Search

Photoexcitation yields of the 115mIn metastable state were measured with Bremsstrahlung γ beams over a range of endpoint energies between 4.5 and 18 MeV. An effective cross section of the 115In(γ,γ′)115mIn photoexcitation cross section was determinedto reproduce the data. This cross section is built from a cross section calculated with the TALYS code, to which an enhancement is added at about 8.5 MeV.

We discuss lower-than-predicted collisional-excitation cross sections for helium-like xenon measured at an Electron Beam Ion Trap facility. In a review paper (H. Chen and P. Beiersdorfer. Can. J. Phys. 86, 55 (2008)), the authors find a significant effect due to the Breit interaction between the free and the bound electrons in the excitation process of He-like xenon. The authors state that the agreement between the measured and calculated cross section values can only be found when the generalized Breit interaction is included in the calculations. We have performed new calculations with a multi-configuration Dirac-Fock code, as well as with the Penn State University suite of codes, and our conclusions are that the contribution of the Breit interaction is much lower than found in the calculations presented in the abovementioned article. In fact, our predictions are subsequently almost twice as large as the experimental values. We present these considerations in hopes of motivating new experimental investigations. Key words: atomic physics, electron-impact excitation, electron beam ion trap, multi-configuration Dirac-Fock, generalized Breit interaction. Nous discutons ici de mesures de sections efficaces d'excitation collisionnelle pour les ions heliumoides de xenon realisees aupres de l'installation Electron Beam Ion Trap. Ces sections mesurees se sont averees plus faibles que les predictions theoriques. Dans une publication recente (H. Chen et P. Beiersdorfer. Can. J. Phys. 86, 55 (2008)), les auteurs trouvent un effet significatif de l'interaction de Breit entre les electrons lies et libres dans le processus d'excitation du xenon heliumoide. Les auteurs soutiennent que l'accord entre les valeurs mesurees et calculees des sections efficaces n'est possible qu'en introduisant l'interaction de Breit generalisee dans les calculs. Nous avons effectue de nouveaux calculs avec un code multi-configurations Dirac-Fock ainsi qu'avec la suite de codes de l'universite Penn State et nos conclusions sont que la contribution de l'interaction de Breit est beaucoup plus faible que celle trouvee dans les calculs cites plus haut. En fait, nos predictions sont deux fois plus importantes que les valeurs experimentales. Nous les presentons dans l'espoir de motiver de nouvelles etudes experimentales. Mots-cles: physique atomique, excitation par impact electronique, piege ionique a faisceau electronique, Dirac-Fock multi-configurations, interaction de Breit generalisee., 1. Introduction A few years ago, in a very useful review paper entitled 'Electronimpact excitation cross-section measurements at Electron Beam Ion Traps (EBITs) from 1986 to 2006', Chen and Beiersdorfer [...]

Exfoliated-compressed graphite materials are examined. A chemical explanation for the pseudo-exfoliation phenomenon is proposed.

The charge state and energy distributions of ions produced by a pulsed 1 J, 9 ns Nd:YAG laser focused onto solid aluminum, copper, and tantalum targets were measured with an electrostatic analyzer coupled with a windowless electron multiplier detector. Special attention was paid to the detector response function measurements and to the determination of the analyzer transmission. Space charge effects are shown to strongly affect this transmission. Measured absolute energy distributions are presented for several charge states. They follow Boltzmannlike functions characterized by an effective ion temperature and an equivalent accelerating voltage. These parameters exhibit power laws as a function of I λ2 which open the possibility to predict the expected shape of the relative energy distributions of ions on a large range of laser intensities (106–1016Wcm–2 µm2). [ABSTRACT FROM AUTHOR]

The charge state and energy distributions of ions produced by a pulsed 1 J, 9 ns Nd:YAG laser focused onto solid aluminum, copper, and tantalum targets were measured with an electrostatic analyzer coupled with a windowless electron multiplier detector. Special attention was paid to the detector response function measurements and to the determination of the analyzer transmission. Space charge effects are shown to strongly affect this transmission. Measured absolute energy distributions are presented for several charge states. They follow Boltzmannlike functions characterized by an effective ion temperature and an equivalent accelerating voltage. These parameters exhibit power laws as a function of I λ2 which open the possibility to predict the expected shape of the relative energy distributions of ions on a large range of laser intensities (106–1016Wcm–2 µm2). [ABSTRACT FROM AUTHOR]

The charge state and energy distributions of ions produced by a pulsed 1 J, 9 ns Nd:YAG laser focused onto solid aluminum, copper, and tantalum targets were measured with an electrostatic analyzer coupled with a windowless electron multiplier detector. Special attention was paid to the detector response function measurements and to the determination of the analyzer transmission. Space charge effects are shown to strongly affect this transmission. Measured absolute energy distributions are presented for several charge states. They follow Boltzmannlike functions characterized by an effective ion temperature and an equivalent accelerating voltage. These parameters exhibit power laws as a function of I λ² which open the possibility to predict the expected shape of the relative energy distributions of ions on a large range of laser intensities (106-1016Wcm-2 μm²). [ABSTRACT FROM AUTHOR]

The charge state and energy distributions of ions produced by a pulsed 1 J, 9 ns Nd:YAG laser focused onto solid aluminum, copper, and tantalum targets were measured with an electrostatic analyzer coupled with a windowless electron multiplier detector. Special attention was paid to the detector response function measurements and to the determination of the analyzer transmission. Space charge effects are shown to strongly affect this transmission. Measured absolute energy distributions are presented for several charge states. They follow Boltzmannlike functions characterized by an effective ion temperature and an equivalent accelerating voltage. These parameters exhibit power laws as a function of I λ² which open the possibility to predict the expected shape of the relative energy distributions of ions on a large range of laser intensities (106-1016Wcm-2 μm²). [ABSTRACT FROM AUTHOR]

Nuclear excitation by electron transition (NEET) is predicted to be the dominant excitation process of the first 201Hg isomeric state in a laser heated plasma. This process may occur when the energy difference between a nuclear transition and an atomic transition is close to zero, provided the quantum selection rules are fulfilled. At local thermodynamic equilibrium, an average atom model may be used, in a first approach, to evaluate the NEET rate in plasma. The statistical nature of the electronic transition spectrum is then described by the means of a Gaussian distribution around the average atom configuration. However, using a continuous function to describe the electronic spectrum is questionable in the framework of a resonant process, such as NEET. In order to get an idea of when it can be relied upon to predict a NEET rate in plasma, we present in this paper a NEET rate calculation using a model derived from detailed configuration accounting. This calculation allows us to define a confidence interval of the NEET rate around its average atom mean value, which is the first step to design a future experiment. [ABSTRACT FROM AUTHOR]