60 



rSOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 3 



The Feather method consists in comparing the absorption curve of the beta 

 emitter being investigated with the curve for an isotope with a simple beta 

 spectrum for which the range is known accurately, such as RaE (476 + 2 

 mg of aluminum per square centimeter [5]). The absorption curve for RaE, 

 measured with aluminum-foil absorbers and corrected for air and window 

 thickness and with the background subtracted, is plotted on semilogarithmic 

 graph paper with range scaled along the abscissa. The total range (476 mg 



10,000 



1,000 



z 



2 



ac 



Q. 



100 



RANGE IN MG/CM 



— n— 



i r 



.5 .6 .7 .8 .9 1.0 



FRACTION, RANGE OF STANDARD 





 .1 



.2 



D 



C 

 < 



— .7 



•8 o 



.1.0 



Fig. 13. Feather method for determining the range of beta particles by comparing the 

 absorption curve with that of beta particles for which the range is accurately known (e.g., 

 RaE for which R = 476 mg/cm 2 ). 



per cm 2 ) is then divided into 10 equal parts, and horizontal lines are drawn 

 through corresponding points on the absorption curve, as shown in Fig. 13. 

 Without altering the counter and sample geometry, a similarly corrected 

 curve is obtained for the test material and plotted on the same graph starting 

 also from the same ordinate for zero absorber thickness. The intersections 

 of the previously drawn horizontal lines when referred to the abscissa give a 

 set of fractional ranges differing from those of RaE. Each of the fractional 

 ranges is then divided by its corresponding decimal fraction (0.1 — 0.9), and 

 the resulting estimates of range are plotted against the same fraction, as 

 illustrated by Fig. 14. A curve drawn through the points thus plotted may 

 then be extrapolated to the point R (abscissa of 1.0) which is the actual 

 range in aluminum. In practice the horizontal lines obtained with the RaE 

 absorption curve are ruled on a vertical scale with the divisions marked to 10 

 to match the corresponding fractional range. The scale may then be used 



