Isotopic Selectivity Research Articles

The role and application of ion beam analysis for studies of plasma-facing components in controlled fusion devices

First wall materials in controlled fusion devices undergo serious modification by several physical and chemical processes arising from plasma–wall interactions. Detailed information is required for the assessment of material lifetime and accumulation of hydrogen isotopes in wall materials. The intention of this work is to give a concise overview of key issues in the characterization of plasma-facing materials and components in tokamaks, especially in JET with an ITER-Like Wall. IBA techniques play a particularly prominent role here because of their isotope selectivity in the low-Z range (1–10), high sensitivity and combination of several methods in a single run. The role of 3He-based NRA, RBS (standard and micro-size beam) and HIERDA in fuel retention and material migration studies is presented. The use of tracer techniques with rare isotopes (e.g. 15N) or marker layers on wall diagnostic components is described. Special instrumentation, development of equipment to enhance research capabilities and issues in handling of contaminated materials are addressed.

Theoretical Investigations on Laser-Assisted Depletion of Gd152 Isotope From Natural Gadolinium

We have proposed laser-assisted depletion of Gd152 isotope from a natural isotopic mixture of Gd to enhance its functional efficiency as a burnable poison. Theoretical investigations on laser-assisted depletion of Gd152 isotope from natural gadolinium have been carried out for two-color resonant three-color photoionization pathways using density matrix formalism. Calculations have been carried out using a density matrix formalism to optimize conditions for high ionization efficiency without much sacrifice in the isotopic selectivity. Optimum conditions for good isotopic selectivity of Gd152 without significant sacrifice in the ion yield have been identified. Under appropriate conditions, all the 17 photoionization schemes are found to be useful for the laser-assisted separation of Gd152 isotopes which can be used for reactor applications. The effect of source, laser, and atom parameters on isotopic selectivity and ionization efficiency has been investigated. Among the photoionization schemes investigated, one of the photoionization scheme has been investigated in detail. Under optimized conditions, this photoionization scheme has resulted in high ionization efficiency (>50%) and high isotopic selectivity (1.2×104).

Hybrid Fuzzy-Genetic Approach Integrating Peak Identification and Spectrum Fitting for Complex Gamma-Ray Spectra Analysis

A novel hybrid approach for analysis of complex gamma-ray spectra of various origins is described and the test results using spectra obtained from a sodium iodide detector (NaI) are presented. This novel approach exploits the synergism of two artificial intelligence tools; fuzzy logic and genetic algorithms, where the two are merged to identify isotopes and their respective contribution in a given spectrum. The fuzzy logic module focuses on identifying isotopes in the spectrum, while the genetic algorithm (GA) fits and subsequently computes the fractional abundances of the identified isotopes. The fitting of the spectrum is controlled by an assessment procedure based on the test for significance of abundance coefficients, and on the computation of Theil coefficients. This unique synergism between fuzzy logic and GA presents a novel mechanism for automated selection of isotopes for use in spectrum fitting, and as a result eliminates manually-based fitting and/or user intervention. A variety of test cases–including NaI real measured spectra–are used to benchmark this new approach. In addition, the performance of the hybrid method is compared to the multiple linear regression (MLR) fitting approach, along with the combination of fuzzy logic with MLR. This comparison demonstrates a slight superiority of this novel approach regarding accuracy, precision and number of reported false detections.

Overcoming Spectral Interferences in the Determination of Cadmium in Various Food Materials Using Isotope Dilution Inductively‐coupled Plasma Mass Spectrometry#

Double isotope dilution inductively‐coupled plasma mass spectrometry (ID ICP/MS) is widely used for the certification of trace elements in candidate reference materials by many national metrology institutes because it allows accurate and reliable determination of the elemental content in complex matrices of food samples. The presence of isobaric interferences, however, may cause nonnegligible biases in isotope ratio measurements, giving erroneous analytical results. In this study, a matrix separation was carried out using anion exchange chromatography to eliminate isobaric interferences so that an accurate determination of Cd in candidate reference materials could be obtained. Synthetic blends of Cd and interfering elements were used to optimize the matrix separation conditions. The isobaric interferences for cadmium isotopes in various food samples were investigated using the optimized method. Without matrix separation, a significant bias, up to 18%, was observed in a soybean sample. It was about 3% in an herb sample. With the proper selection of isotopes and elimination of isobaric interferences, Cd concentrations in food candidate reference materials were robustly certified.

Polarization-based isotope-selective two-color photoionization of atomic samarium using broadband lasers

An isotope separation method based on polarization selection rules is applied to atomic samarium by using two-color resonance ionization spectroscopy with broadband lasers. In this method, odd isotopes with nonzero nuclear spin are selectively excited, while even isotopes with zero nuclear spin are prohibited from excitation using two parallel linearly polarized lasers. We have identified a two-color excitation scheme 0 cm−1 (J = 0) → 15650.5 cm−1 (J = 1) → 33116.8 cm−1 (J = 1) → Sm+ for selective excitation of the odd isotopes of Sm I. Using this scheme, selective excitation of odd isotopes of Sm I (147Sm and 149Sm) with an isotopic selectivity better than 40 has been demonstrated. In addition, the effect of different polarization states of the excitation lasers and relative polarization angle between them on the selectivity of odd isotopes has also been studied. The dependence of the even mass isotope signal on the relative polarization angle followed sin2θ, which is in excellent agreement with theoretical predictions.

From EXILL (EXogam at the ILL) to FIPPS (FIssion Product Promptγ-ray Spectrometer)

Within the EXILL campaign a large and efficient cluster of Ge-detectors was installed around a very well collimated neutron beam. This has allowed to carry out rather complete spectroscopic studies close to the line of stability using the (n,γ) reaction. Neutron rich isotopes were produced by neutron induced fission and prompt spectroscopy was carried out. The isotope selection in this setup was based on a partially known level scheme and the use of triple coincidences. The latter is limiting the statistical sensitivity in the case of weak production yields. Based on the experiences of these campaigns we are currently developing a new setup: FIPPS (FIssion Product Prompt Spectroscopy). This setup combines a collimated neutron beam, a highly efficient cluster of Ge detectors, a gas filled magnet and auxiliary detectors. The presence of the gas filled magnet will allow us to identify fission products directly and should give access to a new quality of studies if compared to the EXILL campaign. The EXILL campaign and the FIPPS project are presented.

Isotopically enriched structural materials in nuclear devices

A large number of materials exist which have been labeled as low activation structural materials (LAM). Most often, these materials have been designed in order to substitute-out or completely remove elements that become activated and contribute significantly to shut-down activity after being irradiated by neutrons in a reactor environment. To date, one of the fundamental principles from which LAMs have been developed is that natural elemental compositions are the building blocks of LAMs. Thus, elements such as Co, Al, Ni, Mo, Nb, N and Cu that produce long-lived decay products are significantly reduced or removed from the LAM composition. These elements have an important part to play in the composition of steels and the removal/substitution can have a negative impact on materials properties such as yield stress and fracture toughness. This paper looks in more detail at whether using isotopic selection of the more mechanically desirable, but prohibited due to activation, elements can improve matters. In particular, this paper focuses on the activation of Eurofer.Carefully chosen isotopically enriched elements, which are normally considered to be on the prohibited element list, are added to EUROFER steel as potential alloying elements. The EUROFER activation results show that some prohibited elements can be used as alloying elements in LAM steels, providing the selected isotopes do not have a significant impact on waste disposal rating or shut-down dose. The economic implications of isotopically enriching elements and the potential implications for decommissioning are considered. It is shown that the addition of molybdenum and nickel in small concentrations (<2% mass) could have the potential to increase availability to such an extent that the capital investment associated with isotope enrichment is negated and profits from electricity sale increased.Another important issue for materials exposed to neutron irradiation is the production of gases, in particular helium, as a result of nuclear interactions. Helium accumulation in materials can cause embrittlement and so mitigating the rate of production is an important consideration when selecting materials. The second part of this paper considers whether helium production can be reduced in CuCrZr by isotopic tailoring. CuCrZr is a candidate bonding material for tungsten at first wall locations, however it suffers from degradation due to helium production. Inventory calculations show that isotopically enriching the copper, in CuCrZr, can reduce helium production by approximately 50%. However, cost–benefit analysis suggests that the cost of enriching copper is not cost-effective due to the high price of electromagnetic enrichment that is required for copper.

HyperBIRD: A Sensitivity‐Enhanced Approach to Collecting Homonuclear‐Decoupled Proton NMR Spectra

AbstractSamples prepared following dissolution dynamic nuclear polarization (DNP) enable the detection of NMR spectra from low‐γ nuclei with outstanding sensitivity, yet have limited use for the enhancement of abundant species like 1H nuclei. Small‐ and intermediate‐sized molecules, however, show strong heteronuclear cross‐relaxation effects: spontaneous processes with an inherent isotopic selectivity, whereby only the 13C‐bonded protons receive a polarization enhancement. These effects are here combined with a recently developed method that delivers homonuclear‐decoupled 1H spectra in natural abundance samples based on heteronuclear couplings to these same, 13C‐bonded nuclei. This results in the HyperBIRD methodology; a single‐shot combination of these two effects that can simultaneously simplify and resolve complex, congested 1H NMR spectra with many overlapping spin multiplets, while achieving 50–100 times sensitivity enhancements over conventional thermal counterparts.

HyperBIRD: a sensitivity-enhanced approach to collecting homonuclear-decoupled proton NMR spectra.

Samples prepared following dissolution dynamic nuclear polarization (DNP) enable the detection of NMR spectra from low-γ nuclei with outstanding sensitivity, yet have limited use for the enhancement of abundant species like (1)H nuclei. Small- and intermediate-sized molecules, however, show strong heteronuclear cross-relaxation effects: spontaneous processes with an inherent isotopic selectivity, whereby only the (13)C-bonded protons receive a polarization enhancement. These effects are here combined with a recently developed method that delivers homonuclear-decoupled (1)H spectra in natural abundance samples based on heteronuclear couplings to these same, (13)C-bonded nuclei. This results in the HyperBIRD methodology; a single-shot combination of these two effects that can simultaneously simplify and resolve complex, congested (1)H NMR spectra with many overlapping spin multiplets, while achieving 50-100 times sensitivity enhancements over conventional thermal counterparts.

Nanoparticle size detection limits by single particle ICP-MS for 40 elements.

The quantification and characterization of natural, engineered, and incidental nano- to micro-size particles are beneficial to assessing a nanomaterial's performance in manufacturing, their fate and transport in the environment, and their potential risk to human health. Single particle inductively coupled plasma mass spectrometry (spICP-MS) can sensitively quantify the amount and size distribution of metallic nanoparticles suspended in aqueous matrices. To accurately obtain the nanoparticle size distribution, it is critical to have knowledge of the size detection limit (denoted as Dmin) using spICP-MS for a wide range of elements (other than a few available assessed ones) that have been or will be synthesized into engineered nanoparticles. Herein is described a method to estimate the size detection limit using spICP-MS and then apply it to nanoparticles composed of 40 different elements. The calculated Dmin values correspond well for a few of the elements with their detectable sizes that are available in the literature. Assuming each nanoparticle sample is composed of one element, Dmin values vary substantially among the 40 elements: Ta, U, Ir, Rh, Th, Ce, and Hf showed the lowest Dmin values, ≤10 nm; Bi, W, In, Pb, Pt, Ag, Au, Tl, Pd, Y, Ru, Cd, and Sb had Dmin in the range of 11-20 nm; Dmin values of Co, Sr, Sn, Zr, Ba, Te, Mo, Ni, V, Cu, Cr, Mg, Zn, Fe, Al, Li, and Ti were located at 21-80 nm; and Se, Ca, and Si showed high Dmin values, greater than 200 nm. A range of parameters that influence the Dmin, such as instrument sensitivity, nanoparticle density, and background noise, is demonstrated. It is observed that, when the background noise is low, the instrument sensitivity and nanoparticle density dominate the Dmin significantly. Approaches for reducing the Dmin, e.g., collision cell technology (CCT) and analyte isotope selection, are also discussed. To validate the Dmin estimation approach, size distributions for three engineered nanoparticle samples were obtained using spICP-MS. The use of this methodology confirms that the observed minimum detectable sizes are consistent with the calculated Dmin values. Overall, this work identifies the elements and nanoparticles to which current spICP-MS approaches can be applied, in order to enable quantification of very small nanoparticles at low concentrations in aqueous media.

Reexamining surface-integral formulations for one-nucleon transfers to bound and resonance states

One-nucleon transfer reactions, in particular (d,p) reactions, have played a central role in nuclear structure studies for many decades. Present theoretical descriptions of the underlying reaction mechanisms are insufficient for addressing the challenges and opportunities that are opening up with new radioactive beam facilities. We investigate a theoretical approach that was proposed recently to address shortcomings in the description of transfers to resonance states. The method builds on ideas from the very successful R-matrix theory; in particular it uses a similar separation of the parameter space into interior and exterior regions, and introduces a parameterization that can be related to physical observables, which, in principle, makes it possible to extract meaningful spectroscopic information from experiments. We carry out calculations, for a selection of isotopes and energies, to test the usefulness of the new approach.

Deuterium and hydrogen tunneling in the hydrogenation of 4-oxocyclohexa-2,5-dienylidene.

4-Oxocyclohexa-2,5-dienylidene is a highly reactive triplet ground state carbene that is hydrogenated in solid H2, HD, and D2 at temperatures as low as 3 K. The mechanism of the insertion of the carbene into dihydrogen was investigated by IR and EPR spectroscopy and by kinetic studies. H or D atoms were observed as products of the reaction with H2 and D2, respectively, whereas HD produces exclusively D atoms. The hydrogenation shows a very large kinetic isotope effect and remarkable isotope selectivity, as was expected for a tunneling reaction. The experiments, therefore, provide clear evidence for both hydrogen tunneling and the rare deuterium tunneling in an intermolecular reaction.

NICKEL-HYDROGEN COLD FUSION BY INTERMEDIATE RYDBERG STATE OF HYDROGEN: SELECTION OF THE ISOTOPES FOR ENERGY OPTIMIZATION AND RADIOACTIVE WASTE MINIMIZATION

The main objection against cold fusion is based on the theoretical understanding that the Coulomb barrier of the very small nucleus is extremely strong. The size of the atomic nucleus is determined by scattering experiments in which a metal target is usually struck by alpha particles. These experiments yield only energy and angular resolution and their interpretation rely on the assumption that the atomic nuclei and all elementary particles are spherical. A non-spherical nucleus made of thinner non-spherical particles like a torus or a twisted or folded torus will provide similar data for a limited range of the particle energy. At the time of Rutherford, alpha particles with energy from 4 to 8 MeV were used. Modern scattering experiments with energy above 25 MeV show a sharp deviation from the Rutherford theory. They also show a wavelike shape of the scattering cross section as a function of scattering angle. A new interpretation of the scattering experiments leads to the idea that the Coulomb field near the nucleus has a manifold shape with a much larger overall size and therefore is not so strong. The BSM-SG models of atomic nuclei are in excellent agreement with this conclusion. Applying the approach described in the monograph Structural Physics of Nuclear Fusion with BSM-SG atomic models, the highly exothermal process between nickel and hydrogen is analyzed. It leads to the conclusion that a proton capture may occur at an accessible temperature in a range of a few hundred degrees. The process is assisted by an intermediate state of hydrogen, known as the Rydberg atom, the magnetic field of which interacts constructively with the recipient nucleus if it is in a proper nuclear spin state. The final conclusion is that it is theoretically possible to obtain nuclear energy without radioactive waste by proper isotope selection of involved elements.

Interferences of polyatomic and doubly charged ions in the multielement analysis of geological samples by inductively coupled plasma mass spectrometry and their minimization on a high-resolution mass spectrometer

The paper is devoted to various significant polyatomic and doubly charged interferences observed for trace elements determined by inductively coupled plasma mass spectrometry in geological samples. It has been shown that most interferences can be minimized or completely excluded using an ELEMENT 2 high-resolution mass spectrometer. The influence of spectral interferences has been quantitatively estimated. Recommendations are given for the selection of isotopes with minimal spectral interferences and an optimal resolution mode. The detection limits for analytes are evaluated for three resolution modes: 300, 4000 and 10000 together with the interferences related to the errors of rare-earth element determination.

ORNL developments in laser ion sources for radioactive ion beam production

The development of a resonant ionization laser ion source (RILIS) for the production of isotopically pure radioactive ion beams is reported. The application of the laser ion source calls for high elemental selectivity, high efficiency, and fast release of short-lived isotopes. A hot-cavity ion source and three Ti:sapphire lasers pulsed at a 10 kHz rate are employed for the RILIS. The Ti:sapphire lasers have been upgraded with individual pump lasers to eliminate intracavity Pockels cells and output losses due to synchronization delays. The development of ionization schemes for a wide range of elements is important to the success of Ti:sapphire-laser-based RILIS. In off-line studies with stable isotopes, resonant ionization of 14 elements has been studied, leading to new ionization schemes for ten elements. The absolute ionization efficiency of the hot-cavity RILIS has been measured to range from 0.9 % to 40 % for different elements. The mechanisms for ion transportation and confinement in the hot-cavity ion source have been studied using the temporal profiles of the laser-ionized ions. The hot-cavity RILIS has provided beams of neutron-rich \(^{83,85,86}\)Ga isotopes for beta decay studies and enabled the first measurement of the beta decay of the exotic \(^{86}\)Ga.

Coupled noble gas–hydrocarbon evolution of the early Earth atmosphere upon solar UV irradiation

Using a new photochemical model of the Earthʼs early atmosphere, the relationship between noble gas photoionization and organic photochemistry has been investigated from the Archean eon to the present day. We have found that the enhanced UV emission of the young Sun triggered a peculiar atmospheric chemistry in a CH4-rich early atmosphere that resulted in the increased formation of an organic haze, similar to the preliminary results of a previous study (Ribas et al., 2010). We have investigated the interaction between this haze and noble gases photoionized by the UV light from the younger Sun. Laboratory experiments have shown indeed that ionized xenon trapping into organics (1) is more efficient that other ionized noble gases trapping and (2) results in a significant enrichment of heavy xenon isotopes relative to the light ones (e.g., Frick et al., 1979; Marrocchi et al., 2011). We find moreover preferential photoionization of xenon that peaks at an altitude range comparable to that of the organic haze formation, in contrast to other noble gases. Trapping and fractioning of ionized xenon in the organic haze could therefore have been far more efficient than for other noble gases, and could have been particularly effective throughout the Archean eon, since the UV irradiation flux from the young Sun was expected to be substantially higher than today (Ribas et al., 2010; Claire et al., 2012). Thus we suspect that the unique isotopic fractionation of atmospheric xenon and its elemental depletion in the atmosphere relative to other noble gases, compared to potential cosmochemical components, could have resulted from a preferential incorporation of the heaviest xenon isotopes into organics. A fraction of atmospheric xenon could have been continuously trapped in the forming haze and enriched in its heavy isotopes, while another fraction would have escaped from the atmosphere to space, with, or without isotope selection of the lightest isotopes. The combination of these two processes over long periods of time provides thereby a key process for explaining the evolution of its isotopic composition in the atmosphere over time that has been observed in Archean archives (Pujol et al., 2011).

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ((16)O,(17)O,(18)O) and sulfur ((32)S, (33)S, (34)S, (36)S) isotope systems and serve as important tracers of past and present atmospheric processes. These unique isotope signatures signify the breakdown of the traditional theory of isotope fractionation, but the physical chemistry of these isotope effects remains poorly understood. We report the production of large sulfur isotope MIF, with Δ(33)S up to 78‰ and Δ(36)S up to 110‰, from the broadband excitation of SO2 in the 250-350-nm absorption region. Acetylene is used to selectively trap the triplet-state SO2 ( (3)B1), which results from intersystem crossing from the excited singlet ( (1)A2/ (1)B1) states. The observed MIF signature differs considerably from that predicted by isotopologue-specific absorption cross-sections of SO2 and is insensitive to the wavelength region of excitation (above or below 300 nm), suggesting that the MIF originates not from the initial excitation of SO2 to the singlet states but from an isotope selective spin-orbit interaction between the singlet ( (1)A2/ (1)B1) and triplet ( (3)B1) manifolds. Calculations based on high-level potential energy surfaces of the multiple excited states show a considerable lifetime anomaly for (33)SO2 and (36)SO2 for the low vibrational levels of the (1)A2 state. These results demonstrate that the isotope selectivity of accidental near-resonance interactions between states is of critical importance in understanding the origin of MIF in photochemical systems.

Preparation of Graphene with Graphane Areas of Controlled Hydrogen Isotope Composition on Opposite Sides.

Monolayer graphene was prepared on an Ir(111) substrate where it exhibits a 25 × 25 Å(2) moiré pattern. Molecular hydrogen was dosed first, allowing it to dissociate on open areas of the Ir substrate. The generated H atoms formed an intercalated reservoir that can bind to the graphene subsequently. Next, atomic hydrogen was dosed, which binds to the graphene sheet and also initiates the transfer of H from the Ir substrate to the graphene sheet. The opposite sides of the sheet can be hydrogenated with isotope selectivity, as a sequence of difference isotopes, H or D, can be chosen at will in the preparation procedure. Sum-frequency generation spectra prove that as consequence of the dosing sequence, C-H bonds are predominantly pointing toward the Ir substrate side when H2 is dosed first and alternatively toward the vacuum side when D2 is dosed first.

Probing the unusual isotope effects in ozone formation: Bath gas and pressure dependence of the non-mass-dependent isotope enrichments in ozone

Laboratory and atmospheric measurements of the isotopic composition of ozone have shown large and unusual ‘non-mass-dependent’ enrichments in 17O and 18O of ∼10% relative to the O2 from which it is formed. We present measurements of the bath gas and pressure dependence of the isotope enrichments in ozone formed by photolysis of O2 in the presence of Ar, O2, CO2, and SF6 from 50 to 760Torr. The results provide new insights into the origin of the dynamically-driven symmetry-related isotope effect involved and new benchmarks for theory, including elimination of all isotope selectivity for ozone formation in SF6 by 700Torr.

Neutrino mass calorimetric searches in the MARE experiment

The international project “Microcalorimeter Arrays for a Rhenium Experiment” (MARE) aims at the direct and calorimetric measurement of the electron neutrino mass with sub-electronvolt sensitivity. Calorimetric neutrino mass experiments measure all the energy released in a beta decay except for the energy carried away by the neutrino, therefore removing the most severe systematic uncertainties which have plagued the traditional and, so far, more sensitive spectrometers. Calorimetric measurements are best realized exploiting the thermal detection technique. This approach uses thermal microcalorimeters whose absorbers contain a low transition energy Q beta decaying isotope. To date the two best options are 187Re and 163Ho. While the first beta decays, the latter decays via electron capture, but both have a Q value around 2.5 keV. The potential of using 187Re for a calorimetric neutrino mass experiment has been already demonstrated. On the contrary, no calorimetric spectrum of 163Ho has been so far measured with the precision required to set a useful limit on the neutrino mass. In this talk we present the status and the perspectives of the MARE project activities for the active isotope selection and the single channel development. We also discuss the neutrino mass statistical sensitivity achievable with both isotopes.