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CERIUM
Natural Abundance, Stable Isobars Ce136, 0.193%, Xe136 Ce138, 0.250%, Ba136 Ce140, 88.48%, Ba138 Ce142, 11.07%, aLa138, Nd142 The only compound which has been used in the separation of cerium isotopes is anhydrous cerium trichloride. The average charge consists of 150 g CeCI3 in a style C-16 graphite bottle. Cerium was found to be the only rare earth whose oxide could not be converted to the trichloride by heating with ammonium chloride, as described in detail under samarium. Cerous chloride also appears to be the only rare earth chloride which can be prepared from solution without undergoing hydrolysis and producing a basic salt. Although many cerium compounds, including the nitrate, sulfate, and oxide, can be converted to the chloride, only the conversion of cerous nitrate will be considered here. Cerous nitrate is dissolved in a minimum of water and filtered. Ammonium carbonate is added to the filtered solution precipitating cerium carbonate. The precipitate is washed with cold water by decantation until the supernatant gives a negative test for nitrate ion. The cerium carbonate is isolated by filtering through paper and then dissolved in hydrochloric acid. Evaporation a hot plate is continued until the cerium chloride solution reaches a viscid and foamy consistency, at which time heat lamps are used to complete the evaporation to dryness. The resulting cake of CeCl3 is broken into small pieces, placed in an outgassing apparatus, and heated to 400°C at a pressure of approximately 100 m for three to four hours. Unresolved cerium charge material is recovered by washing calutron components with a dilute nitric acid solution. Cerium is precipitated from the wash solution with oxalic acid and ignited to cerium oxide. Nitric acid is used to dissolve the oxide, and the resulting solution is treated as above to produce the trichloride. Cerium and its compounds have a low order of toxicity. Normal care in handling cerium compounds provides adequate personnel protection. aLa138, natural abundance 0.089%, is radioactive with a half-life of 1.1 x 1011 years. |
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