Volume 106, Issue 8

Relative fission-yield measurements were made for 50 fission products from 25.6±0.5 MeV α -induced fission of Th-232. Quantitative comparison of these experimentally measured yields with the evaluated fission yields from 14-MeV neutrons on U-235 demonstrates the application of the Bohr-independence hypothesis for measuring fission yields. As optimum particle-target configurations may be impossible or compromised at a given facility, this new approach, fission-proxy, allows the measurement of fission yields for a given compound nucleus from an alternate reaction pathway since formation and subsequent decay are independent processes.

Uranyl sulfate obtained by uranium ore leaching of an industrial sample deposit of Gachin site was used for uranium separation by the solvent extraction technique. The presence of other elements in the sulfate leach liquors has a negative impact on the uranium extraction process using Alamine 336; therefore, the operating costs are increased. In this study, the separation of uranium(VI) and iron(III) by Alamine 336 and kerosene have been examined as an extractant and a diluent, respectively. For this purpose, the effects of operating parameters on the extraction process such as Alamine 336 concentration, modifier concentration, contact time, initial aqueous pH, sulfate ion concentration, temperature, and stripping agents were investigated. Also, the complete removal of iron(III) interference from the sulfate leach liquor before the extraction step has been studied with reducing agents. The equilibrium constants and stoichiometric coefficients for uranium and iron extraction with Alamine 336 in the sulfate leach liquors were calculated. Likewise, the values of the thermodynamic parameters such as Gibbs energy, enthalpy and entropy were determined to prove the exothermic and spontaneous reactions. The mentioned procedure is proposed for the uranium separation from the impurities in the sulfate ores using tertiary amine for production of purified uranium.

Thorium was precipitated homogeneously from a thorium nitrate solution by the thermal decomposition products of urea. The kinetics of the hydrolysis were studied at 90 and 100°C by pH measurement during the initial 5 h and the precipitation efficiencies of thorium and radium were measured over a 24 h period. Precipitation of the radium daughters was closely followed with the aim of co-precipitation of radium with thorium. The CO 2 formed during urea decomposition dissolved in the solution, forming CO 3 2− during the experiment upon reaching a sufficiently high pH level (>7). This allowed radium to co-precipitate partially, thus reducing the activity of the filtrate. After filtration or centrifugation, the precipitate is composed of nanocrystalline thorium dioxide (crystallite size ~10 nm), with weakly bound H 2 O and CO 2 .

The Th solubilities of the sample solutions that initially contained Th(OH) 4 (am) prepared by undersaturation and oversaturation methods in the pH c range of 2.0–8.0 in a 0.5 M ionic strength solution of NaClO 4 and HClO 4 and stored at aging temperatures ( T a ) of 298, 313 and 333 K were investigated in this study. After a certain period of time up to 40 weeks depending on T a , supernatants of the sample solutions were ultrafiltrated through 3 kDa membranes under the measurement temperature ( T m ) of 298, 313 and 333 K. Size distributions of the colloidal species were investigated by ultrafiltration using membranes with different pore sizes ranging from 3 to 100 kDa, and the solid phases were examined by X-ray diffraction (XRD). The solubility of the sample solutions obtained after aging at T a =298 K using undersaturation method with continuous shaking was similar to those of dried precipitate of Th hydroxide. The solubilities obtained after aging at T a =313 and 333 K were lower than those at T a =298 K. The XRD spectra suggested that the crystallization of the solid phase proceeded under these elevated temperatures. The solubility of the sample solutions obtained after aging at T a =333 K using the oversaturation technique were similar to those prepared by undersaturation method and aged at the same T a . A slight temperature dependence of the apparent solubilities on the T m was observed in the sample solutions prepared by both methods. The solubility products (Ksp,Ta(Tm))$({K_{{\text{sp,}}{T_{\text{a}}}}}({T_{\text{m}}}))$ after different T a and T m were determined from the solubility analysis. The observed increase in the formation constant (Ks,Ta(Tm))$({K_{{\text{s,}}{T_{\text{a}}}}}({T_{\text{m}}}))$ of Th 4+ +(4+ x )H 2 O(1)⇌Th(OH) 4 · x H 2 O(s, T a )+4H + with increasing T m indicated that the reaction was endothermic. The enthalpy change (ΔHrm_Ta→cr°)$(\Delta_{r}H_{m\_ T_{\text{a}} \to {\text{cr}}}^{\circ} )$ between the solid phases of Th(OH) 4 · x H 2 O(s, T a ) and ThO 2 (cr) suggested that the solid phase transformation from Th(OH) 4 · x H 2 O(s, T a ) to ThO 2 (cr) contains an endothermic process.

In order to determine favorable and different elements in soil, the rapid and accurate methods are required. In this research, simultaneous prediction of thorium and uranium in soil samples was performed via gamma spectrometry. Then, the acquired data were analyzed with artificial neural network (ANN) and net area peak (NAP). Natural soil samples obtained from thorium ore consisting of thorium and uranium were used to train models (ANN and NAP). The techniques were evaluated with respect to prediction ability of uranium and thorium concentrations and robustness. Using proposed ANN and NAP methods, the thorium concentration was predicted with mean relative error percentage less than 8.27% and 9.30%, respectively. Also, uranium concentration just was determined with ANN because the NAP method cannot measure uranium concentration. The performance of the neural network model and NAP technique were compared with the acquired empirical data. The results showed that the neural network can more accurately predict the thorium and uranium concentrations in soil samples.

A solvent extraction method has been employed to extract and separate zirconium and hafnium from the nitric acid medium using Cyanex-272 and its mixture with TBP in kerosene. The effects of the experimental parameters such as contact time between phases, aging time, nitric acid concentration, Cyanex-272 and TBP concentration on the metals separation, and various stripping agents on the metals back extraction from the loaded organic phase have been investigated. The maximum separation factor of 16 was obtained in the single extraction system with 1% (v/v) Cyanex-272 from 2.5 M HNO 3 solution. The combination of Cyanex-272 with TBP exhibited a significant synergistic effect for Zr extraction and the antagonistic effect for Hf extraction. The proposed novel synergistic mixture consisting of 0.5% (v/v) Cyanex-272 and 20% (v/v) TBP in kerosene offered the maximum separation factor of 99.7 from 2.5 M HNO 3 solution. By applying a slope method, the extracted zirconium species were proposed to be ZrO(NO 3 ) 2 ·2Cyanex272·2TBP in the organic phase. Among the investigated stripping agents, 4 M H 2 SO 4 solution showed the best efficiency for the stripping of zirconium and hafnium from the loaded mixture of Cyanex-272 and TBP with separation factor of 10.1.

A reference source with the granular active portion was made using 152,154 Eu(III) loaded tin tungstate material. Batch equilibration method was used to investigate the interaction of 152,154 Eu(III) radiotracer (10 −4 M) in acid solutions on tin(IV) tungstate gel matrix. The sorption behavior of 152,154 Eu(III) showed high affinity towards tin(IV) tungstate gel matrix at low pH values. Tin tungstate gel matrix was loaded with 152,154 Eu from batch at pH 3. Standardization of the source was done spectroscopically with reference to primary certified set of radioactive sources and with the aid of HPGe detector. Random and true coincidence summing was carried out by following-up coincidence in 152 Eu and possible interference between γ lines of 152 Eu and 154 Eu. The relation between the grain size and the activity of samples was studied. Correction factor for capsule attenuation was applied.

Two novel radiochromic films with 20 μm thickness were made from casting of solutions of polycarbonate (PC) containing 0.5 wt.% tetra phenyl porphyrin (TPPH 2 ) and 5,10,15,20-tetraphenyl-21H,23H-porphine iron(III) chloride (Fe-TPP). Dosimetric characterization of the films as routine dosimeters were studied by spectrophotometric method. On subjecting TPPH 2 /PC and Fe-TPP/PC film dosimeters to gamma radiation, radiolytic bleaching of films was observed. The effects of metal-complexation on the radiation response of the film dosimeters were studied under 60 Co γ-rays exposure in dose range of 0–100 kGy. The results were also compared with the PC/TPPF 20 (PC/tetrakis (pentafluorophenyl) porphyrin) dosimeter to evaluate the substituent effect (role of fluorine groups). Experimental parameters including humidity, temperature and pre-irradiation (shelf-life) and post-irradiation storage in dark and in indirect sunlight were examined. The maximum absorbance of Soret band of dyes had meaningful shifts and reduction which arose from complexation and substituents. The dyed films characteristics were found to be stable enough in media with high degrees of temperature and humidity. The results indicate that the radiation-induced decoloration of TPPH 2 /PC and Fe-TPP/PC films can be reliably tuned and used in high dose dosimetry.

In this research work, human fingernails were utilized to estimate the radiation dose using EPR measurements of radiation-induced radicals. The limiting factors in this research were the presence of mechanical induced EPR signals due to the mechanical stress during the preparation of the samples. The mechanically induced signals overlap with the radiation-induced signal, which considerably can overestimate the dose. Thus, different treatment methods of fingernails were used to reduce the mechanical induced signals. The results demonstrate that the mechanical and radiation induced signals have apparently different microwave power saturation behavior. Also, mechanical induced signal shows a fading evolution vs. time and reaches to a constant value. Chemical treatment using the different reagents showed that the minimum mechanical induced signal was obtained using the dithiothreitol reagent. The dose response curves of the treated samples with dithiothreitol for 30 min demonstrated a more linearity, and closer curves in comparison to those treated in 5 min. Therefore, to find out an unknown absorbed dose in a fingernail sample using a calibration curve, it could be recommended to use the mentioned chemical treatment procedure to reduce the uncertainty.