Geochemical techniques isotope ratios

Concentrations of uranium and thorium are also measured by other techniques (e.g., instmmental neutron activation analysis) and sometimes included in trace element analyses. In geochemical literature the ratio [Th/U] is frequently used. However, Th is the only long-lived thorium isotope and U is a fixed 99.28% of total uranium, so [Th/U] ratios are closely related (3.3% smaller) to atomic Th/ U ratios. The latter ratio has historically been termed k when used in the Pb isotope literature. To further... 

Geochemists were some of the first researchers to realize the enormous benefits of ICP-MS for the determination of trace elements in digested rock samples. Until then, they had been using a number of different techniques, including neutron activation analysis (NAA), thermal ionization mass spectrometry (TIMS), ICP-OES, x-ray techniques, and GFAA. Unfortunately, they all had certain limitations, which meant that no one technique was suitable for all types of geochemical samples. For example, NAA was very sensitive, but when combined with radiochemical separation techniques for the determination of rare earth elements, it was extranely slow and expensive to run. TIMS was the technique of choice for carrying out isotope ratio studies because it offered excellent precision, but unfortunately was painfully slow. Plasma... 

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