Electron Capture Spectroscopy Research Articles

Development of Holmium-163 Electron-Capture Spectroscopy with Transition-Edge Sensors

Calorimetric decay energy spectroscopy of electron-capture-decaying isotopes is a promising method to achieve the sensitivity required for electron neutrino mass measurement. The very low total nuclear decay energy (QEC < 3 keV) and short half-life (4570 y) of 163Ho make it attractive for high-precision electron capture spectroscopy (ECS) near the kinematic endpoint, where the neutrino momentum goes to zero. In the ECS approach, an electron-capture-decaying isotope is embedded inside a microcalorimeter designed to capture and measure the energy of all the decay radiation except that of the escaping neutrino. We have developed a complete process for proton-irradiation-based isotope production, isolation, and purification of 163Ho. We have developed transition-edge sensors for this measurement and methods for incorporating 163Ho into high-resolution microcalorimeters, and have measured the electron-capture spectrum of 163Ho. We present our work in these areas and discuss the measured spectrum and its comparison to current theory.

Combining gas phase electron capture and IRMPD action spectroscopy to probe the electronic structure of a metastable reduced organometallic complex containing a non-innocent ligand.

Combining electron capture dissociation mass spectrometry and infrared multiple photon dissociation action spectroscopy allows the formation, selection and characterisation of reduced metal complexes containing non-innocent ligands. Zinc complexes containing diazafluorenone ligands have been studied and the localisation of the single electron on the metal atom in the mono-ligated complex has been demonstrated.

Integration of Radioactive Material with Microcalorimeter Detectors

Microcalorimeter detectors with embedded radioactive material offer many possibilities for new types of measurements and applications. We will discuss the designs and methods that we are developing for precise deposition of radioactive material and its encapsulation in the absorber of transition-edge sensor (TES) microcalorimeter detectors for two specific applications. The first application is total nuclear reaction energy (Q) spectroscopy for nuclear forensics measurements of trace actinide samples, where the goal is determination of ratios of isotopes with Q values in the range of 5–7 MeV. Simplified, rapid sample preparation and detector assembly is necessary for practical measurements, while maintaining good energy resolution. The second application is electron capture spectroscopy of isotopes with low Q values, such as \(^{163}\)Ho, for measurement of neutrino mass. Detectors for electron capture spectroscopy are designed for measuring energies up to approximately 6 keV. Their smaller heat capacity and physical size present unique challenges. Both applications require precise deposition of radioactive material and encapsulation in an absorber with optimized thermal properties and coupling to the TES. We have made detectors for both applications with a variety of designs and assembly methods, and will present their development.

Characterization of the Superconducting Transition of Thin Ir Films for TES

We are currently producing iridium based TESs for a wide variety of applications such as single photon detection of the visible and infrared light, X-ray spectroscopy and low energy nuclear beta and electron capture spectroscopy for neutrino mass search experiment. We present a study of the TES performance related to the superconductivity properties of the Ir film as function of the production processes, that depend on substrate type: Si or SiN, and of the operating electrical parameters. Moreover we developed a finite element model of thin superconducting film, by which we obtain qualitative agreement between experimental and simulated data.

Electron shuttling in electron transfer dissociation

Ab initio electronic structure calculations have been performed on two model systems containing a disulfide linkage and one or two positively charged sites, aimed at gaining further insight into how and where electrons attach to positively charged peptides under electron capture (ECD) and electron transfer dissociation (ETD) mass spectroscopy conditions. Couplings among electronic states involving (i) an entrance-channel with the excess electron residing on a donor anion interacting with the positively charged peptide, (ii) a state in which the electron has been transferred to the SS σ* orbital to cause bond cleavage, and (iii) a manifold of states in which the electron has been transferred to a ground- or excited-Rydberg orbital on a positive site. The results of this study suggest that specific excited Rydberg states play a key role in effecting electron shuttling to the SS σ* orbital. The excited-Rydberg orbitals close in energy to the SS σ* orbital and with sufficient radial extent to span the distance between the positive site and the SS σ* orbital play the key role. Then, when the anion donor, excited-Rydberg, and SS σ* orbitals achieve spatial proximity and similarity in energies, one can have what is termed here a shuttle of an electron from the donor to the SS σ* orbital, which results in SS bond cleavage. For the singly and doubly charged systems studied here, it was the 3p and 3d Rydberg orbitals, respectively, that met these criteria of spatial and energetic proximity. For other peptides having different charge states, it will be other Rydberg orbitals that meet these criteria because the relative energies of the SS σ* and Rydberg orbitals are governed by the (different) Coulomb stabilizations these orbitals experience. However, the evidence suggests that it is not very high-energy Rydberg states but states with 3 < n < 10 that are involved in the rate limiting steps in ECD, ETD, and ECID experiments.

Theoretical study of through-space and through-bond electron transfer within positively charged peptides in the gas phase

As part of an on-going effort to probe mechanisms for disulfide and backbone N–C α cleavage under electron capture or electron-transfer dissociation mass spectroscopy conditions, theoretical simulations have been carried out to consider the probabilities that a. an electron initially attached to a protonated amine site on a side chain can migrate (through-bond or through-space) to an S–S σ* orbital and thus cause disulfide cleavage; b. an electron initially attached to a protonated site might be transferred (through-bond or through-space) to another protonated site or to a fixed-charge positive site thus allowing the electron to migrate throughout charged sites in a multiply charged peptide. The primary findings of this work include: c. charged-site to S–S σ* orbital through-bond electron transfer can occur at significant probabilities but only over ca. 5 intervening bonds covering up to ca. 15 Å; d. through-space electron transfer from protonated sites to protonated sites or from fixed-charge sites to fixed-charge sites can be facile, but between protonated and fixed-charge sites transfer is very slow; to effect the transfers between equivalent sites, the two sites must come within ca. 5 Å of one another; e. through-space electron transfer from a protonated or fixed-charge site to an S–S σ* orbital can occur with reasonable probability but if the two sites come within ca. 5 Å of one another. Based on these findings, speculation is offered both to interpret recent findings of the McLuckey group on flexible, triply charged peptides and earlier data from the Marshall group on more rigid, helical, doubly charged peptides, both of which contain disulfide linkages that experiments find to be readily cleaved.

Investigation of spin-polarized surfaces with multiple electron capture spectroscopy

Slow, multiply charged ions incident on solid surfaces interact only with a few atomic sites from the top-most surface layer. A novel technique for probing local spin polarization at surfaces was developed, namely multiple electron capture spectroscopy (MECS). This technique is based on the Auger electron emission from doubly excited He atoms formed in front of ferromagnetic surfaces. The temperature dependence of the spin polarization of Fe(110) was obtained and the results are compared with those from the highly polarized Ni(110) surface.

Transfer of spin polarization in ion-surface scattering

Low-energy ion beams impinging under grazing incidence on surfaces interact inherently with the topmost surface layer(s). The method of electron capture spectroscopy in which the degree of polarization of the light emitted by the neutralized projectiles is analyzed has been used to investigate spin polarization effects at Ni(1 1 0) and Fe(1 1 0) surfaces. The results hint at strong spin filtering mechanisms. With multiply charged instead of singly charged ion beams one may obtain access to short range spin ordering at the surface. Progress in the development of this new, so-called multiple electron capture spectroscopy technique is discussed and first results for He 2+ ions interacting with a Ni(1 1 0) surface are presented.

Surface spin polarization in Fe(1 1 0) and Ni(1 1 0)

The magnetism of Ni(110) and Fe(110) surfaces was investigated by electron capture spectroscopy. He+ and He2+ ions impinged on the Fe(110) and Ni(110) surfaces under grazing incidence, and the degree of polarization of the light emitted by the neutralized projectiles was analyzed. Our measurements show that in Ni(110) minority electrons have a higher density of states at the Fermi energy than majority electrons, opposed to the Fe(110) case. From a comparison of our measurements we estimate the ratio between captured minority and majority electrons in Ni(110) to be similar as the ratio between captured majority and minority electrons in Fe(110).

Thin Co films on Cu(111) studied by electron capture spectroscopy

AbstractWe have studied thin films of Co on Cu(111) single crystals with electron capture spectroscopy (ECS). The magnetism from the cobalt layer can be detected clearly in remanence and as a function of the outer magnetic field. The measured circular polarization of the emitted light is related directly to the structural and magnetic changes of the system, depending on the cobalt layer thickness. We find the set‐in of in‐plane magnetization at ∼2 monolayers of cobalt and the saturation of our signal at a film thickness of 7–8 monolayers. At coverages above 3–4 monolayers the increasing growth of hcp cobalt domains at the expense of fcc cobalt domains gives rise to a linearly increasing ECS signal up to 7.5 monolayers. We attribute this to the fact that the fcc cobalt domains are covered with copper, whereas the hcp cobalt domains expose cobalt in the upper layer. Monte‐Carlo simulations of our ion scattering experiments show that great experimental care has to be taken in order to avoid excessive sputtering damage to the sample. By using moderate primary ion energies and small angles of incidence, thin films can be investigated with ECS in the grazing incidence geometry without changing the film structure. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Survey for the occurrence of antifouling paint booster biocides in the aquatic environment of Greece.

Since the restriction imposed by European Union regulations on the use of TBT-based antifouling paints on boats below 25 m in length, new terms have been introduced in the 'small boat' market. Replacement products are generally based on copper metal oxides and organic biocides. Several studies have demonstrated the presence of these biocides in European ports and marinas of Spain, France, Germany and the United Kingdom. An extended survey of the antifouling biocides chlorothalonil, dichlofluanid, irgarol 1051 and sea-nine 211 was carried out in Greek ports and marinas of high boating activities from October 1999 to September 2000. The sampling sites were: Piraeus, Elefsina, Thessaloniki, Patras, Chalkida, Igoumenitsa, and Preveza (Aktio). The extraction of these compounds from the seawater samples was performed off-line with C18 solid phase extraction (SPE) disks while the determination was carried out with gas chromatography coupled to electron capture (ECD), thermionic (FTD) and mass spectroscopy (MS) detectors. The concentration levels of biocides were higher during the period from April to October. This seasonal impact depends on the application time of antifouling paints and mimic trends in the seasonal distribution of biocides in other European sites.

All-electron and pseudopotential study of the spin-polarization of the V(001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local [local spin-density approximation (LSDA)] and semilocal [generalized gradient approximation (GGA]) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron tight-binding linear muffin-tin orbital atomic-sphere approximation and the pseudopotential linear combination of atomic orbitals code SIESTA (Spanish initiative for electronic simulations with thousands of atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film $(7&lt;~N&lt;~15).$ The LSDA approximation leads to a nonmagnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the nonmagnetic solution obtained by means of the all-electron code.

Surface magnetism of ultrathin Cr, Mn, and Fe films on Fe(1 0 0) studied via electron capture spectroscopy

The long-range magnetic ordering at the surface of ultrathin epitaxial films of Cr, Mn, and Fe on Fe(1 0 0) has been studied by electron capture spectroscopy. The observed spin polarization indicates different magnetic orderings comprising parallel and antiparallel coupling of moments. Based on simple assumptions for electron capture, the layer- and coverage-dependent magnetization profile is estimated.

Determination of PCBs and LABs in Sewage Sludge from a Wastewater Treatment Plant

The results from a study of the presence and temporal variability of linear alkylbenzenes (LABs) and polychlorinated biphenyls (PCBs) in sewage sludge are presented in this work. The sewage sludges, with anaerobic treatment, were originated in the Arazuri (Pamplona, Spain) wastewater primary treatment plant, which receives urban and industrial wastewaters. The organic pollutants extracted from the sewage sludge by a Soxhlet apparatus. Then, PCBs and LABs were separated from the rest of the pollutants on a chromatographic column. Some different detectors were flame ionization (FID), electron capture (ECD) and mass spectroscopy (MS). The results showed that LABs concentration varied between 1.4 and 73.0 mg kg−1 dry matter (d.m.). PCBs appear in smaller quantity, between 0.050 and 0.929 mg kg−1 (d.m.). The factor analysis of the results allowed verification of the different origin of PCBs and LABs.

Measuring hystereses of magnetic surfaces by ion scattering

Scattering of He ions off a magnetic surface results in the emission of circularly polarized light from a triplet transition. From the light polarization the spin polarization of the surface electrons can be deduced. We show that this electron capture spectroscopy (ECS) in the grazing incidence mode is an inherently surface sensitive method capable of measuring magnetic hystereses. The temperature dependence of the signal gives clear evidence that ECS is sensitive to the outermost atomic layer only. The signal follows a Bloch law with a surface prefactor of Asurf=3.33×10−5 K−3/2. The signal as a function of the applied magnetic field results in a hysteresis which is compared to a hysteresis obtained by means of the magneto-optical Kerr effect.

Magnetic studies of bct Fe(100)p(1 × 1)/Pd(100) films

Electron capture (ECS) and spin-polarized electron emission spectroscopy (SPEES) studies are performed at surfaces of ultra-thin bct Fe(100)p(1 × 1) films deposited on atomically flat Pd(100) substrates. For well-annealed films, the electron spin polarization (ESP) is oriented in-plane, and ferromagnetic order sets in at a surface Curie temperature T Cs = 662.3 K (4 ML). Near T Cs, the ESP follows the power law ( T Cs — T Cs) β, with a critical exponent β = 0.129 ± 0.01 evaluated near T Cs. Varying the probing depth, it is found that the layer-dependent average (ESP) at the topmost surface layer (37%) is enhanced by 32% as compared to that of bulk layers (28%). Pd Auger electrons emitted from the Fe/Pd interface are spin polarized with their ESP oriented parallel to that of emitted Fe Auger electrons.

Electron capture and emission spectroscopy to study surface and interface magnetism

Electron capture spectroscopy (ECS) and spin-polarized electron emission spectroscopy (SPEES) are extremely sensitive techniques to probe surface magnetic properties. Ultra-thin bct Fe(100)(1×1)/Pd(100) films exhibit 2D Ising critical behavior. The surface electron spin polarization (ESP) follows precisely the exact solution of the 2D Ising model as given by Yang. The average magnetization of the topmost surface layer is enhanced by 32% compared to that of bulk layers. Pd Auger electrons emitted from the Fe/Pd interface are spin-polarized, and the ESP is oriented parallel to that of emitted Fe Auger electrons. At surfaces of 5nm thick hcp Tb(0001)/W(110) films, strong surface magnetic surface anisotropies are found. The onset of ferromagnetism occurs ≈30 K above the bulk Curie temperature (220K) of Tb. For clean Fe and Fe/Pd surfaces, the ESP of low-energy (≈2 eV) emitted electrons is substantially enhanced by Stoner excitations. The existence of a nonzero ESP at O/Fe surfaces demonstrates the absence of a magnetically dead surface layer.

Magnetic order and critical behavior at surfaces of ultrathin Fe(100)p(1×1) films on Pd(100) substrates

The magnetic order and critical behavior at well-defined surfaces of ultrathin (1.9–2.1) monolayer Fe(100)p(1×1) films, deposited at room temperature on atomically flat Pd(100) substrate crystals, is investigated using electron-capture spectroscopy (ECS). Ferromagnetic order sets in at a surface Curie temperature TCs=613.1 K. At room temperature, the long-ranged electron-spin polarization (ESP) amounts to 34% and is oriented in-plane for well-annealed films. Near TCs, the ESP follows the power law (TCs−T)β, with a critical exponent β=0.125±0.01 evaluated near TCs. This result is in good agreement with the exact value β=1/8 of the two-dimensional Ising model with short-ranged forces. For temperatures far from TCs, the ESP follows precisely the temperature dependence of the magnetization as predicted by Yang’s exact solution of the two-dimensional Ising model including long-ranged forces.

Theory of spin-polarized electron-capture spectroscopy in ferromagnetic nickel.

A detailed time-dependent many-body theory is developed for the study of spin-polarized electron-capture spectroscopy. The head-on collisions of ${\mathrm{H}}^{+}$, ${\mathrm{D}}^{+}$, and ${\mathrm{He}}^{++}$ ions with a nickel atom are chosen as models. Ionic trajectories are calculated classically taking fully into account the distance-dependent repulsive potential of the nickel 3d electrons. For the electronic part of the Hamiltonian the most general on-site interaction terms allowed by atomic symmetry are used. The total electronic many-body states are classified by group-theoretical methods with respect to the orbital and spin ``good'' quantum numbers, L, ${\mathit{L}}_{\mathit{z}}$, and ${\mathit{S}}_{\mathit{z}}$; the latter two are conserved during the collision process. The nickel configurations 3${\mathit{d}}^{9}$, 3${\mathit{d}}^{8}$, and 3${\mathit{d}}^{7}$ are taken into account. They correspond to the treatment of elastic scattering, one-electron capture, and two-electron capture on the same footing. The time-dependent Schr\"odinger equation for this system is solved exactly. Experimentally accessible quantities such as the occupation numbers of all the states as well as the zero-, one-, and two-electron-capture probabilities are monitored along the trajectories of the scattering species on the femtosecond time scale. Probabilities of 21% and 0.35% for one- and two-electron capture, respectively are found, in good agreement with experiments on surfaces. Similarly, a spin polarization between -60% and -100% is calculated. It turns out that this predominant capture of minority electrons is a consequence of angular-momentum conservation and is strongly enhanced by electron correlations. The result implies that the probing of magnetism by electron capture occurs on a significantly longer time scale than the probing of single-electron properties.

Non-perturbative theory of spin-polarized electron-capture spectroscopy in ferromagnetic nickel

With the purpose of understanding the interaction of nuclear projectiles with ferromagnetic metallic surfaces, Schrödinger's equation is solved along the classical trajectory for head-on collisions of H + ions with a Ni atom on the femtosecond time scale. Many-body effects are treated exactly within single configurations. Probabilities of (21%) and (0.35%) for one-and two-electron capture and a spin polarization of (−82%) are found, in good agreement with experiment. The predominant capture of minority electrons, caused by angular-momentum conservation, is strongly enhanced by electron correlation. Electron capture probes magnetism as a phenomenon of correlated electrons on a significantly longer time scale than single-electron properties such as charge transfer.