E. Perillo

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.

Proton- and 4He-ion-induced L-shell ionization of Pt, Pb and Bi

L-shell x-ray production cross sections on selected heavy elements (Pt, Pb and Bi), some of which are of great importance from a biological point of view, have been measured by proton and 4He ion impact at energies ranging between 0.3 and 3.2 MeV and between 0.6 and 1.8 MeV, respectively. The data have been compared with the results of other laboratories, whenever existing, obtaining an overall good agreement. L-subshell ionization cross sections have been extracted and compared with the predictions of various theoretical approximations in the description of the ionization process. The disagreement observed at low values of the reduced velocity parameter LR 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, as suggested by our group (ECPSSR-UA), and by replacing the screened hydrogen-like wavefunctions with the more realistic Dirac-Hartree-Slater ones. The application of a modified Coulomb deflection correction, recently suggested by our group, has further reduced the remaining discrepancies, predominantly in the case of impinging 4He ions.

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.

Weighted fit by orthonormal polynomials

Abstract The fitting technique by orthonormal polynomials and Forsythes recurrence relationship, generalized in order to take into account experimental errors, are discussed. Comparison is made between orthonormal and standard fits to point out the improvements on the latter, mainly from a computational point of view.

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.

Preliminary tests on a HgI2 microstrip detector with analog readout proposed as PSD in a Bragg X-ray spectrometer

Abstract Energy and spatial resolution of a HgI2 microstrip detector with six differently spaced (0.05 mm through 1.0 mm interstrip distances) microstrips, have been tested by using a 241Am source by an analog readout and a centroid finding method, with the aim of setting up a high-efficiency position-sensitive detector with spatial resolution of ≈ 50 μm for X-ray energies of ≈ 30 keV, to inserted in a Bragg X-ray spectrometer. Analog readout was preferred with respect to improving the spatial resolution by reducing the strip size, in order to not increase the number of readout channels. The energy resolution observed at a single strip, although worse than the one reported in the literature for HgI2 spectrometers, would allow using the centroid finding technique, but only the regions below the strips appear to be active for detection, i.e. the device is equivalent to one with digital readout for position identification. Thus a microstrip detector with a surface resistive layer between the strips is proposed, in order to enhance the active region of detection and to reach the required spatial resolution. Calculations performed by taking into account the various sources of noise allow getting optimized values for the interstrip distance and resistance.

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.

Compositional analysis of SmBa2Cu3O7−x films produced by laser ablation

The composition of SmBa2Cu3O7−x films deposited by pulsed laser ablation and deposition has been calculated by analyzing the particles-induced X-ray emission (PIXE), Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA) spectra. Data analysis of the RBS and NRA measurements gives an estimation of the thickness of the films. The resistance as a function of the temperature has been measured and discussed in relation to the off-stoichiometry of the films.

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.