376 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 13 



200 



180 



160 



LU 



140 



120 



100 



100 



ATOMIC NUMBER 

 Fig. 106. Saturation backscattering as a function of the atomic number of the back- 

 scatterer. The ordinate represents per cent of the counting rate obtained with a sample 

 support of negligible thickness. [Unpublished data of II. Anger.] 



180 



5 160 

 U 



o 



K 

 Ul 



Q. 140 



120 



100 



0.2 



0.4 



Co' 



60 



0.6 

 .131 



0.8 



1.0 



1.2 



1.4 



1.6 



1.8 



24 



,32 



I'- No 



MAXIMUM BETA ENERGY IN MEV 

 Fig. 107. Saturation backscattering from aluminum, copper, and platinum for a point 

 source as a function of maximum beta-particle energy. The ordinate represents the count- 

 ing rate with respect to a source with no backscatterer (negligibly thick supporting film). 

 [Unpublished data of H. Anger.] 



ing, and when these are compared with various beta-particle samples, the 

 variations in backscattering must be taken into account. Absorption curves 

 taken from samples with saturation backscattering are different from those 

 taken with very thin sample supports because the scattered particles increase 

 the relative number of soft beta particles entering the counter. 



Backscattering can be very nearly eliminated by using extremely thin 



