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 deg. 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 deg. 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: 130Te(n,γ) 131mTe (t1/2=30 h) and 130Te(n,γ) 131Te (t1/2=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 deg. C). From 400 deg. 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 2.5x10-3 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 131I 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 being distributed for its use. The residual activity remains in the second solution and the activated carbon filter