Ayman F. Seliman

Mobility of radionuclides in soil/groundwater system: Comparing the influence of EDTA and four of its degradation products

The adsorption behavior of 241Am, 60Co, 137Cs and 85Sr in the presence and absence of chelating ligands (ethylenediaminetetraacetic acid, ethylenediaminediacetic acid, hydroxyethyliminodiacetic acid, iminodiaceiticacid and methyliminodiacetic acid) was investigated. Sorption affinity in the absence of chelating ligands followed: Am(III)>Co(II)>Cs(I)>Sr(II). The presence of chelating ligands generally had little effect on sorption of 85Sr and 137Cs with Kd values 110 and 690 mL g(-1), respectively. But at 0.02 M of ethylenediaminetetraacetic or hydroxyethyliminodiacetic, the Kd decreased to 5 or 63 mL g(-1), respectively, where thermochemical modeling indicated almost all 85Sr is complexed with these ligands. The Kd values for 241Am and 60Co generally decreased with increasing chelating agent concentrations. In notable cases, the Kd values for Am increased at specific concentrations of 10(-3) M for IDA, MIDA and 10(-4) M for EDDA. This is proposed to be due to formation of a ternary surface complex.

Preparation of polymer-coated, scintillating ion-exchange resins for monitoring of 99Tc in groundwater.

The present study was oriented to prepare new scintillating anion-exchange resins for measurement of (99)TcO(4)(-) in natural waters. The organic fluor 2-(1-naphthyl)-5-phenyloxazole was diffused into (chloromethyl)polystyrene resin. Thereafter, a thin layer of poly[[2-(methacryloyloxy)ethyl]trimethylammonium chloride] was grafted from the resin surface by surface-initiated atom transfer radical polymerization as an attempt to overcome potential problems related to the leaching of fluor molecules during usage. The residual chloromethyl groups of the polymer-coated resin were aminated by reaction with two different tertiary amines, triethylamine (TEA) and methyldioctylamine (MDOA). Off- and on-line quantification of (99)Tc was achieved with high detection efficiencies of 60.72 ± 1.93% and 72.83 ± 0.81% for resin with TEA and MDOA functional groups, respectively. The detection limit was determined to be less than the maximum contaminant level (33 Bq L(-1)) established under the Safe Drinking Water Act. The two functionalized resins were demonstrated to be selective for pertechnetate from synthetic groundwater containing up to 1000 ppm Cl(-), SO(4)(2-), and HCO(3)(-) and up to 1200 ppb Cr(2)O(7)(2-) in an acidic medium.

Development of polymerizable 2-(1-naphthyl)-5-phenyloxazole scintillators for ionizing radiation detection

The synthesis, chemical characterization and optical properties of 2-(1-naphthyl)-4-vinyl-5-phenyloxazole (vNPO) and 2-(1-naphthyl)-4-allyl-5-phenyloxazole (allylNPO) monomers are reported. Starting with the organic fluor 2-(1-naphthyl)-5-phenyloxazole (αNPO), the vNPO and allylNPO monomers were synthesized using Stille coupling followed by purification. The final products were obtained with yields of ∼95% and ∼55% for vNPO and allylNPO. The absorption/emission spectra of αNPO, vNPO and allylNPO revealed that vNPO has the largest red-shifted in emission with an average wavelength of ∼420 nm, which is an advantage for increasing photomultiplier tube sensitivity without the need to add a wavelength shifter. Stable scintillating resin beads were prepared through copolymerization of the newly synthesized fluor monomers with styrene or 4-methylstyrene and divinylbenzene in the presence of toluene porogen. The resin beads were chemically stable and retained the ability to scintillate efficiently after energy deposition of beta particles from 99Tc. This result indicates efficient energy transfer occurs from the base polymer to the covalently attached fluors with subsequent fluorescence in the presence of ionizing radiation.

New Efficient Organic Scintillators Derived from Pyrazoline

We report on the synthesis, spectroscopic and scintillation properties of three new pyrazoline core based fluorophores. Fluorescence properties of the fluorophores have been studied both in a solution state and in a solid polyvinyltoluene (PVT) resin matrix of different porosity. The synthesized fluorophores were found to be promising candidates for application in plastic scintillators for detection of ionizing radiation (alpha, beta particles, γ rays and neutrons) and demonstrated superior efficiency in comparison to the existing commercially used fluorophores (2-(1-naphthyl)-5-phenyloxazole (αNPO), 9,10-diphenylanthracene, etc.). Moreover, the suggested synthetic route allows functionalization of the fluorophores with a vinyl group for further covalent bound to the PVT or other vinyl polymer matrices, which dramatically improves chemical stability of the system simultaneously improving the photoluminescence quantum yield. Possible mechanisms of the enhanced scintillation properties are discussed based on preliminary quantum mechanical calculations and spectroscopic characteristics of the fluorophores under study.

Gradient Elution Method for Successive Separation of Common Cations and Hydrophobic Amines using Suppressed Ion Chromatography

Abstract In mixed waste, the separation and sequential determination of alkali and alkaline earth metals mixed with hydrophobic amines represent a challenging analytical problem. The effect of a new mobile phase (amido‐sulfonic acid, ASA) on the suppressed ion chromatographic separation of alkali and alkaline earth metals and hydrophobic amines on CS12A analytical column was investigated. The addition of surface modifier to the eluent appears to provide better interfacial compatibility between the mobile and stationary phase and facilitates the rapid equilibration of analytes. Incorporation of a very low concentration of the additive may also alter the stationary phase surface by creating a fine tuning and improves the partition characteristics of the analytes. A dramatic and sufficient elution capability of amido‐sulfonic acid (ASA) for sequential separation of the analytes was reported and rational mechanisms for the separated analytes are proposed. ASA can act as an ion pairing agent resulting in the separation of a wide variety of amines. The new mobile phase (ASA) is proven to have more successful separation over methansulfonic acid (MSA), even with eluent free solvent. The proposed method shows that a profound particular effect on the separation of aliphatic diamine (Ethylenediamine) and organic amine (Cyclohexylamine) was achieved in addition to all common cations and amines using isocratic elution of 18 mM of ASA without organic eluent modifier.

Development of Stable Extractive Scintillating Materials for Quantification of Radiostrontium in Aqueous Solutions

The research presented here is the development of sensor materials that are applicable for real-time in situ quantification of radiostrontium in aqueous solutions. Two different approaches were applied to prepare highly selective structures for simultaneous extraction and detection of radiostrontium using online detection methods. Online data were acquired with a flow scintillation analyzer IN/US β-Ram model 5 (LabLogic Systems, Inc) with a 30-s dwell time. Both approached utilized the commercially available SuperLig®620 solid-phase extractant (IBC Technologies, Inc.) to concentrate the strontium in combination with a scintillator to quantify the radioactivity.