P. Cuzzocrea

Light-ion-induced Li ionization of 46 ≤ Z ≤ 60 elements: First-and second-order corrections to PWBA

Abstract Recently measured proton- and 4 He-ion-induced L i -subshell ionization cross sections for the elements with 46 ≤ Z ≤ 60 have been compared with the ECPSSR predictions. A recalculation of the binding correction, which leads, when the incident energy decreases, to a limit of the binding energy of the electrons concerned corresponding to a United-Atom approximation is suggested. A good agreement between the experimental and predicted L-shell ionization cross sections and a satisfactory one for the single L i -subshell ones is obtained. The introduction of vacancy rearrangement effects gives further better agreement, but not enough to reproduce completely the experimental findings.

L-Subshell ionization of Ba, La and Ce by proton and 4He ion impact

Abstract L X-ray production cross sections for proton and 4He ion bombardment of thin targets of Ba, La and Ce have been measured in the energy range 0.25–1.80 MeV for protons and 0.40–1.80 MeV for helium ions. L-subshell ionization cross sections have been extracted and compared with the predictions of the perturbed stationary state theory including energy loss, Coulomb retardation and relativistic effects (ECPSSR). Particular attention has been devoted to the low incident energy region. The possible presence of second order effects (trajectory, vacancy rearrangement) in this region is discussed.

L X-ray production cross sections of 59<or=Z<or=70 elements by proton and 4He ion impact

L X-ray line production cross sections for proton and 4He ion bombardment of elements with atomic number Z ranging from 59 to 70 have been measured in the energy range 0.25-1.80 MeV for protons and 0.40-1.80 MeV for 4He ions. An overall good agreement with the few existing data has been observed. The linear dependence on Z of the logarithm of the cross sections has been confirmed also in this region. The agreement of the measured data with the predictions of a modified ECPSSR model, suggested by the authors and based on a recalculation of the binding correction (UA-ECPSSR), is generally good, except for the lowest incident energies.

Proton- and 4He-ion-induced L-subshell ionization of rare-earth elements

Abstract L X-ray production cross sections for proton and 4 He-ion bombardment of 62 ≤ Z ≤ 70 elements have been measured in the energy range 0.25–1.80 MeV for protons and 0.40–1.80 MeV for helium ions. Subshell ionization cross sections have been extracted and compared with the predictions of the ECPSSR theory and with those of a modified model (UA-ECPSSR) suggested by us, based on a recalculation of the binding correction. Significant improvements have been obtained in the latter case. The residual discrepancies observed at the lowest incident energies have been attributed to the inadequate way of calculating the Coulomb retardation and relativistic corrections. An attempt to remove these discrepancies by introducing the Coulomb correction described in the work of Lapicki and Losonsky [Phys. Rev. A20 (1979) 481], instead of a pure exponential reduction factor of the cross sections, has given satisfactory results.

Proton Induced L-Subshell Ionization on Silver and Iodine

L-x-ray production cross sections were measured in the proton energy range 0.3-5.0 MeV for Ag and I. Sub shell ionization cross sections were extracted and compared with predictions of the perturbed stationary state theory, the binary encounter approximation and the semiclassical approximation with binding, polarization, relativistic, energy loss and Coulomb deflection corrections included (ECPSSR, BEABC, SCABCR). The agreement is quite good especially for the shape and the magnitude of the kink in the L1 subshell cross section due to the node of the 2s wavefunction.

AbsoluteL-subshell ionization cross-sections ofZ∼50 targets by4He ion impact

SummaryThe X-radiation induced by4He ion impact on Ag, Cd, In, Sn, Sb, Te and I has been investigated for incident energies ranging from 0.6 to 0.5 MeV. Production cross-sections for various X-ray lines have been obtained by an internal normalization method, by means of simultaneous backscattering measurements. From the intensities on theLα,Lγ1,5 andLγ2,3 lines theL-subshell ionization cross-sections have been extracted. Comparison with current theories shows systematic discrepancies for all the targets at incident energy below 2.0 MeV and, for Ag, Cd and In, even in the higher-energy region. These are attributed to deviations in the atomic parameters used in the data analysis as well as to a failure of the ionization theories employed.RiassuntoSi sono effettuate misure di fluorescenza X indotta da bombardamento di ioni4He di energia compresa tra 0.6 e 5.0 MeV sugli elementi Ag, Cd, In, Sn, Sb, Te e I. Utilizzando un metodo di normalizzazione interna fondato su contemporanee misure di retrodiffusione Rutherford, si sono ottenute le sezioni d’urto assolute per un certo numero di righe X. Da quelle relative alle righeLα,Lγ1,5 eLγ2,3 si sono poi ricavate le sezioni d’urto di ionizzazione per i diversi sottostratiL. Il confronto con le teorie disponibili ha evidenziato la presenza di sensibili disaccordi per tutti i bersagli al di sotto dell’energia incidente di 2.0 MeV e, per Ag, Cd ed In, anche per energie piú elevate, che sono stati attribuiti in parte ai parametri atomici disponibili per i calcoli delle sezioni d’urto ed in parte all’inadeguatezza delle teorie che descrivono il processo di ionizzazione.

L-subshell ionisation for 4He ion bombardment of tellurium

Abstract L-subshell ionisation cross sections for 4He ion bombardment of Te in the energy range 0.6−5.0 MeV, obtained by means of X-ray production measurements, have been compared with the predictions of different theories (binary encounter approximation, plane-wave Born approximation, semiclassical approximation). The effects of various corrections taking into account binding modifications, polarisation and relativistic motion of the atomic electrons and Coulomb retardation and energy loss of the projectile have been considered. The binding modification turns out to be the most relevant correction, but it is still inadequate to describe the low energy part of the cross sections.

4He-ion-induced L-subshell ionisation on Pd and Cs

L X-ray production cross section for 4He-ion bombardment of Pd and Cs have been measured in the energy range 0.6-5.0 MeV. An analysis, performed by including previous results, in the range of the atomic number Z 46<or=Z<or=55 confirms the linear dependence of the logarithm of the cross sections and the smooth dependence of the vacancy decay parameters around Z=50 in relation to Z. The subshell ionisation cross sections have been compared with the predictions of the semiclassical approximation including binding, energy loss, Coulomb deflection and relativistic corrections (SCACBR) and of the perturbed stationary state theory taking into account energy loss, Coulomb retardation and relativistic effects (ECPSSR). The agreement with the ECPSSR calculations is generally good, except at the lowest incident energies. These remaining discrepancies have been attributed to the inadequate technique used to calculate the mentioned corrections.

LIGHT ION-INDUCED L-SHELL IONIZATION OF HIGH-Z ELEMENTS

L-shell X-ray production cross sections for selected heavy elements (Tl, Pb, Bi), of interest in BIO-PIXE analyses, have been measured by proton and 7Li ion impact in the energy range 0.8–2.6 MeV and 1.8–3.3 MeV respectively. Further, production cross sections for 7Li ion impact on Au between 1.0 and 2.4 MeV have been measured. L-subshell ionization cross sections have been extracted and arranged, together with similar results from other laboratories, in an analysis aiming at testing the performance of various theoretical approximations in the description of the ionization process. The disagreement observed at low values of the reduced velocity parameter ξRL between the data and the predictions of the ECPSSR model is significantly reduced by using a United Atom approximation in the treatment of the binding correction, suggested by our group (ECPSSR-UA). The remaining discrepancies, mostly for the L1-subshell, are almost completely removed by replacing the screened hydrogenlike wave functions with the more realistic Dirac-Hartree-Slater ones. In the case of 7Li ions, especially for L2-subshell, also a more refined Coulomb deflection correction and more sophisticated coupled channel calculations are needed.

Multi-ionisation and electron vacancy decay rates in proton and 4He ion impact on elements with Z approximately 50

An analysis has been performed on previously measured proton- and 4He-ion-induced X-ray production cross sections for Z=47-53 targets. A smoother behaviour in relation to Z than the one predicted by theory has been confirmed for the L1 subshell fluorescence yields and Coster-Kronig rates in this region. In the case of 4He-ion-induced measurements, the relative importance of LM and LN multi-ionisation and their dependence on the incident energy have been extracted by comparing the cross section ratios with the ones obtained using protons as projectiles. The effects predicted on the L-shell fluorescence yields and Coster-Kronig rates, due to the NL multi-ionisation processes, have been confirmed experimentally to be negligible.