NIOBIUM 275 



Intake Levels. In previous American usage, element 41 has been 

 designated as columbium. However, the name niobium has been adopted 

 by the International Union of Chemistry. This element is not an impor- 

 tant naturally occurring constituent of biological materials and has been 

 of interest primarily on account of the production of Nb^^ in the fission 

 process. Nb^° is a daughter of another fission product, Zr^^. 



Radioassay, Although soft-beta counting is most sensitive, the prob- 

 lems of self-absorption will make gamma counting the method of choice. 



Chemistry. Methods are not available for estimation of niobium in 

 biological materials. Routine wet- or dry-ashing methods may be used. 



Typical Methods. In a study with rats (Nb-1), 5 ^c Nb^^ in 0.25 ml of 

 a 0.01 per cent sodium citrate solution (pH 6) was injected by way of the 

 great saphenous vein. Tissue samples were dried, then ashed at650°C 

 for 10 hr, and the ash dissolved in 2 A^ HCl. Ahquots, up to 5 ml, were 

 placed in i-2-oz metal ointment capsules for counting with a thin-mica- 

 window tube. It would be important to check recoveries because of the 

 possible adsorption of niobium on glass surfaces and insolubility in HCl. 



Nb-1. Kawin, Bergene, D. H. Copp, and J. CI. Hamilton: Studies of the Metabolism 

 of Certain Fission Products and Plutonium, UCRL-812, Aug. 7, 1950. 



