The effect of ion kinetic energy on gas phase ion reactivity with ICP-MS/MS was investigated in order to explore tuning strategies for interference removal. The collision/reaction gases CO2, N2O and O2 were used to observe the ion product distribution for 48 elements using an Agilent tandem ICP-MS (ICP-MS/MS) as a function of reaction gas flow rate (pressure) and ion kinetic energy. The kinetic energy of the incident ion was varied by adjusting the octopole bias (Voct). The three gases all form oxides (MO+) as the primary product with differing reaction enthalpies that result in distinct differences in the ion energies required for reaction with product ion distributions that vary with Voct. Consequently, by varying the ion kinetic energy (i.e., Voct), differences in interference reactivity can be used to achieve maximum separation. Three practical application examples were reported to demonstrate how the ion kinetic energy can be varied to achieve the ideal ion product distribution for interference resolution: CO2 for the removal of 238U in Pu analyses, CO2 for the removal of 40Ar16O vs. 56Fe, and O2 for the removal of Sm in Eu analyses, analogous to Pu/Am. The results demonstrate how the starting ion energy defined by Voct is an important factor to fully leverage the utility of any given reaction gas to remove interferences in the mass spectrum using ICP-MS/MS.

Carbonyl sulfide (OCS) was used as a reaction gas to investigate gas phase metal (M+) ion-molecule reactions using the Agilent 8900 inductively coupled plasma tandem mass spectrometer (ICP-MS/MS) to yield insight on how this gas may be used to remove isobaric interferences in analytical measurements. The experimental work was paired with density functional theory (DFT) calculations of the reaction enthalpy to predict whether M+ will react with OCS. A multi-element standard containing 46 elements ranging from 9 to 208 u was analyzed in the presence and absence of OCS. When a reaction was observed, the dominant product was the sulfide (MS+). Oxide products were also observed for many M+ but formation was less efficient with OCS than previously observed with other reaction gases. This is likely due to the weaker OC-S bond that makes MS+ formation more favorable. Increasing the flow rate from 0.1 to 0.2 mL/min (corresponding to a change in reaction gas pressure from 0.35 to 0.53 Pa (2.6 to 4.0 mTorr)) generally resulted in greater MS+ production, including the secondary product MS2+ for a few cations. The early lanthanide series ions (La+, Ce+, Pr+ and Nd+) produced greater quantities of MO+ at the higher pressure, although MS+ products were still the dominant product. The DFT-predicted reaction enthalpies were consistent with the observed sulfide formation, with an accuracy >90%; however, model predictions were less accurate for the minor and higher order products (< 77% for MO+). The work presented here continues a systematic study of ion-molecule reactions in ICP-MS/MS to understand and develop new and novel ways to analyze complex mixtures with minimal pre-analysis treatment.

Carbon dioxide (CO2) was used as a reaction gas to investigate the gas‐phase ion‐molecule interactions using the Agilent 8900 ICP‐MS/MS. A solution containing forty‐five elements representative of the periodic table was used to supply the ions to react with CO2 in the collision/reaction cell (CRC). The only significant product ions formed were monoxides. The general reactivity was shown to be consistent with density functional theory (DFT)‐predicted reaction enthalpies, such that all predicted exothermic reactions produced product ions at levels of at least 1% of the unreacted ion. Most endothermic reactions observed had sufficient kinetic energy in excess of the reaction enthalpies. Our results suggest that reaction enthalpy is a reasonable predictor of reactivity with CO2 on the timescales of the interactions in non‐thermal ICP‐MS/MS systems. The ease and rapidity of data collection with the ICP‐MS/MS and DFT calculations using the NWChem suite has value given the scarcity of thermochemical data of CO2 reactions in the literature. These studies are especially useful for the identification of targeted reaction chemistries to be leveraged for analytical method development, such as for the inline separation of isobaric interferences from analytes of interest.

Many measurements in the physical sciences can be cast as counting experiments, where the number of occurrences of a physical phenomenon informs the prevalence of the phenomenon’s source. Often, detection of the physical phenomenon (termed signal) is difficult to distinguish from naturally occurring phenomena (termed background). In this case, the discrimination of signal events from background can be performed using classifiers, and they may range from simple, threshold-based classifiers to sophisticated neural networks. These classifiers are often trained and validated to obtain optimal accuracy, however we show that the optimal accuracy classifier does not generally coincide with a classifier that provides the lowest detection limit, nor the lowest quantification uncertainty. We present a derivation of the detection limit and quantification uncertainty in the classifier-based counting experiment case. We also present a novel abstention mechanism to minimize the detection limit or quantification uncertainty a posteriori. We illustrate the method on two data sets from the physical sciences, discriminating Ar-37 and Ar-39 radioactive decay from non-radioactive events in a gas proportional counter, and discriminating neutrons from photons in an inorganic scintillator and report results therefrom.

Tandem mass spectrometry (MS/MS) is a fairly recent addition to the analytical chemist toolkit for elemental analysis. Elemental MS/MS instruments have two mass filters with a collision/reaction cell (CRC) in between that can be used to effect desirable ion-molecule reactions. The key analytical advantage of this feature is that it allows for the in-line separation of analytes from isobaric interferences which would otherwise require lengthy off-line and sometimes complicated sample preparations, like ion exchange chemistry. It also enables in situ separations in cases where bench chemical separations are not possible, e.g., in laser ablation sampling. Instrumentation capable of elemental MS/MS have only been commercially available since 2012. In this talk, we will discuss our work in exploring the reactivity of 45 elements spanning almost all groups of the periodic table with N 2 O and CO 2 using the Agilent 8900 QQQ-ICP-MS. Reasonable correlations between independent Density Functional Theory (DFT) derived reaction enthalpies, calculated using NWChem, and the reaction data were found, showing that reactions typically proceed when thermodynamically allowed. Our work demonstrates the utility of two relatively new platforms (commercial elemental ICP-MS/MS and EMSL Arrows interface to the NWChem program suite developed at the Environmental Molecular Science Laboratory (EMSL) at the Pacific Northwest National Lab (PNNL)) for the study of a large number of elements simultaneously and within a very short period of time. The ease and rapidity of data collection and DFT calculations has potential to revolutionize the identification of targeted reaction chemistries to be leveraged for

Nitrous oxide (N2O) was used as a reaction gas to investigate the gas-phase ion-molecule interactions using the Agilent 8900 QQQ-ICP-MS. A multi-element standard containing 45 elements, from Be to Pb, was used for the measurement of ions with QQQ-ICP-MS in the presence and absence of N2O. The main product ion species observed were oxides and nitrides. Comparison of the N2O reaction results with similar measurements conducted with O2 revealed that N2O was more effective at forming oxides in general: The cations Cd+ and Pb+ were shown to produce oxides with N2O where the reaction did not occur with O2. Nitrous oxide was also shown to produce a significant amount of nitride species in a few cases. The general reactivity was shown to be consistent with density functional theory (DFT)-predicted reaction enthalpies, such that all predicted exothermic reactions produced product ions at levels at least 1% of the unreacted ion. Our results show that reaction enthalpy is a reasonable predictor of reactivity with N2O on the timescales of the interactions in non-thermal ICP-MS/MS systems. Our work demonstrates the utility of two relatively new platforms (commercial elemental ICP-MS/MS and EMSL Arrows interface to the NWChem program suite), which allows for the study of a large number of elements within a short period. While DFT with the basis sets utilized here is not the most accurate computational method, it is also not computationally expensive and is shown to be suitable for predicting gas phase reactivity in the QQQ-ICP-MS for the majority of ions studied. The ease and rapidity of data collection and DFT calculations has the potential to be very impactful for the identification of targeted reaction chemistries to be leveraged for analytical method development, such as for the inline separation of isobaric interferences from analytes of interest.

The rapid transient method records time stamps of individual ion arrival for accurate identification and quantification of nanoparticles.

Our previous research has demonstrated the production of ultra-pure isotopes on the ng-μg scale with high purity >99.999% enabled by modifications to an inductively coupled plasma mass spectrometer (ICP-MS). This technique can also be used to improve radiometric measurements for alpha and beta counting using the isotopic selectivity, low-energy ion deposition technique. The results confirm the utility of this method for developing isotope tracers that can improve the precision and accuracy in trace mass spectrometry measurements. In order to increase throughput, a modified implant mechanism has been developed that can rotate thereby allowing several sequential implants without venting the back-end of the instrument. The details of this modification are discussed and results of isolating and implanting several Nd isotopes are presented.

This research demonstrates two methods of quantifying ion yield efficiency using an inductively coupled plasma mass spectrometer. The mass spectrometer is used as a means of separation where individual decay mass-chains are isolated (i.e., implanted) onto a conductive substrate. Quantifying the ion yield of this recovery process is crucial to understanding the abundance of the separated isotope present in the unseparated starting sample. The first method measured the accumulated charge directly incident on the conductive substrate in real-time while the second method performed a full chemical analysis of the substrate after dissolution. Our previous results demonstrated and compared these quantification methods with a multi-element standard of stable isotopes. This research expands on previous results and utilizes the stable mass ion yield to quantify trace amounts of the (radioactive) isotope of interest present in the sample. The mass-separated radioactive isotopes were fission products produced from thermal neutron irradiation of a highly enriched 235U foil. Five peak-yield mass chains were targeted. The results indicate good correlation between the two methods of measuring the ion yield and imply that coupling this method with traditional radiometric counting can result in an accurate means of quantifying radioactive isotopes. The final results we report here are within 1-sigma of the published cumulative fission yields.

Thermal Ionization Mass Spectrometry (TIMS) has been evaluated for the detection of the radioactive isotopes of Sr and Cs. The commercial instrument (i.e., a Thermo Scientific Triton) was investigated for the analysis of isotopic ratios of 89Sr/90Sr and 135Cs/137Cs in the presence of atomic isobars (89Y and 90Zr for 89,90Sr analysis and 135,137Ba for 135,137Cs analysis). The decontamination achievable instrumentally was examined by isotopic ratio measurements of 89Y/88Sr and 90Zr/88Sr for Sr and 135Ba/133Cs and 137Ba/133Cs for Cs. The decontamination found was at or above 2.0E+8 for 90Zr from 88Sr, while the Y demonstrated a temperature dependence as it sublimed from the filament but remained better than ≈ 5E+7. The decontamination of Ba from Cs did not show any temperature dependence and remained above 5E+6 and 8E+6 for 135Ba and 137Ba from 133Cs, respectively. Two standard fusion procedures one with sodium hydroxide (NaOH) plus sodium peroxide (Na2O2) flux, and the second used lithium tetraborate (Li2B4O7) plus lithium metaborate (LiBO2) flux were evaluated for preparation of sample matrices prior to performing chemical separations. Ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) and Sr-spec resin were used to isolate the Cs and Sr, respectively from a prepared background matrix (i.e., Montana Soil). A graded approach, increasing in stable background isotopes, was performed to monitor the chemical and instrumental response. The radioisotopes of Sr and Cs were produced by thermal neutron irradiation of a highly enriched uranium foil. Even though the irradiated sample was not a certified standard it does provide accurate expectation values via the published cumulative fission yield nuclear data in the Evaluated Nuclear Data Files (ENDF) [1]. The intra-element isotopic ratio results presented in this work for 89Sr/90Sr and 135Cs/137Cs agree with the published data at 1σ. Furthermore, the uncertainty of the isotopic ratio measurements with TIMS was a factor of 5–10 improved compared to these published values.

Mass spectrometry (MS) offers an alternative approach to chemical or chromatographic separations to selectively isolate and collect individual isotopes of an element for analytical purposes.

The detection of radioactive noble gas isotopes is one of the key tools in detecting underground nuclear explosions, but other volatile elemental species, that have historically been overlooked, may also migrate to the surface. To investigate this possibility we have been studying which elements are most readily volatilized into air from solid materials (rocks, concrete, glass, etc.) following short duration (60–120 s) spot heating spanning a wide temperature range (100–2000 °C). The widest possible range of elements (Li–U) was monitored during the experiments that produced some unexpected results with regards to the apparent atmospheric persistence of some volatile signatures long after heating had ceased and the sample had returned to room temperature. Results highlighting elemental volatility as a function of temperature from different materials will be presented along with examples illustrating the extended periods over which some elements remain detectable by real time atmospheric sampling.

"Aerodynamic debris" has often been observed from explosion debris collected on the fringe of surface nuclear tests. The material forms small glassy particulates, ranging in shape from near perfectly spherical glassy beads and occasionally agglomerates of two or more particles. Producing material with a similar range of characteristics in the laboratory is quite challenging, as the temperatures required exceed 1800 K. In this paper, we describe an apparatus that can heat lofted sediment particulates very rapidly above their melting points, for seconds to minutes. Examples of the different material forms produced will be compared to real aerodynamic debris recovered from nuclear explosions described in the literature.

Exploding wires can deposit significant amounts of energy on nS–µS timescales into a confined space. Most exploding wire studies have been performed in air but we have started to investigate enclosing the wire element in solid matrices like concrete to mimic the effects of an underground nuclear explosion. Temperatures and pressures achieved are quite sufficient to induce structural cracking and localized flash melting. As a result exploding wires would appear to form the perfect trigger for releasing chemical species in geological media to study migration behavior. Details of the apparatus and some illustrations of its potential will be given.

Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful method for detection and quantification of nanoparticles. Unfortunately, the linear dynamic range of single particle analysis is hindered by "unruly" transient signals, momentary pulse pile-ups at the electron multiplier detector. This study seeks to extend the dynamic range of ICP-MS nanoparticle quantification via addition of a collision gas in the collision cell of the ICP-MS. The collision gas temporally broadens the nanoparticle signal resulting in decreased pulse pile-up and increased integrated intensity, up to a point where scattering losses begin to dominate. We tested collisional broadening with a dual mode simultaneous secondary electron multiplier (pulse counting switching to analog) and the same detector configured for pulse counting only operation. With no collision gas and the detector operating in its standard dual mode, the data shows a linear response for gold nanoparticles from 20 nm (smallest measured size) to 150 nm. With the addition of helium as a collision gas in the cell, the linear range extends up to 250 nm. The data collected exclusively from the pulse counting mode shows that with no collision gas there is a linear response for gold nanoparticles from 20 nm to 60 nm. While the signal slightly improves with the addition of a collision gas, the linear range fails to extend up to 80 nm, the next largest nanoparticle size in this study. The addition of a collision gas used together with the dual mode detector shows a promising path forward towards mitigating unruly transient signals, improving the dynamic range of nanoparticle quantification.

Uranium ores mined for industrial use are typically acid-leached to produce yellowcake and then converted into uranium halides for enrichment and purification. These anthropogenic chemical forms of uranium are distinct from their mineral counterparts. The purpose of this study is to use soft X-ray absorption spectroscopy to characterize several common anthropogenic uranium compounds important to the nuclear fuel cycle. Chemical analyses of these compounds are important for process and environmental monitoring. X-ray absorption techniques have several advantages in this regard, including element-specificity, chemical sensitivity, and high spectral resolution. Oxygen K-edge spectra were collected for uranyl nitrate, uranyl fluoride, and uranyl chloride, and fluorine K-edge spectra were collected for uranyl fluoride and uranium tetrafluoride. Interpretation of the data is aided by comparisons to calculated spectra. The effect of hydration state on the sample, a potential complication in interpreting oxygen K-edge spectra, is discussed. These compounds have unique spectral signatures that can be used to identify unknown samples.

We characterize EUV TOF for trace analysis using NIST glasses and demonstrate nanoscale imaging on uranium oxide particles.

Accelerator mass spectrometry (AMS) is a mass spectrometry technique making use of tandem accelerators and high-charge states for determination of very small isotopic ratios (10−10 to 10−15). The technique takes advantage of the high ion energies achieved and negative ion interferential instabilities to enable extremely low backgrounds to be achieved. AMS developments, instrumentation, and applications are reviewed.