Á Kövér

Electrostatic spectrometer for measurement of internal conversion electrons in the 0.1–20 keV region

Abstract A new second order focusing, n = 1.5 cylindrical mirror electron spectrometer has been built. It enables us to measure the electrons emitted from the radioactive sources in the 0.1–20 keV region with an instrumental energy resolution of 0.1-1%. The ring-shaped input slit serving as a virtual electron optical object together with the large dimensions of the analyser (the total focal length equals 525 mm) allow us to utilize sources up to 1.5 cm 2 area. The spectrometer was adjusted using electron guns and tested also by 57 Co and 169 Yb radioactive sources prepared by vacuum evaporation and mass separation. The instrument operates automatically at oil-free vacuum of 4 × 10 −6 Pa and the electron spectra are scanned in cycles. The background of the channeltron is about 1.5 counts/min.

A study of the angular distribution of the electrons in the peak near υe=υi in the electron spectra from He+-Ar and H2+-Ar collisions

The peak near ve=vi in the electron spectra from He+ (0.8 MeV amu-1), H2+ (0.8 MeV amu-1 and 1.995 MeV amu-1)-Ar collisions was studied at thirteen angles from 0 to 180 degrees . The experimental values for the positions and half widths (FWHM) of these peaks were compared with theoretical calculations. An example is given for the comparison of the actual shapes of the peak for different projectiles with the corresponding theoretical curves. The angular distribution of the electrons in the electron-loss peak (i.e. the single differential cross sections) was plotted together with the theoretical ones.

Electron capture to the continuum at 54.4 eV positron-argon atom collisions

A three-body classical trajectory Monte Carlo method is used to calculate the ionization cross sections for 54.4 eV positron-argon atom collisions. Results for single-, double- and triple-differential cross sections are presented for ionized electrons and scattered positrons as well. We confirm that most positrons in coincidence with ionized electrons are scattered into nonzero angles. We show that the electron capture to the continuum peak exists in the triple-differential cross sections, i.e. the cross sections are differential in the energy of a particle and the solid angles of the ejected electron and the scattered positron.

A distorted field cylindrical mirror electron spectrometer: I. Calculation of the analyzer

Abstract A new “box” type cylindrical mirror electrostatic analyzer (CMA) with second order focusing properties is presented. The effect of the fringing field was taken into consideration in the design, resulting in some advantage (e.g. better dispersion) compared to the classical CMA.

A distorted field cylindrical mirror electron analyzer II Performances and application for studying ion-atom collisions

Abstract A distorted electrostatic field tandem cylindrical mirror electron analyzer (ESA-13) has been developed based on the numerical calculation published earlier. The measured parameters have verified the calculated ones. The relative energy resolution is found to be around ΔE E = 0.3% , without pre-retardation. The spectrometer is capable of analyzing electrons in the whole angular range (0°–180°) of the scattering plane with small acceptance angle and fine angular steps (0.25°).

Existence of the electron capture to the continuum peak at positron impact

Abstract A three-body classical trajectory Monte Carlo (CTMC) method is used to describe the ionization cross sections in positron–argon collisions. The existence of the cusp-like peak at positron impact is shown.

Forward electron ejection in H+-He, He+-He and He2+-He collisions

The dependence of the parameters (width, intensity and shape) of the cusp in the processes of electron capture to the continuum (ECC) and electron loss to the continuum (ELC) has been studied as a function of impact velocity (from 2 to 5 au) for the simple collision systems H+-He, He+-He and He2+-He. An approximately linear increase in the width (FWHM) is found in both cases. There is no difference in this respect within the error limits for He2+ (ECC) and He+ (ELC). Regarding cusp shape, similar symmetry (ELC) and asymmetry (ECC) have been observed as in the case of heavy-ion projectiles. None of the theories satisfactorily describes the experimental absolute cross sections of ECC cusp (He2+), while in the case of the He+ projectile (ELC) rather good agreement with theory can be seen in the higher-velocity region. The deviation at lower velocities in the latter case could be explained by an ECC effect present even in the case of He+. Concerning the dependence of the cusp yield on the Zp value of the projectile, Z02.5+or-0.3 was obtained from the yield in H+-He and He2+-He collisions.

Progress towards a positron reaction microscope

The progress toward the construction of a positron reaction microscope is outlined. The design principles of an electrostatic lens system used to focus and transport the positron beam with a ~ 1 mm diameter spot are briefly discussed. Also presented here are the results obtained from the characterisation of the supersonic gas jet assembly, an increased peaking factor of ~ 4 has been observed along with a centerline density of ~ 1012 cm−3.

High resolution carbon and oxygen K-LL Auger spectra of carbon dioxide

Abstract The proton excited carbon and oxygen K–LL Auger spectra of carbon dioxide were measured using the high-resolution, angular resolving ESA-21 electron spectrometer. The proton impact energy was 1.0 MeV. The transition energies of both K–LL Auger-spectra (oxygen and carbon) are determined and compared with the existing theoretical and earlier experimental data. The experimental line widths full width at half maximum (FWHM) and relative intensities of the Auger lines are determined. The Auger emission was found to be isotropic within the experimental accuracy.

A new method for measurement of post-collision interaction effects in ion-atom collisions

The authors present a new experimental method for determination of the post-collision interaction (PCI) distortions of the lineshape of Auger electrons excited in ion-atom collisions. The method is based on the assumption that the excitation of Auger electrons from a target atom by electron capture on impact of singly charged ions is not influenced by PCI in regard to the absence of charged outgoing particles. Consequently, the detection of Auger electrons following capture a reference line can be obtained which is free of PCI distortions. As a demonstration of the method they have studied the shape of the L3 -M2,3 2 (1 S0 ) Auger line of argon excited by 0.7 MeV protons detecting the electrons in coincidence with the neutralized H0 atoms and without it. Further non-coincidence measurements determining the asymmetry of the L2,3 -M2,3 2 Auger lines as a function of the proton energy and observation angle have also been made. The results are in a qualitative agreement with the semi-classical theory of van der Straten and Morgenstern.