Breit-Wigner formula for the scattering phase in the Stark effect

Near resonance energy, we study the asymptotic behavior of the derivative of the scattering phase as the applied electric field tends to zero. We obtain the leading asymptotics of the spectral function near a simple resonance, and as an application we rigorously prove the Breit-Wigner formula which relates the width of resonances to the time delay of particles in a homogeneous electric field.Supported by Alexander von Humboldt Stiftung     

Multiple resonances in the semi-classical limit

We construct for the Schrödinger operator in the semi-classical limit compact perturbations of a radial symmetric potential which give rise to resonances associated to arbitrarily high order poles for the meromorphic extension of the resolvent. Our results concern the hamiltonianP ₀=–h ²–x ² in the 2-dimensional case, as well as a fairly large class of radial-symmetric potentials in the 3-dimensional case. We show that the poles of the resolvent for such a potential are necessarily simple, and subsequently the degeneracy is due to a lack of symmetry.     

Coulombic potentials in the semi-classical limit

This paper is devoted to Schrödinger operators in two dimensions with singular (Coulombic) potentials. We investigate the behaviour of the eigenvalues at the bottom of the spectrum in the semi-classical limit. To overcome the difficulties due to the singularities, we use some kind of generalisation of the Levi-Civita transform. After this regularisation, we apply the theory of Helffer and Sjöstrand to get the full asymptotics for the eigenvalues.     

中高能电子的散射全截面测量装置

以电子束流光学系统为重点,介绍一台500～4250eV电子的绝对散射全截面测量装置,给出了电子枪和五圆筒透镜的电子光学设计,提供实验对电子光学系统的检验,提出对装置的改进设想。     

Measurement of the total cross-section difference for pp scattering in longitudinal spin states

Theoretical arguments more general than original MIT bag calculation predict exotic charmed-strange scalar mesons with striking signatures in same mass range as F and F¹, on the same basis as the prediction of the low-lying nonexotic qq$\text{qq}$ scalar nonet. Identification of δ (970) as qq$\text{qq}$ state enables rough mass prediction for charmed-strange exotics via charmed-strange analogy. Dominant signatures and decay modes of exotics are discussed.     

New bounds for the total cross-section and the zero-free radius of the scattering amplitude

The upper bound on σ_T(s) is deduced which seems to be an improvement over the existing ones if one supplements it with the behaviour of the slope parameter data. Bound on the zero-free radius of the scattering amplitude is also obtained.     

Correlations in alpha-alpha scattering and semi-classical optical models

We show the equivalence of semi-classical solutions to optical model coupled-channel equations derived from Watson's form of the nucleus-nucleus multiple-scattering series to the Glauber multiple-scattering series. A second-order solution to the semi-classical coupled-channel elastic amplitude is shown to be nearly equivalent to a second-order optical-phase-shift approximation to the Glauber amplitude if the densities of all nuclear excited states are approximated by the ground-state density. Using the Jastrow method to model the two-body density we find an average excited-state density to be of negligible importance in the double-scattering region of alpha-alpha scattering.     

Absolute total cross-section measurements for electron scattering from silicon tetrachloride, SiCl, molecules

The absolute total cross-sections for electron scattering on SiCl₄ molecules have been measured in two distinct electron-transmission experiments, in Gdansk and in Trento laboratory, for impact energy ranging from 0.3 to 250 eV and from 75 to 4000 eV, respectively. The e^--SiCl₄ total cross-section function shows two very distinct resonant-like features: the strong peak at 1.9 eV and much broader main maximum centered near 10 eV with some additional substructure close to 5 eV. The present results are compared with low-energy total experimental data and elastic theoretical calculations for electron collisions with silicon tetrachloride molecules.     

Recalculation of the Brinkman potential constants by inversion of the scattering incomplete total cross-section

A technique for the inversion of the scattering incomplete total cross-section was utilized to obtain a numerical evaluation of the interatomic potential for the combinations K⁺He, K⁺Ne, K⁺Ar, K⁺Kr, K⁺Xe. The results obtained were employed to recalculate, by means of a non-linear best fit, the constants appearing in the Brinkman potential. The new values of these constants were used in the calculation of the sputtering coefficient Ar⁺Cu in the region 0.5–10 keV. The results are in good agreement with the experimental data.     

Measurement of spin-dependent total cross-section difference Δσ L in neutron-proton scattering at 16 MeV

A new measurement of Δσ _L for longitudinally polarized neutrons transmitted through a polarized proton target at 16.2 MeV has been made. This complements our previous measurement of Δσ _T at the same energy and after a phase-shift analysis improves the precision of the previous value of ³ S ₁? ³ D ₁ mixing parameter ε₁. The measurement yields the value Δσ _L = (? 55 ± 20 ± 7) mb. The result of a simple phase shift analysis for ε₁ is presented and compared with the theoretical potential model predictions and other experiments.     

Measurement of spin-dependent total cross-section differenceΔσ T in neutron-proton scattering at 16 MeV

A new measurement ofΔσ _T for polarized neutrons transmitted through a polarized proton target at 16.2 MeV has been made. A polarized neutron beam was produced with the³H(d, n)⁴ He reaction; proton polarization over 90% was achieved in a frozen spin target of 20 cm³ volume. The measurement yields the valueΔσ _T=(?126±21±14) mb. The result of a simple phase shift analysis for the³ S ₁?³ D ₁ mixing parameter ε₁ is presented and compared with the theoretical potential model predictions.     

Boltzmann-Uehling-Uhlenbech calculation of total reaction cross-section and fragmentation cross-section

, and have been calculated via the BUU model with soft EOS and 0.8 times of . The density distribution without any adjustable parameters which comes from the RMF model has been introduced into the BUU calculation to replace the normally used one-parameter square-type distribution. The calculated results can reproduce the experimental data well for both halo- and stable-nuclei-induced reactions. Here or is calculated as the difference between of halo nucleus and core nucleus, by assuming . It indicates that this assumption works very well at high energy in the BUU calculation. More experimental measurements are necessary to test the validity of this assumption at intermediate energy.Received: 12 June 2003, Revised: 29 September 2003, Published online: 27 April 2004PACS: 24.10.-i Nuclear reaction models and methods - 25.60.Dz Interaction and reaction cross-sections - 25.60.Gc Breakup and momentum distributions - 27.20. + n      

On the total cross-section for thermal neutrons of hydrogen in niobium

Neutron transmission experiments have been performed to determine the total cross-section of hydrogen interstitially dissolved in niobium. The wavelength and temperature dependence of the total cross-section can be described by a model with the protons as harmonic oscillators. No changes in the total cross-section were found for the different phases of the interstitials in the niobium host lattice. An upper limit for the jump-time of a proton in diffusion _D is given compared to its mean time of localization _L on an interstitial site. _D <0.2 _L is found.     

Topological cross-section in hadron-nucleus collisions and multiple scattering theory

The multiple scattering theory supplemented with AGK cutting rules is applied to calculation of the hadron-nucleus interaction cross-sections. In contrast to standard Glauber approach neither smallness of the interaction radius compared to the nuclear radii nor Gaussian form of thehN-interaction profile function are assumed. We consistently use the theory of the supercritical Pomeron. However all the results are more general and do not depend on the specific parametrization of the Pomeron pole ampletude. The region of validity of the widely used approximate formulae for topological and totalhA-interaction cross sections are discussed. It is discussed the novel features of particle-nucleus interactions at superhigh energies.     

Diatom-surface scattering in the impulsive collision limit

The scattering of a diatomic molecule from a solid surface is analyzed within an impulsive collision approximation. It is shown that for a particular simple molecule-surface potential function not only does such an assumption permit the separation of the rotationally inelastic contribution from the total scattered intensity, but also it allows one to estimate the importance of translation-rotation energy transfer on the basis of just a few parameters which appear in the chosen diatom-surface potential model. The implications and limitations of the use of such a model in the analysis of scattering data are discussed.     

Predicting phase transition possibility pressure in solids: A semi-classical possibility

Abstract

This is a short review of the physical ideas, algorithm for calculations of the phase transition pressure, and some results of a semi-classical theory of the behavior of materials under high pressure proposed by Savi? and Ka[sbreve]anin. It is based on the Coulomb interaction, supplemented by a microscopic selection rule and a set of experimentally founded postulates. The theory hasbeen applied to cases ranging from DAC experiments to the calculation of models of planetary internal structure.