Volume 105, Issue 6

For the production of the medically interesting radionuclides 76 Br and 77 Br cross sections of α-particle induced reactions on arsenic, leading to the formation of 76,77,78 Br as well as to the non-isotopic impurity 74 As, were measured from their thresholds up to 37 MeV. Sediments of elemental arsenic were used as targets and irradiated, using the established stacked-foil technique. In order to remove discrepancies of the existing literature data, the cross section ratios of the monitor nuclides 67 Ga/ 66 Ga were used for determination of the α-particle energies as well as the effective beam current through all the stacks, thus inferring the experimental cross sections. Compared with the available excitation functions the new data indicate slightly divergent curve shapes. In the case of 76 Br the excitation function seems to be shifted to somewhat lower α-particle energies, and also the maximum cross section of the formation of 77 Br tends to be slightly lower compared with the curve recommended to date. In the case of a re-evaluation, these new data should be taken into account, as they may contribute to enhance the accuracy of the excitation functions.

Room temperature ionic liquids (RTILs) represent a recent new class of solvents with potential application in liquid/liquid extraction based nuclear fuel reprocessing due to their unique physical and chemical properties. The work herein provides a comparison of U(VI) extraction by 8-hydroxyquinoline (HOX) in a commonly used RTIL, i.e. 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim][PF 6 ]) and in conventional solvent, i.e. dichloromethane (CH 2 Cl 2 ). The effect of HOX concentration, solution acidity and nitrate ions on the extraction were discussed in detail, and the speciation analyses of the extracted U(VI) were performed. One of the main emphasis of this work is the extraction mechanism of U(VI) extracted from aqueous phase into RTILs and conventional solvent. In CH 2 Cl 2 , the extraction occurs through a combination of ion change and neutral complexation, and the extracted complex is proposed as UO 2 (OX) 2 HOX. In [C 4 mim][PF 6 ], although a cation-change mechanism as previously reported for RTILs-based system was involved, the extracted complex of UO 2 (OX) 1.5 (HOX) 1.5 (PF6) 0.5 gave a clear indication that the usage of HOX as an acidic extractant markedly inhibited the solubility loss of [C 4 mim][PF 6 ] during the extraction by leaching H + to aqueous phase. Moreover, the extracted U(VI) in [C 4 mim][PF 6 ] can be easily stripped by using 0.01 M nitric acid, which provides a simple way of the ionic liquid recycling.

Amidoxime-functionalized marine fungus Fusarium sp. #ZZF51 (ZGDA) was synthesized and studied to adsorb uranium (VI) from the aqueous solution. Different instrumental techniques such as FTIR, SEM, and TGA were employed for the characterization of the manufactured materials, and theirs ability of removal uranium (VI) was optimized using RSM. The experimental results showed the maximum adsorption capacity for the synthesized materials was 230.78 mg g −1 at the following optimization conditions: S–L ratio 150 mg L −1 , pH 5.13, uranium (VI) initial concentration 40 mg L −1 , and equilibrium time 122.40 min. More than 85% of the absorbed uranium (VI) could be desorbed by 0.5 or 1.0 mol L −1 HCl, and the modified mycelium could be reused at least five times. The thermodynamic experimental data of adsorption uranium (VI) could fit better with Langumir and Freundlich isotherms models, and the pseudo-second-order model was better to interpret the kinetics process. The modified fungus materials exhibited the better sorption capacity for uranium (VI) in comparison with raw biomass should be attributed to the strong chelation of amidoxime to uranium (VI) ions.

β-Zeolite-EDA was modified with ethylenediamine (EDA) after synthesized. The synthesized material was characterized and used for removal of Th(IV) from aqueous solutions. The influences of pH, ionic strength, contact time, temperature and humic acid (HA) on Th(IV) sorption onto synthesized β-zeolite-EDA was studied by batch technique. The dynamic process showed that the sorption of Th(IV) onto β-zeolite-EDA matched the pseudo-second-order kinetics model. The sorption of Th(IV) on β-zeolite-EDA was significantly dependent on pH values, the sorption percentage increased markedly at pH 3.5–4.5, and then maintained a steady state as pH values increased. Through simulating the sorption isotherms by Langmuir, Freundlich and Dubini–Radushkevich (D–R) models, it could be seen respectively that the sorption pattern of Th(IV) on β-zeolite-EDA was mainly controlled by surface complexation, and that the sorption processes was endothermic and spontaneous. The presence of HA increased Th(IV) sorption on β-zeolite-EDA.

This work aims to assess the solubility and the surface reactivity of crystallized thorium at pH 3.0 in presence of three types of solids: synthesized powder at 1300°C, crushed kernel, and intact kernel. In this study, the kernel is composed by the core solid from high temperature reactors (HTR) sphere particles. The originality of this work consisted in following in a sequential order the kinetic of dissolution, the surface reactivity in presence of isotope tracer 229 Th, and its desorption process. Long time experiments (634 days) allowed to get deeper understanding on the behavior of the surface reactivity in contact with the solution. Solubility values are ranging from 0.3×10 −7 mol·L −1 to 3×10 −7 mol·L −1 with a dissolution rate of 10 −6 –10 −4 g·m −2 day −1 . PHREEQC modeling showed that crystallized ThO 2 (cr, 20 nm) phase controls the equilibrium in solution. Isotope exchange between 229 Th and 232 Th indicated that well-crystallized phase exist as an inert surface regarding to the absence of exchange between surface solid and solution.

Ionizing radiation’s effects onto water molecules lead to the ionization and/or the excitation of them. Then, these phenomena are followed by the formation of radicals and molecular products. The linear energy transfer (LET), which defines the energy deposition density along the radiation length, is different according to the nature of ionizing particles. Thus, the values of radiolytic yields, defined as the number of radical and molecular products formed or consumed by unit of deposited energy, evolve according to this parameter. This work consists in following the evolution of radiolytic yield of molecular hydrogen and ferric ions according to the “Track-Segment” LET of ionizing particles (protons, helions). Concerning G(Fe 3+ ) values, it seems that the energy deposited into the Bragg peak does not play the main role for the Fe 3+ radiolytic formation, whereas for the G(H 2 ) it is the case with a component around 40% of the Bragg peak in the dihydrogen production. Therefore, as main results of this work, for high energetic Helion and Proton beams, the G(Fe 3+ ) values, which can be used for further dosimetry studies for example during the α radiolysis experiments, and the primary g(H 2 ) values for the Track-Segment LET, which can be used to determine the dihydrogen production by α -emitters, are published.

Cr(VI) compounds are major water contaminants in most industrial effluents, due to their carcinogenicity, while Cr(III) is an important element for human metabolism. In a previous work, we showed that Cr(VI) was radiolytically reduced to Cr(III) by the CO 2 ˉ • radical at pH 3 N 2 O-saturated solution in the presence of formate. Here in the present work, this removal was investigated by steady state irradiation and pulse radiolysis in aerated solution at neutral pH, which is close to natural conditions in most wastewaters, where the reducing agent is the superoxide radical anion O 2 ˉ • . The degradation of Cr(VI) increased linearly with the absorbed dose and was significantly enhanced by the added formate but not by the radiolitically produced hydrogen peroxide at this pH. The rate constant for this reduction was found to be 1.28×10 8 M −1 s −1 and the absorption spectrum of Cr(V) transient species was obtained. A partial recovery of Cr(VI) is observed over a period of ca . 5 ms following a second order kinetics with a rate constant 8.0×10 6 M −1 s −1 . These outcomes suggest that gamma-irradiation of Cr(VI)-contaminated wastewaters and industrial effluents in presence of formate can be simple, effective and economical means for the remediation of this major contaminant.

We measured the distribution of three naturally occurring radionuclides, 238 U, 232 Th, and 40 K, in soil samples collected from a rainforest in the Western Ghats of India. For each surface sample, we calculated average activity concentration, outdoor terrestrial γ dose rate, annual effective dose equivalent (AEDE), and radiation hazard index. The activity concentrations of surface samples were randomly distributed over space, but differed slightly with different soil depths. The concentration of 232 Th and the average terrestrial γ dose rates were slightly higher than the world averages, so slightly high γ radiation appears to be a general characteristic of the Western Ghats. However, all radiological hazard indices were within the limits proposed by the International Commission on Radiological Protection. The results reported here indicate that, except for 232 Th, the naturally occurring radionuclides in the forest soils of the Western Ghats were within the ranges specified by United Nations Scientific Committee on the Effects of Atomic Radiation for undisturbed virgin soils.