摘要:

The extension of coherent optical techniques to the x‐ray region of the electromagnetic spectrum opens many new opportunities for science and technology based on very short wavelengths and on photon energies which span the primary atomic resonances of many elements.

ISSN:0094-243X    

DOI:10.1063/1.39797

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The excitation of the M shell of atomic copper in the 40–125 eV photon energy range with synchrotron radiation (at LURE in Orsay) followed by the detection of Cu+and Cu2+ions has allowed us to point out a preferential decay of the Rydberg states 3p53d104snl (1=0 and 2) into double ionization channels (3d9and 3d84s final ionic states) in contrast to the relaxation of the core excited states 3p53d104s2(2P3/2and2P1/2) into single ionization routes (satellite 3d84s2&egr;1 channels, with 1=1 and 3). The present study also shows that the contribution of the direct double photoionization involving the 3d subshell is continuously increasing from the double ionization thresholds and reaching about half the single 3d photoionization cross section in the 100–120 eV energy range, i.e. above the 3p single ionization thresholds.

ISSN:0094-243X    

DOI:10.1063/1.39798

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

During the past decade there have been many interesting theoretical calculations and experiments of the photoionization process in complex atoms, which will be reviewed. Particular emphasis will be given to the effects of electron correlations including the processes of relaxation and polarization. The calculation of cross sections of photoionization with excitation is very sensitive to effects of electron correlations in both initial and final states and will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.39799

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper some recent results in the area of excitation and ionization in high energy ion‐atom collisions will be discussed. The first part of this presentation will deal with the effects of the e−–e−interactions in single excitation, SE, and single ionization, SI, in ion‐atom collisions. The last part will deal with multi‐electron processes such as electron transfer plus excitation, TE, electron transfer plus ion ionization, TI, double excitation, DE, and double ionization, DI, and finally some of the more complex and exotic things happening in multiple ionization phenomena.

ISSN:0094-243X    

DOI:10.1063/1.39800

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this article, first the x‐ray generating processes in heavy, few‐electrons projectiles are summarized within the generalized picture of reduced velocities (adiabaticity). The general energy and Z dependences are shown. Then, special emphasis is given to RTE (resonant transfer and excitation, see also [1]) as this process is the dominant one in the treated low intermediate velocity region. The advantage of higher resolving capability at heavier projectiles is elucidated. A method to isolate a single RTE resonance, the one to the 2s2p1P1level for hydrogenic projectiles, is described. The interesting potentiality to utilize RTE for spectroscopic structure studies of heavy few‐electrons projectiles is demonstrated with the investigation of the 2E1 decay of the 1s2s1S0state in He‐like ions. In a last chapter we will change subject and concentrate on multiple‐electron capture yielding to x‐ray emission.

ISSN:0094-243X    

DOI:10.1063/1.39801

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ionized electron spectra have been calculated for 1.4 MeV/u collisions of U32+on Ar. The classical trajectory Monte Carlo method has been utilized with Hartree‐Fock model potentials to represent the uranium ion’s 4f‐shell, and the L‐ and M‐shells of Ar. Singly and doubly differential cross sections in ionized electron energy and angle are presented to illustrate the various collision dynamics. Projectile electron‐loss‐to‐the‐continuum and charge‐transfer‐to‐the‐continuum cross sections near 0° are analyzed and compared to one another. The electrons ionized from the L‐shell are found to be more narrowly peaked in angle than those from the M‐shell of Ar, giving raise to a slight ‘‘ridge’’ in the singly differential cross sections near 0° in the summed ionized electron spectra. The target binary peak found at an ejected electron velocity of 2vpcos&THgr;, is investigated as a function of scattering angle. Anomalously large cross sections for ‘‘hot’’ electrons from the U32+ion are found at velocities significantly above that for projectile binary peak electrons.

ISSN:0094-243X    

DOI:10.1063/1.39802

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Transfer excitation (TE) in ion‐atom collisions is reviewed from the perspective of the present status and current problems. The TE process occurs when electron capture (transfer) and projectile excitation occur together in a single collision, and three modes of TE are identified. A single electron‐electron interaction can lead to resonant transfer excitation (RTE), while independent electron‐nucleus interactions cause nonresonant transfer excitation (NTE) and separate electron‐electron and electron‐nucleus interactions give rise to uncorrelated transfer excitation (UTE). RTE is closely related to dielectronic recombination (DR) and can be used to provide important tests of theoretical calculations for this fundamental recombination process. Measurements of RTE as a function of projectile atomic number and charge state are compared with theory and discrepancies noted. Some of the discrepancies can be explained in terms of NTE or UTE while in other cases the discrepancies are as yet unresolved.

ISSN:0094-243X    

DOI:10.1063/1.39803

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The momentum distribution of bound K‐shell electrons was determined by measuring the electron induced double differential K‐shell ionization cross section. For this purpose thin self supporting Cu and Ag targets were combarded with electrons of 140 and 200 keV and one of the scattered electrons was detected in coincidence with the K‐shell X‐ray emitted subsequent to the ionization process. The deduction of the momentum distribution became possible after factorizing the theoretical expression derived for the description of the cross section in a fully relativistic treatment into a kinematical part and the Compton profile. The method enables to study the momentum distribution of K‐shell wave functions and it furnishes also the possibility to explore the high momentum components, which describe the wave functions in the vicinity of the nucleus and thus in the region that is in general not easily accessible. The ionization cross section is expressed in the one‐photon‐exchange approximation in general form by the so‐called structure functions. This leads to a separation of the cross section into a longitudinal and transverse component. It is the longitudinal part—which is dominant under the present experimental conditions—that can be factorized as indicated above. Experiment and theory give reasonable agreement.

ISSN:0094-243X    

DOI:10.1063/1.39804

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Theoretical calculations of x‐ray and Auger transition rates for atoms based on independent‐particle models and for highly‐charged ions using the multiconfiguration Dirac‐Fock method are reviewed. The deficiency of the independent‐particle model is discussed. Effects of relativity, intermediate coupling and configuration interaction on the transition rates are examined. For the highly‐charged ions with many‐open shells, the trends of Auger rates and oscillator strengths along an isoelectronic sequence are strongly perturbed by the frequent occurrences of level crossings. Care should be taken in identifying the level crossings when using the isoelectronic interpolation or extrapolation to obtain the transition rates.

ISSN:0094-243X    

DOI:10.1063/1.39805

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In the last decade significant improvements of the experimental methods for measuring L‐subshell yields have been achieved. By detecting the electron‐induced x‐ray fluorescence with a high‐resolution crystal‐spectrometer, the fluorescence yields &ohgr;1, &ohgr;2, and &ohgr;3of light and medium heavy elements (28≤Z≤47) have been measured, most of them for the first time. The K&agr;‐L&agr;‐coincidence method has been carefully checked for systematic errors. Recent measurements of the fluorescence yields &ohgr;2and &ohgr;3and the Coster‐Kronig yield f23of heavy elements (Z≥54) by this method have substantially reduced relative uncertainties which in some cases are claimed to be below 1%. Furthermore, a novel method based on selective photoionization of consecutive subshells by using tuneable synchrotron radiation has been introduced which is capable of providing reliable values of all decay yields, i.e., &ohgr;1, &ohgr;2, &ohgr;3, f12, f13, and f23. So far, data for the elements Z=39, 47, and 72–82 have been obtained by this method.

ISSN:0094-243X    

DOI:10.1063/1.39807

出版商:AIP    

年代:1990

数据来源: AIP