Science.gov

Sample records for neutron pairing gap

  1. New model of the average neutron and proton pairing gaps

    NASA Astrophysics Data System (ADS)

    Madland, David G.; Nix, J. Rayford

    1988-01-01

    By use of the BCS approximation applied to a distribution of dense, equally spaced levels, we derive new expressions for the average neutron pairing gap ¯gD n and average proton pairing gap ¯gD p. These expressions, which contain exponential terms, take into account the dependencies of ¯gD n and ¯gD p upon both the relative neutron excess and shape of the nucleus. The three constants that appear are determined by a least-squares adjustment to experimental pairing gaps obtained by use of fourth-order differences of measured masses. For this purpose we use the 1986 Audi-Wapstra mid-stream mass evaluation and take into account experimental uncertainties. Our new model explains not only the dependencies of ¯gD n and ¯gD p upon relative neutron excess and nuclear shape, but also the experimental result that for medium and heavy nuclei ¯gD n is generally smaller than ¯gD p. We also introduce a new expression for the average residual neutron-proton interaction energy ¯gd that appears in the masses of odd-odd nuclei, and determine the constant that appears by an analogous least-squares adjustment to experimental mass differences. Our new expressions for ¯gD n, ¯gD p and ¯gd should permit extrapolation of these quantities to heavier nuclei and to nuclei farther removed from the valley of β stability than do previous parameterizations.

  2. Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Changizi, S. A.; Qi, Chong; Wyss, R.

    2015-08-01

    The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single-j shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula ΔC(3) (N) =1/2 [ B (N, Z) + B (N - 2, Z) - 2 B (N - 1, Z) ] can provide a good measure of the neutron pairing gap in even-N nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around N = Z. We also show that the strength of ΔC(3) (N) can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of ΔC(3) (N) in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.

  3. Induced Pairing Interaction in Neutron Star Matter

    NASA Astrophysics Data System (ADS)

    Lombardo, U.; Schulze, H.-J.; Zuo, W.

    2013-01-01

    The three superfluid phases supposed to occur in neutron stars are reviewed in the framework of the generalized BCS theory with the induced interaction. The structure of neutron stars characterized by beta-stable asymmetric nuclear matter in equilibrium with the gravitational force discloses new aspects of the pairing mechanism. Some of them are discussed in this report, in particular the formation in dense matter of Cooper pairs in the presence of three-body forces and the interplay between repulsive and attractive polarization effects on isospin T = 1 Cooper pairs embedded into the neutron and proton environment. Quantitative estimates of the energy gaps are reported and their sensitivity to the medium effects, i.e., interaction and polarization, is explored.

  4. Neutron-proton pairing correlations in odd mass systems

    SciTech Connect

    Fellah, M. Allal, N. H.; Oudih, M. R.

    2015-03-30

    An expression of the ground-state which describes odd mass systems within the BCS approach in the isovector neutron-proton pairing case is proposed using the blocked level technique. The gap equations as well as the energy expression are then derived. It is shown that they exactly generalize the expressions obtained in the pairing between like-particles case. The various gap parameters and the energy are then numerically studied as a function of the pairing-strength within the schematic one-level model.

  5. Pair correlations in neutron-rich nuclei

    SciTech Connect

    Esbensen, H.

    1995-08-01

    We started a program to study the ground-state properties of heavy, neutron-rich nuclei using the Hartree-Fock-Bogolyubov (HFB) approximation. This appears at present to be the most realistic approach for heavy nuclei that contain many loosely bound valence neutrons. The two-neutron density obtained in this approach can be decomposed into two components, one associated with the mean field and one associated with the pairing field. The latter has a structure that is quite similar to the pair-density obtained by diagonalizing the Hamiltonian for a two-neutron halo, which was studied earlier. This allows comparison of the HFB solutions against numerically exact solutions for two-neutron halos. This work is in progress. We intend to apply the HFB method to predict the ground-state properties of heavier, more neutron-rich nuclei that may be produced at future radioactive beam facilities.

  6. Spatial dependence of the pairing gap in superfluid nuclei

    SciTech Connect

    Vigezzi, E.; Pastore, A.; Potel, G.; Barranco, F.

    2009-05-04

    The spatial structure of pairing correlations in {sup 120}Sn is investigated making use of both the bare nucleon-nucleon potential and the interaction induced by the exchange of collective vibrations, taking into account self-energy effects. The resulting pairing gap is strongly peaked on the nuclear surface.

  7. Pairing in high-density neutron matter including short- and long-range correlations

    NASA Astrophysics Data System (ADS)

    Ding, D.; Rios, A.; Dussan, H.; Dickhoff, W. H.; Witte, S. J.; Carbone, A.; Polls, A.

    2016-08-01

    Pairing gaps in neutron matter need to be computed in a wide range of densities to address open questions in neutron-star phenomenology. Traditionally, the Bardeen-Cooper-Schrieffer approach has been used to compute gaps from bare nucleon-nucleon interactions. Here we incorporate the influence of short- and long-range correlations in the pairing gaps. Short-range correlations are treated, including the appropriate fragmentation of single-particle states, and substantially suppress the gaps. Long-range correlations dress the pairing interaction via density and spin modes and provide a relatively small correction. We use different interactions, some with three-body forces, as a starting point to control for any systematic effects. Results are relevant for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A.

  8. Pairing in high-density neutron matter including short- and long-range correlations

    NASA Astrophysics Data System (ADS)

    Ding, Dong; Rios, Arnau; Dussan, Helber; Dickhoff, Willem; Witte, Sam; Polls, Artur

    2016-03-01

    To address open questions in neutron star phenomenology, pairing gaps of 1S0 and 3P2 -3F2 channels in a wide range of densities has been calculated using three different interactions (AV18 CDbonn N3LO). Traditionally, the Bardeen-Cooper-Schrieffer(BCS) approach has been used to compute gaps from bare nucleon-nucleon interactions. Here, we incorporate the influence of short- and long-range correlations in the pairing gaps. Short-range correlations (SRC) are treated including the appropriate fragmentation of single-particle states, and they suppress the gaps substantially. Long-range correlations(LRC) dress the pairing interaction via density and spin modes, and provide a relatively small correction. Results are relevant and parametrized in a user friendly way for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A.

  9. Pair cascades in the magnetospheres of strongly magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Medin, Zach; Lai, Dong

    2010-08-01

    We present numerical simulations of electron-positron pair cascades in the magnetospheres of magnetic neutron stars for a wide range of surface fields (Bp = 1012-1015 G), rotation periods (0.1-10 s) and field geometries. This has been motivated by the discovery in recent years of a number of radio pulsars with inferred magnetic fields comparable to those of magnetars. Evolving the cascade generated by a primary electron or positron after it has been accelerated in the inner gap of the magnetosphere, we follow the spatial development of the cascade until the secondary photons and electron-positron pairs leave the magnetosphere, and we obtain the pair multiplicity and the energy spectra of the cascade pairs and photons under various conditions. Going beyond previous works, which were restricted to weaker fields (B <~ afew × 1012 G), we have incorporated in our simulations detailed treatments of physical processes that are potentially important (especially in the high-field regime) but were either neglected or crudely treated before, including photon splitting with the correct selection rules for photon polarization modes, one-photon pair production into low Landau levels for the e+/-, and resonant inverse Compton scattering from polar cap hotspots. We find that even for B >> BQ = 4 × 1013 G, photon splitting has a small effect on the multiplicity of the cascade since a majority of the photons in the cascade cannot split. One-photon decay into e+ e- pairs at low Landau levels, however, becomes the dominant pair production channel when B >~ 3 × 1012 G; this tends to suppress synchrotron radiation so that the cascade can develop only at a larger distance from the stellar surface. Nevertheless, we find that the total number of pairs and their energy spectrum produced in the cascade depend mainly on the polar cap voltage BpP-2, and are weakly dependent on Bp (and P) alone. We discuss the implications of our results for the radio pulsar death line and for the hard X

  10. Neutron decay of the Giant Pairing Vibration in 15C

    NASA Astrophysics Data System (ADS)

    Cavallaro, M.; Agodi, C.; Assié, M.; Azaiez, F.; Cappuzzello, F.; Carbone, D.; de Séréville, N.; Foti, A.; Pandola, L.; Scarpaci, J. A.; Sgouros, O.; Soukeras, V.

    2016-06-01

    The neutron decay of the resonant states of light neutron-rich nuclei is an important and poorly explored property, useful to extract valuable nuclear structure information. The neutron decay of the 15C resonances populated via the two-neutron transfer reaction 13C(18O,16O n) at 84 MeV incident energy is studied using an innovative technique which couples the MAGNEX magnetic spectrometer and the EDEN neutron detector array. The data show that the recently observed 15C Giant Pairing Vibration at 13.7 MeV mainly decays via two-neutron emission.

  11. Pairing gaps in the Hartree-Fock-Bogoliubov theory with the Gogny D1S interaction

    NASA Astrophysics Data System (ADS)

    Robledo, L. M.; Bernard, R.; Bertsch, G. F.

    2012-12-01

    As part of a program to study odd-A nuclei in the Hartree-Fock-Bogoliubov (HFB) theory, we have developed a new calculational tool to find the HFB minima of odd-A nuclei based on the gradient method and using interactions of Gogny's form. The HFB minimization includes both time-even and time-odd fields in the energy functional, avoiding the commonly used “filling approximation”. Here we apply the method to calculate neutron pairing gaps in some representative isotope chains of spherical and deformed nuclei, namely the Z=8,50, and 82 spherical chains and the Z=62 and 92 deformed chains. We find that the gradient method is quite robust, permitting us to carry out systematic surveys involving many nuclei. We find that the time-odd field does not have large effect on the pairing gaps calculated with the Gogny D1S interaction. Typically, adding the T-odd field as a perturbation increases the pairing gap by 100 keV, but the re-minimization brings the gap back down. This outcome is very similar to results reported for the Skyrme family of nuclear energy density functionals. Comparing the calculated gaps with the experimental ones, we find that the theoretical errors have both signs implying that the D1S interaction has a reasonable overall strength. However, we find some systematic deficiencies comparing spherical and deformed chains and comparing the lighter chains with the heavier ones. The gaps for heavy spherical nuclei are too high, while those for deformed nuclei tend to be too low. The calculated gaps of spherical nuclei show hardly any A dependence, contrary to the data. Inclusion of the T-odd component of the interaction does not change these qualitative findings.

  12. New magic nuclei and neutron-proton pairing

    SciTech Connect

    Boboshin, I. N.

    2008-07-15

    Special features of new magic nuclei and their connection with the shell structure are considered. The mechanism of neutron-proton pairing is proposed as a basis for the formation of new magic nuclei. A law of nucleon pairing is introduced. Spin-parity values are explained for a number of odd-odd nuclei.

  13. Neutrino-pair bremsstrahlung in a neutron star crust

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.

    2014-11-01

    Based on the formalism by Kaminker et al. (Astron. Astrophys., 343 (1999) 1009) we derive an analytic approximation for neutrino-pair bremsstrahlung emissivity due to scattering of electrons by atomic nuclei in a neutron star crust of any realistic composition. The emissivity is expressed through the generalized Coulomb logarithm which we fit by introducing an effective potential of electron-nucleus scattering. In addition, we study the conditions at which the neutrino bremsstrahlung in the crust is affected by strong magnetic fields. The results can be applied for modelling of many phenomena in neutron stars, such as thermal relaxation in young isolated neutron stars and in accreting neutron stars with overheated crust in soft X-ray transients.

  14. The measurement of capsule heat transfer gaps using neutron radiography.

    NASA Technical Reports Server (NTRS)

    Thaler, L. A.

    1971-01-01

    The use of neutron radiographs to determine dimensional changes of heat transfer gaps in cylindrical nuclear fueled capsules is described. A method was developed which involves scanning a very fine grained neutron radiograph negative with a recording microdensitometer. The output of the densitometer is recorded on graph paper and the heat transfer gap is plotted as a well-defined optical density change. Calibration of the recording microdensitometer ratio arms permits measurements to be made of the heat transfer optical density change from the microdensitometer trace. Total heat transfer gaps, measured by this method, agree with the physical measurements within plus or minus 0.005 cm over a range of gaps from 0.061 to 0.178 cm.

  15. Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian

    SciTech Connect

    Dukelsky, J; Gueorguiev, V G; Van Isacker, P; Dimitrova, S S; Errea, B; H., S L

    2005-12-02

    The complete exact solution of the T = 1 neutron-proton pairing Hamiltonian is presented in the context of the SO(5) Richardson-Gaudin model with non-degenerate single-particle levels and including isospin-symmetry breaking terms. The power of the method is illustrated with a numerical calculation for {sup 64}Ge for a pf + g{sub 9/2} model space which is out of reach of modern shell-model codes.

  16. Measurement of capsule heat transfer gaps using neutron radiography

    NASA Technical Reports Server (NTRS)

    Thaler, L. A.

    1974-01-01

    A technique is described for measuring heat transfer gaps from neutron radiographs. The method involves scanning the radiograph negative with a recording microdensitometer to obtain a trace of the optical density variation across the diameter of the capsule. The optical density change representing the gap is measured from the microdensitometer trace and related to the physical measurement. Heat transfer gaps from 0.061 to 0.178 cm have been determined by this technique and agree with preassembly physical measurements to plus or minus 0.005 cm.

  17. S-pairing in neutron matter: I. Correlated basis function theory

    NASA Astrophysics Data System (ADS)

    Fabrocini, Adelchi; Fantoni, Stefano; Illarionov, Alexey Yu.; Schmidt, Kevin E.

    2008-05-01

    S-wave pairing in neutron matter is studied within an extension of correlated basis function (CBF) theory to include the strong, short range spatial correlations due to realistic nuclear forces and the pairing correlations of the Bardeen, Cooper and Schrieffer (BCS) approach. The correlation operator contains central as well as tensor components. The correlated BCS scheme of [S. Fantoni, Nucl. Phys. A 363 (1981) 381], developed for simple scalar correlations, is generalized to this more realistic case. The energy of the correlated pair condensed phase of neutron matter is evaluated at the two-body order of the cluster expansion, but considering the one-body density and the corresponding energy vertex corrections at the first order of the Power Series expansion. Based on these approximations, we have derived a system of Euler equations for the correlation factors and for the BCS amplitudes, resulting in correlated nonlinear gap equations, formally close to the standard BCS ones. These equations have been solved for the momentum independent part of several realistic potentials (Reid, Argonne v and Argonne v) to stress the role of the tensor correlations and of the many-body effects. Simple Jastrow correlations and/or the lack of the density corrections enhance the gap with respect to uncorrelated BCS, whereas it is reduced according to the strength of the tensor interaction and following the inclusion of many-body contributions.

  18. Two-Gap Superconductivity in LaNiGa_{2} with Nonunitary Triplet Pairing and Even Parity Gap Symmetry.

    PubMed

    Weng, Z F; Zhang, J L; Smidman, M; Shang, T; Quintanilla, J; Annett, J F; Nicklas, M; Pang, G M; Jiao, L; Jiang, W B; Chen, Y; Steglich, F; Yuan, H Q

    2016-07-01

    The nature of the pairing states of superconducting LaNiC_{2} and LaNiGa_{2} has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a nonunitary triplet pairing state. However, all the allowed nonunitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC_{2}. Here we probe the gap symmetry of LaNiGa_{2} by measuring the London penetration depth, specific heat, and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa_{2}, suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wave function has a triplet spin component but isotropic even parity gap symmetry, yet the overall wave function remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results. PMID:27447519

  19. Two-Gap Superconductivity in LaNiGa2 with Nonunitary Triplet Pairing and Even Parity Gap Symmetry

    NASA Astrophysics Data System (ADS)

    Weng, Z. F.; Zhang, J. L.; Smidman, M.; Shang, T.; Quintanilla, J.; Annett, J. F.; Nicklas, M.; Pang, G. M.; Jiao, L.; Jiang, W. B.; Chen, Y.; Steglich, F.; Yuan, H. Q.

    2016-07-01

    The nature of the pairing states of superconducting LaNiC2 and LaNiGa2 has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a nonunitary triplet pairing state. However, all the allowed nonunitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC2 . Here we probe the gap symmetry of LaNiGa2 by measuring the London penetration depth, specific heat, and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa2 , suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wave function has a triplet spin component but isotropic even parity gap symmetry, yet the overall wave function remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results.

  20. Negative refractive index of metallic cross-I-shaped pairs: origin and evolution with pair gap width.

    PubMed

    Ma, Y G; Wang, X C; Ong, C K

    2008-07-01

    A structured composite of the negative index of refraction was fabricated by one layer of cross-I-shaped metal pairs. In this structure, the electric and magnetic inclusions were effectively integrated into one small unit. We varied the spacing of the cross pair to control the location of the magnetic resonance mode and their intercoupling with the electric mode. The frequency dependences of permittivity, permeability, and refractive indices with different gap widths of the pairs were systematically discussed by free-space measurement as well as numerical simulation. A spacing window dependent on the geometrical parameters was found in which the real part of the refractive index could have a negative value. The one-layer cross-pair pattern proposed in this work can be extended to three-dimensional structures with well-controlled interlayer coupling that will greatly facilitate the fabrication and measurement of negative-index materials in high frequencies. PMID:18764072

  1. Bremsstrahlung pair-production of positrons with low neutron background.

    SciTech Connect

    Lessner, E.

    1998-09-16

    Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed.

  2. Neutron-Proton pairing effect on the thermodynamical quantities of even-even proton-rich nuclei

    NASA Astrophysics Data System (ADS)

    Belabbas, M.; Fellah, M.; Allal, N. H.; Ami, I.

    2012-02-01

    Expressions of the thermodynamical quantities, i.e. the energy E, the entropy S and the heat capacity C are established by including the isovector neutron-proton (np) pairing effect. They are deduced using temperature-dependent gap equations . E, S and C are numerically studied as a function of the temperature for some even-even proton-rich nuclei. The single-particle energies used are those of a Woods-Saxon deformed mean field. It is shown that the isovector pairing effect on E, S and C is non-negligible, not only in the 0 <= T <= Tcnp region (Tcnp being the critical temperature beyond which the np pairing vanishes), but also in the Tcnp <= T <= Tcn region (Tcn being the neutron-system critical temperature).

  3. Density of states in gapped superconductors with pairing-potential impurities

    NASA Astrophysics Data System (ADS)

    Bespalov, Anton; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.

    2016-03-01

    We study the density of states in disordered s -wave superconductors with a small gap anisotropy. We consider disorder in the form of common nonmagnetic scatterers and pairing-potential impurities, which interact with electrons via an electric potential and a local distortion of the superconducting gap. Using quasiclassical Green functions, we determine the bound-state spectrum at a single impurity and the density of states at a finite concentration of impurities. We show that, if the gap is isotropic, an isolated impurity with suppressed pairing supports an infinite number of Andreev states. With growing impurity concentration, the energy-dependent density of states evolves from a sharp gap edge with an impurity band below it to a smeared BCS singularity in the so-called universal limit. Within one spin sector, pairing-potential impurities and weak spin-polarized magnetic impurities have essentially the same effect on the density of states. We note that, if a gap anisotropy is present, the density of states becomes sensitive to ordinary potential disorder, and the existence of Andreev states localized at pairing-potential impurities requires special conditions. An unusual feature related to the anisotropy is a nonmonotonic dependence of the gap edge smearing on impurity concentration.

  4. Molecular Pairing and Fully Gapped Superconductivity in Yb-doped CeCoIn5

    NASA Astrophysics Data System (ADS)

    Erten, Onur; Flint, Rebecca; Coleman, Piers

    2015-01-01

    The recent observation of fully gapped superconductivity in Yb doped CeCoIn5 poses a paradox, for the disappearance of nodes suggests that they are accidental, yet d -wave symmetry with protected nodes is well established by experiment. Here, we show that composite pairing provides a natural resolution: in this scenario, Yb doping drives a Lifshitz transition of the nodal Fermi surface, forming a fully gapped d -wave molecular superfluid of composite pairs. The T4 dependence of the penetration depth associated with the sound mode of this condensate is in accordance with observation.

  5. On limits of ab initio calculations of pairing gap in nuclei

    SciTech Connect

    Saperstein, E. E.; Baldo, M.; Lombardo, U.; Pankratov, S. S.; Zverev, M. V.

    2011-11-15

    A brief review of recent microscopic calculations of nuclear pairing gap is given. A semi-microscopic model is suggested in which the ab initio effective pairing interaction is supplemented with a small phenomenological addendum. It involves a parameter which is universal for all medium and heavy nuclei. Calculations for several isotopic and isotonic chains of semi-magic nuclei confirm the relevance of the model.

  6. Photoproduction of π0-pairs off protons and off neutrons

    NASA Astrophysics Data System (ADS)

    Dieterle, M.; Oberle, M.; Ahrens, J.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Bartolome, P. A.; Beck, R.; Bekrenev, V.; Berghäuser, H.; Braghieri, A.; Branford, D.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.; Costanza, S.; Demissie, B.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Fix, A.; Garni, S.; Glazier, D. I.; Hamilton, D.; Heid, E.; Hornidge, D.; Howdle, D.; Huber, G. M.; Jahn, O.; Jude, T. C.; Käser, A.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Krusche, B.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Maghrbi, Y.; Mancell, J.; Manley, D. M.; Marinides, Z.; McGeorge, J. C.; McNicoll, E.; Mekterovic, D.; Metag, V.; Micanovic, S.; Middleton, D. G.; Mushkarenkov, A.; Nikolaev, A.; Novotny, R.; Ostrick, M.; Otte, P.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Prakhov, S.; Robinson, J.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Sober, D. I.; Starostin, A.; Strub, Th.; Supek, I.; Thiel, M.; Thomas, A.; Unverzagt, M.; Walford, N. K.; Watts, D. P.; Werthmüller, D.; Witthauer, L.

    2015-11-01

    Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π0π0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to ≈ 1550 MeV), where both reactions are dominated by the N(1520)3/2- → Δ(1232)3/2+π decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an N^{star}→ Nσ decay for the proton, while the reaction is dominated by a sequential decay via a Δπ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.

  7. Comparison of photon-photon and photon-magnetic field pair production rates. [in neutron stars

    NASA Technical Reports Server (NTRS)

    Burns, M. L.; Harding, A. K.

    1983-01-01

    Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense (10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field (gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

  8. Neutron-pair transfer in the sub-barrier capture process

    NASA Astrophysics Data System (ADS)

    Sargsyan, V. V.; Scamps, G.; Adamian, G. G.; Antonenko, N. V.; Lacroix, D.

    2013-12-01

    Sub-barrier capture reactions following neutron-pair transfer are proposed to be used for the indirect study of the neutron-neutron correlation in the surface region of a nucleus. The strong effect of dineutron-like cluster transfer stemming from the surface of magic and nonmagic nuclei 18O, 48Ca, 64Ni, 94,96Mo, 100,102,104Ru, 104,106,108Pd, and 112,114,116,118,120,124,132Sn is demonstrated. The dominance of the two-neutron transfer channel in the vicinity of the Coulomb barrier is further supported by time-dependent mean-field approaches.

  9. Biophysical properties of gap junctions between freshly dispersed pairs of mouse pancreatic beta cells.

    PubMed Central

    Pérez-Armendariz, M; Roy, C; Spray, D C; Bennett, M V

    1991-01-01

    Coupling between beta cells through gap junctions has been postulated as a principal mechanism of electrical synchronization of glucose-induced activity throughout the islet of Langerhans. We characterized junctional conductance between isolated pairs of mouse pancreatic beta cells by whole-cell recording with two independent patch-clamp circuits. Most pairs were coupled (67%, n = 155), although the mean junctional conductance (gj) (215 +/- 110 pS) was lower than reported in other tissues. Coupling could be recorded for long periods, up to 40 min. Voltage imposed across the junctional or nonjunctional membranes had no effect on gj. Up to several hours of treatment to increase intracellular cAMP levels did not affect gj. Electrically coupled pairs did not show transfer of the dye Lucifer yellow. Octanol (2 mM) reversibly decreased gj. Lower concentrations of octanol (0.5 mM) and heptanol (0.5 mM) than required to uncouple beta cells decreased voltage-dependent K+ and Ca2+ currents in nonjunctional membranes. Although gj recorded in these experiments would be expected to be provided by current flowing through only a few channels of the unitary conductance previously reported for other gap junctions, no unitary junctional currents were observed even during reversible suppression of gj by octanol. This result suggests either that the single channel conductance of gap junction channels between beta cells is smaller than in other tissues (less than 20 pS) or that the small mean conductance is due to transitions between open and closed states that are too rapid or too slow to be resolved. Images FIGURE 1 FIGURE 5 PMID:2015391

  10. Gapped graphene-based Josephson junction with d-wave pair coupling

    NASA Astrophysics Data System (ADS)

    Goudarzi, H.; Khezerlou, M.; Dezhaloud, T.

    2013-06-01

    The Josephson current passing through a S/I/S gapped graphene-based junction, where superconductivity in the S region is induced by depositing unconventional d-wave superconductor is investigated. The energy levels of massive Dirac fermions are exactly found for Andreev bound states. We illustrate the effect of characteristic of d-wave pairing symmetry on the Andreev bound states and the Josephson current. It is shown that the Josephson current vanishes for special range of superconductivity phase, φ = φ1 - φ2 and the position of the maximum current depends on the mass gap of graphene. The critical supercurrent varies in an oscillatory manner as function of the barrier strength, so that the period of oscillations does not change by increasing the effective mass of quasiparticles.

  11. Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures

    SciTech Connect

    Perina, Jan Jr.; Centini, Marco; Sibilia, Concita; Bertolotti, Mario; Scalora, Michael

    2006-03-15

    We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.

  12. Binding energies of electrons by nitrogen pairs in GaP

    NASA Astrophysics Data System (ADS)

    Li, Ming-Fu; Mao, De-Qiang; Ren, Shang-Yuan

    1985-11-01

    Theoretical calculations of binding energies of electrons by nitrogen pairs in GaP are reported. The calculations are based on the Koster-Slater Green's-function equation and the central-cell defect-potential approximation of Hjalmarson et al. [Phys. Rev. Lett. 44, 810 (1980)]. The defect-potential parameters Vs and Vp are adjusted to fit the experimental binding energies of electrons by single N impurity and seven (NN)1 (x=1,2,...,7) pairs. The results are in general agreement for the first time with experiments for either range or ordering of binding energies, and thus strongly support the Hopfield-Thomas-Lynch model for isoelectronic traps. Besides, excited electronic states of (NN)1, (NN)3, (NN)5, and (NN)6 are reported. The energy value of the (NN)1 excited state supports the speculation of Cohen et al.

  13. Using gap symmetry and structure to reveal the pairing mechanism in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Hirschfeld, Peter J.

    2016-01-01

    I review theoretical ideas and implications of experiments for the gap structure and symmetry of the Fe-based superconductors. Unlike any other class of unconventional superconductors, one has in these systems the possibility to tune the interactions by small changes in pressure, doping or disorder. Thus, measurements of order parameter evolution with these parameters should enable a deeper understanding of the underlying interactions. I briefly review the "standard paradigm" for s-wave pairing in these systems, and then focus on developments in the past several years which have challenged this picture. I further discuss the reasons for the apparent close competition between pairing in s- and d-wave channels, particularly in those systems where one type of Fermi surface pocket - hole or electron - is missing. Observation of a transition between s- and d-wave symmetry, possibly via a time reversal symmetry breaking "s + id" state, would provide an important confirmation of these ideas. Several proposals for detecting these novel phases are discussed, including the appearance of order parameter collective modes in Raman and optical conductivities. Transitions between two different types of s-wave states, involving various combinations of signs on Fermi surface pockets, can also proceed through a T-breaking "s + is" state. I discuss recent work that suggests pairing may take place away from the Fermi level over a surprisingly large energy range, as well as the effect of glide plane symmetry of the Fe-based systems on the superconductivity, including various exotic, time and translational invariance breaking pair states that have been proposed. Finally, I address disorder issues, and the various ways systematic introduction of disorder can (and cannot) be used to extract information on gap symmetry and structure.

  14. Vortex pairing in the wake of an oscillating bubble rising in a thin-gap cell

    NASA Astrophysics Data System (ADS)

    Ern, Patricia; Filella, Audrey; Roig, Véronique

    2015-11-01

    We investigate experimentally the oscillatory motion and wake of a bubble rising in a counter flow in a thin gap cell (3 mm) by shadowgraphy and PIV. The equivalent diameter d of the bubble in the plane of the cell is used to define the Archimedes number Ar =√{/gd3 } ν (ν is the kinematic viscosity and g the gravitational acceleration). The counter flow is characterized by the Reynolds number Recf based on the mean liquid velocity and the gap thickness. For 500 <= Ar <= 5500 and 0 <=Recf <= 200 , the mean vertical velocity of the bubble relative to the counter flow, Vbr, corresponds to the mean rising velocity in liquid at rest; and the frequency and the amplitude of the oscillatory motion superpose for all Recf when normalized with Vbr and the timescale d /Vbr . For a given size of the bubble (d 9 . 5 mm and Ar 2800) corresponding to a Reynolds number based on Vbr and d of about 1900, we then investigate in detail the wake associated to the bubble in several counter flows. As Recf increases, the number of vortices released increases. Furthermore, the wake of the bubble undergoes vortex pairing for 0 <=Recf <= 110), whereas no vortex pairing is observed for Recf >= 140 .

  15. Studying temperature dependence of pairing gap parameter in a nucleus as a small superconducting system

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Razavi, R.; Kakavand, T.

    2016-07-01

    In this paper, we have taken the effect of small size of nucleus and static fluctuations into account in the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity calculations of 45Ti nucleus. Thermodynamic quantities of 45Ti have been extracted within the BCS model with the inclusion of the average value of the pairing gap square, extracted by the modified Ginzburg-Landau (MGL) method for small systems. Calculated values of the excitation energy and entropy within the MGL+BCS method improve the extracted results within the usual BCS model and show a smooth behavior around the critical temperature with a very good agreement with the semi-empirical values. The result of using MGL+BCS method for the heat capacity of 45Ti is compared with the corresponding semi-empirical values and the calculated values within the BCS, static path approximation (SPA) and Modified Pairing gap BCS (MPBCS) which is a method that was proposed in our previous publications. Both MGL+BCS and MPBCS avoid the discontinuity of the heat capacity curve, which is observed in the usual BCS method, and lead to an S-shaped curve with a good agreement with the semi-empirical results.

  16. Dirac-Hartree-Bogoliubov calculation for spherical and deformed hot nuclei: Temperature dependence of the pairing energy and gaps, nuclear deformation, nuclear radii, excitation energy, and entropy

    NASA Astrophysics Data System (ADS)

    Lisboa, R.; Malheiro, M.; Carlson, B. V.

    2016-02-01

    Background: Unbound single-particle states become important in determining the properties of a hot nucleus as its temperature increases. We present relativistic mean field (RMF) for hot nuclei considering not only the self-consistent temperature and density dependence of the self-consistent relativistic mean fields but also the vapor phase that takes into account the unbound nucleon states. Purpose: The temperature dependence of the pairing gaps, nuclear deformation, radii, binding energies, entropy, and caloric curves of spherical and deformed nuclei are obtained in self-consistent RMF calculations up to the limit of existence of the nucleus. Method: We perform Dirac-Hartree-Bogoliubov (DHB) calculations for hot nuclei using a zero-range approximation to the relativistic pairing interaction to calculate proton-proton and neutron-neutron pairing energies and gaps. A vapor subtraction procedure is used to account for unbound states and to remove long range Coulomb repulsion between the hot nucleus and the gas as well as the contribution of the external nucleon gas. Results: We show that p -p and n -n pairing gaps in the S10 channel vanish for low critical temperatures in the range Tcp≈0.6 -1.1 MeV for spherical nuclei such as 90Zr, 124Sn, and 140Ce and for both deformed nuclei 150Sm and 168Er. We found that superconducting phase transition occurs at Tcp=1.03 Δp p(0 ) for 90Zr, Tcp=1.16 Δp p(0 ) for 140Ce, Tcp=0.92 Δp p(0 ) for 150Sm, and Tcp=0.97 Δp p(0 ) for 168Er. The superfluidity phase transition occurs at Tcp=0.72 Δn n(0 ) for 124Sn, Tcp=1.22 Δn n(0 ) for 150Sm, and Tcp=1.13 Δn n(0 ) for 168Er. Thus, the nuclear superfluidity phase—at least for this channel—can only survive at very low nuclear temperatures and this phase transition (when the neutron gap vanishes) always occurs before the superconducting one, where the proton gap is zero. For deformed nuclei the nuclear deformation disappear at temperatures of about Tcs=2.0 -4.0 MeV , well above the

  17. Large Gap Size Paired-end Library Construction for Second Generation Sequencing

    SciTech Connect

    Peng, Ze; Hamilton, Matthew; Froula, Jeff; Ewing, Aren; Foster, Brian; Cheng, Jan-Fang

    2010-05-28

    Fosmid or BAC end sequencing plays an important role in de novo assembly of large genomes like fungi and plants. However construction and Sanger sequencing of fosmid or BAC libraries are laborious and costly. The current 454 Paired-End (PE) Library and Illumina Jumping Library construction protocols are limited with the gap sizes of approximately 20 kb and 8 kb, respectively. In the attempt to understand the limitations of constructing PE libraries with greater than 30Kb gaps, we have purified 18, 28, 45, and 65Kb sheared DNA fragments from yeast and circularized the ends using the Cre-loxP approach described in the 454 PE Library protocol. With the increasing fragment sizes, we found a general trend of decreasing library quality in several areas. First, redundant reads and reads containing multiple loxP linkers increase when the average fragment size increases. Second, the contamination of short distance pairs (<10Kb) increases as the fragment size increases. Third, chimeric rate increases with the increasing fragment sizes. We have modified several steps to improve the quality of the long span PE libraries. The modification includes (1) the use of special PFGE program to reduce small fragment contamination; (2) the increase of DNA samples in the circularization step and prior to the PCR to reduce redundant reads; and (3) the decrease of fragment size in the double SPRI size selection to get a higher frequency of LoxP linker containing reads. With these modifications we have generated large gap size PE libraries with a much better quality.

  18. Proton-neutron pairing and alpha-type condensation in nuclei

    SciTech Connect

    Sandulescu, N.; Negrea, D.; Gambacurta, D.

    2015-10-15

    We summarize a recent work (N. Sandulescu et al, arXiv:1507.04144) on isoscalar and isovector proton-neutron pairing treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N=Z) systems of nucleons moving in an axially deformed mean field and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T=0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this formalism is able to describe accurately the pairing correlations energies. It is also shown that, contrary to the majority of HFB calculations, in the present formalism the isovector and isoscalar pairing correlations coexist together for any pairing interactions.

  19. Study on the impact of pair production interaction on D-T controllable neutron density logging.

    PubMed

    Yu, Huawei; Zhang, Li; Hou, Boran

    2016-05-01

    This paper considers the effect of pair production on the precision of D-T controllable neutron source density logging. Firstly, the principle of the traditional density logging and pulsed neutron density logging are analyzed and then gamma ray cross sections as a function of energy for various minerals are compared. In addition, the advantageous areas of Compton scattering and pair production interactions on high-energy gamma ray pulse height spectrum and the errors of a controllable source density measurement are studied using a Monte Carlo simulation method. The results indicate that density logging mainly utilizes the Compton scattering of gamma rays, while the attenuation of neutron induced gamma rays and the precision of neutron gamma density measurements are affected by pair production interactions, particularly in the gamma rays with energy higher than 2MeV. By selecting 0.2-2MeV energy range and performing proper lithology correction, the effect of pair production can be eliminated effectively and the density measurement error can be rendered close to the precision of chemical source density logging. PMID:26945102

  20. Atom Pair Distribution Functions of Liquid Water at 25circC from Neutron Diffraction

    NASA Astrophysics Data System (ADS)

    Narten, A. H.; Thiessen, W. E.; Blum, L.

    1982-09-01

    The structure of liquid water is described by three atom pair distribution functions gOO(r), gOH(r), and gHH(r). These functions have now been derived from neutron diffraction data on four mixtures of light and heavy water. They will provide a crucial and sensitive test for proposed models of liquid water.

  1. Dosimetry of mixed neutron and gamma radiation with paired Fricke solutions in light and heavy water.

    PubMed

    Himit, M; Itoh, T; Endo, S; Fujikawa, K; Hoshi, M

    1996-06-01

    Paired Fricke solutions, made up from light water or heavy water and 0.8N in H2SO4 and 1 mM in Fe(NH4)2(SO4)2 and NaCl, were calibrated with 60Co gamma rays and with mixed neutron and gamma radiation from a 252Cf source. Absorbance increases, AL and AH, in light- and heavy-water Fricke dosimeters, respectively, increased with fast-neutron and gamma-ray tissue doses, Dn (GY) and D gamma (GY), of the mixed radiation as follows: AL = 0.00178Dn + 0.00371D gamma; AH = 0.00121Dn + 0.00442 D gamma. G-values of 7.2 and 5.5 were obtained for 252Cf neutrons in light- and heavy-water Fricke dosimeters, respectively. When we applied the pair of equations to AL and AH values observed after exposure to mixed radiation in a nuclear reactor, resulting Dn and D gamma values agreed within 10% to doses measured with paired ionization chambers. Doses required for Fricke dosimeters were 5 Gy or more. In contrast, we found that micronuclear yields in onion roots can measure the neutron component of mixed radiation fields at the order of 10 cGy with reasonable accuracy even if the neutron to gamma-ray dose ratio is unknown. PMID:8840720

  2. Geometric phase and entanglement of Raman photon pairs in the presence of photonic band gap

    SciTech Connect

    Berrada, K.; Ooi, C. H. Raymond; Abdel-Khalek, S.

    2015-03-28

    Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency.

  3. Neutron-Proton Isovector Pairing Effect on the Nuclear Moment of Inertia

    NASA Astrophysics Data System (ADS)

    Mokhtari, D.; Ami, I.; Fellah, M.; Allal, N. H.

    The neutron-proton (n-p) isovector pairing effect on the nuclear moment of inertia has been studied within the framework of the BCS approximation. An analytical expression of the moment of inertia, that explicitly depends upon the n-p pairing, has been established using the Inglis cranking model. The model was first tested numerically for nuclei such as N = Z and whose experimental values of the moment of inertia are known (i.e. such as 16 ≤ Z ≤ 40). It has been shown that the n-p pairing effect is non-negligible and clearly improves the theoretical predictions when compared to those of the pairing between like particles. Secondly, predictions have been established for even-even proton-rich rare-earth nuclei. It has been shown that the n-p pairing effect is non-negligible when N = Z and rapidly decreases with increasing values of (N-Z).

  4. Interplay between proton-neutron pairing and deformation in self-conjugated medium mass nuclei

    NASA Astrophysics Data System (ADS)

    Gambacurta, Danilo; Lacroix, Denis

    2016-05-01

    We employ a model combining self-consistent mean-field and shell model techniques to study the competition between particle-like and proton-neutron pairing correlations in fp-shell even-even self-conjugate nuclei. Deformation effects are realistically and microscopically described. The resulting approach can give a precise description of pairing correlations and eventually treat the coexistence of different condensate formed of pairs with different total spin/ isospin. The standard BCS calculations are systematically compared with approaches including correlation effects beyond the independent quasi-particle picture. The competition between proton-neutron correlations in the isoscalar and isovector channels is also analyzed, as well as their dependence on the deformation properties.

  5. Distinguishing S-plus-minus and S-plus-plus electron pairing symmetries by neutron spin resonances in superconducting Sodium-Iron-Cobalt-Arsenic (transitional temperature = 18 Kelvin)

    SciTech Connect

    Das, Tanmoy; Balatsky, Alexander V.; Zhang, Chenglin; Li, Haifeng; Su, Yiki; Nethertom, Tucker; Redding, Caleb; Carr, Scott; Schneidewind, Astrid; Faulhaber, Enrico; Li, Shiliang; Yao, Daoxin; Bruckel, Thomas; Dai, Pengchen; Sobolev, Oleg

    2012-06-05

    A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the s{sup {+-}}-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E {le} 2{Delta}). Although the resonances have been observed for various iron pnictide superconductors, they are broad in energy and can also be interpreted as arising from the s{sup ++}-pairing symmetry with E {ge} 2{Delta}. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in the SC NaFe{sub 0.935}Co{sub 0.045}As (T{sub c} = 18 K). By comparing our experiments with calculated spin-excitations spectra within the s{sup {+-}} and s{sup ++}-pairing symmetries, we conclude that the resonance in NaFe{sub 0.935}Co{sub 0.045}As is consistent with the s{sup {+-}}-pairing symmetry, thus eliminating s{sup ++}-pairing symmetry as a candidate for superconductivity.

  6. Isoscalar-isovector proton-neutron pairing and quartet condensation in N =Z nuclei

    NASA Astrophysics Data System (ADS)

    Sambataro, M.; Sandulescu, N.

    2016-05-01

    We show that the correlations generated in the ground state of N =Z nuclei by the isovector and isoscalar pairing forces can be treated with high precision as a condensate of alpha-like quartets. To treat these correlations, the quartet condensation model (QCM) is extended to the treatment of spherically symmetric isovector (T =1 ,J =0 ) and isoscalar (T =0 ,J =1 ) pairing forces. Within the QCM, we discuss the competition between T =1 and T =0 pairing correlations in the case of a two-level model and for N =Z nuclei with nucleons moving in the open shells above 16O,40Ca, and 100Sn. We show that, in N =Z systems, isovector and isoscalar proton-neutron pairing correlations always coexist.

  7. Pair production and annihilation in strong magnetic fields. [of neutron stars and pulsars

    NASA Technical Reports Server (NTRS)

    Daugherty, J. K.; Harding, A. K.

    1983-01-01

    Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high-energy astrophysics. In particular, the process of pair production by single photons in the presence of fields of order 10 to the 12th power Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511-keV line for annihilation at rest, and the possibility for annihilation into a single photon which dominates the two-photon annihilation for B (10 to 13th power Gauss) The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, theoretical work, especially the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.

  8. Analyses of interactions among pair-rule genes and the gap gene Krüppel in Bombyx segmentation.

    PubMed

    Nakao, Hajime

    2015-09-01

    In the short-germ insect Tribolium, a pair-rule gene circuit consisting of the Tribolium homologs of even-skipped, runt, and odd-skipped (Tc-eve, Tc-run and Tc-odd, respectively) has been implicated in segment formation. To examine the application of the model to other taxa, I studied the expression and function of pair-rule genes in Bombyx mori, together with a Bombyx homolog of Krüppel (Bm-Kr), a known gap gene. Knockdown embryos of Bombyx homologs of eve, run and odd (Bm-eve, Bm-run and Bm-odd) exhibited asegmental phenotypes similar to those of Tribolium knockdowns. However, pair-rule gene interactions were similar to those of both Tribolium and Drosophila, which, different from Tribolium, shows a hierarchical segmentation mode. Additionally, the Bm-odd expression pattern shares characteristics with those of Drosophila pair-rule genes that receive upstream regulatory input. On the other hand, Bm-Kr knockdowns exhibited a large posterior segment deletion as observed in short-germ insects. However, a detailed analysis of these embryos indicated that Bm-Kr modulates expression of pair-rule genes like in Drosophila, although the mechanisms appear to be different. This suggested hierarchical interactions between Bm-Kr and pair-rule genes. Based on these results, I concluded that the pair-rule gene circuit model that describes Tribolium development is not applicable to Bombyx. PMID:26102481

  9. ARPES measurements of the superconducting gap of Fe-based superconductors and their implications to the pairing mechanism.

    PubMed

    Richard, P; Qian, T; Ding, H

    2015-07-29

    Its direct momentum sensitivity confers to angle-resolved photoemission spectroscopy (ARPES) a unique perspective in investigating the superconducting gap of multi-band systems. In this review we discuss ARPES studies on the superconducting gap of high-temperature Fe-based superconductors. We show that while Fermi-surface-driven pairing mechanisms fail to provide a universal scheme for the Fe-based superconductors, theoretical approaches based on short-range interactions lead to a more robust and universal description of superconductivity in these materials. Our findings are also discussed in the broader context of unconventional superconductivity. PMID:26153847

  10. Recoil Induced Room Temperature Stable Frenkel Pairs in a-Hafnium Upon Thermal Neutron Capture

    NASA Astrophysics Data System (ADS)

    Butz, Tilman; Das, Satyendra K.; Dey, Chandi C.; Ghoshal, Shamik

    2013-11-01

    Ultrapure hafnium metal (110 ppm zirconium) was neutron activated with a thermal neutron flux of 6:6 · 1012 cm-2s-1 in order to obtain 181Hf for subsequent time differential perturbed angular correlation (TDPAC) experiments using the nuclear probe 181Hf(β-) 181Ta. Apart from the expected nuclear quadrupole interaction (NQI) signal for a hexagonal close-packed (hcp) metal, three further discrete NQIs were observed with a few percent fraction each. The TDPAC spectra were recorded for up to 11 half lives with extreme statistical accuracy. The fitted parameters vary slightly within the temperature range between 248 K and 373 K. The signals corresponding to the three additional sites completely disappear after `annealing' at 453 K for one minute. Based on the symmetry of the additional NQIs and their temperature dependencies, they are tentatively attributed to Frenkel pairs produced by recoil due to the emission of a prompt 5:694 MeV -ray following thermal neutron capture and reported by the nuclear probe in three different positions. These Frenkel pairs are stable up to at least 373 K.

  11. Scrutinizing the double superconducting gaps and strong coupling pairing in (Li1−xFex)OHFeSe

    PubMed Central

    Du, Zengyi; Yang, Xiong; Lin, Hai; Fang, Delong; Du, Guan; Xing, Jie; Yang, Huan; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    In the field of iron-based superconductors, one of the frontier studies is about the pairing mechanism. The recently discovered (Li1−xFex)OHFeSe superconductor with the transition temperature of about 40 K provides a good platform to check the origin of double superconducting gaps and high transition temperature in the monolayer FeSe thin film. Here we report a scanning tunnelling spectroscopy study on the (Li1−xFex)OHFeSe single crystals. The tunnelling spectrum mimics that of the monolayer FeSe thin film and shows double gaps at about 14.3 and 8.6 meV. Further analysis based on the quasiparticle interference allows us to rule out the d-wave gap, and for the first time assign the larger (smaller) gap to the outer (inner) Fermi pockets (after folding) associating with the dxy (dxz/dyz) orbitals, respectively. The gap ratio amounts to 8.7, which demonstrates the strong coupling mechanism in the present superconducting system. PMID:26822281

  12. Superfluid phases of triplet pairing and neutrino emission from neutron stars

    SciTech Connect

    Leinson, L. B.

    2010-12-15

    Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density in the one-component condensate at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.

  13. Moment of inertia of even-even proton-rich nuclei using a particle-number conserving approach in the isovector neutron-proton pairing case

    NASA Astrophysics Data System (ADS)

    Hammache, Faiza; Allal, N. H.; Fellah, M.; Oudih, M. R.

    2016-05-01

    An expression of the particle-number projected nuclear moment of inertia (MOI) has been established in the neutron-proton (np) isovector pairing case within the cranking model. It generalizes the one obtained in the like-particles pairing case. The formalism has been, as a first step, applied to the picket-fence model. As a second step, it has been applied to deformed even-even nuclei such as (N ‑ Z) = 0, 2, 4, and of which the experimentally deduced values of the pairing gap parameters Δtt‧, t,t‧ = n,p, are known. The single-particle energies and eigenstates used are those of a deformed Woods-Saxon mean-field. It was shown, in both models, that the np pairing effect and the projection one are non-negligible. In realistic cases, it also appears that the np pairing effect strongly depends on (N ‑ Z), whereas the projection effect is practically independent from the same quantity.

  14. Effects of interlayer Sn-Sn lone pair interaction on the band gap of bulk and nanosheet SnO

    NASA Astrophysics Data System (ADS)

    Umezawa, Naoto; Zhou, Wei

    2015-03-01

    Effects of interlayer lone-pair interactions on the electronic structure of SnO are firstly explored by the density-functional theory. Our comprehensive study reveals that the band gap of SnO opens as increase in the interlayer Sn-Sn distance. The effect is rationalized by the character of band edges which consists of bonding and anti-bonding states from interlayer lone pair interactions. The band edges for several nanosheets and strained double-layer SnO are estimated. We conclude that the double-layer SnO is a promising material for visible-light driven photocatalyst for hydrogen evolution. This work is supported by the Japan Science and Technology Agency (JST) Precursory Research for Embryonic Science and Technology (PRESTO) program.

  15. Modified Fermi sphere, pairing gap, and critical temperature for the BCS-BEC crossover

    SciTech Connect

    Floerchinger, S.; Wetterich, C.; Scherer, M. M.

    2010-06-15

    We investigate the phase diagram of two-component fermions in the BCS-BEC (Bose-Einstein condensate) crossover. Using functional renormalization-group equations we calculate the effect of quantum fluctuations on the fermionic self-energy parametrized by a wave-function renormalization, an effective Fermi radius, and the gap. This allows us to follow the modifications of the Fermi surface and the dispersion relation for fermionic excitations throughout the whole crossover region. We also determine the critical temperature of the second-order phase transition to superfluidity. Our results are in agreement with BCS theory including Gorkov's correction for a small negative scattering length a and with an interacting Bose gas for a small positive a. At the unitarity point the result for the gap at zero temperature agrees well with quantum Monte Carlo simulations, while the critical temperature differs.

  16. Microfluidic application-specific integrated device for monitoring direct cell-cell communication via gap junctions between individual cell pairs

    NASA Astrophysics Data System (ADS)

    Lee, Philip J.; Hung, Paul J.; Shaw, Robin; Jan, Lily; Lee, Luke P.

    2005-05-01

    Direct cell-cell communication between adjacent cells is vital for the development and regulation of functional tissues. However, current biological techniques are difficult to scale up for high-throughput screening of cell-cell communication in an array format. In order to provide an effective biophysical tool for the analysis of molecular mechanisms of gap junctions that underlie intercellular communication, we have developed a microfluidic device for selective trapping of cell-pairs and simultaneous optical characterizations. Two different cell populations can be brought into membrane contact using an array of trapping channels with a 2μm by 2μm cross section. Device operation was verified by observation of dye transfer between mouse fibroblasts (NIH3T3) placed in membrane contact. Integration with lab-on-a-chip technologies offers promising applications for cell-based analytical tools such as drug screening, clinical diagnostics, and soft-state biophysical devices for the study of gap junction protein channels in cellular communications. Understanding electrical transport mechanisms via gap junctions in soft membranes will impact quantitative biomedical sciences as well as clinical applications.

  17. Evidence for a spin-aligned neutron-proton paired phase from the level structure of (92)Pd.

    PubMed

    Cederwall, B; Moradi, F Ghazi; Bäck, T; Johnson, A; Blomqvist, J; Clément, E; de France, G; Wadsworth, R; Andgren, K; Lagergren, K; Dijon, A; Jaworski, G; Liotta, R; Qi, C; Nyakó, B M; Nyberg, J; Palacz, M; Al-Azri, H; Algora, A; de Angelis, G; Ataç, A; Bhattacharyya, S; Brock, T; Brown, J R; Davies, P; Di Nitto, A; Dombrádi, Zs; Gadea, A; Gál, J; Hadinia, B; Johnston-Theasby, F; Joshi, P; Juhász, K; Julin, R; Jungclaus, A; Kalinka, G; Kara, S O; Khaplanov, A; Kownacki, J; La Rana, G; Lenzi, S M; Molnár, J; Moro, R; Napoli, D R; Singh, B S Nara; Persson, A; Recchia, F; Sandzelius, M; Scheurer, J-N; Sletten, G; Sohler, D; Söderström, P-A; Taylor, M J; Timár, J; Valiente-Dobón, J J; Vardaci, E; Williams, S

    2011-01-01

    Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus (92)Pd. Gamma rays emitted following the (58)Ni((36)Ar,2n)(92)Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis. PMID:21179086

  18. Steric Effects in Ionic Pairing and Polyelectrolyte Interdiffusion within Multilayered Films: A Neutron Reflectometry Study

    SciTech Connect

    Xu, Li; Ankner, John Francis; Sukhishvili, Prof. Svetlana A.

    2011-01-01

    Using a series of polycations synthesized by atom transfer radical polymerization (ATRP), we investigate the effects of the polymer charge density and hydrophobicity on salt-induced interdiffusion of polymer layers within polyelectrolyte multilayer (PEM) films. Polycations with two distinct hydrophobicities and various quaternization degrees (QPDMA and QPDEA) were derived from parent polymers of matched molecular weights poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA) by quaternization with either methyl or ethyl sulfate. Multilayers of these polycations with polystyrene sulfonate (PSS) were assembled in low-salt conditions, and annealed in NaCl solutions to induce layer intermixing. As revealed by neutron reflectometry (NR), polycations with lower charge density resulted in a faster decay of film structure with distance from the substrate. Interestingly, when comparing polymer mobility in QPDEA/PSS and QPDMA/PSS films, layer intermixing was faster in the case of more hydrophobic QPDEA as compared to QPDMA, because of the weaker ionic pairing (due to the presence of a bulky ethyl spacer) between QPDEA and PSS.

  19. Absorption of gamma-ray photons in a vacuum neutron star magnetosphere: I. Electron-positron pair production

    SciTech Connect

    Istomin, Ya. N. Sob'yanin, D. N.

    2011-10-15

    The production of electron-positron pairs in a vacuum neutron star magnetosphere is investigated for both low (compared to the Schwinger one) and high magnetic fields. The case of a strong longitudinal electric field where the produced electrons and positrons acquire a stationary Lorentz factor in a short time is considered. The source of electron-positron pairs has been calculated with allowance made for the pair production by curvature and synchrotron photons. Synchrotron photons are shown to make a major contribution to the total pair production rate in a weak magnetic field. At the same time, the contribution from bremsstrahlung photons may be neglected. The existence of a time delay due to the finiteness of the electron and positron acceleration time leads to a great reduction in the electron-positron plasma generation rate compared to the case of a zero time delay. The effective local source of electron-positron pairs has been constructed. It can be used in the hydrodynamic equations that describe the development of a cascade after the absorption of a photon from the cosmic gamma-ray background in a neutron star magnetosphere.

  20. Hybrid germanium iodide perovskite semiconductors: active lone pairs, structural distortions, direct and indirect energy gaps, and strong nonlinear optical properties.

    PubMed

    Stoumpos, Constantinos C; Frazer, Laszlo; Clark, Daniel J; Kim, Yong Soo; Rhim, Sonny H; Freeman, Arthur J; Ketterson, John B; Jang, Joon I; Kanatzidis, Mercouri G

    2015-06-01

    The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI3 (1) as the prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), and isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1–4 forming 3D perovskite frameworks and 5–7 1D infinite chains. Compounds 1–7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (1), 1.9 eV (2), 2.2 eV (3), and 2.5 eV (4), while the 1D compounds have indirect band gaps of 2.7 eV (5), 2.5 eV (6), and 2.8 eV (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm(2)). The second-order nonlinear susceptibility, χS(2), was determined to be 125.3 ± 10.5 pm/V (1), (161.0 ± 14.5) pm/V (2), 143.0 ± 13.5 pm/V (3), and 57.2 ± 5.5 pm/V (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation. PMID:25950197

  1. Direct assignment of molecular vibrations via normal mode analysis of the neutron dynamic pair distribution function technique

    SciTech Connect

    Fry-Petit, A. M. E-mail: afry@fullerton.edu; Sheckelton, J. P.; McQueen, T. M. E-mail: afry@fullerton.edu; Rebola, A. F.; Fennie, C. J.; Mourigal, M.; Valentine, M.; Drichko, N.

    2015-09-28

    For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn{sub 2}Mo{sub 3}O{sub 8}, this approach allows direct assignment of the constrained rotational mode of Mo{sub 3}O{sub 13} clusters and internal modes of MoO{sub 6} polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems.

  2. Direct assignment of molecular vibrations via normal mode analysis of the neutron dynamic pair distribution function technique.

    PubMed

    Fry-Petit, A M; Rebola, A F; Mourigal, M; Valentine, M; Drichko, N; Sheckelton, J P; Fennie, C J; McQueen, T M

    2015-09-28

    For over a century, vibrational spectroscopy has enhanced the study of materials. Yet, assignment of particular molecular motions to vibrational excitations has relied on indirect methods. Here, we demonstrate that applying group theoretical methods to the dynamic pair distribution function analysis of neutron scattering data provides direct access to the individual atomic displacements responsible for these excitations. Applied to the molecule-based frustrated magnet with a potential magnetic valence-bond state, LiZn2Mo3O8, this approach allows direct assignment of the constrained rotational mode of Mo3O13 clusters and internal modes of MoO6 polyhedra. We anticipate that coupling this well known data analysis technique with dynamic pair distribution function analysis will have broad application in connecting structural dynamics to physical properties in a wide range of molecular and solid state systems. PMID:26429001

  3. Dependence of two-neutron momentum densities on total pair momentum

    SciTech Connect

    Carlson, Joseph A; Wiringa, R B; Schiavilla, R; Pieper, Steven C

    2008-01-01

    Two-nucleon momentum distributions are calculated for the ground states of {sup 3}He and {sup 4}He as a function of the nucleons' relative and total momenta. We use variational Monte Carlo wave functions derived from a realistic Hamiltonian with two- and three-nucleon potentials. The momentum distribution of pp pairs is found to be much smaller than that of pn pairs for values of the relative momentum in the range (300--500) MeV/c and vanishing total momentum. Howeer, as the totalmomentum increases to 400 MeV/c, the ratio of pp to pn pairs in this relative momentum range grows and approaches the limit 1/2 for {sup 3}He and 1/4 for {sup 4}He, corresponding to the ratio of pp to pn pairs in these nuclei. This behavior should be easily observable in two-nucleon knock-out processes, such as A(e, e'pN).

  4. Pair neutron transfer in 60Ni+116Sn probed via γ -particle coincidences

    NASA Astrophysics Data System (ADS)

    Montanari, D.; Corradi, L.; Szilner, S.; Pollarolo, G.; Goasduff, A.; Mijatović, T.; Bazzacco, D.; Birkenbach, B.; Bracco, A.; Charles, L.; Courtin, S.; Désesquelles, P.; Fioretto, E.; Gadea, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Haas, F.; Hess, H.; Jelavić Malenica, D.; Jungclaus, A.; Karolak, M.; Leoni, S.; Maj, A.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Montagnoli, G.; Napoli, D. R.; Pullia, A.; Recchia, F.; Reiter, P.; Rosso, D.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Soić, N.; Stefanini, A. M.; Stezowski, O.; Theisen, Ch.; Ur, C. A.; Valiente-Dobón, J. J.; Varga Pajtler, M.

    2016-05-01

    We performed a γ -particle coincidence experiment for the 60Ni + 116Sn system to investigate whether the population of the two-neutron pickup channel leading to 62Ni is mainly concentrated in the ground-state transition, as has been found in a previous work [D. Montanari et al., Phys. Rev. Lett. 113, 052501 (2014), 10.1103/PhysRevLett.113.052501]. The experiment has been performed by employing the PRISMA magnetic spectrometer coupled to the Advanced Gamma Tracking Array (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one- and two-neutron transfer channels has been extracted. We found that in the two-neutron transfer channel the strength to excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtained results that the 2 n channel is dominated by the ground-state to ground-state transition.

  5. Isospin Dependent Pairing Interactions and BCS-BEC crossover

    SciTech Connect

    Sagawa, H.; Margueron, J.; Hagino, K.

    2008-11-11

    We propose new types of density dependent contact pairing interaction which reproduce the pairing gaps in symmetric and neutron matters obtained by a microscopic treatment based on the realistic nucleon-nucleon interaction. The BCS-BEC crossover of neutrons pairs in symmetric and asymmetric nuclear matters is studied by using these contact interactions. It is shown that the bare and screened pairing interactions lead to different features of the BCS-BEC crossover in symmetric nuclear matter. We perform Hartree-Fock-Bogoliubov (HFB) calculations for semi-magic Calcium, Nickel, Tin and Lead isotopes and N = 20, 28, 50 and 82 isotones using these density-dependent pairing interactions. Our calculations well account for the experimental data for the neutron number dependence of binding energy, two neutrons separation energy, and odd-even mass staggering of these isotopes. Especially the interaction IS+IV Bare without the medium polarization effect gives satisfactory results for all the isotopes.

  6. Quantitative study of coherent pairing modes with two-neutron transfer: Sn isotopes

    NASA Astrophysics Data System (ADS)

    Potel, G.; Idini, A.; Barranco, F.; Vigezzi, E.; Broglia, R. A.

    2013-05-01

    Pairing rotations and pairing vibrations are collective modes associated with a field, the pair field, which changes the number of particles by two. Consequently, they can be studied at profit with the help of two-particle transfer reactions in superfluid and in normal nuclei, respectively. The advent of exotic beams has opened, for the first time, the possibility to carry out such studies in medium heavy nuclei, within the same isotopic chain. The case studied in the present paper is that of the Sn isotopes [essentially from closed (Z=N=50) to closed (Z=50, N=82) shells]. The static and dynamic off-diagonal, long-range order phase coherence in gauge space displayed by pairing rotations and vibrations, respectively, leads to coherent states which behave almost classically. Consequently, these modes are amenable to an accurate nuclear structure description in terms of simple models containing the right physics, in particular, BCS plus quasiparticle random-phase approximation and Hartree-Fock mean field plus random-phase approximation, respectively. The associated two-nucleon transfer spectroscopic amplitudes predicted by such model calculations can thus be viewed as essentially “exact.” This fact, together with the availability of optical potentials for the different real and virtual channels involved in the reactions considered, namely A+2Sn+p, A+1Sn+d, and ASn+t, allows for the calculation of the associated absolute cross sections without, arguably, free parameters. The numerical predictions of the absolute differential cross sections, obtained making use of the above-mentioned nuclear structure and optical potential inputs, within the framework of second-order distorted-wave Born approximation, taking into account simultaneous, successive, and nonorthogonality contributions, provide, within experimental errors in general, and below 10% uncertainty in particular, an overall account of the experimental findings for all of the measured A+2Sn

  7. General relativistic ray-tracing algorithm for the determination of the electron-positron energy deposition rate from neutrino pair annihilation around rotating neutron and quark stars

    NASA Astrophysics Data System (ADS)

    Kovács, Z.; Harko, T.

    2011-11-01

    We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general relativistic Hamilton's equations for neutrinos and derive the spatial distribution of the EMDR due to the annihilations of neutrinos and antineutrinos around rotating neutron and quark stars. We obtain the EMDR for several classes of rotating neutron stars, described by different equations of state of the neutron matter, and for quark stars, described by the Massachusetts Institute of Technology (MIT) bag model equation of state and in the colour-flavour-locked (CFL) phase. The distribution of the total annihilation rate of the neutrino-antineutrino pairs around rotating neutron and quark stars is studied for isothermal discs and accretion discs in thermodynamical equilibrium. We demonstrate both the differences in the equations of state for neutron and quark matter and rotation with the general relativistic effects significantly modify the EMDR of the electrons and positrons generated by the neutrino-antineutrino pair annihilation around compact stellar objects, as measured at infinity.

  8. An effective potential for electron-nucleus scattering in neutrino-pair bremsstrahlung in neutron star crust

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.

    2015-12-01

    We derive an analytic approximation for the emissivity of neutrino-pair bremsstrahlung (NPB) due to scattering of electrons by atomic nuclei in a neutron star (NS) crust of any realistic composition. The emissivity is expressed through generalized Coulomb logarithm by introducing an effective potential of electron-nucleus scattering. In addition, we study the conditions at which NPB in the crust is affected by strong magnetic fields and outline the main effects of the fields on neutrino emission in NSs. The results can be used for modelling of many phenomena in NSs, such as cooling of young isolated NSs, thermal relaxation of accreting NSs with overheated crust in soft X-ray transients and evolution of magnetars.

  9. Evaluation of the β+-decay log ft value with inclusion of the neutron-proton pairing and particle-number projection

    NASA Astrophysics Data System (ADS)

    Kerrouchi, S.; Allal, N. H.; Fellah, M.; Oudih, M. R.

    2016-01-01

    The neutron-proton isovector pairing effect on the beta-plus decay log ft values is studied in typical mirror N≃Z nuclei. The log ft values are calculated by including or not the isovector pairing before and after a particle-number projection using the Sharp-Bardeen-Cooper-Schrieffer (SBCS) method. It is shown that the values obtained after projection in the isovector pairing case are the closest ones to experimental data. The effect of the deformation of the mother and daughter nuclei on the log ft is also studied.

  10. Gaps in nuclear spectra as traces of seniority changes in systems of both neutrons and protons

    NASA Astrophysics Data System (ADS)

    Zamick, Larry

    2016-03-01

    There has been a great deal of attention given to the low-lying energy spectrum in a nucleus because of the abundance of experimental data. Likewise, perhaps to a lesser extent but still significant, the high end for a given configuration has been examined. Here, using single j shell calculations as a guide, we examine the middle part of the spectrum resulting from single j shell calculations. Seniority arguments are used to partially explain the midshell behaviors even though in general seniority is not a good quantum number for mixed systems of neutrons and protons.

  11. Structure of neutron-rich nuclei around the N = 50 shell-gap closure

    SciTech Connect

    Faul, T.; Duchene, G.; Nowacki, F.; Thomas, J.-C.; Huyse, M.; Van Duppen, P.

    2010-04-26

    The structure of neutron-rich nuclei in the vicinity of {sup 78}Ni have been investigated via the beta-decay of {sup 71,73,75}Cu isotopes (ISOLDE, CERN). Experimental results have been compared with shell-model calculations performed with the ANTOINE code using a large (2p{sub 3/2}1 f{sub 5/2}2 p{sub 1/2}1 g{sub 9/2}) valence space and a (56/28)Ni{sub 28} core.

  12. Neutron scattering study of a membrane phase miscibility gap: Coexistence of L3 "sponge" and Lα Lamellar phases

    NASA Astrophysics Data System (ADS)

    Hamilton, W. A.; Porcar, L.

    2010-11-01

    We report on a small angle neutron scattering (SANS) study of a temperature driven first order phase transition in a 25wt% solution of the surfactant AOT (Sodium Di-2-ethylhexyl Sulfosuccinate) in 1.5wt% heavy brine between an isotropic L3 "sponge" state at 27°C and a stacked lamellar Lα monophase 55°C. The prominent scattering features of these phases are correlation peaks due to the mean passage size of the L3 sponge and the Lα stacking separation. This ratio of the monophase peak positions Qα/Q3approx1.3, is consistent with previous observations in this and similar systems. In the present study we tracked this system through the intermediate L3 +Lα biphasic miscibility gap. There the initial appearance of the Lα peak at 33.25°C was at a scattering vector some 23% higher than the final high temperature monophase value. During coexistence both L3 and Lα phase peak positions decreased linearly with increasing temperature maintaining a roughly constant ratio Qα/Q3 ~1.6-1.7. Two phase fits to the scattering data and application of scaling law predictions allow us to obtain local L3 phase volume fractions in the biphasic region and make preliminary determinations of the structural accomodations necessitated by phase coexistence in this system's miscibility gap.

  13. SU-E-T-594: Out-Of-Field Neutron and Gamma Dose Estimated Using TLD-600/700 Pairs in the Wobbling Proton Therapy System

    SciTech Connect

    Chen, Y; Lin, Y; Tsai, H

    2015-06-15

    Purpose: Secondary fast neutrons and gamma rays are mainly produced due to the interaction of the primary proton beam with the beam delivery nozzle. These secondary radiation dose to patients and radiation workers are unwanted. The purpose of this study is to estimate the neutron and gamma dose equivalent out of the treatment volume during the wobbling proton therapy system. Methods: Two types of thermoluminescent (TL) dosimeters, TLD-600 ({sup 6}LiF: Mg, Ti) and TLD-700 ({sup 7}LiF: Mg, Ti) were used in this study. They were calibrated in the standard neutron and gamma sources at National Standards Laboratory. Annealing procedure is 400°C for 1 hour, 100°C for 2 hours and spontaneously cooling down to the room temperature in a programmable oven. Two-peak method (a kind of glow curve analysis technique) was used to evaluate the TL response corresponding to the neutron and gamma dose. The TLD pairs were placed outside the treatment field at the neutron-gamma mixed field with 190-MeV proton beam produced by the wobbling system through the polyethylene plate phantom. The results of TLD measurement were compared to the Monte Carlo simulation. Results: The initial experiment results of calculated dose equivalents are 0.63, 0.38, 0.21 and 0.13 mSv per Gy outside the field at the distance of 50, 100, 150 and 200 cm. Conclusion: The TLD-600 and TLD-700 pairs are convenient to estimate neutron and gamma dosimetry during proton therapy. However, an accurate and suitable glow curve analysis technique is necessary. During the wobbling system proton therapy, our results showed that the neutron and gamma doses outside the treatment field are noticeable. This study was supported by the grants from the Chang Gung Memorial Hospital (CMRPD1C0682)

  14. On the pairing effects in triaxial nuclei

    SciTech Connect

    Oudih, M. R.; Fellah, M.; Allal, N. H.

    2014-03-05

    Triaxial deformation effect on the pairing correlations is studied in the framework of the Skyrme Hartree-Fock-Bogoliubov theory. Quantities such as binding energy, gap parameter and particle-number fluctuation are considered in neutron-rich Mo isotopes. The results are compared with those of axially symmetric calculation and with available experimental data. The role played by the particle-number projection is outlined.

  15. Coherence length of neutron superfluids

    SciTech Connect

    De Blasio, F.V.; Hjorth-Jensen, M.; Lazzari, G.; Baldo, M.; Schulze, H.

    1997-10-01

    The coherence length of superfluid neutron matter is calculated from the microscopic BCS wave function of a Cooper pair in momentum space making use of recent nucleon-nucleon potential models and including polarization (RPA) effects. We find as our main result that the coherence length is proportional to the Fermi momentum to pairing gap ratio, in good agreement with simple estimates used in the literature, with a nearly interaction independent constant of proportionality. Our calculations can be applied to the problem of inhomogeneous superfluidity of hadronic matter in the crust of a neutron star. {copyright} {ital 1997} {ital The American Physical Society}

  16. General Relativistic Effect on the Energy Deposition Rate for Neutrino Pair Annihilation above the Equatorial Plane Along the Symmetry Axis Near a Rotating Neutron Star

    NASA Astrophysics Data System (ADS)

    Mallick, Ritam; Bhattacharyya, Abhijit; Ghosh, Sanjay K.; Raha, Sibaji

    2013-02-01

    The estimate of the energy deposition rate (EDR) for neutrino pair annihilation has been carried out. The EDR for the neutrinos coming from the equatorial plane of a rotating neutron star is calculated along the rotation axis using the Cook-Shapiro-Teukolsky metric. The neutrino trajectories and hence the neutrinos emitted from the disk are affected by the redshift due to disk rotation and gravitation. The EDR is very sensitive to the value of the temperature and its variation along the disk. The rotation of the star has a negative effect on the EDR; it decreases with increase in rotational velocity.

  17. Superfluidity of {Lambda} hyperons in neutron stars

    SciTech Connect

    Wang, Y. N.; Shen, H.

    2010-02-15

    We study the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the {sup 1}S{sub 0} pairing gap of {Lambda} hyperons, we employ several {Lambda}{Lambda} interactions based on the Nijmegen models and used in double-{Lambda} hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the {Lambda}{Lambda} interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons exists in the core of neutron stars mainly depends on the {Lambda}{Lambda} interaction used.

  18. Observation of a vh{sub 11/2} pair alignment in neutron-rich {sup 118}Pd

    SciTech Connect

    Zhang, X. Q.; Hamilton, J. H.; Ramayya, A. V.; Zhu, S. J.; Hwang, J. K.; Beyer, C. J.; Kormicki, J.; Jones, E. F.; Gore, P. M.; Babu, B. R. S.

    2001-02-01

    The yrast band was significantly extended to 14{sup +} and the {gamma} band to 5{sup +} in neutron-rich {sup 118}Pd by measuring the {gamma}-{gamma}-{gamma} coincidences emitted from the spontaneous fission of {sup 252}Cf with Gammasphere. The first band crossing was observed in the yrast band in {sup 118}Pd at a frequency of {Dirac_h}{omega}{approx}0.36 MeV at the starting point of the backbending, which is similar to that found in {sup 112-116}Pd. The first bandbending in the yrast cascade in {sup 118}Pd is interpreted to be built on a two h{sub 11/2} neutron configuration based on its similarity to the yrast bands in even-even {sup 112-116}Pd. Our result indicates {sup 118}Pd still maintains a prolate shape. The quasineutron Routhian calculations indicate a lower crossing frequency for the h{sub 11/2} level.

  19. Determination of the pairing-strength constants in the isovector plus isoscalar pairing case

    NASA Astrophysics Data System (ADS)

    Mokhtari, D.; Fellah, M.; Allal, N. H.

    2016-05-01

    A method for the determination of the pairing-strength constants, in the neutron-proton (n-p) isovector plus isoscalar pairing case, is proposed in the framework of the BCS theory. It is based on the fitting of these constants to reproduce the experimentally known pairing gap parameters as well as the root-mean-squared (r.m.s) charge radii values. The method is applied to some proton-rich even-even nuclei. The single-particle energies used are those of a deformed Woods-Saxon mean field. It is shown that the obtained value of the ratio GnpT=0/G npT=1 is of the same order as the ones, arbitrary chosen, of some previous works. The effect of the inclusion of the isoscalar n-p pairing in the r.m.s matter radii is then numerically studied for the same nuclei.

  20. Gap Resolution

    SciTech Connect

    2009-06-16

    With the continued improvements of next generation DNA sequencing technologies and their advantages over traditional Sanger sequencing, the Joint Genome Institute (JGI) has modified its sequencing pipeline to take advantage of the benefits of such technologies. Currently, standard 454 Titanium, paired end 454 Titanium, and Illumina GAll data are generated for all microbial projects and then assembled using draft assemblies at a much greater throughput than before. However, it also presents us with new challenges. In addition to the increased throughput, we also have to deal with a larger number of gaps in the Newbler genome assemblies. Gaps in these assemblies are usually caused by repeats (Newbler collapses repeat copies into individual contigs, thus creating gaps), strong secondary structures, and artifacts of the PCR process (specific to 454 paired end libraries). Some gaps in draft assemblies can be resolved merely by adding back the collapsed data from repeats. To expedite gap closure and assembly improvement on large numbers of these assemblies, we developed software to address this issue.

  1. Gap Resolution

    Energy Science and Technology Software Center (ESTSC)

    2009-06-16

    With the continued improvements of next generation DNA sequencing technologies and their advantages over traditional Sanger sequencing, the Joint Genome Institute (JGI) has modified its sequencing pipeline to take advantage of the benefits of such technologies. Currently, standard 454 Titanium, paired end 454 Titanium, and Illumina GAll data are generated for all microbial projects and then assembled using draft assemblies at a much greater throughput than before. However, it also presents us with new challenges.more » In addition to the increased throughput, we also have to deal with a larger number of gaps in the Newbler genome assemblies. Gaps in these assemblies are usually caused by repeats (Newbler collapses repeat copies into individual contigs, thus creating gaps), strong secondary structures, and artifacts of the PCR process (specific to 454 paired end libraries). Some gaps in draft assemblies can be resolved merely by adding back the collapsed data from repeats. To expedite gap closure and assembly improvement on large numbers of these assemblies, we developed software to address this issue.« less

  2. Investigation of the pairing effect using newly evaluated empirical studies for 14-15 MeV neutron reaction cross sections

    SciTech Connect

    Tel, E.; Tanir, G.; Aydin, A.

    2007-03-15

    The asymmetry term effects for the cross sections of (n, charged particle) and (n,2n) reactions at 14-15 MeV neutron incident energy have been investigated. The effects of pairing and odd-even nucleon numbers in new data and in the formula of Tel et al. [J. Phys. G. 29, 2169 (2003)] are discussed. We have determined three different parameters groups by the classification of nuclei into even-even, even-odd, and odd-even (n,d) reactions. In addition, since there are not enough experimental data available, we have considered two different parameters groups by the classification of nuclei into odd-A and even-A (n,t) reaction cross sections. The empirical formulas with two parameters for the evaluation of the (n,d) and (n,t) reactions cross sections are discussed in the present study.

  3. On the theory of phase transitions in dense neutron matter with generalized Skyrme interactions and anisotropic spin-triplet p-wave pairing in strong magnetic field

    NASA Astrophysics Data System (ADS)

    Tarasov, A. N.

    2014-03-01

    In the framework of the generalized non-relativistic Fermi-liquid approach we study phase transitions in spatially uniform dense pure neutron matter from normal to superfluid states with a spin-triplet p-wave pairing (similar to anisotropic superfluid phases 3He-A1 and 3He-A2) in a steady and homogeneous strong magnetic field H (but |\\mu_{\\text{n}}| H\\ll E_{\\text{c}}<\\varepsilon_{\\text{F}}(n) , where \\mu_{\\text{n}} is the magnetic dipole moment of a neutron, E_{\\text{c}} is the cutoff energy and \\varepsilon_{\\text{F}}(n) is the Fermi energy in neutron matter with density of particles n). The previously derived general formulas (valid for the arbitrary parametrization of the effective Skyrme interaction in neutron matter) for phase transition (PT) temperatures T_{\\text{c}1,2}(n,H) (which are nonlinear functions of the density n and linear functions of the magnetic field H) are specified here for new generalized BSk20 and BSk21 parameterizations of the Skyrme forces (with additional terms dependent on the density n) in the interval 0.1\\cdot n_{0} < n<3.0\\cdot n_{0} , where n_{0}=0.17\\ \\text{fm}^{-3} is the nuclear density. Our main results are mathematical expressions and figures for PT temperatures in the absence of magnetic field, T_{\\text{c0,BSk20}}(n)< 0.17\\ \\text{MeV} and T_{\\text{c0,BSk21}}(n)< 0.064\\ \\text{MeV} (at E_{\\text{c}}=10\\ \\text{MeV} ), and T_{\\text{c1,2}}(n,H) in strong magnetic fields (which may approach to 10^{17}\\ \\text{G} or even more as in the liquid outer core of magnetars —strongly magnetized neutron stars). These are realistic non-monotone functions with a bell-shaped density profile.

  4. Neutron scattering studies of short-range order, atomic displacements, and effective pair interactions in a null-matrix Ni0.5262Pt0.48 crystal

    NASA Astrophysics Data System (ADS)

    Rodriguez, J. A.; Moss, S. C.; Robertson, J. L.; Copley, J. R. D.; Neumann, D. A.; Major, J.

    2006-09-01

    The best known exception to the Heine-Sampson and Bieber-Gauthier arguments for ordering effects in transition metal alloys (similar to the Hume-Rothery rules) is a NiPt alloy, whose phase diagram is similar to that of the CuAu system. Using neutron scattering we have investigated the local atomic order in a null-matrix Ni0.5262Pt0.48 single crystal. In a null-matrix alloy, the isotopic composition is adjusted so that the average neutron scattering length vanishes ( Ni62 has a negative scattering length nearly equal in magnitude to that of Pt). Consequently, all contributions to the total scattering depending on the average lattice are suppressed. The only remaining components of the elastic scattering are the short-range order (SRO) and size effect terms. These data permit the extraction of the SRO parameters (concentration-concentration correlations) as well as the displacement parameters (concentration-displacement correlations). Using the Krivoglaz-Clapp-Moss theory, we obtain the effective pair interactions (EPIs) between near neighbors in the alloy. The results can be used by theorists to model the alloy in the context of the electronic theory of alloy phase stability, including a preliminary evaluation of the local species-dependent displacements. Our maps of V(q) , the Fourier transform of the EPIs, show very similar shapes in the experimental and reconstructed data. This is of importance when comparing to electronic structure calculations.

  5. Analysis of proton and neutron pair breakings: High-spin structures of 124-127Te isotopes

    NASA Astrophysics Data System (ADS)

    Kumar, Vikas; Srivastava, P. C.; Ermamatov, M. J.; Morales, Irving O.

    2015-10-01

    In the present work recently available experimental data for high-spin states of four nuclei, Te12452, Te12552, Te12652, and Te12752, have been interpreted using state-of-the-art shell model calculations. The calculations have been performed in the 50-82 valence shell composed of 1g7/2, 2d5/2, 1h11/2, 3s1/2, and 2d3/2 orbitals. We have compared our results with the available experimental data for excitation energies and transition probabilities, including high-spin states. The results are in reasonable agreement with the available experimental data. The wave functions, particularly, the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines are discussed. We have also estimated overall contribution of three-body forces in the energy level shifting. Finally, results with modified effective interaction are also reported.

  6. Magnetic Fluctuations in Pair-Density-Wave Superconductors

    NASA Astrophysics Data System (ADS)

    Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.

    2016-04-01

    Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].

  7. Magnetic Fluctuations in Pair-Density-Wave Superconductors.

    PubMed

    Christensen, Morten H; Jacobsen, Henrik; Maier, Thomas A; Andersen, Brian M

    2016-04-22

    Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)]. PMID:27152819

  8. Pairing in bulk nuclear matter beyond BCS

    SciTech Connect

    Ding, D.; Dickhoff, W. H.; Dussan, H.; Witte, S. J.; Rios, A.; Polls, A.

    2014-10-15

    The influence of short-range correlations on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the {sup 3}P{sub 2}−{sup 3}F{sub 2} coupled channel in pure neutron matter. This effect is studied for different realistic interactions including one based on chiral perturbation theory. The gap in this channel vanishes at all relevant densities due to the treatment of these correlations. We also consider the effect of long-range correlations by including polarization terms in addition to the bare interaction which allow the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters allowed to have reasonable values consistent with the available literature. Preliminary results indicate that reasonable values of these parameters do not generate a gap in the {sup 3}P{sub 2}−{sup 3}F{sub 2} coupled channel either for all three realistic interactions although the pairing interaction becomes slightly more attractive.

  9. Miscibility gap and phonon thermodynamics of Fe-Au alloys studied by inelastic neutron scattering and nuclear-resonant inelastic x-ray scattering

    SciTech Connect

    Muñoz, Jorge A.; Fultz, Brent

    2015-07-23

    Recent measurements of the phonon spectra of several Au-rich alloys of face-centered-cubic Fe-Au using inelastic neutron scattering and nuclear-resonant inelastic x-ray scattering are summarized. The Wills-Harrison model, accounting for charge transfer upon alloying, is used to explain the observed negative excess vibrational entropy of mixing, which increases the miscibility gap temperature in the system by an estimated maximum of 550 K and we adjudicate to a charge transfer from the Fe to the Au atoms that results in an increase in the electron density in the free-electron-like states and in stronger sd-hybridization. When Au is the solvent, this softens the Fe–Fe bonds but stiffens the Au–Au and Au–Fe bonds which results in a net stiffening relative to the elemental components.

  10. Effect of polarization on superfluidity in low density neutron matter

    NASA Technical Reports Server (NTRS)

    Clark, J. W.; Kallman, C.-G.; Yang, C.-H.; Chakkalakal, D. A.

    1976-01-01

    The singlet-state quasi-particle interaction in neutron matter is examined on the basis of results of a detailed evaluation of the Landau Fermi-liquid parameters for pure neutron effects, including polarization effects. This means that the interaction induced by exchange of density and spin-density excitations is taken into account. It is shown that polarization actually works to suppress the pairing matrix elements, owing to the spin dependence of the quasi-particle interaction and, ultimately, the balance of attraction, repulsion, and spin dependence in the fundamental two-neutron interaction. Since the isotropic energy gap and the condensation energy in low-density neutron-star matter are extremely sensitive functions of the pairing matrix elements, they will also be suppressed by the polarizability of the neutron medium.

  11. Odd-even staggering in neutron drip line nuclei

    NASA Astrophysics Data System (ADS)

    Changizi, S. A.; Qi, Chong

    2016-07-01

    We have done systematic Hartree-Fock-Bogoliubov calculations in coordinate space on the one-quasi-particle energies and binding energy odd-even staggering (OES) in semi-magic nuclei with the zero-range volume, mixed and surface pairing forces in order to explore the influence of their density dependence. The odd-N isotopes are calculated within the blocking scheme. The strengths for the pairing forces are determined in two schemes by fitting locally to reproduce pairing gap in 120Sn and globally to all available data on the OES of semi-magic nuclei with Z ≥ 8. In the former calculations, there is a noticeable difference between the neutron mean gaps in neutron-rich O, Ca, Ni and Sn isotopes calculated with the surface pairing and those with the mixed and volume pairing. The difference gets much smaller if the globally optimized pairing strengths are employed. The heavier Pb isotopes show the opposite trend. Moreover, large differences between the mean gap and the OES may be expected in both calculations when one goes towards the neutron drip line.

  12. Pairing forces in nuclei

    SciTech Connect

    Chasman, R.R.

    1996-12-31

    In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.

  13. Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductor La2-x(Sr,Ba)xCuO4

    NASA Astrophysics Data System (ADS)

    Wagman, J. J.; Carlo, J. P.; Gaudet, J.; Van Gastel, G.; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Kolesnikov, A. I.; Savici, A. T.; Kim, Y. J.; Zhang, H.; Ellis, D.; Zhao, Y.; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, B. D.

    2016-03-01

    We present time-of-flight neutron scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 ≤x ≤0.095 and La2-xSrxCuO4 (LSCO) with x =0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high-temperature cuprate superconductivity, ranging from insulating, three-dimensional commensurate long-range antiferromagnetic order, for x ≤0.02 , to two-dimensional (2D) incommensurate antiferromagnetism coexisting with superconductivity for x ≥0.05 . Previous work on lightly doped LBCO with x =0.035 showed a clear enhancement of the inelastic scattering coincident with the low-energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore, we show that the low-temperature, low-energy magnetic spectral weight is substantially larger for samples with nonsuperconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low-energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

  14. Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high temperature superconductor La2-x(Sr;Ba)xCuO4

    DOE PAGESBeta

    Wagman, J. J.; Carlo, Jeremy P.; Gaudet, J.; Van Gastel, G. J.; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Kolesnikov, Alexander I.; Savici, Andrei T.; Kim, Young -June; et al

    2016-03-14

    We present time-of-flight neutron-scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 ≤ x ≤ 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional commensurate long range antiferromagnetic order for x ≤ 0.02 to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossings of the highly dispersive spin excitationsmore » and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Lastly spin gaps, suppression of low energy magnetic spectral weight, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO« less

  15. DEATH LINE OF GAMMA-RAY PULSARS WITH OUTER GAPS

    SciTech Connect

    Wang, Ren-Bo; Hirotani, Kouichi E-mail: hirotani@tiara.sinica.edu.tw

    2011-08-01

    We analytically investigate the condition for a particle accelerator to be active in the outer magnetosphere of a rotation-powered pulsar. Within the accelerator (or the gap), the magnetic-field-aligned electric field accelerates electrons and positrons, which emit copious gamma-rays via the curvature process. If one of the gamma-rays emitted by a single pair materializes as a new pair on average, the gap is self-sustained. However, if the neutron-star spin-down rate decreases below a certain limit, the gap becomes no longer self-sustained and the gamma-ray emission ceases. We explicitly compute the multiplicity of cascading pairs and find that the obtained limit corresponds to a modification of the previously derived outer-gap death line. In addition to this traditional death line, we find another death line, which becomes important for millisecond pulsars, by separately considering the threshold of photon-photon pair production. Combining these traditional and new death lines, we give predictions on the detectability of gamma-ray pulsars with Fermi and AGILE. An implication for X-ray observations of heated polar-cap emission is also discussed.

  16. Skyrme-Hartree-Fock-Bogoliubov nuclear mass formulas: crossing the 0.6 MeV accuracy threshold with microscopically deduced pairing.

    PubMed

    Goriely, S; Chamel, N; Pearson, J M

    2009-04-17

    We present a new Skyrme-Hartree-Fock-Bogoliubov nuclear-mass model in which the contact-pairing force is constructed from microscopic pairing gaps of symmetric nuclear matter and neutron matter calculated from realistic two- and three-body forces, with medium-polarization effects included. With the pairing being treated more realistically than in any of our earlier models, the rms deviation with respect to essentially all the available mass data falls to 0.581 MeV, the best value ever found within the mean-field framework. Since our Skyrme force is also constrained by the properties of pure neutron matter, this new model is particularly well suited for application to astrophysical problems involving a neutron-rich environment, such as the elucidation of the r process of nucleosynthesis, and the description of supernova cores and neutron-star crusts. PMID:19518625

  17. Conventional and Unconventional Pairing and Condensates in Dilute Nuclear Matter

    NASA Astrophysics Data System (ADS)

    Clark, John W.; Sedrakian, Armen; Stein, Martin; Huang, Xu-Guang; Khodel, Victor A.; Shaginyan, Vasily R.; Zverev, Mikhail V.

    2016-03-01

    This contribution will survey recent progress toward an understanding of diverse pairing phenomena in dilute nuclear matter at small and moderate isospin asymmetry, with results of potential relevance to supernova envelopes and proto-neutron stars. Application of ab initio many-body techniques has revealed a rich array of temperature-density phase diagrams, indexed by isospin asymmetry, which feature both conventional and unconventional superfluid phases. At low density there exist a homogeneous translationally invariant BCS phase, a homogeneous LOFF phase violating translational invariance, and an inhomogeneous translationally invariant phase-separated BCS phase. The transition from the BCS to the BEC phases is characterized in terms of the evolution, from weak to strong coupling, of the pairing gap, condensate wave function, and quasiparticle occupation numbers and spectra. Additionally, a schematic formal analysis of pairing in neutron matter at low to moderate densities is presented that establishes conditions for the emergence of both conventional and unconventional pairing solutions and encompasses the possibility of dineutron formation.

  18. SPARK GAP SWITCH

    DOEpatents

    Neal, R.B.

    1957-12-17

    An improved triggered spark gap switch is described, capable of precisely controllable firing time while switching very large amounts of power. The invention in general comprises three electrodes adjustably spaced and adapted to have a large potential impressed between the outer electrodes. The central electrode includes two separate elements electrically connected togetaer and spaced apart to define a pair of spark gaps between the end electrodes. Means are provided to cause the gas flow in the switch to pass towards the central electrode, through a passage in each separate element, and out an exit disposed between the two separate central electrode elements in order to withdraw ions from the spark gap.

  19. Micromegas neutron beam monitor neutronics.

    PubMed

    Stephan, Andrew C; Miller, Laurence F

    2005-01-01

    The Micromegas is a type of ionising radiation detector that consists of a gas chamber sandwiched between two parallel plate electrodes, with the gas chamber divided by a Frisch grid into drift and amplification gaps. Investigators have applied it to a number of different applications, such as charged particle, X-ray and neutron detection. A Micromegas device has been tested as a neutron beam monitor at CERN and is expected to be used for that purpose at the Spallation Neutron Source (SNS) under construction in Oak Ridge, TN. For the Micromegas to function effectively as neutron beam monitor, it should cause minimal disruption to the neutron beam in question. Specifically, it should scatter as few neutrons as possible and avoid neutron absorption when it does not contribute to generating useful information concerning the neutron beam. Here, we present the results of Monte Carlo calculations of the effect of different types of wall materials and detector gases on neutron beams and suggest methods for minimising disruption to the beam. PMID:16381746

  20. Bridge the Gap.

    ERIC Educational Resources Information Center

    Klein, Mel; Cufaude, Jeffrey B.

    1989-01-01

    This document consists of two paired articles: the first, "Preparing Faculty Out of Class Experiences," by Mel Klein, and the second, "Help Advisers Be More Than Ghost Signatures," by Jeffrey B. Calfaude. Each article shares insights on how faculty advisers "bridge the gap" between students and faculty. When faculty members are asked to advise…

  1. The Role of Three-Nucleon Forces and Many-Body Processes in Nuclear Pairing

    SciTech Connect

    Holt, Jason D.

    2013-01-01

    We present microscopic valence-shell calculations of pairing gaps in the calcium isotopes, focusing on the role of three-nucleon (3N) forces and manybody processes. In most cases, we find a reduction in pairing strength when the leading chiral 3N forces are included, compared to results with lowmomentum two-nucleon (NN) interactions only. This is in agreement with a recent energy density functional study. At the NN level, calculations that include particle particle and hole hole ladder contributions lead to smaller pairing gaps compared with experiment. When particle hole contributions as well as the normal-ordered one- and two-body parts of 3N forces are consistently included to third order, we find reasonable agreement with experimental three-point mass differences. This highlights the important role of 3N forces and manybody processes for pairing in nuclei. Finally, we relate pairing gaps to the evolution of nuclear structure in neutron-rich calcium isotopes and study the predictions for the 2+ excitation energies, in particular for 54Ca.

  2. Pick a Pair. Pancake Pairs

    ERIC Educational Resources Information Center

    Miller, Pat

    2005-01-01

    Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…

  3. The Subtleties of Pairing and Collective Structures in Deformed Nuclei

    NASA Astrophysics Data System (ADS)

    Sharpey-Schafer, J. F.

    2015-11-01

    It is well known that simple monopole pairing is a pretty crude approximation. It can account for the observations that the ground states of all even-even nuclei have spin-parity 01+ and that there is a pairing gap above the ground state in deformed nuclei before particle-hole configurations can be excited. As an approximation it is best for proton and neutron mid-shell nuclei where the available single particle Nilsson wavefunctions have large overlaps. However at the beginning of regions of deformation, where high-K orbitals can be bought to the Fermi surface from a lower shell, simple monopole pairing is inadequate in describing the physics of the observed data. More recently, with a considerable increase in the quantity and quality of experimental data available, configuration dependent pairing has been used to account for the properties of low-lying first excited 02+ states in N = 88 and 90 nuclei at the onset of deformation in the rare earths. The properties of 02+ states in these and other nuclei at the start of regions of deformation and the effects of blocking of pairing leading to a decrease in the backbending critical frequencies in odd nuclei are presented.

  4. The Slot Gap Model for Pulsar High-Energy Emission

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alexander

    2004-01-01

    A new picture of pulsar high-energy emission is proposed that is different from both the traditional polar cap and outer gap models, but combines elements of each. The slot gap model is based on electron acceleration along the edge of the open field region from the neutron star surface to near the light cylinder. Along the last open field line, the pair formation front rises to very high altitude forming a slot gap, where the accelerating electric field is unscreened by pairs. Electrons continue to accelerate to high altitudes in the slot gap, reaching a radiation reaction-limited energy of several TeV. The resulting radiation pattern features sharp caustics on the trailing edge of the open field region, allowing for the possibility of double-peaked pulse profiles very similar to those observed in gamma-ray pulsars. Since emission from a large range of altitudes arrives in phase, this model very naturally explains the phase alignment of radiation at all wavelengths from the Crab pulsar.

  5. Microscopic Structure of Contact Ion Pairs in Concentrated LiCl- and LiClO4-Tetrahydrofuran Solutions Studied by Low-Frequency Isotropic Raman Scattering and Neutron Diffraction with (6)Li/(7)Li Isotopic Substitution Methods.

    PubMed

    Kameda, Yasuo; Ebina, Saki; Amo, Yuko; Usuki, Takeshi; Otomo, Toshiya

    2016-05-26

    Low-frequency isotropic Raman scattering and time-of-flight neutron diffraction measurements were carried out for (6)Li/(7)Li and H/D isotopically substituted *LiCl- and *LiClO4-tetrahydrofuran (*THF) solutions in order to obtain microscopic insight into solvated Li(+), Li(+)···Cl(-) and Li(+)···ClO4(-) contact ion pairs formed in concentrated THF solutions. Symmetrical stretching vibrational mode of solvated Li(+) in LiCl and LiClO4 solutions was observed at ν = 181-184 and 140 cm(-1), respectively. The stretching vibrational mode of Li(+)···Cl(-) and Li(+)···ClO4(-) solvated contact ion pairs formed in 4 mol % (6)LiCl-THF-h8 and (7)LiCl-THF-h8 solutions was found at ν = 469 and 435 cm(-1), respectively. Detailed structural properties of solvated Li(+) and the contact ion pairs were derived from the least-squares fitting analyses of the first-order difference function, ΔLi(Q), obtained from neutron diffraction measurements on (6)Li/(7)Li isotopically substituted THF-d8 solutions. It has been revealed that Li(+) takes 4-fold coordination in the average local structure of Li(+)X(-)(THF)3, X = Cl and ClO4. The nearest neighbor Li(+)···O(THF) distance was determined to be 2.21 ± 0.01 Å and 2.07 ± 0.01 Å for 4 mol % *LiCl- and 10 mol % *LiClO4-THF-d8 solutions, respectively. The Li(+)···anion distances for Li(+)···Cl(-) and Li(+)···O(ClO4(-)) contact ion pairs were determined to be 2.4 ± 0.1 Å and 2.19 ± 0.01 Å, respectively. The nearest neighbor Li(+)···THF interaction is significantly modified by the anion in the first solvation shell. PMID:27157529

  6. Fiber optic gap gauge

    DOEpatents

    Wood, Billy E.; Groves, Scott E.; Larsen, Greg J.; Sanchez, Roberto J.

    2006-11-14

    A lightweight, small size, high sensitivity gauge for indirectly measuring displacement or absolute gap width by measuring axial strain in an orthogonal direction to the displacement/gap width. The gap gauge includes a preferably titanium base having a central tension bar with springs connecting opposite ends of the tension bar to a pair of end connector bars, and an elongated bow spring connected to the end connector bars with a middle section bowed away from the base to define a gap. The bow spring is capable of producing an axial strain in the base proportional to a displacement of the middle section in a direction orthogonal to the base. And a strain sensor, such as a Fabry-Perot interferometer strain sensor, is connected to measure the axial strain in the base, so that the displacement of the middle section may be indirectly determined from the measurement of the axial strain in the base.

  7. Pairing in hot rotating nuclei

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2008-12-15

    Nuclear pairing properties are studied within an approach that includes the quasiparticle-number fluctuation (QNF) and coupling to the quasiparticle-pair vibrations at finite temperature and angular momentum. The formalism is developed to describe noncollective rotations about the symmetry axis. The numerical calculations are performed within a doubly folded equidistant multilevel model as well as several realistic nuclei. The results obtained for the pairing gap, total energy, and heat capacity show that the QNF smoothes out the sharp SN phase transition and leads to the appearance of a thermally assisted pairing gap in rotating nuclei at finite temperature. The corrections due to the dynamic coupling to SCQRPA vibrations and particle-number projection are analyzed. The effect of backbending of the momentum of inertia as a function of squared angular velocity is also discussed.

  8. Winning Pairs.

    ERIC Educational Resources Information Center

    Monsour, Florence

    2000-01-01

    Mentoring programs that pair experienced and first-time teachers are gaining prominence in supporting, developing, and retaining new teachers. The successful Beginning Teacher Assistance program at University of Wisconsin-River Falls was designed to give new K-12 teachers the opportunity for yearlong, structured support from mentor teachers. (MLH)

  9. Switchable radioactive neutron source device

    DOEpatents

    Stanford, G.S.; Rhodes, E.A.; Devolpi, A.; Boyar, R.E.

    1987-11-06

    This invention is a switchable neutron generating apparatus comprised of a pair of plates, the first plate having an alpha emitter section on it and the second plate having a target material portion on it which generates neutrons when its nuclei absorb an alpha particle. In operation, the alpha portion of the first plate is aligned with the neutron portion of the second plate to produce neutrons and brought out of alignment to cease production of neutrons. 3 figs.

  10. Switchable radioactive neutron source device

    DOEpatents

    Boyar, Robert E.; DeVolpi, Alexander; Stanford, George S.; Rhodes, Edgar A.

    1989-01-01

    This invention is a switchable neutron generating apparatus comprised of a pair of plates, the first plate having an alpha emitter section on it and the second plate having a target material portion on it which generates neutrons when its nuclei absorb an alpha particle. In operation, the alpha portion of the first plate is aligned with the neutron portion of the second plate to produce neutrons and brought out of alignment to cease production of neutrons.

  11. Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Qisi; Park, J. T.; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J. W.; Ivanov, A.; Chi, Songxue; Matsuda, M.; Cao, Huibo; Birgeneau, R. J.; Efremov, D. V.; Zhao, Jun

    2016-05-01

    An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s -wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s± or d -wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in Tc in the S-doped iron selenide superconductors KxFe2 -y(Se1-zSz) 2 . We show that a rather sharp magnetic resonant mode well below the superconducting gap (2 Δ ) in the undoped sample (z =0 ) is replaced by a broad hump structure above 2 Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.

  12. Speciation of As(III) and As(V) in water and sediment using reverse-phase ion-pair high-performance liquid chromatography-neutron activation analysis (HPLC-NAA).

    PubMed

    Tulasi, Delali; Adotey, Dennis; Affum, Andrews; Carboo, Derick; Serfor-Armah, Yaw

    2013-10-01

    Total As content and the As species distribution in water and sediments from the Kwabrafo stream, a major water body draining the Obuasi gold mining community in southwestern Ghana, have been investigated. Total As content was determined by instrumental neutron activation analysis (INAA). Ion-pair reverse phase high-performance liquid chromatography-neutron activation analysis (HPLC-NAA) was used for speciation of As species. Solid phase extraction with phosphate buffer was used to extract soluble As species from lyophilized sediment. The mass balance after phosphate extraction of soluble As species in sediment varied from 89 to 96 %. Compositionally appropriate reference material International Atomic Energy Agency (IAEA)-Lake Sediment (SL)-1 was used to check the validity of INAA method for total As determination. The measured values are in good agreement with the IAEA recommended value and also within the 95 % confidence interval. The accuracy of the measurement in terms of relative deviation from the IAEA recommended value was ±0.83 %. "In-house" prepared As(III) and As(V) standards were used to validate the HPLC-INAA method used for the As species determination. Total As concentration in the water samples ranged from 1.15 to 9.20 mg/L. As(III) species in water varied from 0.13 to 0.7 mg/L, while As(V) species varied from 0.79 to 3.85 mg/L. Total As content in sediment ranged from 2,134 to 3,596 mg/kg dry mass. The levels of As(III) and As(V) species in the sediment ranges from 138 to 506 mg/kg dry mass and 156 to 385 mg/kg dry mass, respectively. PMID:23494192

  13. Breaking of Cooper pairs in 108Pd

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Kakavand, T.; Razavi, R.

    2016-04-01

    In this paper, breaking of Cooper pairs in 108Pd is investigated within the canonical ensemble framework and the BCS model. Our results show an evidence of two phase transitions, which are related to neutron and proton systems. Also, with consideration of pairing interaction, the role of neutron and proton systems in entropy, spin cutoff parameter and as a result in the moment of inertia are investigated. The results show minor role for the proton system at low temperatures and approximately equal roles for both neutron and proton systems after the critical temperature. Good agreement was observed between obtained results and the experimental data.

  14. Isovector pairing effect on the moments of inertia of proton-rich heated nuclei

    NASA Astrophysics Data System (ADS)

    Ami, I.; Fellah, M.; Benhamouda, N.; Allal, N. H.; Belabbas, M.

    2012-02-01

    The perpendicular and parallel moments of inertia are calculated as a function of the temperature by taking into account the isovector pairing. The used single-particles energies are those of a deformed Woods-Saxon mean-field. The obtained results are compared to their homologues of the conventional Finite Temperature BCS (FTBCS) theory. With this aim, the generalized gap equations have been solved for even-even heated deformed nuclei such as Z = 30 - 38 and N - Z = 0, 2, 4. The isovector pairing effect leads to a change in the behavior of the perpendicular and parallel moments of inertia. Moreover, there is a non-negligible discrepancy between the perpendicular and parallel moments of inertia values calculated within the two models when T < Tcnp (Tcnp being the critical temperature beyond which the neutron-proton (np) gap parameter vanishes). Beyond this temperature, a discrepancy between the two models persists. It is due to the shift of the critical temperatures of the proton (Tcpp) and neutron (Tcnn) systems when evaluated with and without inclusion of the isovector pairing effect.

  15. Gap Junctions

    PubMed Central

    Nielsen, Morten Schak; Axelsen, Lene Nygaard; Sorgen, Paul L.; Verma, Vandana; Delmar, Mario; Holstein-Rathlou, Niels-Henrik

    2013-01-01

    Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease. © 2012 American Physiological Society. Compr Physiol 2:1981-2035, 2012. PMID:23723031

  16. Nucleon pairing in Sn isotopes

    NASA Astrophysics Data System (ADS)

    Imasheva, L.; Ishkhanov, B.; Stepanov, M.; Tretyakova, T.

    2016-01-01

    The systematics of excited states in Sn isotopes are discussed on basis of pairing interaction in nuclei. Nucleon paring leads to formation of excited states multiplets. The estimation of multiplet splitting based on experimental nuclear masses allows one to calculate the position of excited states with different seniority in δ-approximation. The wide systematics of the spectra of Sn isotopes gives a possibility to check the pairing interaction for different subshells and consider the multiplets of excited states in the neutron-rich isotopes far from stability.

  17. GUIDE FOR POLARIZED NEUTRONS

    DOEpatents

    Sailor, V.L.; Aichroth, R.W.

    1962-12-01

    The plane of polarization of a beam of polarized neutrons is changed by this invention, and the plane can be flipped back and forth quicitly in two directions in a trouble-free manner. The invention comprises a guide having a plurality of oppositely directed magnets forming a gap for the neutron beam and the gaps are spaced longitudinally in a spiral along the beam at small stepped angles. When it is desired to flip the plane of polarization the magnets are suitably rotated to change the direction of the spiral of the gaps. (AEC)

  18. β -Decay Half-Lives of 110 Neutron-Rich Nuclei across the N =82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process

    NASA Astrophysics Data System (ADS)

    Lorusso, G.; Nishimura, S.; Xu, Z. Y.; Jungclaus, A.; Shimizu, Y.; Simpson, G. S.; Söderström, P.-A.; Watanabe, H.; Browne, F.; Doornenbal, P.; Gey, G.; Jung, H. S.; Meyer, B.; Sumikama, T.; Taprogge, J.; Vajta, Zs.; Wu, J.; Baba, H.; Benzoni, G.; Chae, K. Y.; Crespi, F. C. L.; Fukuda, N.; Gernhäuser, R.; Inabe, N.; Isobe, T.; Kajino, T.; Kameda, D.; Kim, G. D.; Kim, Y.-K.; Kojouharov, I.; Kondev, F. G.; Kubo, T.; Kurz, N.; Kwon, Y. K.; Lane, G. J.; Li, Z.; Montaner-Pizá, A.; Moschner, K.; Naqvi, F.; Niikura, M.; Nishibata, H.; Odahara, A.; Orlandi, R.; Patel, Z.; Podolyák, Zs.; Sakurai, H.; Schaffner, H.; Schury, P.; Shibagaki, S.; Steiger, K.; Suzuki, H.; Takeda, H.; Wendt, A.; Yagi, A.; Yoshinaga, K.

    2015-05-01

    The β -decay half-lives of 110 neutron-rich isotopes of the elements from Rb 37 to Sn 50 were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r -process calculations and reinforce the notion that the second (A ≈130 ) and the rare-earth-element (A ≈160 ) abundance peaks may result from the freeze-out of an (n ,γ )⇄(γ ,n ) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r -process events.

  19. FAST NEUTRON SPECTROMETER USING SPACED SEMICONDUCTORS FOR MEASURING TOTAL ENERGY OF NEUTRONS CAPTURED

    DOEpatents

    Love, T.A.; Murray, R.B.

    1964-04-14

    A fast neutron spectrometer was designed, which utilizes a pair of opposed detectors having a layer of /sup 6/LiF between to produce alpha and T pair for each neutron captured to provide signals, which, when combined, constitute a measure of neutron energy. (AEC)

  20. Contact Pairing Interaction for the Hartree-Fock-Bogoliubov Calculations

    SciTech Connect

    Dobaczewski, J.

    2001-10-18

    Properties of density-dependent contact pairing interactions in nuclei are discussed. It is shown that the pairing interaction that is intermediate between surface and volume pairing forces gives the pairing gaps that are compatible with the experimental odd-even mass staggering. Results of the deformed Hartree-Fock-Bogoliubov calculations for this ''mixed'' pairing interaction, and using the transformed harmonic oscillator basis, are presented.

  1. Pair-Starved Pulsar Magnetospheres

    NASA Technical Reports Server (NTRS)

    Muslimov, Alex G.; Harding, Alice K.

    2009-01-01

    We propose a simple analytic model for the innermost (within the light cylinder of canonical radius, approx. c/Omega) structure of open-magnetic-field lines of a rotating neutron star (NS) with relativistic outflow of charged particles (electrons/positrons) and arbitrary angle between the NS spin and magnetic axes. We present the self-consistent solution of Maxwell's equations for the magnetic field and electric current in the pair-starved regime where the density of electron-positron plasma generated above the pulsar polar cap is not sufficient to completely screen the accelerating electric field and thus establish thee E . B = 0 condition above the pair-formation front up to the very high altitudes within the light cylinder. The proposed mode1 may provide a theoretical framework for developing the refined model of the global pair-starved pulsar magnetosphere.

  2. Magicity of neutron-rich nuclei within relativistic self-consistent approaches

    NASA Astrophysics Data System (ADS)

    Li, Jia Jie; Margueron, Jérôme; Long, Wen Hui; Van Giai, Nguyen

    2016-02-01

    The formation of new shell gaps in intermediate mass neutron-rich nuclei is investigated within the relativistic Hartree-Fock-Bogoliubov theory, and the role of the Lorentz pseudo-vector and tensor interactions is analyzed. Based on the Foldy-Wouthuysen transformation, we discuss in detail the role played by the different terms of the Lorentz pseudo-vector and tensor interactions in the appearing of the N = 16, 32 and 34 shell gaps. The nuclei 24O, 48Si and 52,54Ca are predicted with a large shell gap and zero (24O, 52Ca) or almost zero (48Si, 54Ca) pairing gap, making them candidates for new magic numbers in exotic nuclei. We find from our analysis that the Lorentz pseudo-vector and tensor interactions induce very specific evolutions of single-particle energies, which could clearly sign their presence and reveal the need for relativistic approaches with exchange interactions.

  3. Discovery of 40Mg and 42Al suggests neutron drip-line slant towards heavier isotopes.

    PubMed

    Baumann, T; Amthor, A M; Bazin, D; Brown, B A; Folden, C M; Gade, A; Ginter, T N; Hausmann, M; Matos, M; Morrissey, D J; Portillo, M; Schiller, A; Sherrill, B M; Stolz, A; Tarasov, O B; Thoennessen, M

    2007-10-25

    A fundamental question in nuclear physics is what combinations of neutrons and protons can make up a nucleus. Many hundreds of exotic neutron-rich isotopes have never been observed; the limit of how many neutrons a given number of protons can bind is unknown for all but the lightest elements, owing to the delicate interplay between single particle and collective quantum effects in the nucleus. This limit, known as the neutron drip line, provides a benchmark for models of the atomic nucleus. Here we report a significant advance in the determination of this limit: the discovery of two new neutron-rich isotopes--40Mg and 42Al--that are predicted to be drip-line nuclei. In the past, several attempts to observe 40Mg were unsuccessful; moreover, the observation of 42Al provides an experimental indication that the neutron drip line may be located further towards heavier isotopes in this mass region than is currently believed. In stable nuclei, attractive pairing forces enhance the stability of isotopes with even numbers of protons and neutrons. In contrast, the present work shows that nuclei at the drip line gain stability from an unpaired proton, which narrows the shell gaps and provides the opportunity to bind many more neutrons. PMID:17960237

  4. Nucleon-pair approximation to the nuclear shell model

    NASA Astrophysics Data System (ADS)

    Zhao, Y. M.; Arima, A.

    2014-12-01

    Atomic nuclei are complex systems of nucleons-protons and neutrons. Nucleons interact with each other via an attractive and short-range force. This feature of the interaction leads to a pattern of dominantly monopole and quadrupole correlations between like particles (i.e., proton-proton and neutron-neutron correlations) in low-lying states of atomic nuclei. As a consequence, among dozens or even hundreds of possible types of nucleon pairs, very few nucleon pairs such as proton and neutron pairs with spin zero, two (in some cases spin four), and occasionally isoscalar spin-aligned proton-neutron pairs, play important roles in low-energy nuclear structure. The nucleon-pair approximation therefore provides us with an efficient truncation scheme of the full shell model configurations which are otherwise too large to handle for medium and heavy nuclei in foreseeable future. Furthermore, the nucleon-pair approximation leads to simple pictures in physics, as the dimension of nucleon-pair subspace is always small. The present paper aims at a sound review of its history, formulation, validity, applications, as well as its link to previous approaches, with the focus on the new developments in the last two decades. The applicability of the nucleon-pair approximation and numerical calculations of low-lying states for realistic atomic nuclei are demonstrated with examples. Applications of pair approximations to other problems are also discussed.

  5. Gamma spectrum following neutron capture in {sup 167}Er

    SciTech Connect

    Visser, D.; Khoo, T.L.; Lister, C.J.

    1995-08-01

    Statistical decay from a highly excited state samples all the lower-lying states and, hence, provides a sensitive measure of the level density. Pairing has a major impact on the level density, e.g. creating a pair gap between the 0- and 2-quasiparticle configurations. Hence the shape of the statistical spectrum contains information on pairing, and can be used to provide information on the reduction of pairing with thermal excitation energy. For this reason, we measured the complete spectrum of {gamma}rays following thermal neutron capture in {sup 167}Er. The experiment was performed at the Brookhaven reactor using Compton-suppressed Ge detectors from TESSA. The spectrum, which was corrected for detector response and efficiency, reveals primary (first-step, high-energy) transitions up to nearly 8 MeV, secondary (last-step, lower-energy) transitions, as we as a continuous statistical component. Effort was expanded to identify all lines from contaminant sources and an upper limit of 5% was tentatively set for their contributions. The spectral shape of the statistical spectrum will be compared with theoretical spectra obtained from a calculation of pairing which accounts for a stepwise reduction of the pair correlations as the number of quasiparticles increases. The primary lines which decay directly to the near-yrast states will also be used to deduce the level densities.

  6. Influence of the Isovector Pairing Effect on Nuclear Statistical Quantities in N ≈ Z Even-Even Systems

    NASA Astrophysics Data System (ADS)

    Belabbas, M.; Fellah, M.; Allal, N. H.; Benhamouda, N.; Ami, I.; Oudih, M. R.

    The influence of the isovector neutron-proton (np) pairing effect on nuclear statistical quantities is studied in N ≈ Z even-even systems. Expressions of the energy, the entropy, and the heat capacity are established using a recently proposed temperature-dependent isovector pairing gap equations. They generalize the conventional finite temperature BCS (FTBCS) ones. The model is first numerically tested using the schematic one-level model. As a second step, realistic cases are considered using the single-particle energies of a deformed Woods-Saxon mean-field. It is shown that: (i) the gap parameter Δnp(T) behaves like Δtt(T), t = n, p, in the conventional FTBCS model and the critical temperature value Tcnp is such as Tcnppairing effect on the energy is a lowering of about 1%, on average, for all considered nuclei. Dealing with the entropy and the heat capacity, the np pairing effect appears only if the Tcnp value is sufficiently important.

  7. Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors.

    PubMed

    Wang, Qisi; Park, J T; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J W; Ivanov, A; Chi, Songxue; Matsuda, M; Cao, Huibo; Birgeneau, R J; Efremov, D V; Zhao, Jun

    2016-05-13

    An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s_{±} or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T_{c} in the S-doped iron selenide superconductors K_{x}Fe_{2-y}(Se_{1-z}S_{z})_{2}. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials. PMID:27232038

  8. TU-F-BRE-07: In Vivo Neutron Detection in Patients Undergoing Stereotactic Ablative Radiotherapy (SABR) for Primary Kidney Cancer Using 6Li and 7Li Enriched TLD Pairs

    SciTech Connect

    Lonski, P; Kron, T; Franich, R; Keehan, S; Siva, S; Taylor, M

    2014-06-15

    Purpose: Stereotactic ablative radiotherapy (SABR) for primary kidney cancer often involves the use of high-energy photons combined with a large number of monitor units. While important for risk assessment, the additional neutron dose to untargeted healthy tissue is not accounted for in treatment planning. This work aims to detect out-of-field neutrons in vivo for patients undergoing SABR with high-energy (>10 MV) photons and provides preliminary estimates of neutron effective dose. Methods: 3 variations of high-sensitivity LiF:Mg,Cu,P thermoluminescent dosimeter (TLD) material, each with varying {sup 6}Li / {sup 7}Li concentrations, were used in custom-made Perspex holders for in vivo measurements. The variation in cross section for thermal neutrons between Li isotopes was exploited to distinguish neutron from photon signal. Measurements were made out-of-field for 7 patients, each undergoing 3D-conformal SABR treatment for primary kidney cancer on a Varian 21iX linear accelerator. Results: In vivo measurements show increased signal for the {sup 6}Li enriched material for patients treated with 18 MV photons. Measurements on one SABR patient treated using only 6 MV showed no difference between the 3 TLD materials. The out-of-field photon signal decreased exponentially with distance from the treatment field. The neutron signal, taken as the difference between {sup 6}Li enriched and {sup 7}Li enriched TLD response, remains almost constant up to 50 cm from the beam central axis. Estimates of neutron effective dose from preliminary TLD calibration suggest between 10 and 30 mSv per 1000 MU delivered at 18 MV for the 7 patients. Conclusion: TLD was proven to be a useful tool for the purpose of in vivo neutron detection at out-of-field locations. Further work is required to understand the relationship between TL signal and neutron dose. Dose estimates based on preliminary TLD calibration in a neutron beam suggest the additional neutron dose was <30 mSv per 1000 MU at 18 MV.

  9. Exploring Neutron-Rich Oxygen Isotopes with MoNA

    SciTech Connect

    Frank, N.; Gade, A.; Peters, W. A.; Thoennessen, M.; Baumann, T.; Bazin, D.; Lecouey, J.-L.; Scheit, H.; Schiller, A.; Brown, J.; DeYoung, P. A.; Finck, J. E.; Hinnefeld, J.; Howes, R.; Luther, B.

    2007-11-30

    The Modular Neutron Array (MoNA) was used in conjunction with a large-gap dipole magnet (Sweeper) to measure neutron-unbound states in oxygen isotopes close to the neutron dripline. While no excited states were observed in {sup 24}O, a resonance at 45(2) keV above the neutron separation energy was observed in {sup 23}O.

  10. Effects of tensor couplings of ω and ρ mesons on 1S0 nucleon superfluidity in neutron star matter

    NASA Astrophysics Data System (ADS)

    Huang, Xiu-Lin; Xu, Yan; Liu, Cheng-Zhi; Liu, Guang-Zhou

    2016-03-01

    The 1S 0 nucleon superfluidity in neutron star matter was investigated in the framework of relativistic σ-ω-π-ρ model with the tensor couplings of ω and ρ mesons using the relativistic Hartree-Fock (RHF) approximation. It was found that the tensor couplings of ω and ρ mesons lead to a clear growth of the 1S 0 neutron pairing gap in the density range where there exists 1S 0 neutron superfluidity. The 1S 0 pairing gap of proton with the tensor couplings of ω and ρ mesons in the density range of ρB = 0.0-0.079fm-3 is lower and then in the density range of ρB = 0.079-0.383fm-3 higher than the corresponding value without the tensor couplings of ω and ρ mesons. Our results provide a basic to understand the influence of the tensor couplings of ω and ρ mesons on the cooling properties of neutron star.

  11. Pairing Nambu-Goldstone Modes within Nuclear Density Functional Theory.

    PubMed

    Hinohara, Nobuo; Nazarewicz, Witold

    2016-04-15

    We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the T=1 pairing condensate offers a quantitative description of the binding-energy differences of open-shell superfluid nuclei. We conclude that the pairing-rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing-rotational moments of inertia and demonstrate the mixing of the neutron and proton pairing-rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional. PMID:27127964

  12. Pair Cascades and Deathlines in Offset Magnetic Dipole Fields

    NASA Technical Reports Server (NTRS)

    Harding, Alice; Muslimov, Alex

    2010-01-01

    We investigate electron-positron pair cascades in a dipole magnetic field whose axis is offset from the neutron star center. In such a field geometry, the polar cap is displaced from the neutron star symmetry axis and the field line radius of curvature is modified. Using the modified parallel electric field near the polar cap of an offset dipole, we simulate pair cascades to determine the pair deathlines and pair multiplicities as a function of the offset parameter. We find that the pair multiplicity can change dramatically with a modest offset, with a significant increase on one side of the polar cap. Lower pair deathlines allow a larger fraction of the pulsar population, that include old and millisecond pulsars, to produce cascades with high multiplicity.

  13. Pairing Nambu-Goldstone Modes within Nuclear Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Hinohara, Nobuo; Nazarewicz, Witold

    2016-04-01

    We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the T =1 pairing condensate offers a quantitative description of the binding-energy differences of open-shell superfluid nuclei. We conclude that the pairing-rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing-rotational moments of inertia and demonstrate the mixing of the neutron and proton pairing-rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional.

  14. Counting the number of correlated pairs in a nucleus

    SciTech Connect

    Vanhalst, Maarten; Cosyn, Wim; Ryckebusch, Jan

    2011-09-15

    We suggest that the number of correlated nucleon pairs in an arbitrary nucleus can be estimated by counting the number of proton-neutron, proton-proton, and neutron-neutron pairs residing in a relative S state. We present numerical calculations of those amounts for the nuclei {sup 4}He, {sup 9}Be, {sup 12}C, {sup 27}Al, {sup 40}Ca, {sup 48}Ca, {sup 56}Fe, {sup 63}Cu, {sup 108}Ag, and {sup 197}Au. The results are used to predict the values of the ratios of the per-nucleon electron-nucleus inelastic scattering cross section to the deuteron in the kinematic regime where correlations dominate.

  15. Strong pairing approximation in comparison with the exact solutions to the pairing Hamiltonian

    NASA Astrophysics Data System (ADS)

    Lunyov, A. V.; Mikhajlov, V. M.

    2016-01-01

    Results of the Strong Pairing Approximation (SPA) as a method with the exact particle number conservation are compared with those of the quasiparticle method (QM). It is shown that SPA comes to the same equations as QM for the gap parameter, chemical potential and one- and two-quasiparticle states. Calculations are performed for 14864Gd84 as an example, and compared with the exact solutions to the pairing Hamiltonian.

  16. Neutronic reactor

    DOEpatents

    Wende, Charles W. J.; Babcock, Dale F.; Menegus, Robert L.

    1983-01-01

    A nuclear reactor includes an active portion with fissionable fuel and neutron moderating material surrounded by neutron reflecting material. A control element in the active portion includes a group of movable rods constructed of neutron-absorbing material. Each rod is movable with respect to the other rods to vary the absorption of neutrons and effect control over neutron flux.

  17. Double binding energy differences: Mean-field or pairing effect?

    NASA Astrophysics Data System (ADS)

    Qi, Chong

    2012-10-01

    In this Letter we present a systematic analysis on the average interaction between the last protons and neutrons in atomic nuclei, which can be extracted from the double differences of nuclear binding energies. The empirical average proton-neutron interaction Vpn thus derived from experimental data can be described in a very simple form as the interplay of the nuclear mean field and the pairing interaction. It is found that the smooth behavior as well as the local fluctuations of the Vpn in even-even nuclei with N ≠ Z are dominated by the contribution from the proton-neutron monopole interactions. A strong additional contribution from the isoscalar monopole interaction and isovector proton-neutron pairing interaction is seen in the Vpn for even-even N = Z nuclei and for the adjacent odd-A nuclei with one neutron or proton being subtracted.

  18. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  19. Interpretation of the high spin states in Lu161: A paired and unpaired study

    NASA Astrophysics Data System (ADS)

    Ma, Hai-Liang; Carlsson, B. Gillis; Ragnarsson, Ingemar; Ryde, Hans

    2014-07-01

    A paired cranked Nilsson-Strutinsky-Bogoliubov (CNSB) model is presented, which employs the same method to calculate the liquid-drop energy and moment of inertia as the unpaired cranked Nilsson-Strutinsky (CNS) model. In the CNSB model, the energy minimization is carried out in the mesh of pairing gaps Δ and Fermi levels λ as well as deformation parameters. The high spin states in Lu161 are then investigated with the CNSB and CNS models. The terminating structure shows a striking similarity with these two models. Combining the CNSB and CNS models, a complete understanding of high spin structures, including the normal deformed (ND) and triaxial strongly deformed (TSD) bands and observed side bands in Lu161, is achieved. It appears that the only important paired crossings are the first i13/2 neutron crossing and the first h11/2 proton crossing. For the description of the unpaired high spin crossings, it is important to be able to distinguish between the pseudospin partners in the proton N =4 shell, (d5/2,g7/2) and (d3/2,s1/2). The yrast bands are predicted to terminate, which explains the structure of a TSD-like band X2. A band crossing at I ≈36.5 for the TSD band in Lu161, unique within the chain of even-N Lu isotopes, is well described by the CNSB model.

  20. Bulk viscosity coefficients due to phonons in superfluid neutron stars

    SciTech Connect

    Manuel, Cristina; Tolos, Laura; Tarrús, Jaume E-mail: tarrus@ecm.ub.edu

    2013-07-01

    We calculate the three bulk viscosity coefficients as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system. The solution of the dynamical evolution of the phonon number density allows us to calculate the bulk viscosity coefficients as function of the phonon collisional rate and the phonon dispersion law, which depends on the neutron pairing gap. Our method of computation is rather general, and could be used for different superfluid systems, provided they share the same underlying symmetries. We find that the behavior with temperature of the bulk viscosity coefficients is dominated by the contributions coming from the collinear regime of the 2↔3 phonon processes. For typical star radial pulsation frequencies of ω ∼ 10{sup 4}s{sup −1}, we obtain that the bulk viscosity coefficients at densities n∼>4n{sub 0} are within 10% from its static value for T∼<10{sup 9} K and for the case of strong neutron superfluidity in the core with a maximum value of the {sup 3}P{sub 2} gap above 1 MeV, while, otherwise, the static solution is not a valid approximation to the bulk viscosity coefficients. Compared to previous results from Urca and modified Urca reactions, we conclude that at T ∼ 10{sup 9}K phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ∼ 2n{sub 0} when the opening of the Urca processes takes place.

  1. Matched-pair classification

    SciTech Connect

    Theiler, James P

    2009-01-01

    Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

  2. Vortex pairs on surfaces

    SciTech Connect

    Koiller, Jair

    2009-05-06

    A pair of infinitesimally close opposite vortices moving on a curved surface moves along a geodesic, according to a conjecture by Kimura. We outline a proof. Numerical simulations are presented for a pair of opposite vortices at a close but nonzero distance on a surface of revolution, the catenoid. We conjecture that the vortex pair system on a triaxial ellipsoid is a KAM perturbation of Jacobi's geodesic problem. We outline some preliminary calculations required for this study. Finding the surfaces for which the vortex pair system is integrable is in order.

  3. Short pulse neutron generator

    DOEpatents

    Elizondo-Decanini, Juan M.

    2016-08-02

    Short pulse neutron generators are described herein. In a general embodiment, the short pulse neutron generator includes a Blumlein structure. The Blumlein structure includes a first conductive plate, a second conductive plate, a third conductive plate, at least one of an inductor or a resistor, a switch, and a dielectric material. The first conductive plate is positioned relative to the second conductive plate such that a gap separates these plates. A vacuum chamber is positioned in the gap, and an ion source is positioned to emit ions in the vacuum chamber. The third conductive plate is electrically grounded, and the switch is operable to electrically connect and disconnect the second conductive plate and the third conductive plate. The at least one of the resistor or the inductor is coupled to the first conductive plate and the second conductive plate.

  4. Hard Photodisintegration of a Proton Pair

    DOE PAGESBeta

    Pomerantz, Ishay; Bubis, Nathaniel; Allada, Kalyan; Beck, Arie; Beck, Sara; Berman, Barry L.; Boeglin, Werner U.; Camsonne, Alexandre; Canan, Mustafa; Chirapatpimol, Khem; et al

    2010-01-08

    We present the first study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. An s^{-11} scaling of the cross section was observed, as predicted by the constituent counting rule. The onset of the scaling is at a higher energy and the cross section is significantly lower then for pn pair photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strongmore » energy-dependent structure not observed in deuteron photodisintegration.« less

  5. Hard Photodisintegration of a Proton Pair

    SciTech Connect

    Pomerantz, Ishay; Bubis, Nathaniel; Allada, Kalyan; Beck, Arie; Beck, Sara; Berman, Barry L.; Boeglin, Werner U.; Camsonne, Alexandre; Canan, Mustafa; Chirapatpimol, Khem; Cisbani, Evaristo; Cusanno, Francesco; de Jager, Cornelis W.; Dutta, Chirajib; Garibaldi, Franco; Geagla, Octavian; Gilman, Ronald; Glister, Jacqueline F.; Higinbotham, Douglas W.; Jiang, Xiaodong; Katramatou, A. T.; Khrosinkova, Elena; Lee, B. W.; LeRose, John J.; Lindgren, Richard A.; McCullough, Emily; Meekins, David G.; Michaels, Robert W.; Moffit, Bryan J.; Petratos, Gerassimos G.; Piasetzky, Eliazer I.; Qian, Xin; Qiang, Yi; Rodriguez, I.; Ron, Guy; Saha, Arun; Sarty, Adam J.; Sawatzky, Bradley D.; Schulte, Elaine C.; Shneor, Ran; Sparveris, NIkolaos; Subedi, Ramesh R.; Sulkosky, Vincent A.; Wang, Y.; Wojtsekhowski, Bogdan B.; Yan, X.; Yao, H.; Zhan, Xiaohui; Zheng, Xiaochao

    2010-01-08

    We present the first study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. An s^{-11} scaling of the cross section was observed, as predicted by the constituent counting rule. The onset of the scaling is at a higher energy and the cross section is significantly lower then for pn pair photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration.

  6. Nuclear pairing at finite temperature and angular momentum

    SciTech Connect

    Dang, N. Dinh; Hung, N. Quang

    2009-01-28

    We propose an approach to nuclear pairing at finite temperature and angular momentum. This approach includes the effects due to the quasiparticle-number fluctuation and dynamic coupling to pair vibrations within the self-consistent quasiparticle random-phase approximation. The pairing gaps, total energies, and heat capacities are calculated within a doubly folded multilevel model as well as several realistic nuclei. The results obtained show that, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out. This is manifested in a thermal pairing gap, which does not collapse at a critical temperature predicted by the conventional Bardeen-Cooper-Schrieffer's (BCS) theory, but has a tail extended to high temperatures. Moreover, this approach also predicts the appearance of a thermally assisted pairing at finite angular momentum. The effect of backbending of the momentum of inertia as a function of the square of angular velocity is also discussed.

  7. Topological nodal Cooper pairing in doped Weyl metals

    NASA Astrophysics Data System (ADS)

    Li, Yi; Haldane, F. D. M.

    We generalize the concept of Berry connection of the single-electron band structure to the two-particle Cooper pair states between two Fermi surfaces with opposite Chern numbers. Because of underlying Fermi surface topology, the pairing Berry phase acquires non-trivial monopole structure. Consequently, pairing gap functions have the topologically-protected nodal structure as vortices in the momentum space with the total vorticity solely determined by the monopole charge qp. The pairing nodes behave as the Weyl-Majorana points of the Bogoliubov-de Gennes pairing Hamiltonian. Their relation with the connection patterns of the surface modes from theWeyl band structure and the Majorana surface modes inside the pairing gap is also discussed. Under the approximation of spherical Fermi surfaces, the pairing symmetry are represented by monopole harmonic functions. The lowest possible pairing channel carries angular momentum number j =|qp|, and the corresponding gap functions are holomorphic or anti-holomorphic functions on Fermi surfaces. F.D.M.H. acknowledges the support from MRSEC NSF-DMR-1420541 and the W. M. Keck Foundation.

  8. Neutron stars as cosmic hadron physics laboratories

    NASA Technical Reports Server (NTRS)

    Pines, D.

    1985-01-01

    Extensive observations of Her-1 with the Exosat satellite have led to a new understanding of both the dynamics of neutron-star superfluids and the free precession of neutron stars. Detailed microscopic calculations on neutron matter and the properties of the pinned crustal superfluid are provided to serve as a basis for comparing theory with observation on neutron stars. Topics discussed include the Hadron matter equation of state, neutron star structure, Hadron superfluids, the vortex creep theory, Vela pulsar glitches, astrophysical constraints on neutron matter energy gaps, the 35 day periodicity of Her-1, and the neutron matter equation of state. It is concluded that since the post-glitch fits and the identification of the 35th periodicity in Her X-1 as stellar wobble require a rigid neutron matter equation of state, the astrophysical evidence for such an equation seems strong, as well as that for an intermediate Delta(rho) curve.

  9. Critical Schwinger Pair Production

    NASA Astrophysics Data System (ADS)

    Gies, Holger; Torgrimsson, Greger

    2016-03-01

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential Berezinskii-Kosterlitz-Thouless-type scaling, and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality.

  10. Critical Schwinger Pair Production.

    PubMed

    Gies, Holger; Torgrimsson, Greger

    2016-03-01

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential Berezinskii-Kosterlitz-Thouless-type scaling, and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality. PMID:26991162

  11. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2010-01-08

    Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

  12. Pair contact process with diffusion of pairs

    NASA Astrophysics Data System (ADS)

    Santos, F. L.; Dickman, Ronald; Fulco, U. L.

    2011-03-01

    The pair contact process (PCP) is a nonequilibrium stochastic model which, like the basic contact process (CP), exhibits a phase transition to an absorbing state. The two models belong to the directed percolation (DP) universality class, despite the fact that the PCP possesses infinitely many absorbing configurations whereas the CP has but one. The critical behavior of the PCP with hopping by particles (PCPD) is as yet unclear. Here we study a version of the PCP in which nearest-neighbor particle pairs can hop but individual particles cannot. Using quasistationary simulations for three values of the diffusion probability (D = 0.1, 0.5 and 0.9), we find convincing evidence of DP-like critical behavior.

  13. Surface Mounted Neutron Generators

    NASA Astrophysics Data System (ADS)

    Elizondo-Decanini, Juan M.

    2012-10-01

    A deuterium-tritium (DT) base reaction pulsed neutron generator packaged in a flat computer chip shape of 1.54 cm (0.600 in) wide by 3.175 cm (1.25 in) length and 0.3 cm (0.120 in) thick has been successfully demonstrated to produce 14 MeV neutrons at a rate of 10^9 neutrons per second. The neutron generator is based on a deuterium ion beam accelerated to impact a tritium loaded target. The accelerating voltage is in the 15 to 20 kV in a 3 mm (0.120 in) gap, the ion beam is shaped by using a lens design to produce a flat ion beam that conforms to the flat rectangular target. The ion source is a simple surface mounted deuterium filled titanium film with a fused gap that operates at a current-voltage design to release the deuterium during a pulse length of about 1 μs. We present the general description of the working prototypes, which we have labeled the ``NEUTRISTOR.''[4pt] Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration. Work funded by the LDRD office.

  14. Exotic Paired States with Anisotropic Spin-Dependent Fermi Surfaces

    SciTech Connect

    Feiguin, Adrian E.; Fisher, Matthew P. A.

    2009-07-10

    We propose a model for realizing exotic paired states in cold Fermi gases by using a spin-dependent optical lattice to engineer mismatched Fermi surfaces for each hyperfine species. The BCS phase diagram shows a stable paired superfluid state with coexisting pockets of momentum space with gapless unpaired carriers, similar to the Sarma state in polarized mixtures, but in our case the system is unpolarized. We propose the possible existence of an exotic 'Cooper-pair Bose-metal' phase, which has a gap for single fermion excitations but gapless and uncondensed 'Cooper-pair' excitations residing on a 'Bose surface' in momentum space.

  15. The photon PDF in events with rapidity gaps

    NASA Astrophysics Data System (ADS)

    Harland-Lang, L. A.; Khoze, V. A.; Ryskin, M. G.

    2016-05-01

    We consider photon-initiated events with large rapidity gaps in proton-proton collisions, where one or both protons may break up. We formulate a modified photon PDF that accounts for the specific experimental rapidity gap veto, and demonstrate how the soft survival probability for these gaps may be implemented consistently. Finally, we present some phenomenological results for the two-photon induced production of lepton and W boson pairs.

  16. Primordial nuggets survival and QCD pairing

    NASA Astrophysics Data System (ADS)

    Lugones, G.; Horvath, J. E.

    2004-03-01

    We reexamine the problem of boiling and surface evaporation of quark nuggets in the cosmological quark-hadron transition with the explicit consideration of pairing between quarks in a color-flavor locked state. Assuming that primordial quark nuggets are actually formed, we analyze the consequences of pairing on the rates of boiling and surface evaporation in order to determine whether they could have survived with substantial mass. We find a substantial quenching of the evaporation+boiling processes, which suggests the survival of primordial nuggets for the currently considered range of the pairing gap Δ. Boiling is shown to depend on the competition of an increased stability window and the suppression of the rate, and is not likely to dominate the destruction of the nuggets. If surface evaporation dominates, the fate of the nuggets depends on the features of the initial mass spectrum of the nuggets, their evaporation rate, and the value of the pairing gap, as shown and discussed in the text.

  17. Electron pairing without superconductivity.

    PubMed

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy

    2015-05-14

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. PMID:25971511

  18. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C. Stephen; Levy, Jeremy

    2015-05-01

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.

  19. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. Support from AFOSR, ONR, ARO, NSF, DOE and NSSEFF is gratefully acknowledged.

  20. Thermodynamics of pairing transition in hot nuclei

    NASA Astrophysics Data System (ADS)

    Liu, Lang; Zhang, Zhen-Hua; Zhao, Peng-Wei

    2015-10-01

    The pairing correlations in hot nuclei 162Dy are investigated in terms of the thermodynamical properties by covariant density functional theory. The thermodynamical quantities are evaluated by the canonical ensemble theory and the paring correlations are treated by a shell-model-like approach, in which the particle number is conserved exactly. An S-shaped heat capacity curve as a function of temperature has been obtained. The properties of hot nuclei, such as entropy and level density are studied in terms of defined seniority component. It is found that the one-pair-broken states play crucial roles in the appearance of the S shape of the heat capacity curve. Moreover, due to the effect of the particle-number conservation, the pairing gap varies smoothly with the temperature, which indicates a gradual transition from the superfluid to the normal state.

  1. ACCELERATOR BASED CONTINUOUS NEUTRON SOURCE.

    SciTech Connect

    SHAPIRO,S.M.; RUGGIERO,A.G.; LUDEWIG,H.

    2003-03-25

    Until the last decade, most neutron experiments have been performed at steady-state, reactor-based sources. Recently, however, pulsed spallation sources have been shown to be very useful in a wide range of neutron studies. A major review of neutron sources in the US was conducted by a committee chaired by Nobel laureate Prof. W. Kohn: ''Neutron Sources for America's Future-BESAC Panel on Neutron Sources 1/93''. This distinguished panel concluded that steady state and pulsed sources are complementary and that the nation has need for both to maintain a balanced neutron research program. The report recommended that both a new reactor and a spallation source be built. This complementarity is recognized worldwide. The conclusion of this report is that a new continuous neutron source is needed for the second decade of the 20 year plan to replace aging US research reactors and close the US neutron gap. it is based on spallation production of neutrons using a high power continuous superconducting linac to generate protons impinging on a heavy metal target. There do not appear to be any major technical challenges to the building of such a facility since a continuous spallation source has been operating in Switzerland for several years.

  2. Detonation propagation in narrow gaps with various configurations

    NASA Astrophysics Data System (ADS)

    Monwar, M.; Yamamoto, Y.; Ishii, K.; Tsuboi, T.

    2007-08-01

    In general all detonation waves have cellular structure formed by the trajectory of the triple points. This paper aims to investigate experimentally the propagation of detonation in narrow gaps for hydrogen-oxygen-argon mixtures in terms of various gap heights and gap widths. The gap of total length 1500 mm was constructed by three pair of stainless plates, each of them was 500 mm in length, which were inserted in a detonation tube. The gap heights were varied from 1.2 mm to 3.0 mm while the gap widths were varied from 10 mm to 40 mm. Various argon dilution rates were tested in the present experiments to change the size of cellular structure. Attempts have been made by means of reaction front velocity, shock front velocity, and smoked foil to record variations of cellular structure inside the gaps. A combination probe composed of a pressure and an ion probe detected the arrival of the shock and the reaction front individually at one measurement point. Experimental results show that the number of the triple points contained in detonation front decreases with decrease in the gap heights and gap widths, which lead to larger cellular structures. For mixtures with low detonability, cell size is affected by a certain gap width although conversely cell size is almost independent of gap width. From the present result it was found that detonation propagation inside the gaps is strongly governed by the gap height and effects of gap width is dependent on detonability of mixtures.

  3. Intruder states and the onset of deformation in the neutron-deficient even-even polonium isotopes

    SciTech Connect

    The ISOLDE Collaboration

    1995-12-01

    Alpha- and beta-decay studies of mass-separated Rn and At nuclei reveal the existence of a low-lying 0{sup +} state in {sup 196,198,200,202}Po. The excited 0{sup +} states are interpreted as proton-pair excitations across the {ital Z}=82 shell gap leading to a deformed state, coexisting with the spherical ground state. It is shown that with decreasing neutron number the deformed configuration intrudes to lower excitation energy, increasingly mixing into the ground state. {copyright} {ital 1995 The American Physical Society.}

  4. NATIONAL GAP ANALYSIS PROGRAM

    EPA Science Inventory

    GAP Analysis is a rapid conservation evaluation method for assessing the current status of biodiversity at large spatial scales. GAP Analysis provides a systematic approach for evaluating the protection afforded biodiversity in given areas. It uses Geographic Information System (...

  5. Calculation of two-neutron multiplicity in photonuclear reactions

    NASA Technical Reports Server (NTRS)

    Norbury, John W.; Townsend, Lawrence W.

    1989-01-01

    The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

  6. Calculation of two-neutron multiplicity in photonuclear reactions

    NASA Technical Reports Server (NTRS)

    Norbury, John W.; Townsend, Lawrence W.

    1990-01-01

    The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

  7. Practice Gaps in Pruritus.

    PubMed

    Silverberg, Jonathan I

    2016-07-01

    There are several practice gaps in the evaluation and management of itch. These gaps include a dearth of objective measures of itch, infrequent use of validated patient-reported outcomes for itch, non-evidence-based treatment, and lack of consensus about the ideal workup for generalized itch. The present article reviews these gaps and presents potential solutions. PMID:27363881

  8. Behind the Pay Gap

    ERIC Educational Resources Information Center

    Dey, Judy Goldberg; Hill, Catherine

    2007-01-01

    Women have made remarkable gains in education during the past three decades, yet these achievements have resulted in only modest improvements in pay equity. The gender pay gap has become a fixture of the U.S. workplace and is so ubiquitous that many simply view it as normal. "Behind the Pay Gap" examines the gender pay gap for college graduates.…

  9. Funding Gap Study.

    ERIC Educational Resources Information Center

    Newmyer, Joe; McIntyre, Chuck

    The "funding gap" in public higher education in California represents the difference between state appropriations and the amount needed to fully support each segment's educational mission. This report identifies and defines the funding gap for the California Community Colleges (CCC); measures the consequences of this gap on program quality and…

  10. Paired Straight Hearth Furnace

    SciTech Connect

    2009-04-01

    This factsheet describes a research project whose goals are to design, develop, and evaluate the scalability and commercial feasibility of the PSH Paired Straight Hearth Furnace alternative ironmaking process.

  11. Cooper Pair Insulators

    NASA Astrophysics Data System (ADS)

    Valles, James

    One of the recent advances in the field of the Superconductor to Insulator Transition (SIT) has been the discovery and characterization of the Cooper Pair Insulator phase. This bosonic insulator, which consists of localized Cooper pairs, exhibits activated transport and a giant magneto-resistance peak. These features differ markedly from the weakly localized transport that emerges as pairs break at a ``fermionic'' SIT. I will describe how our experiments on films nano-patterned with a nearly triangular array of holes have enabled us to 1) distinguish bosonic insulators from fermionic insulators, 2) show that Cooper pairs, rather than quasi-particles dominate the transport in the Cooper Pair insulator phase, 3) demonstrate that very weak, sub nano-meter thickness inhomogeneities control whether a bosonic or fermionic insulator forms at an SIT and 4) reveal that Cooper pairs disintegrate rather than becoming more tightly bound deep in the localized phase. We have also developed a method, using a magnetic field, to tune flux disorder reversibly in these films. I will present our latest results on the influence of magnetic flux disorder and random gauge fields on phenomena near bosonic SITs. This work was performed in collaboration with M. D. Stewart, Jr., Hung Q. Nguyen, Shawna M. Hollen, Jimmy Joy, Xue Zhang, Gustavo Fernandez, Jeffrey Shainline and Jimmy Xu. It was supported by NSF Grants DMR 1307290 and DMR-0907357.

  12. SUSANS With Polarized Neutrons

    PubMed Central

    Wagh, Apoorva G.; Rakhecha, Veer Chand; Strobl, Makus; Treimer, Wolfgang

    2005-01-01

    Super Ultra-Small Angle Neutron Scattering (SUSANS) studies over wave vector transfers of 10–4 nm–1 to 10–3 nm–1 afford information on micrometer-size agglomerates in samples. Using a right-angled magnetic air prism, we have achieved a separation of ≈10 arcsec between ≈2 arcsec wide up- and down-spin peaks of 0.54 nm neutrons. The SUSANS instrument has thus been equipped with the polarized neutron option. The samples are placed in a uniform vertical field of 8.8 × 104 A/m (1.1 kOe). Several magnetic alloy ribbon samples broaden the up-spin neutron peak significantly over the ±1.3 × 10–3 nm–1 range, while leaving the down-spin peak essentially unaltered. Fourier transforms of these SUSANS spectra corrected for the instrument resolution, yield micrometer-range pair distribution functions for up- and down-spin neutrons as well as the nuclear and magnetic scattering length density distributions in the samples. PMID:27308127

  13. Atmospheric neutrons

    NASA Technical Reports Server (NTRS)

    Korff, S. A.; Mendell, R. B.; Merker, M.; Light, E. S.; Verschell, H. J.; Sandie, W. S.

    1979-01-01

    Contributions to fast neutron measurements in the atmosphere are outlined. The results of a calculation to determine the production, distribution and final disappearance of atmospheric neutrons over the entire spectrum are presented. An attempt is made to answer questions that relate to processes such as neutron escape from the atmosphere and C-14 production. In addition, since variations of secondary neutrons can be related to variations in the primary radiation, comment on the modulation of both radiation components is made.

  14. Novel neutron detectors

    NASA Astrophysics Data System (ADS)

    Burgett, Eric Anthony

    A new set of thermal neutron detectors has been developed as a near term 3He tube replacement. The zinc oxide scintillator is an ultrafast scintillator which can be doped to have performance equal to or superior to 3He tubes. Originally investigated in the early 1950s, this room temperature semiconductor has been evaluated as a thermal neutron scintillator. Zinc oxide can be doped with different nuclei to tune the band gap, improve optical clarity, and improve the thermal neutron detection efficiency. The effects of various dopant effects on the scintillation properties, materials properties, and crystal growth parameters have been analyzed. Two different growth modalities were investigated: bulk melt grown materials as well as thin film scintillators grown by metalorganic chemical vapor deposition (MOCVD). MOCVD has shown significant advantages including precise thickness control, high dopant incorporation, and epitaxial coatings of neutron target nuclei. Detector designs were modeled and simulated to design an improved thermal neutron detector using doped ZnO layers, conformal coatings and light collection improvements including Bragg reflectors and photonic crystal structures. The detectors have been tested for crystalline quality by XRD and FTIR spectroscopy, for scintillation efficiency by photo-luminescence spectroscopy, and for neutron detection efficiency by alpha and neutron radiation tests. Lastly, a novel method for improving light collection efficiency has been investigated, the creation of a photonic crystal scintillator. Here, the flow of optical light photons is controlled through an engineered structure created with the scintillator materials. This work has resulted in a novel radiation detection material for the near term replacement of 3He tubes with performance characteristics equal to or superior to that of 3He.

  15. Neutron dosimetry

    DOEpatents

    Quinby, Thomas C.

    1976-07-27

    A method of measuring neutron radiation within a nuclear reactor is provided. A sintered oxide wire is disposed within the reactor and exposed to neutron radiation. The induced radioactivity is measured to provide an indication of the neutron energy and flux within the reactor.

  16. Neutron guide

    DOEpatents

    Greene, Geoffrey L.

    1999-01-01

    A neutron guide in which lengths of cylindrical glass tubing have rectangular glass plates properly dimensioned to allow insertion into the cylindrical glass tubing so that a sealed geometrically precise polygonal cross-section is formed in the cylindrical glass tubing. The neutron guide provides easier alignment between adjacent sections than do the neutron guides of the prior art.

  17. A slow neutron polarimeter for the measurement of parity-odd neutron rotary power

    SciTech Connect

    Snow, W. M.; Anderson, E.; Bass, T. D.; Dawkins, J. M.; Fry, J.; Haddock, C.; Horton, J. C.; Luo, D.; Micherdzinska, A. M.; Walbridge, S. B.; Barrón-Palos, L.; Maldonado-Velázquez, M.; Bass, C. D.; Crawford, B. E.; Crawford, C.; Esposito, D.; Gardiner, H.; Gan, K.; Heckel, B. R.; Swanson, H. E. [University of Washington and others

    2015-05-15

    We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10{sup −7} rad/m.

  18. A slow neutron polarimeter for the measurement of parity-odd neutron rotary power.

    PubMed

    Snow, W M; Anderson, E; Barrón-Palos, L; Bass, C D; Bass, T D; Crawford, B E; Crawford, C; Dawkins, J M; Esposito, D; Fry, J; Gardiner, H; Gan, K; Haddock, C; Heckel, B R; Holley, A T; Horton, J C; Huffer, C; Lieffers, J; Luo, D; Maldonado-Velázquez, M; Markoff, D M; Micherdzinska, A M; Mumm, H P; Nico, J S; Sarsour, M; Santra, S; Sharapov, E I; Swanson, H E; Walbridge, S B; Zhumabekova, V

    2015-05-01

    We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10(-7) rad/m. PMID:26026552

  19. A slow neutron polarimeter for the measurement of parity-odd neutron rotary power

    NASA Astrophysics Data System (ADS)

    Snow, W. M.; Anderson, E.; Barrón-Palos, L.; Bass, C. D.; Bass, T. D.; Crawford, B. E.; Crawford, C.; Dawkins, J. M.; Esposito, D.; Fry, J.; Gardiner, H.; Gan, K.; Haddock, C.; Heckel, B. R.; Holley, A. T.; Horton, J. C.; Huffer, C.; Lieffers, J.; Luo, D.; Maldonado-Velázquez, M.; Markoff, D. M.; Micherdzinska, A. M.; Mumm, H. P.; Nico, J. S.; Sarsour, M.; Santra, S.; Sharapov, E. I.; Swanson, H. E.; Walbridge, S. B.; Zhumabekova, V.

    2015-05-01

    We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10-7 rad/m.

  20. A number-projected model with generalized pairing interaction in application to rotating nuclei

    SciTech Connect

    Satula, W. |||; Wyss, R.

    1996-12-31

    A cranked mean-field model that takes into account both T=1 and T=0 pairing interactions is presented. The like-particle pairing interaction is described by means of a standard seniority force. The neutron-proton channel includes simultaneously correlations among particles moving in time reversed orbits (T=1) and identical orbits (T=0). The coupling between different pairing channels and nuclear rotation is taken into account selfconsistently. Approximate number-projection is included by means of the Lipkin-Nogami method. The transitions between different pairing phases are discussed as a function of neutron/proton excess, T{sub z}, and rotational frequency, {Dirac_h}{omega}.

  1. Electron Pairing Without Superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.

    2015-03-01

    Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as T = 900 mK, far above the superconducting transition temperature (Tc 300 mK). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by an attractive-U Hubbard model that describes real-space electron pairing as a precursor to superconductivity. This work was supported by ARO MURI W911NF-08-1-0317 (J.L.), AFOSR MURI FA9550-10-1-0524 (C.-B.E., J.L.) and FA9550-12-1-0342 (C.-B.E.), and grants from the National Science Foundation DMR-1104191 (J.L.), DMR.

  2. Supernovae in paired galaxies

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2014-07-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.

  3. Applications of balanced pairs

    NASA Astrophysics Data System (ADS)

    Li, HuanHuan; Wang, JunFu; Huang, ZhaoYong

    2016-05-01

    Let $(\\mathscr{X}$, $\\mathscr{Y})$ be a balanced pair in an abelian category. We first introduce the notion of cotorsion pairs relative to $(\\mathscr{X}$, $\\mathscr{Y})$, and then give some equivalent characterizations when a relative cotorsion pair is hereditary or perfect. We prove that if the $\\mathscr{X}$-resolution dimension of $\\mathscr{Y}$ (resp. $\\mathscr{Y}$-coresolution dimension of $\\mathscr{X}$) is finite, then the bounded homotopy category of $\\mathscr{Y}$ (resp. $\\mathscr{X}$) is contained in that of $\\mathscr{X}$ (resp. $\\mathscr{Y}$). As a consequence, we get that the right $\\mathscr{X}$-singularity category coincides with the left $\\mathscr{Y}$-singularity category if the $\\mathscr{X}$-resolution dimension of $\\mathscr{Y}$ and the $\\mathscr{Y}$-coresolution dimension of $\\mathscr{X}$ are finite.

  4. Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wambach, J.; Anisworth, T. L.; Pines, D.

    1993-01-01

    A microscopic model for the quaisiparticle interaction in neutron matter is presented. Both particle-particle (pp) and particle-hole (ph) correlation are are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for the particle hole interaction and the scattering amplitude on the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the S-1 gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

  5. Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wambach, J; Ainsworth, T. L.; Pines, D.

    1993-01-01

    A microscopic model for the quasiparticle interaction in neutron matter is presented. Both-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for particle-hole interaction and the scattering amplitude of the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules for the scattering amplitude are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the (1)S(sub 0) gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

  6. The gap gene network

    PubMed Central

    2010-01-01

    Gap genes are involved in segment determination during the early development of the fruit fly Drosophila melanogaster as well as in other insects. This review attempts to synthesize the current knowledge of the gap gene network through a comprehensive survey of the experimental literature. I focus on genetic and molecular evidence, which provides us with an almost-complete picture of the regulatory interactions responsible for trunk gap gene expression. I discuss the regulatory mechanisms involved, and highlight the remaining ambiguities and gaps in the evidence. This is followed by a brief discussion of molecular regulatory mechanisms for transcriptional regulation, as well as precision and size-regulation provided by the system. Finally, I discuss evidence on the evolution of gap gene expression from species other than Drosophila. My survey concludes that studies of the gap gene system continue to reveal interesting and important new insights into the role of gene regulatory networks in development and evolution. PMID:20927566

  7. Pulsar Pair Cascades in a Distorted Magnetic Dipole Field

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2010-01-01

    We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P-P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

  8. Multi-pair states in electron-positron pair creation

    NASA Astrophysics Data System (ADS)

    Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.

    2016-09-01

    Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron-positron pairs.

  9. Pulsar Pair Cascades in Magnetic Fields with Offset Polar Caps

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alex G.

    2012-01-01

    Neutron star magnetic fields may have polar caps (PC) that are offset from the dipole axis, through field-line sweepback near the light cylinder or non-symmetric currents within the star. The effects of such offsets on electron-positron pair cascades are investigated, using simple models of dipole magnetic fields with small distortions that shift the PCs by different amounts or directions. Using a Monte Carlo pair cascade simulation, we explore the changes in the pair spectrum, multiplicity and energy flux across the PC, as well as the trends in pair flux and pair energy flux with spin-down luminosity, L(sub sd). We also give an estimate of the distribution of heating flux from returning positrons on the PC for different offsets. We find that even modest offsets can produce significant increases in pair multiplicity, especially for pulsars that are near or beyond the pair death lines for centered PCs, primarily because of higher accelerating fields. Pair spectra cover several decades in energy, with the spectral range of millisecond pulsars (MSPs) two orders of magnitude higher than for normal pulsars, and PC offsets allow significant extension of all spectra to lower pair energies. We find that the total PC pair luminosity L(sub pair) is proportional to L(sub sd), with L(sub pair) approximates 10(exp -3) L(sub sd) for normal pulsars and L(sub pair) approximates 10(exp -2) L(sub sd) for MSPs. Remarkably, the total PC heating luminosity for even large offsets increases by less than a factor of two, even though the PC area increases by much larger factors, because most of the heating occurs near the magnetic axis.

  10. Neutron detector

    DOEpatents

    Stephan, Andrew C.; Jardret; Vincent D.

    2011-04-05

    A neutron detector has a volume of neutron moderating material and a plurality of individual neutron sensing elements dispersed at selected locations throughout the moderator, and particularly arranged so that some of the detecting elements are closer to the surface of the moderator assembly and others are more deeply embedded. The arrangement captures some thermalized neutrons that might otherwise be scattered away from a single, centrally located detector element. Different geometrical arrangements may be used while preserving its fundamental characteristics. Different types of neutron sensing elements may be used, which may operate on any of a number of physical principles to perform the function of sensing a neutron, either by a capture or a scattering reaction, and converting that reaction to a detectable signal. High detection efficiency, an ability to acquire spectral information, and directional sensitivity may be obtained.

  11. The Parenting Gap

    ERIC Educational Resources Information Center

    Reeves, Richard V.; Howard, Kimberly

    2013-01-01

    The parenting gap is a big factor in the opportunity gap. The chances of upward social mobility are lower for children with parents struggling to do a good job--in terms of creating a supportive and stimulating home environment. Children lucky enough to have strong parents are more likely to succeed at all the critical life stages, which means…

  12. The National "Expertise Gap"

    ERIC Educational Resources Information Center

    Hamilton, Kendra

    2005-01-01

    This article discusses the Woodrow Wilson National Fellowship Foundation's report, "Diversity and the Ph.D.," released in May, which documents in troubling detail the exact dimensions of what the foundation's president, Dr. Robert Weisbuch, is calling the national "expertise gap." Weisbuch states that the expertise gap extends beyond the…

  13. Confronting the Achievement Gap

    ERIC Educational Resources Information Center

    Gardner, David

    2007-01-01

    This article talks about the large achievement gap between children of color and their white peers. The reasons for the achievement gap are varied. First, many urban minorities come from a background of poverty. One of the detrimental effects of growing up in poverty is receiving inadequate nourishment at a time when bodies and brains are rapidly…

  14. States Address Achievement Gaps.

    ERIC Educational Resources Information Center

    Christie, Kathy

    2002-01-01

    Summarizes 2 state initiatives to address the achievement gap: North Carolina's report by the Advisory Commission on Raising Achievement and Closing Gaps, containing an 11-point strategy, and Kentucky's legislation putting in place 10 specific processes. The North Carolina report is available at www.dpi.state.nc.us.closingthegap; Kentucky's…

  15. Narrowing Participation Gaps

    ERIC Educational Resources Information Center

    Hand, Victoria; Kirtley, Karmen; Matassa, Michael

    2015-01-01

    Shrinking the achievement gap in mathematics is a tall order. One way to approach this challenge is to think about how the achievement gap manifests itself in the classroom and take concrete action. For example, opportunities to participate in activities that involve mathematical reasoning and argumentation in a safe and supportive manner are…

  16. β-Decay Half-Lives of 110 Neutron-Rich Nuclei across the N=82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process.

    PubMed

    Lorusso, G; Nishimura, S; Xu, Z Y; Jungclaus, A; Shimizu, Y; Simpson, G S; Söderström, P-A; Watanabe, H; Browne, F; Doornenbal, P; Gey, G; Jung, H S; Meyer, B; Sumikama, T; Taprogge, J; Vajta, Zs; Wu, J; Baba, H; Benzoni, G; Chae, K Y; Crespi, F C L; Fukuda, N; Gernhäuser, R; Inabe, N; Isobe, T; Kajino, T; Kameda, D; Kim, G D; Kim, Y-K; Kojouharov, I; Kondev, F G; Kubo, T; Kurz, N; Kwon, Y K; Lane, G J; Li, Z; Montaner-Pizá, A; Moschner, K; Naqvi, F; Niikura, M; Nishibata, H; Odahara, A; Orlandi, R; Patel, Z; Podolyák, Zs; Sakurai, H; Schaffner, H; Schury, P; Shibagaki, S; Steiger, K; Suzuki, H; Takeda, H; Wendt, A; Yagi, A; Yoshinaga, K

    2015-05-15

    The β-decay half-lives of 110 neutron-rich isotopes of the elements from _{37}Rb to _{50}Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events. PMID:26024165

  17. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGESBeta

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scatteringmore » creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.« less

  18. Protected Flux Pairing Qubit

    NASA Astrophysics Data System (ADS)

    Bell, Matthew; Zhang, Wenyuan; Ioffe, Lev; Gershenson, Michael

    2014-03-01

    We have studied the coherent flux tunneling in a qubit containing two submicron Josephson junctions shunted by a superinductor (a dissipationless inductor with an impedance much greater than the resistance quantum). The two low energy quantum states of this device, 0 and 1, are represented by even and odd number of fluxes in the loop, respectively. This device is dual to the charge pairing Josephson rhombi qubit. The spectrum of the device, studied by microwave spectroscopy, reflects the interference between coherent quantum phase slips in the two junctions (the Aharonov-Casher effect). The time domain measurements demonstrate the suppression of the qubit's energy relaxation in the protected regime, which illustrates the potential of this flux pairing device as a protected quantum circuit. Templeton Foundation, NSF, and ARO.

  19. Molecular Driving Forces behind the Tetrahydrofuran-Water Miscibility Gap.

    PubMed

    Smith, Micholas Dean; Mostofian, Barmak; Petridis, Loukas; Cheng, Xiaolin; Smith, Jeremy C

    2016-02-01

    The tetrahydrofuran-water binary system exhibits an unusual closed-loop miscibility gap (transitions from a miscible regime to an immiscible regime back to another miscible regime as the temperature increases). Here, using all-atom molecular dynamics simulations, we probe the structural and dynamical behavior of the binary system in the temperature regime of this gap at four different mass ratios, and we compare the behavior of bulk water and tetrahydrofuran. The changes in structure and dynamics observed in the simulations indicate that the temperature region associated with the miscibility gap is distinctive. Within the miscibility-gap temperature region, the self-diffusion of water is significantly altered and the second virial coefficients (pair-interaction strengths) show parabolic-like behavior. Overall, the results suggest that the gap is the result of differing trends with temperature of minor structural changes, which produces interaction virials with parabolic temperature dependence near the miscibility gap. PMID:26734991

  20. Studies of isolated and interacting ferromagnetic gapped nanorings

    NASA Astrophysics Data System (ADS)

    Li, Jie; Zhang, Sheng; Bartell, Jason; Grigas, Chris; Nisoli, Cristiano; Lammert, Paul; Crespi, Vincent; Schiffer, Peter

    2011-03-01

    We have used micromagnetic simulation and magnetic force microscopy (MFM) to study isolated and interacting permalloy nanorings that are lithographically fabricated with gaps that prevent a rotationally symmetric magnetic state. The gapped nanorings have inner and outer radii of 200 and 300 nm respectively, and the gap has a subtended width of ~ 20 degrees. The nanorings generate a strong magnetic field only in the gap, and thus the magnetization states of gapped nanorings are much more accessible to MFM imaging than complete rings. We have investigated the properties of these gapped nanorings, including the anisotropy in their coercive field and the relative alignment of the magnetic polarization in coupled pairs. We acknowledge the financial support from DOE and Army Research Office.We are grateful to Professor Chris Leighton and Mike Erickson for assistance with sample preparation.

  1. Compact ion chamber based neutron detector

    SciTech Connect

    Derzon, Mark S.; Galambos, Paul C.; Renzi, Ronald F.

    2015-10-27

    A directional neutron detector has an ion chamber formed in a dielectric material; a signal electrode and a ground electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; readout circuitry which is electrically coupled to the signal and ground electrodes; and a signal processor electrically coupled to the readout circuitry. The ion chamber has a pair of substantially planar electrode surfaces. The chamber pressure of the neutron absorbing material is selected such that the reaction particle ion trail length for neutrons absorbed by the neutron absorbing material is equal to or less than the distance between the electrode surfaces. The signal processor is adapted to determine a path angle for each absorbed neutron based on the rise time of the corresponding pulse in a time-varying detector signal.

  2. Cold Neutrons Trapped in External Fields

    SciTech Connect

    Gandolfi, S.; Carlson, J.; Pieper, Steven C.

    2011-01-07

    The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.

  3. Cold neutrons trapped in external fields.

    SciTech Connect

    Gandolfi, S.; Carlson, J.; Pieper, S. C.

    2011-01-05

    The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker.

  4. Quantum phase transitional patterns in the SD-pair shell model

    SciTech Connect

    Luo Yanan; Meng Xiangfei; Zhang Yu; Pan Feng; Draayer, Jerry P.

    2009-07-15

    Patterns of shape-phase transition in the proton-neutron coupled systems are studied within the SD-pair shell model. The results show that some transitional patterns in the SD-pair shell model are similar to the U(5)-SU(3) and U(5)-SO(6) transitions with signatures of the critical point symmetry of the interacting boson model.

  5. NEUTRONIC REACTOR

    DOEpatents

    Fermi, E.; Zinn, W.H.; Anderson, H.L.

    1958-09-16

    Means are presenied for increasing the reproduction ratio of a gaphite- moderated neutronic reactor by diminishing the neutron loss due to absorption or capture by gaseous impurities within the reactor. This means comprised of a fluid-tight casing or envelope completely enclosing the reactor and provided with a valve through which the casing, and thereby the reactor, may be evacuated of atmospheric air.

  6. Neutronic reactor

    DOEpatents

    Wende, Charles W. J.

    1976-08-17

    A safety rod for a nuclear reactor has an inner end portion having a gamma absorption coefficient and neutron capture cross section approximately equal to those of the adjacent shield, a central portion containing materials of high neutron capture cross section and an outer end portion having a gamma absorption coefficient at least equal to that of the adjacent shield.

  7. Neutron source

    DOEpatents

    Cason, J.L. Jr.; Shaw, C.B.

    1975-10-21

    A neutron source which is particularly useful for neutron radiography consists of a vessel containing a moderating media of relatively low moderating ratio, a flux trap including a moderating media of relatively high moderating ratio at the center of the vessel, a shell of depleted uranium dioxide surrounding the moderating media of relatively high moderating ratio, a plurality of guide tubes each containing a movable source of neutrons surrounding the flux trap, a neutron shield surrounding one part of each guide tube, and at least one collimator extending from the flux trap to the exterior of the neutron source. The shell of depleted uranium dioxide has a window provided with depleted uranium dioxide shutters for each collimator. Reflectors are provided above and below the flux trap and on the guide tubes away from the flux trap.

  8. Neutron tubes

    DOEpatents

    Leung, Ka-Ngo; Lou, Tak Pui; Reijonen, Jani

    2008-03-11

    A neutron tube or generator is based on a RF driven plasma ion source having a quartz or other chamber surrounded by an external RF antenna. A deuterium or mixed deuterium/tritium (or even just a tritium) plasma is generated in the chamber and D or D/T (or T) ions are extracted from the plasma. A neutron generating target is positioned so that the ion beam is incident thereon and loads the target. Incident ions cause D-D or D-T (or T-T) reactions which generate neutrons. Various embodiments differ primarily in size of the chamber and position and shape of the neutron generating target. Some neutron generators are small enough for implantation in the body. The target may be at the end of a catheter-like drift tube. The target may have a tapered or conical surface to increase target surface area.

  9. Hard gap in a normal layer coupled to a superconductor

    NASA Astrophysics Data System (ADS)

    Reeg, Christopher R.; Maslov, Dmitrii L.

    2016-07-01

    The ability to induce a sizable gap in the excitation spectrum of a normal layer placed in contact with a conventional superconductor has become increasingly important in recent years in the context of engineering a topological superconductor. The quasiclassical theory of the proximity effect shows that Andreev reflection at the superconductor/normal interface induces a nonzero pairing amplitude in the metal but does not endow it with a gap. Conversely, when the normal layer is atomically thin, the tunneling of Cooper pairs induces an excitation gap that can be as large as the bulk gap of the superconductor. We study how these two seemingly different views of the proximity effect evolve into one another as the thickness of the normal layer is changed. We show that a fully quantum-mechanical treatment of the problem predicts that the induced gap is always finite but falls off with the thickness of the normal layer d . If d is less than a certain crossover scale, which is much larger than the Fermi wavelength, the induced gap is comparable to the bulk gap. As a result, a sizable excitation gap can be induced in normal layers that are much thicker than the Fermi wavelength.

  10. Existence of best proximity pairs and equilibrium pairs

    NASA Astrophysics Data System (ADS)

    Kim, Won Kyu; Lee, Kyoung Hee

    2006-04-01

    In this paper, using the fixed point theorem for Kakutani factorizable multifunctions, we shall prove new existence theorems of best proximity pairs and equilibrium pairs for free abstract economies, which include the previous fixed point theorems and equilibrium existence theorems.

  11. Isovector Pairing within the so(5) Richardson-Gaudin Exactly Solvable Model

    SciTech Connect

    Dimitrova, S S; Dukelsky, J; Gueorguiev, V G; Van Isacker, P

    2005-10-10

    Properties of a nucleon system interacting via isovector proton-neutron pairing can be described within the so(5) generalized Richardson-Gaudin exactly-solvable model [1]. We present results for a system of 12 nucleon pairs within the full f{sub p} + g{sub 9/2} shell-model space. We discuss coupling constant dependence of the pair energies, total energy of the system, and the occupation numbers.

  12. Fast Pulsing Neutron Generators for Security Application

    SciTech Connect

    Ji, Q.; Regis, M.; Kwan, J. W.

    2009-04-24

    Active neutron interrogation has been demonstrated to be an effective method of detecting shielded fissile material. A fast fall-time/fast pulsing neutron generator is needed primarily for differential die-away technique (DDA) interrogation systems. A compact neutron generator, currently being developed in Lawrence Berkeley National Laboratory, employs an array of 0.6-mm-dia apertures (instead of one 6-mm-dia aperture) such that gating the beamlets can be done with low voltage and a small gap to achieve sub-microsecond ion beam fall time and low background neutrons. Arrays of 16 apertures (4x4) and 100 apertures (10x10) have been designed and fabricated for a beam extraction experiment. The preliminary results showed that, using a gating voltage of 1200 V and a gap distance of 1 mm, the fall time of extracted ion beam pulses is approximately 0.15 mu s at beam energies of 1000 eV.

  13. Photonic band gap materials

    SciTech Connect

    Soukoulis, C.M. |

    1993-12-31

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented.

  14. Gaps in Oncology

    Cancer.gov

    The first plenary of the EPEC-O (Education in Palliative and End-of-Life Care for Oncology) Self-Study Original Version provides background for the curriculum and identifies gaps in current and desired comprehensive cancer care.

  15. The Annular Gap: Gamma-Ray & Radio Emission of Pulsars

    NASA Astrophysics Data System (ADS)

    Qiao, G. J.; Du, Y. J.; Han, J. L.; Xu, R. X.

    2013-01-01

    Pulsars have been found more than 40 years. Observations from radio to gamma-rays present abundant information. However, the radiation mechanism is still an open question. It is found that the annular gap could be formed in the magnetosphere of pulsars (neutron stars or quark stars), which combines the advantages of the polar cap, slot gap and outer gap models. It is emphasized that observations of some radio pulsars, normal and millisecond gamma-ray pulsars (MSGPs) show that the annular gap would play a very important role. Here we show some observational and theoretical evidences about the annular gap. For example, bi-drifting sub-pulses; radio and gamma-ray millisecond pulsars and so on.

  16. Comparison of Photon-photon and Photon-magnetic Field Pair Production Rates

    NASA Technical Reports Server (NTRS)

    Burns, M. L.; Harding, A. K.

    1983-01-01

    Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense ( 10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field ( gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

  17. Magnesium gating of cardiac gap junction channels.

    PubMed

    Matsuda, Hiroyuki; Kurata, Yasutaka; Oka, Chiaki; Matsuoka, Satoshi; Noma, Akinori

    2010-09-01

    We aimed to study kinetics of modulation by intracellular Mg(2+) of cardiac gap junction (Mg(2+) gate). Paired myocytes of guinea-pig ventricle were superfused with solutions containing various concentrations of Mg(2+). In order to rapidly apply Mg(2+) to one aspect of the gap junction, the non-junctional membrane of one of the pair was perforated at nearly the connecting site by pulses of nitrogen laser beam. The gap junction conductance (G(j)) was measured by clamping the membrane potential of the other cell using two-electrode voltage clamp method. The laser perforation immediately increased G(j), followed by slow G(j) change with time constant of 3.5 s at 10 mM Mg(2+). Mg(2+) more than 1.0 mM attenuated dose-dependently the gap junction conductance and lower Mg(2+) (0.6 mM) increased G(j) with a Hill coefficient of 3.4 and a half-maximum effective concentration of 0.6 mM. The time course of G(j) changes was fitted by single exponential function, and the relationship between the reciprocal of time constant and Mg(2+) concentration was almost linear. Based on the experimental data, a mathematical model of Mg(2+) gate with one open state and three closed states well reproduced experimental results. One-dimensional cable model of thirty ventricular myocytes connected to the Mg(2+) gate model suggested a pivotal role of the Mg(2+) gate of gap junction under pathological conditions. PMID:20553744

  18. Odd frequency pairing of interacting Majorana fermions

    NASA Astrophysics Data System (ADS)

    Huang, Zhoushen; Woelfle, Peter; Balatsky, Alexandar

    Majorana fermions are rising as a promising key component in quantum computation. While the prevalent approach is to use a quadratic (i.e. non-interacting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd frequency behavior. It is stabilized when the coupling strength g is above a critical value gc. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory allowing to discuss a possible subleading admixture of even-frequency pairing. Work supported by USDOE DE-AC52-06NA25396 E304, Knut and Alice Wallenberg Foundation, and ERC DM-321031.

  19. Regimes of Pulsar Pair Formation and Particle Energetics

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Muslimov, Alexander G.; Zhang, Bing; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

  20. Pairing-induced speedup of nuclear spontaneous fission

    DOE PAGESBeta

    Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.

    2014-12-22

    Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependentmore » pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. As a result, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.« less

  1. Pairing-induced speedup of nuclear spontaneous fission

    SciTech Connect

    Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.

    2014-12-22

    Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. As a result, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.

  2. Pairing-induced speedup of nuclear spontaneous fission

    NASA Astrophysics Data System (ADS)

    Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.

    2014-12-01

    Background: Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. Purpose: To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. Methods: We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Results: Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. Conclusions: The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.

  3. NEUTRON SOURCE

    DOEpatents

    Bernander, N.K. et al.

    1960-10-18

    An apparatus is described for producing neutrons through target bombardment with deuterons. Deuterium gas is ionized by electron bombardment and the deuteron ions are accelerated through a magnetic field to collimate them into a continuous high intensity beam. The ion beam is directed against a deuteron pervious metal target of substantially the same nnaterial throughout to embed the deuterous therein and react them to produce neutrons. A large quantity of neutrons is produced in this manner due to the increased energy and quantity of ions bombarding the target.

  4. Robotic Tube-Gap Inspector

    NASA Technical Reports Server (NTRS)

    Gilbert, Jeffrey L.; Gutow, David A.; Maslakowski, John E.

    1993-01-01

    Robotic vision system measures small gaps between nearly parallel tubes. Robot-held video camera examines closely spaced tubes while computer determines gaps between tubes. Video monitor simultaneously displays data on gaps.

  5. a Portable Pulsed Neutron Generator

    NASA Astrophysics Data System (ADS)

    Skoulakis, A.; Androulakis, G. C.; Clark, E. L.; Hassan, S. M.; Lee, P.; Chatzakis, J.; Bakarezos, M.; Dimitriou, V.; Petridis, C.; Papadogiannis, N. A.; Tatarakis, M.

    2014-02-01

    The design and construction of a pulsed plasma focus device to be used as a portable neutron source for material analysis such as explosive detection using gamma spectroscopy is presented. The device is capable of operating at a repetitive rate of a few Hz. When deuterium gas is used, up to 105 neutrons per shot are expected to be produced with a temporal pulse width of a few tens of nanoseconds. The pulsed operation of the device and its portable size are its main advantage in comparison with the existing continuous neutron sources. Parts of the device include the electrical charging unit, the capacitor bank, the spark switch (spark gap), the trigger unit and the vacuum-fuel chamber / anode-cathode. Numerical simulations are used for the simulation of the electrical characteristics of the device including the scaling of the capacitor bank energies with total current, the pinch current, and the scaling of neutron yields with energies and currents. The MCNPX code is used to simulate the moderation of the produced neutrons in a simplified geometry and subsequently, the interaction of thermal neutrons with a test target and the corresponding prompt γ-ray generation.

  6. Multiwavelength Emission From Pulsar Slot Gaps

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Stern, Julie; Dyks, Jarek

    2008-01-01

    We present results of a 3D model of optical to gamma-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high altitude in the pulsar magnetosphere at the outer edge of the open field volume, as well as electron-positron pairs on field line interior to the slot gap, radiate curvature, inverse Compton and synchrotron radiation. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles and to produce a broad spectrum of emission from infra-red to GeV energies. Synchrotron radiation from pairs with a power-law energy spectrum dominate the spectrum up to 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. The high-energy pulse profiles are dominated by caustics on trailing field lines. In the case of the Crab pulsar, the radio conal emission may also form caustics in phase with the high-energy peaks. If resonant absorption of radio emission produces high-energy synchroti-on radiation, emission below 200 Mev is expected to exhibit correlations in time and phase with the radio emission.

  7. Thermal neutron detection system

    DOEpatents

    Peurrung, Anthony J.; Stromswold, David C.

    2000-01-01

    According to the present invention, a system for measuring a thermal neutron emission from a neutron source, has a reflector/moderator proximate the neutron source that reflects and moderates neutrons from the neutron source. The reflector/moderator further directs thermal neutrons toward an unmoderated thermal neutron detector.

  8. Pair Production and Annihilation in Strong Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Daugherty, J. K.; Harding, A. K.

    1983-01-01

    Electromagnetic phenomena occurring in the presence of strong magnetic fields are currently of great interest in high-energy astrophysics. In particular, the process of pair production by single photons in the presence of fields of order 10 to the 12th power Gauss is of importance in cascade models of pulsar gamma ray emission, and may also become significant in theories of other radiation phenomena whose sources may be neutron stars (e.g., gamma ray bursts). In addition to pair production, the inverse process of pair annihilation is greatly affected by the presence of superstrong magnetic fields. The most significant departures from annihilation processes in free space are a reduction in the total rate for annihilation into two photons, a broadening of the familiar 511-keV line for annihilation at rest, and the possibility for annihilation into a single photon (which dominates the two-photon annihilation for B ( 10 the 13th power Gauss). The physics of these pair conversion processes, which is reviewed briefly, can become quite complex in the teragauss regime, and can involve calculations which are technically difficult to incorporate into models of emission mechanisms in neutron star magnetospheres. However, theoretical work, especially the case of pair annihilation, also suggests potential techniques for more direct measurements of field strengths near the stellar surface.

  9. NEUTRONIC REACTOR

    DOEpatents

    Wade, E.J.

    1958-09-16

    This patent relates to a reflector means for a neutronic reactor. A reflector comprised of a plurality of vertically movable beryllium control members is provided surrounding the sides of the reactor core. An absorber of fast neutrons comprised of natural uramum surrounds the reflector. An absorber of slow neutrons surrounds the absorber of fast neutrons and is formed of a plurality of beryllium blocks having natural uranium members distributcd therethrough. in addition, a movable body is positioned directly below the core and is comprised of a beryllium reflector and an absorbing member attached to the botiom thereof, the absorbing member containing a substance selected from the goup consisting of natural urantum and Th/sup 232/.

  10. Nucleon pairing in μ- capture by 40Ca

    NASA Astrophysics Data System (ADS)

    Martoff, C. J.; Cummings, W. J.; Poanić, D.; Hanna, S. S.; Ullrich, H.; Furić, M.; Petković, T.; Kozlowski, T.; Perroud, J. P.

    1991-03-01

    Spectra of energetic protons above 35 MeV have been measured following negative muon capture from rest in Ca. The spectrum extends to the kinematic limit near 93 MeV, with a branching ratio of (2.3+/-0.3)×10-4 per capture above 40 MeV. Nuclear cascade calculations of the proton and neutron spectra in this energy region are presented and are consistent with the measured proton spectrum when capture on correlated pp and np pairs in the nucleus is included. The ratio of capture on np to pp pairs is 6.7+/-1.6, which is consistent with results from pion capture.

  11. NEUTRONIC REACTOR

    DOEpatents

    Fraas, A.P.; Mills, C.B.

    1961-11-21

    A neutronic reactor in which neutron moderation is achieved primarily in its reflector is described. The reactor structure consists of a cylindrical central "island" of moderator and a spherical moderating reflector spaced therefrom, thereby providing an annular space. An essentially unmoderated liquid fuel is continuously passed through the annular space and undergoes fission while contained therein. The reactor, because of its small size, is particularly adapted for propulsion uses, including the propulsion of aircraft. (AEC)

  12. NEUTRON SOURCES

    DOEpatents

    Richmond, J.L.; Wells, C.E.

    1963-01-15

    A neutron source is obtained without employing any separate beryllia receptacle, as was formerly required. The new method is safer and faster, and affords a source with both improved yield and symmetry of neutron emission. A Be container is used to hold and react with Pu. This container has a thin isolating layer that does not obstruct the desired Pu--Be reaction and obviates procedures previously employed to disassemble and remove a beryllia receptacle. (AEC)

  13. Pairing in half-filled Landau level

    SciTech Connect

    Wang, Zhiqiang; Mandal, Ipsita; Chung, Suk Bum; Chakravarty, Sudip

    2014-12-15

    Pairing of composite fermions in half-filled Landau level state is reexamined by solving the BCS gap equation with full frequency dependent current–current interactions. Our results show that there can be a continuous transition from the Halperin–Lee–Read state to a chiral odd angular momentum Cooper pair state for short-range contact interaction. This is at odds with the previously established conclusion of first order pairing transition, in which the low frequency effective interaction was assumed for the entire frequency range. We find that even if the low frequency effective interaction is repulsive, it is compensated by the high frequency regime, which is attractive. We construct the phase diagrams and show that ℓ=1 angular momentum channel is quite different from higher angular momenta ℓ≥3. Remarkably, the full frequency dependent analysis applied to the bilayer Hall system with a total filling fraction ν=1/2 +1/2 is quantitatively changed from the previously established results but not qualitatively.

  14. Gap Cycling for SWIFT

    PubMed Central

    Corum, Curtis A.; Idiyatullin, Djaudat; Snyder, Carl J.; Garwood, Michael

    2014-01-01

    Purpose SWIFT (SWeep Imaging with Fourier Transformation) is a non-Cartesian MRI method with unique features and capabilities. In SWIFT, radiofrequency (RF) excitation and reception are performed nearly simultaneously, by rapidly switching between transmit and receive during a frequency-swept RF pulse. Because both the transmitted pulse and data acquisition are simultaneously amplitude-modulated in SWIFT (in contrast to continuous RF excitation and uninterrupted data acquisition in more familiar MRI sequences), crosstalk between different frequency bands occurs in the data. This crosstalk leads to a “bulls-eye” artifact in SWIFT images. We present a method to cancel this inter-band crosstalk by cycling the pulse and receive gap positions relative to the un-gapped pulse shape. We call this strategy “gap cycling.” Methods We carry out theoretical analysis, simulation and experiments to characterize the signal chain, resulting artifacts, and their elimination for SWIFT. Results Theoretical analysis reveals the mechanism for gap-cycling’s effectiveness in canceling inter-band crosstalk in the received data. We show phantom and in-vivo results demonstrating bulls-eye artifact free images. Conclusion Gap cycling is an effective method to remove bulls-eye artifact resulting from inter-band crosstalk in SWIFT data. PMID:24604286

  15. Exact and approximate ensemble treatments of thermal pairing in a multilevel model

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2009-05-15

    A systematic comparison is conducted for pairing properties of finite systems at nonzero temperature as predicted by the exact solutions of the pairing problem embedded in three principal statistical ensembles, as well as the unprojected (FTBCS1+SCQRPA) and Lipkin+Nogami projected (FTLN1+SCQRPA) theories that include the quasiparticle number fluctuation and coupling to pair vibrations within the self-consistent quasiparticle random-phase approximation. The numerical calculations are performed for the pairing gap, total energy, heat capacity, entropy, and microcanonical temperature within the doubly folded equidistant multilevel pairing model. The FTLN1+SCQRPA predictions agree best with the exact grand-canonical results. In general, all approaches clearly show that the superfluid-normal phase transition is smoothed out in finite systems. A novel formula is suggested for extracting the empirical pairing gap in reasonable agreement with the exact canonical results.

  16. Neutron range spectrometer

    DOEpatents

    Manglos, S.H.

    1988-03-10

    A neutron range spectrometer and method for determining the neutron energy spectrum of a neutron emitting source are disclosed. Neutrons from the source are colliminated along a collimation axis and a position sensitive neutron counter is disposed in the path of the collimated neutron beam. The counter determines positions along the collimation axis of interactions between the neutrons in the neutron beam and a neutron-absorbing material in the counter. From the interaction positions, a computer analyzes the data and determines the neutron energy spectrum of the neutron beam. The counter is preferably shielded and a suitable neutron-absorbing material is He-3. 1 fig.

  17. NEUTRONIC REACTOR

    DOEpatents

    Wigner, E.P.

    1958-04-22

    A nuclear reactor for isotope production is described. This reactor is designed to provide a maximum thermal neutron flux in a region adjacent to the periphery of the reactor rather than in the center of the reactor. The core of the reactor is generally centrally located with respect tn a surrounding first reflector, constructed of beryllium. The beryllium reflector is surrounded by a second reflector, constructed of graphite, which, in tune, is surrounded by a conventional thermal shield. Water is circulated through the core and the reflector and functions both as a moderator and a coolant. In order to produce a greatsr maximum thermal neutron flux adjacent to the periphery of the reactor rather than in the core, the reactor is designed so tbat the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the materials in the reflector is approximately twice the ratio of neutron scattering cross section to neutron absorption cross section averaged over all of the material of the core of the reactor.

  18. Multiprocessor switch with selective pairing

    SciTech Connect

    Gara, Alan; Gschwind, Michael K; Salapura, Valentina

    2014-03-11

    System, method and computer program product for a multiprocessing system to offer selective pairing of processor cores for increased processing reliability. A selective pairing facility is provided that selectively connects, i.e., pairs, multiple microprocessor or processor cores to provide one highly reliable thread (or thread group). Each paired microprocessor or processor cores that provide one highly reliable thread for high-reliability connect with a system components such as a memory "nest" (or memory hierarchy), an optional system controller, and optional interrupt controller, optional I/O or peripheral devices, etc. The memory nest is attached to a selective pairing facility via a switch or a bus

  19. Auditory Cortex Is Required for Fear Potentiation of Gap Detection

    PubMed Central

    Weible, Aldis P.; Liu, Christine; Niell, Cristopher M.

    2014-01-01

    Auditory cortex is necessary for the perceptual detection of brief gaps in noise, but is not necessary for many other auditory tasks such as frequency discrimination, prepulse inhibition of startle responses, or fear conditioning with pure tones. It remains unclear why auditory cortex should be necessary for some auditory tasks but not others. One possibility is that auditory cortex is causally involved in gap detection and other forms of temporal processing in order to associate meaning with temporally structured sounds. This predicts that auditory cortex should be necessary for associating meaning with gaps. To test this prediction, we developed a fear conditioning paradigm for mice based on gap detection. We found that pairing a 10 or 100 ms gap with an aversive stimulus caused a robust enhancement of gap detection measured 6 h later, which we refer to as fear potentiation of gap detection. Optogenetic suppression of auditory cortex during pairing abolished this fear potentiation, indicating that auditory cortex is critically involved in associating temporally structured sounds with emotionally salient events. PMID:25392510

  20. FOREWORD: Neutron metrology Neutron metrology

    NASA Astrophysics Data System (ADS)

    Thomas, David J.; Nolte, Ralf; Gressier, Vincent

    2011-12-01

    The International Committee for Weights and Measures (CIPM) has consultative committees covering various areas of metrology. The Consultative Committee for Ionizing Radiation (CCRI) differs from the others in having three sections: Section (I) deals with radiation dosimetry, Section (II) with radionuclide metrology and Section (III) with neutron metrology. In 2003 a proposal was made to publish special issues of Metrologia covering the work of the three Sections. Section (II) was the first to complete their task, and their special issue was published in 2007, volume 44(4). This was followed in 2009 by the special issue on radiation dosimetry, volume 46(2). The present issue, volume 48(6), completes the trilogy and attempts to explain neutron metrology, the youngest of the three disciplines, the neutron only having been discovered in 1932, to a wider audience and to highlight the relevance and importance of this field. When originally approached with the idea of this special issue, Section (III) immediately saw the value of a publication specifically on neutron metrology. It is a topic area where papers tend to be scattered throughout the literature in journals covering, for example, nuclear instrumentation, radiation protection or radiation measurements in general. Review articles tend to be few. People new to the field often ask for an introduction to the various topics. There are some excellent older textbooks, but these are now becoming obsolete. More experienced workers in specific areas of neutron metrology can find it difficult to know the latest position in related areas. The papers in this issue attempt, without presenting a purely historical outline, to describe the field in a sufficiently logical way to provide the novice with a clear introduction, while being sufficiently up-to-date to provide the more experienced reader with the latest scientific developments in the different topic areas. Neutron radiation fields obviously occur throughout the nuclear

  1. FOREWORD: Neutron metrology Neutron metrology

    NASA Astrophysics Data System (ADS)

    Thomas, David J.; Nolte, Ralf; Gressier, Vincent

    2011-12-01

    The International Committee for Weights and Measures (CIPM) has consultative committees covering various areas of metrology. The Consultative Committee for Ionizing Radiation (CCRI) differs from the others in having three sections: Section (I) deals with radiation dosimetry, Section (II) with radionuclide metrology and Section (III) with neutron metrology. In 2003 a proposal was made to publish special issues of Metrologia covering the work of the three Sections. Section (II) was the first to complete their task, and their special issue was published in 2007, volume 44(4). This was followed in 2009 by the special issue on radiation dosimetry, volume 46(2). The present issue, volume 48(6), completes the trilogy and attempts to explain neutron metrology, the youngest of the three disciplines, the neutron only having been discovered in 1932, to a wider audience and to highlight the relevance and importance of this field. When originally approached with the idea of this special issue, Section (III) immediately saw the value of a publication specifically on neutron metrology. It is a topic area where papers tend to be scattered throughout the literature in journals covering, for example, nuclear instrumentation, radiation protection or radiation measurements in general. Review articles tend to be few. People new to the field often ask for an introduction to the various topics. There are some excellent older textbooks, but these are now becoming obsolete. More experienced workers in specific areas of neutron metrology can find it difficult to know the latest position in related areas. The papers in this issue attempt, without presenting a purely historical outline, to describe the field in a sufficiently logical way to provide the novice with a clear introduction, while being sufficiently up-to-date to provide the more experienced reader with the latest scientific developments in the different topic areas. Neutron radiation fields obviously occur throughout the nuclear

  2. Precision gap particle separator

    DOEpatents

    Benett, William J.; Miles, Robin; Jones, II., Leslie M.; Stockton, Cheryl

    2004-06-08

    A system for separating particles entrained in a fluid includes a base with a first channel and a second channel. A precision gap connects the first channel and the second channel. The precision gap is of a size that allows small particles to pass from the first channel into the second channel and prevents large particles from the first channel into the second channel. A cover is positioned over the base unit, the first channel, the precision gap, and the second channel. An port directs the fluid containing the entrained particles into the first channel. An output port directs the large particles out of the first channel. A port connected to the second channel directs the small particles out of the second channel.

  3. MULTIPLE SPARK GAP SWITCH

    DOEpatents

    Schofield, A.E.

    1958-07-22

    A multiple spark gap switch of unique construction is described which will permit controlled, simultaneous discharge of several capacitors into a load. The switch construction includes a disc electrode with a plurality of protuberances of generally convex shape on one surface. A firing electrode is insulatingly supponted In each of the electrode protuberances and extends substantially to the apex thereof. Individual electrodes are disposed on an insulating plate parallel with the disc electrode to form a number of spark gaps with the protuberances. These electrodes are each connected to a separate charged capacitor and when a voltage ls applied simultaneously between the trigger electrodes and the dlsc electrode, each spark gap fires to connect its capacitor to the disc electrode and a subsequent load.

  4. Multiple origins of asteroid pairs

    NASA Astrophysics Data System (ADS)

    Jacobson, Seth A.

    2016-01-01

    Rotationally fissioned asteroids produce unbound asteroid pairs that have very similar heliocentric orbits. Backward integration of their current heliocentric orbits provides an age of closest proximity that can be used to date the rotational fission event. Most asteroid pairs follow a predicted theoretical relationship between the primary spin period and the mass ratio of the two pair members that is a direct consequence of the YORP-induced rotational fission hypothesis. If the progenitor asteroid has strength, asteroid pairs may have higher mass ratios or faster rotating primaries. However, the process of secondary fission leaves the originally predicted trend unaltered. We also describe the characteristics of pair members produced by four alternative routes from a rotational fission event to an asteroid pair. Unlike direct formation from the event itself, the age of closest proximity of these pairs cannot generally be used to date the rotational fission event since considerable time may have passed.

  5. Microwave Type III Pair Bursts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Tan, Baolin; Mészárosová, Hana; Karlický, Marian; Huang, Guangli; Tan, Chengming

    2016-03-01

    A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80-7.60 GHz during 1994-2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08-3.42 GHz and a frequency gap of 10-1700 MHz. The frequency drift increases with the separate frequency (fx), the lifetime of each burst is anti-correlated to fx, while the frequency gap is independent of fx. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about {10}10{--}{10}11 cm-3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares.

  6. Bridging NCL research gaps.

    PubMed

    Stehr, Frank; van der Putten, Herman

    2015-10-01

    The neuronal ceroid lipofuscinoses, collectively called NCLs, are rare and fatal lysosomal storage diseases that mainly affect children. Due to the fact that NCLs are both rare and heterogeneous (mutations in thirteen different genes) significant gaps exist in both preclinical and clinical research. Altogether, these gaps are major hurdles to bring therapies to patients while the need for new therapies is urgent to help them and their families. To define gaps and discuss solutions, a round table discussion involving teams and different stake holders took place during the 14th International Conference on Neuronal Ceroid Lipofuscinoses (Batten Disease) in Cordóba, Argentina. Topics covered by the teams and their leaders (in parentheses) included basic and translational research gaps with regard to large animal models (I. Tammen, D.N. Palmer), human NCL pathology and access to human tissue (J.D. Cooper, H.H. Goebel), rare NCLs (S. Hofman, I. Noher), links of NCLs to other diseases (F.M. Platt), gaps between clinic and clinical trials (H. Adams, A. Schulz), international collaborative efforts working towards a cure (S.E. Mole, H. Band) perspectives on palliative care from patient organizations (M. Frazier, A. West), and issues NCL researchers face when progressing to independent career in academia (M. Bond). Thoughts presented by the team leaders include previously unpublished opinions and information on the lack of understanding of disease pathomechanisms, gene function, assays for drug discovery and target validation, natural history of disease, and biomarkers for monitoring disease progression and treatment effects. This article is not intended to review the NCL literature. It includes personal opinions of the authors and it provides the reader with a summary of gaps discussed and solutions proposed by the teams. This article is part of a Special Issue entitled: Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease). PMID:26056946

  7. The partial pair correlation functions of dense supercritical water

    NASA Astrophysics Data System (ADS)

    Tassaing, T.; Bellissent-Funel, M.-C.; Guillot, B.; Guissani, Y.

    1998-05-01

    Neutron diffraction measurements of heavy water and of two isotopic H2O/D2O mixtures at supercritical state (T = 380 °C and ρD2O = 0.73 g/cm3) are presented. In combining the set of neutron diffraction data with previous X-rays measurements of Yamanaka et al. (J. Chem. Phys., 101 (1994) 9830), it has been possible by using a Monte Carlo method to reach the partial pair correlation functions gOH(r), gHH(r) and gOO(r). The results are compared with molecular-dynamics simulations using the SPCE pair potential for water. These new results confirm that hydrogen bonding is still present in dense supercritical water.

  8. Spark gap electrode erosion

    NASA Astrophysics Data System (ADS)

    Krompholz, H.; Kristiansen, M.

    1984-12-01

    The results of a one-year contract on electrode erosion phenomena are summarized. The arc voltage drop in a spark gap was measured for various electrode, gas, and pressure combinations. A previously developed model of self breakdown voltage distribution was extended. A jet model for electrode erosion was proposed and an experimental arrangement for testing the model was constructed. The effects of inhomogeneities and impurities in the electrodes were investigated. Some of the work described here is scheduled for completion in 1985 under a current grant (AFOSR 84-0032). The areas of investigation described here include: (1) Self breakdown voltage distributions; (2) Electrode erosion; (3) Spark gap voltage recovery.

  9. Future of Semiconductor Based Thermal Neutron Detectors

    SciTech Connect

    Nikolic, R J; Cheung, C L; Reinhardt, C E; Wang, T F

    2006-02-22

    Thermal neutron detectors have seen only incremental improvements over the last decades. In this paper we overview the current technology of choice for thermal neutron detection--{sup 3}He tubes, which suffer from, moderate to poor fieldability, and low absolute efficiency. The need for improved neutron detection is evident due to this technology gap and the fact that neutrons are a highly specific indicator of fissile material. Recognizing this need, we propose to exploit recent advances in microfabrication technology for building the next generation of semiconductor thermal neutron detectors for national security requirements, for applications requiring excellent fieldability of small devices. We have developed an innovative pathway taking advantage of advanced processing and fabrication technology to produce the proposed device. The crucial advantage of our Pillar Detector is that it can simultaneously meet the requirements of high efficiency and fieldability in the optimized configuration, the detector efficiency could be higher than 70%.

  10. Gap Size and Wall Lesion Development Next to Composite

    PubMed Central

    Kuper, N.K.; Opdam, N.J.M.; Ruben, J.L.; de Soet, J.J.; Cenci, M.S.; Bronkhorst, E.M.; Huysmans, M.C.D.N.J.M.

    2014-01-01

    This in situ study investigated whether there is a relationship between gap size and wall lesion development in dentin next to 2 composite materials, and whether a clinically relevant threshold for the gap size could be established. For 21 days, 14 volunteers wore a modified occlusal splint containing human dentin samples with 5 different interfaces: 4 gaps of 50 µm, 100 µm, 200 µm, or 400 µm and 1 non-bonded interface without a gap. Eight times a day, the splint with samples was dipped in a 20% sucrose solution for 10 minutes. Before and after caries development, specimens were imaged with transversal wavelength-independent microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were calculated at the 5 different interfaces. After correction for the confounder location (more mesial or distal), a paired t test clustered within volunteers was performed for comparison of gap widths. Results showed no trend for a relationship between the corrected lesion depth and the gap size. None of the differences in lesion depth for the different gap sizes was statistically significant. Also, the composite material (AP-X or Filtek Supreme) gave no statistically significant differences in lesion depth and mineral loss. A minimum gap size could not be established, although, in a non-bonded interface without a measurable gap, wall lesion development was never observed. PMID:24801597