Spin exchange during collisions of two sodium atoms

Based on data on the singlet (X ¹Σ⁺) and triplet (a ³Σ⁺) potentials describing the interaction of two Na atoms in the ground state, the complex cross sections of spin exchange for the system under investigation are calculated. The obtained cross sections allow one to determine relaxation times, as well as magnetic-resonance frequency shifts caused by spin-exchange Na-Na collisions.     

Spin exchange during collisions of potassium atoms: Complex cross sections

Singlet (X ¹Σ⁺) and triplet (a ³Σ⁺) potentials of interaction of two potassium atoms residing in the ground state (4s ² S _1/2) are presented. Based on the given interaction potentials, the complex cross sections of spin exchange q = [`(q)] + i[`([`(q)])]q = \bar q + i\overline{\overline q} for the system under investigation are calculated. Obtained dependences of the real and imaginary parts of the spin-exchange cross section on temperature allow one to obtain information both on the broadening of a magnetic resonance line of K atoms and on the frequency shift of the magnetic resonance during collision.     

Spin effects in inelastic electron-atom collisions

Recent progress of experimental investigations that show explicitly spin-dependent effects is reported for inelastic electron-atom scattering. In particular the combined effect of exchange scattering and target coupling is discussed in more detail. The experimental investigation of this ‘target-coupling effect’ is a powerful method to study the influence of exchange scattering directly. The experiments that are reviewed are basically target and electron spin-polarization measurements and the determination of the angular momentum state of the atom after scattering.     

Spin exchange and chemi-ionization during collisions of polarized metastable helium atoms with ground-state cesium atoms

The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process (spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined experimentally: C _se=(2.8±0.8)×10⁻⁹ cm³s⁻¹, C _ci=(1.0±0.3)×10⁻⁹ cm³s⁻¹. Zh. Tekh. Fiz. 69, 36–40 (September 1999)     

Energy exchange in atom-surface collisions

Abstract

A theoretical treatment of inelastic scattering of low energy particles from surfaces is developed which treats the regime of multiple quantum phonon exchange. Good agreement is obtained with recently measured multiphonon backgrounds in the scattering of He by alkali halide and metal surfaces over a large range of surface temperatures and incident conditions. The results show that the multiphonon scattered intensity can give important information on the particle-surface interaction potential.     

Spin exchange in iodine-doped polydiacetylene

It is shown that the observed transformation of the ESR spectrum in polydiacetylene films upon doping with iodine agrees with an exchange interaction between the spin systems of localized paramagnetic centers (S) and polaron states (P) by means of which current-carrier transport occurs. The data obtained indicate carrier transport in the form of uncorrelated hops with probability determined by the lifetime of an exchange-coupled (S-P) pair. Fiz. Tverd. Tela (St. Petersburg) 41, 1879–1881 (October 1999)     

Spin state and exchange in the quasi-one-dimensional antiferromagnet KFeS2

We report the optical spectra and single crystal magnetic susceptibility of the one-dimensional antiferromagnet KFeS₂. Measurements have been carried out to ascertain the spin state of Fe³⁺ and the nature of the magnetic interactions in this compound. The optical spectra and magnetic susceptibility could be consistently interpreted using aS=1/2 spin ground state for the Fe³⁺ ion. The features in the optical spectra have been assigned to transitions within thed-electron manifold of the Fe³⁺ ion, and analysed in the strong field limit of the ligand field theory. The high temperature isotropic magnetic susceptibility is typical of a low-dimensional system and exhibits a broad maximum at ∼565K. The susceptibility shows a well defined transition to a three dimensionally ordered antiferromagnetic state atT _N=250 K. The intra and interchain exchange constants,J andJ′, have been evaluated from the experimental susceptibilities using the relationship between these quantities, andχ _max,T _max, andT _N for a spin 1/2 one-dimensional chain. The values areJ=−440.71 K, andJ′=53.94 K. Using these values ofJ andJ′, the susceptibility of a spin 1/2 Heisenberg chain was calculated. A non-interacting spin wave model was used belowT _N. The susceptibility in the paramagnetic region was calculated from the theoretical curves for an infiniteS=1/2 chain. The calculated susceptibility compares well with the experimental data of KFeS₂. Further support for a one-dimensional spin 1/2 model comes from the fact that the calculated perpendicular susceptibility at 0K (2.75×10⁻⁴ emu/mol) evaluated considering the zero point reduction in magnetization from spin wave theory is close to the projected value (2.7×10⁻⁴ emu/mol) obtained from the experimental data.     

Charge exchange in collisions of H+2 with H-

The process of mutual neutralization in slow H+2+H- collisions is considered within the multi-channel Landau-Zener model. The calculated total mutual neutralization cross section is in satisfactory agreement with the experimental data available in the CM energy range 20～2000 eV.     

Spin observables in neutron-proton elastic scattering

The analyzing power, , and the polarization transfer observables , and have been measured in neutron-proton elastic scattering at 260, 318, 386, 472 and 538 MeV for c.m. scattering angles between 64° and 160°. The data were obtained at PSI with a polarized neutron beam and a polarimeter analyzing the transverse polarization of the outgoing proton. They make a significant impact on the knowledge of the Isospin I = 0 nucleon-nucleon scattering. Received: 27 January 1998 / Published online: 30 March 1998     

Spin effects in elastic hadron scattering

Spin effects of the high energy elastic nucleon-nucleon scattering in the whole diffraction domain are examined with taking into account the Coulomb-nuclear interference. A new form of the total phase factor of the electromagnetic-hadron interference is obtained for a wide region of transfer momenta up to the diffraction dip domain, and as a result, additional contributions to the analyzing power A _N and double spin correlation parameter A _NN owing to the electromagnetic-hadron interference are determined in the whole diffraction dip domain of high-energy elastic hadron scattering. The energy dependence of these effects is examined including the region of BNL RHIC energies.     

Spin transfer in deep-inelastic collisions of light ions

The angular correlations of α-particles emitted from the fragments of the reactions ¹⁶O + ¹⁶O, ³²S + ¹⁶O, ³²S + ¹⁶Al were determined in experiments that employed large-area, position-sensitive ionization chambers. The in-plane correlations are isotropic in the rest frame of the emitter, but the out-of-plane correlations have an anisotropy of approximately 3. From the anisotropies the spin projections √〈I_z²〉 onto the z-axis perpendicular to the reaction plane were determined. It is shown that the values of the spin projection can be qualitatively understood by the fractionation of the initial angular momentum under the requirement of energy, angular-momentum and particle-flux conservation.     

Electron-atomic-hydrogen elastic collisions in a laser field

The differential cross-section for electron-hydrogen atom collisions in the presence of a linearly polarized laser field is studied as a function of a scattering angle of low energy electron by employing second-Born approximation (SBA). Detailed analysis is performed in no forward scattering angle.     

Spin effects in elastic antiproton nucleus scattering

Elastic scattering of 180 MeV antiprotons by several closed-shell nuclei are analyzed using Glauber's multiple scattering theory. Spin observables in elastic scattering are obtained within this framework. The sensitivity of the polarizations to the spin-flip amplitudes are discussed in terms of the¯NN potential models used for the calculations. Spineffects in angular distribution are found to be small.     

Spin pumping with coherent elastic waves

We show that the resonant coupling of phonons and magnons can be exploited to generate spin currents at room temperature. Surface acoustic wave pulses with a frequency of 1.55 GHz and duration of 300 ns provide coherent elastic waves in a ferromagnetic thin-film-normal-metal (Co/Pt) bilayer. We use the inverse spin Hall voltage in the Pt as a measure for the spin current and record its evolution as a function of time and external magnetic field magnitude and orientation. Our experiments show that a spin current is generated in the exclusive presence of a resonant elastic excitation. This establishes acoustic spin pumping as a resonant analogue to the spin Seebeck effect.     

Double pomeron exchange in high-energy pp collisions

The double pomeron exchange cross section in high-energy pp collisions is analyzed in detail for different phase-space cuts. The ratio of double pomeron exchange signal to diffraction dissociation background is examined as a function of s. The theoretical predictions are found to be in excellent agreement with the recent results of the experiments at the CERN ISR. The properties of the central cluster as well as the predictions for high energies are discussed.     

Double resonant charge exchange in ion-ion collisions

The process of resonant double charge exchange in low energy ion-ion collisions is considered. The effects of the Coulomb interaction of the nuclei are taken into account. Cross section calculations are performed both for completely and partially stripped projectile ions with 3? Z ? 10.     

Plasma-neutral elastic collisions in monte carlo computational models

Summary Implementation of the elastic scattering event between plasma and neutral particles in a Monte Carlo computational model of the plasma edge in advanced fusion devices is discussed. In the framework of the classical theory of binary collisions, some kind of approximation is required to define elastic-scattering cross-sections between neutral particles and plasma ions because of the long range of this interaction. By assuming certain field forces and neglecting their effect beyond a certain distance, approximate cross-sections are computed and fitting formulae derived for protons interacting with helium. A Monte Carlo scheme for the simulation of this collision is given, essentially based on a random choice of the impact parameter. Relevant effects due to this reaction have been numerically detected in realistic and complex cases.

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Riassunto Per definire le sezioni d’urto dello scattering elastico tra particelle neutre e ioni di un plasma nell’ambito della teoria classica dell’urto binario, è necessario introdurre delle approssimazioni a causa del lungo raggio d’azione di questa interazione. Assumendo un particolare campo di forze e trascurando il suo effetto oltre una certa distanza tra le particelle interagenti, si calcolano qui delle sezioni d’urto approssimate e si danno formule d’interpolazione per protoni collidenti con atomi di elio. Si descrive inoltre uno schema di simulazione Montecarlo della reazione, basato essenzialmente sulla scelta casuale del parametro d’urto. Lo studio è eseguito per energie sotto 20 eV, un intervallo importante nella fisica del controllo delle impurezze per macchine a fusione confinate magneticamente.

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Реюме Обсуждается описание спбытий упругого рассеяния частиц плазмы на нейтральных частицах в рамках компьютерной модели Монте-Карло для ограниченной плазы в современных устройствах для синтеза. В рамках классической тории бинарных соударений требуется определенные аппроксимации для получения поперечных сечений упругого рассеянир ионов плазмы на нейтральных частицах, вследствие длиннодействующего характера взаимодействия. Предполагая некоторые полевые силы и ренебрегая их влиянием на опедленных расстояниях, вычисляются приближенные поперечные сечения, которые соответствуют формулам, выведенным для протонов, взаимодействтвующих с гелием. Предлагается схема Монте-Карло для моделрования этих соударений, которая оснвана на случайном выворе прицедьного рараметра. Соответстствующие эффекя, обусловленняе этой реацией, численно детектируются в реалических и более сложных случаях.

     

Spin anisotropy for excitation in collisions between two one-electron atoms

The singlet and triplet contributions of excitation cross sections are studied theoretically for collisions between various two one-electron atoms. The spin anisotropy is shown to have a general behavior in the important impact energy range. At low energies triplet cross sections dominate completely over the singlet ones while the opposite is true when the active electron and projectile velocities are comparable. Beyond the matching velocity regime singlet and triplet contributions become identical. We propose a general dynamical interpretation based on the analysis of the time dependency of the electron probability density and probability current density.