CHAPTER 8 



INDIRECT METHODS FOR MEASURING DEUTERIUM 



James S. Robertson 



8.1. Introduction. The stable isotopes offer the advantage of avoiding the 

 time limits inherent in many radioactive-isotope experiments. Their 

 abundance can be determined directly with the mass spectrometer (Chap. 9) 

 or indirectly from measurements of those physical properties which vary with 

 isotopic ratio. In general, the detection of small differences in these proper- 

 ties is difficult, and in those cases where there is relatively little difference in 

 the masses of the isotopes involved, even very large changes, say 100 per cent, 

 in isotopic composition cause undetectably small changes in these properties. 

 This, with the added complication that traces of impurities may exert com- 

 paratively large effects, has so far served to render these methods useless 

 for all but two isotopes, deuterium and the heavy isotope of oxygen, O 18 . 



Among the methods based on density differences which have been devel- 

 oped for analysis of deuterium in water are the use of the pycnometer [1,2], 

 the free float [3-10], the falling drop [11-14], and the diffusion gradient 

 [15,16,17]. Methods based on changes in the refractive index [18,19] and in 

 the vapor pressure [74] of water have also been developed for deuterium 

 analysis. The vapor-pressure method has a lower precision than the other 

 methods, but does afford a rapid means for an approximate D2O analysis on 

 a minute amount of material. 



A wide assortment of methods based on changes in other physical properties 

 of water or of hydrogen gas have been used with varying degrees of success. 

 Among these are spectrum analysis [20], thermal conductivity [20-23], the 

 deuterium-lithium nuclear reaction [20,24], electrode potentials [25], viscosity 

 [26], freezing point [27], infrared absorption [28], and gas-density balance 

 [60,61]. Some of these obviously are not suitable for routine applications. 



Density methods have also been used to determine the abundance of O 18 

 in water [29]. 



8.2. Physical Properties of Deuterium Oxide and Water. In this section 

 data available prior to 1941 are summarized. Because of the importance 

 of heavy water in atomic power very little of such information has appeared 

 in the open literature since that date. 



Some of the physical properties of deuterium oxide and of natural water are 

 compared in Table 28, abstracted from a more extensive tabulation in the 



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