Sec. 13.6] 



STANDARDIZATION OF RADIOACTIVE SAMPLES 



367 



absorber of 10 mg per cm'. Usually the RaD is electrolytically deposited 

 in a very thin surface layer, and if sufficient time is allowed, the alpha dis- 

 integration of polonium may be measured to verify the sample activity. 

 RaE has a single beta particle and no gamma rays, but the beta transition 

 is classified as forbidden so that the spectrum is different from that of beta 

 particles in allowed transitions. There is also one alpha particle emitted 

 for about every million betas. The Bureau of Standards [16] has made a 



number of standards of this type for distribution among radioisotope workers. 

 These standards can be used to calibrate the approximate efficiency of 

 Geiger counters for beta radiations. However, when this is done a number 

 of rather complex factors have to be considered. These will be discussed in 

 Sec. 13.10. 



In the method given by Broido et al. [15] for preparation of RaE standards, 

 chemical separation of RaE from RaD and Po 210 is utilized. A mixture of 

 RaD, E, and F should be taken up in 10 ml of 0.1 A hydrochloric acid. Add 

 20 mg powdered nickel, heat the mixture to 80°C, and stir for 3 min. The 

 powdered nickel then takes up the RaE and F. Centrifuge and wash the 

 precipitated nickel three times with 0.1 A hydrochloric acid. Dissolve the 

 nickel with ~1 ml aqua regia and dilute to 10 ml. The nickel may now be 

 separated by addition of 20 mg bismuth carrier and then an excess of ammo- 

 nium hydroxide. Bismuth hydroxide precipitates carrying RaE and 

 fluorine but leaving the nickel in solution. In order to separate the RaF 

 from the RaE an ion exchange column may be used. The bismuth hydroxide 

 is dissolved in hydrochloric acid diluted to an acidity of 0.1 A and passed 

 through a 1-cm diameter column made up of 10 ml 40-60 mesh 1R-1 resin. 

 The bismuth and RaF are absorbed in the column. The bismuth may be 

 eluted with 3A nitric acid (approximately 10 ml.) leaving the RaF in the 

 column. The purity of the RaE preparation may be checked by half-life and 

 absorption measurements and with growth curves of the alpha activity of 

 RaF (Po 210 ). The absolute RaE disintegration rate may be obtained by 

 measuring the absolute RaF activity, // (/), in an alpha-particle chamber and 

 extrapolating back to the amount of RaE at zero time Z«(0), using the 

 equation 



