Neutron-deficient radioisotopes, because of their low production yields, 

 and radioisotopes with half- lives of less than 2 days or greater than 

 15 days were arbitrarily excluded .Table C-l presents some of the data 

 that were used for making the initial selection. Three of the radio- 

 isotopes, 14 °Ba- 140 La, l98 Au, and 133 Xe, were of special interest because 

 of their nuclear properties. 



Table C-l. Comparative Data on Radioisotopes 



Isotope 



Half- 

 Life, 



davs 



Principal 

 Gamma Radi- 

 ation, MeV 



Maximum 

 Permissible 



Burden^ 3 

 (Man), uCi 



Comparative 

 Uptake (Fish), 

 relative units 



lsl Ba 



14C> Ba- 140 La 

 131j 



111 



Ag 



s Xe 



3 Au 



12 



12.8 

 8.05 

 7-5 



5-2 

 2.7 



0.496 (48$) 

 0.124 (28/ ) 



1.596 (96/o) 



0-364 (82$) 



0.247 (ifo) 



0.342 (6/ ) 



0.081 (37/0) 



0.412 (95/o) 



50 



4 



0-7 

 20 



c 

 30 



C. M. Lederer, J. M. Holland, and I. Perlman, Table of Isotopes , 6th ed . , 

 Wiley, New York, I967. 



Handbook No. 69 , U. S. Dept . of Commerce, National Bureau of Standards, 

 , July 5, 1959- 

 'No retention. 



Barium-l40-lanthanum-l40 had been used for sand tracing, and techniques for 

 tagging sand had been developed by the Naval Radiological Defense Labora- 

 tory. However, this radionuclide has two disadvantages: (l) The exces- 

 sively high energy gamma rays (l.6 MeV) make handling and radiation ex- 

 posure control difficult. (2) Tagging sand with 140 Ba- 140 La consists of 

 coating the surface of the sand grains with sodium silicate containing 

 the radionuclide, and initially it was not known whether or not this would 

 affect the hydraulic properties of the sand (later experiments indicated 

 that little, if any, adverse effect resulted from this labeling technique). 



Gold-198 has also been used on various projects, but the evaluation of the 

 198 Au- labeled materials has been very limited. Leaching rates, efficiency 

 of tagging, and actual labeling procedures are not described in detail. 

 Also, it was believed that the half-life of this nuclide (2.7 d) would 

 limit tracing experiments to one week or less. However, - 1 8 Au was main- 

 tained high on the list of useful isotopes since it can be prepared in 

 large quantities at a relatively low cost and the biological hazard is 

 low (Table C-2).(ln a later study, which will be reported separately, it 



C-5 



