Optimal parameters to produce 131I by neutron irradiation and melting of sintered tellurium dioxide

High purity TeO2 was produced by adding 125 ml of 6N HNO3 to 50 g of metallic tellurium (Merck No. 8100) and heating to 330 degrees C till dryness in presence of an air flow. Released vapors of NO2 are dissolved in 3 connected closed water containers. TeO2 is sintered in quartz tube put in an oven and heating gradually to 700 degrees C and then for 5 min at this temperature. The sintered TeO2 is a suitable target to be irradiated with thermal neutrons and induce the nuclear reactions: Te-130(n,gamma) Te-131m (t(1/2) = 30 h) and Te-130(n,gamma) Te-131 (t(1/2) = 24.8 m) for and irradiation time of 24 h. After a cooling time of 48 h, the radioactive source is put in a small electric oven enclosed in an airtight box where a negative pressure is kept along the experiment (0.5 cm of water). There it is heated gradually till melting (733 degrees C). From 400 degrees C on the vapors from the oven are pumped out and bubbled in 2 solutions. First one is 0.1 M NaOH. Second one is 0.02 M Na2CO3 plus 2.5 x 10(-3) M NaHCO3 (40%). Before being released, vapors bubbled in the solution passed an activated carbon filter. The first solution (0.1 M NaOH) catches 99.9% of I-131 activity pumped out (about 300 m Ci for 1.5 h of pumping). This solution is diluted and the pH value fixed at suitable value (7-9) before bring distributed for its use. The residual activity remains in the second solution and the activated carbon filter. (C) 1999 Elsevier Science B.V. All rights reserved.