Global and regional releases of 14C have resulted from nuclear weapons testing activities; assessment of the chemical behavior and mechanisms of environmental transport and deposition of this radionuclide can assist remediation strategy development efforts and provide insights into global carbon cycling processes. This work reports a systematic evaluation of 14C in surface soils taken from the Nevada National Security Site. Surface soil samples are derived from above- and underground test locations, with underground test sites representing a range from near complete containment to uncontrolled radioactive releases. Only one surface soil taken from a underground test location (i.e. the Baneberry shot) shows elevated 14C concentrations (319 ± 9 pMC) in addition to elevated concentrations of 137Cs, 60Co and 152Eu above regional backgrounds. Surface soils from above-ground test locations show extremely high 14C content (~1000 to 10,000 pMC); elevated concentrations of 152Eu and 60Co for these soils are also observed, with 137Cs at or below background levels. Taken together, these data suggest that 14C in surface soils from above-ground tests is primarily derived from in-situ neutron activation of the native soil material, whereas 14C in surface soils from underground tests may be from either recondensed particulate material or soil activation.

A new isotope separator has been designed, constructed, and put into routine operation for separation of 133Xe providing a major advancement and significant cost reduction in preparation of this radioactive isotope. The design features and advantages are discussed that expedite high purity separation of relatively small quantities of this isotope. These advantages could be easily used to expedite separation of other shorter-lived radioactive isotopes.

A new methodology for gas-phase uranium ion formation is described in which UO2 is dissolved in neat N-ethyl,N′-methylimidazolium fluorohydrogenate ionic liquid [EMIm+][F(HF)2.3−], yielding a blue-green solution. The solution was diluted with acetonitrile and then analyzed by electrospray ionization mass spectrometry. UF6− (a U(V) species) was observed at m/z = 352, and other than cluster ions derived from the ionic liquid, nothing else was observed. When the sample was analyzed using infusion desorption chemical ionization, UF6− was the base peak, and it was accompanied by a less intense UF5− that most likely was formed by elimination of a fluorine radical from UF6−. Formation of UF6− required dissolution of UO2 followed by or concurrent with oxidation of uranium from the + 4 to the + 5 state and finally formation of the fluorouranate. Dissolution of UO3 produced a bright yellow solution indicative of a U(VI) species; however, electrospray ionization did not produce abundant U-containing ions. The abundant UF6− provides a vehicle for accurate measurement of uranium isotopic abundances free from interference from minor isotopes of other elements and a convenient ion synthesis route that is needed gas-phase structure and reactivity studies like infrared multiphoton dissociation and ion-molecule dissociation and condensation reactions. The reactive fluorohydrogenate ionic liquid may also enable conversion of uranium in oxidic matrices into uranium fluorides that slowly oxidize to uranyl fluoride under ambient conditions, liberating the metal for facile measurement of isotope ratios without extensive chemical separations.

RATIONALE:Source term attribution of environmental contamination following the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster is complicated by a large number of possible similar emission source terms (e.g. FDNPP reactor cores 1-3 and spent fuel ponds 1-4). Cesium isotopic analyses can be utilized to discriminate between environmental contamination from different FDNPP source terms and, if samples are sufficiently temporally resolved, potentially provide insights into the extent of reactor core damage at a given time.METHODS:Rice, soil, mushroom, and soybean samples taken 100-250 km from the FDNPP site were dissolved using microwave digestion. Radiocesium was extracted and purified using two sequential ammonium molybdophosphate-polyacrylonitrile columns, following which (135)Cs/(137) Cs isotope ratios were measured using thermal ionization mass spectrometry (TIMS). Results were compared with data reported previously from locations to the northwest of FDNPP and 30 km to the south of FDNPP.RESULTS:(135)Cs/(137)Cs isotope ratios from samples 100-250 km to the southwest of the FDNPP site show a consistent value of 0.376 ± 0.008. (135)Cs/(137)Cs versus (134)Cs/(137)Cs correlation plots suggest that radiocesium to the southwest is derived from a mixture of FDNPP reactor cores 1, 2, and 3. Conclusions from the cesium isotopic data are in agreement with those derived independently based upon the event chronology combined with meteorological conditions at the time of the disaster.CONCLUSIONS:Cesium isotopic analyses provide a powerful tool for source term discrimination of environmental radiocesium contamination at the FDNPP site. For higher precision source term attribution and forensic determination of the FDNPP core conditions based upon cesium, analyses of a larger number of samples from locations to the north and south of the FDNPP site (particularly time-resolved air filter samples) are needed.

Metal fluoroanions are of significant interest for fundamental structure and reactivity studies and for making isotope ratio measurements that are free from isobaric overlap. Iron fluoroanions [FeF4]– and [FeF3]– were generated by electrospray ionization of solutions of Fe(III) and Fe(II) with the fluorinating ionic liquid 1-ethyl-3-methylimidazolium fluorohydrogenate [EMIm]+[F(HF)2.3]-. Solutions containing Fe(III) salts produce predominately uncomplexed [FeF4]– in the negative ion spectrum, as do solutions containing salts of Fe(II). This behavior contrasts with that of solutions of FeCl3 and FeCl2 (without [EMIm]+[F(HF)2.3]–) that preserve the solution-phase oxidation state by producing the gas-phase halide complexes [FeCl4]– and [FeCl3]–, respectively. Thus, the electrospray-[EMIm]+[F(HF)2.3]– process is oxidative with respect to Fe(II). The positive ion spectra of Fe with [EMIm]+[F(HF)2.3]– displays cluster ions having the general formula [EMIm]+ (n+1)[FeF4]– n, and DFT calculations predict stable complexes, both of which substantiate the conclusion that [FeF4]– is present in solution stabilized by the imidazolium cation. The negative ion ESI mass spectrum of the Fe-ionic liquid solution has a very low background in the region of the [FeF4]– complex, and isotope ratios measured for both [FeF4]– and adventitious [SiF5]– produced values in close agreement with theoretical values; this suggests that very wide isotope ratio measurements should be attainable with good accuracy and precision when the ion formation scheme is implemented on a dedicated isotope ratio mass spectrometer.

Four of the radioactive xenon isotopes ((131m)Xe, (133m)Xe, (133)Xe and (135)Xe) with half-lives ranging from 9 h to 12 days are produced from nuclear fission and can be detected from days to weeks following their production and release. Being inert gases, they are readily transported through the atmosphere. Sources for release of radioactive xenon isotopes include operating nuclear reactors via leaks in fuel rods, medical isotope production facilities, and nuclear weapons' detonations. They are not normally released from fuel reprocessing due to the short half-lives. The Comprehensive Nuclear-Test-Ban Treaty has led to creation of the International Monitoring System. The International Monitoring System, when fully implemented, will consist of one component with 40 stations monitoring radioactive xenon around the globe. Monitoring these radioactive xenon isotopes is important to the Comprehensive Nuclear-Test-Ban Treaty in determining whether a seismically detected event is or is not a nuclear detonation. A variety of radioactive xenon quality control check standards, quantitatively spiked into various gas matrices, could be used to demonstrate that these stations are operating on the same basis in order to bolster defensibility of data across the International Monitoring System. This paper focuses on Idaho National Laboratory's capability to produce three of the xenon isotopes in pure form and the use of the four xenon isotopes in various combinations to produce radioactive xenon spiked air samples that could be subsequently distributed to participating facilities.

Radiometric and mass spectrometric analyses of Cs contamination in the environment can reveal the location of Cs emission sources, release mechanisms, modes of transport, prediction of future contamination migration, and attribution of contamination to specific generator(s) and/or process(es). The Subsurface Disposal Area (SDA) at Idaho National Laboratory (INL) represents a complicated case study for demonstrating the current capabilities and limitations to environmental Cs analyses. (137)Cs distribution patterns, (135)Cs/(137)Cs isotope ratios, known Cs chemistry at this site, and historical records enable narrowing the list of possible emission sources and release events to a single source and event, with the SDA identified as the emission source and flood transport of material from within Pit 9 and Trench 48 as the primary release event. These data combined allow refining the possible number of waste generators from dozens to a single generator, with INL on-site research and reactor programs identified as the most likely waste generator. A discussion on the ultimate limitations to the information that (135)Cs/(137)Cs ratios alone can provide is presented and includes (1) uncertainties in the exact date of the fission event and (2) possibility of mixing between different Cs source terms (including nuclear weapons fallout and a source of interest).

RATIONALE:New approaches for forming anions are sought that have strong abundance and no isobaric overlap, attributes that are compatible with the measurement of isotope ratios. Fluoroanions are particularly attractive because fluorine is monoisotopic, and thus will not have overlapping isobars with the isotope of interest. Since many elements do not have positive electron affinity values, they do not form stable negative atomic ions, and hence are not compatible with isotope ratio measurement using high sensitivity isotope ratio mass spectrometers such as accelerator mass spectrometers.METHODS:Zirconium fluoroanions were prepared using the fluorinating ionic liquid (IL) 1-ethyl-3-methylimidazolium fluorohydrogenate, which was used to generate abundant [ZrF5](-) ions using electrospray ionization. The IL was dissolved in acetonitrile, combined with a dilute solution of either Zr(4+) or ZrO(2+), and then electrosprayed. Mass analysis and collision-induced dissociation experiments were conducted using a time-of-flight mass spectrometer. Cluster structures were predicted using density functional theory calculations.RESULTS:The fluorohydrogenate IL solutions generated abundant [ZrF5](-) ions starting from solutions of both Zr(4+) and ZrO(2+). The mass spectra also contained IL-bearing cluster ions, whose compositions indicated the presence of [ZrF6](2-) in solution, a conclusion supported by the structural calculations. Rinsing out the zirconium-IL solution with acetonitrile decreased the IL clusters, but enhanced [ZrF5](-), which was sorbed by the polymeric electrospray supply capillary, and then released upon rinsing. This reduced the ion background in the mass spectrum.CONCLUSIONS:The fluorohydrogenate-IL solutions are a facile way to form zirconium fluoroanions in the gas phase using electrospray. The approach has potential as a source of fluoroanions for isotope ratio measurements, which would enable high-sensitivity measurement of minor zirconium isotopes without overlapping isobars caused by the charge carrier (i.e., the monoisotopic fluorine atoms).

Electrospray ionization of the fluorohydrogenate ionic liquid [1-ethyl-3-methylimidazolium][F(HF)2.3] ionic liquid was conducted to understand the nature of the anionic species as they exist in the gas phase. Abundant fluorohydrogenate clusters were produced; however, the dominant anion in the clusters was [FHF(-)], and not the fluoride-bound HF dimers or trimers that are seen in solution. Density functional theory (DFT) calculations suggest that HF molecules are bound to the clusters by about 30 kcal/mol. The DFT-calculated structures of the [FHF(-)]-bearing clusters show that the favored interactions of the anions are with the methynic and acetylenic hydrogen atoms on the imidazolium cation, forming planar structures similar to those observed in the solid state. A second series of abundant negative ions was also formed that contained [SiF5(-)] together with the imidazolium cation and the fluorohydrogenate anions that originate from reaction of the spray solution with silicate surfaces.

Fractionation of the two longer-lived radioactive cesium isotopes ((135)Cs and (137)Cs) produced by above ground nuclear tests have been measured and used to clarify the dispersal mechanisms of cesium deposited in the area between the Nevada Nuclear Security Site and Lake Mead in the southwestern United States. Fractionation of these isotopes is due to the 135-decay chain requiring several days to completely decay to (135)Cs, and the 137-decay chain less than one hour decay to (137)Cs. Since the Cs precursors are gases, iodine and xenon, the (135)Cs plume was deposited farther downwind than the (137)Cs plume. Sediment core samples were obtained from the Las Vegas arm of Lake Mead, sub-sampled and analyzed for (135)Cs/(137)Cs ratios by thermal ionization mass spectrometry. The layers proved to have nearly identical highly fractionated isotope ratios. This information is consistent with a model where the cesium was initially deposited onto the land area draining into Lake Mead and the composite from all of the above ground shots subsequently washed onto Lake Mead by high intensity rain and wind storms producing a layering of Cs activity, where each layer is a portion of the composite.

There are multiple paths by which radioactive cesium can reach the effluent from reactor operations. The radioactive (135)Cs/(137)Cs ratios are controlled by these paths. In an effort to better understand the origin of this radiation, these (135)Cs/(137)Cs ratios in effluents from three power reactor sites have been measured in offsite samples. These ratios are different from global fallout by up to six fold and as such cannot have a significant component from this source. A cesium ratio for a sample collected outside of the plant boundary provides integration over the operating life of the reactor. A sample collected inside the plant at any given time can be much different from this lifetime ratio. The measured cesium ratios vary significantly for the three reactors and indicate that the multiple paths have widely varying levels of contributions. There are too many ways these isotopes can fractionate to be useful for quantitative evaluations of operating parameters in an offsite sample, although it may be possible to obtain limited qualitative information for an onsite sample.

The extent to which thermal ionization mass spectrometry (TIMS) can measure trace quantities of 233U and 236U in the presence of a huge excess of natural uranium is evaluated. This is an important nuclear non-proliferation measurement. Four ion production methods were evaluated with three mass spectrometer combinations. The most favorable combinations are not limited by abundance sensitivity; rather, the limitations are the ability to generate a uranium ion beam of sufficient intensity to obtain the required number of counts on the minor isotopes in relationship to detector background. The most favorable situations can measure isotope ratios in the range of 1×10−10 if sufficient sample intensity is available. These are the triple sector mass spectrometer with porous ion emitters (PIE) and the single sector mass spectrometer with energy filtering.

A new type of porous refractory material has been developed as a thermal ionization emitter that is an improvement over both direct filament and resin bead loading. The porous ion emitter is sintered onto the center of a conventional thermal ionization filament and an aqueous solution containing the sample wicked into this emitter. Application of the porous ion emitter to uranium is demonstrated to provide a utilization efficiency ranging between 1% and 2% across a sample size range of 0 2-10 pg. better than that achieved from resin beads and much better than that achieved with direct loading onto a filament. The technique improves sensitivity and reduces the chance of losing a high value sample when manipulating a single resin bead containing an entire sample. (C) 2010 Elsevier B V All rights reserved.

Lanthanide elements (lanthanum to lutetium) and actinide elements (uranium and plutonium) adsorbed onto resin beads and mounted on rhenium filaments were studied as thermal ionization sources. Temperatures at which these ion sources gave maximum intensities were measured for each of these elements. The temperature trends correlate with the dissociation energies of the corresponding metal dicarbide compounds. The metal dicarbide functions as a carrier to take the lanthanide and actinide elements to higher temperatures than would be attainable otherwise. This results in release of the atomic species at a higher temperature where ionization probability is significantly increased.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The EMSP Program ''High Temperature Condensed Phase Mass Spectrometric Analysis'' was funded in Sep. 1997 for 36 months. The purpose of this program is to address the issues associated with understanding properties and reactions when materials such as glasses and ceramics are heated to high temperatures in a variety of processes. The reason this is important to DOE EM is the fact that many processes are either in operation or are planned that entail the processing of waste materials at high temperatures. These systems have been engineered, but in many cases the actual scientific details of what goes on in these processes are poorly understood. This program was funded to build a high temperature mass spectrometric analysis instrument designed specifically to analyze materials heated to high temperatures that allows the study of materials both held at these temperatures and undergoing chemical reactions at these temperatures. This program is now at the 30 month point, and the end product of this program, a mass spectrometer system with multiple ionization and analysis modes for high temperature samples, is now operational. The instrument is built around a high temperature ''Langmuir evaporation source,'' and has the following ionization modes: (a) Static SIMS for cations and anions. (b) Dynamic SIMS for cations and anions. (c) Surface ionization for cations and anions. (d) Electron impact ionization (EI) for cations. These ionization modes are all designed into a single ion source housing interfaced to a high sensitivity quadrupole mass spectrometer.

The static secondary ionization mass spectrometry (SIMS) spectrum of tri-n-butyl phosphate (TBP) on a variety of basalt and quartz samples is affected by the chemical composition of the mineral surface. When TBP is adsorbed on Fe(II)-bearing surfaces, the compound undergoes concomitant H− abstraction and reduction, followed by the elimination of two C4H8 molecules to form an ion at m/z 137+. When TBP is adsorbed to quartz or other nonreducing surfaces, it merely undergoes protonation and elimination of three C4H8 molecules to form H4PO4+. When TBP is adsorbed to Fe(III)-bearing surfaces, it undergoes H− abstraction and elimination of two C4H8 molecules, to form an ion at m/z 153+. These conclusions are supported by model studies that employed FeO, Fe203, TBP, and tributyl phosphite. The results show that the SIMS spectrum is very sensitive to the mode of TBP adsorption on the mineral surface.

A new instrument has been developed to study the characteristics of charge build-up on insulating materials caused by the sputtering of secondary particles by ion, electron, neutral or photon beams. The instrument utilizes two beam lines: the charging ion beam irradiates the sample while a measurement ion beam is passed parallel to the sample surface and is then deflected by the charge on the sample. The deflection of the measurement beam, which is proportional to the charge on the sample, is measured with a microchannel plate and photodiode array combination. For these experiments the instrument was configured to simulate a secondary ion mass spectrometer using a negative ion primary beam and a secondary ion extraction lens element. The charge build-up on Mylar and Teflon bulk films was measured as a function of extraction voltage and the results were analyzed using the SIMION ion optics code. The samples could be charged negative or positive, depending upon extraction voltage, and the dominant parameter controlling the charging was the shape of the potential field near the sample. The results indicate that the extraction voltage and the design of the sample mount and near-field regions are the important factors controlling sample charging.

Eight samples from a planar cross section of one of the natural fission reactor zones at the Oklo U mine were analyzed to determine the abundances and isotopic composition of U, Mo, Ru, Pd, Ag, Cd, Sn, Te and Nd. Fission product concentrations were calculated from the isotopic compositions. The relative abundances of these fission products are different from those produced by fission i.e. portions have been lost or gained from all the samples. The proportions of Te, Ru, 99Ru, Pd and Mo in the eight samples are invariant. We attribute this regularity to retention at the site of production—primary retention. Based upon this interpretation, we suggest that fixed proportions of Ru, Tc, Pd and Mo have been removed from the reactor zone. In contrast, Nd and Sn have been depleted in some regions of the zone and enriched in others. Portions of Ag and virtually all the fissiogenic Cd have been removed from the reactor zone. By analogy with anthropogenic spent fuel, we suggest that the degree of primary retention was controlled by phase assemblages formed in the Oklo natural reactor fuel in response to microscale conditions of pressure, temperature and composition produced by the nuclear reactions. The ability of these putative minerals to retain nuclear products was a function of their stability under physiochemical conditions established by the geological environment over the last 2 Ga. An integrated study of the natural reactors would test our hypothesis and provide valuable information for evaluating the long-term effectiveness of anthropogenic spent fuel as a container of nuclear waste in the geochemical environment.