الفهرس 
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Abstract
The thesis entitled ’’Preconcentration and Separation of Radioiodine from its Solutions’’ comprises three chapters; Introduction, Experimental, and Results and Discussion. Chapter one, Introduction, includes brief accounts on the iodine radioisotopes, applications of iodine-131 and iodine-125 in nuclear medicine, chemistry and radiochemistry of iodine, chemistry and radiochemistry of tellurium, production routes of iodine-131, iodine-123 and iodine-125 and chemistry of silver. It also includes preconcentration and separation techniques of radioiodine including liquid-liquid extraction, ion-exchange, precipitation and distillation methods (i.e., wet, melting and dry distillation methods). Chapter two, Experimental, includes list of chemicals and solutions as well as specifications of the equipments used in the present study and experimental investigations: 1- Production of 125I and 123mTe radiotracers: target preparation for neutron irradiation and chemical processing of the irradiated targets. 2- Preconcentration of 125I from tellurium solutions. First, onto in-situ precipitated silver hydroxide as a function of silver ion concentration, Ag+:I- molar ratios and dextrose (as reducing agent). Second, onto pre-prepared silver granules via batch distribution and chromatographic column methods. 3- Recovery of radioiodine from: - In-situ precipitated 125I-silver hydroxide. - Batch loaded 125I-silver granules (including the factors which may affect 125I recovery such as presence of dextrose and sodium borohydride, amount of zinc dust, ammonia concentration and contact time).Chromatographic column loaded 125I-silver granules via elution with Na2S solution and batch equilibration with NH3 solution containing Zn dust. 4- Purification of 125I recovered from batch equilibration/chromatographic column 125I-loaded matrices by the wet distillation method. 5- Quality control investigations of the recovered 125I product solution including separation factor, recovery yield, radionuclidic and radiochemical purity and pH-value. Chapter 3, Results and Discussion. The radiotracers used in this study were Na125I dissolved in 0.01M (NaOH + Na2S2O3) mixture solution, tellurium-123m tracer (radiotracer solution a) prepared by dissolving 1.0 g radioactive TeO2 in 30 ml 5M NaOH, and radiotracer solution b consisting of 5 ml of radiotracer solution a, 1.25 ml 125I radiotracer solution and 93.75 ml 5M NaOH. The solutions were analysed by gamma-ray spectrometry and identified from the energy peaks of the corresponding radionuclides. Preconcentration studies of carrier-free 125I from alkaline radiotracer solution b were carried out onto Ag2O (from in-situ precipitated AgOH) and pre-prepared silver granules via batch equilibration and chromatographic column methods. In-situ precipitation method indicated that, for a settling time interval of 1.0 h from the end of Ag+ addition to radiotracer solution b, tellurium-123m was quantitatively detected (i.e., remained) in the supernatant at all Ag+ concentrations under study. 125I removal was gradually increased from 60.6 to 99.99% with increasing Ag+ concentration from 10 to 150 ppm. Quantitative 125I removal was achieved at high Ag+ concentrations from 200 to 500 ppm. It was found that more or less similar results were obtained after settling time intervals of 24 and 48 h. The effect of Ag+:I- molar ratios on the percent removal of 125I from 20 ml tellurium solutions containing constant iodide ion 2.36×10-3M (6 mg I-) and different silver ion concentrations from 4.63×10-4 to 9.27×10-3M (50 to 1000 ppm Ag+), and from solutions at constant silver ion 2.78×10-3M (300 ppm Ag+) and different iodide ion concentrations from 7.09×10-4 to 1.35×10-2M (1.8 to 30.4 mg I-) proved that in both cases Ag+:I- molar ratio 1.0 was the optimum for quantitative elimination of I- anion (corresponding to the stoichiometry of Ag+ and I- =1:1 as in AgI). Whereas, 123mTe was quantitatively remained in the supernatant. The effect of Ag+:I- molar ratio on the removal of 125I (in the presence of 2.36×10-3M I- carrier, 6 mg I-) showed that quantitative removal of 125I from solution has been achieved at Ag+:I- molar ratios ≥ 1. The effect of dextrose, as a reducing agent, on the percent removal of 125I from tellurium solution at different concentrations of silver ion in the range from 10 to 500 ppm and 1.0, 24 and 48 hours settling time, with the notice that molar concentration of dextrose in each vial was twice that of silver, indicated that the percent removal of 125I was 95.7% after a settling time of 1.0 h. Then, 125I was gradually increased in the supernatant with increasing the time interval (i.e., 125I release from the formed Ag2O/AgI precipitate). The percent removal of 125I was decreased to 88% after a settling time of 48.0 h. On the other hand, 9.2% of 123mTe was removed from the supernatant after a settling time of 1.0 h and then, it was gradually increased in the supernatant to 4.0% 123mTe after a settling time of 48.0 h. In the batch equilibration method, 5 ml of radiotracer solution b was completed to 20 ml by the addition of 5M NaOH solution and brought in contact with 0.1 g pre-prepared silver granules for predetermined time intervals at room temperature. The effect of contact time on the percentage removal of 125I and 123mTe proved that 123mTe was remained quantitatively in the aqueous phase over the time intervals of 9.0 h, while the removed percentage of 125I increased gradually with increasing the contact time to 7.0 h at which quantitative removal 99.99% of 125I was achieved. In the chromatographic column method, 20 ml of radiotracer solution b was fed to a Pyrex glass column packed with 1.0 g silver granules of 120-230 mesh size. 125I was quantitatively retained onto the column matrix with removal percent 99.99%, while 123mTe was passed through the column bed and quantitatively collected in the loading effluent. Recovery studies of 125I were carried out from 125I-silver hydroxide and 125I-silver granules using ammonia solutions in the presence of a reducing agent. Iodine-125 was recovered from silver hydroxide-Ag125I precipitate obtained via in-situ precipitation of 500 ppm Ag+ from radiotracer solution b by batch equilibration with 20 ml 2.7M NH3 solution containing 30.3 mg Zn dust for a contact time of 1.0 h. The extractant composition was determined from the optimum conditions for 125I recovery from silver loaded 125I granules. The percent recovery of 125I in the aqueous phase was just 58.0%. The recovery of 125I from silver granules was conducted from NH3 solutions in the presence of reducing agents such as dextrose, sodium borohydride and zinc. The effect of dextrose concentration (20.87, 41.75 and 83.5 mg) onto the percent recovery of 125I from 0.1 g 125I loaded silver granules in 3.31 ml of concentrated NH3 solution (18.1M) indicated that only 1.8% of 125I was recovered in the supernatant after a contact time of 19.0 h. It was found that no 125I was recovered in the supernatant for contact time up to 19.0 h. by adding 4.375, 8.75 and 17.5 mg sodium borohydride in 3.31 ml of concentrated NH3 solution (18.1M) to 0.1 g 125I loaded silver granules. The effect of zinc amount, ammonia concentration and contact time on the percent recovery of 125I from the silver granules proved that the molar ratios of Zn:Ag ≈0.5, NH3:Ag ≈58.2 and NH3:Zn ≈116.5 and the contact time of 1.0 h are the optimum conditions for maximum recovery of 125I from 125I-silver granules with 20 ml of 2.7M NH3 solution containing 30.3 mg of Zn dust. Also, recovery of 125I from 125I-silver granules of the chromatographic column bed, was conducted via two methods namely, dynamic method and batch equilibration. In dynamic method, the column was eluted with 10 ml 0.2M Na2S solution at a flow rate of 1.0 ml/min and 25°C. 125I was eluted with yield of 86.8% from the 125I-silver matrix with passing 8 ml 0.2M Na2S solution in 0.1M NaOH through the column bed. In batch method, the 125I-silver matrix was brought out of the column by pushing 10 ml 2.7M ammonia solution via a syringe through a hose fitted to the column bottom. Then, ammonia solution was completed to 30 ml and finally, the optimum zinc amount was added. It was found that 125I was quantitatively recovered with 99.99% in the aqueous phase. In relation to chemical behavior of the interfering 134Cs, 65Zn and 60Co radionuclides it was found that while 125I was quantitatively retained onto the silver granules, radiotellurium (121m,123mTe) along with 65Zn and 60Co were quantitatively remained in the aqueous phase with 51.1% 134Cs retention onto the silver granules. Purification process of the recovered 125I was done in order to obtain 125I free from interfering radiocontaminants. It was achieved by the wet distillation method in which the recovered 125I solution was acidified to 20% with concentrated H2SO4 acid and oxidized with 2 ml 30% H2O2 solution. The mixture was boiled to distill-off 125I. Purification of 125I recovered from batch equilibrated 125I-silver granules showed that 125I was quantitatively distilledoff from the distillation flask after boiling for 4.0 h. 75% of the distilled-off 125I was recovered in the first alkali receiver containing 10 ml mixture solution of 0.1M NaOH and 0.01M Na2S2O3 with a radionuclidic purity of 99.99% 125I and a radiochemical purity of 98.8% as I- anionsThe sodium sulfide 125I-eluate (from the silver column) was transferred to the distillation flask and then, sulfuric acid was added to obtain pH 1. The solution was gently heated to remove released H2S, due to acidification of Na2S solution, which was collected into a receiver containing 10 ml 0.1M lead acetate connected in place of the first alkali receiver. Lead acetate solution was replaced periodically by fresh solutions until no black color was observed, indicating the cease of H2S evolution. Thereafter, the condenserwas thoroughly washed with distilled war and the alkali receiver wasconnected to the distillation apparatus (instead of the lead acetate receiver)and more concentrated H2SO4 and 2 ml 30% H2O2 was added to the distillation flask to obtain 50 ml 20% H2SO4 solution. The mixture was boiled with radioactive monitoring the evolution of 125I gas for different time intervals. Alternatively, the boiling process was carried out for the acidified mixture (50 ml containing 20% H2SO4) after adding 0.1 g Zn dust and then, 2 ml 30% H2O2. It was found that 125I was quantitatively distilled-off from the still after boiling for 4.0 h. 73.8% of 125I was recovered in the first alkali receiver with radionuclidic purity 99.99% and a radiochemical purity of 98.9%. The mixture of 30 ml 18.1M NH3 solution and 300.3 mg zinc dust was batch equilibrated for 1.0 h with 1.0 g 125I-loaded silver bed of the chromatographic column then, centrifuged and transferred to the distillation flask of the wet distillation apparatus. Thereafter it was acidified with concentrated H2SO4 acid to obtain 60 ml containing 20% H2SO4 and 2 ml 30% H2O2 solution. Radiometric analysis showed that 78.5% 125I was recovered in the first alkali receiver (0.1M NaOH + 0.01M Na2S2O3) after boiling for 4.0 with radionuclidic purity 99.99%, radiochemical purity ~ 98.3% (as I- and pH value of ~13 ion.