366 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 13 



acid. Prepare samples for counting, using a number of aliquots. If standard 

 samples are prepared this way, the corrections for self-absorption and scatter- 

 ing in the sample become considerably simplified. If chemical separation of 

 the decay products of UI is not made, considerable scattering corrections 

 have to be used, such as those determined by Broda [17] and Feather [18]. 



When uranium is used as a secondary standard, it may be prepared as a 

 so-called "thick sample" in a chemical form such as uranium oxide which 



Pa 234 

 (UX 2 ) 



1.14 Minutes 



( UZ ) 

 \ I0"5 sec./ 



0.15 % 

 7 0394 — 

 a L+M (0.5) 



-90 %0~ - 

 045*0.03 



U II 234 



23 x I0 5 Years 



SPIN 



LEVEL 

 ENERGY 



(0,1) 

 2.32 



5 

 1.93 



N 

 (4,5) 



1.48 



M 

 3 



0.85 





 



Fig. 102. Decay scheme for UXo — > UII. All energies are in units of mev. Level energies 

 are given with respect to the 2.32/3" transition. [From II. Bradt and P. Scherrer, Helv. 

 Phys. Acta., 18, 424 (1945).] 



will not change its composition for a long time. The sample is sealed per- 

 manently with aluminum foil. 



b. RaE Standard. In aged rocks containing uranium, the radium and its 

 decay products are in equilibrium and the radium content may be determined, 

 for example, from the radon-producing power. Knowing the radium content, 

 the quantity of RaD can also be calculated and, along with other lead iso- 

 topes, separated quantitatively from the rock sample. Given time, all 

 radioactive lead isotopes except RaD decay completely and equilibrium will 

 be reached between RaD and its daughter substance RaE (see disintegration 

 scheme, Chap. 7, uranium-radium series). The radiations emitted by this 

 sample are then as shown in Table 36. 



The number of disintegrations from RaD and RaE being known, such a 

 sample may be used for beta-particle standardization by absorbing the 

 radiations of the RaD and Po 210 . This may be done with an aluminum 



