 Fig. 2-4. Values of coefficients K, J, and L needed for the evaluation of the correction 

 factors of a thimble chamber (see text). 



Al 



Mg 



AIR 



CARBON 

 H2O 



= Be 







0.5 



20 



2.5 



10 1.5 



PHOTON ENERGY, Mev 

 Fig. 2-5. Thimble chamber corrections calculated by Laurence's formula (7) (see text ) . 



fractional photon intensities, as (photons per square centimeter of energy 

 E divided by the total number of photons per square centimeter), then 



J = XueJe K = ^asKs L = Sa^Ls (8) 



Similarly, if the photon radiation consists of a continuous spectrum 

 defined by dn photons per square centimeter with energy between E and 

 £ + dE, 



