43 16. After plating for 120 min. at 0.5 amperes, the plating solution is made basic with one to three ml of concentrated NH40H. After one minute the plating cell is removed, disassembled and the disc is washed sequentially with distilled water, acetone and finally flamed to a dull red color over a bunson burner. 4,2-2 Chemical procedures for isolating polonium-210. Polonium-210 was determined by spontaneously plating the polonium out of 0.3 M HCL onto silver discs (Beasley, 1969). of 208 Pu was used for the chemical yield determination. A known quantity The procedure is as follows: Chemical Procedures for the Separation and Platingof Polonium from Coralline Sediments 1. An aliquot of dissolved sediment is spiked with a known activity of 208 Pu and evaporated to dryness. 2. The residue is completely converted to chlorides by repeatedly adding distilled 6 M HCL and evaporating to dryness. 3. The residue is dissolved in about 250 ml of 0.3 M HCL (acid and water were both distilled in the laboratory). 4. Reagent grade ascorbic acid is slowly added to the solution until all the iron in solution is complexed, as is judged by the disappearance of any yellowish color, then a small additional amount is added. 5. Polonium is spontaneously plated onto silver discs (one side of the disc is coated with glyptal) by stirring the n solution in which the silver disc is suspended overnight. . The silver discs are removed and lightly patted dry after a distilled water rinse. The side not covered with the glyptal is alpha-counted. 4.2-3 Instrumentation of calibrations The measurement of radioactivity by alpha spectroscopy pra was made by using eight 300 mm2 ORTEC®? silicon surface barrier diodes. Each a. ORTEC, Inc., Oak Ridge, Tenn. 37830.