Chhavi Agarwal

Neutron-irradiation effects on track etching characteristics of polyester nuclear track detector

The effects of reactor neutron irradiation on the etching characteristics of a locally available Garware polyester film have been studied. The effects in the neutron fluence range of 4.57×1015–1.83×1016 n/cm2 on the fission track registration efficiency and the bulk etch rate are investigated. From the results, it is found that the bulk etch rates increase with the increase in neutron fluence. The increase in etch rates can be explained on the basis of scission of the detector due to neutron irradiation which enhances the dissolution rates. From the measured bulk etch rates at different temperatures, the activation energies for bulk etching at different values of neutron fluence have also been determined. The changes induced by neutron irradiation in the polyester detector have also been studied by UV-visible spectroscopic technique. The neutron irradiation enhances the UV absorbance of the detector, which is a direct consequence of the formation of new chemical species due to scission of the detector.

Self-diffusion of ions in Nafion-117 membrane having mixed ionic composition.

The self-diffusion coefficients (SDCs) of Na(+), Cs(+), and Ba(2+) have been determined in Nafion-117 membrane having mixed cationic compositions. Membranes with different proportions of Na(+)-Cs(+), Cs(+)-Ba(2+), Na(+)-Ba(2+), and Ag(+)-Ba(2+) cations have been prepared by equilibrating with solutions containing different ratios of these cations. The SDCs of the cations (D(Na), D(Cs), D(Ba)) and the ionic compositions of the membrane have been determined using a radiotracer method. For the Na-Cs and Cs-Ba systems, the SDCs of the cations have been found to be independent of the ionic compositions of the membrane. In the case of the Na-Ba system, D(Na) does not change with ionic composition, while D(Ba) has been found to be strongly dependent on the ionic composition of the membrane and decreases continuously with increasing Na(+) content in the membrane. Similar results have also been obtained for D(Ba) in the case of the Ag-Ba system. The specific conductivities (κ(imp)) of the membrane in mixed cationic forms have also been obtained from ac impedance measurement and compared with that (κ(cal)) calculated from the SDC data. For the Na-Ba system, the increment of κ(imp) with increase in the Na(+) content of the membrane has been found to be parabolic, whereas for the Na-Cs system the increment is linear. The reason behind the different behaviors for different types of ionic systems has been qualitatively explained based on different transport pathways of the cations in the membrane.

Anion dependence of transport of mercury ion through Nafion-117 membrane.

Studies on isotopic and ion-exchange kinetics of mercury ions in Nafion-117 membrane have been carried out with (203)Hg radiotracer in the presence of Cl(-) and NO(3)(-) in solution. The results of isotopic-exchange kinetics indicate that mercury ions diffuse into the membrane as monovalent cation from HgCl(2) solution while as divalent ion from Hg(NO(3))(2) solution. The studies on the kinetics of ion exchange of Hg(2+) with Na(+) follow the prediction of the Nernst-Planck equation when NaNO(3) is used as an external salt solution. The Nernst-Planck equation fails to predict the kinetics when NaCl is used as an external salt solution, indicating that the complexation of Cl(-) with Hg(2+) in the membrane influences the kinetics. Permeation studies using (203)Hg and (36)Cl radiotracer between two HgCl(2) solutions show that the permeability coefficients of mercury and chloride ions are the same, indicating the cotransport of mercury and chloride ions through the membrane. Ion-exchange equilibrium studies using a mixture of HgCl(2) and HNO(3) solution were carried out to ascertain the species transporting through the membrane. The equilibrium sorption of mercury in the membrane shows the uptake of an ionic species, presumably HgCl(+), not a neutral salt. The speciation diagrams, calculated as a function of pH, show wide divergence of species present in HgCl(2) and Hg(NO(3))(2) solution and explain the difference in membrane transport behavior for HgCl(2) and Hg(NO(3))(2) solution. The results show that any ion-exchange-membrane-based separation of Hg(2+) needs careful consideration regarding the anions present in the solution, as it influences the speciation of mercury and hence its transport behavior through the membrane.

Temperature dependence of ion and water diffusion in crown ether loaded Nafion matrix.

Temperature dependence study of the self-diffusion coefficient of Cs(+) ion in dibenzo-18-crown-6 (DB18C6) modified Nafion-117 (Cs-Naf-CR) was carried out in the temperature range of 50-65 °C. Temperature dependence of water diffusion in Cs-Naf-CR was also studied to understand the mechanism of cation and water transport in the membrane. Because of the very slow kinetics of isotopic exchange, self-diffusion measurement of Na(+) in Na-Naf-CR was carried out only at 60 °C. The result indicates that self-diffusion behavior is governed by the nature of the cation in which the crown ether was loaded in the membrane matrix. The activation energy of diffusion for Cs(+) ion and water in Cs-Naf-CR was found to be much higher than that in the pure Cs(+) form of Nafion (Cs-Naf). Water uptake of the membrane was also found to have reduced compared to Cs/Na-Naf. The results point to the binding of the ions by DB18C6 and the destruction of the water channels in the crown ether loaded membrane. The differential scanning calorimetry (DSC) data supports these observations.

Pore-Filled Scintillating Membrane as Sensing Matrix for α-Emitting Actinides

Pore-filled membranes with scintillating properties have been synthesized for sensing α-emitting radionuclides. The membranes have been prepared by in situ UV-initiator-induced polymerization of monomer bis[2-(methacryloxy)ethyl] phosphate in pores of the host membranes, poly(propylene) and poly(ethersulfone). The polymerization has been carried out in the presence of scintillating molecules, 2,5-diphenyloxazole. These scintillating molecules are physically trapped in the thus formed microgel in the membrane. Much higher α-scintillation efficiency has been obtained for the (241)Am-loaded poly(ethersulfone)-based grafted membrane compared to poly(propylene)-based membrane. This was attributed to the aromatic backbone of the poly(ethersulfone) membrane. The scintillation response of poly(ethersulfone)-based membranes has been found to be linear over the range of (241)Am activity studied. The pore-filled scintillating membranes have been found to be selective toward Pu(4+) ions at higher HNO3 concentration compared to Am(3+). The analytical performance of the pore-filled scintillating membranes has been evaluated. The membranes have been found to be stable and reusable. The scintillating membrane with optimized composition has been applied for quantification of Pu in a soil sample.

Transport Properties of Multivalent Cations in Nafion-117 Membrane with Mixed Ionic Composition

The transport characteristics of multivalent cations like Ba(2+) and Eu(3+) have been studied in bi-ionic form of the Nafion-117 membrane. The membranes have been prepared by loading different proportions of H(+)-Ba(2+)/Mg(2+)-Ba(2+)/Ba(2+)-Eu(3+)/H(+)-Eu(3+)/Na(+)-Eu(3+). The cationic compositions of the membranes have been determined from the measured ion exchange isotherms. Results show that the self-diffusion coefficient of Ba(2+) (D(Ba)) in H-Ba/Mg-Ba systems as well as the self-diffusion coefficient of Eu(3+) (D(Eu)) in H-Eu/Na-Eu systems are strongly dependent on the membrane ionic compositions and decreased continuously with increasing concentration of the highly hydrated ions (H(+)/Na(+)/Mg(2+)) in the membrane. Increase in the proportion of H(+)/Na(+)/Mg(2+) ions in the membrane increases the effective charge on the membrane matrix. This causes stronger electrostatic interaction of the less hydrated multivalent ions (Ba(2+)/Eu(3+)) with the membrane matrix charges, which ultimately results in their slower self-diffusion coefficients. The higher the valence, the stronger the electrostatic interaction is with the fixed ionic charges; hence, in general, D(Eu) is affected more as compared to D(Ba). On the basis of the free-volume theory for polymers, the effective interaction potential (Φ) of the Ba(2+) with the fixed ionic sites in the membrane has been calculated and found to be on the order of approximately millivolts. The higher the proportion of hydrated ion in the membrane, the higher the Φ is and the stronger the ion pair formation is with the fixed ionic sites in the membrane. However, in the Ba-Eu system, as the electrostatic interactions of the two ions with the membrane matrix are close, D(Ba) and D(Eu) are independent of the membrane ionic composition. The ionic composition dependence of D(Ba) in the H-Ba system is reflected in the transport rate of Ba(2+), showing the importance of such measurements in understanding the transport characteristics of the membrane.

Attenuation correction for the assay of uranium(VI) solutions in large cylindrical containers by gamma ray spectrometry.

The Hybrid Monte Carlo method developed for attenuation correction has been extended for 500 ml cylindrical geometry. The method has been experimentally validated. Absolute efficiency studies for 500 ml aqueous, air and point source has been carried out using Monte Carlo simulation. It has been observed that point source efficiency is a good estimate of 500 ml source beyond sample-to-detector distance of 15 cm. It has been found that while HMC method for attenuation correction is valid at all sample-to-detector distances and over all transmittance range, the far-field and near-field formulae available in literature are valid only over a very narrow range of sample-to-detector distance.

Isotopic ratio correlation for the isotopic composition analysis of plutonium in Am–Pu mixed samples having High americium content

Interference of high amount of americium in the plutonium isotopic composition analysis has been studied by simulating gamma-ray spectra for Am-Pu samples over a wide composition range (5-97% (241)Am) for both power and research reactor grade plutonium. An alternate way for isotopic composition analysis has been proposed by correlating the isotopic ratios available in our old database with the experimentally obtained (241)Pu/(239)Pu isotopic ratio. The proposed method has been validated using simulated spectra of known isotopic compositions.

Hybrid organic-inorganic anion-exchange pore-filled membranes for the recovery of nitric acid from highly acidic aqueous waste streams

Recycling of acid from aqueous waste streams is highly important not only from the environmental point of view but also for developing the sustainable technology. One of the effective ways to recover acid from aqueous waste streams is the anion-exchange membrane based diffusion-dialysis. The work presents the synthesis and characterization of anion-exchange pore-filled membranes for the objective of recovery of high concentration of acid by diffusion dialysis. The membranes were prepared by anchoring the guest organic-inorganic anionic gel in the pores of the host poly(propylene) membrane by in situ UV-initiator induced polymerization of the appropriate monomers along with cross-linker. The removal of nitric acid in the presence of different representative monovalent, divalent and trivalent nitrates and the leakage of these ions through anion exchange membrane have been studied by DD technique for optimizing the chemical composition of the membrane. The nitric acid permeation rate of the membrane with the optimized composition has been found to be considerably faster than the commercial Selemion membrane without sacrificing salt leakage. The performance of the optimized pore-filled anion exchange membranes has been found to be independent of the acid concentration, nature of the anion and substrate and has been observed to be solely dependent on the guest inorganic-organic hybrid anionic gel component. The membranes have been found to be stable and reusable for the acid recovery. Removal of nitric acid as high as 90% from the simulated high level nuclear waste with the optimized grafted pore-filled membrane has been achieved with negligible salt transport.

Non-stationary radiotracer method for diffusion coefficients of Cs+, Ba2+, Eu3+ tracers in Nafion-117 membrane

ABSTRACT The ion-exchange kinetics of Az+sol ⇆ Na+mem (Az+ = Cs+/Ba2+/Eu3+) in Nafion-117 have been measured using non-stationary radiotracer technique for trace concentrations of Az+ ions in external solution. A method based on non-steady state Nernst–Planck approach has been developed and used to fit the experimental ion-exchange profiles to obtain the diffusion coefficients (DCs) of these ions. The DCs, thus obtained, have been found to be appreciably lower than the literature-reported self-diffusion coefficients, indicating slower rate of ion-exchange. The results show that membrane DCs of these ions are modified by bulk electrolyte solution.