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91 results on '"Höhr C"'

4. Tensor interaction constraints from beta decay recoil spin asymmetry of trapped atoms

Author

Pitcairn, J. R. A., Roberge, D., Gorelov, A., Ashery, D., Aviv, O., Behr, J. A., Bricault, P. G., Dombsky, M., Holt, J. D., Jackson, K. P., Lee, B., Pearson, M. R., Gaudin, A., Dej, B., Höhr, C., Gwinner, G., and Melconian, D.

Subjects
Nuclear Experiment
Abstract

We have measured the angular distribution of recoiling daughter nuclei emitted from the Gamow-Teller $\beta$ decay of spin-polarized $^{80}$Rb. The asymmetry of this distribution vanishes to lowest order in the Standard Model (SM) in pure Gamow-Teller decays, producing an observable very sensitive to new interactions. We measure the non-SM contribution to the asymmetry to be $A_{T}$= 0.015 $\pm$ 0.029 (stat) $\pm$ 0.019 (syst), consistent with the SM prediction. We constrain higher-order SM corrections using the measured momentum dependence of the asymmetry, and their remaining uncertainty dominates the systematic error. Future progress in determining the weak magnetism term theoretically or experimentally would reduce the final errors. We describe the resulting constraints on fundamental 4-Fermi tensor interactions., Comment: 11 pages, 13 figures; v2 published in Phys. Rev. C, with referee clarifications and figures improved for black-and-white

Published
2008
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8. Improved sub-milimeter range-verification method for proton therapy using a composite hadron tumour marker (HTM).

Author

Kasanda, E, Burbadge, C, Bildstein, V, Bélanger-Champagne, C, Behnamian, H, Höhr, C, and Mücher, D

Subjects
TUMOR markers, PROTON therapy, HADRONS, GERMANIUM detectors, PROTON beams, CANCER treatment
Abstract

Objective. The results of a follow-up experiment investigating a novel method for sub-milimetre range verification (RV) in proton therapy (PT) are presented. Approach. The method consists of implanting a hadron tumour marker (HTM) near the planned treatment volume, and measuring the γ -ray signals emitted as a result of activation by the proton beam. These signals are highly correlated with the energy of the beam impinging on the HTM and can provide an absolute measurement of the range of the beam relative to the position of the HTM, which is independent of any uncertainties in beam delivery. Main results. Three candidate HTM materials were identified and combined into a single composite HTM, which makes use of the strongest reaction in each material. The setup of the previous experiment was improved on by using high-purity germanium detectors to measure the γ -ray signal with a higher resolution than was previously achieved. A PMMA phantom was also used to simulate the γ -ray background from tissue activation. HTM RV using the data collected in this study yielded range measurements whose average deviation from the expected value was 0.13(22)mm. Significance. Range uncertainty in PT limits the prescribed treatment plan for cancer patients with large safety margins and constrains the direction of the proton beam in relation to any organ at risk. The sub-milimetre range uncertainty achieved in this study using HTM RV, if implemented clinically, would allow for a reduction in the size of safety margins, increasing the therapeutic window for PT. [ABSTRACT FROM AUTHOR]

Published
2023
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19. Characterization of the spatiotemporal evolution of laser-generated plasmas.

Author

Kanter, E. P., Santra, R., Höhr, C., Peterson, E. R., Rudati, J., Arms, D. A., Dufresne, E. M., Dunford, R. W., Ederer, D. L., Krässig, B., Landahl, E. C., Southworth, S. H., and Young, L.

Subjects
LASER plasmas, LASERS, IONS, DENSITY, KRYPTON, PLASMA gases
Abstract

We characterize the time evolution of ion spatial distributions in a laser-produced plasma. Krypton ions are produced in strong, linearly and circularly polarized optical laser fields (1014–1015 W/cm2). The Kr+ ions are preferentially detected by resonant x-ray absorption. Using microfocused, tunable x rays from Argonne’s Advanced Photon Source, we measure ion densities as a function of time with 10 μm spatial resolution for times ≤50 ns. For plasma densities of the order of 1014 cm-3, we observe a systematic expansion of the ions outward from the laser focus. We find the expansion timescale to be independent of the plasma density though strongly dependent on the plasma shape and electron temperature. The former is defined by the laser focus, while the latter is controlled by the laser polarization state. We have developed a fluid description assuming a collisionless quasineutral plasma, which is modeled using a particle-in-cell approach. This simulation provides a quantitative description of the observed behavior and demonstrates the role of the very different electron temperatures produced by circularly and linearly polarized light. These results demonstrate the utility of this method as an in situ probe of the time and spatial evolution of laser-produced plasmas. [ABSTRACT FROM AUTHOR]

Published
2008
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20. Dissociative ionization of H2 by fast protons: Three-body breakup and molecular-frame electron emission

Author

Dimopoulou, C., Moshammer, R., Fischer, D., Fainstein, P., Höhr, C., Dorn, A., Crespo López Urrutia, J., Schröter, C., and Kollmus, H.

Subjects
Nuclear Experiment
Abstract

Highly differential cross sections have been obtained for dissociative single ionization of H2 by 6 MeV proton impact by measuring the momentum vectors of the electron and the H+ fragment in coincidence. The investigation of the momentum balance of the fragments along the projectile beam provided detailed insight into the four-particle dynamics, even though the H atom is not detected. Within the axial recoil approximation, molecular-frame angular distributions of emitted electrons have been determined for molecules oriented perpendicular to the projectile beam. They are compared with the predictions of a CDW-EIS calculation.

Published
2005

21. Reply to 'Comment on 'Appearance and disappearance of the second Born effects in the (e,3e) reaction on He' '

Author

Dorn, A., Kheifets, A., Schröter, C., Höhr, C., Sakhelashvili, G., Moshammer, R., Lower, J., and Ullrich, J.

Subjects
Physics::Atomic and Molecular Clusters, Physics::Atomic Physics
Abstract

In this Reply, we demonstrate that at large momentum transfer (|q| = 2 a.u.), within the experimentally accessible angular range of the ionized electrons, there is good agreement between experiment and the first Born calculation concerning the shape of the cross section. Furthermore, we show that the fact that our results for (e,3e) double ionization seemingly "contradict well-accepted results in (e,2e) single ionization" can be traced to a second Born process in which the projectile interacts with both target electrons in sequence. This process competes effectively with other double ionization mechanisms but is relatively unimportant for single ionization.

Published
2005

23. Break-Up of H2 in Singly Ionizing Collisions with Fast Protons: Channel-Selective Low-Energy Electron Spectra

Author

Dimopoulou, C., Moshammer, R., Fischer, D., Höhr, C., Dorn, A., Fainstein, P., Crespo López Urrutia, J., Schröter, C., Kollmus, H., Mann, R., Hagmann, S., and Ullrich, J.

Subjects
Physics::Atomic and Molecular Clusters
Abstract

Dissociative as well as nondissociative single ionization of H2 by 6 MeV proton impact has been studied in a kinematically complete experiment by measuring the momentum vectors of the electron and the H+ fragment or the H2+ target ion, respectively. For the two ionization pathways, the electron spectra reveal the role of autoionization of the doubly and singly excited states of H2. The latter explicitly involve the coupling between the electronic and the nuclear motion of the molecule. This is a clear manifestation of a breakdown of the Born-Oppenheimer approximation.

Published
2004

24. Kinematisch vollständige Experimente zur Ionisation im Elektronenstoß und Laserfeld

Author

Höhr, C.

Subjects
530 Physics
Abstract

In der vorliegenden Arbeit wurde die Elektronenstoßionisation von Helium mit schnellen Elektronen untersucht und kinematisch vollständig vermessen. Durch Verwendung eines sogenannten Reaktionsmikroskops konnten die Impulse aller Stoßfragmente über den vollen Raumwinkel und große Energiebereiche bestimmt werden. Im ersten Teil der Arbeit wurde ein experimenteller Satz von Daten zur Doppelionisation von Helium bei einer Projektilgeschwindigkeit von v_p=6 a.u. gewonnen und mit experimentellen Daten einer höheren Projektilgeschwindigkeit und zwei verschiedenen, theoretischen Rechnungen verglichen. Dabei konnten einzelne Ionisationsmechanismen identifiziert, sowie ihre Abhängigkeit von der Kinematik des Stoßes untersucht werden. Im zweiten Teil der Arbeit wurde erstmals ein Experiment zur Einfachionisation von Helium im intensiven Laserfeld (I = 5*10^12 W/cm^2) durchgeführt. Die resultierenden Wirkungsquerschnitte zeigen signifikante Unterschiede verglichen mit dem feldfreien Stoß. Eine erste quantenmechanische Rechnung kann die gemessenen Wirkungsquerschnitte nicht erklären. Im Rahmen eines einfachen klassischen Modells hingegen, das die Bewegung des emittierten Elektrons im Lichtfeld beschreibt, können die experimentellen Daten qualitativ verstanden werden.

Published
2004
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25. Appearance and Disappearance of Second Born Effects in (e,3e) Reactions in He

Author

Dorn, A., Kheifets, A., Schröter, C., Höhr, C., Sakhelashvili, G., Moshammer, R., Lower, J., and Ullrich, J.

Subjects
Nuclear Experiment
Abstract

We demonstrate, both experimentally and theoretically, clear manifestation of the second Born effects in the angular distributions of two ejected electrons produced by a 500 eV electron impact on the He atom in the so-called (e,3e) reaction. The second Born contribution, due to subsequent interaction of the projectile with the target, is most prominent for glancing collisions with small momentum transfer. However, these effects are absent for hard knock-out collisions with large momentum transfer.

Published
2003

26. Tests of a Laser Ion Source at the Heidelberg Electron Beam Ion Trap

Author

Mironov, V., Trinczek, M., Werdich, A., González Martínez, A., Guo, P., Zhang, X., Braun, J., Crespo López-Urrutia, J., Höhr, C., and Ullrich, J.

Subjects
Physics::Plasma Physics, Physics::Atomic Physics
Abstract

A laser ion source (LIS) has been designed and successfully tested for loading the Heidelberg electron beam ion trap (H-EBIT) with ions of practically all solid-state elements. A pulsed YAG:Nd3þ laser (30 mJ, 8 ns) is used to produce plasma from a solid target. Lowly charged ions are extracted from the plasma and accelerated by a short high-voltage pulse, generating a pulsed ion beam with energy of up to 6 keV per charge. The ion beam is transported into the EBIT, decelerated and captured within it by switching the trapping electrode potentials. The electron beam further ionizes the trapped ions to the desired highly charged states. The experimental setup is described together with the source parameters measured for different target materials. X-ray spectra of up to He-like highly charged ions (Cu, Mo, Pb, Al and Ge) produced in the EBIT after injection from the LIS have been measured. The reliability and convenience of this method allows the use of the LIS to produce highly charged ions of both insulating and conducting solid elements with an EBIT as needed for different experiments.

Published
2003

30. Tensor interaction constraints fromβ-decay recoil spin asymmetry of trapped atoms

Author

Pitcairn, J. R. A., primary, Roberge, D., additional, Gorelov, A., additional, Ashery, D., additional, Aviv, O., additional, Behr, J. A., additional, Bricault, P. G., additional, Dombsky, M., additional, Holt, J. D., additional, Jackson, K. P., additional, Lee, B., additional, Pearson, M. R., additional, Gaudin, A., additional, Dej, B., additional, Höhr, C., additional, Gwinner, G., additional, and Melconian, D., additional

Published
2009
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32. K-edge x-ray-absorption spectroscopy of laser-generatedKr+andKr2+

Author

Southworth, S. H., primary, Arms, D. A., additional, Dufresne, E. M., additional, Dunford, R. W., additional, Ederer, D. L., additional, Höhr, C., additional, Kanter, E. P., additional, Krässig, B., additional, Landahl, E. C., additional, Peterson, E. R., additional, Rudati, J., additional, Santra, R., additional, Walko, D. A., additional, and Young, L., additional

Published
2007
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33. Alignment dynamics in a laser-produced plasma

Author

Höhr, C., primary, Peterson, E. R., additional, Rohringer, N., additional, Rudati, J., additional, Arms, D. A., additional, Dufresne, E. M., additional, Dunford, R. W., additional, Ederer, D. L., additional, Kanter, E. P., additional, Krässig, B., additional, Landahl, E. C., additional, Santra, R., additional, Southworth, S. H., additional, and Young, L., additional

Published
2007
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36. X-Ray Microprobe of Orbital Alignment in Strong-Field Ionized Atoms

Author

Young, L., primary, Arms, D. A., additional, Dufresne, E. M., additional, Dunford, R. W., additional, Ederer, D. L., additional, Höhr, C., additional, Kanter, E. P., additional, Krässig, B., additional, Landahl, E. C., additional, Peterson, E. R., additional, Rudati, J., additional, Santra, R., additional, and Southworth, S. H., additional

Published
2006
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45. Coincident Fragment Detection in Strong Field Photoionization and Dissociation ofH2

Author

Rottke, H., primary, Trump, C., additional, Wittmann, M., additional, Korn, G., additional, Sandner, W., additional, Moshammer, R., additional, Dorn, A., additional, Schröter, C. D., additional, Fischer, D., additional, Crespo Lopez-Urrutia, J. R., additional, Neumayer, P., additional, Deipenwisch, J., additional, Höhr, C., additional, Feuerstein, B., additional, and Ullrich, J., additional

Published
2002
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49. Correlated two-electron dynamics in strong-field double ionization

Author

Moshammer, R., primary, Feuerstein, B., additional, López-Urrutia, J. Crespo, additional, Deipenwisch, J., additional, Dorn, A., additional, Fischer, D., additional, Höhr, C., additional, Neumayer, P., additional, Schröter, C. D., additional, Ullrich, J., additional, Rottke, H., additional, Trump, C., additional, Wittmann, M., additional, Korn, G., additional, and Sandner, W., additional

Published
2002
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50. Double ionization of helium by impact of particles with positive and negative charge.

Author

Fisher, D., Moshammer, R., Dorn, A., López-Urrutia, J. R. Crespo, Feuerstein, B., Höhr, C., Schröter, C. D., Hagmann, S., Kollmus, H., Mann, R., Bapat, B., and Ullrich, J.

Subjects
HELIUM, ELECTRON impact ionization, SCATTERING (Physics), IONIZATION (Atomic physics), BORN approximation
Abstract

Double ionization of helium in collisions with 6 MeV protons (vP = 15.5 a.u.) has been explored in a kinematically complete experiment using a so-called “reaction microscope”. For the first time fully differential cross sections for positively charged particle impact have been obtained and compared to previous (e,3e) results with 2 keV electrons (vP = 12 a.u.). Differences have been found in the angular distribution of the two emitted electrons, which originate from projectile charge effects that are not considered in the first Born approximation. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2003
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