STRONTIUM 303 



Sr/Ca ratios, considered in terms of calcium-intake levels, give an indica- 

 tion of limitations of strontium mass in tracer studies. 



Radioassay. Preparation 8r-89-P is prol)ably the preparation of 

 choice for general tracer studies. The Sr^", which is present in less than 

 10 per cent amount at the time of processing, may become of importance 

 if an old preparation is used. Interference from the Sr^"-Y^'' in the Sr^" 

 preparation can be eliminated by the following procedure: (a) use of an 

 aliquot of the preparation administered to the organism for a standard 

 against which the samples are compared; (h) allowance of about 25 days 

 between taking of sample and measurement to permit attainment of equi- 

 librium between Sr^" and Y^"; (c) recognition of the fact that the self- 

 absorption characteristics will change with the composition of the 

 mixture. Actually the beta energies are sufficiently high so that self- 

 absorption will not be an important factor unless relatively large sample 

 masses are used. Preparation SrY-90-P is equally useful for tracer 

 studies, provided a long half-life is acceptable. Routine hard-beta 

 measurements after the 20- to 25-day waiting period are quite satisfactory 

 (see Chap. 2). Attention is called to the hazard of these radioisotopes, 

 and special emphasis should be placed on the avoidance of conditions 

 under which they might be taken into the body of personnel. 



Chemistry. Routine wet- or dry-ashing methods are satisfactory. 

 Chemical estimation is perhaps best accomplished by spectrographic 

 methods (Sr-1). Chemical procedures developed for the separation of 

 radiostrontium from the fission mixture (Sr-3) may be useful in isolating 

 activity from low-level samples. These methods are usually based on 

 precipitation of the nitrate by the fuming nitric acid procedure. An 

 alternative procedure has been proposed which consists in adding stron- 

 tium carrier to the sample, removing three ferric hydroxide scavenging 

 precipitates, and isolating the strontium as the carbonate (Sr-4). Iden- 

 tification of Sr^" in a sample containing an unknown activity may be 

 easily obtained by carrying out such a separation and observing the 

 growth of the yttrium daughter. For low-level counting of Sr^" there 

 may be some advantage in separating the Y^" daughter; this can be done 

 by precipitation with yttrium or lanthanum carrier (see page 63 for a 

 listing of the advantages of this procedure). 



Typical Methods. In a study of the transmission of Sr^^ from mother 

 to offspring in mice, levels of 0.01 to 5 Aic/g body weight were administered 

 (Sr-5). ^Mothers were measured for activity with a (leiger tube by caging 

 the living animal in a cellulose acetate container (thickness, 0.18 mm) 

 which prohibited movement. Factors for conversion of counts to Sr*^ 

 content were derived from experiments in which luimerous animals were 

 measured in this way and then sacrificed for actual tissue determinations. 

 By standardization of conditions, reasonably reliable estimates were 



