Ionization of atoms by particle and antiparticle impact

Knudsen, H.; Reading, J. F.

doi:10.1016/0370-1573(92)90013-p

Cited by 148 publications

(89 citation statements)

References 218 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…, energy losses in quasimolecular interactions, shows up in fair agreement with theoretical predictions. PACS numbers: 34.50.Bw At low projectile velocities (P ( 5 X 10 2) significant differences in collision dynamics were observed [1,2] from one projectile-target system to another. In particular, the p and p stopping powers are expected to be very different around and below the stopping-power maximum where ionization and excitation decrease rapidly and the electronic capture channel for the proton becomes dominant [3].…”

mentioning

confidence: 99%

Antiproton Slowing Down inH2and He and Evidence of Nuclear Stopping Power

et al. 1995

View full text Add to dashboard Cite

We report stopping powers of hydrogen and helium for antiprotons of kinetic energies ranging from about 0.5 keV to 1.1 MeV. The Barkas effect, i.e. , a difference in the stopping power for antiprotons and protons of the same energy in the same material, shows up clearly in either of the gases. Moreover, below =0.5 keV there is indirect evidence for an increase of the antiproton stopping power. This "nuclear" effect, i.e. , energy losses in quasimolecular interactions, shows up in fair agreement with theoretical predictions. PACS numbers: 34.50.Bw At low projectile velocities (P ( 5 X 10 2) significant differences in collision dynamics were observed [1,2] from one projectile-target system to another. In particular, the p and p stopping powers are expected to be very different around and below the stopping-power maximum where ionization and excitation decrease rapidly and the electronic capture channel for the proton becomes dominant [3]. In the velocity range 10 4~P~5 X 10 3, quasimolecular effects come into play even more strongly and a p will lose energy both through nuclear collisions and through nonadiabatic ionization or excitation of the atom [3 -9]. The p is predicted [5] to have the highest energy loss (the lowest being for p, ) by such collisions between negative-charge projectiles and the atoms of the stopping medium.Moreover, a striking departure from velocity proportionality was reported for protons in He by Golser and Semrad [10] and well reproduced by Kimura [11].In a previous work [2] we found that the stopping power of hydrogen is much smaller for p than for p (Barkas effect [12]) in the energy range from 10 to 120 keV. Moreover, a fast rise of the stopping-power behavior below 1 keV was needed to fit the data in the hypothesis that the capture energy of p lies in the electronvolt range.We report here on the results of new measurements of the p stopping power both in hydrogen and helium. The measurements were performed by the OBELIX spectrometer at the CERN LEAR facility. In hydrogen, new data were taken at the pressures of 2, 5, 10, and 150 mbar [13]. In helium, the measurements were run at target pressures of 4, 8.2, 50, and 150 mbar.By means of suitable thicknesses of material, the highly monocromatic p beam (with an energy of 5.875 MeV and an uncertainty of 10 3) is degraded in order to obtain, at the entrance of the target, a beam with energy continuously distributed starting from E;"=0. Antiprotons enter the target (z = 0) at the time t = 0 and slowdown in a 0.5 T magnetic field oriented along the beam direction 0031-9007/95/74(3)/371(4)$06. 00

show abstract

mentioning

confidence: 99%

Antiproton Slowing Down inH2and He and Evidence of Nuclear Stopping Power

et al. 1995

View full text Add to dashboard Cite

show abstract

“…A significant body of data has been gained using the (e; 2e) method (e.g., [3]) and, more recently, the COLTRIM technique (e.g., [4]), which has been applied to electron, photon, proton, and ion impact. Differential studies with positrons, mainly confined to doubly differential investigations (e.g., [5][6][7]), remain scarce but are desirable both intrinsically and for comparison with equivelocity electrons or protons to probe the role of the projectile charge or mass on the collision dynamics (e.g., [8,9]). In this Letter, we report experimental TDCS results for positron impact ionization of simple molecular and atomic targets that reveal major discrepancies with current quantum-mechanical treatments and should thus provide new insights into the understanding of three-body correlated dynamics.…”

mentioning

confidence: 99%

Energy-Sharing Asymmetries in Ionization by Positron Impact

2005

View full text Add to dashboard Cite

The triply differential cross section of molecular hydrogen for ionization by 50 eV positrons has been determined, for the first time, for both the ejected electron in coincidence with the remnant ion and for the scattered projectile. Asymmetries in the energy sharing between the two light particles in the final state are observed, with the electron spectrum being shifted to significantly lower (and the scattered positron to correspondingly higher) energies than expected. A similar shape is observed in the case of the ejected electron spectrum from a helium target at the same excess energy. DOI: 10.1103/PhysRevLett.95.223202 PACS numbers: 34.85.+x The correlated dynamics of few interacting particles is a fundamental physics problem that may be exemplified through the process of ionization. Despite the tremendous progress in its theoretical description during the past decade or so (e.g., [1,2]), concomitant experimental investigations remain essential in assessing the accuracy of the various approaches and in guiding further developments. In this respect, particularly sensitive are studies in which there are two or more light particles (e.g., an electron and a positron) in the final state and which yield cross sections which are differential in the energy and/or angular distribution of the ejected electron(s) and/or scattered projectile. The most stringent among these is the triply differential cross section (TDCS) in which all the kinematic parameters are determined. A significant body of data has been gained using the (e; 2e) method (e.g., [3]) and, more recently, the COLTRIM technique (e.g., [4]), which has been applied to electron, photon, proton, and ion impact. Differential studies with positrons, mainly confined to doubly differential investigations (e.g., [5][6][7]), remain scarce but are desirable both intrinsically and for comparison with equivelocity electrons or protons to probe the role of the projectile charge or mass on the collision dynamics (e.g., [8,9]). In this Letter, we report experimental TDCS results for positron impact ionization of simple molecular and atomic targets that reveal major discrepancies with current quantum-mechanical treatments and should thus provide new insights into the understanding of three-body correlated dynamics.Over the past decade, sophisticated distorted wave calculations have been developed based on the 3-Coulombwave final-state wave function (3C) of Brauner et al. [10] which approximates the strictly inseparable many-body system in terms of pairs of interacting particles. At lower energies, the use of the eikonal approximation for the initial state has been found to improve agreement with experiments (e.g., [11]). While such methods have been successful with a variety of projectiles and over a wide energy range, nonperturbative approaches remain superior at lower energies. Particularly noteworthy in this respect are the exterior complex scaling (ECS) method (e.g., [2]), which yielded the first accurate TDCS for e ÿ -H ionization for the case of equal energy-s...

show abstract

“…In contrast, for double ionization at intermediate to lower velocities, interference effects between the so-called shake-off and two-step mechanisms can lead to differences associated with the projectile charge. Also, numerous conceptual argumentations such as change of the binding energies of the target electrons, change of the projectile trajectory, momentum transfer to the target, inner-shell contributions, or differences coming from postcollison interaction have been invoked to explain differences in total cross sections resulting from electron and positron impact [14,15].…”

Section: Introductionmentioning

confidence: 99%

Doubly differential multiple ionization of krypton by positron and electron impact

2004

View full text Add to dashboard Cite

Measurements of doubly differential single and multiple ionization of krypton atoms have been performed for 750 eV positron and electron impact. Data were measured as a function of projectile energy-loss and scattering angle. For electrons, the energy-loss range was 0 -85% of the initial projectile energy and scattering angles were between ±22°. Following the procedure adopted previously for argon, the electron impact data were placed on an absolute scale by normalizing to total ionization cross sections available in the literature. The present results for krypton show differences between positron and electron impact that are less pronounced than was found for argon. The difference between the two targets can be understood due to the role of inner-shell ionization.

show abstract

Ionization of atoms by particle and antiparticle impact

Cited by 148 publications

References 218 publications

Antiproton Slowing Down inH2and He and Evidence of Nuclear Stopping Power

Antiproton Slowing Down inH2and He and Evidence of Nuclear Stopping Power

Energy-Sharing Asymmetries in Ionization by Positron Impact

Doubly differential multiple ionization of krypton by positron and electron impact

Contact Info

Product

Resources

About