Radium tracer applications

Tile unit of radioactlvlly is the curie (Ci). It Is defined cis the quantity of radioactive material in which the number of nuclear disintegrations per second is the same as that in 1 g of radium, i.e, 3.7 X 10 (3.7 x 10 °s" ). The curie is a large unit and only millicurles (mCi) are needed for tracer applications. The curie refers to the number of disintegrations actually occurring in a sample rather than the number of disintegrations counted in a radiation counter. 

Analogous to the process releasing Ra to seawater, decay of Th in sediments releases dissolved Ra which is then mixed into the ocean interior. Radium-226 decays through a series of short-lived nuclides to Pb (half-life 22.3 yr) which, like thorium and protactinium, is insoluble and readily sorbs to particles. Radioactive decay of gaseous Rn in the atmosphere also produces Pb, which is then deposited on the sea surface with aerosols and in precipitation. Although Pb and, to a lesser extent, Pa have found many applications as tracers of particle transport, by far the greatest use has been made of thorium isotopes, which form the focus of this review. 

In 1911 Ernest Rutherford asked a student, George de Hevesy, to separate a lead impurity from a decay product of uranimn, radium-D. De Hevesy did not succeed in this task (we now know that radium-D is the radioactive isotope Pb), but this failure gave rise to the idea of using radioactive isotopes as tracers of chemical processes. With Friedrich Paneth in Vieima in 1913, de Hevesy used Pb to measure the solubility of lead salts—the first application of an isotopic tracer technique. De Hevesy went... 

The analytical application of radionuclides, along with other applications in radioanalysis, results directly from Hevesy and Paneth s invention of radio-tracer and radio-indication techniques in 1912. They pointed out that the addition to a solution of an element of its radioactive isotope makes possible the identification and determination of the element. In their first application they labeled a solution of lead with radium-D, a natural radioactive lead isotope and determined the solubility of sparingly soluble lead salts. 

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