SCA Theories Research Articles

Proton induced L-shell cross-sections for some post-transition metals: A comparison of ECPSSR and SCA models

The L-shell ionisation and X-ray production cross-sections of some post-transition elements: In, Sn and Tl, induced by protons of energies 1 MeV–4 MeV, have been calculated. The targets considered have few experimental cross-sections, for indium and tin, while thallium has no existing cross-section values in the database due to its radioactive and toxic nature. The cross-sections for the targets were obtained using computer codes based on the ECPSSR and SCA theories; and were subsequently validated using lead and bismuth targets whose experimental values are known within this energy range. The comparison of the experimental and calculated cross-sections showed that both models are in good agreement within certain proton energy region. However, above 2 MeV, the ECPSSR models should be employed. For the case where the SCA model is to be employed, the energy loss and Coulomb deflection factors should be taken into account.

Measurements of ionization cross sections of Ti and Cu induced by low energy Li and B ion impact

The measurements of K-shell ionization cross sections of Ti and Cu induced by Li and B impact in the energy range of 1.0 MeV < E 0<6.4 MeV are presented. The correction of the fluorescence yield due to the multiple ionization is estimated. Extracted cross sections are compared to the predictions of different models: the ECPSSR theory and the SCA theory where quite a few approaches are used. The ECPSSR theory explains measured cross sections quite well. By including the correction of electron binding energy in the SCA theory in the same way as included in the ECPSSR theory the agreement between the measured and the SCA theoretical cross sections is improved.

L-subshell ionization studies of Au for alpha -particle and lithium-ion bombardment

L-subshell ionization of Au has been investigated for alpha -particle and lithium-ion bombardments with energies 0.54-1.74 MeV u-1 and 0.65-1.44 MeV u-1, respectively. Comparison of experimental X-ray production cross sections with the predictions of the ECPSSR and SCA theories shows reasonably good agreement for Lalpha and Lbeta X-rays, whereas for Lgamma and Lgamma 1+5 the ECPSSR theory underestimates the cross sections by about 60% for both alpha -particle and lithium-ion impact, and the SCA theory agrees reasonably well. The ECPSSR theory underestimates the L1- and L2-subshell ionization cross sections and gives good agreement for the L3-subshell, whereas the SCA theory overestimates the L3-subshell ionization cross sections and gives good agreement for L1 and L2. The experimental data for the total-ionization cross sections are within 25% of the predictions of both the theories.

L-subshell ionization of rare earth elements by carbon ion bombardment

Measurements of L-shell X-ray production cross sections and corresponding L-subshell ionization cross sections for selected rare earth elements (57<or=Z<or=68) have been performed for 12C and 13C ion impact with energies 0.4-2.8 MeV amu-1. The influence of target thickness and projectile charge state on L-subshell ionization is examined experimentally. The measured L-subshell ionization cross sections are compared with the predictions of the ECPSSR and SCA theories. Strong underestimation of the experimental data in the low energy range by both theories is caused by the second-order effects not accounted for in the theoretical description. An agreement of the data with the theoretical predictions is improved by using the 'united atom' limit for the effective binding energies.

L subshell ionization of heavy elements by 3He and 4He ions

L shell X-ray production cross sections for selected heavy elements (72 ≤ Z 2 ≤ 83) have been measured by 3He + and 4He + ions impact. The corresponding L subshell ionization cross sections have been extracted from data and compared with the predictions of the ECPSSR and SCA theories by expressing graphically the ratio σ exp/σ theoryas a function of the corrected reduced velocity parameter ξ L i r . Strong underestimation of experimental data by the ECPSSR and SCA theories has been observed for the lowest energies, especially for the L 2 subshell, up to a factor of 3 and 4 for 3He and 4He ions, respectively. Possible reasons for observed disagreement are discussed.

L-subshell ionization of some rare earth elements by 73Li ion impact

L X-ray line production cross sections for Eu, Tb and Er elements have been measured as a result of 73Li ion bombardment at energies from 4.2 to 19.6 MeV. The corresponding L1-, L2- and L3-subshell ionization cross sections have been calculated and have been compared to the predictions of the ECPSSR and SCA theories. Possible reasons for observed disagreements between experiment and theory are discussed.

L-SUBSHELL IONIZATION OF HEAVY ELEMENTS BY PROTONS AND DEUTERONS

Thin targets of selected heavy elements (72≤Z2≤90) were bombarded by protons and deuterons of energy 0.4–4.0 MeV and 0.3–2.0 MeV, respectively. The Li-subshell ionization cross sections were derived from these measurements and were compared with the ECPSSR and SCA theories by expressing graphically the ratio σexp/σtheory as a function of the corrected reduced velocity parameter.

L-subshell ionization of rare earth elements by light ion bombardment

Thin targets of La, Pr, Nd, Eu, Tb, Ho and Er were bombarded by 1H, 2H, 3He and 4He projectiles. The production cross sections for the Lalpha 1,2, L beta 1,3,4,6, L beta 2,7,9,10,15, L gamma 1,5, Lgamma 2,3, L gamma 4,4 and Ll X-ray transitions have been extracted and corresponding ionization cross sections for L1-, L2- and L3-subshells have been calculated. The ratios of the experimental data to the predictions of the ECPSSR and the SCA theories are presented as a function of the corrected reduced projectile velocity parameter xi Lir. The Coulomb deflection of the projectile by the target nucleus predicted by these two approaches is compared with the experimental data. Possible reasons for the observed disagreement between experiment and theory are discussed.

The measurement of impact parameter dependence of K-shell ionization probability by protons

The absolute impact parameter dependence of K-shell ionization probability P( b) has been measured in the impact parameter range 0.03–0.9 pm at incident proton energy of 2 MeV with a Cu target. The ionization cross section of Cu has also been measured at this energy. Good agreement is found between our data and a modified SCA theory and the measured ionization probability was nearly constant at large scattering angles, in good agreement with predictions from SCA calculation with hyperbolic orbit after binding and relativistic corrections.

L-Subshell ionization probabilities in very asymmetric ion-atom collisions

The L-subshell ionization probabilities have been measured as a function of the impact parameter for proton on Sm, He on Pt, and Ne on Yb and Pt. For the light ions at very low velocities, the experimental Subshell ionization probabilities are in agreement with predictions of the SCA theory. For increasing velocity and increasing projectile nuclear charge, however, severe deviations between theory and experiment are observed. Possible reasons for these deviations could be an omission of collisional coupling between the L-substates, which is neglected in the SCA approach. For p on Sm also the impact parameter dependence of the L III alignment tensor components have been measured. These alignment data also deviate strongly from predictions of the SCA theory.

The influence of the electron wave function on the PtL I andL III ionization probabilities by 3.6 MeV he impact

For 3.6 MeV He impact theLI andLIII subshell ionization probabilities of Pt have been measured. Due to relativistic effects in the electron wave functions, theLI subshell ionization probabilityILI(b) is strongly enhanced at small impact parameters exceeding evenILIII(b) in nice agreement with the SCA theory.

K-shell ionisation by protons, deuterons and alpha particles at low projectile energies

The semiclassical approximation model (SCA) with hyperbolic projectile trajectories, including target recoil and symmetrisation, is used to study Coulomb ionisation in the incident energy range from 50 to 300 keV for a Ni target. Combined with corrections for the binding effect and the relativistic behaviour of the target electrons, the first-order SCA theory yields total cross sections consistent with recent measurements. No variation of parameters is performed.

M-shell X-ray production cross sections in the proton energy range 250-400 keV

Malpha + beta , Mgamma and MIINIVMIIIOI,IV,V lines of the elements with Z=62-79 have been measured with a proton beam energy of 250-400 keV using thin targets. The efficiency of the Si(Li) detector in the low-energy X-ray range was measured with the Kalpha lines of F, Al and Si and the Lalpha line of Ni using known X-ray production cross section values. The target thicknesses are obtained simultaneously by Rutherford backscattering measurements. The production cross sections of the M lines have been compared with the SCA and PWBA theories. The quality of these theories applied to different M-line production cross sections is discussed.

X-rays induced by light ions

The main processes involved in energy loss of charged particles are briefly considered and compared to inner shell innization. Some applications of particle induced X-ray emission are mentioned. The higher order corrections to the PWBA and SCA theories for the ionization cross section are briefly sketched and compared to each other.

K-shell ionisation cross sections for Co, Ni, Cu, Zn, Ge and Se by protons of 0.2–2 MeV

Proton-induced K-shell ionisation cross sections for Co, Ni, Cu, Zn, Ge and Se in the incident energy range 0.2 to 2 MeV obtained from thin target measurements are presented and compared to other available experimental results and to theoretical values pertaining to the SCA and PWBA theories, calculated taking into account electron binding energy, projectile Coulomb retardation and electronic relativistic effects. Theoretical BEA cross sections, corrected for the slowing down of the projectile in the nuclear Coulomb field, are also compared to experiment. The present data show that the correction procedues used on both the SCA and BEA calculations fail to produce acceptable agreement with experiment at low bombarding energies, while those pertinent to the PWBA still need some refinement. K Δ K α ratios are also presented and compared to other experimental values and to the theoretical one-hole values given by Scofield.

Absolute CKx-ray production cross sections for 0.29-16.0-MeV protons on thin carbon foils

Absolute carbon $K$ x-ray production cross sections (${\ensuremath{\sigma}}_{K\mathrm{x}}$) have been measured for 0.29-16.0-MeV protons on thin carbon foils, covering the region below the maximum in ${\ensuremath{\sigma}}_{K\mathrm{x}}$ up to the high-velocity region described by asymptotic (Bethe) theory. An experimental fluorescence yield value ${\ensuremath{\omega}}_{K}=(2.46\ifmmode\pm\else\textpm\fi{}0.35)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ was determined for carbon. Experimental values of ${\ensuremath{\sigma}}_{K}$ are compared to the BEA, SCA, PWBA, and asymptotic theory predictions. At energies close to the maximum in ${\ensuremath{\sigma}}_{K}$ (\ensuremath{\sim}0.5 MeV) the BEA predictions were in good agreement with experiment, while at higher energies the PWBA predictions gave the best agreement. Predictions of asymptotic theory lay somewhat below experiment. The measurements show the predicted $\frac{(\mathrm{ln}E)}{E}$ dependence at higher energies, and experimental values for the two main parameters of the asymptotic theory, viz., ${M}_{\mathrm{tot}}^{2}=0.87$ and ${C}_{\mathrm{tot}}=8.5$ (both \ifmmode\pm\else\textpm\fi{} 20%) were derived from a fit to the data. These values are the first of their kind determined by ion bombardment.