H Kleinpoppen

Electron-photon angular correlations in electron-helium collisions: measurements of complex excitation amplitudes, atomic orientation and alignment

Electron-photon angular correlations were measured by delayed coincidences between electrons scattered inelastically from helium and 58.4 nm photons emitted in the decay of 2 1P state. The ratio of the differential cross sections for exciting the degenerate magnetic sublevels and the relative phase of the corresponding excitation amplitudes for electron scattering angles between 16 degrees and 40 degrees and for incident electron energies in the range 40 to 200 eV is deduced. The data show that a high degree of atomic orientation is produced by collisions in this range of energy and angle. The orientation increases rapidly towards its theoretical limit as the scattering angle is increased, and higher incident energy produces, in general, greater orientation at a fixed scattering angle. The data also show that the alignment of the atomic dipole radiation pattern can depart significantly from the direction of linear momentum transfer at the larger scattering angles. The results are compared with the predictions of the first Born and Glauber approximations, and good agreement is obtained with a recent distorted wave calculation.

Energy dependence of characteristic and bremsstrahlung cross sections of argon induced by electron bombardment at low energies

The energy dependence of characteristic x-ray and bremsstrahlung cross sections of argon has been investigated by electron impact. The incident electron energy was varied between 2.5 keV and 12 keV. From the data, absolute cross sections for Ar-K ionisation are obtained. The experimental data agree reasonably with available theoretical calculations.

L X-ray anisotropy and L3-subshell alignment of heavy atoms induced by ion impact

The anisotropy emission of the Ll X-ray line from heavy atoms (54<or=Z2<or=92) has been investigated experimentally for ion impact (1<or=Z1<or=79) in the energy range 0.15 to 10 MeV amu-1. In the case of single ionisation, the collisionally induced alignment of the L3 subshell can be derived. The data for H and He projectiles are reasonably well described by direct Coulomb ionisation theories. With increasing Z1, the measured anisotropy becomes considerably smaller than for H impact. No pronounced dependence on the projectile nuclear charge is found although for different projectiles different ionisation mechanisms (direct ionisation, promotion of molecular orbitals) dominate.

L-shell alignment of heavy atoms induced by proton impact ionisation

The polarisation of resolved characteristic L X-rays emitted from proton-excited Xe, Dy and Au atoms has been determined from their anisotropic emission. The polarisation is caused by the alignment of the initial vacancy state, which was found to change significantly within the studied proton energy range from 250 keV to 6 MeV. The results follow a universal curve in fair agreement with PWBA calculations.

Electron-photon angular correlations in electron-helium collisions for 31P excitations

Electron-photon angular correlations have been measured by detecting, in delayed coincidence, electrons inelastically scattered from helium and photons emitted in decays from the 31P level. The measurements have been carried out using both the 31P-11S (53.7 nm) line and the 31P-21S (501/6 nm) line. Analysis of the data yields the ratio of differential cross sections for exciting 31P magnetic sublevels lambda and the absolute value of the relative phase mod chi mod between the corresponding excitation amplitudes for electron scattering angles between 10 degrees and 30 degrees at incident electron energies in the range 50 eV to 150 eV. Data on the atomic orientation is also presented. The results are compared with the predictions of the first Born approximation and a recent multichannel eikonal calculation.

Threshold behaviour of Ar K and Xe L3 ionisation by electron impact

Ionisation of the Ar K and Xe L3 shells has been investigated by electron impact with energies from about 10 eV to 1 keV above threshold. The experimental data are compared with the theoretical predictions by Wannier for ionisation near threshold and with more recent plane-wave Born and Coulomb-Born exchange calculations.

The ionisation of polarised potassium atoms by polarised electrons

In a crossed-beam experiment polarised potassium atoms have been ionised with a beam of polarised electrons. A measurement of the ionisation for the two relative spin orientations yields the asymmetry factor A which is related to the total interference cross section for ionisation. The measurements extend over an energy range from 6 to 80 eV. The measurements of A cannot be compared directly with theoretical results since no calculations of the interference cross section have been made for potassium. However, theoretical values of A for lithium and sodium exist and, when plotted against reduced energy units, it is apparent that for energies less than about five times the ionisation energy, the measurements disagree with theory. At higher energies the agreement is satisfactory.

Experimental investigation of the possibility of enhanced photon detection in EPR type experiments

Abstract The polarization properties of the two photons emitted simultaneously in the spontaneous decay of metastable atomic deuterium have been used in an experiment to investigate the possibility of bias or enhancement in the detection process in Einstein-Podolsky-Rosen (EPR) type experiments. No evidence of enhancement has been found.

The two-photon decay of metastable atomic hydrogen

The two-photon decay of metastable atomic hydrogen has been observed for the first time. A series of tests which confirm the observations are described, including preliminary measurements of the angular distributions and spectral distribution for the two-photon decay.

Resonances near threshold in the electron impact excitation and polarization of the 61S0-63P1 line of mercury

Data are presented for the positions and plarizations of resonances occurring within a few volts of threshold of the 2537 AA line of mercury, excited by electron impact. A 127 degrees electron monochromator was used in a standard crossed-beam apparatus, the results being obtained by measuring separately the I/sub /// and Iperpendicular to contributions to the excitation function. The normalization procedure and the checks made on the data are described. Several resonances are clearly observed; a comparison of the measured polarization of one of them with a theoretical value leads to a possible J value for the negative ion state being formed.