Volume 103, Issue 5

Integral cross sections of the reactions 46 Ti( n ,  p ) 46 Sc, 47 Ti( n ,  p ) 47 Sc, 48 Ti( n ,  p ) 48 Sc, 60 Ni( n ,  p ) 60 Co and 64 Zn( n ,  p ) 64 Cu were measured with fast neutrons ( E n  > 1.5MeV) from an Am/Be source. The results were compared with data calculated using the neutron spectral distribution and the excitation function of each reaction given in the data libraries ENDF/B-VII.0, IRDF-2002, JEFF-3.2 and JENDL-4.0. In general, the integral measurement and the integrated value agreed within ±4%, except for the 46 Ti( n ,  p ) 46 Sc reaction where JEFF-3.2 shows a deviation of 7% and the 60 Ni( n ,  p ) 60 Co reaction where ENDF/B-VII.0 and IRDF-2002 exhibit deviations upto 8%.

The radiolytic stability of different substituted diglycolamides such as N , N , N ′, N ′-tetrapentyl diglycolamides(TPDGA), N , N , N ′, N ′-tetrahexyl diglycolamide (THDGA), N , N , N ′, N ′-tetraoctyl diglycolamide (TODGA), N , N , N ′, N ′-tetradecyl diglycolamide (TDDGA) and N , N , N ′, N ′-tetra-2-ethyl hexyl diglycolamide (T2EHDGA) was investigated in solvent systems containing 30% iso -decanol as a phase modifier in n -dodecane kept in contact with a 3 M HNO 3 aqueous solution while irradiating in a gamma ray chamber up to 1000 kGy. The degradation of the solvent systems was qualitatively ascertained from measuring the distribution ratio values at 3 M and 0.2 M HNO 3 which gave a direct indication of the reusability of the solvent for long term reuse in separation processes such as `actinide partitioning'. The effect of irradiation on distribution values of Sr, Pu, U was also investigated with diglycolamide extractants both under extraction and stripping conditions. Stoichiometry of the extracted species was determined for Am(III) extraction using the fresh as well as the irradiated solvent systems involving all the five substituted diglycolamides at 3 M HNO 3 and the results indicated only marginal changes. GC-MS analysis was done for fresh and irradiated solvent systems of all the diglycolamides and attempts were made to identify the degradation products.

The extraction behavior of actinides and lanthanides was investigated by three homologues of H-phosphonates viz. diamylhydrogen phosphonate (DAHP), dihexylhydrogen phosphonate (DHeHP) and dioctylhydrogen phosphonate (DOHP). These compounds were synthesized, characterized by using elemental analysis, IR, NMR ( 1 H, 13 C and 31 P) and mass spectroscopy. The extraction behavior of these ligands was compared with a member of dialkylalkyl phosphonate viz. diamylamyl phosphonate (DAAP). The present study has been taken up to understand the influence of phosphorus bonded hydrogen and alkyl groups in H-phosphonates on the extraction behavior of actinides and lanthanides. The important physicochemical properties such as density, viscosity, phase disengagement time, dispersion number and solubility are also reported for the first time. These compounds extract actinides through the P–OH group which is present in tautomeric equilibrium with the P–H bond at lower acidities, and through the phosphoryl group at higher acidities thus exhibiting a dual behaviour. The physical properties can be modified by suitably designing the extractant based on the requirement for a given purpose. The H-phosphonates have potential applications in pre-concentration of large quantities of dilute solutions of uranium and plutonium.

Partitioning of trivalent americium from fast-reactor (FR) simulated high-level liquid waste (SHLLW) has been demonstrated, for the first time, using a modifier-free organic phase containing an unsymmetrical diglycolamide, N , N ,-didodecyl- N ′, N ′-dioctyl-3-oxapentane-1,5-diamide (D 3 DODGA), in n -dodecane ( n -DD). The extraction behavior of various metal ions present in the FR-SHLLW that contained about 3.2 g/L of trivalent metal ions (Am(III) and Ln(III)) was studied using a solution of 0.1 M D 3 DODGA/ n -DD, by batch equilibration mode. The extraction of Am(III) was accompanied by the co-extraction of all lanthanides and unwanted metal ions such as Zr(IV), Y(III), and Pd(II) from FR-SHLLW. The co-extraction of unwanted metal ions was minimized by adding a suitable aqueous soluble complexing agents to FR-SHLLW, prior to extraction. As a result, trans-1,2-diaminocyclohexane- N,N,N′N′ -tetraacetic acid (CyDTA) was identified as an appropriate reagent for preventing the extraction of zirconium and palladium, that posed problems during recovery of trivalent metal ions from the loaded organic phase. The stripping of behavior of Am(III) and Ln(III) from the loaded organic phase was studied using dilute nitric acid in batch equilibration mode. Based on those results, a counter-current mixer-settler run was performed in a 20-stage mixer-settler. About 99.9% of Am(III), Ln(III) and Y(III) from FR-SHLLW in 0.1 M D 3 DODGA/ n -DD was achieved in 20 contacts and the recovery of Am(III) and other trivalents from the loaded organic phase was achieved in 5 contacts using 0.01 M nitric acid. The study demonstrated the possibility of using the modifier-free reagent, D 3 DODGA, for the separation of trivalent actinides from FR-SHLLW.

Zr-containing layered double hydroxides (LDHs) with variable x Zr solid  = Zr/(Zr + Al) mole fractions were synthesized by a co-precipitation method at ambient conditions. The chemical compositions of samples and corresponding aqueous solutions after syntheses were analyzed by ICP-OES, EDX (Mg, Al, Zr) and ion chromatography (Cl – ). Results of PXRD technique demonstrated that solids with 0 ≤  x Zr solid  ≤ 0.5 show only X-ray reflexes typical for pure LDH compositions, while products of syntheses with x Zr solid  > 0.5 display additional patterns attributed to brucite. ICP-OES and EDX techniques shown that in pure Zr-containing LDHs the Mg/(Al + Zr) ratio is reducing with increase of x Zr solid and the stoichiometry of brucite-like layers corresponds to [Mg 3 – 2 x Al 1 –x Zr x ]. This fact may indicate that the incorporation of 1 Zr-containing specie results in the removal of 1 Al- and 2 Mg-containing species from the pure Mg-Al-composition. Such mechanism may be confirmed by the observation that measured a 0  =  b 0 distances are generally consistent with theoretical estimates obtained from [Mg 3 – 2 x Al 1 –x Zr x ]-stoichiometry. The presence of predominant Mg 2+ , Al(OH) 4 – and Zr(OH) 5 – complexes in aqueous solutions after syntheses was established in thermodynamic calculations by applying GEMS-Selektor v.3. code and, therefore, the reaction: Mg 3 Al 1 (OH) 8 Cl 1 + Zr(OH) 5 – = Mg 1 Zr 1 (OH) 5 Cl 1  + Al(OH) 4 –  + 2 Mg 2+  + 4 OH – can describe a mechanism of Zr-substitution. Estimates of the molar Gibbs free energies of Zr-containing LDHs with 0 ≤  x Zr solid  ≤ 0.5 show that the incorporation of Zr into the LDH increasing significantly their aqueous solubility. Thus, it is not possible to neglect that Zr can be partly localized as Zr(OH) 5 – -ligands in the interlayer space of the LDH structure.

In this study, the solid-phase tea waste procedure was used for separation, preconcentration and determination of uranium from water samples by UV-Vis spectrophotometer. In addition, Box-Behnken experimental design was employed to investigated the influence of six variables including pH, mass of adsorbent, eluent volume, amount of 1-(2-pyridylazo)-2-naphthol (PAN); and sample and eluent flow rates on the extraction of analyte. High determination coefficient ( R 2 ) of 0.972 and adjusted- R 2 of 0.943 showed the satisfactory adjustment of the polynomial regression model. This method was used for the extraction of uranium from real water samples.

The adsorption behaviour of thorium on rice husk has been studied by optimizing different parameters like nature of electrolyte, amount of adsorbent, equilibration time, metal concentration, and temperature, employing batch method and radiotracer technique. Maximum adsorption was observed at 0.0001 mol L – 1 HNO 3 , using 0.1 g of adsorbent for 4 cm 3 of 5.19 · 10 – 5  mol L – 1 of Th +4 solution in fifteen minutes equilibration time. The adsorption phenomenon was verified by FTIR, SEM and EDX techniques. The adsorption data was well fitted to Freundlich, Langmuir and Dubinin-Radushkevich isotherm equations. The characteristic Freundlich constants i.e. 1/ n  = 0.528 ± 0.019 and K  = 4.88 × 10 −4  ± 1.29 · 10 – 5  mol g – 1 whereas the Langmuir constants Q m  = (4.159 ± 0.234) × 10 – 6  mol g – 1 and K L  = (3.627 ± 0.328) × 10 4  dm 3  mol – 1 have been computed for the sorption system. The sorption free energy was found to be 11.24 ± 0.211 kJ mol – 1 showing chemisorption nature of interaction between thorium and rice husk. The results showed that thorium adsorption on rice husk follows pseudo 2 nd order with rate constant = 1.448 g mg – 1  min – 1 . The determined negative values of ΔG indicated spontaneity of the process, whereas the positive values of ΔH and ΔS confirmed endothermic nature and increased randomness during the adsorption process respectively. The removal of Th +4 ions from spiked tap water was checked by employing the optimized experimental parameters which indicated that rice husk is a good adsorbent for thorium ions and may be used for waste management of radionuclides.

Nickel(II) selenide (NiSe) was investigated as a new high-current target material for cyclotron production of radiobromine, as it contains a higher amount of selenium and has a lower melting point than the widely used Cu 2 Se. Using a slanted target system, NiSe was successfully tested up to beam currents of 16 μA so far. With regard to the isolation of no-carrier-added (n.c.a.) radiobromide from the target material, an improved dry distillation device with high yields of 76% – 86% was developed. The implementation of a special custom-made quartz funnel decreased the dead volume of the apparatus and a quartz capillary for trapping the radiobromine allowed to concentrate the radioactivity in a small volume of less than 100 μL of 0.1 M NaOH, ready for immediate subsequent radiosyntheses. Thus, the new apparatus improves the handling of the isolation procedure and the radioactive product. The radiochemical purity of the resulting solution of n.c.a. [ * Br]bromide was verified by radio-IC where no other species were detected.