Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Positron scattering from atoms and molecules using a magnetized beam

James Patrick Sullivan, S. J. Gilbert, Joan P. Marler, R. G. Greaves, Stephen J. Buckman, Clifford M. Surko

Published Oct 15, 2002• 99 citations
Publisher

Abstract

The development of buffer-gas trapping and magnetized beam formation has provided positron beams with significantly improved energy resolution $(\ensuremath{\Delta}E<~0.025\mathrm{eV})$ compared to those available previously. Analysis techniques have been developed to take advantage of the fact that the beam is in a magnetic field of $\ensuremath{\sim}0.1\mathrm{T}.$ This has enabled scattering experiments at lower energies and with significantly improved state selectivity for excitation experiments than had been possible previously. A detailed description of these techniques is presented. Data are presented for a variety of cross sections for scattering of positrons from atomic and molecular targets.

DOI
10.1103/physreva.66.042708

Related papers

Positron Scattering and Annihilation Studies Using a Trap-Based Beam

L. D. Barnes, Joan P. Marler, James Patrick Sullivan +1 more

An overview is presented of recent studies of the interaction of low-energy positrons with atoms and molecules using a trap-based positron beam. The beam is tunable from ~100 meV to many electron volts, with a typical energy resolution of 25 meV (FWHM). A variety of scattering processes are investigated using the properties of positron orbits in a spatially varying magnetic field. Recent scattering measurements are reviewed, and new data for electronic excitation, ionization, and positronium formation in noble gases are presented. In a separate set of experiments, positron annihilation below the threshold for positronium formation is studied in molecules as a function of positron energy. The data show large Feshbach resonances in the range of energies of the molecular vibrations. Within the framework of this model, these results provide the first experimental evidence that positrons bind to hydrocarbon molecules.

Physica Scripta•Jan 1, 2004•11 citations

The Buffer-Gas Positron Accumulator and Resonances in Positron-Molecule Interactions

Clifford M. Surko

This is a personal account of the development of our buffer-gas positron trap and the new generation of cold beams that these traps enabled. Dick Drachman provided much appreciated advice to us from the time we started the project. The physics underlying trap operation is related to resonances (or apparent resonances) in positron-molecule interactions. Amusingly, experiments enabled by the trap allowed us to understand these processes. The positron-resonance "box score" to date is one resounding "yes," namely vibrational Feshbach resonances in positron annihilation on hydrocarbons; a "probably" for positron-impact electronic excitation of CO and NZ;an d a "maybe" for vibrational excitation of selected molecules. Two of these processes enabled the efficient operation of the trap, and one almost killed it in infancy. We conclude with a brief overview of further applications of the trapping technology discussed here, such as "massive" positron storage and beams with meV energy resolution.

•Jan 1, 2007•0 citations

Electron-atom scattering using atomic recoil

Benjamin B. Bederson

This talk will review electron-atom scattering experiments using recoil techniques, wherein observation of the collision process is made on the recoil-scattered atom rather than on the electron. Using this technique it is possible to obtain absolute cross sections without normalization or knowledge of the atom density in the interaction region; atomic state selection and analysis is also more readily performed. Comparisons with theory and with other crossed beam experiments, including those using polarized electrons, will be made. Details of ongoing experiments are presented in companion papers at this conference. A discussion of how laser cooling, and velocity and spatial compression can be employed to improve dramatically spatial and energy resolution and sensitivity will be presented.

Bulletin of the American Physical Society•Dec 1, 1992•1 citation

Ultracold atoms as a target: absolute scattering cross-section measurements

P Würtz, T Gericke, A Vogler +1 more

We report on a new experimental platform for the measurement of absolute scattering cross-sections. The target atoms are trapped in an optical dipole trap and are exposed to an incident particle beam. The exponential decay of the atom number directly yields the absolute total scattering cross-section. The technique can be applied to any atomic or molecular species that can be prepared in an optical dipole trap and provides a large variety of possible scattering scenarios.

arXiv:1011.0860•New Journal of Physics•Jun 28, 2010•12 citations

Electron-Scattering Measurements using a Magneto-Optical Trap

Thad G Walker

Optically trapped atoms are in many ways ideal replacements for atomic beams for scattering experiments. In a typical such experiment, a particle beam ejects atoms from the trap at a rate {Gamma} = {sigma}{phi}, where {phi} is the particle flux density and {sigma} the scattering cross section. {Gamma} is easily measured from trap decay transients. Since the trapped atoms have neV kinetic energies, the method is sensitive to extremely small momentum transfers. Since the beam flux is measured, the absolute target density is not required, removing an important source of error for most atomic beam experiments. At Wisconsin the authors have integrated an electron beam with a magneto-optical trap and performed electron-scattering experiments on Rb atoms in the range of 10-1000 eV. In the first experiment they measured total cross sections for scattering from the 5s state by lowering the capture velocity of the trap below the recoil velocity of the scattered atoms. In the second experiment they isolated the total ionization cross section by operating the trap such that virtually all elastically and inelastically scattered atoms were captured by the trap. These experimental results will test new theoretical methods for calculating total and ionization cross sections. Straightforward extensions ofmore » these methods should allow similar measurements using excited-state atoms (5p, 5d) as well. The techniques should also be readily adaptable to the important case of the metastable noble gases.« less

Bulletin of the American Physical Society•May 1, 1996•0 citations

Ultracold Atoms as a Target: Absolute Scattering Cross-Section Measurements

Tatjana Gericke, Andreas Vogler, Herwig Ott

Abstract. We report on a new experimental platform for the measurement of absolute scattering cross-sections. The target atoms are trapped in an optical dipole trap and are exposed to an incident particle beam. The exponential decay of the atom number directly yields the absolute total scattering cross-section. The technique can be applied to any atomic or molecular species that can be prepared in an optical dipole trap and provides a large variety of possible scattering scenarios. ar X iv

•Aug 16, 2016•9 citations
The development of buffer-gas trapping and magnetized beam formation has provided positron beams with significantly improved energy resolution (\ensuremathΔE< 0.025eV)(\ensuremath{\Delta}E<~0.025\mathrm{eV})(\ensuremathΔE< 0.025eV) compared to those available previously. Analysis techniques have been developed to take advantage of the fact that the beam is in a magnetic field of \ensuremath∼0.1T.\ensuremath{\sim}0.1\mathrm{T}.\ensuremath∼0.1T. This has enabled scattering experiments at lower energies and with significantly improved state selectivity for excitation experiments than had been possible previously. A detailed description of these techniques is presented. Data are presented for a variety of cross sections for scattering of positrons from atomic and molecular targets.
An overview is presented of recent studies of the interaction of low-energy positrons with atoms and molecules using a trap-based positron beam. The beam is tunable from ~100 meV to many electron volts, with a typical energy resolution of 25 meV (FWHM). A variety of scattering processes are investigated using the properties of positron orbits in a spatially varying magnetic field. Recent scattering measurements are reviewed, and new data for electronic excitation, ionization, and positronium formation in noble gases are presented. In a separate set of experiments, positron annihilation below the threshold for positronium formation is studied in molecules as a function of positron energy. The data show large Feshbach resonances in the range of energies of the molecular vibrations. Within the framework of this model, these results provide the first experimental evidence that positrons bind to hydrocarbon molecules.
This is a personal account of the development of our buffer-gas positron trap and the new generation of cold beams that these traps enabled. Dick Drachman provided much appreciated advice to us from the time we started the project. The physics underlying trap operation is related to resonances (or apparent resonances) in positron-molecule interactions. Amusingly, experiments enabled by the trap allowed us to understand these processes. The positron-resonance "box score" to date is one resounding "yes," namely vibrational Feshbach resonances in positron annihilation on hydrocarbons; a "probably" for positron-impact electronic excitation of CO and NZ;an d a "maybe" for vibrational excitation of selected molecules. Two of these processes enabled the efficient operation of the trap, and one almost killed it in infancy. We conclude with a brief overview of further applications of the trapping technology discussed here, such as "massive" positron storage and beams with meV energy resolution.
This talk will review electron-atom scattering experiments using recoil techniques, wherein observation of the collision process is made on the recoil-scattered atom rather than on the electron. Using this technique it is possible to obtain absolute cross sections without normalization or knowledge of the atom density in the interaction region; atomic state selection and analysis is also more readily performed. Comparisons with theory and with other crossed beam experiments, including those using polarized electrons, will be made. Details of ongoing experiments are presented in companion papers at this conference. A discussion of how laser cooling, and velocity and spatial compression can be employed to improve dramatically spatial and energy resolution and sensitivity will be presented.
Optically trapped atoms are in many ways ideal replacements for atomic beams for scattering experiments. In a typical such experiment, a particle beam ejects atoms from the trap at a rate {Gamma} = {sigma}{phi}, where {phi} is the particle flux density and {sigma} the scattering cross section. {Gamma} is easily measured from trap decay transients. Since the trapped atoms have neV kinetic energies, the method is sensitive to extremely small momentum transfers. Since the beam flux is measured, the absolute target density is not required, removing an important source of error for most atomic beam experiments. At Wisconsin the authors have integrated an electron beam with a magneto-optical trap and performed electron-scattering experiments on Rb atoms in the range of 10-1000 eV. In the first experiment they measured total cross sections for scattering from the 5s state by lowering the capture velocity of the trap below the recoil velocity of the scattered atoms. In the second experiment they isolated the total ionization cross section by operating the trap such that virtually all elastically and inelastically scattered atoms were captured by the trap. These experimental results will test new theoretical methods for calculating total and ionization cross sections. Straightforward extensions ofmore » these methods should allow similar measurements using excited-state atoms (5p, 5d) as well. The techniques should also be readily adaptable to the important case of the metastable noble gases.« less