Oxidation-state-specific detection of uranium in aqueous solution by photoacoustic spectroscopy

Parts per billion detection of uranium with a porphyrinoid-containing nanoparticle and in vivo photoacoustic imaging

Chemical tools that can report radioactive isotopes would be of interest to the defense community. Here we report ∼250 nm polymeric nanoparticles containing porphyrinoid macrocycles with and without pre-complexed depleted uranium and demonstrate that the latter species may be detected easily and with high sensitivity via photoacoustic imaging. The porphyrinoid macrocycles used in the present study are non-aromatic in the absence of the uranyl cation, but aromatic after cation complexation. We solubilized both the freebase and metalated forms of the macrocycles in poly(lactic-co-glycolic acid) and found a peak in the photoacoustic spectrum at 910 nm excitation in the case of the uranyl complex. The signal was stable for at least 15 minutes and allowed detection of uranium concentrations down to 6.2 ppb (5.7 nM) in vitro and 0.57 ppm (19 fCi; 0.52 μM) in vivo. To the best of our knowledge, this is the first report of a nanoparticle that detects an actinide cation via photoacoustic imaging.

Optical properties of ammonium uranyl fluoride characterized by photoluminescence and photoacoustic spectroscopy

PL and PAS studies were performed on uranyl compounds viz. uranium oxalate, uranium fluoride and ammonium uranyl fluoride. PL and PAS spectrum of ammonium uranyl fluoride is being reported for the first time. Ammonium uranyl fluoride is blue shifted with respect to uranyl fluoride, as a result of ammonium bonding. The vibronic separations were determined in the excited state and the ground state using excitation/PA spectra and emission spectra respectively. Fluorescence decay data could be fitted only with biexponential decay in all of these compounds indicating the presence of two different environments in these compounds. Low temperature luminescence leads to enhancement in emission intensity and lifetime value. The temperature dependence studies of average fluorescence lifetimes of ammonium uranyl are described in this paper. Based on this studies activation energy value for ammonium uranyl fluoride at which (3)∏ and (1)Σ potential surfaces will cross is calculated.

Laser Photoacoustic Spectroscopy for Trace Level Detection of Actinides in Groundwater

The Basalt Waste Isolation Project (Rockwell Hanford Operations- BWIP) is investigating the feasibility of building a repository in the Columbia River Basalts for the permanent disposal of high-level nuclear waste. One aspect of this effort is to develop an understanding of the chemical behavior of radionuclides in the near-field environment of the waste container. Such information is needed to determine radionuclide release rates from the waste package and to make long-term projections of repository performance. To accomplish this task, ultrasensitive laser- based techniques, such as laser photoacoustic spectroscopy (LPAS) and laser induced fluorescence (LIF), are being developed as analytical methods for the trace-level detection and speciation of actinides in solutions typical of those encountered in groundwaters near the BWIP repository.

Padiolytically Induced Oxidation Reactions of Actinide Ions in Concentrated Salt Solutions

The autoradiolytic oxidation of Pu(IV) and Am(III) has been investigated in saline solution of different NaCl concentrations, pH and specific α-activities. The high linear energy transfer (LET) property of α-radiation in solution enhances the oxidation of the Cl ion and thus increases the redox potential (Eh) of the NaCI solution system to a value of more than +1000 mV vs. NHE. Radiolytic reaction products are found as being comparable with those from the Cl2 saturated NaCl solution 'and create a metastable system consisting of C12/HCl0/Cl0−/Cl−. The oxidation of Pu(IV) and Am(III) in such solutions is dependent on the NaCl concentration, pH and specific a-activity involved. The quantitative oxidation to Pu(VI) and Am(V) is ob- served in the concentrated NaCl solution at pH > 7 with a moderately high specific activity (> 1 Ci/L).

Speciation of Transuranic Ions in Groundwater by Laser-Induced Photoacoustic Spectroscopy (LPAS)

The speciation of the Am(III) ion in various chemical states is illustrated using laser-induced photoacoustic spectroscopy (LPAS). Based on these reference LPAS spectra, the actual chemical states of Am(III) in one of Gorleben groundwaters are systematically verified. The a-radiolytic oxidation of Am(III) to Am(V) in the concentrated NaCl solution and their carbonate complexation are also speciated for the purpose of demonstration.

Solubility and Colloid Generation of Plutonium from Leaching of a HLW Glass in Salt Solutions

Solubilities of Pu from leaching of a simulated HLW glass (C31–3-EC) spiked with 5 wt % Pu and from PuO2 are determined in salt solutions of different NaCl concentration and in groundwaters which are representative for the Gorleben area. Th.e leaching experiment is carried out either in an autoclave at 200 °C or under normal conditions (1 atm, 25°C). Solubilities of Pu in all investigated solutions are observed to be considerably higher than the values known from theoretical estimates. The predominant Pu species in solutions are found to be microcolloids, which are characterized by means of ultrafiltration and pulsed laser-induced photoacoustic spectroscopy.

New laser induced photoacoustic signal measurement method. Example of application: Identification of the uranium(IV)-dioxalato complex in solution

A new laser induced photoacoustic signal measurement method was developed to optimise the parameters of photoacoustic detection: to obtain synchronous measurement, to avoid laser energy fluctuation, to get reproductibility and repeatability. The aim is to apply the technique to solution chemistry, and particularly to studies of the actinides. The initial validation of the new method was done using neodymium(III) and uranium(IV) solutions in acidic media. It was found that the sensitivity of detection of these ions by photoacoustic measurements is improved in comparison with absorption spectrophotometry. This advantage in radiochemistry is the possibility to study actinides at low concentration (<10-4M) to understand their behaviour in solution: speciation, precipitation, kinetics. An example is described and concerns the identification of the uranium(IV)-dioxalato complex in solution by proposing a new mechanism for the precipitation of U(C2O4)2·6H2O.In this work, a measurement device is proposed for rough pressure wave acquisition. It allows sensor definition, local phenomena observation and alternative LIPAS measurement.

Laser-based non-fluorescence detection techniques for liquid separation systems

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.

The Chemical Behavior of Transuranium Elements and Barrier Functions in Natural Aquifer Systems

The chemical behavior of transuranium elements in natural aquifer systems is governed by a variety of geochemical reactions, such as dissolution reaction (solubility), hydrolysis, complexation with inorganics or organics, redox reaction, colloid formation, geochemical interaction with surfaces of various minerals, coprecipitation, mineralization, etc. This paper reviews the present state of knowledge on some of these particular reactions. The emphasis here is on how the individual reactions can be appraised for long-term prediction of the geochemical behavior of transuranium elements in the natural environment. of the various possible reactions, the primary thermodynamic processes are discussed with notable examples: dissolution of transuranium compounds in aquatic solution; complexation with important anions present in groundwater; and colloid generation. Various laser spectroscopic methods in use for chemical speciation are mentioned briefly for their spectroscopic capability, as well as for their applicability. The present paper attempts to better understand the migration behavior of transuranium elements in natural aquifer systems.