U Becker

Pair production with inner-shell capture

The production of electron-positron pairs with simultaneous capture of the electron into bound states of the target is studied for relativistic heavy-ion collisions in the range of energies 1<or=Elab<or=100 GeV amu-1. Impact-parameter-dependent probabilities and cross sections are calculated in the semiclassical approximation by using time-dependent perturbation theory in first order and Coulomb-Dirac wavefunctions for the electron and positron states. The authors predict a cross section of about 70 b for the capture of electrons into the target K shell in U92++U92+ collisions at Elab=100 GeV amu-1.

K-shell ionisation in relativistic heavy-ion collisions

For relativistic heavy-ion collisions K-shell ionisation probabilities are calculated in the semiclassical approximation (SCA) and first-order perturbation theory. Most of the results are obtained for a uranium target and show the increasing importance of the spin-dependent interaction potential for relativistic relative velocities nu /c>0.5. Interesting structures arising in certain partial differential ionisation probabilities are discussed.

Solution of the time-dependent Dirac equation by the finite difference method and application for Ca20++U91+

The Dirac equation for an electron moving in time-dependent electromagnetic fields is solved by the method of finite differences. For simplicity the solution is restricted to problems with a rotational symmetry about an axis. The method is applied to the scattering of Cs20+ on a hydrogen-like U91+ ion at relativistic incident energies. Excitation and ionisation probabilities and the K-shell vacancy production probability are calculated.

Direct electron-positron pair production in relativistic heavy-ion collisions in the semiclassical approximation

The direct production of electron-positron pairs is studied for relativistic heavy-ion collisions in the energy range 20 MeV amu-1<or=Elab<or=100 GeV amu-12. Impact-parameter-dependent probabilities and cross sections are calculated in the semiclassical approximation by using time-dependent perturbation theory in first order and Coulomb-Dirac wavefunctions for the electron and positron states.

Lepton-pair production by brensstrahlung in central relativistic heavy-ion collisions

Abstract We study the production of lepton pairs by classical bremsstrahlung in central relativistic heavy-ion collisions. For the stopping of the nuclei we assume a simple model of point charges and a deceleration time. Pair-creation probabilities are calculated in first-order perturbation theory.

Cross sections for K-shell ionisation in relativistic heavy-ion collisions

For relativistic heavy-ion collisions K-shell ionisation cross sections are calculated in the semiclassical approximation by using a relativistic description of the electronic states. The calculations are compared with measurements with 4.88 GeV protons and 670 MeV amu-1 Ne ions as projectiles.

Coupled-channel formalism for excitation and ionisation in relativistic heavy ion collisions with applications

A relativistic one-centre coupled channel formalism for excitation and ionisation in atomic collisions of high-Z ions is presented which uses Coulomb-Dirac functions of the target ion as a basis. For the continuum wavefunctions time-dependent relativistic wavepackets are employed. As applications the authors calculate probabilities and cross sections for excitation and ionisation in the collision systems Zp+U90+ at Elab=430 MeV/nucleon and Zp+Xe52+ at Elab=82 MeV/nucleon and compare the results with experimental data.

Angular distribution of electrons emitted from 1s1/2 and 2s1/2 states in relativistic heavy-ion collisions

The energy and angular distributions of electrons emitted from the 1s1/2 and 2s1/2 states in relativistic heavy-ion collisions are evaluated in the semiclassical approximation employing the first-order perturbation theory. The angular anisotropy of the electron-emission becomes increasingly peaked in forward direction with growing kinetic energy of the electrons.

Atomic Processes in Relativistic Heavy Ion Collisions

Theoretical methods for the description of atomic processes in relativistic heavy ion collisions are reviewed. We present probabilities and cross sections for K-shell ionisation and pair creation which are obtained by first order perturbation theory, coupled channel and finite difference methods in semiclassical approximation.

Muon pair production with inner-shell capture in relativistic U92+-U92+ collisions

Muon pair production in relativistic heavy-ion collisions with capture of the negative muon into the K shell of the target atom is studied in first-order perturbation theory by using the semiclassical approximation. Impact-parameter-dependent probabilities and cross sections are calculated for the K-shell capture in U92+-U92+ collisions at Elab=10 GeV amu-1. Nuclear size corrections are taken into account.