Science.gov

Sample records for impact single ionization

  1. Single and double ionization of magnesium by electron impact: A classical study

    NASA Astrophysics Data System (ADS)

    Dubois, J.; Berman, S. A.; Chandre, C.; Uzer, T.

    2017-02-01

    We consider electron impact-driven single and double ionization of magnesium in the energy range of 10 to 100 eV. Our classical Hamiltonian model of these (e ,2 e ) and (e ,3 e ) processes sheds light on their total cross sections and reveals the underlying ionization mechanisms. Two pathways are at play in single ionization: delayed and direct. In contrast, only the direct process is observed in double ionization, ruling out the excitation-autoionization channel. We also provide evidence that the so-called Two-Step 2 mechanism predominates over the Two-Step 1 mechanism, in agreement with experiments.

  2. Electron Impact Ionization Cross Sections and Rate Coefficients for Single Carbon Freon Molecules

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra; Kumar, Neeraj

    2015-09-01

    Single carbon Freon molecules or chlorofluorocarbons (CFCs) are important industrial material with wide-ranging applications as refrigerant, aerosol propellant and semiconductor etchant, etc. The large-scale industrial consumption is of particular environmental concern because of its potential for ozone destruction in the stratosphere. In the present work, we have extended and generalized the modified Jain-Khare (JK) semi-empirical formalism for the evaluation of the total ionization cross sections corresponding to the formation of the cations in the electron impact ionization of molecules to the electron impact ionization of single carbon freon molecules, viz. CFCl3, CF2Cl2 and CF3Cl. The integral partial and the total ionization cross sections as function of incident electron energy are evaluated in the energy range varying from ionization threshold to 1000 eV. In absence of available differential cross sections, the corresponding derived partial and total ionization cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. In addition to the differential and integral ionization cross sections, we have also calculated the ionization rate coefficients using the evaluated partial ionization cross sections and the Maxwell-Boltzmann distribution as a function of electron temperature/energy. The work is supported by DST, New Delhi, India.

  3. Single ionization and capture cross sections from biological molecules by bare projectile impact*

    NASA Astrophysics Data System (ADS)

    Quinto, Michele A.; Monti, Juan M.; Montenegro, Pablo D.; Fojón, Omar A.; Champion, Christophe; Rivarola, Roberto D.

    2017-02-01

    We report calculations on single differential and total cross sections for single ionization and single electron capture from biological targets, namely, vapor water and DNA nucleobasese molecules, by bare projectile impact: H+, He2+, and C6+. They are performed within the Continuum Distorted Wave - Eikonal Initial State approximation and compared to several existing experimental data. This study is oriented to the obtention of a reliable set of theoretical data to be used as input in a Monte Carlo code destined to micro- and nano- dosimetry.

  4. Two-effective-center approximation for proton-impact single ionization of hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim

    2015-10-01

    Some closed-form expressions are derived for the partial direct and indirect transition amplitudes for proton-impact single ionization of the hydrogen molecules using a first-order two-effective center continuum-wave approximation. The method satisfies the correct boundary conditions in the entrance channel. The basic assumption in this model is that when the active electron is ionized from one of the atomic centers in the molecule, the other scattering center is completely screened by the passive electron. Consequently, the transition amplitude can be expressed as a superposition of the partial ionization amplitudes from two independent scattering centers located at a constant distance from each other. The superposition of the partial amplitudes leads to different interference patterns for various orientations of the molecular target. The calculated cross sections are compared with the experiments and also with other theories. The comparison shows that the present results are reliable.

  5. STORAGE RING CROSS-SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 9+} AND SINGLE IONIZATION OF Fe{sup 10+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Wolf, A.; Lestinsky, M.; Repnow, R.; Mueller, A.; Schippers, S.; Spruck, K.

    2012-11-20

    We have measured electron impact ionization from the ground state of Fe{sup 9+} and Fe{sup 10+} over the relative electron-ion collision energy ranges 200-1900 eV and 250-1800 eV, respectively. The ions were confined in an ion storage ring long enough for essentially all metastable levels to radiatively relax to the ground state. For single ionization, we find a number of discrepancies between the existing theoretical cross sections and our results. The calculations appear to neglect some excitation-autoionization (EA) channels, particularly from n = 3 to n' excitations, which are important near threshold, and those from n = 2 {yields} 3 excitations, which contribute at about 650 eV. Conversely, at higher energies the calculations appear to overestimate the importance of EA channels due to excitation into levels where n {>=} 4. The resulting experimental rate coefficients agree with the most recent theory for Fe{sup 9+} to within 16% and for Fe{sup 10+} to within 19% at temperatures where these ions are predicted to form in collisional ionization equilibrium. We have also measured double ionization of Fe{sup 9+} forming Fe{sup 11+} in the energy range 450-3000 eV and found that although there is an appreciable cross section for direct double ionization, the dominant mechanism appears to be through direct ionization of an inner shell electron producing an excited state that subsequently stabilizes through autoionization.

  6. Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

    SciTech Connect

    Yan, S.; Zhang, P.; Xu, S.; Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Liu, H. P.

    2010-11-15

    The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

  7. Single and double ionization of helium by the impact of fast charged particles

    NASA Astrophysics Data System (ADS)

    Jones, S.; Madison, D. H.; Macek, Joseph H.

    2005-12-01

    A survey of the recent literature shows that paradoxes abound in electron- and ion-impact ionization of helium. For example, Schulz et al. [M. Schulz, R. Moshammer, D. Fischer, H. Kollmus, D.H. Madison, S. Jones, J. Ullrich, Nature 422 (2003) 48] found that first-Born and three-body distorted-wave (3DW) theories reproduced their data for single ionization of helium by very fast fully stripped carbon ions in the scattering plane, but not outside the scattering plane. For much slower impacting carbon ions, however, Madison et al. [D.H. Madison, D. Fischer, M. Foster, M. Schulz, R. Moshammer, S. Jones, J. Ullrich, Phys. Rev. Lett. 91 (2003) 253201] found good agreement between 3DW theory and experiment, even outside the scattering plane. This creates a dilemma, since distorted-wave perturbation theories are generally thought to improve with increasing, not decreasing, projectile speed! In this contribution, we will address these and other issues, and suggest possible ways of proceeding.

  8. Double-differential cross sections for single ionization of helium by bare ion impact

    NASA Astrophysics Data System (ADS)

    Jana, S.; Samanta, R.; Purkait, M.

    2013-11-01

    Double-differential cross sections (DDCS) for single ionization of helium by impact of proton and highly charged carbon ion have been calculated in the framework of four-body formalism using the three-Coulomb wave model (3C-4B) and first Born approximation (FBA-4B), respectively. The correlated motion of the particles interacting through long-range Coulomb potential is properly taken into account in the final state. In this paper, the energy and angular distributions of DDCS of low- and high-energy electron emission for ground-state helium atoms have been investigated. The ejected electrons are affected by the two-center field of the target and the projectile ion. The two-center effects are confined to comparison with other theoretical results. The results obtained, both from the 3C-4B and FBA-4B models, are compared with other theoretical and experimental findings. The present results are found to reproduce the peak structure of the experimental observations. Large discrepancy occurs between the present two theories at forward and backward angles except about the emission angle 90°. The present computed results obtained by the 3C-4B model are in good agreement with the available experimental findings.

  9. Electron impact ionization of liquid and gaseous water: a single-center partial-wave approach.

    PubMed

    Champion, C

    2010-01-07

    In this work, we report a unified methodology to express the molecular wavefunctions of water in both vapor and liquid phases by means of a single-center approach. These latter are then used as input data in a theoretical treatment--previously published and successfully tested--for describing the water ionization process in the first Born approximation (Champion et al 2006 Phys. Rev. A 73 012717). The multi-differential and total cross sections also obtained are reported for the two thermodynamical phases investigated and compared to the rare existing experimental and theoretical data.

  10. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 13+} AND SINGLE IONIZATION OF Fe{sup 16+} AND Fe{sup 17+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Bernhardt, D.; Mueller, A.; Schippers, S.; Spruck, K.; Lestinsky, M.

    2013-04-10

    We report measurements of electron impact ionization for Fe{sup 13+}, Fe{sup 16+}, and Fe{sup 17+} over collision energies from below threshold to above 3000 eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state. For single ionization of Fe{sup 13+}, we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud and Raymond is more than 30% larger, while that of Dere is about 20% greater. Much of the discrepancy with Dere is due to the theory overestimating the contribution of excitation-autoionization via n = 2 excitations. Double ionization of Fe{sup 13+} is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe{sup 16+} and Fe{sup 17+} agree with theoretical calculations to within the experimental uncertainties.

  11. Effect of initial-state target polarization on the single ionization of helium by 1-keV electron impact

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Yan; Ma, Xiao-Yan; Li, Xia; Miao, Xiang-Yang; Jia, Xiang-Fu

    2012-07-01

    We report new results of triple differential cross sections for the single ionization of helium by 1-KeV electron impact at the ejection energy of 10 eV. Investigations have been made for both the perpendicular plane and the plane perpendicular to the momentum transfer geometries. The present calculation is based on the three-Coulomb wave function. Here we have also incorporated the effect of target polarization in the initial state. A comparison is made between the present calculation with the results of other theoretical methods and a recent experiment [Dürr M, Dimopoulou C, Najjari B, Dorn A, Bartschat K, Bray I, Fursa D V, Chen Z, Madison D H and Ullrich J 2008 Phys. Rev. A 77 032717]. At an impact energy of 1 KeV, the target polarization is found to induce a substantial change of the cross section for the ionization process. We observe that the effect of target polarization plays a dominant role in deciding the shape of triple differential cross sections.

  12. Differential cross sections for the single ionization of H2 by 75 keV proton impact

    NASA Astrophysics Data System (ADS)

    Igarashi, A.; Gulyás, L.

    2017-02-01

    We have calculated the double and triple differential cross sections for electron ejection with energy of 14.6 eV in single ionization of H2 by 75 keV proton impact. A molecular version of the continuum distorted wave-eikonal initial state approach is applied, where the interaction between the projectile and the residual molecular ion is considered more properly than in previous applications of the method. For triple differential cross sections, the present results are in better agreement with the experimental data than those of other descriptions when large momentum transfer values are considered. For double differential cross sections the experimental data are reproduced quite well for both coherent and incoherent proton beams.

  13. Double ionization of single oriented water molecules by electron impact: Second-order Born description

    SciTech Connect

    Dal Cappello, C.; Champion, C.; Kada, I.; Mansouri, A.

    2011-06-15

    The double ionization of isolated water molecules fixed in space is investigated within a theoretical approach based on the second-order Born approximation. Electron angular distributions have been studied for specific kinematical conditions. The three usual mechanisms, the shake-off and the two two-step mechanisms, have been identified. A significant contribution of the two-step mechanism is clearly visible for some particular kinematics.

  14. Single ionization of molecular iodine

    NASA Astrophysics Data System (ADS)

    Smith, Dale L.; Tagliamonti, Vincent; Dragan, James; Gibson, George N.

    2017-01-01

    We performed a study of the single ionization of iodine, I2 over a range of wavelengths. Single ionization of I2 is unexpectedly found to have a contribution from inner molecular orbitals involving the 5 s electrons. The I+I+ dissociation channel was recorded through velocity map imaging, and the kinetic-energy release of each channel was determined with two-dimensional fitting of the images. Most of the measured kinetic-energy data were inconsistent with ionization to the X , A , and B states of I2 + , implying ionization from deeper orbitals. A pump-probe Fourier transform technique was used to look for modulation at the X - and A -state vibrational frequencies to see if they were intermediate states in a two-step process. X - and A -state modulation was seen only for kinetic-energy releases below 0.2 eV, consistent with dissociation through the B state. From these results and intensity-, polarization-, and wavelength-dependent experiments we found no evidence of bond softening, electron rescattering, or photon mediation through the X or A states to higher-energy single-ionization channels.

  15. Double ionization of helium by particle impact

    NASA Technical Reports Server (NTRS)

    Jacobsen, Finn M.

    1990-01-01

    Experimental results are reviewed of the ratio, R sq., of double to single ionization of He by proton, antiproton, electron and positron impact in the energy range from 0.15 to about 10 MeV/amu. At high velocities (greater than 1 to 2 MeV/amu) values of R sq. caused by electron impact merge with those for the proton with the antiproton, electron values being up to a factor of 2 greater than that for the p, positron. At these velocities the single ionization cross sections caused by impact of any of these four particles are indistinguishable.

  16. Doubly differential cross sections and longitudinal momentum distributions in the single ionization of Ne by fast ion impact

    NASA Astrophysics Data System (ADS)

    McSherry, D. M.; O'Rourke, S. F. C.; Crothers, D. S. F.

    2000-10-01

    There are very few experimental data sets for doubly differential cross sections (DDCS) for targets heavier than helium due to the difficulties in collecting data with conventional spectrometers. However with the recent developments in efficient spectrometers combined with recoil momentum spectroscopy, experimental results for the single ionization of Ne by 3.6MeV/u Au^53+ impact were obtained[1]. At the conference we consider these results in the context of our theoretical results achieved using continuum-distorted-wave quantum mechanical models, in particular the CDW-EIS approximation, which has had much success in the non-perturbative regime[2]. Doubly differential cross sections for helium shall also be considered in comparision to Ne and longitudinal electron and recoil ion momentum distributions will be examined. [1]. R. Moshammer, P.D. Fainstein, M.Schulz, W.Schmitt, H.Kollmus, R.Mann, S.Hagmann and J.Ullrich, Phys. Rev. Lett. 83 (1999) 4721. [2]. S.F.C. O'Rourke, I.Shimamura and D.S.F. Crothers, Proc. R. Soc. Lond. A 452 (1996) 175.

  17. A mobile mass spectrometer for comprehensive on-line analysis of trace and bulk components of complex gas mixtures: parallel application of the laser-based ionization methods VUV single-photon ionization, resonant multiphoton ionization, and laser-induced electron impact ionization.

    PubMed

    Mühlberger, F; Zimmermann, R; Kettrup, A

    2001-08-01

    A newly developed compact and mobile time-of-flight mass spectrometer (TOFMS) for on-line analysis and monitoring of complex gas mixtures is presented. The instrument is designed for a (quasi-)simultaneous application of three ionization techniques that exhibit different ionization selectivities. The highly selective resonance-enhanced multiphoton ionization (REMPI) technique, using 266-nm UV laser pulses, is applied for selective and fragmentationless ionization of aromatic compounds at trace levels (parts-per-billion volume range). Mass spectra obtained using this technique show the chemical signature solely of monocyclic (benzene, phenols, etc.) and polycyclic (naphthalene, phenathrene, indol, etc.) aromatic species. Furthermore, the less selective but still fragmentationless single photon ionization (SPI) technique with 118-nm VUV laser pulses allows the ionization of compounds with an ionization potential below 10.5 eV. Mass spectra obtained using this technique show the profile of most organic compounds (aliphatic and aromatic species, like nonane, acetaldehyde, or pyrrol) and some inorganic compounds (e.g., ammonia, nitrogen monoxide). Finally, the nonselective ionization technique laser-induced electron-impact ionization (LEI) is applied. However, the sensitivity of the LEI technique is adjusted to be fairly low. Thus, the LEI signal in the mass spectra gives information on the inorganic bulk constituents of the sample (i.e., compounds such as water, oxygen, nitrogen, and carbon dioxide). Because the three ionization methods (REMPI, SPI, LEI) exhibit largely different ionization selectivities, the isolated application of each method alone solely provides specific mass spectrometric information about the sample composition. Special techniques have been developed and applied which allow the quasi-parallel use of all three ionization techniques for on-line monitoring purposes. Thus, a comprehensive characterization of complex samples is feasible jointly using

  18. Following electron impact excitation of single (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

    L shell and Li subshells ionization cross sections[σL and σLi i = 1, 2, 3 following electron impact on (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) atoms calculated. By using Lotz' equation for non-relativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 21≤Z≤28 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i =1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL, Li subshells σLi studies for single atoms.

  19. Following electron impact excitation of single (N, O, F, Ne, Na, Mg, Al, Si) atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

    L shell and L subshells ionization cross sections σL and σLi (i = 1, 2, 3) following electron impact on (N,O, F, Ne, Na, Mg, Al, Si) atoms calculated. By using Lotz' equation for nonrelativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 7≤Z≤14 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i=1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL and subshells σLi studies for single atoms.

  20. Multiple-ionization of xenon atoms by positron impact

    NASA Technical Reports Server (NTRS)

    Kruse, Georg; Quermann, Andreas; Raith, Wilhelm; Sinapius, Guenther

    1990-01-01

    Previously the cross sections were measured for positronium formation and single ionization by positron impact for He and H2. With the same apparatus, slightly modified, the single and multiple ionization of xenon is now investigated. The principle of the method is the detection of ion and positron in time correlation which allows the discrimination of positronium formation (whereby the positron vanishes) and the destinction of single, double and triple impact ionization (which lead to different ion flight times from the gas target to the ion detector). By using secondary electrons from the positron moderator, similar measurements were performed on electron impact ionization. By comparing with literature values for electron multiple ionization cross sections, the detection-probability ratios were determined for the differently charged ions.

  1. Following electron impact excitations of single Os, Pt, Hg, Pb and Po atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, M.; Aydeniz, D.

    2016-03-01

    L shell ionization cross section and Li subshells ionization cross sections of Os, Pt, Hg, Pb, Po atoms calculated. For each atom, ten different electron impacty energy values Eoi used. Calculations carried out by using nonrelativistic Lotz equation in Matlab. Ionization cross section values obtained for Eoi values in the energy range of ELi ≤Eoi≤4ELi for each atom. Starting allmost from Eoi = ELi (i = 1,2,3) values of the each subshell ionization threshold energy, ionization cross section are increasing rapidly with Eoi. For a fixed Eoi = 3. ELi values, while Z increases from Z = 76 to Z = 84, ionization cross section are decrease. These results help to understand some results which obtained from other electron-sigle atom impact studies on σLi subshells.

  2. Electron-impact ionization of W25+

    NASA Astrophysics Data System (ADS)

    Kynienė, A.; Pakalka, S.; Masys, Š.; Jonauskas, V.

    2016-09-01

    Electron-impact ionization cross sections for the ground level of the W25+ ion have been investigated by performing level-to-level calculations and using the Dirac-Fock-Slater method in the single-configuration approach. The main attention has been focused on the influence of the increasing principal and orbital quantum numbers on the excitation-autoionization (EA) process and its contribution to the total ionization cross sections. The obtained results demonstrate that excitations to the high-nl shells (n≥slant 9) increase cross sections of the indirect ionization process by about 60% compared to the excitations to the lower shells (n≤slant 8). It was established that excitations to the shells with the orbital quantum number l = 4 give the greatest contribution to EA. Maxwellian rate coefficients derived from the cross sections for the ground state are compared with the previously obtained values from the configuration-average distorted-wave (CADW) approximation. The rate coefficients for direct ionization (DI) are smaller than the corresponding CADW values, while the EA rate coefficients are larger than the ones from the CADW calculations. The total DI+EA rate coefficients are about 20% larger than the CADW rate coefficients.

  3. Single differential electron impact ionization cross sections in the binary-encounter-Bethe approximation for the low binding energy regime

    NASA Astrophysics Data System (ADS)

    Guerra, M.; Amaro, P.; Machado, J.; Santos, J. P.

    2015-09-01

    An analytical expression based on the binary-encounter-Bethe model for energy differential cross sections in the low binding energy regime is presented. Both the binary-encounter-Bethe model and its modified counterpart are extended to shells with very low binding energy by removing the constraints in the interference term of the Mott cross section, originally introduced by Kim et al. The influence of the ionic factor is also studied for such targets. All the binary-encounter-Bethe based models presented here are checked against experimental results of low binding energy targets, such as the total ionization cross sections of alkali metals. The energy differential cross sections for H and He, at several incident energies, are also compared to available experimental and theoretical values.

  4. Charged-Particle Impact Ionization of Atoms

    SciTech Connect

    Bartschat, Klaus; Guan Xiaoxu

    2008-08-08

    We have developed a hybrid method to treat charged-particle impact ionization of complex atoms and ions. The essential idea is to describe the interaction between a fast projectile and the target perturbatively, up to second order, while the initial bound state and the ejected-electron--residual-ion interaction can be handled via a convergent R-matrix with pseudo-states (close-coupling) expansion. Example results for ionization of the heavy noble gases (Ne-Xe) by positron and electron impact are presented. The general scheme for a distorted-wave treatment of ionization by heavy-particle impact is described.

  5. Ionization of He, Ne, Ar, Kr, and Xe by proton impact: Single differential distributions in energy and angles

    NASA Astrophysics Data System (ADS)

    Miraglia, J. E.

    2009-02-01

    In this paper we report energy and angular distributions of electrons emitted in collisions of protons with neon-(F-,Ne0,Na+) , argon-(Cl-,Ar0,K+) , krypton-(Br-,Kr0,Rb+) , and xenon-(I-,Xe0) isoelectronic series for high and intermediate impact energies. Calculations were performed within the continuum distorted wave-eikonal initial-state method using an angular expansion in spherical harmonics and a numerical evaluation of the radial functions corresponding to both: the initial (bound) and the final (continuum) states in the same central potential. The first Born approximation was calculated on equal footing. The shellwise local plasma approximation was also calculated when possible. A complete and exhaustive comparison with the available experimental data is carried out. We have spanned almost all the published experiments in our range of interest. Successes and failures of the different theoretical methods are pointed out. Possible signatures of many-electron effects are noticed.

  6. Electron-Impact Ionization and Dissociative Ionization of Biomolecules

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Chaban, Galina M.; Dateo, Christopher E.

    2006-01-01

    It is well recognized that secondary electrons play an important role in radiation damage to humans. Particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. Our study of electron-impact ionization of DNA fragments uses the improved binary-encounter dipole model and covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3(sup prime)- and C5 (sup prime)-deoxyribose-phospate cross sections, differing by less than 5%. Investigation of tandem double lesion initiated by electron-impact dissociative ionization of guanine, followed by proton reaction with the cytosine in the Watson-Crick pair, is currently being studied to see if tandem double lesion can be initiated by electron impact. Up to now only OH-induced tandem double lesion has been studied.

  7. Following electron impact excitations of Rn, Ra, Th, U and Pu single atom L sub-shells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Ayinol, M.; Aydeniz, D.

    2016-03-01

    L shell ionization cross section and Li subshells ionization cross sections of Rn, Ra, Th, U, Pu atoms calculated. For each of atoms, ten different electron impact energy values (Eo) are used. Calculations carried out by using Lotz equation in Matlab. First, calculations done for non-relativistic case by using non-relativistic Lotz equation then repeated with relativistic Lotz equation. σL total and σLi(i = 1,2,3) subshells ionisation cross section values obtained for Eo values in the energy range of ELi ionization threshold energy, σL total and σLi (i = 1,2,3) are increasing rapidly with Eo. For a fixed Eo = 3.ELi), while Z increases from 86impact studies.

  8. Electron-Impact Ionization Cross Section Database

    National Institute of Standards and Technology Data Gateway

    SRD 107 Electron-Impact Ionization Cross Section Database (Web, free access)   This is a database primarily of total ionization cross sections of molecules by electron impact. The database also includes cross sections for a small number of atoms and energy distributions of ejected electrons for H, He, and H2. The cross sections were calculated using the Binary-Encounter-Bethe (BEB) model, which combines the Mott cross section with the high-incident energy behavior of the Bethe cross section. Selected experimental data are included.

  9. Electron impact ionization-excitation of Helium

    NASA Astrophysics Data System (ADS)

    Ancarani, Lorenzo Ugo; Gomez, A. I.; Gasaneo, G.; Mitnik, D. M.; Ambrosio, M. J.

    2016-09-01

    We calculate triple differential cross sections (TDCS) for the process of ionization-excitation of Helium by fast electron impact in which the residual ion is left in the n =2 excited state. We chose the strongly asymmetric kinematics used in the experiment performed by Dupré et al.. In a perturbative scheme, for high projectile energies the four-body problem reduces to a three-body one and, within that framework, we solve the time- independent Schrödinger equation with a Sturmian approach. The method, based on Generalized Sturmian Functions (GSF), is employed to obtain the initial ground state of Helium, the single-continuum state and the scattering wave function; for each of them, the GSF basis is constructed with the corresponding adequate asymptotic conditions. Besides, the method presents the following advantage: the scattering amplitudes can be extracted directly in the asymptotic region of the scattering solution, and thus the TDCS can be obtained without requiring a matrix element evaluation.

  10. Influence of renormalization shielding on the electron-impact ionization process in dense partially ionized plasmas

    SciTech Connect

    Song, Mi-Young; Yoon, Jung-Sik; Jung, Young-Dae

    2015-04-15

    The renormalization shielding effects on the electron-impact ionization of hydrogen atom are investigated in dense partially ionized plasmas. The effective projectile-target interaction Hamiltonian and the semiclassical trajectory method are employed to obtain the transition amplitude as well as the ionization probability as functions of the impact parameter, the collision energy, and the renormalization parameter. It is found that the renormalization shielding effect suppresses the transition amplitude for the electron-impact ionization process in dense partially ionized plasmas. It is also found that the renormalization effect suppresses the differential ionization cross section in the peak impact parameter region. In addition, it is found that the influence of renormalization shielding on the ionization cross section decreases with an increase of the relative collision energy. The variations of the renormalization shielding effects on the electron-impact ionization cross section are also discussed.

  11. Evidence for impact ionization in vanadium dioxide

    SciTech Connect

    Holleman, Joshua; Bishop, Michael M.; Garcia, Carlos; Vellore Winfred, J. S. R.; Lee, Shinbuhm; Lee, Ho Nyung; Beekman, Christianne; Manousakis, Efstratios; McGill, Stephen A.

    2016-10-17

    Pump-probe optical spectroscopy was used to investigate charge carrier multiplication via impact ionization in the M1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed an enhancement of the ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple timescales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that impact ionization acts efficiently as a carrier multiplication process in this prototypical strongly-correlated insulator.

  12. Evidence for impact ionization in vanadium dioxide

    DOE PAGES

    Holleman, Joshua; Bishop, Michael M.; Garcia, Carlos; ...

    2016-10-17

    Pump-probe optical spectroscopy was used to investigate charge carrier multiplication via impact ionization in the M1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed an enhancement of the ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple timescales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that impact ionization acts efficiently as a carrier multiplicationmore » process in this prototypical strongly-correlated insulator.« less

  13. Electron-impact double ionization of magnesium

    SciTech Connect

    Ford, M.J.; El-Marji, B.; Doering, J.P.; Moore, J.H.; Coplan, M.A.; Cooper, J.W.

    1998-01-01

    Electron-impact double-ionization cross sections differential in the angles of the two ejected electrons have been measured at impact energies of 422 and 1052 eV. The energies of the ejected electrons were fixed at 100 eV each. The cross sections are very different at the two incident energies. At 1052 eV the ejected electrons are preferentially found in the forward direction with respect to the incident beam. At 422 eV they are found in the forward and backward directions with approximately equal probability. The 422-eV cross sections are largest when the incident-electron and ejected-electron momentum vectors lie in a common plane. The observations are discussed in the context of several models for double ionization. {copyright} {ital 1998} {ital The American Physical Society}

  14. Dissociative Ionization of Benzene by Electron Impact

    NASA Technical Reports Server (NTRS)

    Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

  15. Electron Impact Ionization of C_2F_6

    NASA Astrophysics Data System (ADS)

    Iga, Ione; Pereira Sanches, Ivana; Srivastava, Santosh Kumar

    2001-10-01

    Besides CF_4, perfluoroethane, C_2F_6, is also one of the fluorocarbon compounds most frequently used in plasma processing applications. Consequently, the knowledge of the ionization properties of C_2F6 is clearly of interest in order to model the plasma-chemical reactions. Nevertheless, only few partial ionization-cross-section measurements [1,2] for this molecule were reported in the literature. Also, the energy range covered in these studies was very limited (below 120 eV). Recently, we have studied these properties. More specifically, partial ionization cross sections (PICS) for the fragments: C^+, F^+, CF^+, CF_2^+, CF_3^+ and C_2F_5^+, produced by electron impact on C_2F_6, were measured in a single-collision condition from near ionization threshold to 1000 eV. In addition, total ionization cross sections (TICS) are also obtained by summing up the PICS's. The comparison of our measured PICS and derived TICS with available data [1-4] will be presented during the Conference. [1] H. U. Poll, J. Meischner, Contrib. Plasma Phys. 27 (1987) 359. [2] C. Q. Jiao, A Garscadden, P. D. Haaland, Chem. Phys. Lett. 310 (1999) 52. [3] H. Nishimura, W. M. Huo, M. A Ali and Y -K. Kim, J. Chem. Phys. 110 (1999) 3811. [4] L. G. Christophorou and J. K. Olthoff, J. Phys. Chem. Ref. Data 27 (1998) 1 and references therein.

  16. Electron-impact dissociation and ionization of NO+ ions

    NASA Astrophysics Data System (ADS)

    Belic, D. S.; Urbain, X.; Cherkani-Hassani, H.; Defrance, P.

    2016-07-01

    Absolute cross sections for electron-impact ionization and dissociation of NO+ ions are reported. Simple ionization to NO2+ ion and production of singly charged N+ and O+ and doubly charged N2+ and O2+ fragments have been investigated. The animated electron-ion crossed-beam method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum of the simple ionization cross section is found to be (3.49 ± 0.07) × 10-17 cm2 at 135 eV. The total cross sections for N+ and O+ fragments at the maximum are found to be (13.9 ± 1.0) × 10-17 cm2 and (14.0 ± 1.4) × 10-17 cm2, respectively, both at an energy of 85 eV. By performing careful magnetic field scans of the detected signal, contributions of dissociative excitation and dissociative ionization to N+ and O+ production are determined separately. The cross sections for asymmetric dissociative ionization to N2+ and O2+ are found to be over one order of magnitude smaller. Distributions of the kinetic energy release to the fragments are determined for all dissociation processes.

  17. Electron-impact Ionization Of Li2 And Li+2

    SciTech Connect

    Colgan, James P

    2008-01-01

    Electron-impact ionization cross sections for Li{sub 2} and Li{sup +}{sub 2} are calculated using a configuration-average distorted-wave method. Bound orbitals for the molecule and its ions are calculated using a single configuration self-consistent field method based on a linear combination of Slater-type orbitals. The bound orbitals are transformed onto a two-dimensional lattice ({tau}, {theta}), which is variable in the radial coordinate and constant in the angular coordinate, from which Hartree with local exchange potentials are constructed. The single particle Schrodinger equation is then solved for continuum distorted-waves with S-matrix boundary conditions. Total ionization cross sections for Li{sub 2} at an equilibrium internuclear separation of R = 5.0 and for Li{sup +}{sub 2} at an equilibrium internuclear separation of R = 5.9 are presented.

  18. Cross sections for short pulse single and double ionization ofhelium

    SciTech Connect

    Palacios, Alicia; Rescigno, Thomas N.; McCurdy, C. William

    2007-11-27

    In a previous publication, procedures were proposed for unambiguously extracting amplitudes for single and double ionization from a time-dependent wavepacket by effectively propagating for an infinite time following a radiation pulse. Here we demonstrate the accuracy and utility of those methods for describing two-photon single and one-photon double ionization of helium. In particular it is shown how narrow features corresponding to autoionizing states are easily resolved with these methods.

  19. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT IONIZATION OF Fe{sup 12+} FORMING Fe{sup 13+} AND Fe{sup 14+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Lestinsky, M.; Mueller, A.; Schippers, S.

    2011-07-10

    We report electron impact ionization cross section measurements for electron impact single ionization of Fe{sup 12+} forming Fe{sup 13+} and electron impact double ionization of Fe{sup 12+} forming Fe{sup 14+}. These are the first electron impact ionization data for any Si-like ion uncontaminated by an unknown metastable fraction. Recent distorted wave calculations agree with our single ionization results to within {approx}15%. Double ionization is dominated by inner shell ionization of a 2l electron resulting in autoionization of a second electron as the inner shell hole is filled.

  20. Double and single ionization of He and H{sub 2} by slow protons and antiprotons

    SciTech Connect

    Kimura, Mineo |; Shimamura, Isao; Inokuti, Mitio

    1994-12-31

    Double and single ionization of He and H{sub 2} by proton (p) and antiproton ({bar p})impact in the energy region below 50 keV was studied theoretically by using the semiclassical molecular picture. As the energy decreased, the ratio of the double- to the single-ionization cross section increased for impact and decreased for p impact for both He and H{sub 2}. These trends are consistent with recent measurements for He. Ionization mechanisms differ distinctly for p impact and {bar p} impact. For p impact, the dominant mechanism for double ionization at the lower energies is sequential ladder climbing by the two electrons through various excited channels and finally into the continuum. For {bar p} impact, in contrast, the approaching negative charge distorts both the He and H{sub 2} electron clouds toward the other side of the nucleus and decreases the electron binding energies. These effects enhance electron-electron interactions, increasing double ionization. For the H{sub 2}, an effect of molecular orientation is an additional complication in determining the dynamics.

  1. Electron Impact Ionization of the Rare Gases

    NASA Astrophysics Data System (ADS)

    Lohmann, Birgit

    2008-10-01

    Detailed information about the electron impact ionization process can be obtained from fully differential cross section measurements, in which the ionized electron is detected in coincidence with the outgoing scattered projectile electron. Incident and outgoing electron momenta are completely determined in these measurements. A considerable body of experimental and theoretical data exists for H and He targets, and the level of agreement between theory and experiment for these simple atoms is exceptional. However, there are still significant discrepancies between theory and experiment in the case of ionization of more complex atomic targets such as the heavier rare gas atoms. In this talk I will present recent measurements and theoretical predictions of fully differential cross sections for ionization of a range of rare gas targets: He, Ne, Ar and Xe. The talk will concentrate primarily on experiments which have been performed by two experimental groups, our group in Australia [1-3] and that of Lahmam-Bennani [3-5] in France. The experimental conditions span two different kinematic regimes, one with intermediate incident electron energy and low ejected electron energy, and the other with higher incident electron energy, and ejected electron energies which correspond to large energy transfer in the collision process. All experiments have been performed in a coplanar asymmetric configuration in which the scattered electron is detected at a small forward scattering angle. The experimental apparatus used in Australia is of quite different design to that in France, and I will present the results of an experiment in which the two groups have collaborated to produce data under identical kinematic conditions and for the same targets, using these two very different experimental approaches. This comprehensive set of experimental data has provided an interesting challenge to theory, and I will discuss the state of play with regard to the alignment between curent state

  2. Ionization of glycerin molecule by electron impact

    NASA Astrophysics Data System (ADS)

    Zavilopulo, A. N.; Shpenik, O. B.; Markush, P. P.; Kontrosh, E. E.

    2015-07-01

    The methods and results of studying the yield of positive ions produced due to direct and dissociative electron impact ionization of the glycerin molecule are described. The experiment is carried out using two independent setups, namely, a setup with a monopole mass spectrometer employing the method of crossing electron and molecular beams and a setup with a hypocycloidal electron spectrometer with the gas-filled cell. The mass spectra of the glycerin molecule are studied in the range of mass numbers of 10-95 amu at various temperatures. The energy dependences of the effective cross sections of the glycerin molecular ions produced by a monoenergetic electron beam are obtained and analyzed; using these dependences, the appearance energies of fragment ions are determined. The dynamics of the glycerin molecule fragment ions formation is investigated in the temperature range of 300-340 K.

  3. Electron impact ionization and multiphoton ionization of doped superfluid helium droplets: A comparison.

    PubMed

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-02-28

    We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters.

  4. Electron impact ionization and multiphoton ionization of doped superfluid helium droplets: A comparison

    PubMed Central

    2016-01-01

    We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters. PMID:26931697

  5. Doubly Differential Multiple Ionization of Neon by Electron Impact*

    NASA Astrophysics Data System (ADS)

    Santos, A. C. F.; Dubois, R. D.; Hasan, A.

    2003-05-01

    Absolute doubly differential cross sections for single, double and triple ionization of Ne atoms have been measured for 750 eV electron impact as a function of projectile energy loss and scattering angle. Angular distributions between 0 and +/- 12 degrees were obtained for energy losses between 0 and 600 eV. In this energy-loss range only L shell electrons are available for target ionization. The data were normalized to total ionization cross sections available in the literature. A comparison is made with photoionization data as well as with argon data taken using similar methods in order to study the role played by the static target potential. 1- R. D. DuBois, C. Doudna, C. Lloyd, M. Kahveci, Kh Khayyat, Y. Zhou, and D. H. Madison, J. Phys. B 34 (2001) L783-L789. 2- R. D. DuBois, Kh Khayyat, C. Doudna, C. Lloyd, NIM B 192 (2002) 63-66. 3- A. C. F. Santos, A. Hasan, T. Yates, R. D. DuBois, submitted to Phys. Rev. A (2003).

  6. A Miniaturized Linear Wire Ion Trap with Electron Ionization and Single Photon Ionization Sources

    NASA Astrophysics Data System (ADS)

    Wu, Qinghao; Tian, Yuan; Li, Ailin; Andrews, Derek; Hawkins, Aaron R.; Austin, Daniel E.

    2017-01-01

    A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline.

  7. Electron impact ionization of the gas-phase sorbitol

    NASA Astrophysics Data System (ADS)

    Chernyshova, Irina; Markush, Pavlo; Zavilopulo, Anatoly; Shpenik, Otto

    2015-03-01

    Ionization and dissociative ionization of the sorbitol molecule by electron impact have been studied using two different experimental methods. In the mass range of m/ z = 10-190, the mass spectra of sorbitol were recorded at the ionizing electron energies of 70 and 30 eV. The ion yield curves for the fragment ions have been analyzed and the appearance energies of these ions have been determined. The relative total ionization cross section of the sorbitol molecule was measured using monoenergetic electron beam. Possible fragmentation pathways for the sorbitol molecule were proposed.

  8. Electron impact ionization of tungsten ions in a statistical model

    NASA Astrophysics Data System (ADS)

    Demura, A. V.; Kadomtsev, M. B.; Lisitsa, V. S.; Shurygin, V. A.

    2015-01-01

    The statistical model for calculations of the electron impact ionization cross sections of multielectron ions is developed for the first time. The model is based on the idea of collective excitations of atomic electrons with the local plasma frequency, while the Thomas-Fermi model is used for atomic electrons density distribution. The electron impact ionization cross sections and related ionization rates of tungsten ions from W+ up to W63+ are calculated and then compared with the vast collection of modern experimental and modeling results. The reasonable correspondence between experimental and theoretical data demonstrates the universal nature of statistical approach to the description of atomic processes in multielectron systems.

  9. Electron Impact Ionization and Dissociative Ionization of C2H2

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.

    1995-01-01

    By utilizing a crossed electron beam collision geometry, a combination of time-of-flight (TOF) and quadrupole mass spectrometers, and the relative flow technique1 normalized values of cross sections and appearance energies (AP) were obtained for the formation of singly and multiply ionized species resulting from the ionization and dissociation of C2H2. Details ont he apparatus and technique have been published previously.2,3.

  10. An atomic model for neutral and singly ionized uranium

    NASA Technical Reports Server (NTRS)

    Maceda, E. L.; Miley, G. H.

    1979-01-01

    A model for the atomic levels above ground state in neutral, U(0), and singly ionized, U(+), uranium is described based on identified atomic transitions. Some 168 states in U(0) and 95 in U(+) are found. A total of 1581 atomic transitions are used to complete this process. Also discussed are the atomic inverse lifetimes and line widths for the radiative transitions as well as the electron collisional cross sections.

  11. Development of a Portable Single Photon Ionization-Photoelectron Ionization Time-of-Flight Mass Spectrometer

    PubMed Central

    Huang, Yunguang; Li, Jinxu; Tang, Bin; Zhu, Liping; Hou, Keyong; Li, Haiyang

    2015-01-01

    A vacuum ultraviolet lamp based single photon ionization- (SPI-) photoelectron ionization (PEI) portable reflecting time-of-flight mass spectrometer (TOFMS) was designed for online monitoring gas samples. It has a dual mode ionization source: SPI for analyte with ionization energy (IE) below 10.6 eV and PEI for IE higher than 10.6 eV. Two kinds of sampling inlets, a capillary inlet and a membrane inlet, are utilized for high concentration and trace volatile organic compounds, respectively. A mass resolution of 1100 at m/z 64 has been obtained with a total size of 40 × 31 × 29 cm, the weight is 27 kg, and the power consumption is only 70 W. A mixture of benzene, toluene, and xylene (BTX), SO2, and discharging products of SF6 were used to test its performance, and the result showed that the limit of quantitation for BTX is as low as 5 ppbv (S/N = 10 : 1) with linear dynamic ranges greater than four orders of magnitude. The portable TOFMS was also evaluated by analyzing volatile organic compounds from wine and decomposition products of SF6 inside of a gas-insulated switchgear. PMID:26587023

  12. Electron-impact ionization of ozone

    NASA Astrophysics Data System (ADS)

    Newson, Karl A.; Luc, Stephanie M.; Price, Stephen D.; Mason, Nigel J.

    1995-10-01

    Partial electron ionization cross-sections of ozone for incident electron energies from 40 to 500 eV have been determined using time-of-flight mass spectrometry. The cross-sections are derived by identifying the contribution of ozone to the ion signals recorded following ionization of a mixture of O2 and O3. Only one previous determination of these cross-sections, for energies up to 100 eV, is available in the literature. The cross-sections derived in the present study at these lower electron energies are in good agreement with the previous determination.

  13. Dissociative Ionization of Pyridine by Electron Impact

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher; Huo, Winifred; Kwak, Dochan (Technical Monitor)

    2002-01-01

    In order to understand the damage of biomolecules by electrons, a process important in radiation damage, we undertake a study of the dissociative ionization (DI) of pyridine (C5H5N) from the low-lying ionization channels. The methodology used is the same as in the benzene study. While no experimental DI data are available, we compare the dissociation products from our calculations with the dissociative photoionization measurements of Tixier et al. using dipole (e, e(+) ion) coincidence spectroscopy. Comparisons with the DI of benzene is also made so as to understand the difference in DI between a heterocyclic and an aromatic molecule.

  14. Electron impact ionization at relativistic energies

    NASA Astrophysics Data System (ADS)

    Belkacem, Ali; Cole, Kyra; Hertlein, Marcus; Feinberg, Benedict; Schriel, Ralf; Adaniya, Hidehito; Neumann, Nadine

    2004-05-01

    We used an ion time-of-flight set up based on a pulsed high-voltage extraction technique to study the charge state distribution of He, Ne, Ar, Kr and Xe atoms after impact of 0.2 to 1.5 GeV electrons. The relativistic electron beam is produced at the booster beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The yield of ions drops drastically with the charge state number. Our measurements show that the ratio of doubly-charge to singly-charged ions reaches an asymptotic limit of 0.0028 for He already at electron energies below 40 MeV. However we observe a very pronounced energy dependence of the ratio of the doubly-charged to singly-charged ions for the heavier atoms such as Kr and Xe in the 0.2 - 1.5 GeV energy range. This energy dependence takes place way above the energy at which theories based on the equivalent photon method or the born- approximation predict the asymptotic limit to be reached. This may be an indication of new physics coming into play in the photoionization process due to relativistic effects.

  15. Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

    NASA Technical Reports Server (NTRS)

    Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

    1993-01-01

    Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

  16. Detection of single atoms by resonance ionization spectroscopy

    SciTech Connect

    Hurst, G.S.

    1986-01-01

    Rutherford's idea for counting individual atoms can, in principle, be implemented for nearly any type of atom, whether stable or radioactive, by using methods of resonance ionization. With the RIS technique, a laser is tuned to a wavelength which will promote a valence electron in a Z-selected atom to an excited level. Additional resonance or nonresonance photoabsorption steps are used to achieve nearly 100% ionization efficiencies. Hence, the RIS process can be saturated for the Z-selected atoms; and since detectors are available for counting either single electrons or positive ions, one-atom detection is possible. Some examples are given of one-atom detection, including that of the noble gases, in order to show complementarity with AMS methods. For instance, the detection of /sup 81/Kr using RIS has interesting applications for solar neutrino research, ice-cap dating, and groundwater dating. 39 refs., 7 figs., 2 tabs.

  17. The ionization rate inversion of H? induced by the single and double UV photon(s)

    NASA Astrophysics Data System (ADS)

    He, Pei-Lun; He, Feng

    2013-11-01

    The ionization of H? in the strong UV laser pulse is studied by numerically solving the time-dependent Schrödinger equation. In analogy to Young's double-slit interference, the ionized electron originating from two nuclei will constructively, or destructively interfere, depending on the UV frequencies. The fluctuation of the ionization rate as a function of the laser frequency is observed. The destructive interference suppresses the single-photon ionization rate, so that the double-photon ionization rate can be larger than the single-photon ionization rate. When such an ionization-rate inversion happens, the electron momentum spectra splits into several peaks.

  18. Impact-Ionization Cooling in Laser-Induced Plasma Filaments

    SciTech Connect

    Filin, A.; Romanov, D. A.; Compton, R.; Levis, R. J.

    2009-04-17

    The ionization rates and subsequent electron dynamics for laser-induced plasma channels are measured for the noble gas series He, Ne, Ar, Kr, and Xe at 1.0 atm. The cw fluorescence emission increases superlinearly in the series from He to Xe in agreement with Ammosov-Delone-Krainov tunnel ionization calculations. The electron temperature after laser-induced plasma formation, measured by four-wave mixing, evolves from >20 eV to <1 eV kinetic energies with time constants ranging from 1 ns for He to 100 ps for Xe in agreement with an impact-ionization cooling model.

  19. Calculation of electron-impact ionization of potassium

    NASA Astrophysics Data System (ADS)

    Bray, I.; Fursa, D. V.; Stelbovics, A. T.

    2009-11-01

    We calculate electron-impact ionization of potassium at a broad range of energies for the case where it is the valence electron that is ejected. The convergent close-coupling method is used to calculate the total and fully differential cross sections. The unusual shape of the total ionization spin asymmetries measured by Baum et al. [1] is explained. However, agreement with the fully differential cross section measurements of Murray [2] is somewhat mixed.

  20. Positron impact ionization of atomic hydrogen

    SciTech Connect

    Acacia, P.; Campeanu, R.I.; Horbatsch, M.

    1993-05-01

    We will present integrated cross sections for ionization of atomic hydrogen by positrons. These have been calculated in a distorted-wave approximation using energy-dependent effective charges in the final channel as well as static and polarization potentials in the initial channel. We present two models for calculating the energy-dependent effective charges both of which produce results in good agreement with the recent experimental measurements of Spicher et al. This is in contrast to previous distorted-wave calculations which used fixed effective charges as well as classical trajectory calculations. Both of these latter methods produced results which were substantially below ours and the experimental data.

  1. The level structure of singly-ionized actinium

    NASA Astrophysics Data System (ADS)

    Ürer, Güldem; Özdemir, Leyla

    2012-08-01

    We have presented a multiconfiguration Dirac-Fock (MCDF) study in the framework of Breit and quantum electrodynamic (QED) effects on the low-lying level structure of singly-ionized actinium (Ac II). The computations have been carried out for 16 even- and 40 odd-parity levels. Excitation energies and electric dipole transition parameters, such as wavelengths, oscillator strengths and transition probabilities (or rates), for these low-lying levels have been reported. Results obtained have been compared with other available works in the literature.

  2. Electron impact ionization of cycloalkanes, aldehydes, and ketones

    SciTech Connect

    Gupta, Dhanoj; Antony, Bobby

    2014-08-07

    The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

  3. Avalanche multiplication and impact ionization in amorphous selenium photoconductive target

    NASA Astrophysics Data System (ADS)

    Park, Wug-Dong; Tanioka, Kenkichi

    2014-03-01

    The avalanche multiplication factor and the hole ionization coefficient in the amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target depend on the electric field. The phenomenon of avalanche multiplication and impact ionization in the 0.4-µm-thick a-Se HARP target is investigated. The hot carrier energy in the 0.4-µm-thick a-Se HARP target increases linearly as the target voltage increases. The energy relaxation length of hot carriers in the a-Se photoconductor of the 0.4-µm-thick HARP target saturates as the electric field increases. The average energy Eav of a hot carrier and the energy relaxation length λE in the a-Se photoconductor of the 0.4-µm-thick HARP target at 1 × 108 V/m were 0.25 eV and 2.5 nm, respectively. In addition, the hole ionization coefficient β and the avalanche multiplication factor M are derived as a function of the electric field, the average energy of a hot carrier, and the impact ionization energy. The experimental hole ionization coefficient β and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

  4. Single ionization of water molecules in collisions with bare ions

    NASA Astrophysics Data System (ADS)

    Mondal, A.; Mandal, C. R.; Purkait, M.

    2016-04-01

    We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.

  5. Ionization detector, electrode configuration and single polarity charge detection method

    DOEpatents

    He, Zhong

    1998-01-01

    An ionization detector, an electrode configuration and a single polarity charge detection method each utilize a boundary electrode which symmetrically surrounds first and second central interlaced and symmetrical electrodes. All of the electrodes are held at a voltage potential of a first polarity type. The first central electrode is held at a higher potential than the second central or boundary electrodes. By forming the first and second central electrodes in a substantially interlaced and symmetrical pattern and forming the boundary electrode symmetrically about the first and second central electrodes, signals generated by charge carriers are substantially of equal strength with respect to both of the central electrodes. The only significant difference in measured signal strength occurs when the charge carriers move to within close proximity of the first central electrode and are received at the first central electrode. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge.

  6. Ionization detector, electrode configuration and single polarity charge detection method

    DOEpatents

    He, Z.

    1998-07-07

    An ionization detector, an electrode configuration and a single polarity charge detection method each utilize a boundary electrode which symmetrically surrounds first and second central interlaced and symmetrical electrodes. All of the electrodes are held at a voltage potential of a first polarity type. The first central electrode is held at a higher potential than the second central or boundary electrodes. By forming the first and second central electrodes in a substantially interlaced and symmetrical pattern and forming the boundary electrode symmetrically about the first and second central electrodes, signals generated by charge carriers are substantially of equal strength with respect to both of the central electrodes. The only significant difference in measured signal strength occurs when the charge carriers move to within close proximity of the first central electrode and are received at the first central electrode. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge. 10 figs.

  7. Depolarizing collisions with hydrogen: Neutral and singly ionized alkaline earths

    SciTech Connect

    Manso Sainz, Rafael; Ramos, Andrés Asensio; Bueno, Javier Trujillo; Aguado, Alfredo

    2014-06-20

    Depolarizing collisions are elastic or quasielastic collisions that equalize the populations and destroy the coherence between the magnetic sublevels of atomic levels. In astrophysical plasmas, the main depolarizing collider is neutral hydrogen. We consider depolarizing rates on the lowest levels of neutral and singly ionized alkali earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II, due to collisions with H°. We compute ab initio potential curves of the atom-H° system and solve the quantum mechanical dynamics. From the scattering amplitudes, we calculate the depolarizing rates for Maxwellian distributions of colliders at temperatures T ≤ 10,000 K. A comparative analysis of our results and previous calculations in the literature is completed. We discuss the effect of these rates on the formation of scattering polarization patterns of resonant lines of alkali earths in the solar atmosphere, and their effect on Hanle effect diagnostics of solar magnetic fields.

  8. Electron-Impact Dissociative Ionization Of Ethylene (Postprint)

    DTIC Science & Technology

    2006-02-01

    seen in Fig. 5 , where the discrepancy between em- pirical calculation and the experiment is more profound, FIG. 2 . Partial ionization cross section...not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YY) 2 . REPORT TYPE 3...ANSI Std. Z39-18 Electron-impact dissociative ionization of ethylene S. Popović,1,* S. Williams, 2 ,† and L. Vušković1,‡ 1Department of Physics, Old

  9. Storage Ring Measurements of Electron Impact Ionization for Solar Physics

    NASA Astrophysics Data System (ADS)

    Hahn, Michael; Becker, A.; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, D. W.

    2013-07-01

    The interpretation of astrophysical spectra requires knowledge of the charge state distribution (CSD) of the plasma. The CSD is determined by the rates of ionization and recombination. Thus, accurate electron impact ionization (EII) data are needed to calculate the CSD of the solar atmosphere as well as for other electron-ionized astrophysical objects, such as stars, supernovae, galaxies, and clusters of galaxies. We are studying EII for astrophysically important ions using the TSR storage ring located at the Max Plank Institute for Nuclear Physics in Heidelberg, Germany. Storage ring measurements are largely free of the metastable contamination found in other experimental geometries, resulting in unambiguous EII data. We have found discrepancies of about 10% - 30% between our measured cross sections and those commonly used in CSD models. Because it is impractical to perform experimental measurements for every astrophysically relevant ion, theory must provide the bulk of the necessary EII data. These experimental results provide an essential benchmark for such EII calculations.

  10. Electron-Impact Total Ionization Cross Sections of Hydrocarbon Ions

    PubMed Central

    Irikura, Karl K.; Kim, Yong-Ki; Ali, M. A.

    2002-01-01

    The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to CH2+, CH3+, CH4+, C2H2+, C2H4+, C2H6+ and H3O+. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H3O+ is found to be almost 1/20 of the present theory at the cross section peak. PMID:27446718

  11. Electron impact ionization of highly charged lithiumlike ions

    SciTech Connect

    Wong, K L

    1992-10-01

    Electron impact ionization cross sections can provide valuable information about the charge-state and power balance of highly charged ions in laboratory and astrophysical plasmas. In the present work, a novel technique based on x-ray measurements has been used to infer the ionization cross section of highly charged lithiumlike ions on the Livermore electron beam ion trap. In particular, a correspondence is established between an observed x ray and an ionization event. The measurements are made at one energy corresponding to approximately 2.3 times the threshold energy for ionization of lithiumlike ions. The technique is applied to the transition metals between Z=22 (titanium, Ti[sup 19+]) and Z=26 (iron, Fe[sup 23+]) and to Z=56 (barium, Ba[sup 53+]). The results for the transition metals, which have an estimated 17-33% uncertainty, are in good overall agreement with a relativistic distorted-wave calculation. However, less good agreement is found for barium, which has a larger uncertainty. Methods for properly accounting for the polarization in the x-ray intensities and for inferring the charge-state abundances from x-ray observations, which were developed for the ionization measurements, as well as an x-ray model that assists in the proper interpretation of the data are also presented.

  12. Double gate impact ionization MOS transistor: Proposal and investigation

    NASA Astrophysics Data System (ADS)

    Yang, Zhaonian; Zhang, Yue; Yang, Yuan; Yu, Ningmei

    2017-02-01

    In this paper, a double gate impact ionization MOS (DG-IMOS) transistor with improved performance is proposed and investigated by TCAD simulation. In the proposed design, a second gate is introduced in a conventional impact ionization MOS (IMOS) transistor that lengthens the equivalent channel length and suppresses the band-to-band tunneling. The OFF-state leakage current is reduced by over four orders of magnitude. At the ON-state, the second gate is negatively biased in order to enhance the electric field in the intrinsic region. As a result, the operating voltage does not increase with the increase in the channel length. The simulation result verifies that the proposed DG-IMOS achieves a better switching characteristic than the conventional is achieved. Lastly, the application of the DG-IMOS is discussed theoretically.

  13. ECC study in positron impact ionization in molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Campeanu, R. I.; Zohouri Haghian, N.

    2012-12-01

    The electron capture to the continuum phenomenon in positron impact ionization of molecular hydrogen is studied with the distorted wave Born approximation. Our theoretical model produces results which are in better agreement with the experiment than the more elaborate models of [J. Fiol, V.D. Rodriguez, R.O. Barrachina, J. Phys. B: At. Mol. Opt. Phys. 34, 933 (2001)] and [A. Benedek, R.I. Campeanu, J. Phys. B: At. Mol. Opt. Phys. 40, 1589 (2007)] previously employed in this study.

  14. Double differential cross sections for electron impact ionization of helium

    NASA Astrophysics Data System (ADS)

    Yun-fei, Yao; Zhang-jin, Chen

    1999-03-01

    The double differential cross sections for electron impact ionization of helium at incident energies of 200 eV, 100 eV and 64.6 eV have been calculated in the BBK model. The present results are found to be in generally good agreement with the latest measurements of Röder et al. and the theoretical results of the convergent close-coupling method although some quantitative discrepancy remains.

  15. Experimental determination of multiple ionization cross sections in Si by electron impact

    NASA Astrophysics Data System (ADS)

    Pérez, Pablo Daniel; Sepúlveda, Andrés; Castellano, Gustavo; Trincavelli, Jorge

    2015-12-01

    The thin sample method is often used to experimentally determine ionization cross sections, especially when focusing on the low overvoltage region. The simplicity of the formalism involved in this method is very appealing, but some experimental complications arise in the preparation of thin films. In this work, a thick sample method was used to measure the Si-K x-ray production cross section by electron impact. The good agreement between the results obtained and the values reported in the literature validates the method and the parameters used. The advantages and disadvantages of the method are discussed and its application is extended to the determination of Si multiple-ionization cross sections, where the very low emission rates (around two orders of magnitude lower than the single-ionization case) make the use of the thin sample method impracticable.

  16. Ionization of biomolecular targets by ion impact: input data for radiobiological applications

    NASA Astrophysics Data System (ADS)

    de Vera, Pablo; Abril, Isabel; Garcia-Molina, Rafael; Solov'yov, Andrey V.

    2013-06-01

    In this work we review and further develop a semiempirical model recently proposed for the ion impact ionization of complex biological media. The model is based on the dielectric formalism, and makes use of a semiempirical parametrization of the optical energy-loss function of bioorganic compounds, allowing the calculation of single and total ionization cross sections and related quantities for condensed biological targets, such as liquid water, DNA and its components, proteins, lipids, carbohydrates or cell constituents. The model shows a very good agreement with experimental data for water, adenine and uracil, and allows the comparison of the ionization efficiency of different biological targets, and also the average kinetic energy of the ejected secondary electrons.

  17. Fast detection of narcotics by single photon ionization mass spectrometry and laser ion mobility spectrometry

    NASA Astrophysics Data System (ADS)

    Laudien, Robert; Schultze, Rainer; Wieser, Jochen

    2010-10-01

    In this contribution two analytical devices for the fast detection of security-relevant substances like narcotics and explosives are presented. One system is based on an ion trap mass spectrometer (ITMS) with single photon ionization (SPI). This soft ionization technique, unlike electron impact ionization (EI), reduces unwanted fragment ions in the mass spectra allowing the clear determination of characteristic (usually molecular) ions. Their enrichment in the ion trap and identification by tandem MS investigations (MS/MS) enables the detection of the target substances in complex matrices at low concentrations without time-consuming sample preparation. For SPI an electron beam pumped excimer light source of own fabrication (E-Lux) is used. The SPI-ITMS system was characterized by the analytical study of different drugs like cannabis, heroin, cocaine, amphetamines, and some precursors. Additionally, it was successfully tested on-site in a closed illegal drug laboratory, where low quantities of MDMA could be directly detected in samples from floors, walls and lab equipments. The second analytical system is based on an ion mobility (IM) spectrometer with resonant multiphoton ionization (REMPI). With the frequency quadrupled Nd:YAG laser (266 nm), used for ionization, a selective and sensitive detection of aromatic compounds is possible. By application of suited aromatic dopants, in addition, also non-aromatic polar compounds are accessible by ion molecule reactions like proton transfer or complex formation. Selected drug precursors could be successfully detected with this device as well, qualifying it to a lower-priced alternative or useful supplement of the SPI-ITMS system for security analysis.

  18. Accuracy of Theoretical Calculations for Electron-Impact Ionization of atoms and Molecules

    NASA Astrophysics Data System (ADS)

    Madison, Don

    2015-09-01

    In the last two decades, there have been several close-coupling approaches developed which can accurately calculate the triply differential cross sections for electron impact ionization of effective one and two electron atoms. The agreement between experiment and theory is not particularly good for more complicated atoms and molecules. Very recently, a B-spline R-matrix with pseudostates (BSRPS) approach was used to investigate low energy electron impact ionization of neon and very good agreement with experiment was found. The perturbative 3-body distorted wave (3DW) approach which includes the exact final state electron-electron interaction (post collision interaction - PCI) gave comparably good agreement with experiment. For ionization of molecules, there have been numerous studies of high-energy electron impact. These studies are called EMS (Electron Momentum Spectroscopy) and they were very valuable in determining the accuracy of molecular wavefunctions since the measured cross sections were proportional to the momentum space molecular wavefunction. More recently, lower energy collisions have started to be measured and these cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. So far, the only close coupling calculation reported for ionization of molecules is the time-dependent close-coupling calculation (TDCC) which has been developed for ionization of H2 and it yields relative good agreement with experiment. Again the molecular 3-body distorted wave (M3DW) gave equally good agreement with experiment. For polyatomic molecules, the only theory available is the M3DW. In this talk, I will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of atoms and molecules. Work supported by the NSF and XSEDE.

  19. Cross Sections for Inner-Shell Ionization by Electron Impact

    SciTech Connect

    Llovet, Xavier; Powell, Cedric J.; Salvat, Francesc; Jablonski, Aleksander

    2014-03-15

    An analysis is presented of measured and calculated cross sections for inner-shell ionization by electron impact. We describe the essentials of classical and semiclassical models and of quantum approximations for computing ionization cross sections. The emphasis is on the recent formulation of the distorted-wave Born approximation by Bote and Salvat [Phys. Rev. A 77, 042701 (2008)] that has been used to generate an extensive database of cross sections for the ionization of the K shell and the L and M subshells of all elements from hydrogen to einsteinium (Z = 1 to Z = 99) by electrons and positrons with kinetic energies up to 1 GeV. We describe a systematic method for evaluating cross sections for emission of x rays and Auger electrons based on atomic transition probabilities from the Evaluated Atomic Data Library of Perkins et al. [Lawrence Livermore National Laboratory, UCRL-ID-50400, 1991]. We made an extensive comparison of measured K-shell, L-subshell, and M-subshell ionization cross sections and of Lα x-ray production cross sections with the corresponding calculated cross sections. We identified elements for which there were at least three (for K shells) or two (for L and M subshells) mutually consistent sets of cross-section measurements and for which the cross sections varied with energy as expected by theory. The overall average root-mean-square deviation between the measured and calculated cross sections was 10.9% and the overall average deviation was −2.5%. This degree of agreement between measured and calculated ionization and x-ray production cross sections was considered to be very satisfactory given the difficulties of these measurements.

  20. Electron impact ionization dynamics of para-benzoquinone

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; Ali, E.; Ning, C. G.; Colgan, J.; Ingólfsson, O.; Madison, D. H.; Brunger, M. J.

    2016-10-01

    Triple differential cross sections (TDCSs) for the electron impact ionization of the unresolved combination of the 4 highest occupied molecular orbitals (4b3g, 5b2u, 1b1g, and 2b3u) of para-benzoquinone are reported. These were obtained in an asymmetric coplanar geometry with the scattered electron being observed at the angles -7.5°, -10.0°, -12.5° and -15.0°. The experimental cross sections are compared to theoretical calculations performed at the molecular 3-body distorted wave level, with a marginal level of agreement between them being found. The character of the ionized orbitals, through calculated momentum profiles, provides some qualitative interpretation for the measured angular distributions of the TDCS.

  1. Electron- and photon-impact ionization of furfural

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; Ali, E.; Nixon, K. L.; Limão-Vieira, P.; Hubin-Franskin, M.-J.; Delwiche, J.; Ning, C. G.; Colgan, J.; Murray, A. J.; Madison, D. H.; Brunger, M. J.

    2015-11-01

    The He(i) photoelectron spectrum of furfural has been investigated, with its vibrational structure assigned for the first time. The ground and excited ionized states are assigned through ab initio calculations performed at the outer-valence Green's function level. Triple differential cross sections (TDCSs) for electron-impact ionization of the unresolved combination of the 4a″ + 21a' highest and next-highest occupied molecular orbitals have also been obtained. Experimental TDCSs are recorded in a combination of asymmetric coplanar and doubly symmetric coplanar kinematics. The experimental TDCSs are compared to theoretical calculations, obtained within a molecular 3-body distorted wave framework that employed either an orientation average or proper TDCS average. The proper average calculations suggest that they may resolve some of the discrepancies regarding the angular distributions of the TDCS, when compared to calculations employing the orbital average.

  2. Electron- and photon-impact ionization of furfural

    SciTech Connect

    Jones, D. B.; Ali, E.; Madison, D. H. E-mail: madison@mst.edu; Nixon, K. L.; Limão-Vieira, P. E-mail: madison@mst.edu; Hubin-Franskin, M.-J.; Delwiche, J.; Ning, C. G.; Colgan, J.; Murray, A. J.; and others

    2015-11-14

    The He(I) photoelectron spectrum of furfural has been investigated, with its vibrational structure assigned for the first time. The ground and excited ionized states are assigned through ab initio calculations performed at the outer-valence Green’s function level. Triple differential cross sections (TDCSs) for electron-impact ionization of the unresolved combination of the 4a″  +  21a′ highest and next-highest occupied molecular orbitals have also been obtained. Experimental TDCSs are recorded in a combination of asymmetric coplanar and doubly symmetric coplanar kinematics. The experimental TDCSs are compared to theoretical calculations, obtained within a molecular 3-body distorted wave framework that employed either an orientation average or proper TDCS average. The proper average calculations suggest that they may resolve some of the discrepancies regarding the angular distributions of the TDCS, when compared to calculations employing the orbital average.

  3. Laser-assisted positron-impact ionization of atomic hydrogen.

    PubMed

    Pan, Juan; Li, Shu-Min; Berakdar, Jamal

    2007-03-15

    We study the ionization of atomic hydrogen by a fast positron in the presence of an external linearly polarized laser field. We concentrate on the limit of a small momentum transfer and describe the fast positron's continuum states by Volkov wave functions. The ejected electron is described by a Coulomb-Volkov wave function. We are limited to small laser intensities such that the dressed state of the target is treatable within the time-dependent perturbation theory, even though the laser intensity is still quite high by laboratory standards. Numerical results for the triply differential cross sections and their dependencies on laser-field parameters are discussed and compared with the results of laser-assisted ionization by electron impact.

  4. Ghost peaks observed after AP-MALDI experiment may disclose new ionization mechanism of matrix assisted hypersonic velocity impact ionization

    PubMed Central

    Moskovets, Eugene

    2015-01-01

    RATIONALE Understanding the mechanisms of MALDI promises improvements in the sensitivity and specificity of many established applications in the field of mass spectrometry. This paper reports a serendipitous observation of a significant ion yield in a post-ionization experiment conducted after the sample has been removed from a standard atmospheric pressure (AP)-MALDI source. This post-ionization is interpreted in terms of collisions of microparticles moving with a hypersonic velocity into a solid surface. Calculations show that the thermal energy released during such collisions is close to that absorbed by the top matrix layer in traditional MALDI. The microparticles, containing both the matrix and analytes, could be detached from a film produced inside the inlet capillary during the sample ablation and accelerated by the flow rushing through the capillary. These observations contribute some new perspective to ion formation in both laser and laserless matrix-assisted ionization. METHODS An AP-MALDI ion source hyphenated with a three-stage high-pressure ion funnel system was utilized for peptide mass analysis. After the laser was turned off and MALDI sample was removed, ions were detected during a gradual reduction of the background pressure in the first funnel. The constant-rate pressure reduction led to the reproducible appearance of different singly- and doubly-charged peptide peaks in mass spectra taken a few seconds after the end of the MALDI analysis of a dried-droplet spot. RESULTS The ion yield as well as the mass range of ions observed with a significant delay after a completion of the primary MALDI analysis depended primarily on the background pressure inside the first funnel. The production of ions in this post-ionization step was exclusively observed during the pressure drop. A lower matrix background and significant increase in relative yield of double-protonated ions are reported. CONCLUSIONS The observations were partially consistent with a model of

  5. Scaling law for total electron-impact ionization cross sections of Li-like ions

    SciTech Connect

    Ancarani, L.U.; Hervieux, P.-A.

    2005-09-15

    Experimental total cross sections for direct electron-impact ionization of the valence electron of several Li-like ions are seen to follow a new ab initio scaling law which is inspired by a Coulomb-Born model and the frozen-core Hartree-Fock approximation. The predictive character of this scaling law should be very useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies. A single-parameter fit of the best available experimental data, once scaled, provides us with a single formula, for moderately charged Li-like ions, which is more accurate than Lotz semiempirical formula.

  6. Role of ionization-excitation processes in the cross section for direct ionization of heavy atomic ions by electron impact

    NASA Astrophysics Data System (ADS)

    Zeng, J. L.; Liu, L. P.; Liu, P. F.; Yuan, J. M.

    2014-10-01

    The contribution to the ionization cross section of ionization-excitation processes by electron impact is usually negligibly small for low- and medium-Z elements. We demonstrate here, however, that for heavy atomic ions with the outermost shell being n d (n =4 ,5 ) the ionization-excitation processes play an evident role in the ionization cross section. For the 4 s24 p64 d10 ground level of Gd18 +, the ionization-excitation cross section due to the excitation of levels in the 4 s24 p64 d84 f configuration is comparable to the direct 4 p and 4 s ionization cross sections of (4s24 p54 d10) 1 /2 and (4s 4 p64 d10) 1 /2. The total ionization cross section will be underestimated by 15% without including the contribution from ionization-excitation processes. This is a general conclusion for heavy atomic ions, which is verified by taking Pd-like ions of Sn4 +,Ba10 +,Nd14 +,Tb19 +,Yb24 +, and W28 + as examples. The role of ionization-excitation processes can be understood from the overlapping of the wave functions between the 4 d and 4 f orbitals.

  7. Threshold electron attachment and electron impact ionization involving oxygen dimers

    NASA Astrophysics Data System (ADS)

    Kreil, J.; Ruf, M.-W.; Hotop, H.; Ettischer, I.; Buck, U.

    1998-12-01

    Using two different crossed-beams machines we have carried out the first quantitative study of threshold electron attachment and electron impact-induced ionization and fragmentation involving oxygen dimers (O 2) 2. In the electron attachment experiment we study electron transfer from state-selected Ar **(20d) Rydberg atoms to O 2 molecules and dimers in a skimmed supersonic beam at variable nozzle temperatures ( T0) and stagnation pressures ( p0). The relative dimer density is determined through measurements of Penning ionization by metastable Ne *(3s 3P2,0) atoms and used to estimate the absolute cross-section for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 dimers to be nearly 10 -17 m 2, almost four orders of magnitude larger than that for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 monomers. The fragmentation of the oxygen cluster beam is quantitatively characterized by the transverse helium beam scattering method which allows us to spatially separate different clusters. It is shown that in 70 eV electron impact of (O 2) 2 only 3.6(4)% of the dimers are detected as dimer ions (O 2) 2+. In additional experiments involving SF 6 clusters we show that SF 6 dimers fragment nearly completely upon 70 eV electron impact, yielding SF 5+ ions (probability for (SF 6)·SF 5+ production at most 0.3%).

  8. Irradiation Damage in Gd2Ti2O7 Single Crystals: Ballistic vs Ionization Processes

    SciTech Connect

    Moll, Sandra; Sattonnay, Gael; Thome, Lionel; Jagielski, Jacek; Decorse, C; Simon, Patrick; Monnet, Isabelle; Weber, William J

    2011-01-01

    The structural transformations induced in Gd2Ti2O7 single crystals irradiated at high energies (870 MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4 MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling, Raman spectroscopy and transmission electron microscopy experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic energy deposition from ionization, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters determined from RBS/C and TEM data lie in the range 6-8 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both the direct-impact/defect stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher (0.5 ion nm-2) at low energy than at high energy (0.05 ion nm-2), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm).

  9. Single ionization in highly charged ion-atom collisions at low to intermediate velocities

    NASA Astrophysics Data System (ADS)

    Abdallah, Mohammad Abdallah

    1998-11-01

    Single electron ejection from neutral targets (He and Ne) by the impact of low to highly charged ions (p, He+,/ Ne+,/ He2+,/ C6+,/ O8+, and Ne10+) at low to intermediate impact velocities is studied. A novel technique of electron momentum imaging is implemented. In this technique two-dimensional electron momentum distributions are produced in coincidence with recoil ions and projectile ions. In first generation experiments we studied the ejected electron momentum distributions without analyzing recoil ions momentum. This series of experiments revealed a charge-state dependence and velocity dependence that are contradictory to a dominant saddle point ionization mechanism at intermediate velocities. It showed a possibility of an agreement with a saddle centered distributions for low charge states at low collision velocities. To pursue the problem in more detail, we developed a second generation spectrometer which allowed us to fully determine the recoil ions momentum. This allowed us to determine the collision plane, energy loss (Q-value), and impact parameter for every collision that resulted in a single (target) electron ejection. This series of experiments revealed for the first time very marked structure in electron spectra that were impossible to observe in other experiments. These structures indicate the quasi-molecular nature of the collision process even at velocities comparable to the electron 'classical' orbital velocity. For the collisions of p, He+, and He2+ with He, a π-orbital shape of the electron momentum distribution is observed. This indicates the importance of the rotational coupling 2p/sigma/to2p/pi in the initial promotion of the ground state electron. This is followed by further promotions to the continuum. This agrees with the 'classical' description implied by the saddle-point ionization mechanism picture.

  10. Electron Impact Ionization of He atom using screening potential

    NASA Astrophysics Data System (ADS)

    Saha, Hari P.

    2012-06-01

    We will report the results of our investigation on electron impact ionization of helium atom using our extended MCHF method [1] for electron impact ionization of atoms. The initial state wave function will be calculated with both HF and MCHF approximations and the electron correlation between the two final state continuum electrons will be obtained using the screening potential [2-4]. Calculations will be made for triple differential cross sections for 4 eV excess energy sharing equally by the two final state continuum electrons. The results will be presented for all scattering angles and all kinematics. Comparison will be made with available experimental and theoretical data. [4pt] [1] Hari P. Saha, Phys. Rev. A82, 042703 (2010); J.Phys. B44, 065202 (2011).[0pt] [2] M.R.H. Rudge and M.J. Seaton, Proc. Roy. Soc. A293. 262 (1965).[0pt] [3] M.R.H. Rudge, Rev. Mod. Phys. 40, 564 (1968).[0pt] [4] C.Pan and A.F Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992).

  11. Absolute electron-impact total ionization cross sections of chlorofluoromethanes

    NASA Astrophysics Data System (ADS)

    Martínez, Roberto; Sierra, Borja; Redondo, Carolina; Rayo, María N. Sánchez; Castaño, Fernando

    2004-12-01

    An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles—as a function of the electron-impact energy—have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n⩾3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.

  12. Impact ionization engineered avalanche photodiode arrays for free space optical communication

    NASA Astrophysics Data System (ADS)

    Ferraro, Mike S.; Rabinovich, William S.; Clark, William R.; Waters, William D.; Campbell, Joe C.; Mahon, Rita; Vaccaro, Kenneth; Krejca, Brian D.

    2016-03-01

    High sensitivity photodetectors serve two purposes in free space optical communication: data reception and position sensing for pointing, tracking, and stabilization. Because of conflicting performance criteria, two separate detectors are traditionally utilized to perform these tasks but recent advances in the fabrication and development of large area, low noise avalanche photodiode (APD) arrays have enabled these devices to be used both as position sensitive detectors (PSD) and as communications receivers. Combining these functionalities allows for more flexibility and simplicity in optical assembly design without sacrificing the sensitivity and bandwidth performance of smaller, single element data receivers. Beyond eliminating the need to separate the return beam into two separate paths, these devices enable implementation of adaptive approaches to compensate for focal plane beam wander and breakup often seen in highly scintillated terrestrial and maritime optical links. While the Naval Research Laboratory (NRL) and Optogration Inc, have recently demonstrated the performance of single period, InAlAs/InGaAs APD arrays as combined data reception and tracking sensors, an impact ionization engineered (I2E) epilayer design achieves even lower carrier ionization ratios by incorporating multiple multiplication periods engineered to suppress lower ionization rate carriers while enhancing the higher ionization rate carriers of interest. This work presents a three period I2E concentric, five element avalanche photodiode array rated for bandwidths beyond 1GHz with measured carrier ionization ratios of 0.05-0.1 at moderate APD gains. The epilayer design of the device will be discussed along with initial device characterization and high speed performance measurements.

  13. Angular distributions in the double ionization of DNA bases by electron impact

    NASA Astrophysics Data System (ADS)

    Khelladi, M. F.; Mansouri, A.; Dal Cappello, C.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Roy, A. C.

    2016-11-01

    Ab initio calculations of the five-fold differential cross sections for electron-impact double ionization of thymine, cytosine, adenine and guanine are performed in the first Born approximation for an incident energy close to 5500 eV. The wavefunctions of the DNA bases are constructed using the multi-center wave functions from the Gaussian 03 program. These multi-center wave functions are converted into single-center expansions of Slater-type functions. For the final state, the two ejected electrons are described by two Coulomb wave functions. The electron-electron repulsion between the two ejected electrons is also taken into account. Mechanisms of the double ionization are discussed for each case and the best choices of the kinematical parameters are determined for next experiments.

  14. Electron-impact ionization of helium: A comprehensive experiment benchmarks theory

    SciTech Connect

    Ren, X.; Pflueger, T.; Senftleben, A.; Xu, S.; Dorn, A.; Ullrich, J.; Bray, I.; Fursa, D.V.; Colgan, J.; Pindzola, M.S.

    2011-05-15

    Single ionization of helium by 70.6-eV electron impact is studied in a comprehensive experiment covering a major part of the entire collision kinematics and the full 4{pi} solid angle for the emitted electron. The absolutely normalized triple-differential experimental cross sections are compared with results from the convergent close-coupling (CCC) and the time-dependent close-coupling (TDCC) theories. Whereas excellent agreement with the TDCC prediction is only found for equal energy sharing, the CCC calculations are in excellent agreement with essentially all experimentally observed dynamical features, including the absolute magnitude of the cross sections.

  15. Semirelativistic model for ionization of atomic hydrogen by electron impact

    NASA Astrophysics Data System (ADS)

    Attaourti, Y.; Taj, S.; Manaut, B.

    2005-06-01

    We present a semirelativistic model for the description of the ionization process of atomic hydrogen by electron impact in the first Born approximation by using the Darwin wave function to describe the bound state of atomic hydrogen and the Sommerfeld-Maue wave function to describe the ejected electron. This model, accurate to first order in Z/c in the relativistic correction, shows that, even at low kinetic energies of the incident electron, spin effects are small but not negligible. These effects become noticeable with increasing incident electron energies. All analytical calculations are exact and our semirelativistic results are compared with the results obtained in the nonrelativistic Coulomb Born approximation both for the coplanar asymmetric and the binary coplanar geometries.

  16. Semirelativistic model for ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.; Manaut, B.

    2005-06-15

    We present a semirelativistic model for the description of the ionization process of atomic hydrogen by electron impact in the first Born approximation by using the Darwin wave function to describe the bound state of atomic hydrogen and the Sommerfeld-Maue wave function to describe the ejected electron. This model, accurate to first order in Z/c in the relativistic correction, shows that, even at low kinetic energies of the incident electron, spin effects are small but not negligible. These effects become noticeable with increasing incident electron energies. All analytical calculations are exact and our semirelativistic results are compared with the results obtained in the nonrelativistic Coulomb Born approximation both for the coplanar asymmetric and the binary coplanar geometries.

  17. The formation of molecules in interstellar clouds from singly and multiply ionized atoms

    NASA Technical Reports Server (NTRS)

    Langer, W. D.

    1978-01-01

    The suggestion is considered that multiply ionized atoms produced by K- and L-shell X-ray ionization and cosmic-ray ionization can undergo ion-molecule reactions and also initiate molecule production. The role of X-rays in molecule production in general is discussed, and the contribution to molecule production of the C(+) radiative association with hydrogen is examined. Such gas-phase reactions of singly and multiply ionized atoms are used to calculate molecular abundances of carbon-, nitrogen-, and oxygen-bearing species. The column densities of the molecules are evaluated on the basis of a modified version of previously developed isobaric cloud models. It is found that reactions of multiply ionized carbon with H2 can contribute a significant fraction of the observed CH in diffuse interstellar clouds in the presence of diffuse X-ray structures or discrete X-ray sources and that substantial amounts of CH(+) can be produced under certain conditions.

  18. Relativistic contributions to single and double core electron ionization energies of noble gases.

    PubMed

    Niskanen, J; Norman, P; Aksela, H; Agren, H

    2011-08-07

    We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac-Coulomb Hamiltonian is found to predict a scaling ratio of ∼4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.

  19. Theory of steady-state plane tunneling-assisted impact ionization waves

    SciTech Connect

    Kyuregyan, A. S.

    2013-07-15

    The effect of band-to-band and trap-assisted tunneling on the properties of steady-state plane ionization waves in p{sup +}-n-n{sup +} structures is theoretically analyzed. It is shown that such tunneling-assisted impact ionization waves do not differ in a qualitative sense from ordinary impact ionization waves propagating due to the avalanche multiplication of uniformly distributed seed electrons and holes. The quantitative differences of tunneling-assisted impact ionization waves from impact ionization waves are reduced to a slightly different relation between the wave velocity u and the maximum field strength E{sub M} at the front. It is shown that disregarding impact ionization does not exclude the possibility of the existence of tunneling-assisted ionization waves; however, their structure radically changes, and their velocity strongly decreases for the same E{sub M}. A comparison of the dependences u(E{sub M}) for various ionization-wave types makes it possible to determine the conditions under which one of them is dominant. In conclusion, unresolved problems concerning the theory of tunneling-assisted impact ionization waves are discussed and the directions of further studies are outlined.

  20. Electron impact ionization cross sections of beryllium-tungsten clusters*

    NASA Astrophysics Data System (ADS)

    Sukuba, Ivan; Kaiser, Alexander; Huber, Stefan E.; Urban, Jan; Probst, Michael

    2016-01-01

    We report calculated electron impact ionization cross sections (EICSs) of beryllium-tungsten clusters, BenW with n = 1,...,12, from the ionization threshold to 10 keV using the Deutsch-Märk (DM) and the binary-encounter-Bethe (BEB) formalisms. The positions of the maxima of DM and BEB cross sections are mostly close to each other. The DM cross sections are more sensitive with respect to the cluster size. For the clusters smaller than Be4W they yield smaller cross sections than BEB and vice versa larger cross sections than BEB for clusters larger than Be6W. The maximum cross section values for the singlet-spin groundstate clusters range from 7.0 × 10-16 cm2 at 28 eV (BeW) to 54.2 × 10-16 cm2 at 43 eV (Be12W) for the DM cross sections and from 13.5 × 10-16 cm2 at 43 eV (BeW) to 38.9 × 10-16 cm2 at 43 eV (Be12W) for the BEB cross sections. Differences of the EICSs in different isomers and between singlet and triplet states are also explored. Both the DM and BEB cross sections could be fitted perfectly to a simple expression used in modeling and simulation codes in the framework of nuclear fusion research. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2015-60583-7

  1. Charge cluster distribution in nanosites traversed by a single ionizing particle An experimental approach

    NASA Astrophysics Data System (ADS)

    Pszona, S.; Bantsar, A.; Kula, J.

    2008-11-01

    A method for modeling charge cluster formation by a single ionizing particle in nanoelectronic structures of few nanometres size is presented. The method is based on experimental modeling of charge formation in the equivalent gaseous nanosites irradiated by single charged particles and the subsequent scaling procedure to a needed medium. Propane irradiated by alpha particles is presented as an example.

  2. The biobehavioral and neuroimmune impact of low-dose ionizing radiation

    PubMed Central

    York, Jason M; Blevins, Neil A; Meling, Daryl D; Peterlin, Molly B; Gridley, Daila S; Cengel, Keith A; Freund, Gregory G

    2011-01-01

    In the clinical setting, repeated exposures (10–30) to low-doses of ionizing radiation (≤ 200 cGy), as seen in radiotherapy for cancer, causes fatigue. Almost nothing is known, however, about the fatigue inducing effects of a single exposure to environmental low-dose ionizing radiation that might occur during high-altitude commercial air flight, a nuclear reactor accident or a solar particle event (SPE). To investigate the short-term impact of low-dose ionizing radiation on mouse biobehaviors and neuroimmunity, male CD-1 mice were whole body irradiated with 50 cGy or 200 cGy of gamma or proton radiation. Gamma radiation was found to reduce spontaneous locomotor activity by 35% and 36%, respectively, 6 h post irradiation. In contrast, the motivated behavior of social exploration was un-impacted by gamma radiation. Examination of pro-inflammatory cytokine gene transcripts in the brain demonstrated that gamma radiation increased hippocampal TNF-α expression as early as 4 h post-irradiation. This was coupled to subsequent increases in IL-1RA (8 h and 12 h post irradiation) in the cortex and hippocampus and reductions in activity-regulated cytoskeleton-associated protein (Arc) (24 h post irradiation) in the cortex. Finally, restraint stress was a significant modulator of the neuroimmune response to radiation blocking the ability of 200 cGy gamma radiation from impairing locomotor activity and altering the brain-based inflammatory response to irradiation. Taken together, these findings indicate that low-dose ionizing radiation rapidly activates the neuroimmune system potentially causing early onset fatigue-like symptoms in mice. PMID:21958477

  3. Single- and multi-photon ionization studies of organosulfur species

    SciTech Connect

    Cheung, Yu -San

    1999-02-12

    Accurate ionization energies (IE`s) for molecular species are used for prediction of chemical reactivity and are of fundamental importance to chemists. The IE of a gaseous molecule can be determined routinely in a photoionization or a photoelectron experiment. IE determinations made in conventional photoionization and photoelectron studies have uncertainties in the range of 3--100 meV (25--250 cm-1). In the past decade, the most exciting development in the field of photoionization and photoelectron spectroscopy has been the availability of high resolution, tunable ultraviolet (UV) and vacuum ultraviolet (VUV) laser sources. The laser pulsed field ionization photoelectron (PFI-PE) scheme is currently the state-of-the-art photoelectron spectroscopic technique and is capable of providing photoelectron energy resolution close to the optical resolution. The author has focused attention on the photoionization processes of some sulfur-containing species. The studies of the photoionization and photodissociation on sulfur-containing compounds [such as CS2, CH3SH, CH3SSCH3, CH3CH2SCH2CH3, HSCH2CH2SH and C4H4S (thiophene) and sulfur-containing radicals, such as HS, CS, CH3S, CH3CH2S and CH3SS], have been the major subjects in the group because sulfur is an important species contributing to air pollution in the atmosphere. The modeling of the combustion and oxidation of sulfur compounds represents important steps for the control of both the production and the elimination of sulfur-containing pollutants. Chapter 1 is a general introduction of the thesis. Chapters 2 and 6 contain five papers published in, or accepted for publication in, academic periodicals. In Chapter 7, the progress of the construction in the laboratory of a new vacuum ultraviolet laser system equipped with a reflectron mass

  4. Auger spectrum of a water molecule after single and double core ionization.

    PubMed

    Inhester, L; Burmeister, C F; Groenhof, G; Grubmüller, H

    2012-04-14

    The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schrödinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  5. Auger spectrum of a water molecule after single and double core ionization

    SciTech Connect

    Inhester, L.; Burmeister, C. F.; Groenhof, G.; Grubmueller, H.

    2012-04-14

    The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schroedinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  6. Observation of an impact-parameter window in low-velocity ionizing collisions of Ne+ on Ne proceeding through quasimolecular states

    NASA Astrophysics Data System (ADS)

    Abdallah, M. A.; Wolff, W.; Wolf, H. E.; Cocke, C. L.; Stöckli, M.

    1998-11-01

    Target ionization in collisions of singly charged Ne+ ions with Ne has been investigated at projectile velocities from 0.25 to 0.55 a.u. using electron and recoil momentum imaging techniques. The momentum distributions of the ejected electrons were found to carry a distinct signature strongly suggesting that ionization is taking place by successive promotions through molecular orbitals. The observed recoil transverse momentum distributions are donut-shaped, indicating that single ionization is confined to a well-defined impact-parameter window.

  7. Positron Impact Ionization in Noble Gas Atoms and Diatomic Molecules

    NASA Astrophysics Data System (ADS)

    Marler, J. P.

    2005-05-01

    Results are presented for absolute positronium formation and direct ionization by positron impact on Ne, Ar, Kr, Xe, N2, CO and O2 at energies from threshold up to 90 eV. The experiments use a high-resolution, trap-based positron beam and exploit the properties of positron orbits in a magnetic field [1]. Results for the noble gases are compared with theoretical predictions and with measurements obtained using a significantly different method [2]. Results for diatomic molecules are compared to other available measurements and theoretical calculations where available. There is generally good agreement between the experimental measurements, providing an important benchmark for theoretical calculations. Intriguing features in Ar and O2 will be discussed. [1] J.P. Sullivan, S.J. Gilbert, J.P. Marler, R.G. Greaves, S.J. Buckman and C.M. Surko., Phys. Rev. A. 66, 042708 (2002) [2] J.P. Marler, J.P. Sullivan and C.M. Surko, Phys. Rev. A (2005), in press.

  8. Momentum spectra for single and double electron ionization of He in relativistic collisions

    NASA Astrophysics Data System (ADS)

    Wood, C. J.; Olson, R. E.; Schmitt, W.; Moshammer, R.; Ullrich, J.

    1997-11-01

    The complete momentum spectra for single and double ionization of He by 1-GeV/u (β=0.88) U92+ have been investigated using a classical trajectory Monte Carlo method corrected for the relativistic projectile. The 1/r12 electron-electron interaction has been included in the post-collision region for double ionization to incorporate the effects of both the nuclear-electron and electron-electron ionizing interactions, and to access the effects of electron correlation in the electron spectra. Experimental measurements were able to determine the longitudinal momentum spectra for single ionization; these observations are in accordance with the theoretical predictions for the three-body momentum balance between projectile, recoil ion, and ionized electron. In particular, the Lorentz contraction of the Coulomb interaction of the projectile manifests itself in the decrease of the post-collision interaction of the projectile with the electron and recoil ion, causing them to recoil back-to-back as in the case for a short electromagnetic pulse. This feature is clearly displayed in both the theoretical and experimental longitudinal momentum spectra, and by comparing to calculations that are performed at the same collision speed but do not include the relativistic potentials. Moreover, collision plane spectra of the three particles demonstrate that the momenta of the recoil ion and ionized electron are preferentially equal, and opposite, to each other. The electron spectra for double ionization show that the inclusion of the electron-electron interaction in the post-collision regime partitions the combined ionization momentum of the electrons so that the electrons are preferentially emitted in opposite azimuthal angles to one another. This is in contrast to calculations made assuming independent electrons.

  9. Photoelectron emission as an alternative electron impact ionization source for ion trap mass spectrometry.

    PubMed

    Gamez, Gerardo; Zhu, Liang; Schmitz, Thomas A; Zenobi, Renato

    2008-09-01

    Electron impact ionization has several known advantages; however, heated filament electron sources have pressure limitations and their power consumption can be significant for certain applications, such as in field-portable instruments. Herein, we evaluate a VUV krypton lamp as an alternative source for ionization inside the ion trap of a mass spectrometer. The observed fragmentation patterns are more characteristic of electron impact ionization than photoionization. In addition, mass spectra of analytes with ionization potentials higher than the lamp's photon energy (10.6 eV) can be easily obtained. A photoelectron impact ionization mechanism is suggested by the observed data allowed by the work function of the ion trap electrodes (4.5 eV), which is well within the lamp's photon energy. In this case, the photoelectrons emitted at the surface of the ion trap end-cap electrode are accelerated by the applied rf field to the ring electrode. This allows the photoelectrons to gain sufficient energy to ionize compounds with high ionization potentials to yield mass spectra characteristic of electron impact. In this manner, electron impact ionization can be used in ion trap mass spectrometers at low powers and without the limitations imposed by elevated pressures on heated filaments.

  10. Impact of APCI ionization source in liquid chromatography tandem mass spectrometry based tissue distribution studies.

    PubMed

    Khatal, Laxman; Gaur, Ashwani; Naphade, Ashish; Kandikere, Vishwottam; Mookhtiar, Kasim

    2016-10-01

    Measurement of test article concentration in tissue samples has been an important part of pharmacokinetic study and has helped to co-relate pharmacokinetic/pharmacodynamic relationships since the 1950s. Bioanalysis of tissue samples using LC-MS/MS comes with unique challenges in terms of sample handling and inconsistent analyte response owing to nonvolatile matrix components. Matrix effect is a phenomenon where the target analyte response is either suppressed or enhanced in the presence of matrix components. Based on previous reports electrospray ionization (ESI) mode of ionization is believed to be more affected by matrix components than atmospheric pressure chemical ionization (APCI) or atmospheric pressure photoionization. To explore the impact of ionization source with respect to bioanalysis of tissue samples, five structurally diverse compounds - atenolol, verapamil, diclofenac, propranolol and flufenamic acid - were selected. Quality control standards were spiked into 10 different biological matrices like whole blood, liver, heart, brain, spleen, kidney, skeletal muscle, eye and skin tissue and were quantified against calibration standards prepared in rat plasma. Quantitative bioanalysis was performed utilizing both APCI and ESI mode and results were compared. Quality control standards when analyzed with APCI mode were found to be more consistent in terms of accuracy and precision as compared with ESI mode. Additionally, for some instances, up to 20-fold broader dynamic linearity range was observed with APCI mode as compared with ESI mode. As phospholid interferences have poor response in APCI mode, protein precipitation extraction technique can be used for multimatrix quantitation, which is more amenable to automation. The approach of multiple biological matrix quantitation against a single calibration curve helps bioanalysts to reduce turnaround time. Copyright © 2016 John Wiley & Sons, Ltd.

  11. Relativistic effects on giant resonances in electron-impact double ionization

    SciTech Connect

    Pindzola, M.S.

    1987-06-01

    The electron-impact double-ionization cross section for Fr/sup +/ is calculated in the distorted-wave Born approximation. A giant resonance in the 5d subshell ionization-autoionization contribution to the cross section is found to be quite sensitive to changes in the double-well potential caused by relativistic effects on bound-state wave functions.

  12. Electron impact ionization and attachment cross sections for H2S. [in comet and planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Rao, M. V. V. S.; Srivastava, S. K.

    1993-01-01

    Experiments were performed to measure, by electron impact, appearance potentials and the cross sections for ionization, dissociative ionization, and electron attachment for H2S. Results are presented, and discussed individually, for both positive and negative ions. A schematic diagram of the experimental setup is included.

  13. Parametrization of electron impact ionization cross sections for CO, CO2, NH3 and SO2

    NASA Technical Reports Server (NTRS)

    Srivastava, Santosh K.; Nguyen, Hung P.

    1987-01-01

    The electron impact ionization and dissociative ionization cross section data of CO, CO2, CH4, NH3, and SO2, measured in the laboratory, were parameterized utilizing an empirical formula based on the Born approximation. For this purpose an chi squared minimization technique was employed which provided an excellent fit to the experimental data.

  14. Numerical simulation of the double-to-single ionization ratio for the helium atom in strong laser fields

    NASA Astrophysics Data System (ADS)

    Chen, Zhangjin; Zheng, Yanyan; Yang, Weifeng; Song, Xiaohong; Xu, Junliang; DiMauro, L. F.; Zatsarinny, Oleg; Bartschat, Klaus; Morishita, Toru; Zhao, Song-Feng; Lin, C. D.

    2015-12-01

    We present calculations on the ratio between double and single ionization of helium by a strong laser pulse at a wavelength of 780 nm using the quantitative rescattering (QRS) model. According to this model, the yield for the doubly charged ion He+2 can be obtained by multiplying the returning electron wave packet (RWP) with the total cross sections (TCSs) for electron impact ionization and electron impact excitation of +He in the singlet spin channel. The singlet constraint was imposed since the interaction of the helium atom with the laser and the recollision processes both preserve the total spin of the system. An R -matrix (close-coupling) code is used to obtain accurate TCSs, while the RWPs, according to the QRS, are calculated by the strong-field approximation for high-energy photoelectrons. The laser field, which lowers the required energy for the electron to escape from the nucleus at the time of recollision, is also taken into account. The simulated results are in good agreement with the measured He+2/+He ratio over a broad range of laser intensities. The result demonstrates that the QRS approach based on the rescattering model is fully capable of quantitatively interpreting nonsequential double ionization processes.

  15. Auger spectrum of a water molecule after single and double core ionization

    NASA Astrophysics Data System (ADS)

    Inhester, Ludger; Burmeister, Carl F.; Groenhof, Gerrit; Grubmueller, Helmut

    2012-06-01

    The high intensity of Free Electron Lasers (FEL) opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules radiation damage induced by absorption of intense x-ray radiation is not yet fully understood. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From MD trajectories photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schr"odinger equations. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were accumulated according to the obtained time-dependent populations. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint on the electron emission spectra. In addition, the lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  16. Miniaturized ionization gas sensors from single metal oxide nanowires.

    PubMed

    Hernandez-Ramirez, Francisco; Prades, Juan Daniel; Hackner, Angelika; Fischer, Thomas; Mueller, Gerhard; Mathur, Sanjay; Morante, Joan Ramon

    2011-02-01

    Gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. These devices were found to work at much lower temperatures (T≈280 °C) and bias voltages (V≈2 V) than their micro-counterparts, thereby demonstrating the inherent potential of individual nanostructures in building functional nanodevices. High selectivity of our miniaturized sensors emerges from the dissimilar sensing mechanisms of those typical of standard resistive-type sensors (RES). Therefore, by employing this detection principle (SI) together with RES measurements, better selectivity than that observed in standard metal oxide sensors could be demonstrated. Simplicity and specificity of the gas detection as well as low-power consumption make these single nanowire devices promising technological alternatives to overcome the major drawbacks of solid-state sensor technologies.

  17. [Development of a membrane inlet-single photon ionization/chemical ionization-mass spectrometer for online analysis of VOCs in water].

    PubMed

    Hua, Lei; Wu, Qing-Hao; Hou, Ke-Yong; Cui, Hua-Peng; Chen, Ping; Zhao, Wu-Duo; Xie, Yuan-Yuan; Li, Hai-Yang

    2011-12-01

    A home-made membrane inlet- single photon ionization/chemical ionization- time-of-flight mass spectrometer has been described. A vacuum ultraviolet (VUV) lamp with photon energy of 10.6 eV was used as the light source for single photon ionization (SPI). Chemical ionization (CI) was achieved through ion-molecule reactions with O2- reactant ions generated by photoelectron ionization. The two ionization modes could be rapidly switched by adjusting electric field in the ionization region within 2 s. Membrane inlet system used for rapid enrichment of volatile organic compounds (VOCs) in water was constructed by using a polydimethylsiloxane (PDMS) membrane with a thickness of 50 microm. A purge gas was added to accelerate desorption of analytes from the membrane surface. The purge gas could also help to prevent the pump oil back-streaming into the ionization region from the analyzer chamber and improve the signal to noise ratio (S/N). Achieved detection limits were 2 microg x L(-1) for methyl tert-butyl ether (MTBE) in SPI mode and 1 microg x L(-1) for chloroform in SPI-CI mode within 10 s analysis time, respectively. The instrument has been successfully applied to the rapid analysis of MTBE in simulated underground water nearby petrol station and VOCs in disinfected drinking water. The results indicate that the instrument has a great application prospect for online analysis of VOCs in water.

  18. The interaction of an ionizing ligand with enzymes having a single ionizing group. Implications for the reaction of folate analogues with dihydrofolate reductase.

    PubMed

    Stone, S R; Morrison, J F

    1983-06-29

    Binding theory has been developed for the reaction of an ionizing enzyme with an ionizing ligand. Consideration has been given to the most general scheme in which all possible reactions and interconversions occur as well as to schemes in which certain interactions do not take place. Equations have been derived in terms of the variation of the apparent dissociation constant (Kiapp) as a function of pH. These equations indicate that plots of pKiapp against pH can be wave-, half-bell- or bell-shaped according to the reactions involved. A wave is obtained whenever there is formation of the enzyme-ligand complexes, ionized enzyme . ionized ligand and protonated enzyme . protonated ligand. The additional formation of singly protonated enzyme-ligand complexes does not affect the wave form of the plot, but can influence the shape of the overall curve. The formation of either ionized enzyme . ionized ligand or protonated enzyme . protonated ligand, with or without singly protonated enzyme-ligand species, gives rise to a half-bell-shaped plot. If only singly protonated enzyme-ligand complexes are formed the plots are bell-shaped, but it is not possible to deduce the ionic forms of the reactants that participate in complex formation. Depending on the reaction pathways, true values for the ionization and dissociation constants may or may not be determined.

  19. Full hyperfine structure analysis of singly ionized molybdenum

    NASA Astrophysics Data System (ADS)

    Bouazza, Safa

    2017-03-01

    For a first time a parametric study of hyperfine structure of Mo II configuration levels is presented. The newly measured A and B hyperfine structure (hfs) constants values of Mo II 4d5, 4d45s and 4d35s2 configuration levels, for both 95 and 97 isotopes, using Fast-ion-beam laser-induced fluorescence spectroscopy [1] are gathered with other few data available in literature. A fitting procedure of an isolated set of these three lowest even-parity configuration levels has been performed by taking into account second-order of perturbation theory including the effects of closed shell-open shell excitations. Moreover the same study was done for Mo II odd-parity levels; for both parities two sets of fine structure parameters as well as the leading eigenvector percentages of levels and Landé-factor gJ, relevant for this paper are given. We present also predicted singlet, triplet and quintet positions of missing experimental levels up to 85000 cm-1. The single-electron hfs parameter values were extracted in their entirety for 97Mo II and for 95Mo II: for instance for 95Mo II, a4d01 =-133.37 MHz and a5p01 =-160.25 MHz for 4d45p; a4d01 =-140.84 MHz, a5p01 =-170.18 MHz and a5s10 =-2898 MHz for 4d35s5p; a5s10 =-2529 (2) MHz and a4d01 =-135.17 (0.44) MHz for the 4d45s. These parameter values were analysed and compared with diverse ab-initio calculations. We closed this work with giving predicted values of magnetic dipole and electric quadrupole hfs constants of all known levels, whose splitting are not yet measured.

  20. Frustrated double and single ionization in a two-electron triatomic molecule H+ 3

    NASA Astrophysics Data System (ADS)

    Chen, A.; Lazarou, C.; Price, H.; Emmanouilidou, A.

    2016-12-01

    Using a semi-classical model, we study the formation of highly excited neutral fragments during the fragmentation of {{{H}}}3+, a two-electron triatomic molecule, driven by an intense near-IR laser field. To do so, we first formulate a microcanonical distribution for arbitrary one-electron triatomic molecules. We then study frustrated double and single ionization in strongly driven {{{H}}}3+ and compute the kinetic energy release of the nuclei for these two processes. Moreover, we investigate the dependence of frustrated ionization on the strength of the laser field as well as on the geometry of the initial molecular state.

  1. Feasibility of coherent xuv spectroscopy on the 1S-2S transition in singly ionized helium

    SciTech Connect

    Herrmann, M.; Saathoff, G.; Gohle, C.; Ozawa, A.; Batteiger, V.; Knuenz, S.; Kolachevsky, N.; Udem, Th.; Haas, M.; Jentschura, U. D.; Kottmann, F.; Leibfried, D.; Schuessler, H. A.; Haensch, T. W.

    2009-05-15

    The 1S-2S two-photon transition in singly ionized helium is a highly interesting candidate for precision tests of bound-state quantum electrodynamics (QED). With the recent advent of extreme ultraviolet frequency combs, highly coherent quasi-continuous-wave light sources at 61 nm have become available, and precision spectroscopy of this transition now comes into reach for the first time. We discuss quantitatively the feasibility of such an experiment by analyzing excitation and ionization rates, propose an experimental scheme, and explore the potential for QED tests.

  2. On the intermolecular Coulombic decay of singly and doubly ionized states of water dimer.

    PubMed

    Stoychev, Spas D; Kuleff, Alexander I; Cederbaum, Lorenz S

    2010-10-21

    A semiquantitative study of the intermolecular Coulombic decay (ICD) of singly and doubly ionized water dimer has been carried out with the help of ab initio computed ionization spectra and potential energy curves (PECs). These PECs are particular cuts through the (H(2)O)(2), (H(2)O)(2) (+), and (H(2)O)(2) (++) hypersurfaces along the distance between the two oxygen atoms. A comparison with the recently published experimental data for the ICD in singly ionized water dimers [T. Jahnke, H. Sann, T. Havermeier et al., Nat. Phys. 6, 139 (2010)] and in large water clusters [M. Mucke, M. Braune, S. Barth et al., Nat. Phys. 6, 143 (2010)] shows that such a simplified description in which the internal degrees of freedom of the water molecules are frozen gives surprisingly useful results. Other possible decay channels of the singly ionized water dimer are also investigated and the influence of the H-atom participating in the hydrogen bond on the spectra of the proton-donor and proton-acceptor molecules in the dimer is discussed. Importantly, the decay processes of one-site dicationic states of water dimer are discussed and an estimate of the ICD-electron spectra is made. More than 33% of the dications produced by Auger decay are found to undergo ICD. The qualitative results show that the ICD following Auger decay in water is also expected to be an additional source of low-energy electrons proven to be extremely important for causing damages to living tissues.

  3. Charge trapping in aligned single-walled carbon nanotube arrays induced by ionizing radiation exposure

    SciTech Connect

    Esqueda, Ivan S.; Cress, Cory D.; Che, Yuchi; Cao, Yu; Zhou, Chongwu

    2014-02-07

    The effects of near-interfacial trapping induced by ionizing radiation exposure of aligned single-walled carbon nanotube (SWCNT) arrays are investigated via measurements of gate hysteresis in the transfer characteristics of aligned SWCNT field-effect transistors. Gate hysteresis is attributed to charge injection (i.e., trapping) from the SWCNTs into radiation-induced traps in regions near the SWCNT/dielectric interface. Self-consistent calculations of surface-potential, carrier density, and trapped charge are used to describe hysteresis as a function of ionizing radiation exposure. Hysteresis width (h) and its dependence on gate sweep range are investigated analytically. The effects of non-uniform trap energy distributions on the relationship between hysteresis, gate sweep range, and total ionizing dose are demonstrated with simulations and verified experimentally.

  4. Photon Energy Deposition in Strong-Field Single Ionization of Multielectron Molecules.

    PubMed

    Zhang, Wenbin; Li, Zhichao; Lu, Peifen; Gong, Xiaochun; Song, Qiying; Ji, Qinying; Lin, Kang; Ma, Junyang; He, Feng; Zeng, Heping; Wu, Jian

    2016-09-02

    Molecules exposed to strong laser fields may coherently absorb multiple photons and deposit the energy into electrons and nuclei, triggering the succeeding dynamics as the primary stage of the light-molecule interaction. We experimentally explore the electron-nuclear sharing of the absorbed photon energy in above-threshold multiphoton single ionization of multielectron molecules. Using CO as a prototype, vibrational and orbital resolved electron-nuclear sharing of the photon energy is observed. Different from the simplest one- or two-electron systems, the participation of the multiple orbitals and the coupling of various electronic states in the strong-field ionization and dissociation processes alter the photon energy deposition dynamics of the multielectron molecule. The population of numerous vibrational states of the molecular cation as the energy reservoir in the ionization process plays an important role in photon energy sharing between the emitted electron and the nuclear fragments.

  5. Comparison of experimental and theoretical electron-impact-ionization triple-differential cross sections for ethane

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Nixon, Kate; Murray, Andrew; Ning, Chuangang; Colgan, James; Madison, Don

    2015-10-01

    We have recently examined electron-impact ionization of molecules that have one large atom at the center, surrounded by H nuclei (H2O , N H3 , C H4 ). All of these molecules have ten electrons; however, they vary in their molecular symmetry. We found that the triple-differential cross sections (TDCSs) for the highest occupied molecular orbitals (HOMOs) were similar, as was the character of the HOMO orbitals which had a p -type "peanut" shape. In this work, we examine ethane (C2H6 ) which is a molecule that has two large atoms surrounded by H nuclei, so that its HOMO has a double-peanut shape. The experiment was performed using a coplanar symmetric geometry (equal final-state energies and angles). We find the TDCS for ethane is similar to the single-center molecules at higher energies, and is similar to a diatomic molecule at lower energies.

  6. Strong molecular alignment dependence of H2 electron impact ionization dynamics.

    PubMed

    Ren, X; Pflüger, T; Xu, S; Colgan, J; Pindzola, M S; Senftleben, A; Ullrich, J; Dorn, A

    2012-09-21

    Low-energy (E(0) = 54 eV) electron impact single ionization of molecular hydrogen (H(2)) has been investigated as a function of molecular alignment in order to benchmark recent theoretical predictions [Colgan et al., Phys. Rev. Lett. 101, 233201 (2008) and Al-Hagan et al., Nature Phys. 5, 59 (2009)]. In contrast to any previous work, we observe distinct alignment dependence of the (e,2e) cross sections in the perpendicular plane in good overall agreement with results from time-dependent close-coupling calculations. The cross section behavior can be consistently explained by a rescattering of the ejected electron in the molecular potential resulting in an effective focusing along the molecular axis.

  7. Strong Molecular Alignment Dependence of H2 Electron Impact Ionization Dynamics

    NASA Astrophysics Data System (ADS)

    Ren, X.; Pflüger, T.; Xu, S.; Colgan, J.; Pindzola, M. S.; Senftleben, A.; Ullrich, J.; Dorn, A.

    2012-09-01

    Low-energy (E0=54eV) electron impact single ionization of molecular hydrogen (H2) has been investigated as a function of molecular alignment in order to benchmark recent theoretical predictions [Colgan , Phys. Rev. Lett.PRLTAO0031-9007 101, 233201 (2008)10.1103/PhysRevLett.101.233201 and Al-Hagan , Nature Phys.NPAHAX1745-2473 5, 59 (2009)10.1038/nphys1135]. In contrast to any previous work, we observe distinct alignment dependence of the (e,2e) cross sections in the perpendicular plane in good overall agreement with results from time-dependent close-coupling calculations. The cross section behavior can be consistently explained by a rescattering of the ejected electron in the molecular potential resulting in an effective focusing along the molecular axis.

  8. Scaling Cross Sections for Ion-atom Impact Ionization

    SciTech Connect

    Igor D. Kaganovich; Edward Startsev; Ronald C. Davidson

    2003-06-06

    The values of ion-atom ionization cross sections are frequently needed for many applications that utilize the propagation of fast ions through matter. When experimental data and theoretical calculations are not available, approximate formulas are frequently used. This paper briefly summarizes the most important theoretical results and approaches to cross section calculations in order to place the discussion in historical perspective and offer a concise introduction to the topic. Based on experimental data and theoretical predictions, a new fit for ionization cross sections is proposed. The range of validity and accuracy of several frequently used approximations (classical trajectory, the Born approximation, and so forth) are discussed using, as examples, the ionization cross sections of hydrogen and helium atoms by various fully stripped ions.

  9. Electron impact ionization of Io's sodium emission cloud

    NASA Technical Reports Server (NTRS)

    Carlson, R. W.; Matson, D. L.; Johnson, T. V.

    1975-01-01

    The geometry of the sodium cloud associated with Io (Jupiter I) indicates that the lifetime of the neutral sodium atoms is an order of magnitude less than the photoionization lifetime. We suggest that ionization by thermal plasma electrons in the Jovian magnetosphere is the dominant Na loss process. Using plasma densities deduced from Pioneer 10 measurements, the lifetime and density distributions are calculated for Na and other species which may be present in the cloud around Io. Electron ionization of Na is found to be an order of magnitude faster than photoionization, in agreement with the lifetime deduced from Na cloud observations.

  10. Electron Impact Ionization Cross Sections of n-decane

    NASA Astrophysics Data System (ADS)

    Jiao, Charles; Dejoseph, Charles; Garscadden, Alan

    2001-10-01

    The ionization and dissociation of hydrocarbon fuels with various plasma excitation schemes including pulsed high E/n discharges have been proposed to alleviate the problem of ignition in supersonic flow combustors and operations at high altitudes. The fuel which is also used for cooling, must not pyrolyse at operational temperatures. We have examined the electron ionization collision processes in n-decane using high resolution Fourier transform mass spectrometry that permits measurements of the 24 ions with cross sections larger than 10-19cm2. These generally fall into two broad categories: those with five or more carbon atoms whose ionization cross sections rise rapidly and essentially saturate within twice the appearance potential and those with four carbon atoms and less whose cross sections rise more gradually and are only saturating at energies above 70 eV. The total ionization cross section is large, rising to 7x10-16cm2. Studies were made with deuterated samples to distinguish the potential mechanisms in fragment ion induced dissociation of the parent gas. The results are compared with similar data for octane.

  11. Electron-Impact Excitation and Ionization in Air

    DTIC Science & Technology

    2009-09-01

    also exist in other disciplines dealing with plasma, including astrophysics , fusion science, plasma processing in microelectronics, etc. While the...cross sections, and ionization fractions for astrophysically abundant elements. I. Carbon and nitrogen,” The Astrophysical Journal Supplement Series Vol

  12. Evidence for unnatural-parity contributions to electron-impact ionization of laser-aligned atoms

    SciTech Connect

    Armstrong, Gregory S. J.; Colgan, James Patrick; Pindzola, M. S.; Amami, S.; Madison, D. H.; Pursehouse, J.; Nixon, K. L.; Murray, A. J.

    2015-09-11

    Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this paper we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. Finally, we demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionization from excited Ca and Na atoms.

  13. Observation of two-center interference effects for electron impact ionization of N2

    NASA Astrophysics Data System (ADS)

    Chaluvadi, Hari; Nur Ozer, Zehra; Dogan, Mevlut; Ning, Chuangang; Colgan, James; Madison, Don

    2015-08-01

    In 1966, Cohen and Fano (1966 Phys. Rev. 150 30) suggested that one should be able to observe the equivalent of Young’s double slit interference if the double slits were replaced by a diatomic molecule. This suggestion inspired many experimental and theoretical studies searching for double slit interference effects both for photon and particle ionization of diatomic molecules. These effects turned out to be so small for particle ionization that this work proceeded slowly and evidence for interference effects were only found by looking at cross section ratios. Most of the early particle work concentrated on double differential cross sections for heavy particle scattering and the first evidence for two-center interference for electron-impact triple differential cross section (TDCS) did not appear until 2006 for ionization of H2. Subsequent work has now firmly established that two-center interference effects can be seen in the TDCS for electron-impact ionization of H2. However, in spite of several experimental and theoretical studies, similar effects have not been found for electron-impact ionization of N2. Here we report the first evidence for two-center interference for electron-impact ionization of N2.

  14. Electron impact ionization rates for interstellar neutral H and He atoms near interplanetary shocks: Ulysses observations

    NASA Technical Reports Server (NTRS)

    Feldman, W. C.; Phillips, J. L.; Gosling, J. T.; Isenberg, P. A.

    1995-01-01

    During average solar wind flow conditions at 1 AU, ionization rates of interstellar neutrals that penetrate into the inner heliosphere are dominated by charge exchange with solar wind protons for H atoms, and by photoionization for He atoms. During occurrences of strong, coronal mass ejection (CME)-driven interplanetary shock waves near 1 AU, electron impact ionization can make substantial, if not dominating, contributions to interstellar neutral ionization rates in the regions downstream of the shocks. However, electron impact ionization is expected to be relatively less important with increasing heliocentric distance because of the decrease in electron temperature. Ulysses encountered many CME-driven shocks during its journey to and beyond Jupiter, and in addition, encountered a number of strong corotating interaction region (CIR) shocks. These shocks generally occur only beyond approximately 2 AU. Many of the CIR shocks were very strong rivalling the Earth's bow shock in electron heating. We have compared electron impact ionization rates calculated from electron velocity distributions measured downstream from CIR shocks using the Ulysses SWOOPS experiment to charge-exchange rates calculated from measured proton number fluxes and the photoionization rate estimated from an assumed solar photon spectrum typical of solar maximum conditions. We find that, although normally the ratio of electron-impact ionization rates to charge-exchange (for H) and to photoionization (for He) rates amounts to only about one and a few tens of percent, respectively, downstream of some of the stronger CIR shocks they amount to more than 10% and greater than 100%, respectively.

  15. Hyperfine structure and isotope shifts of transitions in neutral and singly ionized ytterbium

    NASA Technical Reports Server (NTRS)

    Berends, R. W.; Maleki, L.

    1992-01-01

    The present experimental investigation of the hyperfine structure and isotopic shifts of transitions in neutral and singly-ionized Yb, which constitute a system of some interest to microwave-frequency standards, used counterpropagating pump and probe laser beams directed through a hollow-cathode discharge lamp. The results obtained are in agreement with previous measurements except in the case of the Yb-173(+) 6 2P0 sub 3/2 state, which is more accurately determined.

  16. [Real-time analysis of polyvinyl chloride thermal decomposition/combustion products with single photon ionization/photoelectron ionization online mass spectrometer].

    PubMed

    Chen, Wen-Dong; Hou, Ke-Yong; Chen, Ping; Li, Fang-Long; Zhao, Wu-Duo; Cui, Hua-Peng; Hua, Lei; Xie, Yuan-Yuan; Li, Hai-Yang

    2013-01-01

    With the features of a broad range of ionizable compounds, reduced fragments and simple mass spectrum, a homemade magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) for time-of-flight mass spectrometer was built and applied to analyze thermal decomposition/combustion products of polyvinyl chloride (PVC). The combined ion source can be switched very fast between SPI mode and SPI-MEPEI mode for detecting different targeted compounds, and only adjusting the voltage of the electrode in the ionization region to trigger the switch. Among the PVC thermal decomposition/combustion products, HCl and CO2, which ionization energies (12.74 eV, 13.77 eV respectively) were higher than the energy of photon (10.60 eV), were ionized by MEPEI, while alkenes, dichloroethylene, benzene and its homologs, monochlorobenzene, styrene, indane, naphthalene and its homologs were ionized by SPI and MEPEI simultaneously. Spectra of interested products as a function of temperatures indicated that products are formed via two main mechanisms: (1) dechlorination and intramolecular cyclization can lead to the formation of HCl, benzene and naphthalene at 250-370 degrees C; (2) intermolecular crosslinking leads to the formation of alkyl aromatics such as toluene and xylene/ethylbenzene at 380-510 degrees C. The experimental results show that the combined ion source of SPI/ SPI-MEPEI for TOF-MS has broad application prospects in the online analysis field.

  17. Consultative committee on ionizing radiation: Impact on radionuclide metrology.

    PubMed

    Karam, L R; Ratel, G

    2016-03-01

    In response to the CIPM MRA, and to improve radioactivity measurements in the face of advancing technologies, the CIPM's consultative committee on ionizing radiation developed a strategic approach to the realization and validation of measurement traceability for radionuclide metrology. As a consequence, measurement institutions throughout the world have devoted no small effort to establish radionuclide metrology capabilities, supported by active quality management systems and validated through prioritized participation in international comparisons, providing a varied stakeholder community with measurement confidence.

  18. Consultative Committee on Ionizing Radiation: Impact on Radionuclide Metrology

    PubMed Central

    Karam, L.R.; Ratel, G.

    2016-01-01

    In response to the CIPM MRA, and to improve radioactivity measurements in the face of advancing technologies, the CIPM’s consultative committee on ionizing radiation developed a strategic approach to the realization and validation of measurement traceability for radionuclide metrology. As a consequence, measurement institutions throughout the world have devoted no small effort to establish radionuclide metrology capabilities, supported by active quality management systems and validated through prioritized participation in international comparisons, providing a varied stakeholder community with measurement confidence. PMID:26688351

  19. All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry.

    PubMed

    Yuan, Chengqian; Liu, Xianhu; Zeng, Chenghui; Zhang, Hanyu; Jia, Meiye; Wu, Yishi; Luo, Zhixun; Fu, Hongbing; Yao, Jiannian

    2016-02-01

    We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.

  20. All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Yuan, Chengqian; Liu, Xianhu; Zeng, Chenghui; Zhang, Hanyu; Jia, Meiye; Wu, Yishi; Luo, Zhixun; Fu, Hongbing; Yao, Jiannian

    2016-02-01

    We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ˜15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.

  1. Use of the Bethe equation for inner-shell ionization by electron impact

    NASA Astrophysics Data System (ADS)

    Powell, Cedric J.; Llovet, Xavier; Salvat, Francesc

    2016-05-01

    We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, L3-subshell ionization cross sections for Xe, and M-shell ionization cross sections for three elements. The validity (or otherwise) of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti [in Electron Impact Ionization, edited by T. D. Märk and G. H. Dunn, (Springer-Verlag, Vienna, 1985), Chap. 7, pp. 232-276]. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used.

  2. Electron-Impact Total Ionization Cross Sections of CH and C2H2

    PubMed Central

    Kim, Yong-Ki; Ali, M. Asgar; Rudd, M. Eugene

    1997-01-01

    Electron-impact total ionization cross sections for the CH radical and C2H2 (acetylene) have been calculated using the Binary-Encounter-Bethe (BEB) model. The BEB model combines the Mott cross section and the asymptotic form of the Bethe theory, and has been shown to generate reliable ionization cross sections for a large variety of molecules. The BEB cross sections for CH and C2H2 are in good agreement with the available experimental data from ionization thresholds to hundreds of eV in incident energies. PMID:27805116

  3. Electron Impact Ionization Cross Sections in Rb and Cs.

    NASA Astrophysics Data System (ADS)

    Reddish, T. J.; Lukomski, M.; Sutton, S.; Kedzierski, W.; McConkey, J. W.; Bartschat, K.; Bartlett, P. L.; Stelbovics, A. T.; Bray, I.

    2006-05-01

    We present a new atom trapping technique for determining absolute, total ionisation cross sections (TICS) out of an excited atom. The novel feature of this method is in utilizing Doppler cooling of neutral atoms to determine ionisation cross sections. This fluorescence-monitoring experiment, which is a variant of the `trap loss' technique, has enabled us to obtain the experimental electron impact ionisation cross sections out of the Cs 6^2P3/2 excited state between 7 - 400 eV. New CCC, R-Matrix with Pseudo-States (RMPS), and Born approximation single ionisation cross sections (SICS) are also presented for both the ground and excited states of Cs and Rb, and compared with the available experimental data. The comparison of the results reveals the importance of the autoionisation and multiple ionisation contributions to the TICS. The autoionisation contribution appears to be substantial for ionisation out of the Cs 6^2P and Rb 5^2P excited states; ˜ 3-4 larger than the direct ionisation contribution predicted by CCC at ˜ 30-50 eV. This surprising result shows the importance of multi-electron processes in determining the ionisation cross sections of heavy alkali atoms.

  4. Second-order Born approximation for the ionization of molecules by electron and positron impact

    SciTech Connect

    Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.

    2011-09-15

    Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.

  5. Light-particle single ionization of argon: Influence of the projectile charge sign

    SciTech Connect

    Otranto, S.; Olson, R. E.

    2009-07-15

    The ionization of the 3p orbital of argon by incident electrons and positrons is studied by means of the post version of the continuum distorted wave-eikonal initial-state model. Results are presented at both 200 and 500 eV impact energies for conditions amenable to present experiments. Differences in the fully differential cross sections (FDCSs) are analyzed and the influence of the projectile charge sign on the emission dynamics is discussed. The FDCSs are found to display the classic binary plus recoil peak structure at 500 eV, but transition to a more complicated four-lobed structure at the lower impact energy.

  6. Absolute partial and total electron-impact-ionization cross sections for CF4 from threshold up to 500 eV

    NASA Astrophysics Data System (ADS)

    Ma, Ce; Bruce, M. R.; Bonham, R. A.

    1991-09-01

    Electron-impact dissociative ionization of tetrafluoromethane (CF4) was studied with the use of a pulsed electron beam time-of-flight apparatus. The absolute partial ionization cross sections of CF+3, CF+2, CF2+3, CF+, CF2+2, F+, and C+ were measured from threshold up to 500 eV. The total ionization cross section was obtained by charge weighted summing of all the observed partial ionization cross sections. A total cross section for dissociation into neutral fragments was inferred from our total ionization cross section and the total dissociation cross section of Winters and Inokuti [Phys. Rev. A 25, 1420 (1982)]. The present results for the partial ionization cross sections are as much as 9% (CF+3) to 81% (F+) higher than the previously published absolute measurements of Stephan, Deutsch, and Märk [J. Chem. Phys. 83, 5712 (1985)] at 80 eV, but are in agreement with their recently revised estimates for the singly charged ions. We also found that dissociative ionization was a dominant process for electron-impact energies above 30 eV, accounting for 85% of the total dissociation cross section at 80 eV.

  7. Nanophotonic ionization for ultratrace and single-cell analysis by mass spectrometry.

    PubMed

    Walker, Bennett N; Stolee, Jessica A; Vertes, Akos

    2012-09-18

    Recent mechanistic studies have indicated that at subwavelength post diameters and selected aspect ratios nanopost arrays (NAPA) exhibit ion yield resonances ( Walker , B. N. , Stolee , J. A. , Pickel , D. L. , Retterer , S. T. , and Vertes , A. J. Phys. Chem. C 2010 , 114 , 4835 - 4840 ). In this contribution we explore the analytical utility of these optimized structures as matrix-free platforms for laser desorption ionization mass spectrometry (LDI-MS). Using NAPA, we show that high ionization efficiencies enable the detection of ultratrace amounts of analytes (e.g., ∼800 zmol of verapamil) with a dynamic range spanning up to 4 orders of magnitude. Due to the clean nanofabrication process and the lack of matrix material, minimal background interferences are present in the low-mass range. We demonstrate that LDI from NAPA ionizes a broad class of small molecules including pharmaceuticals, natural products, metabolites, and explosives. Quantitation of resveratrol in red wine samples shows that the analysis of targeted analytes in complex mixtures is feasible with minimal sample preparation using NAPA-based LDI. We also describe how multiple metabolite species can be directly detected in single yeast cells deposited on the NAPA chip. Twenty-four metabolites, or 4% of the yeast metabolome, were identified in the single-cell spectra.

  8. Characterization of breakdown behavior of diamond Schottky barrier diodes using impact ionization coefficients

    NASA Astrophysics Data System (ADS)

    Driche, Khaled; Umezawa, Hitoshi; Rouger, Nicolas; Chicot, Gauthier; Gheeraert, Etienne

    2017-04-01

    Diamond has the advantage of having an exceptionally high critical electric field owing to its large band gap, which implies its high ability to withstand high voltages. At this maximum electric field, the operation of Schottky barrier diodes (SBDs), as well as FETs, may be limited by impact ionization, leading to avalanche multiplication, and hence the devices may breakdown. In this study, three of the reported impact ionization coefficients for electrons, αn, and holes, αp, in diamond at room temperature (300 K) are analyzed. Experimental data on reverse operation characteristics obtained from two different diamond SBDs are compared with those obtained from their corresponding simulated structures. Owing to the crucial role played by the impact ionization rate in determining the carrier transport, the three reported avalanche parameters implemented affect the behavior not only of the breakdown voltage but also of the leakage current for the same structure.

  9. Calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-12-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the {(2s2p)}3P and {(2s2p)}1P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.

  10. Electron-impact total ionization cross sections of DNA sugar-phosphate backbone and an additivity principle

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Dateo, Christopher E.

    2005-01-01

    The improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64, 042719-1 (2001)l is used to study the total ionization cross sections of the DNA sugar-phosphate backbone by electron impact. Calculations using neutral fragments found that the total ionization cross sections of C3' - and C5', -deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3' - and C5" -deoxyribose-phospate cross sections, differing by less than 10%. The result implies that certain properties of the-DNA, like the total singly ionization cross section, are localized properties and a building-up or additivity principle may apply. This allows us to obtain accurate properties of larger molecular systems built up from the results of smaller subsystem fragments. Calculations are underway using a negatively charged sugar-phosphate backbone with a metal counter-ion.

  11. Superelastic rescattering in single ionization of helium in strong laser fields

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Chao; Jaron-Becker, Agnieszka; He, Feng

    2016-10-01

    Rescattering is a central process in ultrafast physics, in which an electron, freed from an atom and accelerated by a laser field, loses its energy by producing high-order harmonics or multiple ionization. Here, taking helium as a prototypical atom, we demonstrate numerically superelastic rescattering in single ionization of an atom. In this scenario, the absorption of a high-energy extreme ultraviolet photon leads to emission of one electron and excitation of the second one into its first excited state, forming He+*. A time-delayed midinfrared laser pulse accelerates the freed electron, drives it back to the He+*, and induces the transition of the bound electron to the ground state of the ion. Identification of the superelastic rescattering process in the photoelectron momentum spectra provides a means to determine the photoelectron momentum at the time of rescattering without using any information of the time-delayed probe laser pulse.

  12. Detection of singly ionized energetic lunar pick-up ions upstream of earth's bow shock

    NASA Technical Reports Server (NTRS)

    Hilchenbach, M.; Hovestadt, D.; Klecker, B.; Moebius, E.

    1992-01-01

    Singly ionized suprathermal ions upstream of the earth's bow shock have been detected by using the time-of-flight spectrometer SULEICA on the AMPTE/IRM satellite. The data were collected between August and December 1985. The flux of the ions in the mass range between 23 and 37 amu is highly anisotropic towards the earth. The ions are observed with a period of about 29 days around new moon (+/- 3 days). The correlation of the energy of the ions with the solar wind speed and the interplanetary magnetic field orientation indicates the relation to the pick-up process. We conclude that the source of these pick-up ions is the moon. We argue that due to the impinging solar wind, atoms are sputtered off the lunar surface, ionized in the sputtering process or by ensuing photoionization and picked up by the solar wind.

  13. EXTENDED ANALYSIS OF THE SPECTRUM OF SINGLY IONIZED CHROMIUM (Cr II)

    SciTech Connect

    Sansonetti, Craig J.; Nave, Gillian

    2014-08-01

    We have made new observations of the spectrum of singly ionized chromium (Cr II) in the region 2850-37900 Å with the National Institute of Standards and Technology 2 m Fourier transform spectrometer. These data extend our previously reported observations in the near-ultra-violet region. We present a comprehensive list of more than 5300 Cr II lines classified as transitions among 456 even and 457 odd levels, 179 of which are newly located in this work. Using highly excited levels of the 3d {sup 4}({sup 5} D)5g, 3d {sup 4}({sup 5} D)6g, and 3d {sup 4}({sup 5}D)6h configurations, we derive an improved ionization energy of 132971.02 ± 0.12 cm{sup –1} (16.486305 ± 0.000015 eV)

  14. Extended Analysis of the Spectrum of Singly Ionized Chromium (Cr II)

    NASA Astrophysics Data System (ADS)

    Sansonetti, Craig J.; Nave, Gillian

    2014-08-01

    We have made new observations of the spectrum of singly ionized chromium (Cr II) in the region 2850-37900 Å with the National Institute of Standards and Technology 2 m Fourier transform spectrometer. These data extend our previously reported observations in the near-ultra-violet region. We present a comprehensive list of more than 5300 Cr II lines classified as transitions among 456 even and 457 odd levels, 179 of which are newly located in this work. Using highly excited levels of the 3d 4(5 D)5g, 3d 4(5 D)6g, and 3d 4(5D)6h configurations, we derive an improved ionization energy of 132971.02 ± 0.12 cm-1 (16.486305 ± 0.000015 eV).

  15. Near-threshold electron-impact doubly differential cross sections for the ionization of argon and krypton

    SciTech Connect

    Yates, Brent R.; Khakoo, Murtadha A.

    2011-04-15

    We present normalized doubly differential cross sections (DDCS's) for the near-threshold, electron-impact single ionization of argon and krypton, similar to those taken earlier for Ne and Xe [Yates et al., J. Phys. B 42, 095206 (2009)]. The Ar measurements were taken at incident energies of 17, 18, 20, and 30 eV while the Kr measurements were taken at 15, 16, 17.5, and 20 eV. The DDCS scattering angles range from 15 deg. to 120 deg. The differential data are initially normalized to available experimental cross sections for excitation of the ground np{sup 6} to the np{sup 5}(n+1)s excited states of the noble gas and, after integration, to well-established experimental total ionization cross sections of Rapp and Englander-Golden [J. Chem. Phys. 43, 1464 (1965)].

  16. Electron Impact Ionization cross sections and rate coefficients for α-tetra hydro furfuryl alcohol

    NASA Astrophysics Data System (ADS)

    Kumar, Neeraj; Pal, Satyendra

    2013-09-01

    α - tetrahydrofurfuryl alcohol (THFA; C5H10O2) is an aromatic compound having the molecular structure similar to that of 2-deoxy-D-ribose (deoxyribose). This molecule has attracted enormous interest in the field of research because its electron charge cloud possesses a quite significant spatial extent (dipole polarizability, α = 70.18 au) and has a relatively strong permanent dipole moment (μ ~ 2D). In the present work, we have extended and generalized the modified Jain-Khare semi-empirical formalism for the evaluation of the total ionization cross sections corresponding to the formation of the cations in the electron impact ionization of molecules to the electron impact ionization of α-tetrahydrofurfuryl alcohol (THFA; C5H10O2) , in the energy range varying from ionization threshold to 1000 eV. The evaluated cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. We have also calculated the ionization rate coefficients as a function of electron energy, using the evaluated total ionization cross sections and the Maxwell-Boltzmann distribution.

  17. Electron-impact-ionization dynamics of five C2 to C4 perfluorocarbons

    NASA Astrophysics Data System (ADS)

    Bull, James N.; Bart, Mark; Vallance, Claire; Harland, Peter W.

    2013-12-01

    Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for the fragments arising from five C2 to C4 PFCs, namely, C2F6, C3F8, C3F6, CF2=CF-CF=CF2, and CF3-C≡C-CF3, over the energy range from threshold to ˜210 eV. Care was taken to maximize ion collection efficiency and to minimize discrimination against ions produced with high kinetic-energy release, and the measured cross sections have been calibrated using independent absolute total (gross) ionization efficiency curves measured previously in the same laboratory with an instrument that was designed to essentially have unit detection efficiency. Total ionization cross sections have also been modeled using the binary-encounter Bethe model, and the shortcomings of the model when applied to perfluorinated compounds are discussed. Analysis of the mass spectral fragmentation patterns in combination with ab initio energetics suggests that nonstatistical dissociative ionization processes play a significant role in the fragmentation dynamics of saturated PFCs. In contrast, unsaturated PFCs exhibit long-lived parent ions, which tend to undergo a higher degree of statistical dissociation following ionization, involving considerable intramolecular rearrangement.

  18. Evidence for unnatural-parity contributions to electron-impact ionization of laser-aligned atoms

    DOE PAGES

    Armstrong, Gregory S. J.; Colgan, James Patrick; Pindzola, M. S.; ...

    2015-09-11

    Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this paper we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. Finally, we demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionizationmore » from excited Ca and Na atoms.« less

  19. Electron-impact ionization cross sections out of the ground and excited states of cesium

    SciTech Connect

    Lukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-15

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the 'trap loss' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs state between 7 eV and 400 eV. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11 eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  20. Impact ionization in N-polar AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Uren, M. J.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Keller, S.; Kolluri, S.; Mishra, U. K.

    2014-08-11

    The existence of impact ionization as one of the open questions for GaN device reliability was studied in N-polar AlGaN/GaN high electron mobility transistors. Electroluminescence (EL) imaging and spectroscopy from underneath the device gate contact revealed the presence of hot electrons in excess of the GaN bandgap energy even at moderate on-state bias conditions, enabling impact ionization with hole currents up to several hundreds of pA/mm. The detection of high energy luminescence from hot electrons demonstrates that EL analysis is a highly sensitive tool to study degradation mechanisms in GaN devices.

  1. Multifluid Modeling of the Partially Ionized Chromosphere with Effects of Impact Ionization, Radiative Recombination and Charge Exchange

    NASA Astrophysics Data System (ADS)

    Maneva, Y. G.; Poedts, D. S.; Alvarez Laguna, A.; Lani, A.

    2015-12-01

    Neutrals play an important role in the evolution of the weakly ionized solar chromosphere where the number density of neutrals can vastly exceed the number density of protons. Therefore modeling the neutral-ion interactions and studying the effect of neutrals on the ambient plasma properties is an important task for better understanding the observed emission lines and the propagation of disturbances from the photosphere to the transition region and the corona. To pursue this goal we have developed two-fluid and three-fluid simulation setups to study the interaction between electrons, ions and neutrals in a reactive gravitationally stratified collisional media. The model considers the electrons and ions within the resistive MHD approach with Coulomb collisions and anisotropic heat flux determined by Braginskii's transport coefficients. The electromagnetic fields are evolved according to the full Maxwell equations, allowing for propagation of higher frequency waves neglected by the standard MHD approximation. Separate mass, momentum and energy conservation equations are considered for the neutrals and the interaction between the different fluids is determined by the chemical reactions, such as impact ionization, radiative recombination and charge exchange, provided as additional source terms. To initialize the system we consider an ideal gas equation of state with equal initial temperatures for the electrons, ions and the neutrals and different density profiles. The initial temperature and density profiles are height-dependent and follow VAL C atmospheric model for the solar chromosphere. We have searched for a chemical and collisional equilibrium between the ions and the neutrals in the hydrostatic case to avoid unphysical outflows and artificial heating induced by initial pressure imbalances. Next we consider ion-neutral interactions in magnetized plasma with an initial magnetic profile, corresponding to emerging magnetic funnel. Finally we include an external

  2. Fully differential cross section for single ionization of helium by 1 KeV electrons in the eikonal approximation

    NASA Astrophysics Data System (ADS)

    Dey, R.; Roy, A. C.

    2009-07-01

    We report new results for fully differential cross sections for the single ionization of helium by 1 KeV electron impact at the ejection energy of 10 eV. Investigations have been made for both the scattering and perpendicular planes. The present calculation is based on the eikonal approximation due to Glauber. Here we have also incorporated the effect of classical post collision interaction (PCI) in the Glauber approximation (GA). A comparison is made of the present calculation with the results of other theoretical methods and the recent experiment [M. Dürr, C. Dimopoulou, B. Najjari, A. Dorn, K. Bartschat, I. Bray, D.V. Fursa, Z. Chen, D.H. Madison, J. Ullrich, Phys. Rev. A 77 (2008) 032717]. The Glauber results are in good agreement with the experiment in the scattering plane, but strong discrepancies are observed in the plane perpendicular to it. The effect of PCI is not substantial in the present kinematics.

  3. Measurement and calculation of the Stark-broadening parameters for the resonance lines of singly ionized calcium and magnesium.

    NASA Technical Reports Server (NTRS)

    Jones, W. W.; Sanchez, A.; Greig, J. R.; Griem, H. R.

    1972-01-01

    The electron-impact-broadened profiles of the resonance lines of singly ionized calcium and magnesium have been measured using an electromagnetically driven shock tube and a rapid-scanning Fabry-Perot spectrometer. For an electron density of 10 to the 17th power per cu cm and a temperature of 19,000 K, we found the Lorentzian half-width of the Ca+ line to be 0.086 A plus or minus 10% and of the Mg+ line to be 0.044 A plus or minus 10%. Using the quantum-mechanical theory of Barnes and Peach and our semiclassical calculation for the calcium lines, we found that the temperature dependence of the theoretical curves is close to that measured, although both theories predict actual values which are somewhat large.

  4. Properties of Hollow Molecules Probed by Single-Photon Double Ionization

    SciTech Connect

    Lablanquie, P.; Penent, F.; Palaudoux, J.; Selles, P.; Carniato, S.; Andric, L.; Bucar, K.; Zitnik, M.; Huttula, M.; Eland, J. H. D.; Shigemasa, E.; Soejima, K.; Hikosaka, Y.; Suzuki, I. H.; Nakano, M.; Ito, K.

    2011-02-11

    The formation of hollow molecules (with a completely empty K shell in one constituent atom) through single-photon core double ionization has been demonstrated using a sensitive magnetic bottle experimental technique combined with synchrotron radiation. Detailed properties are presented such as the spectroscopy, formation, and decay dynamics of the N{sub 2}{sup 2+} K{sup -2} main and satellite states and the strong chemical shifts of double K holes on an oxygen atom in CO, CO{sub 2}, and O{sub 2} molecules.

  5. COMPREHENSIVE OBSERVATIONS OF THE ULTRAVIOLET SPECTRUM AND IMPROVED ENERGY LEVELS FOR SINGLY IONIZED CHROMIUM (Cr II)

    SciTech Connect

    Sansonetti, Craig J.; Nave, Gillian; Reader, Joseph; Kerber, Florian

    2012-10-15

    We report new observations of the spectrum of singly ionized chromium (Cr II) in the region 1142-3954 A. The spectra were recorded with the National Institute of Standards and Technology 10.7 m normal-incidence vacuum spectrograph and FT700 vacuum ultraviolet Fourier transform spectrometer. More than 3600 lines are classified as transitions among 283 even and 368 odd levels. The new spectral data are used to re-optimize the energy levels, reducing their uncertainties by a typical factor of 20.

  6. Comprehensive Observations of the Ultraviolet Spectrum and Improved Energy Levels for Singly Ionized Chromium (Cr II)

    NASA Astrophysics Data System (ADS)

    Sansonetti, Craig J.; Nave, Gillian; Reader, Joseph; Kerber, Florian

    2012-10-01

    We report new observations of the spectrum of singly ionized chromium (Cr II) in the region 1142-3954 Å. The spectra were recorded with the National Institute of Standards and Technology 10.7 m normal-incidence vacuum spectrograph and FT700 vacuum ultraviolet Fourier transform spectrometer. More than 3600 lines are classified as transitions among 283 even and 368 odd levels. The new spectral data are used to re-optimize the energy levels, reducing their uncertainties by a typical factor of 20.

  7. Comprehensive Wavelengths, Energy Levels, and Hyperfine Structure Parameters of Singly-Ionized Iron-Group Elements

    NASA Astrophysics Data System (ADS)

    Nave, Gillian

    We propose to measure wavelengths, energy levels, and hyperfine structure parameters of Ni II, Mn II, Sc II and other singly-ionized iron-group elements, covering the wavelength range 80 nm to 5500 nm. We shall use archival data from spectrometers at NIST and Kitt Peak National Observatory for spectra above 140 nm. Additional experimental observations will be taken if needed using Fourier transform spectrometers at NIST. Spectra will be taken using our normal incidence grating spectrograph to provide better sensitivity than the FT spectra and to extend the wavelength range down to 80 nm. We aim to produce a comprehensive description of the spectra of all singly-ionized iron- group elements. The wavelength uncertainty of the strong lines will be better than 1 part in 10^7. For most singly-ionized iron-group elements available laboratory data have uncertainties an order of magnitude larger than astronomical observations over wide spectra ranges. Some of these laboratory measurements date back to the 1960's. Since then, Fourier transform spectroscopy has made significant progress in improving the accuracy and quantity of data in the UV-vis-IR region, but high quality Fourier transform spectra are still needed for Mn II, Ni II and Sc II. Fourier transform spectroscopy has low sensitivity in the VUV region and is limited to wavelengths above 140 nm. Spectra measured with high-resolution grating spectrographs are needed in this region in order to obtain laboratory data of comparable quality to the STIS and COS spectrographs on the Hubble Space Telescope. Currently, such data exist only for Fe II and Cr II. Lines of Sc II, V II, and Mn II show hyperfine structure, but hyperfine structure parameters have been measured for relatively few lines of these elements. Significant errors can occur if hyperfine structure is neglected when abundances are determined from stellar spectra. Measurements of hyperfine structure parameters will be made using Fourier transform spectroscopy

  8. Dynamical orientation effects in atomic ionization by impact of protons and positrons

    NASA Astrophysics Data System (ADS)

    Fregenal, Daniel; Barrachina, Raúl; Bernardi, Guillermo; Suárez, Sergio; Fiol, Juan

    2011-10-01

    Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. This work was partially supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas, Universidad Nacional de Cuyo and Fundacion Balseiro.

  9. Electron-impact excitation and ionization of boron

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-09-01

    We present a comprehensive study of electron collisions with neutral boron atoms. The calculations were performed with the B-Spline R-matrix (close-coupling) method, by employing a parallelized version of the associated computer code. Elastic, momentum-transfer, excitation, and ionization cross sections were obtained for all transitions involving the lowest 11 states of boron, for incident electron energies ranging from threshold to 100 eV. A multi-configuration Hartree-Fock method with non-orthogonal term-dependent orbitals was used to generate accurate wavefunctions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo-states were set up to check the sensitivity of the predictions to variations in the theoretical model. The cross-section dataset generated in this work is expected to be the most accurate one available today and should be sufficiently comprehensive for most modeling applications involving neutral boron. Work supported by the China Scholarship Council and the United States National Science Foundation under grants PHY-1403245 and PHY-1520970, and by the XSEDE allocation PHY-090031.

  10. Molecular Data for a Biochemical Model of DNA Radiation Damage: Electron Impact Ionization and Dissociative Ionization of DNA Bases and Sugar-Phosphate Backbone

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Fletcher, Graham D.

    2004-01-01

    As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of C3'- and C5'-deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3'- and C5'-deoxyribose-phospate cross sections, differing by less than 10%. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-Hl)(+), with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 17.1 eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage.

  11. Impact ionization in quantum well infrared photodetectors with different number of periods

    NASA Astrophysics Data System (ADS)

    Dong, Shan; Li, Ning; Chen, Sihai; Liu, Xihui; Lu, Wei

    2012-02-01

    This paper presents the detailed investigation of the photocurrent accompanied with impact ionization effect in In0.15Ga0.85As/GaAs multiple quantum well infrared photodetectors (QWIPs) with 10 and 50 periods. The sample with 50 periods exhibits remarkable enhancement at high electric field while a negative differential conductivity (NDC) phenomenon is observed in the sample with 10 periods. The enhancement at high electric field is attributed to impact ionization across the conduction-band-edge discontinuity between incident hot electrons and the electrons confined in the wells. The different behavior of these two samples indicates that the length of the multiplication region strongly affects the multiplication factor M. We also measured the photocurrent of GaAs/Al0.15Ga0.85As QWIPs, which do not show an obvious multiplication phenomenon. This is attributed to a different impact ionization coefficient α. A theoretical model of the multiplication factor M varying with impact ionization coefficient α, capture probability pc, and well number N is provided to clarify these phenomena and compared with experimental result.

  12. The impact of ionizing radiation on placental trophoblasts

    PubMed Central

    Kanter, D.J.; O'Brien, M.B.; Shi, X.-H.; Chu, T.; Mishima, T.; Beriwal, S.; Epperly, M.W.; Wipf, P.; Greenberger, J.S.; Sadovsky, Y.

    2014-01-01

    Introduction Exposure to low-dose radiation is widespread and attributable to natural sources. However, occupational, medical, accidental, and terrorist-related exposures remain a significant threat. Information on radiation injury to the feto-placental unit is scant and largely observational. We hypothesized that radiation causes trophoblast injury, and alters the expression of injury-related transcripts in vitro or in vivo, thus affecting fetal growth. Methods Primary human trophoblasts (PHTs), BeWo or NCCIT cells were irradiated in vitro, and cell number and viability were determined. Pregnant C57Bl/6HNsd mice were externally irradiated on E13.5, and placentas examined on E17.5. RNA expression was analyzed using microarrays and RT-qPCR. The experiments were repeated in the presence of the gramicidin S (GS)-derived nitroxide JP4-039, used to mitigate radiation-induced cell injury. Results We found that survival of in vitro–irradiated PHT cell was better than that of irradiated BeWo trophoblast cell line or the radiosensitive NCCIT mixed germ cell tumor line. Radiation altered the expression of several trophoblast genes, with a most dramatic effect on CDKN1A (p21, CIP1). Mice exposed to radiation at E13.5 exhibited a 25% reduction in mean weight by E17.5, and a 9% reduction in placental weight, which was associated with relatively small changes in placental gene expression. JP4-039 had a minimal effect on feto-placental growth or on gene expression in irradiated PHT cells or mouse placenta. Discussion and conclusion While radiation affects placental trophoblasts, the established placenta is fairly resistant to radiation, and changes in this tissue may not fully account for fetal growth restriction induced by ionizing radiation. PMID:24418702

  13. Integrated Microfluidic Device for Automated Single Cell Analysis using Electrophoretic Separation and Electrospray Ionization Mass Spectrometry

    PubMed Central

    Mellors, J. Scott; Jorabchi, Kaveh; Smith, Lloyd M.; Ramsey, J. Michael

    2010-01-01

    A microfabricated fluidic device was developed for the automated real-time analysis of individual cells using capillary electrophoresis (CE) and electrospray ionization-mass spectrometry (ESI-MS). The microfluidic structure incorporates a means for rapid lysis of single cells within a free solution electrophoresis channel where cellular constituents were separated and an integrated electrospray emitter for ionization of separated components. The eluent was characterized using mass spectrometry. Human erythrocytes were used as a model system for this study. In this monolithically integrated device, cell lysis occurs at a channel intersection using a combination of rapid buffer exchange and an increase in electric field strength. An electroosmotic pump is incorporated at the end of the electrophoretic separation channel to direct eluent to the integrated electrospray emitter. The dissociated heme group and the α and β subunits of hemoglobin from individual erythrocytes were detected as cells continuously flowed through the device. The average analysis throughput was approximately 12 cells per minute demonstrating the potential of this method for high-throughput single cell analysis. PMID:20058879

  14. Qualitative and quantitative metabolomic investigation of single neurons by capillary electrophoresis electrospray ionization mass spectrometry

    PubMed Central

    Nemes, Peter; Rubakhin, Stanislav S.; Aerts, Jordan T.; Sweedler, Jonathan V.

    2013-01-01

    Single-cell mass spectrometry (MS) empowers metabolomic investigations by decreasing analytical dimensions to the size of individual cells and subcellular structures. We describe a protocol for investigating and quantifying metabolites in individual isolated neurons using single-cell capillary electrophoresis hyphenated to electrospray ionization time-of-flight MS. The protocol requires ~2 h for sample preparation, neuron isolation, and metabolite extraction, and 1 h for metabolic measurement. The approach was used to detect more than 300 distinct compounds in the mass range of typical metabolites in various individual neurons (25–500-µm in diameter) isolated from the sea slug (Aplysia californica) central and rat (Rattus norvegicus) peripheral nervous systems. A subset of identified compounds was sufficient to reveal metabolic differences among freshly isolated neurons of different types and changes in the metabolite profiles of cultured neurons. The protocol can be applied to the characterization of the metabolome in a variety of smaller cells and/or subcellular domains. PMID:23538882

  15. Electron capture and single ionization in H+ + Ar collisions: classical calculations

    NASA Astrophysics Data System (ADS)

    Frémont, F.

    2016-03-01

    A classical model is used to study electron capture and single ionization (SI) following H+ + Ar collisions at projectile energies varying from 400 to 40 keV. In the present model, the Ar electrons are treated independently from each other, and only the 3s and 3p electrons are supposed to be captured by the projectile. In addition, a Coulombic potential with an effective charge Z eff = 6.75, derived from Slater rules, is used in the calculations to simulate the screening of the Ar nucleus due to the presence of the core and 2l electrons. Total cross sections for single electron capture and SI are calculated and compared with previous experiments and earlier calculations based on a semiclassical approach. The reasonable agreement we observed allows a preliminary study of double electron capture (DC). The total cross section for DC is found to be much larger than the experimental one. Possible reasons for this disagreement are discussed.

  16. Impact ionization of molecular oxygen by 3.5-MeV/u bare carbon ions

    NASA Astrophysics Data System (ADS)

    Nandi, Saikat; Agnihotri, Aditya N.; Kasthurirangan, S.; Kumar, Ajay; Tachino, Carmen A.; Rivarola, Roberto D.; Martín, F.; Tribedi, Lokesh C.

    2012-06-01

    We have measured the absolute double-differential cross sections (DDCSs) for electron emission in ionization of O2 molecules under the impact of 3.5-MeV/u C6+ ions. The data were collected between 10 and 600 eV, in an angular range of 30∘ to 150∘. The single-differential cross sections (SDCSs) in emission angle and electron energy are deduced from the electron DDCS spectra. Also, the total cross section has been obtained from the SDCS spectra. The DDCS spectra as well as the SDCS spectra are compared with continuum distorted-wave eikonal initial-state calculations which employ molecular wave functions built as linear combinations of atomic orbitals. The DDCS ratio i.e. σO2/2σO, derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show any primary or secondary oscillations arising from Young-type interference, which is apparently in contrast to what has been observed earlier for H2 and in agreement with the model calculation. Similarly, the forward-backward angular asymmetry increases monotonically with the velocity of the emitted electrons. However, the results on the DDCSs, SDCSs, the asymmetry parameter, and the nonexistence of oscillations are in qualitative agreement with the predictions of the model used.

  17. Dopingless impact ionization MOS (DL-IMOS)—a remedy for complex process flow

    NASA Astrophysics Data System (ADS)

    Singh, Sangeeta; Kondekar, P. N.

    2015-07-01

    We propose a unique approach for realizing dopingless impact ionization MOS (DL-IMOS) based on the charge plasma concept as a remedy for complex process flow. It uses work-function engineering of electrodes to form charge plasma as surrogate doping. This charge plasma induces a uniform p-region in the source side and an n-region in the drain side on intrinsic silicon film with a thickness less than the intrinsic Debye length. DL-IMOS offers a simple fabrication process flow as it avoids the need of ion implantation, photo masking and complicated thermal budget via annealing devices. The lower thermal budget is required for DL-IMOS fabrication enables its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. It is highly immune to process variations, doping control issues and random dopant fluctuations, while retaining the inherent advantages of conventional IMOS. To epitomize the fabrication process flow for the proposed device a virtual fabrication flow is also proposed here. Extensive device simulation of the major device performance metrics such as subthreshold slope, threshold voltage, drain induced current enhancement, and breakdown voltage have been done for a wide range of electrodes work-function. To evaluate the potential applications of the proposed device at circuit level, its mixed mode simulations are also carried out.

  18. Angular distribution of Auger electrons due to 3d-shell impact ionization of krypton

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1977-01-01

    Cross sections for electron impact ionization of krypton due to ejection of a 3d-shell electron have been calculated using screened hydrogenic and Hartree-Slater wavefunctions for the target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3d electrons, are widely different in the two approximations. The angular distribution due to the Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

  19. Electron-impact ionization of the K-shells of Heavy Atoms

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.

    2016-05-01

    Fully-relativistic subconfiguration-average distorted-wave (SCADW) calculations are made for the electron-impact ionization of the K-shells of heavy atoms. One set of calculations only include the two-body electrostatic interaction, while the other set includes the full two-body retarded electromagnetic interaction. The SCADW retarded electromagnetic calculations are found to be in good agreement with recent measurements made at the Institute for Physics at the University of Sao Paulo, Brazil for Au and Bi atoms. Calculations and measurements will also be presented for the K-shell ionization of the Ta atom. Work supported in part by Grants from NSF and DOE.

  20. Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Zagorodskikh, S.; Zhaunerchyk, V.; Mucke, M.; Eland, J. H. D.; Squibb, R. J.; Karlsson, L.; Linusson, P.; Feifel, R.

    2015-12-01

    Single-photon multiple ionization processes of acetaldehyde (ethanal) have been experimentally investigated by utilizing a multi-particle coincidence technique based on the time-of-flight magnetic bottle principle, in combination with either a synchrotron radiation source or a pulsed helium discharge lamp. The processes investigated include double and triple ionization in the valence region as well as single and double Auger decay of core-ionized acetaldehyde. The latter are studied site-selectively for chemically different carbon core vacancies, scrutinizing early theoretical predictions specifically made for the case of acetaldehyde. Moreover, Auger processes in shake-up and core-valence ionized states are investigated. In the cases where the processes involve simultaneous emission of two electrons, the distributions of the energy sharing are presented, emphasizing either the knock-out or shake-off mechanism.

  1. Ionization of 2,5-dimethylfuran by electron impact and resulting ion-parent molecule reactions

    SciTech Connect

    Jiao, C. Q.; Adams, S. F.; Garscadden, A.

    2009-07-01

    2,5-dimethylfuran (C{sub 6}H{sub 8}O) is an important fuel additive and a possible renewable liquid fuel for the future. This paper presents a recent Fourier transfer mass spectrometry study on the formation of ions from C{sub 6}H{sub 8}O by electron impact ionization and by ion-molecule reactions. Cross sections of the partial electron impact ionization have been measured and the pathways of major fragmentation channels of the parent ion have been examined. The kinetics of the reactions of C{sub 6}H{sub 8}O with selected product ions from electron impact and Ar{sup +} have been studied.

  2. Ionization of 4,4'-bis(phenylethynyl) anthracene by electron impact.

    PubMed

    Kukhta, A V; Kukhta, I N; Zavilopulo, A N; Agafonova, A S; Shpenik, O B

    2009-01-01

    Ionization of a 4,4'-bis(phenylethynyl)anthracene (C(30)H(18), BPEA) molecule is studied for the first time at different energies of bombarding electrons in crossed electron and molecular beams. The relative cross-section of single ionization of a BPEA molecule in the energy range of 5-55 eV is measured. The ionization potential, E(I) = 7.62 +/- 0.2 eV, is determined using the threshold region of C(30)H(18)(+) ion yield energy dependence. A scheme of the BPEA molecule fragmentation is proposed. Experimental results are in reasonable accordance with calculations made in the framework of the density functional theory.

  3. Comparison of plasma excitation, ionization, and energy influx in single and dual frequency capacitive discharges

    NASA Astrophysics Data System (ADS)

    Sahu, B. B.; Han, Jeon G.

    2016-12-01

    Argon (Ar) plasma characteristics in a single and dual-frequency (DF), capacitively coupled plasma processing system are compared for drive frequencies 13.56 MHz, 320 MHz and their mixture as dual frequencies (DF). We present frequency dependent changes that occur in discharges in terms of plasma parameters such as plasma density, electron temperature, electron energy distribution function, optical emission, gas temperature, and metastable Ar density in a pressure range of 10-150 mTorr. Additionally, this work also presents the formulation and characterization of energy fluxes from plasma to a substrate/probe during the plasma generation. By variation of the operating pressure and plasma excitation frequency, the different contributions originating from the kinetic energy, the recombination of charge carriers such as electrons and ions at the surface along with the contributions from the neutral and excited species are determined. Data reveals that Ar metastable density in low-frequency radio frequency (RF) plasma is not a strong function of operating pressure even though plasma ionization increases with pressure. However, in the case of high-frequency and DF, the excitation of Ar metastable decreases and ionization increases due to enhanced collisions and efficient electron-neutral momentum/energy transfer. Also, data reveals that energy flux in the low-frequency RF plasmas is very high compared to that of high-frequency and DF operations.

  4. Cyclic acyloxonium ions as diagnostic aids in the characterization of chloropropanol esters under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions.

    PubMed

    Rahn, Anja K K; Yaylayan, Varoujan A

    2013-06-26

    During mass spectrometric analysis of various lipids and lipid derivatives such as the chlorinated counterparts of triacylglycerols, the detailed structure of the characteristic and common ions formed under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions by the loss of a single fatty acid remains ambiguous. These ions are designated in the literature as "diacylglyceride ions" and are frequently depicted with a molecular formula without showing any structural features and sometimes represented as cyclic acyloxonium ions. Characterization of these ions is of considerable importance due to their utility in structural identification of lipid derivatives. This study provides complementary evidence on the cyclic nature of "diacylglyceride ions" through the use of the simplest 3-monochloropropanediol diester as a model and the use of isotope labeling technique. Tandem MS/MS studies have indicated that the ion at m/z 135.6 generated from 1,2-bis(acetoyl)-3-chloropropane through the loss of an acetyl group was identical to the ion at m/z 135.6 generated from 4-chloromethyl-2,2-dimethyl-1,3-dioxolane, the latter being generated from a cyclic precursor through the loss of a methyl radical, keeping the dioxolane ring structure intact, thus confirming the cyclic nature of these ions. The corresponding cyclic oxonium ions generated from longer chain chloropropanol diesters, such as the ion at m/z 331.2 originating from 3-monochloropropanediol (3-MCPD) diesters containing palmitic acid(s), could serve as chemical markers for the presence chloropropanol esters.

  5. Energy levels of neutral and singly ionized berkelium, /sup 249/Bk I and II

    SciTech Connect

    Worden, E.F.; Conway, J.G.; Blaise, J.

    1987-09-01

    Energy-level analyses of the observed emission spectrum of berkelium have yielded 179 odd and 186 even levels of neutral berkelium Bk I, and 42 odd and 117 even levels of singly ionized berkelium Bk II. The levels are tabulated with the J value, the g value, the configuration and hyperfine constants A and B, and the width given for many of the levels. The ground states of Bk I and Bk II are (Rn)5f/sup 9/7s/sup 2/ /sup 6/H/sup 0//sub 15/2/ and (Rn)5f/sup 9/7s /sup 7/H/sup 0//sub 8/, respectively. A table lists the lowest level of each identified electronic configuration of Bk I and Bk II.

  6. Single ionization of CH{sub 4} by bare ions: Fully differential cross sections

    SciTech Connect

    Fernandez-Menchero, L.; Otranto, S.

    2010-08-15

    A theoretical study of fully differential cross sections for the single ionization of CH{sub 4} by collisions with H{sup +}, He{sup 2+}, and C{sup 6+} ions at energies in the order of MeV/amu is presented. We work in terms of the Born-3DW model, which considers a non-Coulomb central potential for the interaction of the active electron with the molecular core. Results obtained with the Born-3DW model are compared to those obtained with the Born-C3 model, which assumes this potential as purely Coulombic. The anisotropic potential of the CH{sub 4} molecule is smoothed through an angular integration, and results are averaged over all the possible orientations of the target molecule. Results for the lesser bound molecular orbitals (1T and 2A{sub 1}) are presented and discussed for different projectile momentum transfers for the coplanar geometry.

  7. Single-photon double K-shell ionization of low-Z atoms

    NASA Astrophysics Data System (ADS)

    Hoszowska, J.; Kheifets, A. S.; Dousse, J.-Cl; Bray, I.; Cao, W.; Fennane, K.; Kayser, Y.; Kavčič, M.; Szlachetko, J.; Szlachetko, M.

    2010-02-01

    The photon energy dependence of the double K-shell ionization of light atoms is reported. Experimental double-to-single photoionization cross section ratios for Mg, Al, Si and Ca were obtained from measurements of high-resolution x-ray emission spectra. The double photoionization (DPI) cross-sections for K-shell hollow atom production are compared to convergent close-coupling calculations (CCC) for neutral atoms and He-like ions. The relative importance of the initial-state and final-state electron-electron interactions to the K-shell DPI in many-electron atoms and two-electron ions is addressed. Physical mechanisms and scaling laws of the K-shell double photoionization are examined. A semiempirical universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms 2<=Z<=47 is established.

  8. Simultaneous ESI-APCI+ ionization and fragmentation pathways for nine benzodiazepines and zolpidem using single quadrupole LC-MS.

    PubMed

    Galaon, Toma; Vacaresteanu, Catalina; Anghel, Dan-Florin; David, Victor

    2014-05-01

    Nine important 1,4-benzodiazepines and zolpidem were characterized by liquid chromatography-mass spectrometry using a multimode ionization source able to generate ions using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and a single quadrupole mass analyzer. An optimum chromatographic separation was applied for all target compounds in less than 8 minutes using a Zorbax Eclipse Plus column (100 × 4.6 mm, 3.5 µm) kept at 35°C and a 0.3% HCOOH/ACN/IPA (61:34:5) mobile phase pumped at 1 ml/min. Optimization of LC-MS method generated low limit of quantitation (LOQ) values situated in the range 0.3-20.5 ng/ml. Comparison between differences in method sensitivity, under specified chromatographic conditions, when using ESI-only, APCI-only, and simultaneous ESI-APCI ionization with such a multimode source was discussed. Mixed ESI-APCI(+) mode proved to be the most sensitive ionization generating an average 35% detector response increase compared to ESI-only ionization and 350% detector response increase with respect to APCI-only ionization. Characterization of the nine benzodiazepines and zolpidem concerning their MS fragmentation pathway following 'in-source' collision-induced dissociation is discussed in detail and some general trends regarding these fragmentations are set.

  9. Double and single ionization of He and other targets studied using cold target recoil momentum spectroscopy

    SciTech Connect

    Doerner, R.; Feagin, J. M.; Brauning, H.; Jagutzki, O.; Jung, M.; Kanter, E. P.; Khemliche, H.; Kravis, S.; Mergel, V.; Prior, M. H.; Schmidt-Boeking, H.; Spielberger, L.; Ullrich, J.; Unverzagt, M.; Vogt, T.

    1997-04-01

    Double ionization of an atom by a single photon is the simplest and most fundamental many-electron process. The ejection of two electrons following the absorption of one photon is strictly prohibited in an independent electron approximation. Thus determining the probability of double photoionization alone is already a challenging test of the understanding of electron-electron correlation. Furthermore, in the slow breakup of a bound system into three charged particles, the final state wave function must represent a high degree of few-body Coulomb correlation involving the simultaneous interaction of all three particles. The case of double photoionization is again particularly well suited to study this problem as the energy and the angular momentum delivered to the system can be very well controlled. Helium, as the most basic three body system, has been the target of extensive studies over the past decades. The purpose of this project has been to study double and single ionization using cold target recoil ion momentum spectroscopy (COLTRIMS). This technique has been widely applied within the area of ion-atom collisions to study the dynamics of energy and momentum transfer in collisions between few-electron systems, and the entire technical machinery has been transferred to photon-atom collisions. The technique uses space- and time-imaging of He{sup +} and He{sup ++} recoil ions created in photon-He collisions to measure the full momentum vector of each ion produced. Event-mode recording is used and a solid angle of nearly 4{pi} is realized, allowing an extremely high data-collection efficiency. In order to reduce the initial momentum spread of the He target a precooled supersonic He jet is used.

  10. Possible detection of singly ionized oxygen in the Type Ia SN 2010kg

    NASA Astrophysics Data System (ADS)

    Barna, B.; Vinko, J.; Silverman, J. M.; Marion, G. H.; Wheeler, J. C.

    2016-04-01

    We present direct spectroscopic modelling of 11 high signal-to-noise ratio observed spectra of the Type Ia supernova (SN) 2010kg, taken between -10 and +5 d with respect to B-maximum. The synthetic spectra, calculated with the SYN++ code, span the range between 4100 and 8500 Å. Our results are in good agreement with previous findings for other Type Ia SNe. Most of the spectral features are formed at or close to the photosphere, but some ions, like Fe II and Mg II, also form features at ˜2000-5000 km s-1 above the photosphere. The well-known high-velocity features of the Ca II IR-triplet as well as Si II λ6355 are also detected. The single absorption feature at ˜4400 Å, which usually has been identified as due to Si III, is poorly fit with Si III in SN 2010kg. We find that the fit can be improved by assuming that this feature is due to either C III or O II, located in the outermost part of the ejecta, ˜4000-5000 km s-1 above the photosphere. Since the presence of C III is unlikely, because of the lack of the necessary excitation/ionization conditions in the outer ejecta, we identify this feature as due to O II. The simultaneous presence of O I and O II is in good agreement with the optical depth calculations and the temperature distribution in the ejecta of SN 2010kg. This could be the first identification of singly ionized oxygen in a Type Ia SN atmosphere.

  11. Coupled Cluster Studies of Ionization Potentials and Electron Affinities of Single-Walled Carbon Nanotubes.

    PubMed

    Peng, Bo; Govind, Niranjan; Aprà, Edoardo; Klemm, Michael; Hammond, Jeff R; Kowalski, Karol

    2017-02-16

    In this paper, we apply equation-of-motion coupled cluster (EOM-CC) methods in the studies of the vertical ionization potentials (IPs) and electron affinities (EAs) for a series of single-walled carbon nanotubes (SWCNT). The EOM-CC formulations for IPs and EAs employing excitation manifolds spanned by single and double excitations (IP/EA-EOM-CCSD) are used to study the IPs and EAs of the SWCNTs as a function of the nanotube length. Several armchair nanotubes corresponding to C20nH20 models with n = 2-6 have been used in benchmark calculations. In agreement with previous studies, we demonstrate that the electronegativity of C20nH20 systems remains, to a large extent, independent of the nanotube length. We also compare IP/EA-EOM-CCSD results with those obtained with coupled cluster models with single and double excitations corrected by perturbative triples, CCSD(T), and density functional theory (DFT) using global and range-separated hybrid exchange-correlation functionals.

  12. Destabilization of a cylindrically confined electron cloud by impact ionization of background neutrals: 2D3v PIC simulation with Monte-Carlo-collisions

    NASA Astrophysics Data System (ADS)

    Sengupta, M.; Ganesh, R.

    2017-03-01

    In this paper, we have investigated, through simulation, the process of destabilization of a cylindrically confined electron cloud due to the presence of a single species of neutral atoms, Ar in the background of the trap at a pressure relevant to experiments. The destabilization occurs because of a gradual accumulation of Ar+ in the cloud by the electron-impact ionization of the background neutrals. The trapped ions gradually collectively form a sizeable ion cloud which engages in a rotational two-stream instability (the ion resonance instability) with the electron cloud. The instability excites a growing fundamental diocotron mode on both components of the mixed non-neutral cloud. With the help of a set of numerical diagnostics, we have investigated the nonlinear evolution of the excited fundamental mode under the combined influence of two ongoing processes viz, (i) the changing electron and ion populations caused by electron impact ionization of the background Ar, and also by the radial loss of both charged species to the grounded trap wall at later stages and (ii) the elastic scattering of electrons and ions that make non-ionizing collisions with the background neutrals. The 2D collisionless dynamics of the instability has been simulated using a 2D Particle-in-Cell code operating on a Cartesian grid laid out on the cylindrical trap's cross-section, and the 3D ionizing and non-ionizing collisions between charged particles and background neutrals have been simulated using the technique of Monte-Carlo-Collisions.

  13. Electron emission from single-electron capture with simultaneous single-ionization reactions in 30-keV/u He{sup 2+}-on-argon collisions

    SciTech Connect

    Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Li, B.; Liu, H. P.; Zhang, R. T.; Guo, D. L.; Yan, S. C.; Zhang, P. J.; Wang, Q.; Li, C. Y.; Wang, J. G.

    2011-05-15

    Electron emission from the single-electron capture with simultaneous single ionization in 30 keV/u He{sup 2+} on argon was investigated using a reaction microscope, providing the electron energy spectra and momentum distributions. Intensive peaks for electrons with near-zero kinetic energies have been observed. It is demonstrated that mechanisms contributing to the electron emission include direct transfer ionization (DTI), double-electron capture with autoionization (DECA), and single-electron capture with autoionization (SECA) of target. Comparison of resonance energies shows that Ar{sup +} ions in SECA decay mainly through the 3s3p{sup 5}3d states by emitting Auger electrons, and He** in DECA decay through the 2l2l' states. The dependence of electron emission on the transverse momentum exchange has been studied. In the transfer ionization channel studied here, the DTI process dominates the electron emission, and no saddle point electron mechanism has been found.

  14. Electron emission from single-electron capture with simultaneous single-ionization reactions in 30-keV/u He2+-on-argon collisions

    NASA Astrophysics Data System (ADS)

    Ma, X.; Zhang, R. T.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Guo, D. L.; Li, B.; Liu, H. P.; Li, C. Y.; Wang, J. G.; Yan, S. C.; Zhang, P. J.; Wang, Q.

    2011-05-01

    Electron emission from the single-electron capture with simultaneous single ionization in 30 keV/u He2+ on argon was investigated using a reaction microscope, providing the electron energy spectra and momentum distributions. Intensive peaks for electrons with near-zero kinetic energies have been observed. It is demonstrated that mechanisms contributing to the electron emission include direct transfer ionization (DTI), double-electron capture with autoionization (DECA), and single-electron capture with autoionization (SECA) of target. Comparison of resonance energies shows that Ar+ ions in SECA decay mainly through the 3s3p53d states by emitting Auger electrons, and He** in DECA decay through the 2l2l' states. The dependence of electron emission on the transverse momentum exchange has been studied. In the transfer ionization channel studied here, the DTI process dominates the electron emission, and no saddle point electron mechanism has been found.

  15. Electron impact ionization cross-sections for few-electron uranium ions

    NASA Astrophysics Data System (ADS)

    Guerra, M.; Stöhlker, Th; Amaro, P.; Machado, J.; Santos, J. P.

    2015-07-01

    Electron impact ionization cross sections for the U88+, U89+, U90+ and U91+ ions were calculated with the relativistic binary encounter Bethe model (RBEB), the modified RBEB (MRBEB) and the new MRBEB corrected by the ionic factor (MRBR-IF). Our results were compared with the available three sets of experimental data and the most used theoretical results. The MRBEB-IF results are the ones that better agree with the experimental data of the four analysed ions.

  16. Positron-impact ionization, positronium formation, and electronic excitation cross sections for diatomic molecules

    SciTech Connect

    Marler, J. P.; Surko, C. M.

    2005-12-15

    Absolute measurements are presented for the positron-impact cross sections for positronium formation, direct ionization, and total ionization of the diatomic molecules N{sub 2}, CO, and O{sub 2}, in the range of energies from threshold to 90 eV. Cross sections for the electronic excitation of the a {sup 1}{pi} and a{sup '} {sup 1}{sigma} state in N{sub 2} and the A {sup 1}{pi} state in CO near threshold are also presented. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. In O{sub 2}, a feature previously seen in the total ionization cross section is observed in both the positronium formation and total ionization cross sections. The possible origin of this feature and its relationship to positron-induced dissociation is discussed. In N{sub 2}, the near-threshold electronic excitation cross section is larger than that for positronium formation. This likely explains the relatively high efficiency of this molecule when used for buffer-gas positron trapping.

  17. Electron Impact Ionization and Fragmentation Dynamics of Small Atomic and Molecular Clusters

    NASA Astrophysics Data System (ADS)

    Dorn, Alexander

    2016-09-01

    New ionization and fragmentation reactions emerge if target atoms or molecules are embedded in an environment as it is the case in small clusters or in the condensed phase. These can be intermolecular energy and charge transfer processes or a completely modified fragmentation behavior of the molecular ions. Here we study low energy electron impact induced ionization with a multi-electron and ion imaging spectrometer (reaction microscope) and a supersonic gas jet target which can produce small clusters of various target species. Interatomic reactions are studied for the model system of weakly bound Ar2 dimers. Here, the coincident detection of three electrons and two ions gives detailed insight in interatomic Coulombic decay and radiative charge transfer processes. Such processes were also found in bio-relevant systems like water clusters. We studied pure and water-mixed clusters of tetrahydrofuran (C4H8O, THF) which is the simplest analog of deoxyribose in the DNA backbone. One observation is that ionization of the outermost valence orbital for the monomer leads to stable THF ions. In contrast if THF is bound to another THF or a water molecule the molecular ring breaks. In addition we identify intermolecular Coulombic decay induced by energy transfer from a water molecule ionized in the inner valence shell to the neighboring THF molecule.

  18. Dissociative Ionization and Product Distributions of Benzene and Pyridine by Electron Impact

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Huo, Winifred M.; Fletcher, Graham D.

    2003-01-01

    We report a theoretical study of the dissociative ionization (DI) and product distributions of benzene (C6H6) and pyridine (C5H5N) from their low-lying ionization channels. Our approach makes use of the fact that electronic motion is much faster than nuclear motion allowing DI to be treated as a two-step process. The first step is the electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step, the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64,042719-I (2001)]. For the unimolecular dissociation, we use multiconfigurational self-consistent field (MCSCF) methods to determine the steepest descent pathways to the possible product channels. More accurate methods are then used to obtain better energetics of the paths which are used to determine unimolecular dissociation probabilities and product distributions. Our analysis of the dissociation products and the thresholds of their productions for benzene are compared with the recent dissociative photoionization meausurements of benzene by Feng et al. [R. Feng, G. Cooper, C.E. Brion, J. Electron Spectrosc. Relat. Phenom. 123,211 (2002)] and the dissociative photoionization measurements of pyridine by Tixier et al. [S. Tixier, G. Cooper, R. Feng, C.E. Brion, J. Electron Spectrosc. Relat. Phenom. 123,185 (2002)] using dipole (e,e+ion) coincidence spectroscopy.

  19. Strong nonlinear electron multiplication without impact ionization in dielectric nanoparticles embedded in optical materials

    SciTech Connect

    Duchateau, Guillaume

    2013-02-15

    The interaction of a dielectric nano-particle or nano-defect, embedded in the bulk of an optical material, with an intense and short laser pulse is addressed. Due to the finite size of the target and the possible large production of electrons in the conduction band, large electric field enhancement or surintensity may be induced inside the particle. Since ionization rates also depend on the instantaneous electric field, a strong time-dependent connection between electron production and surintensity may take place. Such a connection is shown to possibly lead to a nonlinear temporal increase in the free electron density relevant from an avalanche process, called optical avalanche, similar to the one induced by electron impact ionization. However, the present build-up in the electron density clearly exhibits more nonlinear features than traditional collisional avalanche, which is shown to induce an exponential growth of the density: when the optical avalanche is engaged, the temporal electron evolution exhibits an explosive behavior. That leads to a nanometric plasma at solid density whose subsequent laser heating may lead locally to matter under extreme conditions. Furthermore, we show that the defect induces a change in the ionization mechanism in the course of interaction: a transition from multiphoton to tunnel ionization may take place.

  20. Scaling properties of field ionization of Rydberg atoms in single-cycle THz pulses: 1D considerations

    NASA Astrophysics Data System (ADS)

    Agueny, H.; Chovancova, M.; Hansen, J. P.; Kocbach, L.

    2016-12-01

    In recent experiments of single-cycle field ionization of excited Na(nd) atoms with principal quantum number n\\in [6,15] (Li and Jones 2014 Phys. Rev. Lett. 112 143006) it was shown that the maximum field intensity necessary to ionize 10% of the atoms decreases with increasing n according to an {n}-3 power law dependence. This scaling property at the same ionization probability was confirmed in classical trajectory Monte Carlo calculations. In this work we note that the scaling relation in the experiment is much more general, it is in fact valid for all ionization probabilities. When applied to the emitted electron energies it places a very wide distribution of electron momenta from different initial states onto a narrow range. These aspects are investigated in a one-dimensional model with a 3D hydrogen-like spectrum. Calculations confirm the general {n}-3 scaling relation for the ionization probability and that this particular scaling of the kinetic emission spectrum puts the ejected electron momenta on a narrow common scale. The ionization mechanism itself is identified as quantum mechanical tunneling and the nature of the tunneling process is the direct origin of the scaling law.

  1. Compendium of Single Event Effects, Total Ionizing Dose, and Displacement Damage for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    LaBel, Kenneth A.; OBryan, Martha V.; Chen, Dakai; Campola, Michael J.; Casey, Megan C.; Pellish, Jonathan A.; Lauenstein, Jean-Marie; Wilcox, Edward P.; Topper, Alyson D.; Ladbury, Raymond L.; Berg, Melanie D.; Gigliuto, Robert A.; Boutte, Alvin J.; Cochran, Donna J.; Buchner, Stephen P.; Violette, Daniel P.

    2014-01-01

    We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to proton and heavy ion induced single event effects (SEE), proton-induced displacement damage (DD), and total ionizing dose (TID). Introduction: This paper is a summary of test results.NASA spacecraft are subjected to a harsh space environment that includes exposure to various types of ionizing radiation. The performance of electronic devices in a space radiation environment is often limited by its susceptibility to single event effects (SEE), total ionizing dose (TID), and displacement damage (DD). Ground-based testing is used to evaluate candidate spacecraft electronics to determine risk to spaceflight applications. Interpreting the results of radiation testing of complex devices is quite difficult. Given the rapidly changing nature of technology, radiation test data are most often application-specific and adequate understanding of the test conditions is critical. Studies discussed herein were undertaken to establish the application-specific sensitivities of candidate spacecraft and emerging electronic devices to single-event upset (SEU), single-event latchup (SEL), single-event gate rupture (SEGR), single-event burnout (SEB), single-event transient (SET), TID, enhanced low dose rate sensitivity (ELDRS), and DD effects.

  2. Theoretical and experimental quantification of doubly and singly differential cross sections for electron-induced ionization of isolated tetrahydrofuran molecules

    DOE PAGES

    Champion, Christophe; Quinto, Michele A.; Bug, Marion U.; ...

    2014-07-29

    Electron-induced ionization of the commonly used surrogate of the DNA sugar-phosphate backbone, namely, the tetrahydrofuran molecule, is here theoretically described within the 1st Born approximation by means of quantum-mechanical approach. Comparisons between theory and recent experiments are reported in terms of doubly and singly differential cross sections.

  3. Theoretical and experimental quantification of doubly and singly differential cross sections for electron-induced ionization of isolated tetrahydrofuran molecules

    SciTech Connect

    Champion, Christophe; Quinto, Michele A.; Bug, Marion U.; Baek, Woon Y.; Weck, Philippe F.

    2014-07-29

    Electron-induced ionization of the commonly used surrogate of the DNA sugar-phosphate backbone, namely, the tetrahydrofuran molecule, is here theoretically described within the 1st Born approximation by means of quantum-mechanical approach. Comparisons between theory and recent experiments are reported in terms of doubly and singly differential cross sections.

  4. Compendium of Single Event Effects, Total Ionizing Dose, and Displacement Damage for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    LaBel, Kenneth A.; O'Bryan, Martha V.; Chen, Dakai; Campola, Michael J.; Casey, Megan C.; Pellish, Jonathan A.; Lauenstein, Jean-Marie; Wilcox, Edward P.; Topper, Alyson D.; Ladbury, Raymond L.; Berg, Melanie D.; Gigliuto, Robert A.; Boutte, Alvin J.; Cochran, Donna J.; Buchner, Stephen P.; Violette, Daniel P.

    2014-01-01

    We present results and analysis investigating the effects of radiation on a variety of candidate spacecraft electronics to proton and heavy ion-induced single-event effects (SEE), proton-induced displacement damage (DD), and total ionizing dose (TID). This paper is a summary of test results.

  5. One- and two-photon ionization of DNA single and double helices studied by laser flash photolysis at 266 nm.

    PubMed

    Marguet, Sylvie; Markovitsi, Dimitra; Talbot, Francis

    2006-06-15

    The ionization of the DNA single and double helices (dA)20, (dT)20, (dAdT)10(dAdT)10 and (dA)20(dT)20, induced by nanosecond pulses at 266 nm, is studied by time-resolved absorption spectroscopy. The variation of the hydrated electron concentration with the absorbed laser intensity shows that, in addition to two-photon ionization, one-photon ionization takes place for (dAdT)10(dAdT)10, (dA)20(dT)20 and (dA)20 but not for (dT)20. The spectra of all adenine-containing oligomers at the microsecond time-scale correspond to the adenine deprotonated radical formed in concentrations comparable to that of the hydrated electron. The quantum yield for one-photon ionization of the oligomers (ca. 10(-3)) is higher by at least 1 order of magnitude than that of dAMP, showing clearly that organization of the bases in single and double helices leads to an important lowering of the ionization potential. The propensity of (dAdT)10(dAdT)10, containing alternating adenine-thymine sequences, to undergo one-photon ionization is lower than that of (dA)20(dT)20 and (dA)20, containing adenine runs. Pairing of the (dA)20 with the complementary strand leads to a decrease of quantum yield for one photon ionization by about a factor of 2.

  6. Single-photon ionization and detection of Ga, In, and Asn species in GaAs growth

    NASA Astrophysics Data System (ADS)

    Alstrin, April L.; Strupp, Paul G.; Cook, Laura; Leone, Stephen R.

    1993-04-01

    In this paper, single photon ionization time-of-flight mass spectroscopy (SPI-TOFMS) is used to monitor chemical fluxes of In, Ga, and Asn, relevant in molecular beam epitaxy of GaAs. With single photon ionization at 118 nm (10.5 eV), the photon energy is large enough to ionize the species, but not sufficient to ionize and fragment. The lack of molecular dissociation of species such as As2 and As4 greatly simplifies the interpretation of mass spectra. SPI-TOFMS provides the ability to measure densities, and hence fluxes, of multiple chemical species above a substrate noninvasively and in real time during conventional molecular beam epitaxy. The relative ionization efficiencies of Ga and the Asn species at 118 nm are determined. Additionally, this laser probing technique is used to study the isothermal and temperature programmed desorption of arsenic from Si(100). The catalytic cracking of As4 on Si is also examined and discussed. This technique promises to be a valuable in-situ optical diagnostic for III-V and II-VI molecular beam epitaxy.

  7. Electron-impact ionization excitation of helium in the quasiphoton regime

    SciTech Connect

    Ngoko Djiokap, J. M.; Foumouo, E.; Urbain, X.; Piraux, B.; Kwato Njock, M. G.

    2010-04-15

    The triply differential cross section of ionization excitation of helium, leaving the residual ion in the n=2 excited states, is evaluated for the kinematics considered experimentally by Dupreet al. [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described at the first order, while the interaction of the ejected electron with the residual ion is treated very accurately within the formalism of the Jacobi matrix method. In the quasiphoton limit and for low ejected electron energies, the presence of series of doubly excited states, mainly below the n=3 single ionization threshold in helium, makes the triply differential cross sections extremely sensitive to both the energy and the emission angle of the ejected electron. We show that the convolution of our results with a Gaussian energy profile, in which the full width at half-maximum corresponds to the energy resolution in the experiment, has a significant effect. Our results suggest that it is also important to account for the finite resolution on the measurement of the scattering angle when the experimental data are compared to the theoretical predictions. Comparison of our theoretical results convoluted both in energy and in angle with the experimental data demonstrates the importance of an accurate description of the helium spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed to explain the remaining discrepancies.

  8. Electron-impact ionization excitation of helium in the quasiphoton regime

    NASA Astrophysics Data System (ADS)

    Ngoko Djiokap, J. M.; Foumouo, E.; Kwato Njock, M. G.; Urbain, X.; Piraux, B.

    2010-04-01

    The triply differential cross section of ionization excitation of helium, leaving the residual ion in the n=2 excited states, is evaluated for the kinematics considered experimentally by Dupré [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described at the first order, while the interaction of the ejected electron with the residual ion is treated very accurately within the formalism of the Jacobi matrix method. In the quasiphoton limit and for low ejected electron energies, the presence of series of doubly excited states, mainly below the n=3 single ionization threshold in helium, makes the triply differential cross sections extremely sensitive to both the energy and the emission angle of the ejected electron. We show that the convolution of our results with a Gaussian energy profile, in which the full width at half-maximum corresponds to the energy resolution in the experiment, has a significant effect. Our results suggest that it is also important to account for the finite resolution on the measurement of the scattering angle when the experimental data are compared to the theoretical predictions. Comparison of our theoretical results convoluted both in energy and in angle with the experimental data demonstrates the importance of an accurate description of the helium spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed to explain the remaining discrepancies.

  9. Electron-impact ionization-excitation of helium in the quasi-photon regime

    NASA Astrophysics Data System (ADS)

    Marcel Ngoko Djiokap, Jean; Foumouo, Emmanuel; Njock, Moise Godfroy Kwato; Urbain, Xavier; Piraux, Bernard

    2010-03-01

    The triply differential cross section (TDCS) for ionization and excitation of helium (leaving the residual ion in the n=2 excited states) is evaluated for the kinematics considered experimentally by Dupr'e et al. [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described in first order, while that of the ejected electron with the residual ion is treated accurately within the Jacobi matrix method formalism. In the quasi-photon limit and for small ejected electron energies, the presence of series of doubly excited states below the n=3 single ionization threshold in helium makes the TDCS extremely sensitive to both the energy and angle of the ejected electron. Comparison of our theoretical results (convoluted both in energy and angle) with the experimental data demonstrates the importance of an accurate description of the He spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed in order to explain the remaining discrepancies.

  10. Investigation of Ionization and Dissociation Processes Produced by Electron Impact on Molecules.

    NASA Astrophysics Data System (ADS)

    Ma, Ce.

    1990-01-01

    Absolute electron impact partial ionization cross sections for Ar and CF_4 were measured by use of a newly built pulsed electron beam time-of-flight apparatus for incident electron energies from thresholds to 500 eV. The apparatus employed consisted of a low energy electron gun, 40 mm diameter ion extraction gold screens, time-of-flight drift tubes, micro-channel plate detectors and fast time to digital electronics. A pulsed electron beam was obtained by pulsing the control grid of the electron gun. Both beam - beam experiments and beam - constant gas target pressure experiments were carried out to determine the absolute partial ionization cross sections for Ar ^{+}, Ar^{2+ }, Ar^{3+} from an argon gas target, and for CF_sp {3}{+}, CF_sp {2}{+}, CF_sp {3}{2+}, CF^ {+}, CF_sp{2} {2+}, F^{+}, C^{+} from a CF _4 gas target. By charge weighted summing of the partial ionization cross sections, the total ionization cross sections of Ar and CF_4 were obtained. The total neutral dissociation cross section for CF_4 was inferred from the total ionization cross section and the total dissociation cross section. Also, a new method for determining absolute total electron scattering cross sections with corrections for forward scattering was developed. The electron beam current was measured as function of gas target pressure and the scattering path length. The total electron scattering cross section obtained from the new model is as much as 6% larger than the cross section derived from the traditional Beer's law for Ar at an incident electron energy of 300 eV. This method is capable of yielding reliable total cross section up to 10 keV. Finally, a study of the secondary electron emission as a function of ejection angle and ejection energy for CO, the doubly differential cross section (DDCS), is presented.

  11. Analysis and simulation for a model of electron impact excitation/deexcitation and ionization/recombination

    SciTech Connect

    Yan, Bokai; Caflisch, Russel E.; Barekat, Farzin; Cambier, Jean-Luc

    2015-10-15

    This paper describes a kinetic model and a corresponding Monte Carlo simulation method for excitation/deexcitation and ionization/recombination by electron impact in a plasma free of external fields. The atoms and ions in the plasma are represented by continuum densities and the electrons by a particle distribution. A Boltzmann-type equation is formulated and a corresponding H-theorem is formally derived. An efficient Monte Carlo method is developed for an idealized analytic model of the excitation and ionization collision cross sections. To accelerate the simulation, the reduced rejection method and binary search method are used to overcome the singular rate in the recombination process. Numerical results are presented to demonstrate the efficiency of the method on spatially homogeneous problems. The evolution of the electron distribution function and atomic states is studied, revealing the possibility under certain circumstances of system relaxation towards stationary states that are not the equilibrium states, a potential non-ergodic behavior.

  12. Total Electron-Impact Ionization Cross-Sections of CFx and NFx (x = 1 - 3)

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Tarnovsky, Vladimir; Becker, Kurt H.; Kwak, Dochan (Technical Monitor)

    2001-01-01

    The discrepancy between experimental and theoretical total electron-impact ionization cross sections for a group of fluorides, CFx, and NFx, (x = 1 - 3), is attributed to the inadequacies in previous theoretical models. Cross-sections calculated using a recently developed siBED (simulation Binary-Encounter-Dipole) model that takes into account the shielding of the long-range dipole potential between the scattering electron and target are in agreement with experimentation. The present study also carefully reanalyzed the previously reported experimental data to account for the possibility of incomplete collection of fragment ions and the presence of ion-pair formation channels. For NF3, our experimental and theoretical cross-sections compare well with the total ionization cross-sections recently reported by Haaland et al. in the region below dication formation.

  13. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT IONIZATION OF Fe{sup 7+}

    SciTech Connect

    Hahn, M.; Novotný, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Bernhardt, D.; Müller, A.; Schippers, S.; Spruck, K.; Lestinsky, M.

    2015-11-01

    We have measured electron impact ionization for Fe{sup 7+} from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurements to remove most metastables, resulting in a beam of 94% ground-level ions. Comparing with the previously recommended atomic data, we find that the Arnaud and Raymond cross section is up to about 40% larger than our measurement, with the largest discrepancies below about 400 eV. The cross section of Dere agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between our measurement and the Dere calculations are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution.

  14. Storage ring cross section measurements for electron impact ionization of Fe8+

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Becker, A.; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Pindzola, M. S.; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, D. W.

    2016-04-01

    We have measured electron impact ionization (EII) for Fe8+ forming Fe9+ from below the ionization threshold to 1200 eV. These measurements were carried out at the TSR heavy ion storage ring. The objective of using a storage ring is to store the ion beam initially so that metastable levels decay, thereby allowing for measurements on a well-defined ground-level ion beam. In this case, however, some metastable levels were too long lived to be removed. We discuss several methods for quantifying the metastable fraction, which we estimate to be ˜30%-40%. Although metastables remain problematic, the present storage ring work improves upon other experimental geometries by limiting the metastable contamination to only a few long-lived excited levels. We discuss some future prospects for obtaining improved measurements of Fe8+ and other ions with long-lived metastable levels.

  15. Ionization impact on molecular clouds and star formation. Numerical simulations and observations

    NASA Astrophysics Data System (ADS)

    Tremblin, P.

    2012-11-01

    At all the scales of Astrophysics, the impact of the ionization from massive stars is a crucial issue. At the galactic scale, the ionization can regulate star formation by supporting molecular clouds against gravitational collapse and at the stellar scale, indications point toward a possible birth place of the Solar System close to massive stars. At the molecular cloud scale, it is clear that the hot ionized gas compresses the surrounding cold gas, leading to the formation of pillars, globules, and shells of dense gas in which some young stellar objects are observed. What are the formation mechanisms of these structures? Are the formation of these young stellar objects triggered or would have they formed anyway? Do massive stars have an impact on the distribution of the surrounding gas? Do they have an impact on the mass distribution of stars (the initial mass function, IMF)? This thesis aims at shedding some light on these questions, by focusing especially on the formation of the structures between the cold and the ionized gas. We present the state of the art of the theoretical and observational works on ionized regions (H ii regions) and we introduce the numerical tools that have been developed to model the ionization in the hydrodynamic simulations with turbulence performed with the HERACLES code. Thanks to the simulations, we present a new model for the formation of pillars based on the curvature and collapse of the dense shell on itself and a new model for the formations of cometary globules based on the turbulence of the cold gas. Several diagnostics have been developed to test these new models in the observations. If pillars are formed by the collapse of the dense shell on itself, the velocity spectrum of a nascent pillar presents a large spectra with a red-shifted and a blue-shifted components that are caused by the foreground and background parts of the shell that collapse along the line of sight. If cometary globules emerge because of the turbulence of

  16. Assessing the impact of ionizing radiation on aquatic invertebrates: a critical review.

    PubMed

    Dallas, Lorna J; Keith-Roach, Miranda; Lyons, Brett P; Jha, Awadhesh N

    2012-05-01

    There is growing scientific, regulatory and public concern over anthropogenic input of radionuclides to the aquatic environment, especially given the issues surrounding existing nuclear waste, future energy demand and past or potential nuclear accidents. A change in the approach to how we protect the environment from ionizing radiation has also underlined the importance of assessing its impact on nonhuman biota. This review presents a thorough and critical examination of the available information on the effects of ionizing radiation on aquatic invertebrates, which constitute approximately 90% of extant life on the planet and play vital roles in ecosystem functioning. The aim of the review was to assess the progress made so far, addressing any concerns and identifying the knowledge gaps in the field. The critical analysis of the available information included determining yearly publications in the field, qualities of radiation used, group(s) of animals studied, and levels of biological organization at which effects were examined. The overwhelming conclusion from analysis of the available information is that more data are needed in almost every area. However, in light of the current priorities in human and environmental health, and considering regulatory developments, the following are areas of particular interest for future research on the effects of ionizing radiation on nonhuman biota in general and aquatic invertebrates in particular: (1) studies that use end points across multiple levels of biological organization, including an ecosystem level approach where appropriate, (2) multiple species studies that produce comparable data across phylogenetic groups, and (3) determination of the modifying (i.e. antagonistic, additive or synergistic) effects of biotic and abiotic factors on the impact of ionizing radiation. It is essential that all of these issues are examined in the context of well-defined radiation exposure and total doses received and consider the life

  17. Recoil Momentum Spectroscopy of Double and Single Ionization of He by 80-400 eV Photons

    NASA Astrophysics Data System (ADS)

    Dörner, R.; Kravis, S.; Cocke, C. L.; Vogt, T.; Mergel, V.; Unverzagt, M.; Spielberger, L.; Damrau, M.; Jagutzki, O.; Ali, I.; Weaver, B.; Ullmann, K.; Schmidt-Böcking, H.; Khemliche, H.; Prior, M. H.; Warwick, T.; Ullrich, J.; Jung, M.; Kanter, E. P.; Hsu, C. C.; Sonntag, B.; Rotenberg, E.; Denlinger, J.; Manson, S. T.; Feagin, J.

    1996-05-01

    We have measured the ratio (R) between double and single ionization of He by photons between 85 eV and 400 eV using COLTRIMS.(J. Ullrich et al., Comm. At. Mol. Phys. \\underline30), 285 (1994). The experiment, performed at the Berkeley ALS, eliminates many systematic errors which have plagued previous attempts to measure R. The values of R obtained are about 25% below those previously reported but are in good agreement with several recent theoretical calculations. We also report preliminary results of triply differential cross sections for double ionization of He measured near threshold.

  18. Ion time-of-flight determinations of doubly to singly ionized mercury ion ratios from a mercury electron bombardment discharge

    NASA Technical Reports Server (NTRS)

    Sellen, J. M., Jr.; Kemp, R. F.; Hall, D. F.

    1973-01-01

    Doubly to singly charged mercury ion ratios in electron bombardment ion thruster exhaust beams have been determined as functions of bombardment discharge potential, thrust beam current, thrust beam radial position, acceleration-deceleration voltage ratio, and propellant utilization fraction. A mathematical model for two-step ionization processes has been derived, and calculated ion ratios are compared to observed ratios. Production of Hg(++) appears to result primarily from sequential ionization of Hg(+) in the discharge. Experimental and analytical results are presented, and design, construction, and operation features of an electrostatic deflection ion time-of-flight analyzer for the determination of the above-mentioned ratios are reviewed.

  19. Laser ablation of ceramic Al{sub 2}O{sub 3} at 193 nm and 248 nm: The importance of single-photon ionization processes

    SciTech Connect

    Pelaez, R. J.; Afonso, C. N.; Bator, M.; Lippert, T.

    2013-06-14

    The aim of this work is to demonstrate that single-photon photoionization processes make a significant difference in the expansion and temperature of the plasma produced by laser ablation of ceramic Al{sub 2}O{sub 3} in vacuum as well as to show their consequences in the kinetic energy distribution of the species that eventually will impact on the film properties produced by pulsed laser deposition. This work compares results obtained by mass spectrometry and optical spectroscopy on the composition and features of the plasma produced by laser ablation at 193 nm and 248 nm, i.e., photon energies that are, respectively, above and below the ionization potential of Al, and for fluences between threshold for visible plasma and up to Almost-Equal-To 2 times higher. The results show that the ionic composition and excitation of the plasma as well as the ion kinetic energies are much higher at 193 nm than at 248 nm and, in the latter case, the population of excited ions is even negligible. The comparison of Maxwell-Boltzmann temperature, electron temperatures, and densities of the plasmas produced with the two laser wavelengths suggests that the expansion of the plasma produced at 248 nm is dominated by a single population. Instead, the one produced at 193 nm is consistent with the existence of two populations of cold and hot species, the latter associated to Al{sup +} ions that travel at the forefront and produced by single photon ionization as well as Al neutrals and double ionized ions produced by electron-ion impact. The results also show that the most energetic Al neutrals in the plasma produced at the two studied wavelengths are in the ground state.

  20. Triple Differential Cross Sections for single ionization of the Ethane molecule

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Nixon, Kate; Ning, Chuangang; Murray, Andrew; Madison, Don

    2015-09-01

    We report experimental and theoretical results for electron-impact (e,2e) ionization of the Ethane molecule (C2H6) in the coplanar scattering geometry for four different ejected electron energies Ea = 5,10,15, and 20 eV respectively, and for each ejected electron energy, the projectile scattering angle is fixed at 10°. We will show that the TDCS is very sensitive for the case of two heavy nuclei surrounded by lighter H nuclei. On the theoretical side, we have used the M3DW coupled with the Orientation Averaged Molecular Orbital (OAMO) approximation and proper average (PA) over all orientations. These approximations show good agreement with experimental data for the binary peaks. However, for the recoil peak region, experiment finds a noticeable peak while theory predicts no peak. No recoil peak suggests no (or very weak) nuclear scattering, so we have investigated the importance of nuclear scattering by moving the nuclei closer to the center of mass. This work is supported by the US National Science Foundation under Grant No. PHY-1068237 and XSEDE resources provided by the Texas Advanced Computing Center (Grant No. TG-MCA07S029).

  1. Development of a compact laser-based single photon ionization time-of-flight mass spectrometer

    NASA Astrophysics Data System (ADS)

    Tonokura, Kenichi; Kanno, Nozomu; Yamamoto, Yukio; Yamada, Hiroyuki

    2010-02-01

    We have developed a compact, laser-based, single photon ionization time-of-flight mass spectrometer (SPI-TOF-MS) for on-line monitoring of trace organic species. To obtain the mass spectrum, we use a nearly fragmentation-free SPI technique with 10.5 eV (118 nm) vacuum ultraviolet laser pulses generated by frequency tripling of the third harmonic of an Nd:YAG laser. The instrument can be operated in a linear TOF-MS mode or a reflectron TOF-MS mode in the coaxial design. We designed ion optics to optimize detection sensitivity and mass resolution. For data acquisition, the instrument is controlled using LabVIEW control software. The total power requirement for the vacuum unit, control electronics unit, ion optics, and detection system is approximately 100 W. We achieve a detection limit of parts per billion by volume (ppbv) for on-line trace analysis of several organic compounds. A mass resolution of 800 at about 100 amu is obtained for reflectron TOF-MS mode in a 0.35 m long instrument. The application of on-line monitoring of diesel engine exhaust was demonstrated.

  2. 20-150-keV proton-impact-induced ionization of uracil: Fragmentation ratios and branching ratios for electron capture and direct ionization

    SciTech Connect

    Tabet, J.; Eden, S.; Feil, S.; Abdoul-Carime, H.; Farizon, B.; Farizon, M.; Ouaskit, S.; Maerk, T. D.

    2010-01-15

    Fragmentation ratios and branching ratios are measured for ionization and dissociative ionization for 20-150 keV (0.9-2.4v{sub 0}) proton collisions with gas-phase uracil molecules. Through event-by-event determination of the postcollision projectile charge, it is possible for such a key biomolecule to distinguish between electron capture (EC) by the incident proton and direct ionization (DI) without projectile neutralization. While the same fragment ion groups are observed in the mass spectra for both processes, EC induces dissociation with greater efficiency than DI in the impact energy range of 35-150 keV (1.2-2.4v{sub 0}). In this range EC is also less abundant than DI with a branching ratio for EC/total ionization of <50%. Moreover, whereas fragmentation ratios do not change with energy in the case of EC, DI mass spectra show a tendency for increased fragmentation at lower impact energies.

  3. Single Low-Dose Ionizing Radiation Induces Genotoxicity in Adult Zebrafish and its Non-Irradiated Progeny.

    PubMed

    Lemos, J; Neuparth, T; Trigo, M; Costa, P; Vieira, D; Cunha, L; Ponte, F; Costa, P S; Metello, L F; Carvalho, A P

    2017-02-01

    This study investigated to what extent a single exposure to low doses of ionizing radiation can induce genotoxic damage in irradiated adult zebrafish (Danio rerio) and its non-irradiated F1 progeny. Four groups of adult zebrafish were irradiated with a single dose of X-rays at 0 (control), 100, 500 and 1000 mGy, respectively, and couples of each group were allowed to reproduce following irradiation. Blood of parental fish and whole-body offspring were analysed by the comet assay for detection of DNA damage. The level of DNA damage in irradiated parental fish increased in a radiation dose-dependent manner at day 1 post-irradiation, but returned to the control level thereafter. The level of DNA damage in the progeny was directly correlated with the parental irradiation dose. Results highlight the genotoxic risk of a single exposure to low-dose ionizing radiation in irradiated individuals and also in its non-irradiated progeny.

  4. Low-energy triple differential cross sections for electron-impact ionization of helium

    NASA Astrophysics Data System (ADS)

    Chen, Zhangjin; Zhang, Suimeng; Shi, Qicun; Chen, Ji; Xu, Kezun

    1997-11-01

    The BBK model is modified by the introduction of effective Sommerfeld parameters for both symmetric and asymmetric geometries on an empirical basis, while still maintaining the philosophy that all three Coulomb interactions are included on an equal footing. The triple differential cross sections for electron-impact ionization of atomic helium at an incident energy of 40 eV in an asymmetric geometry are calculated. Results of this approach are compared with the absolute measurements and the only existing theoretical results of the convergent close-coupling method.

  5. Threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact

    SciTech Connect

    Ju, Yuanyuan; Zhang, Qingming

    2015-12-15

    Molecular dynamics method is used to study the threshold for plasma phase transition of aluminum single crystal induced by hypervelocity impact. Two effective simulation methods, piston-driven method and multi-scale shock technique, are used to simulate the shock wave. The simulation results from the two methods agree well with the experimental data, indicating that the shock wave velocity is linearly dependent on the particle velocity. The atom is considered to be ionized if the increase of its internal energy is larger than the first ionization energy. The critical impact velocity for plasma phase transition is about 13.0 km/s, corresponding to the threshold of pressure and temperature which is about 220 GPa and 11.0 × 10{sup 3 }K on the shock Hugoniot, respectively.

  6. Hyperfine structure constants of singly ionized manganese obtained from analysis of Fourier Transform spectra

    NASA Astrophysics Data System (ADS)

    Townley-Smith, Keeley; Nave, Gillian; Imperial College London

    2016-01-01

    There is an on-going project in the Atomic Spectroscopy Group at NIST to obtain comprehensive spectral data for all of the singly ionized iron group elements and acquire more accurate energy levels, wavelengths and hyperfine structure (HFS) constants. The heavy abundance of the iron group elements and their contributions to a wide range of stellar spectra makes them of interest for astrophysical observations.Existing spectroscopic data for Mn are insufficient to model spectra obtained from HgMn stars such as HD 175640. Since manganese has an odd number of nucleons, its spectral lines generally exhibit HFS, a relativistic effect due to interaction between the magnetic moment of the nucleus and the orbiting electrons. If proper treatment of line broadening effects such as HFS is not taken, there is a poor fit of the lines in stellar spectra, leading to an overestimate of the abundance of Mn. The abnormally high abundance of manganese in HgMn stars means both weak and strong transitions are important. Weak lines may not be observed in the laboratory, but HFS constants for them can be derived from stronger transitions that combine with the two levels involved in the weak transition.Holt et al. (1999) measured HFS constants for 56 energy levels using laser spectroscopy. We have analyzed Fourier Transform spectra of a high current Mn/Ni hollow cathode lamp to obtain magnetic dipole A constants levels of Mn II. The A constants of Holt et al. (1999, MNRAS 306, 1007) for the z5P, z7P2, a5P and z5F levels were the starting point for our analysis, from which we derived A constants for 71 energy levels, including 51 previously unstudied levels. Our A constant for the a7S3 ground level differs by 5x10-4 cm-1 from that of Blackwell-Whitehead et al. (2005, ApJS 157, 402) and has a factor of 6 lower uncertainty.

  7. Experimental and theoretical fully differential study of coherence effects in ionization of He by proton impact

    NASA Astrophysics Data System (ADS)

    Schulz, Michael; Arthanayaka, Thusitha; Lamichhane, Basu; Hasan, Ahmad; Gurung, Sudip; Remolina, Juan; Borbely, Sandor; Jarai-Szabo, Ferenc; Nagy, Ladislau

    2016-09-01

    We have measured and calculated fully differential cross sections (FDCS) for ionization of He by 75 keV proton impact. Results were obtained for transverse projectile coherence lengths of 3.3 and 1.0 a.u. The coherence length is related to the maximum dimension of a diffracting object that can be coherently illuminated by the projectiles. In the calculation impact parameter dependent amplitudes a(b) are computed and multiplied by a wave packet of varying width, reflecting the coherence length, which describes the projectile. The scattering angle dependent transition amplitude is then obtained from a Fourier transform. Pronounced coherence effects observed in the data are qualitatively well reproduced by the calculation. Along with extensive data published already the present work therefore confirms the presence of such effects beyond reasonable doubt. Work supported by NSF Grant No. PHY-1401586.

  8. Matrix-assisted laser desorption/ionization mass spectrometry method for selectively producing either singly or multiply charged molecular ions.

    PubMed

    Trimpin, Sarah; Inutan, Ellen D; Herath, Thushani N; McEwen, Charles N

    2010-01-01

    Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is noted for its ability to produce primarily singly charged ions. This is an attribute when using direct ionization for complex mixtures such as protein digests or synthetic polymers. However, the ability to produce multiply charged ions, as with electrospray ionization (ESI), has advantages such as extending the mass range on mass spectrometers with limited mass-to-charge (m/z) range and enhancing fragmentation for structural characterization. We designed and fabricated a novel field free transmission geometry atmopsheric pressure (AP) MALDI source mounted to a high-mass resolution Orbitrap Exactive mass spectrometer. We report the ability to produce at will either singly charged ions or highly charged ions using a MALDI process by simply changing the matrix or the matrix preparation conditions. Mass spectra with multiply charged ions very similar to those obtained with ESI of proteins such as cytochrome c and ubiquitin are obtained with low femtomole amounts applied to the MALDI target plate and for peptides such as angiotensin I and II with application of attomole amounts. Single scan acquisitions produce sufficient ion current even from proteins.

  9. Electron impact total ionization cross sections for simple bio-molecules (H2CO, HCOOH and CH3COOH) using ICSP-ic method

    NASA Astrophysics Data System (ADS)

    Bhutadia, Harshad; Vinodkumar, Minaxi; Antony, Bobby

    2012-11-01

    In the present work we compute total ionization cross sections for simple bio-molecules viz. formaldehyde, formic acid and acetic acid on electron impact. The total ionization cross sections are extracted from total inelastic cross section using Improved Complex Scattering Potential-ionization contribution method.

  10. Laserspray ionization on a commercial atmospheric pressure-MALDI mass spectrometer ion source: selecting singly or multiply charged ions.

    PubMed

    McEwen, Charles N; Larsen, Barbara S; Trimpin, Sarah

    2010-06-15

    Multiply charged ions, similar to those obtained with electrospray ionization, are produced at atmospheric pressure (AP) using standard MALDI conditions of laser fluence and reflective geometry. Further, the charge state can be switched to singly charged ions nearly instantaneously by changing the voltage applied to the MALDI target plate. Under normal AP-MALDI operating conditions in which a voltage is applied to the target plate, primarily singly charged ions are observed, but at or near zero volts, highly charged ions are observed for peptides and proteins. Thus, switching between singly and multiply charged ions requires only manipulation of a single voltage. As in ESI, multiple charging, produced using the AP-MALDI source, allows compounds with molecular weights beyond the mass-to-charge limit of the mass spectrometer to be observed and improves the fragmentation relative to singly charged ions.

  11. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, P.

    1996-06-25

    An ionization detector electrode and signal subtraction apparatus and method provide at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector. 9 figs.

  12. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, Paul

    1996-01-01

    An ionization detector electrode and signal subtraction apparatus and method provides at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector.

  13. Small-signal modeling with direct parameter extraction for impact ionization effect in high-electron-mobility transistors

    SciTech Connect

    Guan, He; Lv, Hongliang; Guo, Hui Zhang, Yuming

    2015-11-21

    Impact ionization affects the radio-frequency (RF) behavior of high-electron-mobility transistors (HEMTs), which have narrow-bandgap semiconductor channels, and this necessitates complex parameter extraction procedures for HEMT modeling. In this paper, an enhanced small-signal equivalent circuit model is developed to investigate the impact ionization, and an improved method is presented in detail for direct extraction of intrinsic parameters using two-step measurements in low-frequency and high-frequency regimes. The practicability of the enhanced model and the proposed direct parameter extraction method are verified by comparing the simulated S-parameters with published experimental data from an InAs/AlSb HEMT operating over a wide frequency range. The results demonstrate that the enhanced model with optimal intrinsic parameter values that were obtained by the direct extraction approach can effectively characterize the effects of impact ionization on the RF performance of HEMTs.

  14. Impact of ionizing radiation on the life cycle of Saccharomyces cerevisiae Ty1 retrotransposon.

    PubMed

    Sacerdot, Christine; Mercier, Géraldine; Todeschini, Anne-Laure; Dutreix, Marie; Springer, Mathias; Lesage, Pascale

    2005-04-30

    Ty1 elements, LTR-retrotransposons of Saccharomyces cerevisiae, are known to be activated by genetic and environmental stress. Several DNA-damaging agents have been shown to increase both Ty1 transcription and retrotransposition. To explore further the relationship between Ty1 mobility and DNA damage, we have studied the impact of ionizing radiation at different steps of the Ty1 life cycle. We have shown that Ty1 transposition is strongly activated by gamma-irradiation and we have analysed its effect on Ty1 transcription, TyA1 protein and Ty1 cDNA levels. The activation of transposition rises with increasing doses of gamma-rays and is stronger for Ty1 elements than for the related Ty2 elements. Ty1 RNA levels are markedly elevated upon irradiation; however, no significant increase of TyA1 protein was detected as measured by TYA1-lacZ fusions and by Western blot. A moderate increase in Ty1 cDNA levels was also observed, indicating that ionizing radiation can induce the synthesis of Ty1 cDNA. In diploid cells and ste12 mutants, where both Ty1 transcription and transposition are repressed, gamma-irradiation is able to activate Ty1 transposition and increases Ty1 RNA levels. These results suggest the existence of a specific regulatory pathway involved in Ty1 response to the gamma-irradiation that would be independent of Ste12 and mating-type factors. Our findings also indicate that ionizing radiation acts on several steps of the Ty1 life cycle.

  15. Quasi-simultaneous acquisition of hard electron ionization and soft single-photon ionization mass spectra during GC/MS analysis by rapid switching between both ionization methods: analytical concept, setup, and application on diesel fuel.

    PubMed

    Eschner, Markus S; Gröger, Thomas M; Horvath, Thomas; Gonin, Marc; Zimmermann, Ralf

    2011-05-15

    This work describes the realization of rapid switching between hard electron ionization (EI) and soft single-photon ionization (SPI) integrated in a compact orthogonal acceleration time-of-flight mass spectrometer. Vacuum-ultraviolet (VUV) photons of 9.8 eV (126 nm) emitted from the innovative electron-beam-pumped rare-gas excimer light source (EBEL) filled with argon are focused into the ion chamber by an ellipsoidal mirror optic for accomplishing of SPI. This novel orthogonal acceleration time-of-flight mass spectrometer with switching capability was hyphenated to one-dimensional gas chromatography (GC) and comprehensive two-dimensional (2D) gas chromatography (GC × GC) for the first time. Within this demonstration study, a maximum switching frequency of 80 Hz was applied for investigation of a mineral-oil-type diesel sample. This approach allows the quasi-simultaneous acquisition of complementary information about the fragmentation pattern (EI) as well as the molecular mass (SPI) of compounds within a single analysis. Furthermore, by application of a polar GC column for separation, the SPI data can be displayed in a 2D contour plot, leading to a comprehensive 2D characterization (GC × MS), whereas the typical group-type assignment for diesel is also met.

  16. Electron-impact ionization cross sections out of the ground and 6P2 excited states of cesium

    NASA Astrophysics Data System (ADS)

    Łukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-01

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the “trap loss” technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs 6P3/22 state between 7eV and 400eV . CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  17. INFLUENCE OF ELECTRON-IMPACT MULTIPLE IONIZATION ON EQUILIBRIUM AND DYNAMIC CHARGE STATE DISTRIBUTIONS: A CASE STUDY USING IRON

    SciTech Connect

    Hahn, M.; Savin, D. W.

    2015-02-10

    We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. Previous ionization balance calculations have largely neglected EIMI. Here, EIMI cross-section data are incorporated into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

  18. Impact ionization in the base of a hot-electron AlSb/InAs bipolar transistor

    NASA Technical Reports Server (NTRS)

    Vengurlekar, Arvind S.; Capasso, Federico; Chiu, T. Heng

    1990-01-01

    The operation of a new AlSb/InAs heterojunction bipolar transistor is studied. The electrons are injected into a p-InAs base across the AlSb/InAs heterojunction. The conduction-band discontinuity at this heterojunction is sufficiently large so that energy of the electrons injected into InAs exceeds the threshold for generating electron-hole pairs by impact ionization. The observed incremental common base current at zero collector-base bias decreases and becomes negative as the emitter current is increased, thus providing direct evidence for impact ionization entirely by band-edge discontinuities.

  19. Total ionizing dose and single-event effect in vertical channel double-gate nMOSFETs

    NASA Astrophysics Data System (ADS)

    Tan, Fei; An, Xia; Xue, Shoubin; Huang, Liangxi; Wu, Weikang; Zhang, Xing; Huang, Ru

    2013-05-01

    In this paper, the total ionizing dose (TID) and single-event effect (SEE) in vertical channel double-gate (DG) nMOSFETs are comprehensively investigated. Due to the vertical channel structure and the excellent gate control capability, the vertical channel DG transistor is relatively resistant to TID and transient ionization effect. However, the dc characteristics of vertical channel DG device are very sensitive to permanent damage induced by a few ions hitting the device. The on-state current and transconductance of the vertical channel DG MOSFETs show significant degradation after exposure to heavy ions, which is attributed to the formation of displacement damage in the channel. As the device feature size scales down to the deca-nanometer regime, the influence of permanent damage induced by a few ions striking the device static performance cannot be ignored and should be seriously considered in radiation-hardened technologies.

  20. Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

    SciTech Connect

    Ralchenko, Yu. Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de

    2008-07-15

    Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n{<=}4 are treated individually, while the states with n{>=}5 are considered degenerate. For the processes involving transitions to and from n{>=}5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.

  1. Relativistic electronic dressing in laser-assisted ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.

    2004-06-01

    Within the framework of the coplanar binary geometry where it is justified to use plane wave solutions for the study of the (e,2e) reaction and in the presence of a circularly polarized laser field, we introduce as a first step the Dirac-Volkov plane wave Born approximation 1 where we take into account only the relativistic dressing of the incident and scattered electrons. Then, we introduce the Dirac-Volkov plane wave Born approximation 2 where we take totally into account the relativistic dressing of the incident, scattered, and ejected electrons. We then compare the corresponding triple differential cross sections for laser-assisted ionization of atomic hydrogen by electron impact both for the nonrelativistic and the relativistic regime.

  2. Triple Differential Cross Sections for Ionization of Laser-Aligned Mg Atoms by electron impact

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Madison, Don; Nixon, Kate; Murray, Andrew

    2013-09-01

    3DW (3-body distorted wave) triple differential cross sections have been calculated for electron impact ionization of magnesium atoms aligned by lasers. Calculations have been performed for the kinematics of the experiment performed by Kate Nixon and Andrew Murray at Manchester, England [K. L. Nixon and A. J. Murray 2011 Phys. Rev. Lett. 106, 123201]. An incident projectile was produced with energy of 41.91eV, scattered and ejected electrons were detected with equal energies (E1 =E2 =20eV), the scattered projectile was detected at a fixed angle of 30deg, and the ejected electrons were detected at angles ranging between 0circ; - 180circ; . The theoretical 3DW results will be compared with the experimental data. This work is supported by the US National Science Foundation under Grant.No.PHY-1068237.

  3. Ionizing stellar population in the disc of NGC 3310 - I. The impact of a minor merger on galaxy evolution

    NASA Astrophysics Data System (ADS)

    Miralles-Caballero, D.; Díaz, A. I.; Rosales-Ortega, F. F.; Pérez-Montero, E.; Sánchez, S. F.

    2014-05-01

    Numerical simulations of minor mergers predict little enhancement in the global star formation activity. However, it is still unclear the impact they have on the chemical state of the whole galaxy and on the mass build-up in the galaxy bulge and disc. We present a two-dimensional analysis of NCG 3310, currently undergoing an intense starburst likely caused by a recent minor interaction, using data from the PPAK Integral Field Spectroscopy Nearby Galaxies Survey (PINGS). With data from a large sample of about a hundred H II regions identified throughout the disc and spiral arms, we derive, using strong-line metallicity indicators and direct derivations, a rather flat gaseous abundance gradient. Thus, metal mixing processes occurred, as in observed galaxy interactions. Spectra from PINGS data and additional multiwavelength imaging were used to perform a spectral energy distribution fitting to the stellar emission and a photoionization modelling of the nebulae. The ionizing stellar population is characterized by single populations with a narrow age range (2.5-5 Myr) and a broad range of masses (104-6 × 106 M⊙). The effect of dust grains in the nebulae is important, indicating that 25-70 per cent of the ultraviolet photons can be absorbed by dust. The ionizing stellar population within the H II regions represents typically a few per cent of the total stellar mass. This ratio, a proxy to the specific star formation rate, presents a flat or negative radial gradient. Therefore, minor interactions may indeed play an important role in the mass build-up of the bulge.

  4. Observation of terahertz-radiation-induced ionization in a single nano island

    NASA Astrophysics Data System (ADS)

    Seo, Minah; Kang, Ji-Hun; Kim, Hyo-Suk; Hyong Cho, Joon; Choi, Jaebin; Min Jhon, Young; Lee, Seok; Hun Kim, Jae; Lee, Taikjin; Park, Q.-Han; Kim, Chulki

    2015-05-01

    Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves.

  5. Observation of terahertz-radiation-induced ionization in a single nano island

    PubMed Central

    Seo, Minah; Kang, Ji-Hun; Kim, Hyo-Suk; Hyong Cho, Joon; Choi, Jaebin; Min Jhon, Young; Lee, Seok; Hun Kim, Jae; Lee, Taikjin; Park, Q-Han; Kim, Chulki

    2015-01-01

    Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves. PMID:25998840

  6. The Impact of Ionizing Radiation on the Microbial Reduction of Fe(III)

    NASA Astrophysics Data System (ADS)

    Brown, A.; Correa, E. S.; Xu, Y.; Vaughan, D. J.; Pimblott, S. M.; Goodacre, R.; Lloyd, J. R.

    2014-12-01

    Biogeochemical processes mediated by Fe(III)-reducing bacteria have the potential to impact on the post-closure evolution of a geological disposal facility (GDF) for radioactive waste. However, the organisms promoting these processes will likely be subject to significant radiation fluxes. Therefore, the impact of acute doses of ionizing radiation on the physiological status of the model Fe(III)-reducing bacterium Shewanella oneidensis was assessed. FT-IR spectroscopy and MALDI-TOF-MS suggested that the metabolic response to radiation is underpinned by alterations to lipids and proteins. Furthermore, the irradiated phenotype exhibits enhanced Fe(III)-reduction. The impact of radiation on the extracellular environment was also assessed. Exposure to gamma radiation caused activation of ferrihydrite and hematite for enzymatic reduction by S. oneidensis. TEM, SAED and Mössbauer spectroscopy revealed that this effect was a result of radiation induced changes to crystallinity leading to an increase in bioavailability of Fe(III) for respiration. To assess the impact of radiation on sediment microbial communities, a series of microcosm experiments were constructed and gamma irradiated over a two month period. Sediments irradiated at a dose rate of 0.5 Gy h-1 exhibited enhanced Fe(III) reduction despite receiving doses potentially lethal to indigenous microorganisms, whilst biogeochemical processes in sediments irradiated with 30 Gy h-1 were only partially restricted. Despite this, 16S rRNA gene pyrosequencing revealed significant dose-dependent shifts in the microbial communities in tandem with changes in microcosm biogeochemical profiles. Collectively, these results indicate that, despite significant total absorbed doses, biogeochemical processes will likely not be restricted by dose rates expected in a deep geological repository. Indeed, electron accepting processes in such environments may even be stimulated by radiation.

  7. Electron-impact dissociative excitation and ionization of N2D+

    SciTech Connect

    FogleJr, Michael R; Bahati Musafiri, Eric; Bannister, Mark E; Deng, Shihu; Vane, C Randy; Thomas, R. D.; Zhaunerchyk, Vitali

    2011-01-01

    Absolute cross sections for electron-impact dissociation of N{sub 2}D{sub +} producing N{sub 2}{sub +}, ND{sub +}, and N{sub +} ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N{sub 2}{sub +} production dominates. The N{sub 2}{sub +} + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [ M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas and V. Zhaunerchyk Phys. Rev. A 82 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N{sub 2}{sub +}, ND{sub +}, and N{sub +} ion fragment production are comparable. The observance of the ND{sub +} and N{sub +} ion fragments indicate breaking of the N - N bond along certain dissociation channels.

  8. Electron-impact dissociative excitation and ionization of N{sub 2}D{sup +}

    SciTech Connect

    Fogle, M.; Bahati, E. M.; Bannister, M. E.; Deng, S. H. M.; Vane, C. R.; Thomas, R. D.; Zhaunerchyk, V.

    2011-09-15

    Absolute cross sections for electron-impact dissociation of N{sub 2}D{sup +} producing N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N{sub 2}{sup +} production dominates. The N{sub 2}{sup +} + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragment production are comparable. The observance of the ND{sup +} and N{sup +} ion fragments indicate breaking of the N - N bond along certain dissociation channels.

  9. "DUST BUSTER" - A Single Photon Ionization TOF MS for Cometary Dusts

    NASA Technical Reports Server (NTRS)

    Chen, C.-Y.; Calaway, W. F.; Lee, Typhoon; Moore, J. F.; Pellin, M. J.; Veryovkin, I. V.

    2003-01-01

    It is hard to predict the properties and composition of dust that will be returned by STARDUST from WED- 2. The most interesting but challenging case would be grains, pg to fg in weight, each carrying its own isotopic signature characteristic of its source zones in a variety of stars. How do we extract the maximum amount of science from such grains? Clearly, the best that can be accomplished is to measure every atom in each grain.Academia Sinica and Argonne National Laboratory (ANL) have entered into a collaboration to develop a SPI TOF MS instrument for analysis of stardust grains. A new instrument will be built at Academia Sinica based on the new TOF mass spectrometer design developed, built and operating at ANL. The instrument is intended for SPI TOF MS analysis of elements from Ca to Cu plus Li after first using SIMS to measure H, C, N, 0, Si, and S. There are still technical challenges facing the technique. We will need to improve submicrometer sample handling, avoid the effects of space charge, and increase the Mamie range of the detector. The most difficult obstacle to overcome may be the fact that the flux density of present high repetition rate, WV lasers is below the level needed to ensure full ionization (saturation) in the source region, which must be several mm in size to achieve the high useful yield needed for analysis of small stardust grains. A potential breakthrough effort is to exploit the novel free electron laser being pioneered at ANL. In principle, this FEL can reach ionization saturation and is tunable up to photon energies of 25 eV, which is higher than the ionization potential of any element.

  10. Ensemble Monte Carlo calculation of the hole initiated impact ionization rate in bulk GaAs and silicon using a k-dependent, numerical transition rate formulation

    NASA Technical Reports Server (NTRS)

    Oguzman, Ismail H.; Wang, Yang; Kolnik, Jan; Brennan, Kevin F.

    1995-01-01

    The hole initiated impact ionization rate in bulk silicon and GaAs is calculated using a numerical formulation of the impact ionization transition rate incorporated into an ensemble Monte Carlo simulation. The transition rate is calculated from Fermi's golden rule using a two-body screened Coulomb interaction including a wavevector dependent dielectric function. It is found that the effective threshold for hole initiated ionization is relatively soft in both materials, that the split-off band dominates the ionization process in GaAs. and that no clear dominance by any one band is observed in silicon, though the rate out of the light hole band is greatest.

  11. Theoretical and experimental (e ,2 e ) study of electron-impact ionization of laser-aligned Mg atoms

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Murray, Andrew; Stauffer, Al; Nixon, Kate; Armstrong, Gregory; Colgan, James; Madison, Don

    2014-12-01

    We have performed calculations of the fully differential cross sections for electron-impact ionization of magnesium atoms. Three theoretical approximations, the time-dependent close coupling, the three-body distorted wave, and the distorted wave Born approximation, are compared with experiment in this article. Results will be shown for ionization of the 3 s ground state of Mg for both asymmetric and symmetric coplanar geometries. Results will also be shown for ionization of the 3 p state which has been excited by a linearly polarized laser which produces a charge cloud aligned perpendicular to the laser beam direction and parallel to the linear polarization. Theoretical and experimental results will be compared for several different alignment angles, both in the scattering plane as well as in the plane perpendicular to the incident beam direction.

  12. Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N{sub 2} and CO{sub 2}

    SciTech Connect

    Jin Cheng; Zhao Songfeng; Le, Anh-Thu; Lin, C. D.; Lucchese, R. R.

    2010-03-15

    We calculate photoelectron angular distributions (PADs) resulting from single-photon (43 eV) ionization of molecules that have been transiently aligned with a short laser pulse. The total ionization cross sections of N{sub 2} and CO{sub 2} vs the time delay between the aligning laser pulse and the soft x-ray photon are calculated and compared to experimental results reported by I. Thomann et al. [J. Phys. Chem. A 112, 9382 (2008)]. We present the PADs from these aligned molecules in the laboratory frame which can be compared directly with future experiments from aligned N{sub 2} and CO{sub 2}. The alignment dependence of single-photon ionization, multiphoton ionization, and high-order harmonic generation are also analyzed.

  13. Grid-based methods for diatomic quantum scattering problems II: Time-dependent treatment of single- and two-photon ionization of H2+

    SciTech Connect

    Rescigno, Thomas N.; Tao, L.; McCurdy, C.W.

    2009-04-20

    The time-dependent Schr\\"odinger equation for H2+ in a time-varying electromagnetic field is solved in the fixed-nuclei approximation using a previously developed finite-element/ discrete variable representation in prolate spheroidal coordinates. Amplitudes for single- and two-photon ionization are obtained using the method of exterior complex scaling to effectively propagate the field-free solutions from the end of the radiation pulse to infinite times. Cross sections are presented for one-and two-photon ionization for both parallel and perpendicular polarization of the photon field, as well as photoelectron angular distributions for two-photon ionization.

  14. Nonperturbative Treatment of Electron-Impact Ionization of Ar(3p)

    NASA Astrophysics Data System (ADS)

    Bartschat, Klaus; Zatsarinny, Oleg

    2012-06-01

    We present triple-differential cross sections for electron-impact ionization of a 3p electron in Ar. Results from a fully non-perturbative close-coupling formalism using our B-Spline R-matrix with Pseudo-States (BSRMPS) approach [1] are compared with those from a hybrid distorted-wave plus R-matrix expansion [2] as well as recent experimental data [3]. We find overall good agreement between the two sets of entirely independent theoretical predictions, but serious discrepancies with the published experimental data. A detailed investigation of the dependence of the results on the fixed detection angle of the ``scattered projectile'', i.e., the faster of the two outgoing electrons, suggests that obtaining reliable results, both experimentally and theoretically, is highly challenging in the regime where the largest discrepancies occur. Consequently, care should be taken before much weight is put on the remaining deviations between experiment and theory. Further independent tests seem highly desirable.[4pt] [1] O. Zatsarinny and K. Bartschat, Phys. Rev. Lett. 107 (2011) 023203.[0pt] [2] K. Bartschat and O. K. Vorov, Phys. Rev. A 72 (2005) 022728.[0pt] [3] X. Ren, A. Senftleben, T. Pfl"uger, A. Dorn, K. Bartschat, and J. Ullrich, Phys. Rev. A 83 (2011) 052714.

  15. Impact on radiogenic cancer risk of persons exhibiting abnormal sensitivity to ionizing radiation

    SciTech Connect

    Gentner, N.E.; Morrison, D.P.; Myers, D.K.

    1988-08-01

    Human genotypes are known that confer both increased susceptibility or resistance to DNA damage and increased cancer risk after exposure to carcinogenic agents, including ionizing radiation (NAS 1980). The existence of sensitive subgroups at elevated risk, if they are of appreciable size, could have significant impact on the actual distribution of risk. The radiosensitive disorder ataxia-telangiectasia (A-T) serves as a good example: the significant at risk group, A-T heterozygotes, is estimated to comprise between 0.5% and 5% of the total population, and has a twofold elevated lifetime risk of fatal neoplasia. Other genetic syndromes that manifest abnormal radiosensitivity are also known, but no estimates are available for the population frequency of all such phenotypes, or for their overall degree of increased risk. As the first part of a program addressing these questions, we have developed a rapid and inexpensive assay for screening members of the general population for abnormal radiosensitivity; such persons would be regarded as at presumptive elevated risk of radiogenic cancer. Our method utilizes lymphoblastoid cell lines and chronic as opposed to acute gamma-ray exposure to amplify the difference between normal and somewhat sensitive strains. A simple grow-back assay assesses the survival response. Information on the extent of natural variation in inherited susceptibility to radiogenic cancers could be most useful for radiation protection in the future.

  16. State-resolved ultrafast dynamics of impact ionization in InSb

    PubMed Central

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2014-01-01

    Impact ionization (IMP) is a fundamental process in semiconductors, which results in carrier multiplication through the decay of a hot electron into a low-energy state while generating an electron-hole pair. IMP is essentially a state selective process, which is triggered by electron-electron interaction involving four electronic states specified precisely by energy and momentum conservations. However, important state-selective features remain undetermined due to methodological limitations in identifying the energy and momentum of the states involved, at sufficient temporal resolution, to reveal the fundamental dynamics. Here we report state-resolved ultrafast hot electron dynamics of IMP in InSb, a semiconductor with the lowest band-gap energy. The ultrafast decay of state-resolved hot-electron populations and the corresponding population increase at the conduction band minimum are directly captured, and the rate of IMP is unambiguously determined. Our analysis, based on the direct knowledge of state-resolved hot electrons, provides far deeper insight into the physics of ultrafast electron correlation in semiconductors. PMID:25355408

  17. Electron impact fragmentation of adenine: partial ionization cross sections for positive fragments

    NASA Astrophysics Data System (ADS)

    van der Burgt, Peter J. M.; Finnegan, Sinead; Eden, Samuel

    2015-07-01

    Using computer-controlled data acquisition we have measured mass spectra of positive ions for electron impact on adenine, with electron energies up to 100 eV. Ion yield curves for 50 ions have been obtained and normalized by comparing their sum to the average of calculated total ionization cross sections. Appearance energies have been determined for 37 ions; for 20 ions for the first time. All appearance energies are consistent with the fragmentation pathways identified in the literature. Second onset energies have been determined for 12 fragment ions (for 11 ions for the first time), indicating the occurrence of more than one fragmentation process e.g. for 39 u (C2HN+) and 70 u (C2H4N3+). Matching ion yield shapes (118-120 u, 107-108 u, 91-92 u, and 54-56 u) provide new evidence supporting closely related fragmentation pathways and are attributed to hydrogen rearrangement immediately preceding the fragmentation. We present the first measurement of the ion yield curve of the doubly charged parent ion (67.5 u), with an appearance energy of 23.5 ± 1.0 eV. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.

  18. Experimental and Theoretical Fully differential cross sections for electron impact ionization of furfuryl molecules

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Jones, Darryl; Nixon, Kate; Ning, Chuangang; Brunger, Michael; Murray, Andrew; Madison, Don

    2015-09-01

    Experimental and theoretical Fully Differential Cross Sections (FDCS) are presented for 250 eV electron impact ionization of the highest and next highest occupied molecular orbitals (HOMO and NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of 5°, 10°, and 15°. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations. These approximations show good agreement with experimental data for binary peaks. However, for the recoil peak region, experiment finds a noticeable peak while theory predicts no peak. No recoil peak suggests no (or very weak) nuclear scattering, so we have investigated the importance of nuclear scattering by moving the nuclei closer to the center of mass. This work is supported by the US National Science Foundation under Grant No. PHY-1068237 and XSEDE resources provided by the Texas Advanced Computing Center (Grant No. TG-MCA07S029).

  19. Deep minimum in the triple differential cross sections for the electron-impact ionization of He

    NASA Astrophysics Data System (ADS)

    Colgan, James; Feagin, James; Pindzola, Michael

    2012-06-01

    We further explore the unusual deep minimum found in the triple differential cross sections for the electron-impact ionization of helium. This feature has been observed experimentally more than 15 years ago [1] and confirmed via close-coupling calculations [2]. A recent study [3] identified the minimum with a vortex in the two-electron continuum, and an analytic expansion of the electron pair about the vortex has recently been derived [4]. The imaging theorem [3] is invoked to compute the TDCS from the radial wavefunctions propagated in time via solution of the time-dependent Schr"odinger equation for the electron helium system. This allows us to more easily visualize the portion of the wavefunction that contributes to the TDCS at the specific ejected electron angles where the deep minimum is observed. Interesting features in the radial wavefunction as a function of time are found, which appear to be consistent with the prediction [3] that a vortex in the two-electron wavefunction is responsible for the observed deep minimum. [1] A. J. Murray and F. H. Read, J. Phys. B 26, L359 (1993). [2] J. Colgan et al, J. Phys. B. 42, 171001 2009. [3] J. H. Macek, et al, Phys. Rev. Letts. 104, 033201 (2010). [4] J. M. F Feagin, J. Phys. B 44, 011001 (2011).

  20. Analysis of the Lifecycle Impacts and Potential for Avoided Impacts Associated with Single Family Homes

    EPA Pesticide Factsheets

    Learn how recovering construction and demolition materials from single-family homes and reusing them in building and road construction and other applications helps offset the environmental impacts associated with single-family homes.

  1. Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

    NASA Astrophysics Data System (ADS)

    Torres, I.; Martínez, R.; Sánchez Rayo, M. N.; Castaño, F.

    2001-09-01

    The experimental electron-impact total ionization cross sections (TICSs, ICSs) of CF4, CHF3, CH2F2, and CH3F fluoromethanes reported so far and a new set of data obtained with a linear double focusing time-of-flight mass spectrometer have been compared with the ab initio and (semi)empirical based ICS available methods. TICSs computational methods include: two approximations of the binary-encounter dipole (BED) referred to hereafter as Kim (Kim-BEB) and Khare (Khare-BEB) methods, the Deutsch and Märk (DM) formalism, also requiring atomic and molecular ab initio information, the modified additivity rule (MAR), and the Harland and Vallance (HV) methods, both based on semiempirical or empirical correlations. The molecular ab initio information required by the Kim, Khare, and DM methods has been computed at a variety of quantum chemistry levels, with and without electron correlation and a comprehensive series of basis sets. The general conclusions are summarized as follows: the Kim method yields TICS in excellent agreement with the experimental method; the Khare method provides TICS very close to that of Kim at low electron-impact energies (<100 eV), but their Mott and Bethe contributions are noticeably different; in the Kim and Khare approximations the electron correlation methods improve the fittings to the experimental profiles in contrast with the large basis sets, that leads to poorer results; the DM formalism yields TICS profiles with shapes similar to the experimental and the BEB methods, but consistently lower and with the profiles maxima shifted towards lower incident electron energies; the MAR method supplies very good ICS profiles, between those of BEB and DM methods; finally, the empirical HV method provides rather poor fittings concomitant with the simplicity and the few empirical parameters used.

  2. Theoretical predictions for ionization cross sections of DNA nucleobases impacted by light ions.

    PubMed

    Champion, C; Lekadir, H; Galassi, M E; Fojón, O; Rivarola, R D; Hanssen, J

    2010-10-21

    Induction of DNA double strand breaks after irradiation is considered of prime importance for producing radio-induced cellular death or injury. However, up to now ion-induced collisions on DNA bases remain essentially experimentally approached and a theoretical model for cross section calculation is still lacking. Under these conditions, we here propose a quantum mechanical description of the ionization process induced by light bare ions on DNA bases. Theoretical predictions in terms of differential and total cross sections for proton, α-particle and bare ion carbon beams impacting on adenine, cytosine, thymine and guanine bases are then reported in the 10 keV amu(-1)-10 MeV amu(-1) energy range. The calculations are performed within the first-order Born approximation (FBA) with biological targets described at the restricted Hartree-Fock level with geometry optimization. Comparisons to recent theoretical data for collisions between protons and cytosine point out huge discrepancies in terms of differential as well as total cross sections whereas very good agreement is shown with our previous classical predictions, especially at high impact energies (E(i) ≥ 100 keV amu(-1)). Finally, in comparison to the rare existing experimental data a systematic underestimation is observed in particular for adenine and thymine whereas a good agreement is reported for cytosine. Thus, further improvements appear as necessary, in particular by using higher order theories like the continuum-distorted-wave one in order to obtain a better understanding of the underlying physics involved in such ion-DNA reactions.

  3. Ionization of high-density deep donor defect states explains the low photovoltage of iron pyrite single crystals.

    PubMed

    Cabán-Acevedo, Miguel; Kaiser, Nicholas S; English, Caroline R; Liang, Dong; Thompson, Blaise J; Chen, Hong-En; Czech, Kyle J; Wright, John C; Hamers, Robert J; Jin, Song

    2014-12-10

    Iron pyrite (FeS2) is considered a promising earth-abundant semiconductor for solar energy conversion with the potential to achieve terawatt-scale deployment. However, despite extensive efforts and progress, the solar conversion efficiency of iron pyrite remains below 3%, primarily due to a low open circuit voltage (VOC). Here we report a comprehensive investigation on {100}-faceted n-type iron pyrite single crystals to understand its puzzling low VOC. We utilized electrical transport, optical spectroscopy, surface photovoltage, photoelectrochemical measurements in aqueous and acetonitrile electrolytes, UV and X-ray photoelectron spectroscopy, and Kelvin force microscopy to characterize the bulk and surface defect states and their influence on the semiconducting properties and solar conversion efficiency of iron pyrite single crystals. These insights were used to develop a circuit model analysis for the electrochemical impedance spectroscopy that allowed a complete characterization of the bulk and surface defect states and the construction of a detailed energy band diagram for iron pyrite crystals. A holistic evaluation revealed that the high-density of intrinsic surface states cannot satisfactorily explain the low photovoltage; instead, the ionization of high-density bulk deep donor states, likely resulting from bulk sulfur vacancies, creates a nonconstant charge distribution and a very narrow surface space charge region that limits the total barrier height, thus satisfactorily explaining the limited photovoltage and poor photoconversion efficiency of iron pyrite single crystals. These findings lead to suggestions to improve single crystal pyrite and nanocrystalline or polycrystalline pyrite films for successful solar applications.

  4. General model of depolarization and transfer of polarization of singly ionized atoms by collisions with hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Derouich, M.

    2017-02-01

    Simulations of the generation of the atomic polarization is necessary for interpreting the second solar spectrum. For this purpose, it is important to rigorously determine the effects of the isotropic collisions with neutral hydrogen on the atomic polarization of the neutral atoms, ionized atoms and molecules. Our aim is to treat in generality the problem of depolarizing isotropic collisions between singly ionized atoms and neutral hydrogen in its ground state. Using our numerical code, we computed the collisional depolarization rates of the p-levels of ions for large number of values of the effective principal quantum number n* and the Unsöld energy Ep. Then, genetic programming has been utilized to fit the available depolarization rates. As a result, strongly non-linear relationships between the collisional depolarization rates, n* and Ep are obtained, and are shown to reproduce the original data with accuracy clearly better than 10%. These relationships allow quick calculations of the depolarizing collisional rates of any simple ion which is very useful for the solar physics community. In addition, the depolarization rates associated to the complex ions and to the hyperfine levels can be easily derived from our results. In this work we have shown that by using powerful numerical approach and our collisional method, general model giving the depolarization of the ions can be obtained to be exploited for solar applications.

  5. Impacts of Ionizing Radiation on the Different Compartments of the Tumor Microenvironment

    PubMed Central

    Leroi, Natacha; Lallemand, François; Coucke, Philippe; Noel, Agnès; Martinive, Philippe

    2016-01-01

    Radiotherapy (RT) is one of the most important modalities for cancer treatment. For many years, the impact of RT on cancer cells has been extensively studied. Recently, the tumor microenvironment (TME) emerged as one of the key factors in therapy resistance. RT is known to influence and modify diverse components of the TME. Hence, we intent to review data from the literature on the impact of low and high single dose, as well as fractionated RT on host cells (endothelial cells, fibroblasts, immune and inflammatory cells) and the extracellular matrix. Optimizing the schedule of RT (i.e., dose per fraction) and other treatment modalities is a current challenge. A better understanding of the cascade of events and TME remodeling following RT would be helpful to design optimal treatment combination. PMID:27064581

  6. Regularities And Irregularities Of The Stark Parameters For Single Ionized Noble Gases

    NASA Astrophysics Data System (ADS)

    Peláez, R. J.; Djurovic, S.; Cirišan, M.; Aparicio, J. A.; Mar S.

    2010-07-01

    Spectroscopy of ionized noble gases has a great importance for the laboratory and astrophysical plasmas. Generally, spectra of inert gases are important for many physics areas, for example laser physics, fusion diagnostics, photoelectron spectroscopy, collision physics, astrophysics etc. Stark halfwidths as well as shifts of spectral lines are usually employed for plasma diagnostic purposes. For example atomic data of argon krypton and xenon will be useful for the spectral diagnostic of ITER. In addition, the software used for stellar atmosphere simulation like TMAP, and SMART require a large amount of atomic and spectroscopic data. Availability of these parameters will be useful for a further development of stellar atmosphere and evolution models. Stark parameters data of spectral lines can also be useful for verification of theoretical calculations and investigation of regularities and systematic trends of these parameters within a multiplet, supermultiplet or transition array. In the last years, different trends and regularities of Stark parameters (halwidths and shifts of spectral lines) have been analyzed. The conditions related with atomic structure of the element as well as plasma conditions are responsible for regular or irregular behaviors of the Stark parameters. The absence of very close perturbing levels makes Ne II as a good candidate for analysis of the regularities. Other two considered elements Kr II and Xe II with complex spectra present strong perturbations and in some cases an irregularities in Stark parameters appear. In this work we analyze the influence of the perturbations to Stark parameters within the multiplets.

  7. Benchmark experiment for electron-impact ionization of argon: Absolute triple-differential cross sections via three-dimensional electron emission images

    SciTech Connect

    Ren Xueguang; Senftleben, Arne; Pflueger, Thomas; Dorn, Alexander; Ullrich, Joachim; Bartschat, Klaus

    2011-05-15

    Single ionization of argon by 195-eV electron impact is studied in an experiment, where the absolute triple-differential cross sections are presented as three-dimensional electron emission images for a series of kinematic conditions. Thereby a comprehensive set of experimental data for electron-impact ionization of a many-electron system is produced to provide a benchmark for comparison with theoretical predictions. Theoretical models using a hybrid first-order and second-order distorted-wave Born plus R-matrix approach are employed to compare their predictions with the experimental data. While the relative shape of the calculated cross section is generally in reasonable agreement with experiment, the magnitude appears to be the most significant problem with the theoretical treatment for the conditions studied in the present work. This suggests that the most significant challenge in the further development of theory for this process may lie in the reproduction of the absolute scale rather than the angular dependence of the cross section.

  8. Single-photon double ionization of H2 away from equilibrium: A showcase of two-center electron interference

    NASA Astrophysics Data System (ADS)

    Serov, Vladislav V.; Ivanov, I. A.; Kheifets, A. S.

    2012-08-01

    We demonstrate the effect of two-center interference on single-photon double ionization [double photoionization (DPI)] of the aligned H2 molecule when it shrinks or expands from the equilibrium internuclear distance. This interference affects the first stage of the DPI process in which the primary photoelectron is ejected predominantly along the polarization axis of light and its geometrical interference factor is most sensitive to the internuclear distance in the parallel (Σ) orientation of the internuclear and polarization axes. This effect is responsible for strong modification of the DPI amplitude in the parallel orientation while the corresponding amplitude for the perpendicular (Π) orientation is rather insensitive to the internuclear distance. The combination of these two factors explains the profound kinetic energy release effect on the fully differential cross sections of DPI of H2.

  9. Auger Recombination and Impact Ionization in Semiconductor Lasers and Avalanche Photodiodes.

    NASA Astrophysics Data System (ADS)

    Jiang, Yuan

    The telecommunication industry has been advancing very fast. Having used.8 μm optical fiber systems for a short time, the industry has quickly shifted to 1.3 and 1.5 μm optical fiber communication systems to achieve lower loss and longer distance between repeaters. However, the performance of the transmitters and receivers in the current long wavelength communication systems is not able to match that in the 0.8 μm communication system. The most serious problem with InGaAsP/InP lasers for 1.3 and 1.5 μm communications is their poor temperature performance. The threshold current of these lasers increases drastically with temperature at room temperature. This either causes thermal-run-off or makes a thermal controller a necessity even for a low -power laser. Studies have shown that the poor temperature performance in InGaAsP/InP lasers is caused by Auger recombination carrier losses. In GaAs lasers, Auger recombination carrier loss is not severe enough to degrade performance. However, it has been the major problem for most long-wavelength semiconductor lasers, such as InGaAsP/InP lasers for 1.3 and 1.5 μm communications. Not only transmitters, but also receivers for 1.3 and 1.5 μm communications face similar challenge. The performance of the InGaAsP/InP avalanche photodiodes (APDs) used in current systems is far from that of the Si APDs, which are nearly perfect, used in 0.8 μm systems. Avalanche (impact ionization) processes are the reverse Auger processes --carrier creation processes. They provide current amplification. Because virtually only one type of carrier (electron) multiplies in Si, the APDs have low noise figure and high gain-bandwidth products. The electron and hole impact ionization rates in InP are alike, which means the multiplication is a delayed positive feedback process. Therefore, these APDs are noisy amplifiers and have low gain-bandwidth products. At the best operating condition, the gain for a Si APD of several hundreds is typical, whereas

  10. Ionization of a lithium ion by electron impact in a strong laser field

    SciTech Connect

    Ghosh Deb, S.; Sinha, C.; Chattopadhyay, A.

    2011-12-15

    The modification in the dynamics of the electron-impact ionization process of a Li{sup +} ion due to an intense linearly polarized monochromatic laser field (n{gamma}e,2e) is studied theoretically using coplanar geometry. Significant laser modifications are noted due to multiphoton effects both in the shape and magnitude of the triple-differential cross sections (TDCSs) with respect to the field-free (FF) situation. The net effect of the laser field is to suppress the FF cross sections in the zeroth-order approximation [Coulomb-Volkov (CV)] of the ejected electron wave function, while in the first order [modified Coulomb-Volkov (MCV)], the TDCSs are found to be enhanced or suppressed depending on the kinematics of the process. The strong FF recoil dominance for the (e,2e) process of an ionic target at low incident energy is destroyed in the presence of the laser field. The FF binary-to-recoil ratio changes remarkably in the presence of the laser field, particularly at low incident energies. The difference between the multiphoton CV and the FF results indicates that for the ionic target, the Kroll-Watson sum rule does not hold well at the present energy range in contrast to the neutral atom (He) case. The TDCSs are found to be quite sensitive with respect to the initial phase of the laser field, particularly at higher incident energies. A significant qualitative difference is noted in the multiphoton ejected energy distribution (double-differential cross sections) between the CV and the MCV models. Variation of the TDCSs with respect to the laser phase is also studied.

  11. The second Born approximation for the double ionization of N2 by electron impact

    NASA Astrophysics Data System (ADS)

    Lamy, P.; Dal Cappello, C.; Charpentier, I.; Ruiz-Lopez, M. F.; Hervieux, P. A.

    2016-07-01

    In their (e,3e) and (e,3-1e) experiments of the double ionization (DI) of the outermost orbital of N2, Li et al (2012 J. Phys. B: At. Mol. Opt. Phys. 45 135201) recently showed that the process is largely dominated by a two-step-2 mechanism, which is a double interaction of the incident electron with the target. From a theoretical point of view, this should entail the use of the second Born approximation. In the past, very few theoretical calculations had been carried out this way because it requires a difficult numerical triple integration. We propose here to take into account the second Born approximation for the DI of N2 by using the closure approximation. The initial state is described by a single-center wave function derived from the usual multi-center wave function obtained in the self-consistent-field Hartree-Fock method using the linear combination of atomic orbitals-molecular orbital (LCAO-MO) approximation. The final state describes the interaction between each of the ejected electrons and the target by a Coulomb wave and the interaction between the two ejected electrons with the use of the Gamow factor. We calculate differential cross sections using the same kinematic conditions as Li et al (intermediate incident energy about 600 eV) for (e,3e) and (e,3-1e) DI of N2. The results show that the model does not allow a shift of the variation of the four-fold differential cross section near the momentum transfer to be obtained nor its opposite when we include the contribution given by the second Born approximation, as in (e,3-1e) experiments.

  12. Total ionizing dose (TID) effect and single event effect (SEE) in quasi-SOI nMOSFETs

    NASA Astrophysics Data System (ADS)

    Tan, Fei; Huang, Ru; An, Xia; Wu, Weikang; Feng, Hui; Huang, Liangxi; Fan, Jiewen; Zhang, Xing; Wang, Yangyuan

    2014-01-01

    This paper studies the total ionizing dose (TID) and single event effect (SEE) in quasi-SOI nMOSFETs for the first time. After exposure to gamma rays, the off-state leakage current (Ioff) of a quasi-SOI device increases with the accumulating TID, and the on-state bias configuration is shown to be the worst-case bias configuration during irradiation. Although an additional TID-sensitive region is introduced by the unique structure of the quasi-SOI device, the influence of positive charge trapped in L-type oxide layers on the degradation of device performance is neglectable. Since the TID-induced leakage path in the quasi-SOI device is greatly reduced due to the isolation of L-type oxide layers, the TID-induced Ioff degradation in the quasi-SOI device is greatly suppressed. In addition, 3D simulation is performed to investigate the SEE of the quasi-SOI device. The full-width at half-maximum (FWHM) of worst-case drain current transient and collected charges of the quasi-SOI device after single-ion-striking is smaller than in a bulk Si device, indicating that the quasi-SOI device inherits the advantage of an SOI device in single event transient immunity. Therefore, the quasi-SOI device, which has improved electrical properties and radiation-hardened characteristics for both TID and SEE, can be considered as one of the promising candidates for space applications.

  13. Complete momentum balance in ionization of H2 by 75-keV-proton impact for varying projectile coherence

    NASA Astrophysics Data System (ADS)

    Sharma, S.; Arthanayaka, T. P.; Hasan, A.; Lamichhane, B. R.; Remolina, J.; Smith, A.; Schulz, M.

    2014-05-01

    We report on a kinematically complete experiment on ionization of H2 by proton impact. While a significant impact of the projectile coherence properties on the scattering-angle dependence of double-differential cross sections (DDCSs), reported earlier, is confirmed by the present data, only weak coherence effects are found in the electron and recoil-ion momentum dependence of the DDCSs. This suggests that the phase angle in the interference term is determined primarily by the projectile momentum transfer rather than by the recoil-ion momentum. We therefore cannot rule out the possibility that the interference observed in our data is not primarily due to a two-center effect.

  14. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  15. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3 p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  16. The kinetic energy spectrum of protons produced by the dissociative ionization of H2 by electron impact

    NASA Technical Reports Server (NTRS)

    Khakoo, M. A.; Srivastava, S. K.

    1985-01-01

    The kinetic energy spectra of protons resulting from the dissociative ionization of H2 by electron impact have been measured for electron impact energies from threshold (approximately 17 eV) to 160 eV at 90 deg and 30 deg detection angles, using a crossed-beam experimental arrangement. To check reliability, two separate proton energy analysis methods have been employed, i.e., a time-of-flight proton energy analysis and an electrostatic hemispherical energy analyzer. The present results are compared with previous measurements.

  17. Ion-Atom/Argon—Calculation of ionization cross sections by fast ion impact for neutral target atoms ranging from hydrogen to argon

    NASA Astrophysics Data System (ADS)

    McSherry, D. M.; O'Rourke, S. F. C.; Crothers, D. S. F.

    2003-10-01

    A FORTRAN 90 program is presented which calculates the total cross sections, and the electron energy spectra of the singly and doubly differential cross sections for the single target ionization of neutral atoms ranging from hydrogen up to and including argon. The code is applicable for the case of both high and low Z projectile impact in fast ion-atom collisions. The theoretical models provided for the program user are based on two quantum mechanical approximations which have proved to be very successful in the study of ionization in ion-atom collisions. These are the continuum-distorted-wave (CDW) and continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximations. The codes presented here extend previously published codes for single ionization of target hydrogen [Crothers and McCartney, Comput. Phys. Commun. 72 (1992) 288], target helium [Nesbitt, O'Rourke and Crothers, Comput. Phys. Commun. 114 (1998) 385] and target atoms ranging from lithium to neon [O'Rourke, McSherry and Crothers, Comput. Phys. Commun. 131 (2000) 129]. Cross sections for all of these target atoms may be obtained as limiting cases from the present code. Program summaryTitle of program: ARGON Catalogue identifier: ADSE Program summary URL:http://cpc.cs.qub.ac.uk/cpc/summaries/ADSE Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Computer for which the program is designed and others on which it is operable: Computers: Four by 200 MHz Pro Pentium Linux server, DEC Alpha 21164; Four by 400 MHz Pentium 2 Xeon 450 Linux server, IBM SP2 and SUN Enterprise 3500 Installations: Queen's University, Belfast Operating systems under which the program has been tested: Red-hat Linux 5.2, Digital UNIX Version 4.0d, AIX, Solaris SunOS 5.7 Compilers: PGI workstations, DEC CAMPUS Programming language used: FORTRAN 90 with MPI directives No. of bits in a word: 64, except on Linux servers 32 Number of processors used: any number Has the

  18. Isomer and Fluorination Effects among Fluorine Substituted Hydrocarbon C3/C4 Molecules in Electron Impact Ionization

    NASA Astrophysics Data System (ADS)

    Patel, U. R.; Joshipura, K. N.

    2015-05-01

    Electron collision processes are very important in both man-made and natural plasmas, for determining the energy balances and transport properties of electrons. Electron -molecule scattering leading to ionization represents one of the most fundamental processes in collision physics. In the gas phase, the total efficiency of the process is described by the absolute total electron impact ionization cross section. Carbon based materials are some of the widely used materials for a divertor plate and magnetically confined fusion devices. In the ``ITER,'' it is very important for steady state operation to have an estimate of the lifetime of carbon plasma facing components. Apart from fusion plasma relevance, the present theoretical study is very important in modeling and controlling other electron assisted processes in many areas. Hydrocarbons play an important role for plasma diagnostics as impurities in the Tokamak fusion divertor, as seed gases for the production of radicals and ions in low temperature plasma processing. Fluorine substituted hydrocarbons (perfluorocarbons) are important as reactants in plasma assisted fabrication processes. In the present work, we have calculated total ionization cross sections Qion for C3/C4 Hydrocarbon isomers by electron impact, and comparisons are made mutually to observe isomer effect. Comparisons are also made by substituting H atom by F atom and revealing fluorination effect. The present calculations are quite significant owing to the lack of experimental data, with just an isolated previous theoretical work in some cases.

  19. Impact of electron ionization on the generation of high-order harmonics from molecules

    SciTech Connect

    Brener, S.; Moiseyev, N.; Ivanov, M. V.

    2003-08-01

    When the laser frequency is tuned to be equal to the molecular electronic excitation, high-order harmonics are generated due to the electronic dipole transitions between the corresponding two potential-energy surfaces (PES). A natural, often taken, choice is the PES of the field-free molecular system. In this special choice the ionization phenomenon is not considered. Only the effect of the dissociation is considered. The method we developed enables one to remain within the framework of the 2-PES approximation and yet to include also the ionization effect in the calculations of molecular high-order harmonic generation spectra. In this approach the coupling between the electronic and nuclear motions is taken into consideration by using coupled complex adiabatic PES. As an illustrative numerical example, we calculated the high harmonic generation (HHG) spectra of H{sub 2}{sup +} in a 730-nm laser with the intensity of 8.77x10{sup 13} W/cm{sup 2}. The inclusion of the ionization in our approach not only enables the electrons to tunnel through the effective static potential barrier, but also apply an asymmetric force which accelerates the electron before ionization takes place. Therefore, indirectly the inclusion of the ionization by the laser field may lead eventually to an enhanced HHG spectra in comparison with the calculated one when the ''natural'' choice of the field-free 2PES is taken.

  20. Reducing Collisional Breakup Of A System Of Charged Particles To Practical Computation: Electron-Impact Ionization Of Hydrogen

    SciTech Connect

    McCurdy, C.W.; Baertschy, M.; Isaacs, W.A.; Rescigno, T.N.

    2001-08-24

    It has been a goal of researchers in the area of atomic collisions for nearly half a century to reduce to practical computation the simplest problem in collisional ionization: the electron-impact ionization of atomic hydrogen. The principal barrier to solving this problem has been the difficult boundary conditions that apply to the complete breakup of a system charged particles. We describe how this goal has been accomplished in the last five years by the application of the mathematical transformation of ''exterior complex scaling'' together with an appropriate formalism for computing the breakup amplitudes from a numerical representation of the complete solution of the Schrodinger equation. Some successes of other recent approaches to this problem are also described.

  1. Impact of Dielectronic Recombination on Ionization Dynamics and Spectroscopy of Z-pinch Stainless Steel Plasma

    SciTech Connect

    Dasgupta, A.; Davis, J.; Thornhill, J. W.; Giuliani, J. L.; Chong, Y. K.; Clark, R. W.; Whitney, K. G.

    2009-01-21

    The implosion dynamics of an array of stainless steel (SS) wires on the Z and/or ZR accelerator produces an abundance of radiation from the K- and L-shell ionization stages. As the plasma assembles on axis, a number of time resolved snapshots provide temperature and density profiles and size of the emitting region. The non-LTE populations will be obtained by using detailed atomic models that include all important excitation, ionization, and recombination processes. In particular, we will investigate the effects of dielectronic recombination (DR) which is the most important recombination process for moderate to high Z plasma such as iron at moderate densities. We will analyze the ionization dynamics and generate K- and L-shell spectra using the temperature and density conditions generated in the Z and/or ZR accelerator describing the implosion with a 1-D non-LTE radiation hydrodynamics model.

  2. Single cell ionization by a laser trap: a preliminary study in measuring radiation dose and charge in BT20 breast carcinoma cells

    PubMed Central

    Kelley, Michele; Gao, Ying; Erenso, Daniel

    2016-01-01

    In this work, a preliminary study in the application of a laser trap for ionization of living carcinoma cells is presented. The study was conducted using BT20 breast carcinoma cells cultured and harvested in our laboratory. Each cell, for a total of 50 cells, was trapped and ionized by a high intensity infrared laser at 1064 nm. The threshold radiation dose and the resultant charge from the ionization for each cell were determined. With the laser trap serving as a radiation source, the cell underwent dielectric breakdown of the membrane. When this process occurs, the cell becomes highly charged and its dielectric susceptibility changes. The charge creates an increasing electrostatic force while the changing dielectric susceptibility diminishes the strength of the trapping force. Consequently, at some instant of time the cell gets ejected from the trap. The time inside the trap while the cell is being ionized, the intensity of the radiation, and the post ionization trajectory of the cell were used to determine the threshold radiation dose and the charge for each cell. The measurement of the charge vs ionization radiation dose at single cell level could be useful in the accuracy of radiotherapy as the individual charges can collectively create a strong enough electrical interaction to cause dielectric breakdown in other cells in a tumor. PMID:27699110

  3. Single differential projectile ionization cross sections d σ/dEe for 50 AMeV U28+ in the ESR storage ring

    NASA Astrophysics Data System (ADS)

    Hagmann, Siegbert; Hillenbrand, Pierre-Michel; Stoehlker, Thomas; Litvinov, Yuri; Appa-Sparc Collaboration

    2013-05-01

    The very high intensity beams of relativistic high Z ions with incident collision energies up to 2.7AGeV requested for experiments using the SIS100 synchrotron of FAIR require that 1.3 1011 ions at 2.6Hz be injected from SIS12/18 into SIS100. The needed luminosity of the beam can only be achieved for such high Z ions when - considering the space charge limit (~A/q2) - a low charge state q of the ion to be accelerated keeps the particle density at the highest feasible level. For a thorough understanding of beam loss it is imperative that the mechanisms active in projectile ionization be understood quantitatively to provide benchmarks for advancedab initio theories beyond first order. We have embarked on an experimental investigation of single differential projectile ionization cross sections d σ/dEe (SDCS) for single and multiple ionization of U28+in the ESR storage ring by measuring the electron loss to continuum (ELC) cusp at 00 with respect to the beam axis employing our imaging forward electron spectrometer. This was motivated by the high relative fraction of multiple ionization estimated to exceed 40%. We report first results for absolute projectile ionization SDCS for U28+. We find a remarkably high asymmetry for the ELC cusp. This is at strong variance with the line shape expected for validity of first order theories.

  4. Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 MeV by electron spectroscopy

    SciTech Connect

    Iriki, Y.; Kikuchi, Y.; Imai, M.; Itoh, A.

    2011-11-15

    Double-differential ionization cross sections (DDCSs) of vapor-phase adenine molecules (C{sub 5}H{sub 5}N{sub 5}) by 0.5- and 2.0-MeV proton impact have been measured by the electron spectroscopy method. Electrons ejected from adenine were analyzed by a 45 Degree-Sign parallel-plate electrostatic spectrometer over an energy range of 1.0-1000 eV at emission angles from 15 Degree-Sign to 165 Degree-Sign . Single-differential cross sections (SDCSs) and total ionization cross sections (TICSs) were also deduced. It was found from the Platzman plot, defined as SDCSs divided by the classical Rutherford knock-on cross sections per target electron, that the SDCSs at higher electron energies are proportional to the total number of valence electrons (50) of adenine, while those at low-energy electrons are highly enhanced due to dipole and higher-order interactions. The present results of TICS are in fairly good agreement with recent classical trajectory Monte Carlo calculations, and moreover, a simple analytical formula gives nearly equivalent cross sections in magnitude at the incident proton energies investigated.

  5. Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 MeV by electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Iriki, Y.; Kikuchi, Y.; Imai, M.; Itoh, A.

    2011-11-01

    Double-differential ionization cross sections (DDCSs) of vapor-phase adenine molecules (C5H5N5) by 0.5- and 2.0-MeV proton impact have been measured by the electron spectroscopy method. Electrons ejected from adenine were analyzed by a 45∘ parallel-plate electrostatic spectrometer over an energy range of 1.0-1000 eV at emission angles from 15∘ to 165∘. Single-differential cross sections (SDCSs) and total ionization cross sections (TICSs) were also deduced. It was found from the Platzman plot, defined as SDCSs divided by the classical Rutherford knock-on cross sections per target electron, that the SDCSs at higher electron energies are proportional to the total number of valence electrons (50) of adenine, while those at low-energy electrons are highly enhanced due to dipole and higher-order interactions. The present results of TICS are in fairly good agreement with recent classical trajectory Monte Carlo calculations, and moreover, a simple analytical formula gives nearly equivalent cross sections in magnitude at the incident proton energies investigated.

  6. Impact of Spacecraft Shielding on Direct Ionization Soft Error Rates for sub-130 nm Technologies

    NASA Technical Reports Server (NTRS)

    Pellish, Jonathan A.; Xapsos, Michael A.; Stauffer, Craig A.; Jordan, Michael M.; Sanders, Anthony B.; Ladbury, Raymond L.; Oldham, Timothy R.; Marshall, Paul W.; Heidel, David F.; Rodbell, Kenneth P.

    2010-01-01

    We use ray tracing software to model various levels of spacecraft shielding complexity and energy deposition pulse height analysis to study how it affects the direct ionization soft error rate of microelectronic components in space. The analysis incorporates the galactic cosmic ray background, trapped proton, and solar heavy ion environments as well as the October 1989 and July 2000 solar particle events.

  7. Use of Relativistic Effective Core Potentials in the Calculation of Electron-Impact Ionization Cross Sections

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Kim, Yong-Ki

    1999-01-01

    Based on the Binary-Encounter-Bethe (BEB) model, the advantage of using relativistic effective core potentials (RECP) in the calculation of total ionization cross sections of heavy atoms or molecules containing heavy atoms is discussed. Numerical examples for Ar, Kr, Xe, and WF6 are presented.

  8. New Measurement of Singly Ionized Selenium Spectra by High Resolution Fourier Transform and Grating Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hala, Noman; Nave, G.; Kramida, A.; Ahmad, T.; Nahar, S.; Pradhan, A.

    2015-05-01

    We report new measurements of singly ionised selenium, an element of the iron group detected in nearly twice as many planetary nebulae as any other trans-iron element. We use the NIST 2 m UV/Vis/IR and FT700 UV/Vis Fourier transform spectrometers over the wavelength range of 2000 Å-2.5 μm, supplemented in the lower wavelength region 300-2400 Å with grating spectra taken on a 3-m normal incidence vacuum spectrograph. The analysis of Se II is being extended, covering the wide spectral region from UV to IR. From our investigation, we found serious inconsistency and incompleteness in the previously published results, where several levels were reported without any designation. The analysis is being revised and extended with the help of semiempirical quasi-relativistic Hartree-Fock calculations, starting with the 4s24p3- [4s24p2(4d +5d +5s +6s) +4s4p4] transition array. Out of fifty-two previously reported levels, we rejected thirteen and found several new level values. With the new measurements, we expect to observe transitions between 4s24p2(4d +5s) and 4s24p2(5p +4f), lying in the visible and IR region. A complete interpretation of the level system of both parities will be assisted by least squares fitted parametric calculations. In all, we have already classified about 450 observed lines involving 89 energy levels.

  9. Single-frequency 571nm VECSEL for photo-ionization of magnesium

    NASA Astrophysics Data System (ADS)

    Burd, S. C.; Leinonen, T.; Penttinen, J. P.; Allcock, D. T. C.; Slichter, D. H.; Srinivas, R.; Wilson, A. C.; Guina, M.; Leibfried, D.; Wineland, D. J.

    2016-06-01

    We report the development of an intracavity-frequency-doubled vertical external-cavity surface-emitting laser (VECSEL) emitting at 571 nm for photoionization of magnesium. The laser employs a V-cavity geometry with a gain chip at the end of one cavity arm and a lithium triborate (LBO) crystal for second harmonic generation. The gain chip has a bottom-emitting design with ten GaInAs quantum wells of 7 nm thickness, which are strain compensated by GaAsP. The system is capable of producing up to 2.4 +/- 0.1 W (total power in two separate output beams) in the visible. The free-running relative intensity noise was measured to be below -55 dBc/Hz over all frequencies from 1 Hz to 1 MHz. With acoustic isolation and temperature regulation of the laser breadboard, the mode-hop free operation time is typically over 5 hrs. To improve the long-term frequency stability, the laser can be locked to a Doppler-free transition of molecular iodine. To estimate the short-term linewidth, the laser was tuned to the resonance of a reference cavity. From analysis of the on-resonance Hänsch-Couillaud error signal we infer a linewidth of 50 +/- 10 kHz. Light at 285 nm is generated with an external build-up cavity containing a β-barium borate (BBO) crystal. The UV light is used for loading 25Mg+ ions in a surface-electrode RF Paul trap. These results demonstrate the applicability and versatility of high-power, single-frequency VECSELs with intracavity harmonic generation for applications in atomic and molecular physics.

  10. Resonance Ionization of Heavy Noble Gases: The Potential of KR and Xe Measurements from Single Pre-Solar Grains

    NASA Astrophysics Data System (ADS)

    Thonnard, N.

    1995-09-01

    measure noble gases from fourteen individual "X" SiC grains, previously identified by ion microprobe analysis, was unsuccessful with the 2,000 132Xe atom detection limit of the mass spectrometer [12,13]. From the Kr concentration measurements of SiC particles KJF by Lewis et al. [6], a 2 micrometer diameter particle will on average contain 134 Kr atoms. If only 4% of the SiC grains contain the majority of the noble gas atoms, then a single gas rich grain will contain 3,350 Kr atoms, or 12, 75, 385, 398, 1910, and 580 atoms for 78Kr through 86Kr, respectively. The Xe single-grain abundances would be similar. Resonance ionization, an emerging laser-based element analysis technique, is being harnessed to a wide variety of problems in which minute quantities of a particular element need to be measured efficiently in the presence of an overwhelmingly larger background of other materials [14]. By utilizing lasers tuned to specific atomic energy levels of the analyte element, ions are produced selectively in a mass spectrometer with much higher efficiency than possible using conventional methods, such as electron bombardment, thermal ionization, or ion sputtering. In a static resonance ionization system for noble gases, the combination of high ionization efficiency and sample concentrator results in an extremely fast (~3 min. detection half-life vs. ~60 min. for conventional systems) analyzer with a detection limit of ~100 85Kr atoms [15]. In addition to the almost complete absence of interferences, the short analysis time significantly reduces the background contribution of outgassing in the mass spectrometer. Although using a less efficient laser scheme resulting in slightly slower analyses, a similar system has recently been completed and dedicated to extraterrestrial Xe measurements [16]. At the newly formed Institute for Rare Isotope Measurements [17], the noble gas equipment that had previously been at Atom Sciences [14,15] is being re-installed and upgraded to provide

  11. Electron Impact Ionization: A New Parameterization for 100 eV to 1 MeV Electrons

    NASA Technical Reports Server (NTRS)

    Fang, Xiaohua; Randall, Cora E.; Lummerzheim, Dirk; Solomon, Stanley C.; Mills, Michael J.; Marsh, Daniel; Jackman, Charles H.; Wang, Wenbin; Lu, Gang

    2008-01-01

    Low, medium and high energy electrons can penetrate to the thermosphere (90-400 km; 55-240 miles) and mesosphere (50-90 km; 30-55 miles). These precipitating electrons ionize that region of the atmosphere, creating positively charged atoms and molecules and knocking off other negatively charged electrons. The precipitating electrons also create nitrogen-containing compounds along with other constituents. Since the electron precipitation amounts change within minutes, it is necessary to have a rapid method of computing the ionization and production of nitrogen-containing compounds for inclusion in computationally-demanding global models. A new methodology has been developed, which has parameterized a more detailed model computation of the ionizing impact of precipitating electrons over the very large range of 100 eV up to 1,000,000 eV. This new parameterization method is more accurate than a previous parameterization scheme, when compared with the more detailed model computation. Global models at the National Center for Atmospheric Research will use this new parameterization method in the near future.

  12. Time-dependent configuration-interaction-singles calculation of the 5 p -subshell two-photon ionization cross section in xenon

    NASA Astrophysics Data System (ADS)

    Karamatskou, Antonia; Santra, Robin

    2017-01-01

    The 5 p two-photon ionization cross section of xenon in the photon-energy range below the one-photon ionization threshold is calculated within the time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS calculations are compared to random-phase-approximation calculations [Wendin et al., J. Opt. Soc. Am. B 4, 833 (1987), 10.1364/JOSAB.4.000833] and are found to reproduce the energy positions of the intermediate Rydberg states reasonably well. The effect of interchannel coupling is also investigated and found to change the cross section of the 5 p shell only slightly compared to the intrachannel case.

  13. New instrument for tribocharge measurement due to single particle impacts

    NASA Astrophysics Data System (ADS)

    Watanabe, Hideo; Ghadiri, Mojtaba; Matsuyama, Tatsushi; Long Ding, Yu; Pitt, Kendal G.

    2007-02-01

    During particulate solid processing, particle-particle and particle-wall collisions can generate electrostatic charges. This may lead to a variety of problems ranging from fire and explosion hazards to segregation, caking, and blocking. A fundamental understanding of the particle charging in such situations is therefore essential. For this purpose we have developed a new device that can measure charge transfer due to impact between a single particle and a metal plate. The device consists of an impact test system and two sets of Faraday cage and preamplifier for charge measurement. With current amplifiers, high-resolution measurements of particle charges of approximately 1 and 10fC have been achieved before and after the impact, respectively. The device allows charge measurements of single particles with a size as small as ˜100μm impacting on the target at different incident angles with a velocity up to about 80m/s. Further analyses of the charge transfer as a function of particle initial charge define an equilibrium charge, i.e., an initial charge level prior to impact for which no net charge transfer would occur as a result of impact.

  14. New instrument for tribocharge measurement due to single particle impacts

    SciTech Connect

    Watanabe, Hideo; Ghadiri, Mojtaba; Matsuyama, Tatsushi; Ding Yulong; Pitt, Kendal G.

    2007-02-15

    During particulate solid processing, particle-particle and particle-wall collisions can generate electrostatic charges. This may lead to a variety of problems ranging from fire and explosion hazards to segregation, caking, and blocking. A fundamental understanding of the particle charging in such situations is therefore essential. For this purpose we have developed a new device that can measure charge transfer due to impact between a single particle and a metal plate. The device consists of an impact test system and two sets of Faraday cage and preamplifier for charge measurement. With current amplifiers, high-resolution measurements of particle charges of approximately 1 and 10 fC have been achieved before and after the impact, respectively. The device allows charge measurements of single particles with a size as small as {approx}100 {mu}m impacting on the target at different incident angles with a velocity up to about 80 m/s. Further analyses of the charge transfer as a function of particle initial charge define an equilibrium charge, i.e., an initial charge level prior to impact for which no net charge transfer would occur as a result of impact.

  15. New instrument for tribocharge measurement due to single particle impacts.

    PubMed

    Watanabe, Hideo; Ghadiri, Mojtaba; Matsuyama, Tatsushi; Ding, Yu Long; Pitt, Kendal G

    2007-02-01

    During particulate solid processing, particle-particle and particle-wall collisions can generate electrostatic charges. This may lead to a variety of problems ranging from fire and explosion hazards to segregation, caking, and blocking. A fundamental understanding of the particle charging in such situations is therefore essential. For this purpose we have developed a new device that can measure charge transfer due to impact between a single particle and a metal plate. The device consists of an impact test system and two sets of Faraday cage and preamplifier for charge measurement. With current amplifiers, high-resolution measurements of particle charges of approximately 1 and 10 fC have been achieved before and after the impact, respectively. The device allows charge measurements of single particles with a size as small as approximately 100 microm impacting on the target at different incident angles with a velocity up to about 80 m/s. Further analyses of the charge transfer as a function of particle initial charge define an equilibrium charge, i.e., an initial charge level prior to impact for which no net charge transfer would occur as a result of impact.

  16. STORAGE RING MEASUREMENT OF ELECTRON IMPACT IONIZATION FOR Mg{sup 7+} FORMING Mg{sup 8+}

    SciTech Connect

    Hahn, M.; Lestinsky, M.; Novotny, O.; Savin, D. W.; Bernhardt, D.; Mueller, A.; Schippers, S.; Wolf, A.

    2010-04-01

    We report electron impact ionization cross section measurements for Mg{sup 7+} forming Mg{sup 8+} at center of mass energies from approximately 200 eV to 2000 eV. The experimental work was performed using the heavy-ion storage ring TSR located at the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. We find good agreement with distorted wave calculations using both the GIPPER code of the Los Alamos Atomic Physics Code suite and using the Flexible Atomic Code.

  17. Low energy electron-impact ionization of hydrogen atom for coplanar equal-energy-sharing kinematics in Debye plasmas

    NASA Astrophysics Data System (ADS)

    Li, Jun; Zhang, Song Bin; Ye, Bang Jiao; Wang, Jian Guo; Janev, R. K.

    2016-12-01

    Low energy electron-impact ionization of hydrogen atom in Debye plasmas has been investigated by employing the exterior complex scaling method. The interactions between the charged particles in the plasma have been represented by Debye-Hückel potentials. Triple differential cross sections (TDCS) in the coplanar equal-energy-sharing geometry at an incident energy of 15.6 eV for different screening lengths are reported. As the screening strength increases, TDCS change significantly. The evolutions of dominant typical peak structures of the TDCS are studied in detail for different screening lengths and for different coplanar equal-energy-sharing geometries.

  18. Ion kinetic energy distributions and cross sections for the electron impact ionization of ethyl tert-butyl ether

    NASA Astrophysics Data System (ADS)

    Di Palma, T. M.; Apicella, B.; Armenante, M.; Velotta, R.; Wang, X.; Spinelli, N.

    2005-11-01

    The kinetic energy distributions and the cross sections of the ions produced in the electron impact of ethyl tert-butyl ether (ETBE) have been studied by time of flight (TOF) mass spectrometry. The kinetic energy distributions have been deduced from the TOF peak shape analysis and a Montecarlo simulation method of the ion trajectories has been used to evaluate the collection efficiency of the spectrometer as a function of the ion initial kinetic energy. The measured ion yields have been corrected for the collection efficiency and the partial and total ionization cross sections of ETBE determined in the range 20-150 eV.

  19. Novel charge plasma based dielectric modulated impact ionization MOSFET as a biosensor for label-free detection

    NASA Astrophysics Data System (ADS)

    Chanda, Manash; Dey, Prithu; De, Swapnadip; Sarkar, Chandan Kumar

    2015-10-01

    In this paper a charge plasma based dielectric modulated impact ionization MOSFET (CP-DIMOSFET) has been proposed for the first time to ease the label free detection of biomolecules. The concept of CP-DIMOSFET is proposed and analyzed on basis of simulated data using SILVACO ATLAS. Low thermal budgeting and thin silicon layer without any dopant implantations make the proposed structure advantageous compared to the existing MOSFET based biosensors. The results show that the proposed device is capable to detect the presence of biomolecules. Simple fabrication schemes, miniaturization, high sensitivity, dominance of dielectric modulation make the proposed biosensor a promising one that could one day revolutionize the healthcare industry.

  20. Agent-specific impact of single trades in financial markets

    NASA Astrophysics Data System (ADS)

    Bladon, Alex J.; Moro, Esteban; Galla, Tobias

    2012-03-01

    We present an analysis of the price impact associated with single trades effected by different financial firms. Using data from the Spanish Stock Market, we find a high degree of heterogeneity across different market members, both in the instantaneous impact functions and in the time-dependent market response to trades by individual members. This heterogeneity is statistically incompatible with the existence of market-wide universal impact dynamics that apply uniformly to all trades and suggest that, rather, market dynamics emerge from the complex interaction of different behaviors of market participants. Several possible reasons for this are discussed, along with potential extensions one may consider to increase the range of applicability of existing models of market impact.

  1. Ionization potentials of transparent conductive indium tin oxide films covered with a single layer of fluorine-doped tin oxide nanoparticles grown by spray pyrolysis deposition

    SciTech Connect

    Fukano, Tatsuo; Motohiro, Tomoyoshi; Ida, Takashi; Hashizume, Hiroo

    2005-04-15

    Indium tin oxide (ITO) films deposited with single layers of monodispersive fluorine-doped tin oxide (FTO) nanoparticles of several nanometers in size were grown on glass substrates by intermittent spray pyrolysis deposition using conventional atomizers. These films have significantly higher ionization potentials than the bare ITO and FTO films grown using the same technique. The ITO films covered with FTO particles of 7 nm in average size show an ionization potential of 5.01 eV, as compared with {approx}4.76 and {approx}4.64 eV in ITO and FTO films, respectively, which decreases as the FTO particle size increases. The ionization potentials are practically invariant against oxidation and reduction treatments, promising a wide application of the films to transparent conducting oxide electrodes in organic electroluminescent devices and light-emitting devices of high efficiencies.

  2. Investigation of the photoionization properties of pharmaceutically relevant substances by resonance-enhanced multiphoton ionization spectroscopy and single-photon ionization spectroscopy using synchrotron radiation.

    PubMed

    Kleeblatt, Juliane; Ehlert, Sven; Hölzer, Jasper; Sklorz, Martin; Rittgen, Jan; Baumgärtel, Peter; Schubert, Jochen K; Zimmermann, Ralf

    2013-08-01

    The photoionization properties of the pharmaceutically relevant substances amantadine, diazepam, dimethyltryptamine, etomidate, ketamine, mescaline, methadone, and propofol were determined. At beamline U125/2-10m-NIM of the BESSY II synchrotron facility (Berlin, Germany) vacuum ultraviolet (VUV) photoionization spectra were recorded in the energy range 7.1 to 11.9 eV (174.6 to 104.2 nm), showing the hitherto unknown ionization energies and fragmentation appearance energies of the compounds under investigation. Furthermore, (1+1)-resonance-enhanced multiphoton ionization (REMPI) spectra of selected compounds (amantadine, diazepam, etomidate, ketamine, and propofol) were recorded by a continuous scan in the energy range between 3.6 and 5.7 eV (345 to 218 nm) using a tunable optical parametric oscillator (spectral resolution: 0.1 nm) laser system. The resulting REMPI wavelength spectra of these compounds are discussed and put into context with already known UV absorption data. Time-of-flight mass spectrometry was used for ion detection in both experiments. Finally, the implications of the obtained physical-chemical results for potential analytical applications are discussed. In this context, fast detection approaches for the considered compounds from breath gas using photoionization mass spectrometry and a rapid pre-concentration step (e.g., needle trap device) are of interest.

  3. Charge enhancement of single-stranded DNA in negative electrospray ionization using the supercharging reagent meta-nitrobenzyl alcohol.

    PubMed

    Brahim, Bessem; Alves, Sandra; Cole, Richard B; Tabet, Jean-Claude

    2013-12-01

    Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1% m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1% m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase.

  4. Charge Enhancement of Single-Stranded DNA in Negative Electrospray Ionization Using the Supercharging Reagent Meta-nitrobenzyl Alcohol

    NASA Astrophysics Data System (ADS)

    Brahim, Bessem; Alves, Sandra; Cole, Richard B.; Tabet, Jean-Claude

    2013-12-01

    Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1 % m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1 % m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase.

  5. On a source of electron impact ionization in Io's upstream atmosphere

    NASA Astrophysics Data System (ADS)

    Shaposhnikov, V. E.; Zaitsev, V. V.; Rucker, H. O.; Litvinenko, G. V.; Konovalenko, A. A.

    2013-09-01

    A mechanism for the ionization of Io's atmosphere due to the moon's motion through the Jovian magnetic field is considered. Attention is paid to the important role of charge separation in the upstream part of Io's ionosphere and accumulation of electrons and positive ions on the low and top ionospheric boundaries which results in (a) the creation of longitudinal component (with respect to the Jovian magnetic field lines) of polarization electric field, (b) the driving of Bounemann plasma turbulence, and (c) the heating of electrons and the ionization of neutrals. Estimations show that the proposed mechanism can essentially heat the electrons and increase the electron density. The increase with the plasma density and the electron temperature can result in an ionospheric plasma distribution and overcomes the difficulty with generation of the most bright part of UV emission of the Io's equatorial spots.

  6. Direct evidence of two interatomic relaxation mechanisms in argon dimers ionized by electron impact

    PubMed Central

    Ren, Xueguang; Jabbour Al Maalouf, Elias; Dorn, Alexander; Denifl, Stephan

    2016-01-01

    In weakly bound systems like liquids and clusters electronically excited states can relax in inter-particle reactions via the interplay of electronic and nuclear dynamics. Here we report on the identification of two prominent examples, interatomic Coulombic decay (ICD) and radiative charge transfer (RCT), which are induced in argon dimers by electron collisions. After initial ionization of one dimer constituent ICD and RCT lead to the ionization of its neighbour either by energy transfer to or by electron transfer from the neighbour, respectively. By full quintuple-coincidence measurements, we unambiguously identify ICD and RCT, and trace the relaxation dynamics as function of the collisional excited state energies. Such interatomic processes multiply the number of electrons and shift their energies down to the critical 1–10 eV range, which can efficiently cause chemical degradation of biomolecules. Therefore, the observed relaxation channels might contribute to cause efficient radiation damage in biological systems. PMID:27000407

  7. Electron impact ionization of helium from its ground and metastable states

    NASA Astrophysics Data System (ADS)

    Zhang-jin, Chen; Ke-zun, Xu

    1999-05-01

    The triple differential cross sections for the ionization of helium from its ground state 1 1S and metastable states 2 1S and 2 3S in coplanar asymmetric geometry by 150, 250 and 400 eV electrons have been calculated in the BBK model. The present results are compared with the experimental data and/or the other theoretical ones. It has been found that the structures for the metastable states differ markedly from those for the ground state. The collision mechanisms for the new structures appearing in the cross sections for the ionization from metastable states have been analysed. And it has been shown how the intensity of recoil peak changes due to the size of the electron orbital. In addition, the optimal kinematical situations for the cross sections are explored for future experiment.

  8. Screened-exchange density functional approach to Auger recombination and impact ionization rates in InGaAs

    NASA Astrophysics Data System (ADS)

    Picozzi, Silvia; Asahi, Ryoji; Geller, Clint; Freeman, Arthur

    2004-03-01

    We present an ab-initio modeling approach for Auger recombination and impact ionization in semiconductors directed at i) quantitative rate determinations and 2) elucidating trends with respect to alloy composition, carrier concentration and temperature. We present a fully first-principles formalism (S.Picozzi, R.Asahi, C.B. Geller and A.J.Freeman, Phys.Rev.Lett. 89, 197601 (2002); Phys.Rev.B 65, 113206 (2002).), based on accurate energy bands and wave functions within the screened exchange local density approximation and the full-potential linearized augmented plane wave (FLAPW) method (E.Wimmer, H.Krakauer, M.Weinert, A.J.Freeman, Phys.Rev.B 24, 864 (1981)). Results are presented for electron- and hole-initiated impact ionization processes and Auger recombinations for p-type and n-type InGaAs. Anisotropy and composition effects in the related rates are discussed in terms of the underlying band-structures. Calculated Auger lifetimes, in general agreement with experiments, are studied for different recombination mechanisms (i.e. CCCH, CHHL, CHHS, involving conduction electrons (C), heavy- (H) and light-hole (L), spin split-off (S) band) in order to understand the dominant mechanism.

  9. Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

    NASA Astrophysics Data System (ADS)

    Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

    2013-09-01

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n- and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy (1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a

  10. Double ionization of neon by electron impact: use of correlated wave functions*

    NASA Astrophysics Data System (ADS)

    Kada, Imene; Cappello, Claude Dal; Mansouri, Abdelaziz

    2017-02-01

    A model including correlation both in the initial state and in the final state is applied to the case of the double ionization of neon. The results of our model are compared to the available experimental data performed at high incident energy. Fully (fivefold) differential cross sections (FDCS) have been studied by applying the first Born approximation. Four ion states of Ne++, which are not resolved in the experiments, have been included in our calculation. Contribution to the Topical Issue "Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces", edited by A.N. Grum-Grzhimailo, E.V. Gryzlova, Yu V. Popov, and A.V. Solov'yov.

  11. Coulomb three-body effects in low-energy impact ionization of H(1{ital s})

    SciTech Connect

    Roeder, J.; Rasch, J.; Jung, K.; Whelan, C.T.; Ehrhardt, H.; Allan, R.J.; Walters, H.R. |||

    1996-01-01

    The different kinematical and geometrical arrangements that may be used in ({ital e},2{ital e}) studies are briefly reviewed. The ionization of H(1{ital s}) is considered, and within the confines of a relatively simple theoretical model, it is shown how to define experimental setups where one may extract information on the role of Coulomb three-body effects in the incident and final channels. Theoretical and experimental results are presented for coplanar constant geometry where the focus is primarily on incident channel effects. {copyright} {ital 1996 The American Physical Society.}

  12. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials

    SciTech Connect

    Artemyev, Anton N.; Müller, Anne D.; Demekhin, Philipp V.; Hochstuhl, David

    2015-06-28

    A theoretical method to study the angle-resolved multiphoton ionization of polyatomic molecules is developed. It is based on the time-dependent formulation of the Single Center (TDSC) method and consists in the propagation of single-active-electron wave packets in the effective molecular potentials in the presence of intense laser pulses. For this purpose, the time-dependent Schrödinger equation for one electron, moving in a molecular field and interacting with an arbitrary laser pulse, is solved in spherical coordinates by an efficient numerical approach. As a test, the method is applied to the one- and two-photon ionizations of a model methane-like chiral system by circularly polarized short intense high-frequency laser pulses. Thereby, we analyze the photoelectron circular dichroism (PECD) in the momentum distribution. The considered model application illustrates the capability of the TDSC method to study multiphoton PECD in fixed-in-space and randomly oriented chiral molecules.

  13. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials

    NASA Astrophysics Data System (ADS)

    Artemyev, Anton N.; Müller, Anne D.; Hochstuhl, David; Demekhin, Philipp V.

    2015-06-01

    A theoretical method to study the angle-resolved multiphoton ionization of polyatomic molecules is developed. It is based on the time-dependent formulation of the Single Center (TDSC) method and consists in the propagation of single-active-electron wave packets in the effective molecular potentials in the presence of intense laser pulses. For this purpose, the time-dependent Schrödinger equation for one electron, moving in a molecular field and interacting with an arbitrary laser pulse, is solved in spherical coordinates by an efficient numerical approach. As a test, the method is applied to the one- and two-photon ionizations of a model methane-like chiral system by circularly polarized short intense high-frequency laser pulses. Thereby, we analyze the photoelectron circular dichroism (PECD) in the momentum distribution. The considered model application illustrates the capability of the TDSC method to study multiphoton PECD in fixed-in-space and randomly oriented chiral molecules.

  14. Benchmark calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-09-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium for energies from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with previous results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a shape resonance. The ionization from the (2 s 2 p) 3 P and (2 s 2 p) 1 P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications. This work was supported by the United States National Science Foundation (OZ and KB) and the Australian Research Council (DVF and IB).

  15. Electron-impact total ionization cross sections of CF4, C2F6, and C3F8

    NASA Astrophysics Data System (ADS)

    Nishimura, H.; Huo, Winifred M.; Ali, M. A.; Kim, Yong-Ki

    1999-02-01

    Both theoretical and experimental electron-impact total ionization cross sections of CF4, C2F6, and C3F8 are presented. The experimental cross sections have been measured as a function of incident electron energy T from threshold to 3 keV. A parallel plate condenser type apparatus was used. The molecular polarizability for C3F8 was empirically estimated to be α=10.6 Å3±0.8 Å3. Theoretical cross sections calculated from the binary-encounter-Bethe (BEB) method, which combines a modified form of the Mott cross section and the Bethe cross section, are compared with the experimental cross sections. The BEB cross sections calculated from correlated molecular wave functions with theoretical estimates for multiple ionization are about 10% higher than the experimental data at the peak for CF4, while they are in excellent agreement with the experimental data for C2F6 and C3F8. Our analysis shows that the BEB theory implicitly includes part of neutral dissociation, such as CF4→CF3+F, and hence tends to be an upper limit to the total ionization cross section. We found that the difference between our best theory for CF4 and the present experimental cross section exhibits a remarkable similarity to the shape of the recently measured cross section for neutral dissociation, though there is no a priori reason for the similarity. Owing to the large number of bound electrons, the correlation included in our wave functions for C2F6 and C3F8 is more limited than for CF4. Hence, we believe that for these two molecules the calculated cross sections are lower than the true BEB values, in spite of the apparent excellent agreement between the theory and the experiment.

  16. Validation of an "Intelligent Mouthguard" Single Event Head Impact Dosimeter.

    PubMed

    Bartsch, Adam; Samorezov, Sergey; Benzel, Edward; Miele, Vincent; Brett, Daniel

    2014-11-01

    Dating to Colonel John Paul Stapp MD in 1975, scientists have desired to measure live human head impacts with accuracy and precision. But no instrument exists to accurately and precisely quantify single head impact events. Our goal is to develop a practical single event head impact dosimeter known as "Intelligent Mouthguard" and quantify its performance on the benchtop, in vitro and in vivo. In the Intelligent Mouthguard hardware, limited gyroscope bandwidth requires an algorithm-based correction as a function of impact duration. After we apply gyroscope correction algorithm, Intelligent Mouthguard results at time of CG linear acceleration peak correlate to the Reference Hybrid III within our tested range of pulse durations and impact acceleration profiles in American football and Boxing in vitro tests: American football, IMG=1.00REF-1.1g, R2=0.99; maximum time of peak XYZ component imprecision 3.6g and 370 rad/s2; maximum time of peak azimuth and elevation imprecision 4.8° and 2.9°; maximum average XYZ component temporal imprecision 3.3g and 390 rad/s2. Boxing, IMG=1.00REF-0.9 g, R2=0.99, R2=0.98; maximum time of peak XYZ component imprecision 3.9 g and 390 rad/s2, maximum time of peak azimuth and elevation imprecision 2.9° and 2.1°; average XYZ component temporal imprecision 4.0 g and 440 rad/s2. In vivo Intelligent Mouthguard true positive head impacts from American football players and amateur boxers have temporal characteristics (first harmonic frequency from 35 Hz to 79 Hz) within our tested benchtop (first harmonic frequency<180 Hz) and in vitro (first harmonic frequency<100 Hz) ranges. Our conclusions apply only to situations where the rigid body assumption is valid, sensor-skull coupling is maintained and the ranges of tested parameters and harmonics fall within the boundaries of harmonics validated in vitro. For these situations, Intelligent Mouthguard qualifies as a single event dosimeter in American football and Boxing.

  17. Application and field test of a mobile thermal desorption - single photon ionization - ion trap mass spectrometer (TD-SPI-ITMS) for trace detection of security relevant substances

    NASA Astrophysics Data System (ADS)

    Schramm, Elisabeth; Heindl, Thomas; Hölzer, Jasper; McNeish, Alexander; Puetz, Michael; Ries, Hermann; Schall, Patricia; Schulte-Ladbeck, Rasmus; Schultze, Rainer; Sklorz, Martin; Spieker, Gerd; Trebbe, Roman; Ulrich, Andreas; Wieser, Jochen; Zimmermann, Ralf

    2009-05-01

    The objective of this accomplished project funded by the German BMBF was to develop a single photon ionization ion trap mass spectrometer (SPI-ITMS) for detection of security relevant substances in complex matrices at low concentrations. The advantage of such a soft ionization technique is a reduction of target ion fragmentation allowing identification of signals from complex matrices and enabling MS/MS capability. To obtain low detection limits, the applied photon energy has to be below the ionization potential (IP) of the bulk matrix components. Therefore, photon energies between 8 eV (155 nm) and 12 eV (103 nm) are necessary which was achieved with newly developed electron beam excimer lamps (EBEL). They generate light at different wavelengths depending on the selected rare gas emitting wavelengths adapted to the analyzed substances. So, e.g. with a krypton-EBEL with 8.4 eV photon energy most narcotics can be ionized without notable fragmentation. Due to their higher IPs, EBEL with higher photon energy have to be used for most explosives. Very low false-positive and false-negative rates have been achieved using MS/MS studies. First field tests of a demonstrator provided the proof of principle.

  18. Resonance-enhanced multiphoton ionization and VUV-single photon ionization as soft and selective laser ionization methods for on-line time-of-flight mass spectrometry: investigation of the pyrolysis of typical organic contaminants in the steel recycling process.

    PubMed

    Cao, L; Mühlberger, F; Adam, T; Streibel, T; Wang, H Z; Kettrup, A; Zimmermann, R

    2003-11-01

    A newly conceived compact and mobile time-of flight mass spectrometer (TOFMS) for real-time monitoring of highly complex gas mixtures is presented. The device utilizes two selective and sensitive soft ionization techniques, viz., resonance-enhanced multiphoton ionization (REMPI) and single-photon ionization (SPI) in a (quasi)-simultaneous mode. Both methods allow a fragmentationless ionization. The REMPI method selectively addresses aromatic species, while with SPI applying vacuum ultaviolet light (118 nm) in principle all compounds with an ionization potential below 10.5 eV are accessible. This provides comprehensive information of the chemical composition of complex matrixes. The combustion and pyrolysis behavior of five organic materials typically used in steel processing in China was studied. The trace amounts of organic compounds in the gas phase during combustion and pyrolysis were monitored selectively and sensitively by real-time SPI/REMPI-TOFMS. The measurements were carried out at several constant temperatures in the range from 300 to 1190 degrees C in both synthetic air and nitrogen. Timely resolved mass spectra reveal the formation and subsequent growth of aromatic molecules. At lower temperatures, highly alkylated PAHs predominate, while at temperatures above 800 degrees C, the more stable benzene and PAHs without side chains prevail. Potential hyphenation of SPI/REMPI-TOFMS to methods of thermal analysis is discussed.

  19. Electron ionization cross-section calculations for liquid water at high impact energies

    NASA Astrophysics Data System (ADS)

    Bousis, C.; Emfietzoglou, D.; Hadjidoukas, P.; Nikjoo, H.; Pathak, A.

    2008-04-01

    Cross-sections for the ionization of liquid water is perhaps the most essential set of data needed for modeling electron transport in biological matter. The complexity of ab initio calculations for any multi-electron target has led to largely heuristic semi-empirical models which take advantage elements of the Bethe, dielectric and binary collision theories. In this work we present various theoretical models for calculating total ionization cross-sections (TICSs) for liquid water over the 10 keV-1 MeV electron energy range. In particular, we extend our recent dielectric model calculations for liquid water to relativistic energies using both the appropriate kinematic corrections and the transverse part. Comparisons are made with widely used atomic and molecular TICS models such as those of Khare and co-workers, Kim-Rudd, Deutsch-Märk, Vriens and Gryzinski. The required dipole oscillator strength was provided by our recent optical-data model which is based on the latest experimental data for liquid water. The TICSs computed by the above models differ by up to 40% from the dielectric results. The best agreement (to within ∼10%) was obtained by Khare's original model and an approximate form of Gryzinski's model. In contrast, the binary-encounter-dipole (BED) models of both Kim-Rudd and Khare and co-workers resulted in ∼10-20% higher TICS values, while discrepancies increased to ∼30-40% when their simpler binary-encounter-Bethe (BEB) versions were used. Finally, we discuss to what extent the accuracy of the TICS is indicative of the reliability of the underlying differential cross-sections.

  20. In situ probing of cholesterol in astrocytes at the single-cell level using laser desorption ionization mass spectrometric imaging with colloidal silver.

    PubMed

    Perdian, D C; Cha, Sangwon; Oh, Jisun; Sakaguchi, Donald S; Yeung, Edward S; Lee, Young Jin

    2010-04-30

    Mass spectrometric imaging has been utilized to localize individual astrocytes and to obtain cholesterol populations at the single-cell level in laser desorption ionization (LDI) with colloidal silver. The silver ion adduct of membrane-bound cholesterol was monitored to detect individual cells. Good correlation between mass spectrometric and optical images at different cell densities indicates the ability to perform single-cell studies of cholesterol abundance. The feasibility of quantification is confirmed by the agreement between the LDI-MS ion signals and the results from a traditional enzymatic fluorometric assay. We propose that this approach could be an effective tool to study chemical populations at the cellular level.

  1. In Situ Probing of Cholesterol in Astrocytes at the Single Cell Level using Laser Desorption Ionization Mass Spectrometric Imaging with Colloidal Silver

    SciTech Connect

    Perdian, D.C.; Cha, Sangwon; Oh, Jisun; Sakaguchi, Donald S.; Yeung, Edward S.; and Lee, Young Jin

    2010-03-18

    Mass spectrometric imaging has been utilized to localize individual astrocytes and to obtain cholesterol populations at the single-cell level in laser desorption ionization (LDI) with colloidal silver. The silver ion adduct of membrane-bound cholesterol was monitored to detect individual cells. Good correlation between mass spectrometric and optical images at different cell densities indicates the ability to perform single-cell studies of cholesterol abundance. The feasibility of quantification is confirmed by the agreement between the LDI-MS ion signals and the results from a traditional enzymatic fluorometric assay. We propose that this approach could be an effective tool to study chemical populations at the cellular level.

  2. Evaluation of binding selectivity of a polyamide probe to single base-pair different DNA in A.T-rich region by electrospray ionization mass spectrometry.

    PubMed

    Li, Huihui; Yuan, Gu

    2006-12-01

    In this study, electrospray ionization mass spectrometry (ESI-MS) was used for the evaluation of the binding selectivity of a polyamide probe to single-base pair different DNA in an A.T-rich region. In this procedure, DeltaIr(dsn) was introduced as a parameter to compare the binding affinities of the polyamides with the duplex DNA. The results show that ESI-MS is a very useful tool for analysis of binding selectivity of a polyamide probe to single-base pair different DNA.

  3. Single attosecond pulse generation in He{sup +} by controlling the instant ionization rate using attosecond pulse trains combined with an intense laser pulse

    SciTech Connect

    He Xinkui; Jia, T. Q.; Zhang, Jun; Suzuki, M.; Baba, M.; Kuroda, Hiroto; Ozaki, T.; Li Ruxin; Xu Zhizhan

    2007-08-15

    High-order harmonics and single attosecond pulse generation by using an infrared laser pulse combined with attosecond pulse trains (APT) interacting with He{sup +} have been investigated. We show that the ionization for different instant time intervals can be controlled by altering the time delay between the APT and the infrared pulse. Consequently, APT can be used as a tool to control the efficiency of high-order harmonics emitted at different times. By choosing appropriate APT and time delay, the driving pulse width for single attosecond pulse generation can be extended up to six optical cycles.

  4. Effect of the Mo/ller interaction on electron-impact ionization of high-Z hydrogenlike ions

    NASA Astrophysics Data System (ADS)

    Moores, D. L.; Reed, K. J.

    1995-01-01

    We have investigated the effects of the Mo/ller interaction in relativistic distorted-wave calculations of cross sections for electron-impact ionization of high-Z hydrogenlike ions. We found that the Mo/ller interaction significantly increases the cross section for hydrogenlike uranium, and brings our calculated results into very good agreement with experimental results reported by Marrs, Elliott, and Knapp [Phys. Rev. Lett. 72, 4082 (1994)]. We found similar increases in the cross sections for other hydrogenlike ions. Our results also show that these effects become important at much lower collision energy than previously reported [D. L. Moores and M. S. Pindzola, Phys. Rev. A 41, 3603 (1990)]. With the Mo/ller interaction included, our cross sections for these ions are in good agreement with preliminary results obtained in recent experiments on the electron-beam ion trap (EBIT).

  5. Non-targeted effects induced by ionizing radiation: mechanisms and potential impact on radiation induced health effects.

    PubMed

    Morgan, William F; Sowa, Marianne B

    2015-01-01

    Not-targeted effects represent a paradigm shift from the "DNA centric" view that ionizing radiation only elicits biological effects and subsequent health consequences as a result of an energy deposition event in the cell nucleus. While this is likely true at higher radiation doses (>1 Gy), at low doses (<100 mGy) non-targeted effects associated with radiation exposure might play a significant role. Here definitions of non-targeted effects are presented, the potential mechanisms for the communication of signals and signaling networks from irradiated cells/tissues are proposed, and the various effects of this intra- and intercellular signaling are described. We conclude with speculation on how these observations might lead to and impact long-term human health outcomes.

  6. Non-Targeted Effects Induced by Ionizing Radiation: Mechanisms and Potential Impact on Radiation Induced Health Effects

    SciTech Connect

    Morgan, William F.; Sowa, Marianne B.

    2015-01-01

    Not-targeted effects represent a paradigm shift from the "DNA centric" view that ionizing radiation only elicits biological effects and subsequent health consequences as a result of an energy deposition event in the cell nucleus. While this is likely true at higher radiation doses (> 1Gy), at low doses (< 100mGy) non-targeted effects associated with radiation exposure might play a significant role. Here definitions of non-targeted effects are presented, the potential mechanisms for the communication of signals and signaling networks from irradiated cells/tissues are proposed, and the various effects of this intra- and intercellular signaling are described. We conclude with speculation on how these observations might lead to and impact long-term human health outcomes.

  7. Highly Charged Ions from Laser-Cluster Interactions: Local-Field-Enhanced Impact Ionization and Frustrated Electron-Ion Recombination

    SciTech Connect

    Fennel, Thomas; Ramunno, Lora; Brabec, Thomas

    2007-12-07

    Our molecular dynamics analysis of Xe{sub 147-5083} clusters identifies two mechanisms that contribute to the yet unexplained observation of extremely highly charged ions in intense laser cluster experiments. First, electron impact ionization is enhanced by the local cluster electric field, increasing the highest charge states by up to 40%; a corresponding theoretical method is developed. Second, electron-ion recombination after the laser pulse is frustrated by acceleration electric fields typically used in ion detectors. This increases the highest charge states by up to 90%, as compared to the usual assumption of total recombination of all cluster-bound electrons. Both effects together augment the highest charge states by up to 120%, in reasonable agreement with experiments.

  8. Accurate first-principles detailed-balance determination of auger recombination and impact ionization rates in semiconductors.

    PubMed

    Picozzi, S; Asahi, R; Geller, C B; Freeman, A J

    2002-11-04

    The technologically important prediction of Auger recombination lifetimes in semiconductors is addressed by means of a fully first-principles formalism, based on precise energy bands and wave functions provided by the full-potential linearized augmented plane wave code. The minority carrier Auger lifetime is determined by two related approaches: (i) a direct evaluation within Fermi's golden rule, and (ii) an indirect evaluation, based on a detailed balance formulation combining Auger recombination and its inverse process, impact ionization, in a unified framework. Lifetimes determined with the direct and indirect methods show excellent consistency between them (i) for n-doped GaAs and (ii) with measured values for GaAs and InGaAs. This indicates the computational formalism as a new sensitive tool for use in materials performance optimization.

  9. Highly charged ions from laser-cluster interactions: local-field-enhanced impact ionization and frustrated electron-ion recombination.

    PubMed

    Fennel, Thomas; Ramunno, Lora; Brabec, Thomas

    2007-12-07

    Our molecular dynamics analysis of Xe_{147-5083} clusters identifies two mechanisms that contribute to the yet unexplained observation of extremely highly charged ions in intense laser cluster experiments. First, electron impact ionization is enhanced by the local cluster electric field, increasing the highest charge states by up to 40%; a corresponding theoretical method is developed. Second, electron-ion recombination after the laser pulse is frustrated by acceleration electric fields typically used in ion detectors. This increases the highest charge states by up to 90%, as compared to the usual assumption of total recombination of all cluster-bound electrons. Both effects together augment the highest charge states by up to 120%, in reasonable agreement with experiments.

  10. Ionization behavior of amino lipids for siRNA delivery: determination of ionization constants, SAR, and the impact of lipid pKa on cationic lipid-biomembrane interactions.

    PubMed

    Zhang, Jingtao; Fan, Haihong; Levorse, Dorothy A; Crocker, Louis S

    2011-03-01

    Ionizable amino lipids are being pursued as an important class of materials for delivering small interfering RNA (siRNA) therapeutics, and research is being conducted to elucidate the structure-activity relationships (SAR) of these lipids. The pK(a) of cationic lipid headgroups is one of the critical physiochemical properties of interest due to the strong impact of lipid ionization on the assembly and performance of these lipids. This research focused on developing approaches that permit the rapid determination of the relevant pK(a) of the ionizable amino lipids. Two distinct approaches were investigated: (1) potentiometric titration of amino lipids dissolved in neutral surfactant micelles; and (2) pH-dependent partitioning of a fluorescent dye to cationic liposomes formulated from amino lipids. Using the approaches developed here, the pK(a) values of cationic lipids with distinct headgroups were measured and found to be significantly lower than calculated values. It was also found that lipid-lipid interaction has a strong impact on the pK(a) values of lipids. Lysis of model biomembranes by cationic lipids was used to evaluate the impact of lipid pK(a) on the interaction between cationic lipids and cell membranes. It was found that cationic lipid-biomembrane interaction depends strongly on lipid pK(a) and solution pH, and this interaction is much stronger when amino lipids are highly charged. The presence of an optimal pK(a) range of ionizable amino lipids for siRNA delivery was suggested based on these results. The pK(a) methods reported here can be used to support the SAR screen of cationic lipids for siRNA delivery, and the information revealed through studying the impact of pK(a) on the interaction between cationic lipids and cell membranes will contribute significantly to the design of more efficient siRNA delivery vehicles.

  11. Desorption/Ionization Fluence Thresholds and Improved Mass Spectral Consistency Measured Using a Flattop Laser Profile in the Bioaerosol Mass Spectrometry of Single Bacillus Endospores

    SciTech Connect

    Steele, P T; Srivastava, A; Pitesky, M E; Fergenson, D P; Tobias, H J; Gard, E E; Frank, M

    2004-11-30

    Bioaerosol mass spectrometry (BAMS) is being developed to analyze and identify biological aerosols in real-time. Mass spectra of individual Bacillus endospores were measured here with a bipolar aerosol time-of-flight mass spectrometer in which molecular desorption and ionization were produced using a single laser pulse from a Q-switched, frequency-quadrupled Nd:YAG laser that was modified to have an approximately flattop profile. The flattened laser profile allowed the minimum fluence required to desorb and ionize significant numbers of ions from single aerosol particles to be determined. For Bacillus spores this threshold had a mean value of approximately 1 nJ/{micro}m{sup 2} (0.1 J/cm{sup 2}). Thresholds for individual spores, however, could apparently deviate by 20% or more from the mean. Threshold distributions for clumps of MS2 bacteriophage and bovine serum albumin were subsequently determined. Finally, the flattened profile was observed to increase the reproducibility of single spore mass spectra. This is consistent with the general conclusions of our earlier paper on the fluence dependence of single spore mass spectra and is particularly significant because it is expected to enable more robust differentiation and identification of single bioaerosol particles.

  12. Detection and Mapping of Cannabinoids in Single Hair Samples through Rapid Derivatization and Matrix-Assisted Laser Desorption Ionization Mass Spectrometry.

    PubMed

    Beasley, Emma; Francese, Simona; Bassindale, Tom

    2016-10-18

    The sample preparation method reported in this work has permitted for the first time the application of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) profiling and imaging for the detection and mapping of cannabinoids in a single hair sample. MALDI-MS imaging analysis of hair samples has recently been suggested as an alternative technique to traditional methods of GC/MS and LC/MS due to simpler sample preparation, the ability to detect a narrower time frame of drug use, and a reduction in sample amount required. However, despite cannabis being the most commonly used illicit drug worldwide, a MALDI-MS method for the detection and mapping of cannabinoids in a single hair has not been reported. This is probably due to the poor ionization efficiency of the drug and its metabolites and low concentration incorporated into hair. This research showed that in situ derivatization of cannabinoids through addition of an N-methylpyridium group resulted in improved ionization efficiency, permitting both detection and mapping of Δ(9)-tetrahydrocannabinol (THC), cannabinol (CBN), cannabidiol (CBD), and the metabolites 11-nor-9-carboxy-Δ(9)-tetrahydrocannabinol (THC-COOH), 11-hydroxy-Δ(9)-tetrahydrocannabinol (11-OH-THC), and 11-nor-9-carboxy-Δ(9)-tetrahydrocannabinol glucuronide (THC-COO-glu). Additionally, for the first time an in-source rearrangement of THC was observed and characterized in this paper, thus contributing to new and accurate knowledge in the analysis of this drug by MALDI-MS.

  13. Nanomanipulation-Coupled Matrix-Assisted Laser Desorption/ Ionization-Direct Organelle Mass Spectrometry: A Technique for the Detailed Analysis of Single Organelles

    NASA Astrophysics Data System (ADS)

    Phelps, Mandy S.; Sturtevant, Drew; Chapman, Kent D.; Verbeck, Guido F.

    2016-02-01

    We describe a novel technique combining precise organelle microextraction with deposition and matrix-assisted laser desorption/ionization (MALDI) for a rapid, minimally invasive mass spectrometry (MS) analysis of single organelles from living cells. A dual-positioner nanomanipulator workstation was utilized for both extraction of organelle content and precise co-deposition of analyte and matrix solution for MALDI-direct organelle mass spectrometry (DOMS) analysis. Here, the triacylglycerol (TAG) profiles of single lipid droplets from 3T3-L1 adipocytes were acquired and results validated with nanoelectrospray ionization (NSI) MS. The results demonstrate the utility of the MALDI-DOMS technique as it enabled longer mass analysis time, higher ionization efficiency, MS imaging of the co-deposited spot, and subsequent MS/MS capabilities of localized lipid content in comparison to NSI-DOMS. This method provides selective organellar resolution, which complements current biochemical analyses and prompts for subsequent subcellular studies to be performed where limited samples and analyte volume are of concern.

  14. Nanomanipulation-Coupled Matrix-Assisted Laser Desorption/ Ionization-Direct Organelle Mass Spectrometry: A Technique for the Detailed Analysis of Single Organelles.

    PubMed

    Phelps, Mandy S; Sturtevant, Drew; Chapman, Kent D; Verbeck, Guido F

    2016-02-01

    We describe a novel technique combining precise organelle microextraction with deposition and matrix-assisted laser desorption/ionization (MALDI) for a rapid, minimally invasive mass spectrometry (MS) analysis of single organelles from living cells. A dual-positioner nanomanipulator workstation was utilized for both extraction of organelle content and precise co-deposition of analyte and matrix solution for MALDI-direct organelle mass spectrometry (DOMS) analysis. Here, the triacylglycerol (TAG) profiles of single lipid droplets from 3T3-L1 adipocytes were acquired and results validated with nanoelectrospray ionization (NSI) MS. The results demonstrate the utility of the MALDI-DOMS technique as it enabled longer mass analysis time, higher ionization efficiency, MS imaging of the co-deposited spot, and subsequent MS/MS capabilities of localized lipid content in comparison to NSI-DOMS. This method provides selective organellar resolution, which complements current biochemical analyses and prompts for subsequent subcellular studies to be performed where limited samples and analyte volume are of concern. Graphical Abstract ᅟ.

  15. Single photon ionization of hydrogen bonded clusters with a soft x-ray laser: (HCOOH)x and (HCOOH)y(H2O)z

    NASA Astrophysics Data System (ADS)

    Heinbuch, S.; Dong, F.; Rocca, J. J.; Bernstein, E. R.

    2007-06-01

    Pure, neutral formic acid (HCOOH)n+1 clusters and mixed (HCOOH)/(H2O) clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5eV using a very compact, capillary discharge, soft x-ray laser. During the ionization process, neutral clusters suffer little fragmentation because almost all excess energy above the vertical ionization energy is taken away by the photoelectron, leaving only a small part of the photon energy deposited into the (HCOOH)n +1+ cluster. The vertical ionization energy minus the adiabatic ionization energy is enough excess energy in the clusters to surmount the proton transfer energy barrier and induce the reaction (HCOOH)n +1+→(HCOOH)nH++HCOO making the protonated (HCOOH)nH+ series dominant in all data obtained. The distribution of pure (HCOOH)nH+ clusters is dependent on experimental conditions. Under certain conditions, a magic number is found at n =5. Metastable dissociation rate constants of (HCOOH)nH+ are measured in the range (0.1-0.8)×104s-1 for cluster sizes 4

  16. Impact of ionizing radiation exposure on in vitro differentiation of preosteoblastic cell lines

    NASA Astrophysics Data System (ADS)

    Hu, Yueyuan; Lau, Patrick; Hellweg, Christine; Baumstark-Khan, Christa; Reitz, Guenther

    Bone demineralization of astronauts during residence in microgravity is a well known phe-nomenon during space travel. Besides altered gravity conditions, radiation risk is considered to be one of the major health hazards for astronauts in both orbital and interplanetary space. Un-til know, little is known about the effects of space radiation on the skeletal system especially on the bone forming osteoblasts. Accelerator facilities are used to simulate parts of the radiation environment in space. We examined the effects of heavy ion exposure on osteoblastic differ-entiation of murine preosteoblastic cell lines to gain insight into potential cellular mechanisms involved in bone cellular response after exposure to heavy ions. Therefore, we examined gene expression modulation of bone specific transcription factors, osteoblast specific marker genes as well as genes function as coupling factors that link bone resorption to bone formation. mRNA levels were determined using quantitative real time reverse transcriptase PCR (qRT-PCR). Expression of a target gene was standardized to unregulated reference genes. We investigated the transcriptional regulation of Osteocalcin (OCN) as well as TGF-β1, p21(CDKN1A) and the bone specific transcription factor Runx2 (cbfa1). We investigated gene expression modula-tions after exposure to energetic carbon ions (35 MeV/u, 73 keV/µm), iron ions (1000 MeV/u, 150 keV/µm) and lead ions (29 MeV/u, 9600 keV/µm) versus low LET X-rays. X-irradiation dose-dependently increased the mRNA levels of p21(CDKN1A) and Runx2 (cbfa1) whereas expression of OCN and TGF-β1 were elevated at later time points. Exposure to heavy ions provoked a more pronounced effect on osteoblastic specific gene expression within the dif-ferentiation process. Collectively, our results indicate that heavy ions facilitate osteoblastic differentiation more effectively than X-ray. Using the proposed in vitro model we confirmed that exposure to ionizing radiation significantly

  17. Single-shot carrier-envelope-phase-tagged ion-momentum imaging of nonsequential double ionization of argon in intense 4-fs laser fields

    SciTech Connect

    Johnson, Nora G.; Herrwerth, O.; Wirth, A.; De, S.; Ben-Itzhak, I.; Lezius, M.; Bergues, B.; Kling, M. F.; Senftleben, A.; Schroeter, C. D.; Moshammer, R.; Ullrich, J.; Betsch, K. J.; Jones, R. R.; Sayler, A. M.; Rathje, T.; Ruehle, K.; Mueller, W.; Paulus, G. G.

    2011-01-15

    Single-shot carrier-envelope-phase (CEP) tagging is combined with a reaction mircoscope (REMI) to investigate CEP-dependent processes in atoms. Excellent experimental stability and data acquisition longevity are achieved. Using this approach, we study the CEP effects for nonsequential double ionization of argon in 4-fs laser fields at 750 nm and an intensity of 1.6x10{sup 14} W/cm{sup 2}. The Ar{sup 2+} ionization yield shows a pronounced CEP dependence which compares well with recent theoretical predictions employing quantitative rescattering theory [S. Micheau et al., Phys. Rev. A 79, 013417 (2009)]. Furthermore, we find strong CEP influences on the Ar{sup 2+} momentum spectra along the laser polarization axis.

  18. Electron-impact excitation and ionization of atomic boron at low and intermediate energies

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-05-01

    We present a comprehensive study of electron collisions with neutral boron atoms. The calculations were performed with the B-Spline R-matrix (close-coupling) method, by employing a parallelized version of the associated computer code. Elastic, excitation, and ionization cross sections were obtained for all transitions involving the lowest 11 states of boron, for incident electron energies ranging from threshold to 100 eV. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was used to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo states were set up to check the sensitivity of the predictions to variations in the theoretical model. The cross-section dataset generated in this work is expected to be the most accurate one available today and should be sufficiently comprehensive for most modeling applications involving neutral boron. Work supported by the China Scholarship Council and the United States National Science Foundation under Grants PHY-1403245 and PHY-1520970, and by the XSEDE allocation PHY-090031.

  19. Radiation damage from single heavy ion impacts on metal surfaces

    SciTech Connect

    Donnelly, S.E.; Birtcher, R.C.

    1998-06-01

    The effects of single ion impacts on the surfaces of films of Au, Ag, In and Pb have been studied using in-situ transmission electron microscopy. On all of these materials, individual ion impacts produce surface craters, in some cases, with associated expelled material. The cratering efficiency scales with the density of the irradiated metal. For very thin Au foils ({approx} 20--50 nm), in some cases individual ions are seen to punch small holes completely through the foil. Continued irradiation results in a thickening of the foil. The process giving rise to crater and hole formation and other changes observed in the thin foils has been found to be due to pulsed localized flow--i.e. melting and flow due to the thermal spikes arising from individual ion impacts. Experiments carried out on thin films of silver sandwiched between SiO{sub 2} layers have indicated that pulsed localized flow also occurs in this system and contributes to the formation of Ag nanoclusters in SiO{sub 2}--a system of interest for its non-linear optical properties. Calculation indicates that, when ion-induced, collision cascades occur near surfaces (within {approx} 5 nm) with energy densities sufficient to cause melting, craters are formed. Crater formation occurs as a result of the explosive outflow of material from the hot molten core of the cascade. Processes occurring in the sandwiched layer are less well understood.

  20. Impact ionization in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} avalanche photodiodes

    SciTech Connect

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-21

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  1. FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

    SciTech Connect

    Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

    2015-01-01

    Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas.

  2. Single and multiple impact ignition of new and aged high explosives in the Steven Impact Test

    SciTech Connect

    Chidester, S K; DePiero, A H; Garza, R G; Tarver, C M

    1999-06-01

    Threshold impact velocities for ignition of exothermic reaction were determined for several new and aged HMX-based solid high explosives using three types of projectiles in the Steven Test. Multiple impact threshold velocities were found to be approximately 10% lower in damaged charges that did not react in one or more prior impacts. Projectiles with protrusions that concentrate the friction work in a small volume of explosive reduced the threshold velocities by approximately 30%. Flat projectiles required nearly twice as high velocities for ignition as rounded projectiles. Blast overpressure gauges were used for both pristine and damaged charges to quantitatively measure reaction violence. Reactive flow calculations of single and multiple impacts with various projectiles suggest that the ignition rates double in damaged charges.

  3. Calibration of impact ionization cosmic dust detectors: first tests to investigate how the dust density influences the signal

    NASA Astrophysics Data System (ADS)

    Jasmin Sterken, Veerle; Moragas-Klostermeyer, Georg; Hillier, Jon; Fielding, Lee; Lovett, Joseph; Armes, Steven; Fechler, Nina; Srama, Ralf; Bugiel, Sebastian; Hornung, Klaus

    2016-10-01

    Impact ionization experiments have been performed since more than 40 years for calibrating cosmic dust detectors. A linear Van de Graaff dust accelerator was used to accelerate the cosmic dust analogues of submicron to micron-size to speeds up to 80 km s^-1. Different materials have been used for calibration: iron, carbon, metal-coated minerals and most recently, minerals coated with conductive polymers. While different materials with different densities have been used for instrument calibration, a comparative analysis of dust impacts of equal material but different density is necessary: porous or aggregate-like particles are increasingly found to be present in the solar system: e.g. dust from comet 67P Churyumov-Gerasimenko [Fulle et al 2015], aggregate particles from the plumes of Enceladus [Gao et al 2016], and low-density interstellar dust [Westphal 2014 et al, Sterken et al 2015]. These recalibrations are relevant for measuring the size distributions of interplanetary and interstellar dust and thus mass budgets like the gas-to-dust mass ratio in the local interstellar cloud.We report about the calibrations that have been performed at the Heidelberg dust accelerator facility for investigating the influence of particle density on the impact ionization charge. We used the Cassini Cosmic Dust Analyzer for the target, and compared hollow versus compact silica particles in our study as a first attempt to investigate experimentally the influence of dust density on the signals obtained. Also, preliminary tests with carbon aerogel were performed, and (unsuccessful) attempts to accelerate silica aerogel. In this talk we explain the motivation of the study, the experiment set-up, the preparation of — and the materials used, the results and plans and recommendations for future tests.Fulle, M. et al 2015, The Astrophysical Journal Letters, Volume 802, Issue 1, article id. L12, 5 pp. (2015)Gao, P. et al 2016, Icarus, Volume 264, p. 227-238Westphal, A. et al 2014, Science

  4. Soft or hard ionization of molecules in helium nanodroplets? An electron impact investigation of alcohols and ethers.

    PubMed

    Yang, Shengfu; Brereton, Scott M; Wheeler, Martyn D; Ellis, Andrew M

    2005-12-21

    Electron impact (70 eV) mass spectra of a series of C1-C6 alcohols encased in large superfluid liquid helium nanodroplets (approximately 60,000 helium atoms) have been recorded. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others, most notably cleavage of the C(alpha)-H bond in the parent ion to form the corresponding oxonium ion. Parent ion intensities are also enhanced by the helium, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. To demonstrate that these findings are not unique to alcohols, we have also investigated several ethers. The results obtained for both alcohols and ethers are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels. The set of molecules explored in this work suggest that electron impact ionization of doped helium nanodroplets does not provide a sufficiently large softening effect to be useful in analytical mass spectrometry.

  5. Sputtering of Au induced by single Xe ion impacts

    SciTech Connect

    Birtcher, R. C.; Donnelly, S. E.

    1999-12-06

    Sputtering of Au thin films has been determined for Xe ions with energies between 50 and 600 keV. In-situ transmission electron microscopy was used to observe sputtered Au during deposition on a carbon foil near the specimen. Total reflection and transmission sputtering yields for a 62 nm thick Au thin film were determined by ex-situ measurement of the total amount of Au on the carbon foils. In situ observations show that individual Xe ions eject Au nanoparticles as large as 7 nm in diameter with an average diameter of approximately 3 nm. Particle emission correlates with crater formation due to single ion impacts. Nanoparticle emission contributes significantly to the total sputtering yield for Xe ions in this energy range in either reflection or transmission geometry.

  6. Impact of oncogenic K-RAS on YB-1 phosphorylation induced by ionizing radiation

    PubMed Central

    2011-01-01

    Introduction Expression of Y-box binding protein-1 (YB-1) is associated with tumor progression and drug resistance. Phosphorylation of YB-1 at serine residue 102 (S102) in response to growth factors is required for its transcriptional activity and is thought to be regulated by cytoplasmic signaling phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways. These pathways can be activated by growth factors and by exposure to ionizing radiation (IR). So far, however, no studies have been conducted on IR-induced YB-1 phosphorylation. Methods IR-induced YB-1 phosphorylation in K-RAS wild-type (K-RASwt) and K-RAS-mutated (K-RASmt) breast cancer cell lines was investigated. Using pharmacological inhibitors, small interfering RNA (siRNA) and plasmid-based overexpression approaches, we analyzed pathways involved in YB-1 phosphorylation by IR. Using γ-H2AX foci and standard colony formation assays, we investigated the function of YB-1 in repair of IR-induced DNA double-stranded breaks (DNA-DSB) and postirradiation survival was investigated. Results The average level of phosphorylation of YB-1 in the breast cancer cell lines SKBr3, MCF-7, HBL100 and MDA-MB-231 was significantly higher than that in normal cells. Exposure to IR and stimulation with erbB1 ligands resulted in phosphorylation of YB-1 in K-RASwt SKBr3, MCF-7 and HBL100 cells, which was shown to be K-Ras-independent. In contrast, lack of YB-1 phosphorylation after stimulation with either IR or erbB1 ligands was observed in K-RASmt MDA-MB-231 cells. Similarly to MDA-MB-231 cells, YB-1 became constitutively phosphorylated in K-RASwt cells following the overexpression of mutated K-RAS, and its phosphorylation was not further enhanced by IR. Phosphorylation of YB-1 as a result of irradiation or K-RAS mutation was dependent on erbB1 and its downstream pathways, PI3K and MAPK/ERK. In K-RASmt cells K-RAS siRNA as well as YB-1 siRNA blocked

  7. Investigation of the Impact of Desorption Electrospray Ionization Sprayer Geometry on Its Performance in Imaging of Biological Tissue.

    PubMed

    Tillner, Jocelyn; McKenzie, James S; Jones, Emrys A; Speller, Abigail V M; Walsh, James L; Veselkov, Kirill A; Bunch, Josephine; Takats, Zoltan; Gilmore, Ian S

    2016-05-03

    In this study, the impact of sprayer design and geometry on performance in desorption electrospray ionization mass spectrometry (DESI-MS) is assessed, as the sprayer is thought to be a major source of variability. Absolute intensity repeatability, spectral composition, and classification accuracy for biological tissues are considered. Marked differences in tissue analysis performance are seen between the commercially available and a lab-built sprayer. These are thought to be associated with the geometry of the solvent capillary and the resulting shape of the primary electrospray. Experiments with a sprayer with a fixed solvent capillary position show that capillary orientation has a crucial impact on tissue complex lipid signal and can lead to an almost complete loss of signal. Absolute intensity repeatability is compared for five lab-built sprayers using pork liver sections. Repeatability ranges from 1 to 224% for individual sprayers and peaks of different spectral abundance. Between sprayers, repeatability is 16%, 9%, 23%, and 34% for high, medium, low, and very low abundance peaks, respectively. To assess the impact of sprayer variability on tissue classification using multivariate statistical tools, nine human colorectal adenocarcinoma sections are analyzed with three lab-built sprayers, and classification accuracy for adenocarcinoma versus the surrounding stroma is assessed. It ranges from 80.7 to 94.5% between the three sprayers and is 86.5% overall. The presented results confirm that the sprayer setup needs to be closely controlled to obtain reliable data, and a new sprayer setup with a fixed solvent capillary geometry should be developed.

  8. Absolute total and partial cross sections for ionization of nucleobases by proton impact in the Bragg peak velocity range

    SciTech Connect

    Tabet, J.; Eden, S.; Feil, S.; Abdoul-Carime, H.; Farizon, B.; Farizon, M.; Ouaskit, S.; Maerk, T. D.

    2010-08-15

    We present experimental results for proton ionization of nucleobases (adenine, cytosine, thymine, and uracil) based on an event-by-event analysis of the different ions produced combined with an absolute target density determination. We are able to disentangle in detail the various proton ionization channels from mass-analyzed product ion signals in coincidence with the charge-analyzed projectile. In addition we are able to determine a complete set of cross sections for the ionization of these molecular targets by 20-150 keV protons including the total and partial cross sections and the direct-ionization and electron-capture cross sections.

  9. Single photon simultaneous K-shell ionization and K-shell excitation. II. Specificities of hollow nitrogen molecular ions

    SciTech Connect

    Carniato, S. Selles, P.; Andric, L.; Palaudoux, J.; Penent, F.; Lablanquie, P.; Žitnik, M.; Bučar, K.; Nakano, M.; Hikosaka, Y.; Ito, K.

    2015-01-07

    The formalism developed in the companion Paper I is used here for the interpretation of spectra obtained recently on the nitrogen molecule. Double core-hole ionization K{sup −2} and core ionization-core excitation K{sup −2}V processes have been observed by coincidence electron spectroscopy after ionization by synchrotron radiation at different photon energies. Theoretical and experimental cross sections reported on an absolute scale are in satisfactory agreement. The evolution with photon energy of the relative contribution of shake-up and conjugate shake-up processes is discussed. The first main resonance in the K{sup −2}V spectrum is assigned to a K{sup −2}π{sup ∗} state mainly populated by the 1s→ lowest unoccupied molecular orbital dipolar excitation, as it is in the K{sup −1}V NEXAFS (Near-Edge X-ray Absorption Fine Structure) signals. Closer to the K{sup −2} threshold Rydberg resonances have been also identified, and among them a K{sup −2}σ{sup ∗} resonance characterized by a large amount of 2s/2p hybridization, and double K{sup −2}(2σ{sup ∗}/1π/3σ){sup −1}1π{sup ∗2} shake-up states. These resonances correspond in NEXAFS spectra to, respectively, the well-known σ{sup ∗} shape resonance and double excitation K{sup −1}(2σ{sup ∗}/1π/3σ){sup −1}1π{sup ∗2} resonances, all being positioned above the threshold.

  10. A Critical Compilation of Energy Levels, Spectral Lines, and Transition Probabilities of Singly Ionized Silver, Ag II.

    PubMed

    Kramida, Alexander

    2013-01-01

    All available experimental measurements of the spectrum of the Ag(+) ion are critically reviewed. Systematic shifts are removed from the measured wavelengths. The compiled list of critically evaluated wavelengths is used to derive a comprehensive list of energy levels with well-defined uncertainties. Eigenvector compositions and level designations are found in two alternate coupling schemes. Some of the older work is found to be incorrect. A revised value of the ionization energy, 173283(7) cm(-1), equivalent to 21.4844(8) eV, is derived from the new energy levels. A set of critically evaluated transition probabilities is given.

  11. High-resolution (e, 2e + ion) study of electron-impact ionization and fragmentation of methane

    SciTech Connect

    Ren, Xueguang Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yong; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

    2015-05-07

    The ionization and fragmentation of methane induced by low-energy (E{sub 0} = 66 eV) electron-impact is investigated using a reaction microscope. The momentum vectors of all three charged final state particles, two outgoing electrons, and one fragment ion, are detected in coincidence. Compared to the earlier study [Xu et al., J. Chem. Phys. 138, 134307 (2013)], considerable improvements to the instrumental mass and energy resolutions have been achieved. The fragment products CH{sub 4}{sup +}, CH{sub 3}{sup +}, CH{sub 2}{sup +}, CH{sup +}, and C{sup +} are clearly resolved. The binding energy resolution of ΔE = 2.0 eV is a factor of three better than in the earlier measurements. The fragmentation channels are investigated by measuring the ion kinetic energy distributions and the binding energy spectra. While being mostly in consistence with existing photoionization studies the results show differences including missing fragmentation channels and previously unseen channels.

  12. Investigation of a vortex in Coulomb-Born calculations of inner-shell ionization of carbon by electron impact

    NASA Astrophysics Data System (ADS)

    Ward, S. J.; Macek, J. H.

    2013-05-01

    Previously, we reported vortices in Coulomb-Born calculations of inner-shell ionization of carbon by electron impact. A vortex was obtained for the kinematics of an incident energy Ei = 1801 . 2 eV , scattering angle θf =4° , energy of the ejected electron Ek = 5 . 524 eV and angle of the ejected electron θk =239° . We showed that for this set of kinematics, the real and imaginary parts of the T-matrix are zero at the same angle (to a good approximation). Furthermore, we showed the velocity field rotates about the position of the vortex. Recently, following the treatment of Botero and Macek, we decomposed the Coulomb-Born T-matrix into its multipole components. We show that the T-matrix and the quintuple differential cross section obtained by simply adding the l = 1 , m = +/- 1 multipole components to the l = 0 --> 4 , m = 0 components is very close to the Coulomb-Born T-matrix and the quintuple differential cross section, respectively. Our analysis shows the importance of the l = 1 , m = +/- 1 multipole components in obtaining a vortex in the Coulomb-Born calculation. S.J.W. acknowledges support from NSF under grant no. PHYS-0968638. J.H.M. acknowledges support by the D.O.E. under grant number DE-FG02-02ER15283.

  13. Ultrafast electron dynamics following outer-valence ionization: The impact of low-lying relaxation satellite states

    NASA Astrophysics Data System (ADS)

    Lünnemann, Siegfried; Kuleff, Alexander I.; Cederbaum, Lorenz S.

    2009-04-01

    Low-lying relaxation satellites give rise to ultrafast electron dynamics following outer-valence ionization of a molecular system. To demonstrate the impact of such satellites, the evolution of the electronic cloud after sudden removal of an electron from the highest occupied molecular orbital (HOMO) of the organic unsaturated nitroso compound 2-nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using ab initio methods only. Our results show that the initially created hole charge remains stationary but on top of it the system reacts by an ultrafast π-π ∗ excitation followed by a cyclic excitation-de-excitation process which leads to a redistribution of the charge. The π-π ∗ excitation following the removal of the HOMO electron takes place on a subfemtosecond time scale and the period of the excitation-de-excitation alternations is about 1.4 fs. In real space the processes of excitation and de-excitation represent ultrafast delocalization and localization of the charge. The results are analyzed by simple two- and three-state models.

  14. Partial-ionization cross sections of a CO{sub 2} molecule due to impact of 10-26-keV electrons

    SciTech Connect

    Bhatt, Pragya; Singh, Raj; Yadav, Namita; Shanker, R.

    2010-10-15

    Experimental data on total- and partial-ionization cross sections of ionic fragments of CO{sub 2} molecule produced by impact of 10-26-keV electrons are obtained on a crossed-beam apparatus in our laboratory. An ejected electron-produced ion-coincidence technique is employed together with a time-of-flight mass spectrometer for analysis of the ions. The six ionic fragments, CO{sub 2}{sup +}, CO{sup +}, CO{sub 2}{sup 2+}, O{sup +}, C{sup +}, and C{sup 2+}, resulting from dissociative ionization of the CO{sub 2} molecule are observed and identified; their relative ionization cross sections and branching ratios are determined as a function of impact energy. The binary-encounter Bethe model is found to overestimate the experimental data for total-ionization cross sections of the observed ions. No other experimental or theoretical data exist in the investigated energy range to make a direct comparison with the present results.

  15. Calculations for ion-impact induced ionization and fragmentation of water molecules

    NASA Astrophysics Data System (ADS)

    Kirchner, Tom; Murakami, Mitsuko; Horbatsch, Marko; Jürgen Lüdde, Hans

    2012-10-01

    Charge-state correlated cross sections for single- and multiple-electron removal processes in proton-water-molecule collisions are calculated by using the non-perturbative basis generator method adapted for ion-molecule collisions [1,2]. A fragmentation model is then applied to calculate the yields of H2O^+, OH^+, H^+, and O^+ ions emerging after H2O^q+ formation [3]. A detailed comparison is made with experimental data from three groups covering the energy range from 20--5000 keV. It is found that multiple electron processes with q<=3 play an important role at the lower end of this range and are calculated accurately within an independent particle model. We are currently completing the analogous analysis for He^+-H2O collisions for which the presence of the projectile electron poses some additional challenges. [4pt] [1] H.J. L"udde et al, Phys. Rev. A 80, 060702(R) (2009)[0pt] [2] M. Murakami et al, Phys. Rev. A 85, 052704 (2012)[0pt] [3] M. Murakami et al, Phys. Rev. A 85, 052713 (2012)

  16. Experimental and theoretical triple differential cross sections for electron-impact ionization of Ar (3p) for equal energy final state electrons

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Ozer, Zehra N.; Dogan, Mevlut; Yavuz, Murat; Varol, Onur; Madison, Don

    2016-09-01

    There have been several studies of electron-impact ionization of inert gases for asymmetric final state energy sharing and normally one electron has an energy significantly higher than the other. However, there have been relatively few studies examining equal energy final state electrons. Here we report experimental and theoretical triple differential cross sections for electron impact ionization of Ar (3p) for equal energy sharing of the outgoing electrons. Previous experimental results combined with some new measurements are compared with distorted wave born approximation (DWBA) results, DWBA results using the Ward-Macek (WM) approximation for the post collision interaction (PCI), and three-body distorted wave (3DW) which includes PCI without approximation. The results show that it is crucially important to include PCI in the calculation particularly for lower energies and that the WM approximation is valid only for high energies. The 3DW, on the other hand, is in reasonably good agreement with data down to fairly low energies.

  17. Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m

    NASA Astrophysics Data System (ADS)

    Heinbuch, S.; Dong, F.; Rocca, J. J.; Bernstein, E. R.

    2006-10-01

    Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5)×104s-1 for cluster sizes of 5⩽n⩽16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n + cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2)(H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed.

  18. Rapid Identification and Quantification of Linear Olefin Isomers by Online Ozonolysis-Single Photon Ionization Time-of-Flight Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Xie, Yuanyuan; Chen, Ping; Hua, Lei; Hou, Keyong; Wang, Yongchao; Wang, Haiyan; Li, Haiyang

    2016-01-01

    The specific locations of the double bonds in linear olefins can facilitate olefin catalytic synthetic reactions to improve the quality of target olefin products. We developed a simple and efficient approach based on single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) combined with online ozonolysis to identify and quantify the linear olefin double bond positional isomers. The online ozonolysis cleaved the olefins at the double bond positions that led to formation of corresponding characteristic aldehydes. The aldehydes were then detected by SPI-TOFMS to achieve unique spectrometric "fingerprints" for each linear olefin to successfully identify the isomeric ones. To accurately quantify the isomeric components in olefin mixtures, an algorithm was proposed to quantify three isomeric olefin mixtures based on characteristic ion intensities and their equivalent ionization coefficients. The relative concentration errors for the olefin components were lower than 2.5% while the total analysis time was less than 2 min. These results demonstrate that the online ozonolysis SPI-TOFMS has the potential for real-time monitoring of catalytic olefin synthetic reactions.

  19. Compendium of Single-Event Latchup and Total Ionizing Dose Test Results of Commercial Analog to Digital Converters

    NASA Technical Reports Server (NTRS)

    Irom, Farokh; Agarwal, Shri G.

    2012-01-01

    This paper reports single-event latchup and total dose results for a variety of analog to digital converters targeted for possible use in NASA spacecraft's. The compendium covers devices tested over the last 15 years.

  20. Single electron ionization and electron capture cross sections for (C6+, H2O) interaction within the Classical Trajectory Monte Carlo (CTMC) approach

    NASA Astrophysics Data System (ADS)

    Tran, H. N.; Dao, D. D.; Incerti, S.; Bernal, M. A.; Karamitros, M.; Nhan Hao, T. V.; Dang, T. M.; Francis, Z.

    2016-01-01

    In this work, we present a derivation of cross sections for single ionization and electron capture processes within the Classical Trajectory Monte Carlo (CTMC) approach. Specifically, we have used a potential stemming from an ab initio calculation in Green et al.'s framework to describe the dynamics of the water molecule system. Proposing a modified version of the Classical Over-Barrier (COB) potential, we have found that a cut-off of roughly 28 a.u. on the initial distance of the projectile produced a reasonable accuracy. A global agreement has been obtained in our calculations compared to experimental and other theoretical results for C6+ ion energies ranging from 10 keV/u to 10 MeV/u.

  1. Rapid comprehensive characterization of crude oils by thermogravimetry coupled to fast modulated gas chromatography-single photon ionization time-of-flight mass spectrometry.

    PubMed

    Wohlfahrt, S; Fischer, M; Saraji-Bozorgzad, M; Matuschek, G; Streibel, T; Post, E; Denner, T; Zimmermann, R

    2013-09-01

    Comprehensive multi-dimensional hyphenation of a thermogravimetry device (i.e. a thermobalance) to gas chromatography and single photon ionization-time-of-flight mass spectrometry (TG-GC×SPI-MS) has been used to investigate two crude oil samples of different geographical origin. The source of the applied vacuum ultraviolet radiation is an electron beam pumped rare gas excimer lamp (EBEL). The soft photoionization favors the formation of molecular ions. Introduction of a fast, rapidly modulated gas chromatographic separation step in comparison with solely TG-SPI-MS enables strongly enhanced detection especially with such highly complex organic matrices as crude oil. In contrast with former TG-SPI-MS measurements, separation and identification of overlying substances is possible because of different GC retention times. The specific contribution of isobaric compounds to one mass signal is determined for alkanes, naphthalenes, alkylated benzenes, and other compounds.

  2. Precision treatment of single and double multiphoton ionization of He atoms by strong laser fields: Time-dependent generalized pseudospectral method in internal coordinates

    NASA Astrophysics Data System (ADS)

    Telnov, Dmitry A.; Heslar, John; Chu, Shih-I.

    2012-06-01

    We have developed a new computational method for accurate and efficient numerical solution of the time-dependent Schr"odinger equation for two-electron atoms. Our approach is full-dimensional and makes use of the internal coordinates of the electrons in the plane defined by the electrons and the nucleus (r1, r2, and θ12) as well as Euler angles which determine the orientation of the plane in space. The internal coordinates can be optimally discretized by means of the generalized pseudospectral method while the Euler angles appear through the basis set functions with the definite total angular momentum and its projections. The results of the single and double ionization of the helium atom by strong 800 nm laser fields will be presented. The accurate time-dependent electron density obtained can be used for testing and improvement of various approximate exchange-correlation functionals of the time-dependent density functional theory.

  3. SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Yan, Renbin; Bundy, Kevin; Bershady, Matthew; Haffner, L. Matthew; Walterbos, René; Maiolino, Roberto; Tremonti, Christy; Thomas, Daniel; Drory, Niv; Jones, Amy; Belfiore, Francesco; Sánchez, Sebastian F.; Diamond-Stanic, Aleksandar M.; Bizyaev, Dmitry; Nitschelm, Christian; Andrews, Brett; Brinkmann, Jon; Brownstein, Joel R.; Cheung, Edmond; Li, Cheng; Law, David R.; Roman Lopes, Alexandre; Oravetz, Daniel; Pan, Kaike; Storchi Bergmann, Thaisa; Simmons, Audrey

    2017-04-01

    Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission-line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S II]/Hα, [N II]/Hα, [O II]/Hβ and [O I]/Hα. The gradients in these line ratios are determined by metallicity gradients and ΣHα. In line ratio diagnostic diagrams, contamination by DIG moves H II regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H II region models can only shift line ratios slightly relative to H II region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R23, N2 = [N II]/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H II region models that fail to describe the DIG.

  4. Cross sections for ionization of K, L and M shells of atoms by impact of electrons and positrons with energies up to 1 GeV: Analytical formulas

    SciTech Connect

    Bote, David; Salvat, Francesc Jablonski, Aleksander

    2009-11-15

    Analytical formulas are presented for the easy calculation of cross sections for ionization of K, L and M shells of neutral atoms by impact of electrons and positrons with kinetic energies up to 1 GeV. Each formula contains a number of parameters that are characteristic of the element, the active electron shell and the projectile particle. The values of these parameters were determined by fitting the cross section values in an extensive database that was calculated recently by means of a composite algorithm that combines the distorted-wave and plane-wave Born approximations. Tables of parameter values are given for all elements, from hydrogen (Z=1) to einsteinium (Z=99). The proposed analytical expressions yield ionization cross sections that agree with those in the numerical database to within about 1%, except for projectiles with near-threshold energies.

  5. Electron impact ionization of individual sub-shells and total of L and M shells of atomic targets with Z = 38–92

    NASA Astrophysics Data System (ADS)

    Haque, A. K. F.; Maaza, M.; Uddin, M. A.; Patoary, M. Atiqur R.; Ismail Hossain, M.; Basak, A. K.; Saha, B. C.; Mahbub, M. Selim

    2017-03-01

    We report an extension and modification of the MCN model of Haque et al (2013 Rad. Phys. Chem. 91 50–9) (XMCN) to study the electron impact ionization of inner L and M shells of neutral atoms by introducing new parameters of the MCN model. The extended XMCN model, including the relativistic effect, has been applied with success to evaluate ionization cross-sections of various atomic targets with Z = 38–92 for both individual subshells and total L-shell and the corresponding cross-sections for the M shell for Z = 79–92 at incident energies E Threshold ≤slant T ≤slant 1 GeV. A comparison with other available theoretical and experimental cross-sections reveals that our results reproduce the experimental measurements with a reasonable accuracy.

  6. Structural determination of zinc dithiophosphates in lubricating oils by gas chromatography-mass spectrometry with electron impact and electron-capture negative ion chemical ionization.

    PubMed

    Becchi, M; Perret, F; Carraze, B; Beziau, J F; Michel, J P

    2001-01-05

    Pentafluorobenzyl ester derivatives were used to identify zinc dialkyldithiophosphates and diaryldithiophosphates antiwear engine oil additives by GC-electron impact ionization (EI) MS and GC-electron-capture negative ion chemical ionization (ECNCI) MS analysis. GC-EI-MS of the dialkyldithiophosphate-pentafluorobenzyl derivatives afforded characteristic fragment ions corresponding to the cleavage of one and two alkyl radicals. In most cases, information was only obtained on one alkyl chain. Additional and complete information was obtained with retention time indices using synthetic derivatives and with GC-ECNCI-MS analysis. ECNCI afforded characteristic dithiophosphate anions which allowed the determination of the total number of carbon atoms in the alkyl radicals. The diastereoisomer mixtures of 2-hydroxy-sec.-alkyl radicals were completely separated on GC analysis.

  7. Fragmentation dynamics of argon clusters (Arn, n =2 to 11) following electron-impact ionization: Modeling and comparison with experiment

    NASA Astrophysics Data System (ADS)

    Bonhommeau, David; Halberstadt, Nadine; Viel, Alexandra

    2006-05-01

    The fragmentation dynamics of argon clusters ionized by electron impact is investigated for initial cluster sizes up to n =11 atoms. The dynamics of the argon atoms is modeled using a mixed quantum-classical method in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model with the addition of the induced dipole-induced dipole and spin-orbit interactions. The results show extensive and fast fragmentation. The dimer is the most abundant ionic fragment, with a proportion increasing from 66% for n =2 to a maximum of 95% for n =6 and then decreasing down to 67% for n =11. The next abundant fragment is the monomer for n <7 and the trimer otherwise. The parent ion dissociation lifetimes are all in the range of 1ps. Long-lived trajectories appear for initial cluster sizes of seven and higher, and favor the formation of the larger fragments (trimers and tetramers). Our results show quantitative agreement with available experimental results concerning the extensive character of the fragmentation: Ar+ and Ar2+ are the only ionic fragments for sizes up to five atoms; their overall proportion is in quantitative agreement for all the studied sizes; Ar2+ is the main fragment for all sizes; stable Ar3+ fragments only appear for n ⩾5, and their proportion increases smoothly with cluster size from there. However, the individual ionic monomer and dimer fragment proportions differ. The experimental ones exhibit oscillations with initial cluster size, with a slight tendency to decrease on average for the monomer. In contrast our results show a monotonic, systematic evolution, similar to what was found in our earlier studies on neon and krypton clusters. Several hypotheses are discussed in order to find the origin of this discrepancy. Finally, the metastable II(1/2)u and II(1/2)g states of Ar2+ are found to decay with a lifetime of 3.5 and 0.1ps

  8. Ionizing radiation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This chapter gives a comprehensive review on ionizing irradiation of fresh fruits and vegetables. Topics include principles of ionizing radiation, its effects on pathogenic and spoilage microorganisms, shelf-life, sensory quality, nutritional and phytochemical composition, as well as physiologic and...

  9. Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH4-NH3 gas mixtures.

    PubMed

    Eustergerling, Brett; Hèden, Martin; Shi, Yujun

    2007-11-01

    The application of a laser-induced electron impact (LIEI) ionization source in studying the gas-phase chemistry of the SiH(4)/NH(3) hot-wire chemical vapor deposition (HWCVD) system has been investigated. The LIEI source is achieved by directing an unfocused laser beam containing both 118 nm (10.5 eV) vacuum ultraviolet (VUV) and 355 nm UV radiations to the repeller plate in a time-of-flight mass spectrometer. Comparison of the LIEI source with the conventional 118 nm VUV single-photon ionization (SPI) method has demonstrated that the intensities of the chemical species with ionization potentials (IP) above 10.5 eV, e.g., H(2), N(2) and He, have been significantly enhanced with the incorporation of the LIEI source. It is found that the SPI source due to the 118 nm VUV light coexists in the LIEI source. This allows simultaneous observations of parent ions with enhanced intensity from VUV SPI and their "fingerprint" fragmentation ions from LIEI. It is, therefore, an effective tool to diagnose the gas-phase chemical species involved with both NH(3) and SiH(4) in the HWCVD reactor. In using the LIEI source to SiH(4), NH(3) and their mixtures, it has been shown that the NH(3) decomposition is suppressed with the addition of SiH(4) molecules. Examination of the NH(3) decomposition percentage and the time to reach the N(2) and H(2) steady-state intensities for various NH(3)/SiH(4) mixtures suggests that the extent of the suppression is enhanced with more SiH(4) content in the mixture. With increasing filament temperatures, the negative effect of SiH(4) becomes less important.

  10. Single photon ionization of van der Waals clusters with a soft x-ray laser: (SO2)n and (SO2)n(H2O)m

    NASA Astrophysics Data System (ADS)

    Dong, F.; Heinbuch, S.; Rocca, J. J.; Bernstein, E. R.

    2006-10-01

    van der Waals cluster (SO2)n is investigated by using single photon ionization of a 26.5eV soft x-ray laser. During the ionization process, neutral clusters suffer a small fragmentation because almost all energy is taken away by the photoelectron and a small part of the photon energy is deposited into the (SO2)n cluster. The distribution of (SO2)n clusters decreases roughly exponentially with increasing cluster size. The photoionization dissociation fraction of I[(SO2)n-1SO+]/I[(SO2)n+] decreases with increasing cluster size due to the formation of cluster. The metastable dissociation rate constants of (SO2)n+ are measured in the range of (0.6-1.5)×104s-1 for cluster sizes 5⩽n⩽16. Mixed SO2-H2O clusters are studied at different experimental conditions. At the condition of high SO2 concentration (20% SO2 partial pressure), (SO2)n + cluster ions dominate the mass spectrum, and the unprotonated mixed cluster ions (SO2)nH2O+ (1⩽n⩽5) are observed. At the condition of low SO2 concentration (5% SO2 partial pressure) (H2O)nH+ cluster ions are the dominant signals, and protonated cluster ions (SO2)(H2O)nH+ are observed. The mixed clusters, containing only one SO2 or H2O molecule, SO2(H2O)nH+ and (SO2)nH2O+ are observed, respectively.

  11. Use of microextraction by packed sorbent directly coupled to an electron ionization single quadrupole mass spectrometer as an alternative for non-separative determinations.

    PubMed

    Casas Ferreira, Ana María; Moreno Cordero, Bernardo; Pérez Pavón, José Luis

    2017-02-01

    Sometimes it is not necessary to separate the individual compounds of a sample to resolve an analytical problem, it is enough to obtain a signal profile of the sample formed by all the components integrating it. Within this strategy, electronic noses based on the direct coupling of a headspace sampler with a mass spectrometer (HS-MS) have been proposed. Nevertheless, this coupling is not suitable for the analysis of non-volatile compounds. In order to propose an alternative to HS-MS determinations for non-volatile compounds, here we present the first 'proof of concept' use of the direct coupling of microextraction by packed sorbents (MEPS) to a mass spectrometer device using an electron ionization (EI) and a single quadrupole as ionization source and analyzer, respectively. As target compounds, a set of analytes with different physic-chemical properties were evaluated (2-ethyl-1-hexanol, styrene, 2-heptanone, among others). The use of MEPS extraction present many advantages, such as it is fast, simple, easy to automate and requires small volumes of sample and organic solvents. Moreover, MEPS cartridges are re-usable as samples can be extracted more than 100 times using the same syringe. In order to introduce into the system all the elution volume from the MEPS extraction, a programmable temperature vaporizer (PTV) is proposed as the injector device. Results obtained with the proposed methodology (MEPS-PTV/MS) were compared with the ones obtained based on the separative scheme, i.e. using gas chromatography separation (MEPS-PTV-GC/MS), and both methods provided similar results. Limits of detection were found to be between 3.26 and 146.6μgL(-1) in the non-separative scheme and between 0.02 and 1.72μgL(-1) when the separative methodology was used. Repeatability and reproducibility were evaluated with values below 17% in all cases.

  12. Theoretical study of hole initiated impact ionization in bulk silicon and GaAs using a wave-vector-dependent numerical transition rate formulation within an ensemble Monte Carlo calculation

    NASA Technical Reports Server (NTRS)

    Oguzman, Ismail H.; Wang, Yang; Kolnik, Jan; Brennan, Kevin F.

    1995-01-01

    In this paper, calculations of the hole initiated interband impact ionization rate in bulk silicon and GaAs are presented based on an ensemble Monte Carlo simulation with the inclusion of a wave-vector-dependent numerical transition rate formulation. The ionization transition rate is determined for each of the three valence bands, heavy, light, and split-off, using Fermi's golden rule with a two-body, screened Coulomb interaction. The dielectric function used within the calculation is assumed to be wave-vector-dependent. Calculations of the field-dependent impact ionization rate as well as the quantum yield are presented. It is found from both the quantum yield results and examination of the hole distribution function that the effective threshold energy for hole initiated impact ionization is relatively soft, similar to that predicted for the corresponding electron initiated ionization events occur more frequently than either heavy or split-offf initiated ionization events in bulk silicon over the applied electric field strengths examined here, 250-500 kV/cm. Conversely,in GaAs, the vast majority of hole initated ionization events originate from holes within the split-off band.

  13. Automated cell-by-cell tissue imaging and single-cell analysis for targeted morphologies by laser ablation electrospray ionization mass spectrometry.

    PubMed

    Li, Hang; Smith, Brian K; Shrestha, Bindesh; Márk, László; Vertes, Akos

    2015-01-01

    Mass spectrometry imaging (MSI) is an emerging technology for the mapping of molecular distributions in tissues. In most of the existing studies, imaging is performed by sampling on a predefined rectangular grid that does not reflect the natural cellular pattern of the tissue. Delivering laser pulses by a sharpened optical fiber in laser ablation electrospray ionization (LAESI) mass spectrometry (MS) has enabled the direct analysis of single cells and subcellular compartments. Cell-by-cell imaging had been demonstrated using LAESI-MS, where individual cells were manually selected to serve as natural pixels for tissue imaging. Here we describe a protocol for a novel cell-by-cell LAESI imaging approach that automates cell recognition and addressing for systematic ablation of individual cells. Cell types with particular morphologies can also be selected for analysis. First, the cells are recognized as objects in a microscope image. The coordinates of their centroids are used by a stage-control program to sequentially position the cells under the optical fiber tip for laser ablation. This approach increases the image acquisition efficiency and stability, and enables the investigation of extended or selected tissue areas. In the LAESI process, the ablation events result in mass spectra that represent the metabolite levels in the ablated cells. Peak intensities of selected ions are used to represent the metabolite distributions in the tissue with single-cell resolution.

  14. Double L{sub 3}M ionization of Pd induced by impact with medium-energy electrons

    SciTech Connect

    Cao, W.; Dousse, J.-Cl.; Hoszowska, J.; Kayser, Y.; Schenker, J.-L.; Kavcic, M.; Zitnik, M.

    2011-02-15

    The electron-induced L{sub 3}M two-step double ionization cross sections of metallic Pd were determined experimentally for incident electron beam energies ranging from the double ionization threshold up to 18 keV. The double L{sub 3}M ionization cross sections were derived from the intensity ratios (I{sub L{alpha}M}:I{sub L{alpha}}) of the resolved M satellites to the parent diagram lines. The sample was bombarded with monoenergetic electrons from an energy-tunable 20-kV electron gun. The diagram and M-satellite x-ray lines were measured by means of high-resolution x-ray spectroscopy, using a reflection-type von Hamos bent crystal spectrometer. The two-step partial cross sections were determined by subtracting from the measured total double ionization cross sections the contributions due to the shake process and L{sub 1}-L{sub 3}M{sub 4,5} Coster-Kronig transitions. Despite the thick target employed in the present study, the dependence of the two-step cross sections on the incoming electron energy could be derived using a target slice decomposition method. It is shown that the obtained energy dependence can be well reproduced by the semiempirical parametrization model of Pattard and Rost.

  15. Cross sections of electron capture and electron capture with ionization of argon atoms by fast 3He2+ ions at various impact parameters

    NASA Astrophysics Data System (ADS)

    Afrosimov, V. V.; Basalaev, A. A.; Panov, M. N.

    2017-01-01

    The absolute differential cross sections of scattering of fast particles formed in processes with capture of one or two electrons from Ar atoms have been measured for 6-keV He2+ ions in the interval of scattering angles within 0°-2.5°. The cross sections of electron capture and electron capture with ionization have been determined as functions of the impact parameter. The probabilities of these processes are compared to the distribution of electron density in various shells of target atoms. Applicability of the models of screened Coulomb interaction potentials to description of the scattering of recharged particles is assessed.

  16. Cross section database for carbon atoms and ions: Electron-impact ionization, excitation, and charge exchange in collisions with hydrogen atoms

    SciTech Connect

    Suno, Hiroya . E-mail: suno@jamstec.go.jp; Kato, Takako

    2006-07-15

    A database has been constructed consisting of the recommended cross sections for electron-impact excitation and ionization of carbon atoms and ions C, C{sup +}-C{sup 5+}, asl as for charge exchange processes between carbon ions C{sup +}-C{sup 6+} and hydrogen atoms. We have collected a large amount of theoretical and experimental cross section data from the literature, and have critically assessed their accuracy. The recommended cross sections, the best values for use, are expressed in the form of simple analytical functions. These are also presented in graphical form.

  17. Phototriggered formation and repair of DNA containing a site-specific single strand break of the type produced by ionizing radiation or AP lyase activity.

    PubMed

    Zhang, K; Taylor, J S

    2001-01-09

    DNA strand breaks are produced by a variety of agents and processes such as ionizing radiation, xenobiotics, oxidative metabolism, and enzymatic processing of DNA base damage. One of the major types of strand breaks produced by these processes is a single nucleotide gap terminating in 5'- and 3'-phosphates. Previously, we had developed a method for sequence-specifically producing such phosphate-terminated strand breaks in an oligodeoxynucleotide by way of two photochemically activated (caged) building blocks placed in tandem. We now report the design and synthesis of a single caged building block consisting of 1,3-(2-nitrophenyl)-1,3-propanediol, for producing phosphate-terminated strand breaks, and its use producing such a break at a specific site in a double-stranded circular DNA vector. To produce the site-specific break in a duplex vector, a primer containing the caged single strand break was extended opposite the single strand form of a circular DNA vector followed by enzymatic ligation and purification. The single strand break could then be formed in quantitative yield by irradiation of the vector with 365 nm light. In contrast to a previous study, it was found that the strand break can be repaired by Escherichia coli DNA polymerase I and E. coli DNA ligase alone, though less efficiently than in the presence of the 3'-phosphate processing enzyme E. coli endonuclease IV. Repair in the absence of endonuclease IV could be attributed to hydrolysis of the 3'-phosphate in the presence of dNTP and to a lesser extent to exonucleolytic removal of the 3'-phosphate-bearing terminal nucleotide by way of the 3' --> 5' exonuclease activity of polymerase I. This work demonstrates that specialized 3'-end processing enzymes such as endonuclease IV or exonuclease III are not absolutely required for repair of phosphate-terminated gaps. In addition to preparing single strand breaks, the caged building block described should also be useful for preparing double strand breaks and

  18. Quantitation of triacylglycerols in edible oils by off-line comprehensive two-dimensional liquid chromatography-atmospheric pressure chemical ionization mass spectrometry using a single column.

    PubMed

    Wei, Fang; Hu, Na; Lv, Xin; Dong, Xu-Yan; Chen, Hong

    2015-07-24

    In this investigation, off-line comprehensive two-dimensional liquid chromatography-atmospheric pressure chemical ionization mass spectrometry using a single column has been applied for the identification and quantification of triacylglycerols in edible oils. A novel mixed-mode phenyl-hexyl chromatographic column was employed in this off-line two-dimensional separation system. The phenyl-hexyl column combined the features of traditional C18 and silver-ion columns, which could provide hydrophobic interactions with triacylglycerols under acetonitrile conditions and can offer π-π interactions with triacylglycerols under methanol conditions. When compared with traditional off-line comprehensive two-dimensional liquid chromatography employing two different chromatographic columns (C18 and silver-ion column) and using elution solvents comprised of two phases (reversed-phase/normal-phase) for triacylglycerols separation, the novel off-line comprehensive two-dimensional liquid chromatography using a single column can be achieved by simply altering the mobile phase between acetonitrile and methanol, which exhibited a much higher selectivity for the separation of triacylglycerols with great efficiency and rapid speed. In addition, an approach based on the use of response factor with atmospheric pressure chemical ionization mass spectrometry has been developed for triacylglycerols quantification. Due to the differences between saturated and unsaturated acyl chains, the use of response factors significantly improves the quantitation of triacylglycerols. This two-dimensional liquid chromatography-mass spectrometry system was successfully applied for the profiling of triacylglycerols in soybean oils, peanut oils and lord oils. A total of 68 triacylglycerols including 40 triacylglycerols in soybean oils, 50 triacylglycerols in peanut oils and 44 triacylglycerols in lord oils have been identified and quantified. The liquid chromatography-mass spectrometry data were analyzed

  19. Ionizing radiation from tobacco

    SciTech Connect

    Westin, J.B.

    1987-04-24

    Accidents at nuclear power facilities seem inevitably to bring in their wake a great deal of concern on the part of both the lay and medical communities. Relatively little attention, however, is given to what may be the largest single worldwide source of effectively carcinogenic ionizing radiation: tobacco. The risk of cancer deaths from the Chernobyl disaster are tobacco smoke is discussed.

  20. B-spline R-matrix-with-pseudostates calculations for electron-impact excitation and ionization of nitrogen

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zatsarinny, Oleg; Bartschat, Klaus

    2014-06-01

    The B-spline R-matrix-with-pseudostates (BSR) method is employed to treat electron collisions with nitrogen atoms. Predictions for elastic scattering, excitation, and ionization are presented for all transitions between the lowest 21 states of nitrogen in the energy range from threshold to 120 eV. The structure description has been further improved compared to a previous BSR calculation by Tayal and Zatsarinny [J. Phys. B 38, 3631 (2005), 10.1088/0953-4075/38/20/001]. This change in the structure model, together with the inclusion of a large number of pseudostates in the close-coupling expansion, has a major influence on the theoretical predictions, especially at intermediate energies, where many of the excitation cross sections are reduced significantly. Ionization cross sections for the ground and metastable initial states are also provided. Finally, we carry out an accurate ab initio treatment of the prominent shape resonance just above the elastic threshold.

  1. Simulated Space Radiation: Impact of Four Different Types of High-Dose Ionizing Radiation on the Lichen Xanthoria elegans.

    PubMed

    Brandt, Annette; Meeßen, Joachim; Jänicke, Reiner U; Raguse, Marina; Ott, Sieglinde

    2017-02-01

    This study addresses the viability of the lichen Xanthoria elegans after high-dose ionizing irradiation in the frame of the STARLIFE campaign. The first set of experiments was intended to resemble several types of galactic cosmic radiation (GCR) as present beyond the magnetic shield of Earth. In the second set of experiments, γ radiation up to 113 kGy was applied to test the limit of lichen resistance to ionizing radiation. Entire thalli of Xanthoria elegans were irradiated in the anhydrobiotic state. After STARLIFE 1, the metabolic activity of both symbionts was quantified by live/dead staining with confocal laser scanning microscopy. The photosynthetic activity was measured after the respective irradiation to assess the ability of the symbiotic green algae to restore photosynthesis after irradiation. The STARLIFE campaign complements the results of the LIFE experiments at the EXPOSE-E facility on the International Space Station by testing the model organism Xanthoria elegans on its resistance to hazardous radiation that might be accumulated during long-term space exposure. In addition, the photosynthetic activity of metabolically active lichen was investigated after X-ray irradiation up to 100 Gy (3.3 Gy/min). Since previous astrobiological experiments were mostly performed with anhydrobiotic lichen, these experiments will broaden our knowledge on the correlation of physiological state and astrobiological stressors. Key Words: Astrobiology-Extremotolerance-Gamma rays-Ionizing radiation-Lichens-Viability. Astrobiology 17, 136-144.

  2. Investigation of mono/competitive adsorption of environmentally relevant ionized weak acids on graphite: impact of molecular properties and thermodynamics.

    PubMed

    Moustafa, Ahmed M A; McPhedran, Kerry N; Moreira, Jesús; Gamal El-Din, Mohamed

    2014-12-16

    The thermodynamics of adsorption and competitive interactions of five weak acids on a graphite surface was assessed in alkaline solutions. Adsorption of the acids in mono- and multicompound solutions followed their Freundlich isotherms which suggest a diversity of graphite adsorption sites as confirmed by the presence of carboxylic and phenolic groups observed on graphite surfaces. Thermodynamic calculations assigned the formation of the negatively charged assisted hydrogen bond (-CAHB) between ionized solutes and adsorbent surface groups as the possible adsorption mechanism. However, the similar pKa values of current acids resulted in comparable free energies for -CAHB formation (ΔG(-CAHB)) being less than solvation free energies (ΔGSolv). Thus, additional ΔG is supplemented by increased hydrophobicity due to proton exchange of ionized acids with water (ΔΔG Hydrophobicity). Adsorption capacities and competition coefficients indicated that ΔΔG Hydrophobicity values depend on the neutral and ionized acid Kow. Competitive adsorption implies that multilayer adsorption may occur via hydrophobic bonding with the CH3 ends of the self-assembled layer which affects the acid adsorption capacities in mixtures as compared to monocompound solutions. The determination of adsorption mechanisms will assist in understanding of the fate and bioavailability of emerging and classical weak acids released into natural waters.

  3. Multi-fluid Modeling of Magnetosonic Wave Propagation in the Solar Chromosphere: Effects of Impact Ionization and Radiative Recombination

    NASA Astrophysics Data System (ADS)

    Maneva, Yana G.; Alvarez Laguna, Alejandro; Lani, Andrea; Poedts, Stefaan

    2017-02-01

    In order to study chromospheric magnetosonic wave propagation including, for the first time, the effects of ion–neutral interactions in the partially ionized solar chromosphere, we have developed a new multi-fluid computational model accounting for ionization and recombination reactions in gravitationally stratified magnetized collisional media. The two-fluid model used in our 2D numerical simulations treats neutrals as a separate fluid and considers charged species (electrons and ions) within the resistive MHD approach with Coulomb collisions and anisotropic heat flux determined by Braginskiis transport coefficients. The electromagnetic fields are evolved according to the full Maxwell equations and the solenoidality of the magnetic field is enforced with a hyperbolic divergence-cleaning scheme. The initial density and temperature profiles are similar to VAL III chromospheric model in which dynamical, thermal, and chemical equilibrium are considered to ensure comparison to existing MHD models and avoid artificial numerical heating. In this initial setup we include simple homogeneous flux tube magnetic field configuration and an external photospheric velocity driver to simulate the propagation of MHD waves in the partially ionized reactive chromosphere. In particular, we investigate the loss of chemical equilibrium and the plasma heating related to the steepening of fast magnetosonic wave fronts in the gravitationally stratified medium.

  4. Electron ionization of acetylene.

    PubMed

    King, Simon J; Price, Stephen D

    2007-11-07

    Relative partial ionization cross sections and precursor specific relative partial ionization cross sections for fragment ions formed by electron ionization of C2H2 have been measured using time-of-flight mass spectrometry coupled with a 2D ion-ion coincidence technique. We report data for the formation of H+, H+2, C2+, C+/C2+ 2, CH+/C2H+2, CH+2, C+2, and C2H+ relative to the formation of C2H+2, as a function of ionizing electron energy from 30-200 eV. While excellent agreement is found between our data and one set of previously published absolute partial ionization cross sections, some discrepancies exist between the results presented here and two other recent determinations of these absolute partial ionization cross sections. We attribute these differences to the loss of some translationally energetic fragment ions in these earlier studies. Our relative precursor-specific partial ionization cross sections enable us, for the first time, to quantify the contribution to the yield of each fragment ion from single, double, and triple ionization. Analysis shows that at 50 eV double ionization contributes 2% to the total ion yield, increasing to over 10% at an ionizing energy of 100 eV. From our ion-ion coincidence data, we have derived branching ratios for charge separating dissociations of the acetylene dication. Comparison of our data to recent ab initio/RRKM calculations suggest that close to the double ionization potential C2H2+2 dissociates predominantly on the ground triplet potential energy surface (3Sigma*g) with a much smaller contribution from dissociation via the lowest singlet potential energy surface (1Delta g). Measurements of the kinetic energy released in the fragmentation reactions of C2H2+2 have been used to obtain precursor state energies for the formation of product ion pairs, and are shown to be in good agreement with available experimental data and with theory.

  5. The SILCC project - IV. Impact of dissociating and ionizing radiation on the interstellar medium and Hα emission as a tracer of the star formation rate

    NASA Astrophysics Data System (ADS)

    Peters, Thomas; Naab, Thorsten; Walch, Stefanie; Glover, Simon C. O.; Girichidis, Philipp; Pellegrini, Eric; Klessen, Ralf S.; Wünsch, Richard; Gatto, Andrea; Baczynski, Christian

    2017-04-01

    We present three-dimensional radiation-hydrodynamical simulations of the impact of stellar winds, photoelectric heating, photodissociating and photoionizing radiation, and supernovae on the chemical composition and star formation in a stratified disc model. This is followed by a sink-based model for star clusters with populations of individual massive stars. Stellar winds and ionizing radiation regulate the star formation rate at a factor of ∼10 below the simulation with only supernova feedback due to their immediate impact on the ambient interstellar medium after star formation. Ionizing radiation (with winds and supernovae) significantly reduces the ambient densities for most supernova explosions to ρ < 10-25 g cm-3, compared to 10-23g cm-3 for the model with only winds and supernovae. Radiation from massive stars reduces the amount of molecular hydrogen and increases the neutral hydrogen mass and volume filling fraction. Only this model results in a molecular gas depletion time-scale of 2 Gyr and shows the best agreement with observations. In the radiative models, the Hα emission is dominated by radiative recombination as opposed to collisional excitation (the dominant emission in non-radiative models), which only contributes ∼1-10 per cent to the total Hα emission. Individual massive stars (M ≥ 30 M⊙) with short lifetimes are responsible for significant fluctuations in the Hα luminosities. The corresponding inferred star formation rates can underestimate the true instantaneous star formation rate by a factor of ∼10.

  6. The impact of single substitutions on multiple sequence alignments.

    PubMed

    Klaere, Steffen; Gesell, Tanja; von Haeseler, Arndt

    2008-12-27

    We introduce another view of sequence evolution. Contrary to other approaches, we model the substitution process in two steps. First we assume (arbitrary) scaled branch lengths on a given phylogenetic tree. Second we allocate a Poisson distributed number of substitutions on the branches. The probability to place a mutation on a branch is proportional to its relative branch length. More importantly, the action of a single mutation on an alignment column is described by a doubly stochastic matrix, the so-called one-step mutation matrix. This matrix leads to analytical formulae for the posterior probability distribution of the number of substitutions for an alignment column.

  7. Interfacing droplet microfluidics with matrix-assisted laser desorption/ionization mass spectrometry: label-free content analysis of single droplets.

    PubMed

    Küster, Simon K; Fagerer, Stephan R; Verboket, Pascal E; Eyer, Klaus; Jefimovs, Konstantins; Zenobi, Renato; Dittrich, Petra S

    2013-02-05

    Droplet-based microfluidic systems have become a very powerful tool to miniaturize chemical and biological reactions. However, droplet content analysis remains challenging and relies almost exclusively on optical methods such as fluorescence spectroscopy. Hence, labeling of the analyte is typically required which impedes a more universal applicability of microdroplets. Here we present a novel interface coupling droplet microfluidics and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for label-free content analysis of single droplets. Nanoliter aqueous droplets immersed in perfluorinated oil are created in a microfluidic T-junction, transferred into a capillary, and deposited on a high-density microarray MALDI plate mounted on a motorized xy-stage. The fully automated system is robust and reliable due to two unique features. First, a simple optical droplet detection system is used to synchronize stage movement and exit of droplets from the capillary. Second, the microarray plate contains an array of over 26,000 hydrophilic spots within a hydrophobic coating, each spot acting as a recipient to confine the droplets and to prevent cross-contamination. The MALDI matrix can also be applied using our system by spotting matrix droplets on the microarray in a separate run. To demonstrate the potential of our system, we studied the enzymatic cleavage of angiotensin I by angiotensin converting enzyme and monitored the increasing concentration of the product angiotensin II over time. The interface provides a robust and fully automated method for rapid label-free and information-rich content analysis of single droplets. With the high number of droplets per plate, this method is particularly suitable for high-throughput screening applications.

  8. Out-of-School Time Program Test Score Impact for Black Children of Single-Parents

    ERIC Educational Resources Information Center

    Nagle, Barry T.

    2013-01-01

    Out-of-School Time programs and their impact on standardized college entrance exam scores for black or African-American children of single parents who have applied for a competitive college scholarship program is the study focus. Study importance is supported by the large percentage of black children raised by single parents, the large percentage…

  9. Theoretical investigation of wave-vector-dependent analytical and numerical formulations of the interband impact-ionization transition rate for electrons in bulk silicon and GaAs

    NASA Technical Reports Server (NTRS)

    Kolnik, Jan; Wang, Yang; Oguzman, Ismail H.; Brennan, Kevin F.

    1994-01-01

    The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E. Scholl, and M. Rudan (1993), and a more exact, numerical method of Y. Wang and K. F. Brennan (1994). Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formular, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with the completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to the overlap intergrals of the Bloch state which

  10. Theoretical Investigation of Wave-Vector-Dependent Analytical and Numerical Formulations of the Interband Impact-Ionization Transition Rate for Electron in Bulk Silicon and GaAs

    NASA Technical Reports Server (NTRS)

    Kolnik, Jan; Wang, Yang; Oguzman, Ismail H.; Brennan, Kevin F.

    1994-01-01

    The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E Scholl, and M. Rudan, and a more exact, numerical method of Y. Wang and K. F. Brennan. Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formula, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with (he completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to (he overlap integrals of the Bloch state which can only be

  11. Ionization chamber

    DOEpatents

    Walenta, Albert H.

    1981-01-01

    An ionization chamber has separate drift and detection regions electrically isolated from each other by a fine wire grid. A relatively weak electric field can be maintained in the drift region when the grid and another electrode in the chamber are connected to a high voltage source. A much stronger electric field can be provided in the detection region by connecting wire electrodes therein to another high voltage source. The detection region can thus be operated in a proportional mode when a suitable gas is contained in the chamber. High resolution output pulse waveforms are provided across a resistor connected to the detection region anode, after ionizing radiation enters the drift region and ionize the gas.

  12. Single cell viability and impact of heating by laser absorption.

    PubMed

    Wetzel, Franziska; Rönicke, Susanne; Müller, Karla; Gyger, Markus; Rose, Daniel; Zink, Mareike; Käs, Josef

    2011-09-01

    Optical traps such as tweezers and stretchers are widely used to probe the mechanical properties of cells. Beyond their large range of applications, the use of infrared laser light in optical traps causes significant heating effects in the cell. This study investigated the effect of laser-induced heating on cell viability. Common viability assays are not very sensitive to damages caused in short periods of time or are not practicable for single cell analysis. We used cell spreading, a vital ability of cells, as a new sensitive viability marker. The optical stretcher, a two beam laser trap, was used to simulate heat shocks that cells typically experience during measurements in optical traps. The results show that about 60% of the cells survived heat shocks without vital damage at temperatures of up to 58 ± 2°C for 0.5 s. By varying the duration of the heat shocks, it was shown that 60% of the cells stayed viable when exposed to 48 ± 2°C for 5 s.

  13. Simulated Space Radiation: Impact of Four Different Types of High-Dose Ionizing Radiation on the Lichen Xanthoria elegans

    NASA Astrophysics Data System (ADS)

    Brandt, Annette; Meeßen, Joachim; Jänicke, Reiner U.; Raguse, Marina; Ott, Sieglinde

    2017-02-01

    This study addresses the viability of the lichen Xanthoria elegans after high-dose ionizing irradiation in the frame of the STARLIFE campaign. The first set of experiments was intended to resemble several types of galactic cosmic radiation (GCR) as present beyond the magnetic shield of Earth. In the second set of experiments, γ radiation up to 113 kGy was applied to test the limit of lichen resistance to ionizing radiation. Entire thalli of Xanthoria elegans were irradiated in the anhydrobiotic state. After STARLIFE 1, the metabolic activity of both symbionts was quantified by live/dead staining with confocal laser scanning microscopy. The photosynthetic activity was measured after the respective irradiation to assess the ability of the symbiotic green algae to restore photosynthesis after irradiation. The STARLIFE campaign complements the results of the LIFE experiments at the EXPOSE-E facility on the International Space Station by testing the model organism Xanthoria elegans on its resistance to hazardous radiation that might be accumulated during long-term space exposure. In addition, the photosynthetic activity of metabolically active lichen was investigated after X-ray irradiation up to 100 Gy (3.3 Gy/min). Since previous astrobiological experiments were mostly performed with anhydrobiotic lichen, these experiments will broaden our knowledge on the correlation of physiological state and astrobiological stressors.

  14. IONIZATION CHAMBER

    DOEpatents

    Redman, W.C.; Shonka, F.R.

    1958-02-18

    This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

  15. Study on numerical simulation of the dynamic impact effect for optical glass grinding with single grit

    NASA Astrophysics Data System (ADS)

    Chen, Jiang; Zhang, Feihu; Hang, Zhao; Yong, Zhang; Su, Jianbo

    It studies failure mechanism of optical glass with impact stress from grit, according to the dynamic impact effect in the process of optical glass grinding with single grit. With the distribution regularity of crack which from the grit dynamic impact, it established mathematical model of cylindrical stress wave which coaxial with wavefront. Analyzing and establishing the control equations for cylindrical stress wave, using finite-difference technique to simulate the dynamic impact effect for optical glass grinding with single grit and adopting Zwas numerical methods with source term hyperbolic curve partial differential equations to analysis and study the dissemination rule, diffusion rule and change rule, the simulation analysis shows that in the dissemination process of grit impact wave , wavefront occurred diffusion and there are tensile stress generated as well as oscillation.

  16. Secondary ion counting for surface-sensitive chemical analysis of organic compounds using time-of-flight secondary ion mass spectroscopy with cluster ion impact ionization

    SciTech Connect

    Hirata, K.; Saitoh, Y.; Chiba, A.; Yamada, K.; Takahashi, Y.; Narumi, K.

    2011-03-15

    We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C{sub 8} and C{sub 60} cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.

  17. Electron-Impact Ionization of Multicharged Ions: Cross-Sections Data from Oak Ridge National Laboratory (ORNL) and the Controlled Fusion Atomic Data Center (CFADC)

    DOE Data Explorer

    This website presents experimental ionization cross sections measured using the Electron-Ion Crossed Beams apparatus in the Multicharged Ion Research Facility (MIRF) at the Physics Division of Oak Ridge National Laboratory (ORNL). The data are given in both graphical and tabular form along with the reference to the original publication of the experimental results. Also presented in the figures are theoretical cross sections supporting the experiments. For details of the theoretical work, refer to the original publication given for the particular experiment. These pages are based primarily on three technical memorandums issued by ORNL: 1(D. H. Crandall, R. A. Phaneuf, and D. C. Gregory, Electron Impact Ionization of Multicharged Ions, ORNL/TM-7020, Oak Ridge National Laboratory, 1979; 2) D. C. Gregory, D. H. Crandall, R. A. Phaneuf, A. M. Howald, G. H. Dunn, R. A. Also presented are more recent (1993-present) data, both published and unpublished. The data pages feature dynamic plotting, allowing the user to choose which sets of data to plot and zoom in on regions of interest within the plot. [Taken from http://www-cfadc.phy.ornl.gov/xbeam/index.html

  18. Electron-impact ionization of H2O at low projectile energy: Internormalized triple-differential cross sections in three-dimensional kinematics

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Amami, Sadek; Hossen, Khokon; Ali, Esam; Ning, ChuanGang; Colgan, James; Madison, Don; Dorn, Alexander

    2017-02-01

    We report a combined experimental and theoretical study of the electron-impact ionization of water (H2O ) at the relatively low incident energy of E0=81 eV in which either the 1 b1 or 3 a1 orbitals are ionized leading to the stable H2O+ cation. The experimental data were measured by using a reaction microscope, which can cover nearly the entire 4 π solid angle for the secondary electron emission over a range of ejection energies. We present experimental data for the scattering angles of 6∘ and 10∘ for the faster of the two outgoing electrons as a function of the detection angle of the secondary electron with energies of 5 and 10 eV. The experimental triple-differential cross sections are internormalized across the measured scattering angles and ejected energies. The experimental data are compared with predictions from two molecular three-body distorted-wave approaches: one applying the orientation-averaged molecular orbital (OAMO) approximation and one using a proper average (PA) over orientation-dependent cross sections. The PA calculations are in better agreement with the experimental data than the OAMO calculations for both the angular dependence and the relative magnitude of the observed cross-section structures.

  19. Effusive molecular beam-sampled Knudsen flow reactor coupled to vacuum ultraviolet single photon ionization mass spectrometry using an external free radical source

    SciTech Connect

    Leplat, N.; Rossi, M. J.

    2013-11-15

    A new apparatus using vacuum ultraviolet single photon ionization mass spectrometry (VUV SPIMS) of an effusive molecular beam emanating from a Knudsen flow reactor is described. It was designed to study free radical-molecule kinetics over a significant temperature range (300–630 K). Its salient features are: (1) external free radical source, (2) counterpropagating molecular beam and diffuse VUV photon beam meeting in a crossed-beam ion source of a quadrupole mass spectrometer with perpendicular ion extraction, (3) analog detection of the photocurrent of the free radical molecular cation, and (4) possibility of detecting both free radicals and closed shell species in the same apparatus and under identical reaction conditions owing to the presence of photoelectrons generated by the photoelectric effect of the used VUV-photons. The measured thermal molecular beam-to-background ratio was 6.35 ± 0.39 for Ar and 10.86 ± 1.59 for i-C{sub 4}H{sub 10} at 300 K, a factor of 2.52 and 1.50 smaller, respectively, than predicted from basic gas-dynamic considerations. Operating parameters as well as the performance of key elements of the instrument are presented and discussed. Coupled to an external free radical source a steady-state specific exit flow of 1.6 × 10{sup 11} and 5.0 × 10{sup 11} molecule s{sup −1} cm{sup −3} of C{sub 2}H{sub 5}{sup •} (ethyl) and t-C{sub 4}H{sub 9}{sup •} (t-butyl) free radicals have been detected using VUV SPIMS at their molecular ion m/z 29 and 57, respectively, at 300 K.

  20. Online monitoring of trace chlorinated benzenes in flue gas of municipal solid waste incinerator by windowless VUV lamp single photon ionization TOFMS coupled with automatic enrichment system.

    PubMed

    Liu, Wei; Jiang, Jichun; Hou, Keyong; Wang, Weiguo; Qi, Yachen; Wang, Yan; Xie, Yuanyuan; Hua, Lei; Li, Haiyang

    2016-12-01

    Chlorinated benzenes are typical precursors and indicators for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from waste incinerators. Online and real-time monitoring of chlorobenzenes is a challenge due to their low concentration and complex nature of the flue gas. In this work, a continuous online monitoring system was built for detection of trace chlorinated benzenes based on a time-of-flight mass spectrometer (TOFMS). A single photon ionization (SPI) source based on a radiofrequency-excited windowless vacuum ultraviolet (VUV) lamp was developed for the first time to eliminate the signal attenuation resulting from the contamination of magnesium fluoride windows and to avoid the fragment ions. An automatic enrichment system including three parallel Tenax TA adsorption tubes was designed and coupled to the TOFMS to achieve the required ultrahigh sensitivity. The limits of quantitation at 7.65, 5.37 and 6.77pptv were obtained for monochlorobenzene (MCBz), dichlorobenzene (DCBz) and trichlorobenzene (TrCBz), respectively, within a 29-min analytical period. Moreover, this apparatus was applied to continuously online monitor the actual flue gas from a waste incinerator for three months. During this period, the concentrations of MCBz, DCBz and TrCBz detected in the flue gas were in the range of 100-1200, 50-800 and 50-300pptv, respectively. The relative standard deviation (RSD) of the sensitivity for the windowless VUV lamp ion source was 9.71% evaluated by the internal standard benzene over the 3-months flue gas monitoring. These results demonstrated the capability of this method in long-term analysis of the trace chlorinated benzenes in the flue gas.

  1. Thermophysics Characterization of Multiply Ionized Air Plasma Absorption of Laser Radiation

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Rhodes, Robert; Turner, Jim (Technical Monitor)

    2002-01-01

    The impact of multiple ionization of air plasma on the inverse Bremsstrahlung absorption of laser radiation is investigated for air breathing laser propulsion. Thermochemical properties of multiply ionized air plasma species are computed for temperatures up to 200,000 deg K, using hydrogenic approximation of the electronic partition function; And those for neutral air molecules are also updated for temperatures up to 50,000 deg K, using available literature data. Three formulas for absorption are calculated and a general formula is recommended for multiple ionization absorption calculation. The plasma composition required for absorption calculation is obtained by increasing the degree of ionization sequentially, up to quadruple ionization, with a series of thermal equilibrium computations. The calculated second ionization absorption coefficient agrees reasonably well with that of available data. The importance of multiple ionization modeling is demonstrated with the finding that area under the quadruple ionization curve of absorption is found to be twice that of single ionization. The effort of this work is beneficial to the computational plasma aerodynamics modeling of laser lightcraft performance.

  2. Multiple Scattering Effects in Ionization Processes

    NASA Astrophysics Data System (ADS)

    Barrachina, R. O.

    2011-10-01

    The momentum distributions of electrons emitted in the ionization of atoms and molecules by the impact of photons or massive particles usually present interference patterns similar to those of the demonstrations with light proposed by Thomas Young more than two centuries ago. Furthermore, these cross sections also display richer structures due to the same multiple-scattering effects that are at the origin of different techniques to probe atomic aggregates and solid samples. In this talk, I will review these effects and discuss some of their most important characteristics, showing that they lead to distortions that are not fully replicated by non-scattering or even single-scattering approximations.

  3. Development of a large area InGaAs APD receiver based on an impact ionization engineered detector for free-space lasercomm applications

    NASA Astrophysics Data System (ADS)

    Burris, H. R.; Ferraro, M. S.; Freeman, W. T.; Moore, C. I.; Murphy, J. L.; Rabinovich, W. S.; Smith, W. R.; Summers, L. L.; Thomas, L. M.; Vilcheck, M. J.; Clark, W. R.; Waters, W. D.

    2012-06-01

    The U.S. Naval Research Laboratory (NRL) is developing a small size, weight and power (SWaP) free space lasercomm terminal for small unmanned airborne platforms. The terminal is based on a small gimbal developed by CloudCap Technology. A receiver with a large field of view and with sensitivity sufficient to meet the program range goals is required for this terminal. An InGaAs Avalanche Photodiode (APD) with internal structures engineered to reduce excess noise and keff in high gain applications was selected as the detector. The detector is a 350 micron diameter impact ionization engineered (I2E) APD developed by Optogration, Inc. Results of development and characterization of the receiver will be presented.

  4. Single-event upset and snapback in silicon-on-insulator devices

    SciTech Connect

    DODD,PAUL E.; SHANEYFELT,MARTY R.; SCHWANK,JAMES R.; HASH,GERALD L.; DRAPER,BRUCE L.; WINOKUR,PETER S.

    2000-02-23

    SEU is studied in SOI transistors and circuits with various body tie structures. The importance of impact ionization effects, including single-event snapback, is explored. Implications for hardness assurance testing of SOI integrated circuits are discussed.

  5. Nearly equidistant single swift heavy ion impact sites through nanoporous alumina masks

    SciTech Connect

    Cauchy, Xavier; Roorda, Sjoerd

    2013-04-19

    A semi-ordered pattern of 70 MeV Ag single ion impact sites on a fused silica sample was achieved by irradiation through a free-standing 10 {mu}m through-pore ordered nanoporous alumina membrane. The membranes were fabricated by constant voltage anodization in oxalic acid with a two-step replication process. An apparatus and a method were developed to realize the alignment of the pores parallel to the ion beam. Measurements of the surface, by atomic force microscopy, confirm the presence of a semi-ordered pattern of single ion impact sites.

  6. Impact of a single drop on the same liquid: formation, growth and disintegration of jets

    NASA Astrophysics Data System (ADS)

    Agbaglah, G. Gilou; Deegan, Robert

    2015-11-01

    One of the simplest splashing scenarios results from the impact of a single drop on on the same liquid. The traditional understanding of this process is that the impact generates a jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are bifurcations in the multiplicity of jets. First, we study the formation, growth and disintegration of jets following the impact of a drop on a thin film of the same liquid using a combination of numerical simulations and linear stability theory. We obtain scaling relations from our simulations and use these as inputs to our stability analysis. We also use experiments and numerical simulations of a single drop impacting on a deep pool to examine the bifurcation from a single jet into two jets. Using high speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet.

  7. Geochemical implications of the formation of the moon by a single giant impact

    NASA Astrophysics Data System (ADS)

    Newsom, H. E.; Taylor, S. R.

    1989-03-01

    The origin of the moon by a single massive impact of a body slightly larger than Mars with the earth can explain the angular momentum, orbital characteristics and unique nature of the earth-moon system. The density and chemical differences between the earth and the moon are accounted for by deriving the moon from the mantle of the impactor. A cosmochemically plausible impactor can be formed in the region of the inner Solar System, lending support to the impact hypothesis.

  8. Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume

    SciTech Connect

    Verkhoturov, Stanislav V.; Geng, Sheng; Schweikert, Emile A.; Czerwinski, Bartlomiej; Young, Amanda E.; Delcorte, Arnaud

    2015-10-28

    We present the first data from individual C{sub 60} impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C{sub n}{sup −} clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of C{sub n}{sup −} with those of C{sub n}{sup 0} from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C{sub n}{sup −} emission can also explain the emission of electrons. The interaction of C{sub 60} with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.

  9. Electron-impact ionization of air molecules and its application to the abatement of volatile organic compounds

    SciTech Connect

    Penetrante, B.M.; Hsiao, M.C.; Bardsley, J.N.; Merritt, B.T.; Vogtlin, G.E.; Wallman, P.H.; Kuthi, A.; Burkhart, C.P.; Bayless, J.R.

    1995-05-21

    In this paper the authors present data on the non-thermal plasma processing of two representative VOCs: carbon tetrachloride and methanol. The investigation used a compact electron beam reactor, and two types of discharge reactors: a pulsed corona and a dielectric-barrier discharge. To the knowledge of the authors, this is the first comparison of the energy efficiency of electron beam, pulsed corona and dielectric-barrier discharge processing of these VOCs under identical gas conditions. For most electrical discharge reactors the analysis suggests that the attainable electron mean energy is rather limited and cannot be significantly enhanced by changing the electrode configuration or voltage waveform. The experimental data confirms that there is no significant difference in the performance of the pulsed corona and dielectric-barrier discharge reactors. The authors observe that electron beam processing is remarkably more energy efficiency than electrical discharge processing in decomposing either of these VOC molecules. During electron beam processing, the specific energy consumption is consistent with the energy required for the ionization of the background air molecules. For carbon tetrachloride, the dominant decomposition pathway is dissociative electron attachment. For methanol, the dominant decomposition pathway is dissociative charge exchange.

  10. Impact of Ionization DEPLETIONS/TEC Bite-Outs of Equatorial Plasma Structures on Transionospheric Satellite Signals Using Global Positioning System (GPS)

    NASA Astrophysics Data System (ADS)

    Das, Tanmay

    2016-07-01

    This paper represents the impact of ionization depletions/TEC bite-outs of equatorial plasma structures on transionospheric satellite signals received from Calcutta (latitude: 22.58oN, longitude: 88.38oE geographic; 32oN magnetic dip) is situated near the northern crest of the equatorial ionization anomaly (EIA) in the Indian longitude sector, using Global Positioning System (GPS) during the equinoctial months of February-April 2011, August-October, 2011 and February-April 2012. It is observed that when a bubble moves across a satellite link, scintillations and ionization are usually encountered. The apparent duration of the bite-outs may be different from the true east-west duration, as observed with geostationary links, because of the presence of a relative velocity between the irregularity cloud and the satellite. The trajectory of a GPS satellite plays a vital role in observing the bubble characteristics. The distributions of amplitude and the parameters characterizing the ionization depletions, namely, the duration, depth and the leading and trailing edge slopes of the bubbles have been obtained during the same equinoctial months of 2011 and 2012. It is evident that the range error, extent of the bubble and ionization gradients measured in these equinoctial months of the equatorial region provides the worst case figures for system designers. The high range error (~ 3-4 m) is observed during these equinoctial months. The statistical distribution of the TEC depletions showed some significant results. Out of 29 bite-outs in February-April, 2011 equinox, the maximum amplitude was found to be about 23.25 TECU with a median depletion of about 5.92 TECU. The maximum amplitude corresponds to a range error of about 3.7 m at GPS L1 frequency. The majority of the bubbles were found to have observed duration between 10-20 minutes with a maximum of 28.14 minutes. The median value of actual duration 2.37 minutes translates to nearly 150sec of possible satellite signal

  11. Online profiling of triacylglycerols in plant oils by two-dimensional liquid chromatography using a single column coupled with atmospheric pressure chemical ionization mass spectrometry.

    PubMed

    Wei, Fang; Ji, Shu-Xian; Hu, Na; Lv, Xin; Dong, Xu-Yan; Feng, Yu-Qi; Chen, Hong

    2013-10-18

    The complexity of natural triacylglycerols (TAGs) in various edible oils is high because of the hundreds of TAG compositions, which makes the profiling of TAGs quite difficult. In this investigation, a rapid and high-throughput method for online profiling of TAGs in plant oils by two-dimensional (2D) liquid chromatography using a single column coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry was reported. A novel mixed-mode 2D chromatographic column packed with silver-ion-modified octyl and sulfonic co-bonded silica was employed in this online 2D separation system. This novel 2D column combined the features of C8 column and silver-ion. In comparison with the traditional C18 column and silver-ion column, which are the two main columns used for the separation of complex TAGs in natural oil samples, this novel 2D column, could provide hydrophobic interactions as well as π-complexation interactions. It exhibited much higher selectivity for the separation of TAGs, and the separation was rapid. This online 2D separation system was successful in the separation of a large number of TAG solutes, and the TAG structures were evaluated by analyzing their APCI mass spectra information. This system was applied for the profiling of TAGs in peanut oils, corn oils, and soybean oils. 30 TAGs in peanut oils, 18 TAGs in corn oils, and 21 TAGs in soybean oils were determined and quantified. The highest relative content of TAGs was LLL, which was found in corn oil with the relative content up to 45.43 (%, w/w), and the lowest relative content of TAGs was LLS and OSS, which was found in soybean oil and corn oil respectively, with the relative content only 0.01 (%, w/w). In addition, the TAG data were analyzed by principal component analysis (PCA). Results of PCA enabled a clear identification of different plant oils. This method provided an efficient and convenient chromatographic technology for the fast characterization and quantification of complex TAGs

  12. 75 FR 65558 - Final Supplemental Environmental Impact Statement, Single Nuclear Unit at the Bellefonte Plant...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-25

    ... Final Supplemental Environmental Impact Statement, Single Nuclear Unit at the Bellefonte Plant Site... Nuclear Unit at the Bellefonte Plant Site (final SEIS) on September 9, 2010. The location of the proposed nuclear plant site was stated incorrectly in the heading of the ROD. TVA prepared the final SEIS to...

  13. Retrospective Biological Dosimetry at Low and High Doses of Radiation and Radioiodine Impact on Individual Susceptibility to Ionizing Radiation

    PubMed Central

    Cebulska-Wasilewska, Antonina; Krzysiek, Mateusz; Krajewska, Grażyna; Stępień, Artur; Krajewski, Paweł

    2017-01-01

    Iodine-131 (I-131) is often used in thyroid diagnostics and therapy. External and internal exposure to radioiodine can lead to molecular and cellular damage in peripheral blood lymphocytes. The aim of this study was to explore the influence of low and high doses of I-131 on susceptibility to ionizing radiation. Study groups consisted of 30 individuals free of thyroid diseases, 41 patients exposed diagnostically to low doses of I-131, and 37 hyperthyroidism patients exposed therapeutically to high doses. The standardized DNA repair competence assay was used to test the efficacy of the fast DNA repair process in G0 cells. Cytogenetic preparations were made in fresh blood samples before and after challenging cells in vitro with X-ray dose. The frequency of sister chromatid exchanges (SCE) and percentage of cells with significantly elevated numbers of SCE were used as cytogenetic biomarkers associated to homologous recombination and compared to reported earlier cytogenetic biomarkers of cancer risk. Strong individual variation in the biomarkers is observed in all investigated groups before and after challenging. Nevertheless, the efficiency of post challenging fast repair is significantly high in the patients exposed to diagnostic I-131 doses than in unexposed control group and linked to decreased cytogenetic damage. However, 5 weeks after administration of therapeutic doses, significant increases of unrepaired post challenging DNA and cytogenetic damages were observed indicating a health risk. Results also suggest that the appearance of cancers in immediate families might influence DNA repair differently in patients exposed to low than to high doses. PMID:28250909

  14. Measurements of absolute total and partial cross sections for the electron ionization of tungsten hexafluoride (WF6)

    NASA Astrophysics Data System (ADS)

    Basner, R.; Schmidt, M.; Becker, K.

    2004-04-01

    We measured absolute partial cross sections for the formation of positive ions followed by electron impact on tungsten hexafluoride (WF6) from threshold to 900 eV using a time-of-flight mass spectrometer (TOF-MS). Dissociative ionization processes resulting in seven different singly charged ions (F+, W+, WFx+, x=1-5) and five doubly charged ions (W2+, WFx2+, x=1-4) were found to be the dominant ionization channels. The ion spectrum at all impact energies is dominated by WF5+ fragment ions. At 120 eV impact energy, the partial WF5+ ionization cross section has a maximum value of 3.92×10-16 cm2 that corresponds to 43% of the total ion yield. The cross section values of all the other singly charged fragment ions at 120 eV range between 0.39×10-16 and 0.73×10-16 cm2. The ionization cross sections of the doubly charged ions are more than one order of magnitude lower than the cross section of WF5+. Double ionization processes account for 21% of the total ion yield at 120 eV. The absolute total ionization cross section of WF6 was obtained as the sum of all measured partial ionization cross sections and is compared with available calculated cross sections.

  15. A 0.18 micrometer CMOS Thermopile Readout ASIC Immune to 50 MRAD Total Ionizing Dose (SI) and Single Event Latchup to 174MeV-cm(exp 2)/mg

    NASA Technical Reports Server (NTRS)

    Quilligan, Gerard T.; Aslam, Shahid; Lakew, Brook; DuMonthier, Jeffery J.; Katz, Richard B.; Kleyner, Igor

    2014-01-01

    Radiation hardened by design (RHBD) techniques allow commercial CMOS circuits to operate in high total ionizing dose and particle fluence environments. Our radiation hard multi-channel digitizer (MCD) ASIC (Figure 1) is a versatile analog system on a chip (SoC) fabricated in 180nm CMOS. It provides 18 chopper stabilized amplifier channels, a 16- bit sigma-delta analog-digital converter (SDADC) and an on-chip controller. The MCD was evaluated at Goddard Space Flight Center and Texas A&M University's radiation effects facilities and found to be immune to single event latchup (SEL) and total ionizing dose (TID) at 174 MeV-cm(exp 2)/mg and 50 Mrad (Si) respectively.

  16. THE FATE OF TRACE METALS IN A ROTARY KILN INCINERATOR WITH A SINGLE-STAGE IONIZING WET SCRUBBER - VOLUME II: APPENDICES

    EPA Science Inventory

    A series of pilot-scale incineration tests was performed at EPA's Incineration Research Facility (IRF) in Jefferson, Arkansas, to evaluate the fate of trace metals fed to a rotary kiln incinerator equipped with an ionizing wet scrubber (IWS) for particulate and acid gas control. ...

  17. FATE OF TRACE METALS IN A ROTARY KILN INCINERATOR WITH A SINGLE-STAGE IONIZING WET SCRUBBER. VOLUME 1. TECHNICAL RESULTS.

    EPA Science Inventory

    A series of pilot-scale incineration tests was performed at EPA's Incineration Research Facility (IRF) in Jefferson, Arkansas, to evaluate the fate of trace metals fed to a rotary kiln incinerator equipped with an ionizing wet scrubber (IWS) for particulate and acid gas control. ...

  18. Impact of Anthropogenic Noise on Aquatic Animals: From Single Species to Community-Level Effects.

    PubMed

    Sabet, Saeed Shafiei; Neo, Yik Yaw; Slabbekoorn, Hans

    2016-01-01

    Anthropogenic noise underwater is on the rise and may affect aquatic animals of marine and freshwater ecosystems. Many recent studies concern some sort of impact assessment of a single species. Few studies addressed the noise impact on species interactions underwater, whereas there are some studies that address community-level impact but only on land in air. Key processes such as predator-prey or competitor interactions may be affected by the masking of auditory cues, noise-related disturbance, or attentional interference. Noise-associated changes in these interactions can cause shifts in species abundance and modify communities, leading to fundamental ecosystem changes. To gain further insight into the mechanism and generality of earlier findings, we investigated the impact on both a predator and a prey species in captivity, zebrafish (Danio rerio) preying on waterfleas (Daphnia magna).

  19. Polarization phenomena in multiphoton ionization of atoms.

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The theory of multiphoton ionization for an atomic system of arbitrary complexity is developed using a density matrix formalism. An expression is obtained which determines the differential N-photon ionization cross section as a function of the polarization states of the target atom and the incident radiation. The parameters which characterize the photo-electron angular distribution are related to the general reduced matrix elements for the N-photon transition. Two-photon ionization of unpolarized atoms is treated as an illustration of the use of the theory. The dependence of the multiphoton ionization cross section on the polarization state of the incident radiation, which has been observed in two- and three-photon ionization of Cs, is accounted for by the theory. Finally, the photoelectron spin polarization produced by the multiphoton ionization of unpolarized atoms, like the analogous polarization resulting from single-photon ionization, is found to depend on the circular polarization of the incident radiation.

  20. Polarization phenomena in multiphoton ionization of atoms

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The theory of multiphoton ionization for an atomic system of arbitrary complexity is developed using a density matrix formalism. An expression is obtained which determines the differential N-photon ionization cross section as a function of the polarization states of the target atom and the incident radiation. The parameters which characterize the photoelectron angular distribution are related to the general reduced matrix elements for the N-photon transition. Two-photon ionization of unpolarized atoms is treated as an illustration of the use of the theory. The dependence of the multiphoton ionization cross section on the polarization state of the incident radiation, which has been observed in two- and three-photon ionization of Cs, is accounted for by the theory. Finally, the photoelectron spin polarization produced by the multiphoton ionization of unpolarized atoms, like the analogous polarization resulting from single-photon ionization, is found to depend on the circular polarization of the incident radiation.

  1. Defect mediated desorption of the KBr(001) surface induced by single highly charged ion impact.

    PubMed

    Heller, R; Facsko, S; Wilhelm, R A; Möller, W

    2008-08-29

    The individual impacts of slow (300 eV/amu) highly charged Xe ions induce nanometer sized pitlike structures on the KBr (001) surface. The volume of these structures shows a strong dependence on the ions potential energy. Total potential sputter yields from atomically flat (001) terraces are determined by imaging single ion impact sites. The dependence of the sputter yield on the ions initial charge state combined with structure formation at low and high-fluence irradiations indicates that agglomeration of defects into complex centers plays a major role in the desorption process induced by the potential energy.

  2. Single wheel hub motor failures and their impact on vehicle and driver behaviour

    NASA Astrophysics Data System (ADS)

    Wanner, Daniel; Kreußlein, Maria; Augusto, Bruno; Drugge, Lars; Stensson Trigell, Annika

    2016-10-01

    This research work studies the impact of single wheel hub motor failures on the dynamic behaviour of electric vehicles and the corresponding driver reactions. An experimental study in a moving-base driving simulator is conducted to analyse the influence of single wheel hub motor failures for motorway speeds. Driver reaction times are derived from the measured data and discussed in their experimental context. The failure is rated objectively on the dynamic behaviour of the vehicle and compared to the subjective evaluation. Findings indicate that critical traffic situations impairing traffic safety can occur for motorway speeds. Clear counteractions by the drivers had to be taken.

  3. X-ray emission following K-L double ionization by electron impact and K capture: Vacancy-production probabilities and structure of the Kα satellite spectra

    NASA Astrophysics Data System (ADS)

    Li-Scholz, Angela; Leiberich, A.; Scholz, W.

    1982-12-01

    Kα x-ray satellites following K-electron capture in 55Fe and electron impact on Mn have been measured with a high-resolution spectrometer. Ratios of double- to single-vacancy-production probability are found to be PKL=(2.5+/-0.5)×10-3 and (9.5+/-0.9)×10-3 for capture and impact, respectively. An evaluation of vacancy rearrangement in the L shell before satellite emission has been carried out with the use of published level widths. It is found that in electron impact, as distinct from K capture, essentially only satellites associated with a 2p spectator vacancy are observed. This observation is at variance with certain commonly used satellite assignments. Energies and intensities of the satellite transitions have been calculated in intermediate coupling and coordinations are proposed for the stronger lines.

  4. The influence of molecular pre-orientation on the resonance-enhanced multi-photon ionization dynamics

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Miao; Li, Jing-Lun; Yu, Jie; Cong, Shu-Lin

    2017-03-01

    We investigate theoretically the influence of molecular pre-orientation on the resonance-enhanced multi-photon ionization (REMPI) dynamics, taking the LiH molecule for example. The LiH molecule is first pre-oriented by a single-cycle pulse (SCP) in terahertz (THz) region, and then excited by the femtosecond pump pulse, and finally ionized by the femtosecond probe pulse. We focus on the impact of the pre-orientation on the ionization probability, energy- and angle-resolved photoelectron spectra and photoelectron angular distribution (PAD). It is found that the ionization probability and peak intensity of energy-resolved photoelectron spectra are significantly affected by molecular orientation. The angle-resolved photoelectron spectra are related to the molecular orientation. The PAD can be changed by varying the delay time between the THz SCP and pump pulse. We also investigate the effect of temperature on excitation and ionization dynamics.

  5. Fundamental mechanisms of laser damage of dielectric crystals by ultrashort pulse: ionization dynamics for the Keldysh model

    NASA Astrophysics Data System (ADS)

    Gruzdev, Vitaly

    2014-12-01

    Laser-induced ionization is a major process that initiates and drives the initial stages of laser-induced damage (LID) of high-quality transparent solids. The ionization and its contribution to LID are characterized in terms of the time-dependent ionization rate and conduction-band electron density. Considering femtosecond pulses of various durations (from 35 to 706 fs) and variable peak irradiances (from 0.01 to 60 TW/cm2), we use a single-rate equation to simulate time variations of conduction-band electron density and rates of the photoionization and impact ionization. The photoionization rate is evaluated with the Keldysh equation. At low irradiance, the electron density and total ionization rate demonstrate power scaling characteristic of multiphoton ionization. With the increase of irradiance, there is observed a saturation of the photoionization rate due to photoionization suppression by the Keldysh-type singularity during the increase in the number of simultaneously absorbed photons by 1. A striking result is that the saturation is followed by a stepwise transition from the ionization regime which is completely dominated by the photoionization to a regime totally dominated by the impact ionization. The transition results in the increase of the electron density by a few orders of magnitude induced by a variation of peak laser irradiance by about 15% to 20%. The physical effects that are involved are discussed.

  6. Vanadium fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser–solid experiments

    SciTech Connect

    Palmeri, P.; Quinet, P.; Batani, D.

    2015-09-15

    The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser–solid experiments through the K-shell emission cross section. In addition, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al. (2012)), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the vanadium isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent vanadium ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 20 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic behavior of the modified relativistic binary encounter Bethe model (MRBEB) of Guerra et al. (2012) with the density-effect correction proposed by Davies et al. (2013)

  7. An (e, 2e + ion) study of low-energy electron-impact ionization and fragmentation of tetrahydrofuran with high mass and energy resolutions

    SciTech Connect

    Ren, Xueguang Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yoon; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

    2014-10-07

    We study the low-energy (E{sub 0} = 26 eV) electron-impact induced ionization and fragmentation of tetrahydrofuran using a reaction microscope. All three final-state charged particles, i.e., two outgoing electrons and one fragment ion, are detected in triple coincidence such that the momentum vectors and, consequently, the kinetic energies for charged reaction products are determined. The ionic fragments are clearly identified in the experiment with a mass resolution of 1 amu. The fragmentation pathways of tetrahydrofuran are investigated by measuring the ion kinetic energy spectra and the binding energy spectra where an energy resolution of 1.5 eV has been achieved using the recently developed photoemission electron source. Here, we will discuss the fragmentation reactions for the cations C{sub 4}H{sub 8}O{sup +}, C{sub 4}H{sub 7}O{sup +}, C{sub 2}H{sub 3}O{sup +}, C{sub 3}H{sub 6}{sup +}, C{sub 3}H{sub 5}{sup +}, C{sub 3}H{sub 3}{sup +}, CH{sub 3}O{sup +}, CHO{sup +}, and C{sub 2}H{sub 3}{sup +}.

  8. Copper fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser-solid experiments

    SciTech Connect

    Palmeri, P.; Quinet, P.; Batani, D.

    2015-03-15

    The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser-solid experiments through the K-shell emission cross section. In addition, copper is a material that has been often used in those experiments because it has a maximum total K-shell emission yield. Furthermore, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al., 2012), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the copper isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent copper ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 10 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic form proposed by Davies et al. (2013)

  9. Impact of copper and silver ionization on fungal colonization of the water supply in health care centers: implications for immunocompromised patients.

    PubMed

    Pedro-Botet, Maria Luisa; Sanchez, Inma; Sabria, Miquel; Sopena, Nieves; Mateu, Lourdes; García-Núñez, Marian; Rey-Joly, Celestino

    2007-07-01

    Copper and silver ionization is a well-recognized disinfection method to control Legionella species in water distribution systems in hospitals. These systems may also serve as a potential indoor reservoir for fungi. The prevalence of fungi was significantly lower in ionized than in nonionized water samples from health care facilities. The clinical consequences of this finding require further investigation.

  10. Evaluation of Single-Impact-Induced Cartilage Degeneration by Optical Coherence Tomography

    PubMed Central

    de Bont, Florence; Brill, Nicolai; Schmitt, Robert; Tingart, Markus; Rath, Björn; Pufe, Thomas; Jahr, Holger; Nebelung, Sven

    2015-01-01

    Posttraumatic osteoarthritis constitutes a major cause of disability in our increasingly elderly population. Unfortunately, current imaging modalities are too insensitive to detect early degenerative changes of this disease. Optical coherence tomography (OCT) is a promising nondestructive imaging technique that allows surface and subsurface imaging of cartilage, at near-histological resolution, and is principally applicable in vivo during arthroscopy. Thirty-four macroscopically normal human cartilage-bone samples obtained from total joint replacements were subjected to standardized single impacts in vitro (range: 0.25 J to 0.98 J). 3D OCT measurements of impact area and adjacent tissue were performed prior to impaction, directly after impaction, and 1, 4, and 8 days later. OCT images were assessed qualitatively (DJD classification) and quantitatively using established parameters (OII, Optical Irregularity Index; OHI, Optical Homogeneity Index; OAI, Optical Attenuation Index) and compared to corresponding histological sections. While OAI and OHI scores were not significantly changed in response to low- or moderate-impact energies, high-impact energies significantly increased mean DJD grades (histology and OCT) and OII scores. In conclusion, OCT-based parameterization and quantification are able to reliably detect loss of cartilage surface integrity after high-energy traumatic insults and hold potential to be used for clinical screening of early osteoarthritis. PMID:26229959

  11. Environmental Impacts from Photovoltaic Solar Cells Made with Single Walled Carbon Nanotubes.

    PubMed

    Celik, Ilke; Mason, Brooke E; Phillips, Adam B; Heben, Michael J; Apul, Defne

    2017-03-30

    An ex-ante life cycle inventory was developed for single walled carbon nanotube (SWCNT) PV cells, including a laboratory-made 1% efficient device and an aspirational 28% efficient four-cell tandem device. The environmental impact of unit energy generation from the mono-Si PV technology was used as a reference point. Compared to monocrystalline Si (mono-Si), the environmental impacts from 1% SWCNT was ∼18 times higher due mainly to the short lifetime of three years. However, even with the same short lifetime, the 28% cell had lower environmental impacts than mono-Si. The effects of lifetime and efficiency on the environmental impacts were further examined. This analysis showed that if the SWCNT device efficiency had the same value as the best efficiency of the material under comparison, to match the total normalized impacts of the mono- and poly-Si, CIGS, CdTe, and a-Si devices, the SWCNT devices would need a lifetime of 2.8, 3.5, 5.3, 5.1, and 10.8 years, respectively. It was also found that if the SWCNT PV has an efficiency of 4.5% or higher, its energy payback time would be lower than other existing and emerging PV technologies. The major impacts of SWCNT PV came from the cell's materials synthesis.

  12. WWC Review of the Report "Incentives, Selection, and Teacher Performance: Evidence from IMPACT." What Works Clearinghouse Single Study Review

    ERIC Educational Resources Information Center

    What Works Clearinghouse, 2014

    2014-01-01

    The 2013 study, "Incentives, Selection, and Teacher Performance: Evidence from IMPACT" examined the effects of "IMPACT," a teacher evaluation system used in the District of Columbia Public Schools, on teacher retention and performance. "IMPACT" assigns each teacher a single performance score based on classroom…

  13. Single photon simultaneous K-shell ionization and K-shell excitation. I. Theoretical model applied to the interpretation of experimental results on H{sub 2}O

    SciTech Connect

    Carniato, S. Selles, P.; Andric, L.; Palaudoux, J.; Penent, F.; Lablanquie, P.; Žitnik, M.; Bučar, K.; Nakano, M.; Hikosaka, Y.; Ito, K.

    2015-01-07

    We present in detail a theoretical model that provides absolute cross sections for simultaneous core-ionization core-excitation (K{sup −2}V ) and compare its predictions with experimental results obtained on the water molecule after photoionization by synchrotron radiation. Two resonances of different symmetries are assigned in the main K{sup −2}V peak and comparable contributions from monopolar (direct shake-up) and dipolar (conjugate shake-up) core-valence excitations are identified. The main peak is observed with a much greater width than the total experimental resolution. This broadening is the signature of nuclear dynamics.

  14. Structure and hydration of the C4H4●+ ion formed by electron impact ionization of acetylene clusters.

    PubMed

    Momoh, Paul O; Hamid, Ahmed M; Abrash, Samuel A; El-Shall, M Samy

    2011-05-28

    Here we report ion mobility experiments and theoretical studies aimed at elucidating the identity of the acetylene dimer cation and its hydrated structures. The mobility measurement indicates the presence of more than one isomer for the C(4)H(4)(●+) ion in the cluster beam. The measured average collision cross section of the C(4)H(4)(●+) isomers in helium (38.9 ± 1 Å(2)) is consistent with the calculated cross sections of the four most stable covalent structures calculated for the C(4)H(4)(●+) ion [methylenecyclopropene (39.9 Å(2)), 1,2,3-butatriene (41.1 Å(2)), cyclobutadiene (38.6 Å(2)), and vinyl acetylene (41.1 Å(2))]. However, none of the single isomers is able to reproduce the experimental arrival time distribution of the C(4)H(4)(●+) ion. Combinations of cyclobutadiene and vinyl acetylene isomers show excellent agreement with the experimental mobility profile and the measured collision cross section. The fragment ions obtained by the dissociation of the C(4)H(4)(●+) ion are consistent with the cyclobutadiene structure in agreement with the vibrational predissociation spectrum of the acetylene dimer cation (C(2)H(2))(2)(●+) [R. A. Relph, J. C. Bopp, J. R. Roscioli, and M. A. Johnson, J. Chem. Phys. 131, 114305 (2009)]. The stepwise hydration experiments show that dissociative proton transfer reactions occur within the C(4)H(4)(●+)(H(2)O)(n) clusters with n ≥ 3 resulting in the formation of protonated water clusters. The measured binding energy of the C(4)H(4)(●+)H(2)O cluster, 38.7 ± 4 kJ/mol, is in excellent agreement with the G3(MP2) calculated binding energy of cyclobutadiene(●+)·H(2)O cluster (41 kJ/mol). The binding energies of the C(4)H(4)(●+)(H(2)O)(n) clusters change little from n = 1 to 5 (39-48 kJ/mol) suggesting the presence of multiple binding sites with comparable energies for the water-C(4)H(4)(●+) and water-water interactions. A significant entropy loss is measured for the addition of the fifth water

  15. Structure and hydration of the C4H4•+ ion formed by electron impact ionization of acetylene clusters

    NASA Astrophysics Data System (ADS)

    Momoh, Paul O.; Hamid, Ahmed M.; Abrash, Samuel A.; Samy El-Shall, M.

    2011-05-01

    Here we report ion mobility experiments and theoretical studies aimed at elucidating the identity of the acetylene dimer cation and its hydrated structures. The mobility measurement indicates the presence of more than one isomer for the C4H4•+ ion in the cluster beam. The measured average collision cross section of the C4H4•+ isomers in helium (38.9 ± 1 Å2) is consistent with the calculated cross sections of the four most stable covalent structures calculated for the C4H4•+ ion [methylenecyclopropene (39.9 Å2), 1,2,3-butatriene (41.1 Å2), cyclobutadiene (38.6 Å2), and vinyl acetylene (41.1 Å2)]. However, none of the single isomers is able to reproduce the experimental arrival time distribution of the C4H4•+ ion. Combinations of cyclobutadiene and vinyl acetylene isomers show excellent agreement with the experimental mobility profile and the measured collision cross section. The fragment ions obtained by the dissociation of the C4H4•+ ion are consistent with the cyclobutadiene structure in agreement with the vibrational predissociation spectrum of the acetylene dimer cation (C2H2)2•+ [R. A. Relph, J. C. Bopp, J. R. Roscioli, and M. A. Johnson, J. Chem. Phys. 131, 114305 (2009)], 10.1063/1.3212595. The stepwise hydration experiments show that dissociative proton transfer reactions occur within the C4H4•+(H2O)n clusters with n ≥ 3 resulting in the formation of protonated water clusters. The measured binding energy of the C4H4•+H2O cluster, 38.7 ± 4 kJ/mol, is in excellent agreement with the G3(MP2) calculated binding energy of cyclobutadiene•+.H2O cluster (41 kJ/mol). The binding energies of the C4H4•+(H2O)n clusters change little from n = 1 to 5 (39-48 kJ/mol) suggesting the presence of multiple binding sites with comparable energies for the water-C4H4•+ and water-water interactions. A significant entropy loss is measured for the addition of the fifth water molecule suggesting a structure with restrained water molecules, probably a

  16. Resistance and rupture analysis of single- and few-layer graphene nanosheets impacted by various projectiles

    NASA Astrophysics Data System (ADS)

    Sadeghzadeh, Sadegh; Liu, Ling

    2016-09-01

    In this paper, a quasi-classical model for the collision of various nanoparticles with single- and few-layer graphene nanosheets was introduced as a multi-scale approach that couples non-equilibrium molecular dynamics with the Finite Element Method. As a resistance criterion, it was observed that the coefficient of restitution and the induced stresses depend on the impact velocity of projectile. These parameters were evaluated computationally, and it was revealed that certain resulting behaviors differ from behaviors at the macro scale. By obtaining an out-of-plane yield stress limit of 1.0 TPa for graphene, the stress analysis of single- and multi-layer graphene sheets revealed that the limit projectile velocity needed for the yielding of graphene sheets increases with the increase in the number of layers. For aluminum nanoparticles, this increase is almost linear, and for other metals, it slightly deviates from the linear trend. It was also observed that the graphene sheets have a different rupture form when impacted by gaseous molecules than by metal particles. Considering the very high momentum of gas molecules and their shock-like behavior during high-speed collisions with a graphene sheet, pores with a size of one carbon atom can be created in graphene sheets. Since a single-layer graphene sheet can withstand a projectile which is 3.64 times larger than a projectile impacting a 20-layer graphene sheet, spaced graphene sheets seem to be more effective in absorbing the impact energy of projectiles than conventional few-layer graphene sheets.

  17. Tunable single-photon ionization TOF mass spectrometry using laser-produced plasma as the table-top VUV light source.

    PubMed

    Di Palma, Tonia M; Prati, Maria V; Borghese, Antonio

    2009-12-01

    Here we report on a laser plasma-based tunable VUV photoionization time-of-flight (TOF) mass spectrometer conceived mainly to study complex gaseous mixtures. Ionizing photons at tunable vacuum UV (VUV) wavelengths are generated by a gas-target laser-produced plasma, spectrally dispersed in the range 100-160 nm and efficiently focused onto a sample molecular beam. As a test case, we studied the exhaust gas of a four-stroke moped, a typical example of a complex gaseous mixture. Due to the VUV "soft" ionization, the mass spectra are less congested and more easily interpretable. Substituted benzene derivatives are found to give the most intense signals. Several aliphatic hydrocarbons are also detected. The use of tunable VUV radiation allowed the investigation of the contribution of isomers in the mass spectrum from the onset and shape of the photoionization efficiency spectra. Semiquantitative analysis was performed using known literature data detailing the photoionization cross sections. Our findings suggest that using combined data on the mass/photoionization efficiency spectra may be very helpful for a comprehensive analysis of complex gaseous mixtures.

  18. Ionization Potentials for Isoelectronic Series.

    ERIC Educational Resources Information Center

    Agmon, Noam

    1988-01-01

    Presents a quantitative treatment of ionization potentials of isoelectronic atoms. By looking at the single-electron view of calculating the total energy of an atom, trends in the screening and effective quantum number parameters are examined. Approaches the question of determining electron affinities. (CW)

  19. Initial results of positron ionization mass spectrometry

    NASA Technical Reports Server (NTRS)

    Donohue, D. L.; Hulett, L. D., Jr.; Mcluckey, S. A.; Glish, G. L.; Eckenrode, B. A.

    1990-01-01

    The use of monoenergetic positrons for the ionization of organic molecules in the gas phase is described. The ionic products are analyzed with a time-of-flight mass spectrometer and detected to produce a mass spectrum. The ionization mechanisms which can be studied in this way include positron impact at energies above the ionization limit of the target molecules, positronium formation in the Ore gap energy range, and positron attachment at energies less than 1eV. The technique of positron ionization mass spectrometry (PIMS) may have analytical utility in that chemical selectivity is observed for one or more of these processes.

  20. Impact of repeated single-metal and multi-metal pollution events on soil quality.

    PubMed

    Burges, Aritz; Epelde, Lur; Garbisu, Carlos

    2015-02-01

    Most frequently, soil metal pollution results from the occurrence of repeated single-metal and, above all, multi-metal pollution events, with concomitant adverse consequences for soil quality. Therefore, in this study, we evaluated the impact of repeated single-metal and multi-metal (Cd, Pb, Cu, Zn) pollution events on soil quality, as reflected by the values of a variety of soil microbial parameters with potential as bioindicators of soil functioning. Specifically, parameters of microbial activity (potentially mineralizable nitrogen, β-glucosidase and acid phosphatase activity) and biomass (fungal and bacterial gene abundance by RT-qPCR) were determined, in the artificially metal-polluted soil samples, at regular intervals over a period of 26 weeks. Similarly, we studied the evolution over time of CaCl2-extractable metal fractions, in order to estimate metal bioavailability in soil. Different metals showed different values of bioavailability and relative bioavailability ([metal]bio/[metal]tot) in soil throughout the experiment, under both repeated single-metal and multi-metal pollution events. Both repeated Zn-pollution and multi-metal pollution events led to a significant reduction in the values of acid phosphatase activity, and bacterial and fungal gene abundance, reflecting the negative impact of these repeated events on soil microbial activity and biomass, and, hence, soil quality.

  1. Simulation of Low Gain Avalanche Detector characteristics based on the concept of negative feedback in irradiated silicon detectors with carrier impact ionization

    NASA Astrophysics Data System (ADS)

    Verbitskaya, E.; Eremin, V.; Zabrodskii, A.; Luukka, P.

    2016-12-01

    In this study the main characteristics of silicon Low Gain Avalanche Detectors (LGAD), the dependencies of the collected charge versus bias voltage and fluence, are calculated to fit experimental data. The calculations are based on two previously developed Ioffe Institute models of radiation degradation in Si detectors: 1) a model of two effective energy levels of radiation-induced defects, and 2) a mechanism of internal negative feedback responsible for the gain degradation in irradiated Si detectors originating from the avalanche multiplication at the detector junction. The combination of these models describes well the properties of irradiated p-i-n detectors in a wide range of fluences. For simulating the LGAD characteristics the models are adapted to its n+-pbi-p-p+ structure, where the built-in boron-doped layer pbi produces high electric field sufficient for carrier impact ionization. It is shown that the developed models give adequate quantitative description of the experimental results for the LGADs up to the fluence of 2×1015 n/cm2 including the detector pulse response; however, additional boron removal from the pbi layer is required to have the best correlation with the experimental data. Similar to the physical model developed for silicon strip detectors operated at high voltage, the results are interpreted in terms of the internal negative feedback mechanism. It is shown that in irradiated LGADs this feedback leads to the transfer of a significant fraction of the potential drop from the built-in layer toward the p+ contact. It initiates two negative effects, which both cause the gain degradation with irradiation: the lowering of the electric field in the n+-pbi region that reduces the multiplication probability, and the increase of the collection time and trapping-related charge losses.

  2. National impacts of the Weatherization Assistance Program in single-family and small multifamily dwellings

    SciTech Connect

    Brown, M.A.; Berry, L.G.; Balzer, R.A.; Faby, E.

    1993-05-01

    Since 1976, the US Department of Energy (DOE) has operated one of the largest energy conservation programs in the nation -- the low-income Weatherization Assistance Program. The program strives to increase the energy efficiency of dwellings occupied by low-income persons in order to reduce their energy consumption, lower their fuel bills, increase the comfort of their homes, and safeguard their health. It targets vulnerable groups including the elderly, people with disabilities, and families with children. The most recent national evaluation of the impacts of the Program was completed in 1984 based on energy consumption data for households weatherized in 1981. DOE Program regulations and operations have changed substantially since then: new funding sources, management principles, diagnostic procedures, and weatherization technologies have been incorporated. Many of these new features have been studied in isolation or at a local level; however, no recent evaluation has assessed their combined, nationwide impacts to date or their potential for the future. In 1990, DOE initiated such an evaluation. This evaluation is comprised of three ``impact`` studies (the Single-Family Study, High-Density Multifamily Study, and Fuel-Oil Study) and two ``policy`` studies. Altogether, these five studies will provide a comprehensive national assessment of the Weatherization Assistance Program as it existed in the 1989 Program Year (PY 1989). This report presents the results of the first phase of the Single-Family Study. It evaluates the energy savings and cost effectiveness of the Program as it has been applied to the largest portion of its client base -- low-income households that occupy single-family dwellings, mobile homes, and small (2- to 4-unit) multifamily dwellings. It is based upon a representative national sample that covers the full range of conditions under which the program was implemented in PY 1989.

  3. The origin of the moon and the single impact hypothesis. III

    NASA Technical Reports Server (NTRS)

    Benz, W.; Cameron, A. G. W.; Melosh, H. J.

    1989-01-01

    Calculations of the single-impact hypothesis for the origin of the moon were performed using the smoothed particle hydrodynamics (SPH) code developed by Benz et al. (1986). Results are presented from calculations of a relatively low-level collision with an impactor mass in the range 6-8 x 10 to the 26th g. Several runs of the calculations are conducted for this mass range with variations in the SPH code, the equation of state, and the initial planetary models. The effects of these variations are compared. It is found that the orbiting mass is injected by gravitational torques.

  4. The impact of single-gender classrooms on science achievement of middle school gifted girls

    NASA Astrophysics Data System (ADS)

    Ulkins, David S.

    Studies indicate a gap in science achievement and positive attitudes towards science between gifted male and female students with females performing less than the males. This study investigated the impact of a single-gender classroom environment as opposed to a mixed-gender classroom, on motivation, locus of control, self-concept, and science achievement of middle school gifted girls. The Motivated Strategies for Learning Questionnaire (MSLQ), Review of Personal Effectiveness with Locus of Control (ROPELOC), Test of Science Related Attitudes (TOSRA), and Stanford Achievement Test 10th Edition, were used to measure the dependent variables respectively. The independent-measure t test was used to compare the differences between girls in a single-gender classroom with the ones in a mixed-gender classroom. A significant difference in the external locus of control resulted for girls in the single gender classroom. However, there were no significant differences found in science achievement, motivation, and the attitudes toward science between the two groups. The implication is that a single-gender learning environment and the use of differentiated teaching strategies can help lessen the negative effects of societal stereotypes in today's classrooms. These, along with being cognizant of the differences in learning styles of girls and their male counterparts, will result in a greater level of success for gifted females in the area of science education.

  5. Monte Carlo approach to calculate ionization dynamics of hot solid-density plasmas within particle-in-cell simulations.

    PubMed

    Wu, D; He, X T; Yu, W; Fritzsche, S

    2017-02-01

    A physical model based on a Monte Carlo approach is proposed to calculate the ionization dynamics of hot-solid-density plasmas within particle-in-cell (PIC) simulations, and where the impact (collision) ionization (CI), electron-ion recombination (RE), and ionization potential depression (IPD) by surrounding plasmas are taken into consideration self-consistently. When compared with other models, which are applied in the literature for plasmas near thermal equilibrium, the temporal relaxation of ionization dynamics can also be simulated by the proposed model. Besides, this model is general and can be applied for both single elements and alloys with quite different compositions. The proposed model is implemented into a PIC code, with (final) ionization equilibriums sustained by competitions between CI and its inverse process (i.e., RE). Comparisons between the full model and model without IPD or RE are performed. Our results indicate that for bulk aluminium at temperature of 1 to 1000 eV, (i) the averaged ionization degree increases by including IPD; while (ii) the averaged ionization degree is significantly over estimated when the RE is neglected. A direct comparison from the PIC code is made with the existing models for the dependence of averaged ionization degree on thermal equilibrium temperatures and shows good agreements with that generated from Saha-Boltzmann model and/or FLYCHK code.

  6. Monte Carlo approach to calculate ionization dynamics of hot solid-density plasmas within particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Wu, D.; He, X. T.; Yu, W.; Fritzsche, S.

    2017-02-01

    A physical model based on a Monte Carlo approach is proposed to calculate the ionization dynamics of hot-solid-density plasmas within particle-in-cell (PIC) simulations, and where the impact (collision) ionization (CI), electron-ion recombination (RE), and ionization potential depression (IPD) by surrounding plasmas are taken into consideration self-consistently. When compared with other models, which are applied in the literature for plasmas near thermal equilibrium, the temporal relaxation of ionization dynamics can also be simulated by the proposed model. Besides, this model is general and can be applied for both single elements and alloys with quite different compositions. The proposed model is implemented into a PIC code, with (final) ionization equilibriums sustained by competitions between CI and its inverse process (i.e., RE). Comparisons between the full model and model without IPD or RE are performed. Our results indicate that for bulk aluminium at temperature of 1 to 1000 eV, (i) the averaged ionization degree increases by including IPD; while (ii) the averaged ionization degree is significantly over estimated when the RE is neglected. A direct comparison from the PIC code is made with the existing models for the dependence of averaged ionization degree on thermal equilibrium temperatures and shows good agreements with that generated from Saha-Boltzmann model and/or FLYCHK code.

  7. Impact of single walled carbon nanotubes (SWNTs) on wastewater microbial communities

    NASA Astrophysics Data System (ADS)

    Goyal, Deepankar

    Aim: Carbon nanotubes (CNTs) hold great promise in advancing our future, with potential applications such as adsorbents, conductive composites, energy storage devices, and more. Despite of numerous potential applications of CNTs, almost nothing so far is known about how such carbon-based nanomaterials would in future impact environmental processes such as wastewater treatment. The objective of the current study was to evaluate the impact of single-walled carbon nanotubes (SWNTs) on microbial communities and wastewater treatment processes in activated sludge bioreactors. Method: Closed system batch-scale reactors were used to simulate the activated sludge process. Two sets of triplicate reactors were analyzed to determine the effects of SWNTs and associated impurities compared to control reactors that contained no CNTs. Sub-samples for microbial community analyses were aseptically removed periodically from the bioreactors every ˜1 hour 15 minutes and held at -80°C until analyzed. Genomic DNA was extracted from bioreactor samples, and molecular profiles of the bacterial communities were determined using automated ribosomal intergenic spacer analysis (ARISA). The clones for the ARISA profiles having distinct ARISA peaks were picked and sequenced. Result: ARISA profiles revealed adverse changes in CNT-exposed bacterial communities compared to control reactors associated with CNTs. The phylogenetic analysis of cloned insert containing Internal Transcribed Spacer (ITS) region plus the 16S rRNA genes identified them belonging to taxonomic groups of the families Sphingomonadaceae and Cytophagacaceae , and the genus Zoogloea. Changes in community structure were observed in both SWNT-exposed and control reactors over the experimental time period. Also the date on which activated sludge was obtained from a wastewater treatment plant facility seemed to play a critical role in changing the community structure altogether, indicating the importance of analyzing microbial

  8. Ionization of excited xenon atoms by electrons

    NASA Astrophysics Data System (ADS)

    Erwin, Daniel A.; Kunc, Joseph A.

    2004-08-01

    Measured cross sections for electron-impact ionization of excited Xe atoms are not presently available. Therefore, we combine in this work the formalisms of the binary encounter approximation and Sommerfeld’s quantization of atomic orbits and derive from first-principles cross sections for ionization of excited atoms by electrons of low and moderate energies (up to a few hundred eV ). The approach of this work can be used to calculate the cross sections for electron-impact ionization of excited atoms and atomic ions other than xenon.

  9. Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line, real-time process gas analysis.

    PubMed

    Mühlberger, F; Wieser, J; Ulrich, A; Zimmermann, R

    2002-08-01

    Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region

  10. Single-source impact analysis using three-dimensional air quality models.

    PubMed

    Bergin, Michelle S; Russell, Armistead G; Odman, Mehmet T; Cohan, Daniel S; Chameides, William L

    2008-10-01

    Isolating the effects of an individual emissions source on secondary air pollutants such as ozone and some components of particulate matter must incorporate complex nonlinear processes, be sensitive to small emissions perturbations, and account for impacts that may occur hundreds of kilometers away. The ability to evaluate these impacts is becoming increasingly important for efficient air quality management. Here, as part of a recent compliance enforcement action for a violation of the Clean Air Act and as an evaluation of ozone response to single-source emissions plumes, two three-dimensional regional photochemical air quality models are used to assess the impact on ozone from approximately 2000 to 3000 excess t/month of nitrogen oxides emitted from a single power plant in Ohio. Periods in May, July, and August are evaluated. Two sensitivity methods are applied: the "brute-force" (B-F) method and the decoupled direct method (DDM). Using DDM, maximum 1-hr averaged ozone concentrations are found to increase by up to 1.8, 1.3, and 2.2 ppbv during May, July, and August episodes, respectively, and concentration increases greater than 0.5 ppbv occur in Ohio, Pennsylvania, Maryland, New York, West Virginia, Virginia, and North and South Carolina. B-F results for the August episode show a maximum 1-hr averaged ozone concentration increase of 2.3 ppbv. Significant localized decreases are also simulated, with a maximum of 3.6 ppbv in Ohio during the August episode and decreases of 0.50 ppbv and greater in Ohio, Pennsylvania, Maryland, West Virginia, and Virginia. Maximum increases are compared with maximum decreases for the August period using second-order DDM and are found, in aggregate, to be greater in magnitude by 42%. When evaluated during hours when ozone concentrations exceed 0.060 ppm, the maximum increases in ozone are higher than decreases by 82%. The spatial extent of ozone increase in both cases is about triple that of reduction.

  11. Scaling Impacts on Electromigration in Narrow Single-Damascene Cu Interconnects

    SciTech Connect

    Yokogawa, Shinji; Tsuchiya, Hideaki

    2004-12-08

    This paper presents scaling impacts on electromigration-induced mass transport in narrow single damascene Cu interconnects. The Kawasaki-Hu test structure was used to investigate such impacts. Line widths ranging from 0.12 {mu}m to 0.20 {mu}m were used to demonstrate the scaling impact that is due to the electromigration-induced diffusion. Lifetime that is determined by resistance degradation decreases according to the decreasing line width at a fixed current density. This is caused by decrease of the effective incubation time and increase of the drift velocity. A product of drift velocity and a square line width has a linear dependence on current density. The activation energy is 1.2 eV for the effective incubation time, and is 1.1 eV for the drift velocity, respectively. They are independent of the line width. The activation energy suggests that the effective incubation time is the time to void growth from the Cu/SiCN interface to trench bottom through Cu grain boundaries. The grain boundaries provide nucleation sites for void growth in bamboo structures. Similarly, the interface diffusion at the Cu/metal liner on the sidewalls of the line contributes to void growth.

  12. Fate of trace metals in a rotary-kiln incinerator with a single-stage ionizing wet scrubber. Volume 1. Technical results

    SciTech Connect

    Fournier, D.J.; Waterland, L.R.

    1991-07-01

    A series of pilot-scale incineration tests was performed at EPA's Incineration Research Facility (IRF) in Jefferson, Arkansas, to evaluate the fate of trace metals fed to a rotary kiln incinerator equipped with an ionizing wet scrubber (IWS) for particulate and acid gas control. Test variables were kiln temperature, ranging from 816 to 927 C (1500 to 1700 F); afterburner temperature, ranging from 982 to 1204 C (1800 to 2200 F); and feed chlorine content, ranging from 0 to 8 percent. The test program evaluated the fate of five hazardous constituent trace metals (arsenic, barium, cadmium, chromium, and lead) and four nonhazardous constituent trace metals (bismuth, copper, magnesium, and strontium). The test results indicate that cadmium and bismuth were relatively volatile, with an average of less than 40 percent discharged with the kiln ash. Arsenic, barium, chromium, copper, lead, magnesium, and strontium were relatively nonvolatile, with an average of greater than 80 percent discharged with the kiln ash. Observed relative metal volatilities generally agreed with the volatilities predicted based on vapor pressure/temperature relationships, with the exception of arsenic which was much less volatile than predicted. The volatility of cadmium, bismuth, and lead increased as kiln temperature was increased; the discharge distributions of the remaining metals were not significantly affected by changes in kiln temperature. Apparent scrubber collection efficiencies for the metals averaged 22 to 71 percent, and were generally higher for the less volatile metals. The overall average metal collection efficiency was 43 percent.

  13. Size dependence of the polarizability and Haynes rule for an exciton bound to an ionized donor in a single spherical quantum dot

    SciTech Connect

    Feddi, E. Zouitine, A.; Oukerroum, A.; Zazoui, M.; Dujardin, F.; Assaid, E.

    2015-02-14

    We study the effect of an external electric field on an exciton bound to an ionized donor (D{sup +}, X) confined in a spherical quantum dot using a perturbative-variational method where the wave function and energy are developed in series of powers of the electric field strength. After testing this new approach in the determination of the band gap for some semiconductor materials, we generalize it to the case of (D{sup +}, X) in the presence of the electric field and for several materials ZnO, PbSe, and InAs, with significant values of the mass ratio. Three interesting results can be deduced: First, we show that the present method allows to determine the ground state energy in the presence of a weak electric field in a simple way (E = E{sub 0} − αf{sup 2}) using the energy without electric field E{sub 0} and the polarizability α. The second point is that our theoretical predictions show that the polarizability of (D{sup +}, X) varies proportionally to R{sup 3.5} and follows an ordering α{sub D{sup 0}}<α{sub X}<α{sub (D{sup +},X)}. The last point to highlight is that the Haynes rule remains valid even in the presence of a weak electric field.

  14. Assessing Model Characterization of Single Source Secondary Pollutant Impacts Using 2013 SENEX Field Study Measurements.

    PubMed

    Baker, Kirk R; Woody, Matthew C

    2017-03-15

    Aircraft measurements made downwind from specific coal fired power plants during the 2013 Southeast Nexus field campaign provide a unique opportunity to evaluate single source photochemical model predictions of both O3 and secondary PM2.5 species. The model did well at predicting downwind plume placement. The model shows similar patterns of an increasing fraction of PM2.5 sulfate ion to the sum of SO2 and PM2.5 sulfate ion by distance from the source compared with ambient based estimates. The model was less consistent in capturing downwind ambient based trends in conversion of NOX to NOY from these sources. Source sensitivity approaches capture near-source O3 titration by fresh NO emissions, in particular subgrid plume treatment. However, capturing this near-source chemical feature did not translate into better downwind peak estimates of single source O3 impacts. The model estimated O3 production from these sources but often was lower than ambient based source production. The downwind transect ambient measurements, in particular secondary PM2.5 and O3, have some level of contribution from other sources which makes direct comparison with model source contribution challenging. Model source attribution results suggest contribution to secondary pollutants from multiple sources even where primary pollutants indicate the presence of a single source.

  15. Dielectric relaxation related to single-ionized oxygen vacancies in (Pb{sub 1-x}La{sub x})(Zr{sub 0.90}Ti{sub 0.10}){sub 1-x/4}O{sub 3} ceramics

    SciTech Connect

    Pelaiz-Barranco, A.; Guerra, J.D.S.

    2010-09-15

    The dielectric relaxation phenomenon has been studied in lanthanum modified lead zirconate titanate ceramics in the high temperature paraelectric phase. The high temperature dielectric response revealed an anomalous behavior, which is characterized by an increase of the real component of the dielectric permittivity with the increase of the temperature. At the same time, a similar behavior, with very high values, has been observed in the imaginary component of the dielectric permittivity, which can be associated with conduction effects related to the conductivity losses. The frequency and temperature behavior of the complex dielectric permittivity has been analyzed considering the semi-empirical complex Cole-Cole equation. The activation energy value, obtained from the Arrhenius' dependence for the relaxation time, was found to decreases with the increase of the lanthanum concentration and has been associated with single-ionized oxygen vacancies. The short-range hopping of oxygen vacancies is discussed as the main cause of the dielectric relaxation.

  16. Analysis of Antiretrovirals in Single Hair Strands for Evaluation of Drug Adherence with Infrared-Matrix-Assisted Laser Desorption Electrospray Ionization Mass Spectrometry Imaging.

    PubMed

    Rosen, Elias P; Thompson, Corbin G; Bokhart, Mark T; Prince, Heather M A; Sykes, Craig; Muddiman, David C; Kashuba, Angela D M

    2016-01-19

    Adherence to a drug regimen can be a strong predictor of health outcomes, and validated measures of adherence are necessary at all stages of therapy from drug development to prescription. Many of the existing metrics of drug adherence (e.g., self-report, pill counts, blood monitoring) have limitations, and analysis of hair strands has recently emerged as an objective alternative. Traditional methods of hair analysis based on LC-MS/MS (segmenting strands at ≥1 cm length) are not capable of preserving a temporal record of drug intake at higher resolution than approximately 1 month. Here, we evaluated the detectability of HIV antiretrovirals (ARVs) in hair from a range of drug classes using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging (MSI) with 100 μm resolution. Infrared laser desorption of hair strands was shown to penetrate into the strand cortex, allowing direct measurement by MSI without analyte extraction. Using optimized desorption conditions, a linear correlation between IR-MALDESI ion abundance and LC-MS/MS response was observed for six common ARVs with estimated limits of detection less than or equal to 1.6 ng/mg hair. The distribution of efavirenz (EFV) was then monitored in a series of hair strands collected from HIV infected, virologically suppressed patients. Because of the role hair melanin plays in accumulation of basic drugs (like most ARVs), an MSI method to quantify the melanin biomarker pyrrole-2,3,5-tricarboxylic acid (PTCA) was evaluated as a means of normalizing drug response between patients to develop broadly applicable adherence criteria.

  17. Ionized cluster beam deposition

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, A. R.

    1983-01-01

    Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

  18. Effect of ionizing radiation on dielectric characteristics of Cu2ZnSn(S x Se1- x )4 single crystals

    NASA Astrophysics Data System (ADS)

    Hurtavy, V. G.; Sheleg, A. U.

    2017-02-01

    The effect of electron irradiation on conductivity and dielectric permeability of Cu2ZnSnS4 and Cu2ZnSnSe4 single crystals and solid solutions based on them is studied. It is shown that values of dielectric permeability decrease with an increase in the irradiation dose while those of specific electric conductivity sharply increase.

  19. Cross sections for ionization of tetrahydrofuran by protons at energies between 300 and 3000 keV

    NASA Astrophysics Data System (ADS)

    Wang, Mingjie; Rudek, Benedikt; Bennett, Daniel; de Vera, Pablo; Bug, Marion; Buhr, Ticia; Baek, Woon Yong; Hilgers, Gerhard; Rabus, Hans

    2016-05-01

    Double-differential cross sections for ionization of tetrahydrofuran by protons with energies from 300 to 3000 keV were measured at the Physikalisch-Technische Bundesanstalt ion accelerator facility. The electrons emitted at angles between 15∘ and 150∘ relative to the ion-beam direction were detected with an electrostatic hemispherical electron spectrometer. Single-differential and total ionization cross sections have been derived by integration. The experimental results are compared to the semiempirical Hansen-Kocbach-Stolterfoht model as well as to the recently reported method based on the dielectric formalism. The comparison to the latter showed good agreement with experimental data in a broad range of emission angles and energies of secondary electrons. The scaling property of ionization cross sections for tetrahydrofuran was also investigated. Compared to molecules of different size, the ionization cross sections of tetrahydrofuran were found to scale with the number of valence electrons at large impact parameters.

  20. Ionization potentials of seaborgium

    SciTech Connect

    Johnson, E.; Pershina, V.; Fricke, B.

    1999-10-21

    Multiconfiguration relativistic Dirac-Fock values were calculated for the first six ionization potentials of seaborgium and of the other group 6 elements. No experimental ionization potentials are available for seaborgium. Accurate experimental values are not available for all of the other ionization potentials. Ionic radii for the 4+ through 6+ ions of seaborgium are also presented. The ionization potentials and ionic radii obtained will be used to predict some physiochemical properties of seaborgium and its compounds.

  1. Modeling of Ionization Physics with the PIC Code OSIRIS

    SciTech Connect

    Deng, S.; Tsung, F.; Lee, S.; Lu, W.; Mori, W.B.; Katsouleas, T.; Muggli, P.; Blue, B.E.; Clayton, C.E.; O'Connell, C.; Dodd, E.; Decker, F.J.; Huang, C.; Hogan, M.J.; Hemker, R.; Iverson, R.H.; Joshi, C.; Ren, C.; Raimondi, P.; Wang, S.; Walz, D.; /Southern California U. /UCLA /SLAC

    2005-09-27

    When considering intense particle or laser beams propagating in dense plasma or gas, ionization plays an important role. Impact ionization and tunnel ionization may create new plasma electrons, altering the physics of wakefield accelerators, causing blue shifts in laser spectra, creating and modifying instabilities, etc. Here we describe the addition of an impact ionization package into the 3-D, object-oriented, fully parallel PIC code OSIRIS. We apply the simulation tool to simulate the parameters of the upcoming E164 Plasma Wakefield Accelerator experiment at the Stanford Linear Accelerator Center (SLAC). We find that impact ionization is dominated by the plasma electrons moving in the wake rather than the 30 GeV drive beam electrons. Impact ionization leads to a significant number of trapped electrons accelerated from rest in the wake.

  2. Ionization Energies of Lanthanides

    ERIC Educational Resources Information Center

    Lang, Peter F.; Smith, Barry C.

    2010-01-01

    This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above…

  3. Impact of sleep difficulty on single and repeated injuries in adolescents.

    PubMed

    Chau, Kénora

    2015-08-01

    Injuries are frequent and may be caused by sleep difficulty in youth. This study assessed the impact of sleep difficulty on single and repeated school and out-of-school injuries and the confounding role of socioeconomic factors and school, behaviour and health-related difficulties among adolescents. The study population included 1559 middle-school adolescents from north-eastern France (mean age 13.5, SD 1.3) who completed at the end of school year a self-administered questionnaire to gather school and out-of-school injuries during the school year, and to assess sleep difficulty and previous injury risk factors which were socioeconomic factors (family structure, parents' education, father's occupation, and family income), school performance, obesity, alcohol/tobacco/cannabis/hard drugs use, health status, psychological health, and involvement-in-violence. For sleep difficulty and behaviour and health-related difficulties their first occurring over adolescent's life course was gathered. Multinomial logistic regression models were used retaining only sleep difficulty and other risk factors which had started before the school year (thus before the injuries studied). School and out-of-school injuries and sleep difficulty were frequent. The adolescents with sleep difficulty without medical treatment had a higher risk of single school and out-of-school injuries (gender-age-adjusted odds ratio gaOR 1.86 and 1.76, respectively) and a much higher risk of repeated school and out-of-school injuries (≥2 injuries; gaOR 2.43 and 3.73, respectively). The adolescents with persistent sleep difficulty despite a medical treatment also had a higher risk of single school and out-of-school injury (gaOR 2.31 and 1.78, respectively), and a much higher risk of repeated school and out-of-school injuries (gaOR 4.92 and 4.36, respectively). Socioeconomic factors had a moderate contribution (<27%) while school, behaviour and health-related difficulties had a high contribution (reaching 71

  4. Impact of ethnicity, donor status and HLA matching on renal allograft survival: a single center study.

    PubMed

    Chelluri, Lakshmi Kiran; Vasantha, Adavi; Ratnakar, Kamaraju S

    2009-11-01

    The role of histocompatibility testing in renal transplantation is passing through an immense debate on its utility in predicting long-term graft survival. The current study, which includes fifty-one patients with end-stage renal disease, aims at evaluating the impact of the HLA matching in live related donor (LRD) (parents, siblings and near relatives) and live unrelated donor (LURD) transplants on one year graft survival rates, in a single center. Patients were followed-up for one-year after renal transplantation and observed for renal complications inclu-ding infections and rejection. The incidence of acute rejection episodes was found to be lower in LRD transplantation complying with many reports published so far. HLA matching was found to be beneficial in obtaining better graft function and one-year graft survival rate. The current study found that patients from Far East of India have lower graft survival rates as against patients from other regions of the country. India, with its vast racial distribution, has a need to look into the ethnic variation and its impact on allograft survival.

  5. Effect of single dose preoperative intramuscular dexamethasone injection on lower impacted third molar surgery.

    PubMed

    Klongnoi, Boworn; Kaewpradub, Pariya; Boonsiriseth, Kiatanant; Wongsirichat, Natthamet

    2012-03-01

    This study aimed to investigate the effects of dexamethasone intramuscular injection 1h preoperatively, in reducing facial swelling, pain and trismus after lower impacted third molar (LITM) surgery. Twenty healthy Thai patients with both LITM surgical extraction were enrolled in the study. The washout period was 1 month after the first operation. Clinical assessment of the facial swelling, pain and trismus were measured before and after operation for 7 days and the patient's total analgesic consumption was recorded. The level of significance used in the statistical decisions was P<0.05. Preoperative intramuscular injection of single-dose 8mg dexamethasone reduced postoperative swelling after LITM surgical extraction significantly on the second postoperative day, but immediately after surgery and on day 7 after the surgical extraction, no significant difference was found between the dexamethasone and control groups. Dexamethasone also reduced postoperative pain after LITM surgical extraction significantly on postoperative days 2 and 7. Additionally, the amount of paracetamol decreased significantly. There were no significant differences in trismus in the study and control groups 7 days after LITM operation. Single-dose intramuscular injection of dexamethasone can reduce postoperative facial swelling and pain, without affecting trismus after LITM surgical extraction.

  6. The total cavopulmonary connection resistance: a significant impact on single ventricle hemodynamics at rest and exercise

    PubMed Central

    Sundareswaran, Kartik S.; Pekkan, Kerem; Dasi, Lakshmi P.; Whitehead, Kevin; Sharma, Shiva; Kanter, Kirk R.; Fogel, Mark A.; Yoganathan, Ajit P.

    2008-01-01

    Little is known about the impact of the total cavopulmonary connection (TCPC) on resting and exercise hemodynamics in a single ventricle (SV) circulation. The aim of this study was to elucidate this mechanism using a lumped parameter model of the SV circulation. Pulmonary vascular resistance (1.96 ± 0.80 WU) and systemic vascular resistances (18.4 ± 7.2 WU) were obtained from catheterization data on 40 patients with a TCPC. TCPC resistances (0.39 ± 0.26 WU) were established using computational fluid dynamic simulations conducted on anatomically accurate three-dimensional models reconstructed from MRI (n = 16). These parameters were used in a lumped parameter model of the SV circulation to investigate the impact of TCPC resistance on SV hemodynamics under resting and exercise conditions. A biventricular model was used for comparison. For a biventricular circulation, the cardiac output (CO) dependence on TCPC resistance was negligible (sensitivity = −0.064 l·min−1·WU−1) but not for the SV circulation (sensitivity = −0.88 l·min−1·WU−1). The capacity to increase CO with heart rate was also severely reduced for the SV. At a simulated heart rate of 150 beats/min, the SV patient with the highest resistance (1.08 WU) had a significantly lower increase in CO (20.5%) compared with the SV patient with the lowest resistance (50%) and normal circulation (119%). This was due to the increased afterload (+35%) and decreased preload (−12%) associated with the SV circulation. In conclusion, TCPC resistance has a significant impact on resting hemodynamics and the exercise capacity of patients with a SV physiology. PMID:18931028

  7. Impact of solution chemistry on viral removal by a single-walled carbon nanotube filter.

    PubMed

    Brady-Estévez, Anna S; Nguyen, Thanh H; Gutierrez, Leonardo; Elimelech, Menachem

    2010-07-01

    This study investigates the effectiveness of a single-walled carbon nanotube (SWNT) filter for removal of viruses from water. MS2 bacteriophage viral removal was examined over a range of environmentally relevant solution chemistries, spanning various ionic strengths, monovalent and divalent salts, pH, and natural organic matter (NOM) concentrations. Viral removal by the SWNT filter was governed by physicochemical (depth) filtration. The removal of viruses increased at higher ionic strengths (NaCl) due to suppression of repulsive electrostatic interactions between viruses and SWNTs. Addition of divalent salts, however, had varying impacts. While CaCl(2) increased virus removal, likely due to complexation of calcium ions to viral surfaces, addition of MgCl(2) reduced viral removal by the SWNT filter. Solution pH also had significant impact on viral removal as the interactions between viral particles and SWNTs changed from attractive below the virus isoelectric point (about pH 3.9) to repulsive at higher pH. Suwannee River NOM was shown to be detrimental to filter viral removal. Reduction of viral removal by NOM was attributed to adsorption of NOM macromolecules to viruses and SWNTs, thereby resulting in steric repulsive forces. Modifications of the filter to incorporate thicker SWNT layers mitigate the negative impacts of NOM on filter performance. This study has shown that while it is possible to attain high levels of viral removal over a broad range of solution chemistries, the extent of viral removal will be highly dependent on the specific solution chemistry of the treated water.

  8. The design and application of a field-transportable time- of-flight mass spectrometer (ATOFMS) and use of two-step laser desorption/ionization (L2MS) to determine PAH in single particles

    NASA Astrophysics Data System (ADS)

    Morrical, Bradley Douglas

    2000-11-01

    In order to improve the ability of aerosol time-of-flight mass spectrometry (ATOFMS) to achieve the complete chemical characterization of single particles, new refinements in instrumentation and techniques have been developed. This thesis describes the design and construction of two field transportable ATOFMS instruments that allows for real-time single particle aerosol measurements for the first time in remote locations. Additionally, this new ATOFMS instrument is capable of obtaining both positive and negative ion spectra simultaneously, enabling easier identification of chemical species on a particle. Improvements to the particle inlet interface, particle sizing, and integration of electronics were also realized by the new design. To demonstrate proof of concept, the field transportable ATOFMS instruments were used to make field measurements in September and October of 1996. From field data collected, heterogeneous chemical reactions were observed for two different types of chemical systems, namely the formation of NaNO3 in sea salt particles in Long Beach, CA and the formation of NH4NO 3 on particles in Riverside, CA. It was found that both chemical systems depended heavily on wind trajectories and the length of time an air parcel remained stagnated over urban areas. Quantitation of NH4 + and NO3- is achieved by calibrating ATOFMS counts and ion signal to measured NH4+ and NO3- concentrations from conventional sampling and analysis. The second part of this thesis describes the development of a new laser ionization technique, two step laser desorption/ionization (L2MS), in order to improve the chemical characterization of organic compounds on single particles. Using L2MS, identification of a large number of polycyclic aromatic hydrocarbons (PAH) is achieved with several common combustion sources. An attempt is made to use selected PAH as markers for different combustion sources. Method of sample collection is also explored to understand the bias that particle

  9. Picosecond ionization dynamics in femtosecond filaments at high pressures

    NASA Astrophysics Data System (ADS)

    Gao, Xiaohui; Patwardhan, Gauri; Schrauth, Samuel; Zhu, Daiwei; Popmintchev, Tenio; Kapteyn, Henry C.; Murnane, Margaret M.; Romanov, Dmitri A.; Levis, Robert J.; Gaeta, Alexander L.

    2017-01-01

    We investigate the plasma dynamics inside a femtosecond-pulse-induced filament generated in an argon gas for a wide range of pressures up to 60 bar. At higher pressures, we observe ionization immediately following a pulse, with up to a threefold increase in the electron density within 30 ps after the filamentary propagation of a femtosecond pulse. Our study suggests that this picosecond evolution can be attributed to collisional ionization including Penning and associative ionizations and electron-impact ionization of excited atoms generated during the pulse. The dominance of excited atoms over ionized atoms at the end of the pulse also indicates an intrapulse inhibition of avalanche ionization. This delayed ionization dynamics provides evidence for diagnosing atomic and molecular excitation and ionization in intense laser interaction with high-pressure gases.

  10. Ultraviolet laser desorption/ionization mass spectrometry of single-core and multi-core polyaromatic hydrocarbons under variable conditions of collisional cooling: insights into the generation of molecular ions, fragments and oligomers.

    PubMed

    Gámez, Francisco; Hortal, Ana R; Martínez-Haya, Bruno; Soltwisch, Jens; Dreisewerd, Klaus

    2014-11-01

    The ultraviolet laser desorption/ionization of polyaromatic hydrocarbons (PAHs) has been investigated under different background pressures of an inert gas (up to 1.2 mbar of N2) in the ion source of a hybrid, orthogonal-extracting time-of-flight mass spectrometer (oTOF-MS). The study includes an ensemble of six model PAHs with isolated single polyaromatic cores and four ones with multiple cross-linked aromatic and polyaromatic cores. In combination with a weak ion extraction field, the variation of the buffer gas pressure allowed to control the degree of collisional cooling of the desorbed PAHs and, thus, to modulate their decomposition into fragments. The dominant fragmentation channels observed are related to dehydrogenation of the PAHs, in most cases through the cleavage of even numbers of C-H bonds. Breakage of C-C bonds leading to the fragmentation of rings, side chains and core linkages is also observed, in particular, at low buffer gas pressures. The precise patterns of the combined fragmentation processes vary significantly between the PAHs. The highest abundances of molecular PAH ions and cleanest mass spectra were consistently obtained at the highest buffer gas pressure of 1.2 mbar. The effective quenching of the fragmentation pathways at this elevated pressure improves the sensitivity and data interpretation for analytical applications, although the fragmentation of side chains and of bonds between (poly)aromatic cores is not completely suppressed in all cases. Moreover, these results suggest that the detected fragments are generated through thermal equilibrium processes rather than as a result of rapid photolysis. This assumption is further corroborated by a laser desorption/ionization post-source decay analysis using an axial time-of-flight MS. In line with these findings, covalent oligomers of the PAHs, which are presumably formed by association of two or more dehydrogenated fragments, are detected with higher abundances at the lower buffer gas

  11. RAYLEIGH-TAYLOR INSTABILITY IN PARTIALLY IONIZED COMPRESSIBLE PLASMAS

    SciTech Connect

    Diaz, A. J.; Ballester, J. L. E-mail: roberto.soler@wis.kuleuven.be

    2012-07-20

    We study the modification of the classical criterion for the linear onset and growing rate of the Rayleigh-Taylor instability (RTI) in a partially ionized plasma in the two-fluid description. The plasma is composed of a neutral fluid and an electron-ion fluid, coupled by means of particle collisions. The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The limits of collisionless, no gravity, and incompressible fluids are checked before addressing the general case. We find that both compressibility and ion-neutral collisions lower the linear growth rate, but do not affect the critical threshold of the onset of the RTI. The configuration is always unstable when a lighter plasma is below a heavier plasma regardless the value of the magnetic field strength, the ionization degree, and the ion-neutral collision frequency. However, ion-neutral collisions have a strong impact on the RTI growth rate, which can be decreased by an order of magnitude compared to the value in the collisionless case. Ion-neutral collisions are necessary to accurately describe the evolution of the RTI in partially ionized plasmas such as prominences. The timescale for the development of the instability is much longer than in the classical incompressible fully ionized case. This result may explain the existence of prominence fine structures with life times of the order of 30 minutes. The timescales derived from the classical theory are about one order of magnitude shorter and incompatible with the observed life times.

  12. Development of gas chromatography-flame ionization detection system with a single column and liquid nitrogen-free for measuring atmospheric C2-C12 hydrocarbons.

    PubMed

    Liu, Chengtang; Mu, Yujing; Zhang, Chenglong; Zhang, Zhibo; Zhang, Yuanyuan; Liu, Junfeng; Sheng, Jiujiang; Quan, Jiannong

    2016-01-04

    A liquid nitrogen-free GC-FID system equipped with a single column has been developed for measuring atmospheric C2-C12 hydrocarbons. The system is consisted of a cooling unit, a sampling unit and a separation unit. The cooling unit is used to meet the temperature needs of the sampling unit and the separation unit. The sampling unit includes a dehydration tube and an enrichment tube. No breakthrough of the hydrocarbons was detected when the temperature of the enrichment tube was kept at -90 °C and sampling volume was 400 mL. The separation unit is a small round oven attached on the cooling column. A single capillary column (OV-1, 30 m × 0.32 mm I.D.) was used to separate the hydrocarbons. An optimal program temperature (-60 ∼ 170 °C) of the oven was achieved to efficiently separate C2-C12 hydrocarbons. There were good linear correlations (R(2)=0.993-0.999) between the signals of the hydrocarbons and the enrichment amount of hydrocarbons, and the relative standard deviation (RSD) was less than 5%, and the method detection limits (MDLs) for the hydrocarbons were in the range of 0.02-0.10 ppbv for sampling volume of 400 mL. Field measurements were also conducted and more than 50 hydrocarbons from C2 to C12 were detected in Beijing city.

  13. Detritus in K/T boundary clays of western North America - Evidence against a single oceanic impact

    NASA Technical Reports Server (NTRS)

    Sharpton, V. L.; Schuraytz, B. C.; Burke, K.; Murali, A. V.; Ryder, G.

    1990-01-01

    Understanding the crustal signature of impact ejecta contained in the Cretaceous/Tertiary (K/T) boundary layer is crucial to constraining the possible site(s) of the postulated K/T impact event. The relatively unaltered clastic constituents of the boundary layer at widely separated outcrops within the western interior of North America are not compatible with a single oceanic impact but require instead an impact site on a continent or continental margin. On the other hand, chemical compositions of highly altered K/T boundary layer components in some marine sections have suggested to others an impact into oceanic crust. We suspect that post-depositional alteration within the marine setting accounts for this apparent oceanic affinity. If, however, this is not the case, multiple simultaneous impacts, striking continent as well as ocean floor, would seem to be required.

  14. Ejection-ionization of molecules from free standing graphene

    NASA Astrophysics Data System (ADS)

    Verkhoturov, Stanislav V.; Czerwinski, Bartlomiej; Verkhoturov, Dmitriy S.; Geng, Sheng; Delcorte, Arnaud; Schweikert, Emile A.

    2017-02-01

    We present the first data on emission of -C60 stimulated by single impacts of 50 keV C60+2 on the self-assembled molecular layer of C60 deposited on free standing 2 layer graphene. The yield, Y, of -C60 emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules, we have measured the emission of -C60 from the surface of bulk C60 (Y = 3.7%) and from a single layer of C60 deposited on bulk pyrolytic graphite (Y = 3.3%). To gain insight into the mechanism(s) of ejection, molecular dynamic simulations were performed. The scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C60+2 impacts on graphene plus C60, the C atoms of the projectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energy of the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impact site. The ejection of molecules from the rim is a result of collective movement of the molecules and graphene membrane, where the membrane movement provides the impulse for ejection. The efficient emission of the intact molecular ions implies an effective ionization probability of intact C60. The proposed mechanism of ionization involves the tunneling of electrons from the vibrationally exited area around the hole to the ejecta.

  15. Functional Impact of 14 Single Nucleotide Polymorphisms Causing Missense Mutations of Human α7 Nicotinic Receptor.

    PubMed

    Zhang, Qinhui; Du, Yingjie; Zhang, Jianliang; Xu, Xiaojun; Xue, Fenqin; Guo, Cong; Huang, Yao; Lukas, Ronald J; Chang, Yongchang

    2015-01-01

    The α7nicotinic receptor (nAChR) is a major subtype of the nAChRs in the central nervous system, and the receptor plays an important role in brain function. In the dbSNP database, there are 55 single nucleotide polymorphisms (SNPs) that cause missense mutations of the human α7nAChR in the coding region. In this study, we tested the impact of 14 SNPs that cause missense mutations in the agonist binding site or the coupling region between binding site and channel gate on the receptor function. The wild type or mutant receptors were expressed or co-expressed in Xenopus oocytes, and the agonist-induced currents were tested using two-electrode voltage clamp. Our results demonstrated that 6 mutants were nonfunctional, 4 mutants had reduced current expression, and 1 mutants altered ACh and nicotine efficacy in the opposite direction, and one additional mutant had slightly reduced agonist sensitivity. Interestingly, the function of most of these nonfunctional mutants could be rescued by α7nAChR positive allosteric modulator PNU-120596 and agonist-PAM 4BP-TQS. Finally, when coexpressed with the wild type, the nonfunctional mutants could also influence the receptor function. These changes of the receptor properties by the mutations could potentially have an impact on the physiological function of the α7nAChR-mediated cholinergic synaptic transmission and anti-inflammatory effects in the human SNP carriers. Rescuing the nonfunctional mutants could provide a novel way to treat the related disorders.

  16. Impact of a compound droplet on a flat surface: A model for single cell epitaxy

    PubMed Central

    Tasoglu, Savas; Kaynak, Gozde; Szeri, Andrew J.; Demirci, Utkan; Muradoglu, Metin

    2010-01-01

    The impact and spreading of a compound viscous droplet on a flat surface are studied computationally using a front-tracking method as a model for the single cell epitaxy. This is a technology developed to create two-dimensional and three-dimensional tissue constructs cell by cell by printing cell-encapsulating droplets precisely on a substrate using an existing ink-jet printing method. The success of cell printing mainly depends on the cell viability during the printing process, which requires a deeper understanding of the impact dynamics of encapsulated cells onto a solid surface. The present study is a first step in developing a model for deposition of cell-encapsulating droplets. The inner droplet representing the cell, the encapsulating droplet, and the ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters to probe the deformation and rate of deformation of the encapsulated cell, which are both hypothesized to be related to cell damage. The deformation of the inner droplet consistently increases: as the Reynolds number increases; as the diameter ratio of the encapsulating droplet to the cell decreases; as the ratio of surface tensions of the air-solution interface to the solution-cell interface increases; as the viscosity ratio of the cell to encapsulating droplet decreases; or as the equilibrium contact angle decreases. It is observed that maximum deformation for a range of Weber numbers has (at least) one local minimum at We=2. Thereafter, the effects of cell deformation on viability are estimated by employing a correlation based on the experimental data of compression of cells between parallel plates. These results provide insight into achieving optimal parameter ranges for maximal cell viability during cell printing. PMID:20838481

  17. Impact of a compound droplet on a flat surface: A model for single cell epitaxy

    NASA Astrophysics Data System (ADS)

    Tasoglu, Savas; Kaynak, Gozde; Szeri, Andrew J.; Demirci, Utkan; Muradoglu, Metin

    2010-08-01

    The impact and spreading of a compound viscous droplet on a flat surface are studied computationally using a front-tracking method as a model for the single cell epitaxy. This is a technology developed to create two-dimensional and three-dimensional tissue constructs cell by cell by printing cell-encapsulating droplets precisely on a substrate using an existing ink-jet printing method. The success of cell printing mainly depends on the cell viability during the printing process, which requires a deeper understanding of the impact dynamics of encapsulated cells onto a solid surface. The present study is a first step in developing a model for deposition of cell-encapsulating droplets. The inner droplet representing the cell, the encapsulating droplet, and the ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters to probe the deformation and rate of deformation of the encapsulated cell, which are both hypothesized to be related to cell damage. The deformation of the inner droplet consistently increases: as the Reynolds number increases; as the diameter ratio of the encapsulating droplet to the cell decreases; as the ratio of surface tensions of the air-solution interface to the solution-cell interface increases; as the viscosity ratio of the cell to encapsulating droplet decreases; or as the equilibrium contact angle decreases. It is observed that maximum deformation for a range of Weber numbers has (at least) one local minimum at We=2. Thereafter, the effects of cell deformation on viability are estimated by employing a correlation based on the experimental data of compression of cells between parallel plates. These results provide insight into achieving optimal parameter ranges for maximal cell viability during cell printing.

  18. The impact of Doppler lidar wind observations on a single-level meteorological analysis

    NASA Technical Reports Server (NTRS)

    Riishojgaard, L. P.; Atlas, R.; Emmitt, G. D.

    2001-01-01

    Through the use of observation operators, modern data assimilation systems have the capability to ingest observations of quantities that are not themselves model variables, but are mathematically related to those variables. An example of this are the so-called LOS (line of sight) winds that a Doppler wind Lidar can provide. The model - or data assimilation system - needs information about both components of the horizontal wind vectors, whereas the observations in this case only provide the projection of the wind vector onto a given direction. The analyzed value is then calculated essentially based on a comparison between the observation itself and the model-simulated value of the observed quantity. However, in order to assess the expected impact of such an observing system, it is important to examine the extent to which a meteorological analysis can be constrained by the LOS winds. The answer to this question depends on the fundamental character of the atmospheric flow fields that are analyzed, but more importantly it also depends on the real and assumed error covariance characteristics of these fields. A single-level wind analysis system designed to explore these issues has been built at the NASA Data Assimilation Office. In this system, simulated wind observations can be evaluated in terms of their impact on the analysis quality under various assumptions about their spatial distribution and error characteristics and about the error covariance of the background fields. The basic design of the system will be presented along with experimental results obtained with it. In particular, the value of simultaneously measuring LOS winds along two different directions for a given location will be discussed.

  19. Impact of hybrid SPECT/CT imaging on the detection of single parathyroid adenoma

    NASA Astrophysics Data System (ADS)

    Morrison, Antony; Brennan, Patrick C.; Reed, Warren; Pietrzyk, Mariusz; Schembri, Geoff; Bailey, Elizabeth; Roach, Paul; Evanoff, Michael; Kench, Peter L.

    2011-03-01

    Objective: The aim of this investigation is to determine the impact of hybrid single photon emission computed tomography/computed tomography (SPECT/CT) on the detection of parathyroid adenoma. Materials and methods: 16 patients presented with suspected parathyroid adenoma localised within the neck. All patients were injected with Tc-99m sestamibi and were scanned with a GE Infinia Hawkeye SPECT/CT. There were six negative and ten positive confirmed cases. Five expert radiologists specializing in nuclear medicine were asked to report on the 16 planar and SPECT data sets and were then asked to report on the same randomly ordered data sets with the addition of CT. Receiver operating characteristic (ROC) analysis was performed using the Dorfman-Berbaum-Metz multireadermulticase methodology and sensitivity and specificity values were generated. A significance level of p <= 0.05 was set for all comparisons. Results: ROC analysis demonstrated an AUC of 0.64 and 0.69 for SPECT and SPECT/CT respectively (p = 0.31). Mean sensitivity scores increased from 0.64 to 0.80 (p = 0.17) and specificity scores decreased from 0.57 to 0.40 (p = 0.17) with the addition of the CT data. Conclusion: This preliminary investigation suggests that extra CT information may increase lesion detection as well as false positive rates for SPECT-based investigations of a single parathyroid adenoma. However the difference in diagnostic efficacy between the two groups was not found to be statistically significant therefore requiring further investigation. These findings have implications beyond the clinical situation described here.

  20. A new method for describing soil detachment by a single waterdrop impact

    NASA Astrophysics Data System (ADS)

    Ryżak, Magdalena; Bieganowski, Andrzej

    2013-04-01

    Soil is one of the elements that determine the water cycle due to its retention ability; it is also a landscape-shaping element and the basis of agricultural production. It is a limited and non-renewable element of the geographical environment at a certain stage of Earth's history, and should therefore be protected. One of the physical processes of soil degradation is water erosion. In the first phase, there is detachment of particles eroded from the surface, i.e. splash. Depending on the energy and intensity of precipitation and the terrain features, this can lead to runoff, in the next stage, and in extreme cases to rainwash of soil. Methods used previously in studies of splash were mainly based on weight measurements of collected soil material that had splashed. This requires treatment of the total material collected, as the mass of soil displaced by the impact a single drop is so small that it is not measurable even when using a very accurate weight. In the proposed method of measurements, the splashed soil material was collected on filter paper, allowing determination of the distance over which the displacement of the particles occurred followed by an analysis of the soil material displaced at a given distance under the microscope. As a result of the measurements, the relationships between the following parameters were determined: - the distances of splash, - the surface areas of splash tracks into relation to distance, - the surface area of the solid phase transported over a given distance, - the ratio of the solid phase to the splash track area in relation to distance. Differences were observed between the results obtained for both the soils of different granulometric composition as well as for the same soil with varying humidity. The use of optical methods in the analysis of microscopic images gave new opportunities to describe the initial phase of water erosion - splash. It facilitates analysis of splash (in the laboratory) caused by a single drop of

  1. Impact of Initial Norwood Shunt Type on Right Ventricular Deformation: The Single Ventricle Reconstruction Trial

    PubMed Central

    Hill, Garick D.; Frommelt, Peter C.; Stetler, Jessica; Campbell, M. Jay; Cohen, Meryl S.; Kharouf, Rami; Lai, Wyman W.; Levine, Jami C.; Lu, Jimmy C.; Menon, Shaji C.; Slesnick, Timothy C.; Wong, Pierre C.; Saudek, David E.

    2015-01-01

    Background The Single Ventricle Reconstruction (SVR) trial demonstrated a transplant-free survival advantage at 12 month follow up for patients with right-ventricle-pulmonary-artery shunt (RVPAS) at Norwood procedure versus modified Blalock-Taussig shunt (MBTS) but similar survival and decreased global right ventricular (RV) function on longer term follow-up. The impact of the required ventriculotomy for the RVPAS remains unknown. We compared echo-derived RV deformation indices after stage 2 procedure in survivors with single RV anomalies enrolled in the SVR trial. Methods Global and regional RV systolic longitudinal and circumferential strain and strain rate, ejection fraction, and short axis % fractional area change were all derived by speckle tracking echocardiography from protocol echocardiograms performed at 14.3±1.2 months. Student’s t-test or Wilcoxon rank sum test was used to compare groups. Results The cohort included 275 subjects (129 MBTS and 146 RVPAS). Longitudinal deformation could be quantified in 214 (78%) subjects and circumferential measures in 182 (66%) subjects. RV ejection fraction and % fractional area change did not differ between groups. There were no significant differences between groups for global or regional longitudinal deformation. Circumferential indices showed abnormalities in deformation in the RVPAS group with decreased global circumferential strain (p=0.05), strain rate (p=0.09) and anterior regional strain rate (p=0.07) that approached statistical significance. Conclusion RV myocardial deformation at 14 months, after stage 2 procedure, is not significantly altered by the type of initial shunt placed. However, abnormal trends were appreciated in circumferential deformation for the RVPAS group in the area of ventriculotomy that may represent early myocardial dysfunction. These data provide a basis for longer-term RV deformation assessment in survivors after Norwood procedure. PMID:25690998

  2. A Sturmian approach for ionization processes of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Ancarani, Lorenzo Ugo

    2016-09-01

    The Sturmian approach, using Generalized Sturmian Functions (GSF), is a spectral method that has been applied successfully both for structure calculations and for the study of several ionization processes with atomic targets. GSF are two-body functions that solve a Sturm-Liouville problem. They can be used as a basis set to deal with two- or three-body bound or scattering problems. By construction, the whole GSF set can be chosen to possess asymptotic conditions appropriate for the physical problem under consideration: bound-type behavior with a specific asymptotic charge are chosen for bound states, while - for example - outgoing behavior with a given adequate energy are taken for solving scattering processes. This important intrinsic property makes GSF basis sets - and thus the whole approach - computationally efficient. In the case of ionization, a specific feature of our methodology is that the scattering amplitude and the corresponding cross section are extracted directly from the asymptotic part of the scattering function without requiring the evaluation of a matrix element. Compared to the case of many-electron atoms several extra challenges occur for molecules: the scattering problem is generally multicenter and highly non-central, and the molecular orientation must also be taken into account. These features make the computational task much more cumbersome and expensive than for atomic targets. The Sturmian approach with GSF has been recently extended and implemented to study single ionization of small polyatomic molecules by photon and electron impact. Results for a variety of single and double ionization processes will be presented. This work has been done in collaboration with G. Gasaneo, D.M. Mitnik, J.M. Randazzo, F.D. Colavecchia, M.J. Ambrosio, J.A. Del Punta and C.M. Granados-Castro. We would like to acknowledge the CNRS funding (PICS project N. 06304).

  3. A singly charged ion source for radioactive {sup 11}C ion acceleration

    SciTech Connect

    Katagiri, K.; Noda, A.; Nagatsu, K.; Nakao, M.; Hojo, S.; Muramatsu, M.; Suzuki, K.; Wakui, T.; Noda, K.

    2016-02-15

    A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive {sup 11}C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source was found to have favorable performance as a singly charged ion source.

  4. A singly charged ion source for radioactive 11C ion acceleration

    NASA Astrophysics Data System (ADS)

    Katagiri, K.; Noda, A.; Nagatsu, K.; Nakao, M.; Hojo, S.; Muramatsu, M.; Suzuki, K.; Wakui, T.; Noda, K.

    2016-02-01

    A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive 11C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source was found to have favorable performance as a singly charged ion source.

  5. Oxygen reduction mediated by single nanodroplets containing attomoles of vitamin B12: electrocatalytic nano-impacts method.

    PubMed

    Cheng, Wei; Compton, Richard G

    2015-06-08

    We report the use of single Vitamin B12 nanodroplets to mediate the reduction of oxygen in neutral buffer. Electron transfer to single Vitamin B12 nanodroplets is observed using the nano-impacts method and shown to be quantitative. The mechanism of mediated oxygen reduction by single VB12 droplets is revealed as via both Co(II) and Co(I) reduced from Co(III) in VB12 through one or two electron transfer followed by the four-electron reduction of oxygen.

  6. Comparison of continuous and discontinuous collisional bumpers: Dimensionally scaled impact experiments into single wire meshes

    NASA Technical Reports Server (NTRS)

    Hoerz, Friedrich; Cintala, Mark; See, Thomas; Bernhard, Ronald; Cardenas, Frank; Davidson, William; Haynes, Jerry

    1992-01-01

    An experimental inquiry into the utility of discontinuous bumpers was conducted to investigate the collisional outcomes of impacts into single grid-like targets and to compare the results with more traditional bumper designs that employ continuous sheet stock. We performed some 35 experiments using 6.3 and 3.2 mm diameter spherical soda-lime glass projectiles at low velocities (less than 2.5 km/s) and 13 at velocities between 5 and 6 km/s, using 3.2 mm spheres only. The thrust of the experiments related to the characterization of collisional fragments as a function of target thickness or areal shield mass of both bumper designs. The primary product of these experiments was witness plates that record the resulting population of collisional fragments. Substantial interpretive and predictive insights into bumper performance were obtained. All qualitative observations (on the witness plates) and detailed measurements of displaced masses seem simply and consistently related only to bumper mass available for interaction with the impactor. This renders the grid bumper into the superior shield design. These findings present evidence that discontinuous bumpers are a viable concept for collisional shields, possibly superior to continuous geometries.

  7. Numerical analysis of single particle impact in the context of Cold Spray: a new adhesion model

    NASA Astrophysics Data System (ADS)

    Profizi, P.; Combescure, A.; Ogawa, K.

    2016-03-01

    A new adhesion model for numerical simulation of single particle impact in the context of Cold Spray is introduced. As in other studies, cohesive forces are put between the particle and substrate to account for adhesion. In this study however, the forces are put only when a local physical criterion is met. The physical phenomenon most often attributed to Cold Spray adhesion is a shear stress instability. The Johnson-Cook material law is used with a shear damage softening law to enable strong localization at the interface without the need for an extremely fine mesh. This localization is then detected as a drop in local yield stress value by the algorithm, which then implements a local cohesive force. The evolution of this cohesive force is defined by an energy dissipative cohesive model, using a surface adhesion energy as a material parameter. Each cohesive link is broken once all its associated surface energy is dissipated. A criterion on the damage value is also used to break a cohesive bond prematurely, to account for the effect of erosion at higher speeds. This model is found to reproduce the Cold Spray-like adhesion behavior with observed critical and maximum speeds.

  8. Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta

    USGS Publications Warehouse

    Krogh, T.E.; Kamo, S.L.; Bohor, B.F.

    1993-01-01

    UPb isotopic dating of single 1-3 ??g zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 ?? 5 Ma primary age for a component of the target site, white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 ?? 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With UPb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age. ?? 1993.

  9. Fingerprinting the K/T impact site and determining the time of impact by U-Pb dating of single shocked zircons from distal ejecta

    NASA Technical Reports Server (NTRS)

    Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

    1993-01-01

    U-Pb isotopic dating of single 1 - 3 micrograms zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 +/- 5 Ma primary age for a component of the target site, while those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 +/- 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With U-Pb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age.

  10. Comparison Of Quantum Mechanical And Classical Trajectory Calculations Of Cross Sections For Ion-Atom Impact Ionization of Negative - And Positive -Ions For Heavy Ion Fusion Applications

    SciTech Connect

    Igor D. Kaganovich; Edward A. Startsev; Ronald C. Davidson

    2003-05-15

    Stripping cross sections in nitrogen have been calculated using the classical trajectory approximation and the Born approximation of quantum mechanics for the outer shell electrons of 3.2GeV I{sup -} and Cs{sup +} ions. A large difference in cross section, up to a factor of six, calculated in quantum mechanics and classical mechanics, has been obtained. Because at such high velocities the Born approximation is well validated, the classical trajectory approach fails to correctly predict the stripping cross sections at high energies for electron orbitals with low ionization potential.

  11. The Impact of Welfare Benefits on Single Motherhood and Headship of Young Women: Evidence from the Census

    ERIC Educational Resources Information Center

    Blau, Francine D.; Kahn, Lawrence M.; Waldfogel, Jane

    2004-01-01

    This paper uses data from the 1970, 1980, and 1990 Censuses to investigate the impact of welfare benefits across Metropolitan Statistical Areas (MSAs) on the incidence of single motherhood and headship for young women. A contribution of the paper is the inclusion of both MSA fixed effects and MSA-specific time trends to account for fixed and…

  12. Effect of Compton scattering on the double-to-single photoionization ratio in helium

    NASA Astrophysics Data System (ADS)

    Sagurton, M.; Bartlett, R. J.; Samson, J. A. R.; He, Z. X.; Morgan, D.

    1995-10-01

    The effect of Compton scattering on the ratio of double-to-single ionization from photon impact in helium has been measured for 2.1<=hν<=5.5 keV using a time-of-flight ion spectrometer with a high relative collection efficiency for Compton ions. Single ionization from Compton scattering is found to contribute measurably to a reduction in the ionization ratio for hν>~3.5 keV. Our measurements are compared with predictions based on recent calculations of the single and double ionization cross sections for photoabsorption and Compton scattering by Hino et al. [Phys. Rev. A 48, 1271 (1993), Phys. Rev. Lett. 72, 1620 (1994)], Andersson et al. [Phys. Rev. Lett. 71, 50 (1993)], and Surić et al. [Phys. Rev. Lett. 73, 790 (1994)].

  13. Analytical instruments, ionization sources, and ionization methods

    DOEpatents

    Atkinson, David A.; Mottishaw, Paul

    2006-04-11

    Methods and apparatus for simultaneous vaporization and ionization of a sample in a spectrometer prior to introducing the sample into the drift tube of the analyzer are disclosed. The apparatus includes a vaporization/ionization source having an electrically conductive conduit configured to receive sample particulate which is conveyed to a discharge end of the conduit. Positioned proximate to the discharge end of the conduit is an electrically conductive reference device. The conduit and the reference device act as electrodes and have an electrical potential maintained between them sufficient to cause a corona effect, which will cause at least partial simultaneous ionization and vaporization of the sample particulate. The electrical potential can be maintained to establish a continuous corona, or can be held slightly below the breakdown potential such that arrival of particulate at the point of proximity of the electrodes disrupts the potential, causing arcing and the corona effect. The electrical potential can also be varied to cause periodic arcing between the electrodes such that particulate passing through the arc is simultaneously vaporized and ionized. The invention further includes a spectrometer containing the source. The invention is particularly useful for ion mobility spectrometers and atmospheric pressure ionization mass spectrometers.

  14. Matrix-free UV-laser desorption/ionization (LDI) mass spectrometric imaging at the single-cell level: distribution of secondary metabolites of Arabidopsis thaliana and Hypericum species.

    PubMed

    Hölscher, Dirk; Shroff, Rohit; Knop, Katrin; Gottschaldt, Michael; Crecelius, Anna; Schneider, Bernd; Heckel, David G; Schubert, Ulrich S; Svatos, Ales

    2009-12-01

    The present paper describes matrix-free laser desorption/ionisation mass spectrometric imaging (LDI-MSI) of highly localized UV-absorbing secondary metabolites in plant tissues at single-cell resolution. The scope and limitations of the method are discussed with regard to plants of the genus Hypericum. Naphthodianthrones such as hypericin and pseudohypericin are traceable in dark glands on Hypericum leaves, placenta, stamens and styli; biflavonoids are also traceable in the pollen of this important phytomedical plant. The highest spatial resolution achieved, 10 microm, was much higher than that achieved by commonly used matrix-assisted laser desorption/ionization (MALDI) imaging protocols. The data from imaging experiments were supported by independent LDI-TOF/MS analysis of cryo-sectioned, laser-microdissected and freshly cut plant material. The results confirmed the suitability of combining laser microdissection (LMD) and LDI-TOF/MS or LDI-MSI to analyse localized plant secondary metabolites. Furthermore, Arabidopsis thaliana was analysed to demonstrate the feasibility of LDI-MSI for other commonly occurring compounds such as flavonoids. The organ-specific distribution of kaempferol, quercetin and isorhamnetin, and their glycosides, was imaged at the cellular level.

  15. Agronomic and environmental impacts of a single application of heat-dried sludge on an Alfisol.

    PubMed

    Gavalda, D; Scheiner, J D; Revel, J C; Merlina, G; Kaemmerer, M; Pinelli, E; Guiresse, M

    2005-05-01

    A field experiment was conducted on Alfisols in South-West France to assess the agronomic and environmental impacts of a single application of heat-dried sludge pellets at 11.1 Mg dry matter ha-1. The sludge pellets, with a moisture level of 9.5%, were spread on an irrigated crop of maize (Zea mays L.). This treatment was compared with inorganic fertilization (urea and diammonium phosphate mixed with KCl). Soil properties, yield and the composition of maize and the quality of drained water were monitored over 1 year to detect any changes resulting from sludge application. Amongst several determined soil properties, only two were significantly modified by the sludge application: The nitric nitrogen stock of the soil was higher in the inorganic fertilized plot, whereas Olsen-P soil content was higher in the sludge-amended plot. Agronomic recovery rates of N and P added by sludge were high: For the first crop following application, total amounts of N and P supplied by the sludge had the same efficiency as approximately 45% of the N and P amounts supplied by inorganic fertilizer. This ratio was 7% for the N uptake by the second maize crop. The quality and quantity of maize were equally good with both types of fertilization. During the 2 years following sludge spreading, N leaching remained as low in the sludged plot as in the inorganically fertilized one. The Cu, Zn, Cr, Cd, Pb and Ni composition of the drainage water was affected by neither of the types of amendment. From the heavy-metal contents of the soil, water and maize monitored over 1 year in the field experiment and from literature data for cow manure and atmospheric emissions, a theoretical balance between crop soil heavy-metal input and output over one century was drawn up. The long-term impact of cow manure on Zn, Ni and Cr in soil is higher than that of the studied heat-dried sludge. Obviously, sludge tended to cause a strong increase in soil Cu storage, valued for these soils, which are otherwise very Cu

  16. A single frequency component-based re-estimated MUSIC algorithm for impact localization on complex composite structures

    NASA Astrophysics Data System (ADS)

    Yuan, Shenfang; Bao, Qiao; Qiu, Lei; Zhong, Yongteng

    2015-10-01

    The growing use of composite materials on aircraft structures has attracted much attention for impact monitoring as a kind of structural health monitoring (SHM) method. Multiple signal classification (MUSIC)-based monitoring technology is a promising method because of its directional scanning ability and easy arrangement of the sensor array. However, for applications on real complex structures, some challenges still exist. The impact-induced elastic waves usually exhibit a wide-band performance, giving rise to the difficulty in obtaining the phase velocity directly. In addition, composite structures usually have obvious anisotropy, and the complex structural style of real aircrafts further enhances this performance, which greatly reduces the localization precision of the MUSIC-based method. To improve the MUSIC-based impact monitoring method, this paper first analyzes and demonstrates the influence of measurement precision of the phase velocity on the localization results of the MUSIC impact localization method. In order to improve the accuracy of the phase velocity measurement, a single frequency component extraction method is presented. Additionally, a single frequency component-based re-estimated MUSIC (SFCBR-MUSIC) algorithm is proposed to reduce the localization error caused by the anisotropy of the complex composite structure. The proposed method is verified on a real composite aircraft wing box, which has T-stiffeners and screw holes. Three typical categories of 41 impacts are monitored. Experimental results show that the SFCBR-MUSIC algorithm can localize impact on complex composite structures with an obviously improved accuracy.

  17. Resonant ionization spectroscopy of autoionizing Rydberg states in cobalt and redetermination of its ionization potential

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Gottwald, T.; Mattolat, C.; Wendt, K.

    2017-04-01

    Multi-step resonance ionization spectroscopy of cobalt has been performed using a hot-cavity laser ion source and three Ti:Sapphire lasers. The photoionization spectra revealed members of five new autoionizing Rydberg series that originate from three different lower levels of 3d 74s5s h 4F9/2, 3d 74s4d f 4G11/2, and 3d 74s4d f 4H13/2 and converge to the first four excited states of singly ionized Co. The analyses of the Rydberg series yield 63 564.689 ± 0.036 cm‑1 as the first ionization potential of Co, which is an order of magnitude more accurate than the previous estimation. Using a three-step resonance ionization scheme that employs an autoinizing Rydberg state in the last transition, we obtained an overall ionization efficiency of about 18% for Co. ).

  18. Resonant effects in above-threshold ionization

    NASA Astrophysics Data System (ADS)

    Hertlein, Marcus P.

    2000-09-01

    The ionization of noble gases in high intensity laser fields produces an electron spectrum with characteristic peaks corresponding to atomic levels of the atom. While many of the features in the low energy part of the spectrum have been explained qualitatively, current models are incomplete and are not able to account for the recurrence of ionization probability for higher energy electrons. In particular, one of the basic questions arising is the importance of multiple ionization in these spectra. While the light intensities are in the regime where multiple ionization is known to occur, it was not clear whether the higher energy (or plateau) electrons are a result of this, and whether multiple ionization even leaves a signature in the electron spectrum. In this dissertation, we use several experimental techniques to explore this problem in argon. Our results show that although multiple ionization occurs, electrons from this process do not appear in the observed electron spectrum. Furthermore, the appearance intensities of the peaks visible in the plateau region of the electron spectrum and of the resonance peaks in the well- understood low energy part show a strong correlation, suggestion a common origin of production. Accurate computer simulations of the process, using a single- active-electron model, reproduce all essential features of the experimental spectra. Our results support the conclusion that all high energy electrons observed in our experiments can be explained with single-electron effects.

  19. Quantum-mechanical predictions of DNA and RNA ionization by energetic proton beams.

    PubMed

    Galassi, M E; Champion, C; Weck, P F; Rivarola, R D; Fojón, O; Hanssen, J

    2012-04-07

    Among the numerous constituents of eukaryotic cells, the DNA macromolecule is considered as the most important critical target for radiation-induced damages. However, up to now ion-induced collisions on DNA components remain scarcely approached and theoretical support is still lacking for describing the main ionizing processes. In this context, we here report a theoretical description of the proton-induced ionization of the DNA and RNA bases as well as the sugar-phosphate backbone. Two different quantum-mechanical models are proposed: the first one based on a continuum distorted wave-eikonal initial state treatment and the second perturbative one developed within the first Born approximation with correct boundary conditions (CB1). Besides, the molecular structure information of the biological targets studied here was determined by ab initio calculations with the Gaussian 09 software at the restricted Hartree-Fock level of theory with geometry optimization. Doubly, singly differential and total ionization cross sections also provided by the two models were compared for a large range of incident and ejection energies and a very good agreement was observed for all the configurations investigated. Finally, in comparison with the rare experiment, we have noted a large underestimation of the total ionization cross sections of uracil impacted by 80 keV protons,whereas a very good agreement was shown with the recently reported ionization cross sections for protons on adenine, at both the differential and the total scale.

  20. Ionization and positronium formation in noble gases

    SciTech Connect

    Marler, J.P.; Sullivan, J.P.; Surko, C.M.

    2005-02-01

    Absolute measurements are presented for the positron-impact cross sections for direct ionization and positronium formation of noble gas atoms in the range of energies from threshold to 90 eV. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. The current data show generally good, quantitative agreement with previous measurements taken using a qualitatively different method. However, significant differences in the cross sections for both direct ionization and positronium formation are also observed. An analysis is presented that yields another, independent measurement of the direct ionization and positronium formation cross sections that is in agreement with the present, direct measurements to within {+-}10% for argon, krypton, and xenon. Comparison with available theoretical predictions yields good quantitative agreement for direct ionization cross sections, and qualitative agreement in the case of positronium formation.