Impact parameter dependence of theL-subshell ionization probabilities and of theL 3-subshell alignment tensor components in 4 MeVp-Sm collisions

The ionization of theL-subshells of Samarium by the impact of 4 MeV protons was examined by measuring the coincidence between x rays and scattered protons. TheL ₃-subshell ionization probability agrees well with the SCA predictions, for theL ₁-subshell and theL ₂-subshell ionization probabilities and also for theL ₃-alignment tensor components the results are not in agreement with SCA. Possible reasons for these deviations could be a neglect of collisional coupling between theL-substates.     

A method to determineL-subshell ionization cross sections for medium and heavy elements

We have developed a method to determineL-subshell ionization cross sections and report here on the first measurements of electron inducedL-subshell cross sections for target elements (29≦Z≦79) at electron bombarding energies between 50≦E ₀≦200 keV. The method involves the detection of characteristic X rays by means of a high resolution flat crystal spectrometer of known reflectivity and is based on the correlation of measured X ray intensities, Auger- and Coster-Kronig yields and radiative transition probabilities with theL-subshell cross section.     

Measurements ofL-subshell fluorescence yields for light and medium heavy elements (28≤Z≤47)

We report on the first determination ofL-subshell fluorescence yields, ω_Li, for various elements with 28≤Z≤47. The method applied is based on the subshell ionization by relativistic electron impact with an electron energy ofE ₀=50 keV and the detection of characteristic X rays by means of a high resolution crystal spectrometer calibrated absolutely with respect to its transmission and reflectivity. The number of initialL vacancies and its subshell distribution as well as the normalized X-ray transition probabilities, the Coster-Kronig yields and theK-shell Auger transition rates are taken from theory. The results obtained for ω_Li yield values that are for all three subshells in agreement with the predictions of a widely used semi-empirical formula and for ω _L2 and ω _L3 also with theoretical calculations. The values of ω _L1, however, exceed the theory systematically.     

L-shell ionization in Au by O5+-and Ni5+-ion impact

TheL X-ray production cross sections in gold by 60 to 72 MeV O⁵⁺ ions and 58 to 87 MeV Ni⁵⁺-ions have been measured. TheL-subshell ionization cross sections derived from these experimental results have been compared with the direct ionization theories viz. plane wave Born approximation (PWBA) theory and modified perturbed-stationary-state theory with energy loss, Coulomb deflection and relativistic effects (MECPSSR). A new procedure has been described to account for the change in the yield ratioLβ₁/Lβ_{2, 15} with energy, for Ni⁵⁺-ion impact on gold. TheL sub-shell ionization cross sections have been derived fromLβ₁,Lβ₄ andLβ_{2, 15} lines of theLβ group in addition to those calculated by the conventional Datz TRY3 technique usingLα,Lγ₁ andLγ_{2, 3} X-ray lines. From the shift in the energies of variousL X-ray lines and changes in their intensities, 3 and 5 spectator vacancies in theM- andN-shells in gold have been estimated with O⁵⁺-ion impact while 7, 20 and 4 to 6 spectator vacancies have been inferred in theM-,N-andO-shells respectively with Ni⁵⁺-ion impact in the energy range of the projectiles undertaken in the present studies.     

Distribution ofK α L n satellite yields for mediumZ elements bombarded with16O ions

K _α X-ray spectra were measured with a Du Mond type curves crystal spectrometer for₄₂Mo and₄₆Pd targets bombarded with oxygen ions at 5.5 MeV/u energy (i.e. at velocity closely matching those of the targetL-shell electrons). The distribution ofL-shell vacancies produced in collisions with simultaneousK-shell ionization is deduced from the measured yield distribution of theK _α X-ray satellites. The distribution shows deviations from the binomial ones. The deviations can be accounted for by assuming that theL-shell vacancy production is due to two uncorrelated processes: the direct ionization by impact and the electron capture from theL-shell of the target atom into theK-shell of the projectile, both occurring at nearly central collisions. The corresponding probability values are deduced using simple statistical considerations.     

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 theL _I andL _III subshell ionization probabilities of Pt have been measured. Due to relativistic effects in the electron wave functions, theL _I subshell ionization probabilityI _LI (b) is strongly enhanced at small impact parameters exceeding evenI _LIII (b) in nice agreement with the SCA theory.     

Solid-gas effect inK-vacancy production in near symmetric slow heavy-ion-atom collisions

We have measured the target thickness dependence ofK-vacancy production probabilities and total cross sections for 40.6 MeV Ar ions hitting Ca and Cu targets. The probabilities were measured as a function of the scattering angle between 0.13° and 1.4° by means of aK x-ray-particle coincidence. By integrating the measured probabilities over the impact parameter a significantly lower total cross section was obtained than the directly measured value. The maximum seen in the impact parameter dependent probability varies with decreasing target thickness towards the results obtained with molecular and atomic gas targets. From these observations a multiple collisionL-vacancy process prior to 2pπ-2pσ rational coupling is concluded.     

On the vibrational dependence of electron impact ionization of diatomic molecules

The dependence of the Na₂ electron impact ionization rate is measured as a function of vibrational excitation in a crossed molecule-electron beamm arrangement at collision energiesE _coll ≤ 3 eV above the ionization threshold. Specific vibrational distributions in theX ¹∑ _g ⁺ state with average vibrational energies of 0.17 eV, 0.276 eV, and 0.349 eV, are prepared via Franck-Condon pumping using a narrow-band cw laser. Enhancement of the ionization rate is observed only at impact energies near the ionization threshold where the ionization rate increases linearly as a function of vibrational excitation. Analysis of the experimental data is based on three model calculations. The first of these calculations equates vibrational energy with kinetic energy and agrees well with the experimental data. A second, more refined model allows for differences in state-to-state ionization rates and uses Franck-Condon factors to estimate transition probabilities, but leads to a less favorable agreement. The third one employs a semi-classical formulation of the Franck-Condon principle. It provides the best agreement with the experimental data. In contrast with an earlier study of electron impact ionization of diatomic molecules [20], we find no evidence of dynamical modification of the ionization rate, due to vibrational motion of the nuclei, at the present level of accuracy of our data and analysis.     

K-shell ionization in 7.5- and 8.6-MeV/a.m.u. U+U collisions at very small impact parameters

K-vacancy production probabilities in elastic 7.5- and 8.6-MeV/a.m.u. U+U collisions are reported for impact parameters less than 15 fm. In 7.5-MeV/a.m.u. U+U collisions the ionization probability rises above the trend indicated by larger impact parameter measurements, increasing to 1.8 vacancies per collision at the smallest impact parameter. The measured probabilities for 8.6-MeV/a.m.u. collisions increase to a maximum value of slightly less than 2 vacancies per collision at the smallest impact parameters. The data is compared to previous results and existing theory.     

A systematic investigation of ionization occurring in few electron collision systems: H0, He0 impact on He

Absolute doubly differential cross sections for electron emission occurring in fast (0.5 MeV/amu) H⁰ — and He⁰ — He collisions have been measured using standard non-coincidence techniques as well as emitted electron — charge state analysed projectile coincidence techniques. The comparison of these data with results obtained for H⁺ and He⁺ impact provides insight into the influence of one or two loosely bound projectile electrons on the probabilities for projectile, target, and simultaneous projectile — target ionization. PWBA calculations for these systems demonstrate good agreement with the experimental data for target and projectile ionization and indicate the importance of including simultaneous ionization processes in the theoretical treatment.     

K-shell ionization induced by 30 MeV/u argon and neon beams

We have studiedK-shell ionization induced by 30 MeV/u Ne and Ar projectiles on target atoms with atomic numbers ranging from 27 to 90. X-ray production cross sections and energy shifts were measured with Si(Li) detectors. In most cases satisfactory agreement between measurements and theoretical direct ionization cross sections is obtained when the contribution of electron capture is included. The influence of multiple ionization on the fluorescence yield ω _K is discussed.     

Chemical shift and intensity ratio values of dyspersium, holmium and erbium L X-ray emission lines

A systematic study of L X-ray spectrum has been made on the elements Dy, Ho and Er in the pure form elements and compounds to look into the influence of chemical effect. The vacancies were created by 59.54 keV γ-rays from an ²⁴¹Am radioactive source. The L X-ray emission spectra of heavy elements taken with the currently available Si(Li) detectors show four or five distinct peaks. Corrections for sample absorption and spectrometer efficiency were applied to the measured relative intensities. The results show agreement with the theoretical predictions of Scofield (Scofield, 1974a).     

Adsorption of radioactive iodide by natural zeolites

The vacancy transfer probabilities of K to L₁, L₂ and L₃ shell were measured with a new method. The L X-ray yields of targets excited by 59.5 keV incident photons, i.e., above the K edge of elements, were detected with a high-resolution Si(Li) detector. For comparison with the experimental results, theoretical calculations were made using data available on radiative and radiationless transitions. The radiative transition values of these elements were taken from the relativistic Hartree-Slater model, those of the radiationless transitions from the Dirac-Hartree-Slater model. The measured values were found to be in good agreement with theoretical ones. The h_KLi (i = 1, 2, 3) values were calculated by measuring the L_1x, L_2x and L_3x X-ray production cross-sections.     

Measurements of radiative vacancy transfer probabilities from L3 subshells to M,N and O shells and subshells in the atomic range 72⩽Z⩽92

The probabilities of vacancy transfer, η_L3M, ηL₃M₁, ηL₃M₄, ηL₃M₅, η_L3N, ηL₃N₁, ηL₃N₄, ηL₃N₅, ηL₃O₁ and ηL₃O_4,5 from L₃ subshell to M, N and O shells and subshells for the elements Hf, Ta, W, Re, Pt, Au, HgO, Tl, Pb, Bi, Th, U have been measured using L shell fluorescence yields and X-ray intensity ratios. These experimental values were obtained from samples excited by 59.5-keV γ-rays, which were emitted from an ²⁴¹Am radioisotope source. Also K and L X-rays emitted from samples were measured by means of Si(Li) detector with a resolution of 155 at 5.9 keV. The results obtained from this study are compared with the results of other studies.     

Measurement of L x-ray production cross sections by 60 keV photons and average L shell fluorescence yields of lanthanides

L x-ray production cross sections have been measured for lanthanides with 60 keV. The measured L x-ray production cross section values for the lanthanides are in good agreement with the theoretical ones evaluated using L _i subshell fluorescence yields ω_i, Coster-Kronig transition probabilities ? _ij based on the Relativistic-Hartree-Slater theory, K to L _i subshell vacancy transfer probabilities n _KLi, fractions of the ratiative width of the subshell F _ny and L _i subshell photoionisation cross section σ_Pi. The average L shell fluorescence yields ω_L have also been derived using the presently measured total L x-ray production cross section values and the theoretical K to L shell vacancy transfer probabilities. These results are compared with theoretically predicted values.     

Measurement of L subshell photoionisation cross sections of Th and U at 22.6, 25.8, 29.2 and 32.9 kev

Bremsstrahlung from an X-ray tube was used to excite secondary targets of Ag, Sn, I and Ba to get nearly monochromatic excitation energies of 22.6, 25.8, 29.2 and 32.9 keV, respectively. Th and U were used as targets. The L X-ray fluorescence cross sections of different lines from the targets have been measured. Of the several methods to obtain L subshell photoionisation cross sections from these fluorescence data, the merits and demerits of four common methods have been explained and the method with least uncertainty was suggested as the best one for such analysis. Following this method, with intensities of the resolved L_γ lines, three L subshell photoionisation cross sections have been obtained using six different sets of atomic parameters. The variation of these cross sections with different atomic parameters has been discussed. For σ₁, all the derived values are within 30% of one other while for σ₂ and σ₃, they are within 12%. Measured cross sections have been compared with the data of others and with the theoretical values of Scofield. Finally, the intensity ratios of different L lines have also been compared with available data and the theoretical values. Within experimental errors, our data are in good agreement with the data of others and with the theoretical predictions.     

p3/2-alignment following heavy ion impact

The energy dependence of the alignment of₄₂Mo,₄₇AgL ₃ shell and₇₉Au,₉₀ThM ₃ shell following impact ionization by ions with atomic numberZ ₁=2 (helium) toZ ₁=18 (argon) was studied with a 5 in Johansson crystal spectrometer analyzing the degree of X-ray polarization. Experimental information about the amount of multiple ionization was obtained. The observed small negative alignment is concerned to be due to dealignment by couplings between the created vacancies. Large positive values of the alignment parameter as previously reported for the₇₉AuL ₃ shell is slow heavy ion collisions were not observed.     

Electron impact and single photon ionization cross sections of neutral silver clusters

Neutral silver atoms and small clusters Ag _n (n=1...4) were generated by sputtering, i.e. by bombarding a polycrystalline silver surface with Ar⁺ ions of 5 keV. The sputtered particles were ionized by a crossed electron beam and subsequently detected by a quadrupole mass spectrometer. In alternative to the electron impact ionization, the same neutral species were also ionized by single photon absorption from a pulsed VUV laser (photon energy 7.9 eV), and the photoionization cross sections were evaluated from the laser intensity dependence of the measured signals. By in situ combining both ionization mechanisms, absolute values of the ratio σ _e (Ag _n )/σ _e (Ag) between the electron impact ionization cross sections of silver clusters and atoms could be determined for a fixed electron energy of 46 eV. These values can then be used to calibrate previously measured relative ionization functions. By calibrating the results using literature data measured for silver atoms, we present absolute cross sections for electron impact ionization of neutral Ag₂, Ag₃ and Ag₄ as a function of the electron energy between threshold and 125 eV.     

Probabilistic comparison and assessment of proficiency testing schemes and laboratories in the somatic cell count of raw milk

The somatic cell count (SCC) of milk is one of the main indicators of the udder health status of lactating mammals and is a hygiene criterion of raw milk used to manufacture dairy products. An increase in SCC is regarded as one of the primary indicators of inflammation of the mammary gland. Therefore, SCC is relevant in food legislation as well as in the payment of ex-farm raw milk and it has a major impact on farm management and breeding programs. Its determination is one of the most frequently performed analytical tests worldwide. Routine measurements of SCC are almost exclusively done using automated fluoro-opto-electronic counting. However, certified reference materials for SCC are lacking, and the microscopic reference method is not reliable because of serious inherent weaknesses. A reference system approach may help to largely overcome these deficiencies and help to assure equivalence in SCC worldwide. The approach is characterised as a positioning system fed by different types of information from various sources. A statistical approach for comparing proficiency tests (PTs) by assessing them using a quality index P _Q and assessing participating laboratories using a quality index P _L, both deriving from probabilities, is proposed. The basic assumption is that PT schemes are conducted according to recognised guidelines in order to compute performance characteristics, such as z-scores, repeatability and reproducibility standard deviations. Standard deviations are compared with the method validation data from the ISO method. Input quantities close to or smaller than the reference data of the method validation or the assigned value of the PT result in values for P _Q and P _L close to the maximum value. Evaluation examples of well-known PTs show the practicability of the proposed approach.     

Measurement of K shell radiative transition probabilities and K, L2 and L3 shell/subshell fluorescence yields of some elements in the atomic number range 30 ≤ Z ≤ 40

K shell radiative transition probabilities and K, L₂ and L₃ shell/subshell fluorescence yields were measured using the K_β/K_α intensity ratio for seven elements in the atomic number range 30≤Z≤40 (Zn, As, Se, Rb, Sr, Y and Zr). The targets were irradiated with γ photons of energy 59.5 keV from Am-241. The obtained values were compared with the theoretical values. It was observed that the present values agree with previous theoretical results. The L₂ and L₃ subshell fluorescence yields were the first measured for the present elements.