Average Fluorescence Yields Research Articles

Theoretical Lifetimes, X-Ray Transition Energies and Fluorescence Yields for Double K Vacancy Configurations of Multiply-Ionized Fluorine

Theoretical x-ray transition energies, lifetimes, partial multiplet fluorescence yields and average fluorescence yields have been calculated for various fluorine ions with a double K-shell vacancy.

Lifetimes and Fluorescence Yields of States Produced in Heavy Ion-Atom Collisions

Recent theoretical results for few-electron metastable states are presented along with the experimental data. Average fluorescence yields are given for different atomic numbers.

Coincidence measurements of M-shell excitation in slow Xe-Xe collisions

Ion-photon and ion-Auger-electron coincidence measurements have been performed to study the impact parameter dependence of Xe M-shell excitation in 1.05 MeV Xe3+-Xe collisions. The experimental results are found to be consistent with the prediction of the molecular orbital model of atomic collisions. The average fluorescence yield for the Xe M shell is found to be strongly dependent on the impact parameter. This is ascribed to the production of highly charged Xe ions in close collisions.

Foil thickness dependence of Ar K X-rays from 56 MeV Ar12+bombarding carbon foils

The average X-ray production cross sections and energies for Ar projectile Kalpha , Kbeta and K REC (radiative electron capture) rays were measured for C target foils of effective thicknesses 8-450 mu g cm-2. A model is constructed which describes these yields, the several parameters employed being fitted to the data by a chi-square fit program. The parameters involved represent the main Ar K vacancy production (a single cross section parameter, sigma v'), the Auger and X-ray decay modes for projectiles within and after the foil, and the in-foil radiative and non-radiative electron capture (REC and NREC, respectively) decay modes. Variations in these parameters with projectile energy are estimated, and in-foil collisionally induced configuration alteration effects are considered. From the fit parameters it is possible to estimate several projectile characteristics, e.g. Ar K vacancy and Kalpha and Kbeta X-ray production cross section, in-foil and post-foil average fluorescence yields and the NREC cross section. From the energy measurements the average Ar projectile configuration of an ion with a K vacancy in the thin target foil limit is estimated.

Fluorescence yields for the rhodium L shell

Individual L-subshell fluorescence yields and the average L-shell fluorescence yield have been measured for rhodium (Z=45). A graphite mosaic crystal spectrometer was employed to resolve the LX-ray spectrum from the decay of 17 d 103Pd. The average fluorescence yields, omega L and omega KL, were measured in singles and coincidence experiments using Si(Li) and Ge(Li) detectors. Satellites from the decay of double-vacancy states in the L shell were detected and included in the analysis which yielded: omega 1/ omega L=0.411+or-0.013, omega 2/ omega L=0.927+or-0.021, omega 3/ Omega L=0.941+or-0.038, omega L=0.038+or-0.04, omega KL=0.036+or-0.06.

AverageL-shell fluorescence, Auger, and electron yields

The dependence of the average L-shell fluorescence and Auger yields on the initial vacancy distribution is shown to be small. By contrast, the average electron yield pertaining to both Auger and Coster-Kronig transitions is shown to display a strong dependence. Numerical examples are given on the basis of Krause's evaluation of subshell radiative and radiationless yields. Average yields are calculated for widely differing vacancy distributions and are intercompared graphically for 40< or =Z< or =100 in the case of the fluorescence and Auger yields, and 12< or =Z< or =100 in the case of the electron yield. Average fluorescence and Auger yields are found to differ by less than 7% from the respective L/sub 3/ subshell yields in most cases of inner-shell ionization.

X-ray production by electron excitation, ionization, and capture forFq+(q=1−9) ions in collisions with a He gas target

$K$ x-ray transitions resulting from collisions between F projectiles, with charge states ranging from ${1}^{+}$ to ${9}^{+}$, and He atoms have been observed. Production mechanisms leading to projectile $K$ x rays include $K$-shell electron excitation, single $K$-shell multiple $L$-shell vacancy production, and electron capture. The measured F $K$ x-ray production cross sections range from ${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$ for low charge states to ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ for incident bare ions. Using calculated average fluorescence yields, the $K$-shell electron excitation, single $K$-shell, single $K$-shell + single $L$-shell, single $K$-shell + double $L$-shell ionization, and electron-capture cross sections have been determined. The measured ionization cross sections are found to decrease with the increase in projectile charge state, whereas single-$K$-shell electron-excitation cross sections increase with the increase in projectile charge state.

SiK-shell ionization and electron transfer cross sections: Solid targets

The Si K x-ray production cross sections for F/sup q/+(q = 3--9) ion impact in the energy range of 0.4--2.2 MeV/amu are determined in the limit of a vanishingly thin target from the observed target thickness dependence of the x-ray yields. The ionization cross sections are deduced from the measured x-ray production cross sections using an average fluorescence yield (omega-tilde = 1.5..omega../sub 0/, where ..omega../sub 0/ is the fluorescence yield for an atom with single K vacancy) determined from high-resolution x-ray spectra and configuration fluorescence yields. For F/sup q/+ (q < or = 6) ion impact, the measured ionization cross sections are compared with the plane-wave-Born-approximation prediction with and without the Coulomb deflection and increased-binding-energy effects. The Si K shell to F K shell electron-transfer cross sections are determined from the difference between the ionization cross sections for F/sup 9 +/ ions and those for F/sup q/+ ions (q < or = 6). The results are compared with the prediction based on the two-state atomic-expansion method and that based on the modified Oppenheimer-Brinkman-Kramers approximation. A comparison is also made between the Si solid-target measurements with those obtained for gaseous Ne and Ar gas targets. The solid-target and gas-target data aremore » consistent at 1.58 MeV/amu. Finally, from a comparison between the measured equilibrium x-ray yields and the calculated x-ray yields using the equilibrium charge distribution of projectiles after passing through foils, it is found that the projectiles have a considerably larger number of K-shell vacancies inside solids than after passing through solids at lower-impact energies.« less

The study of the L-shell fluorescence yields of xenon

The wall-less proportional counter was used as an electron spectrometer. From the spectra of electrons generated by photoelectric excitation of separate L-subshells the following subshell and average fluorescence yields were extracted: ω 3 = 0.099 ± 0.002; ν 2 = 0.106 ± 0.007; ν 1 = 0.09 ± 0.03; ω 23 = 0.102 ± 0.001; and ω L = 0.100 ± 0.003 . Taking into account the theoretical values for Coster-Kronig transition probabilities the L 2 and L 1 subshell fluorescence yields were determined as ω 2 = 0.089 ± 0.008 and ω 1 = 0.05 ± 0.03.

Excitation Efficiencies for K and L X-Ray Fluorescence by a Mo Transmission Tube

The excitation efficiencies for K- and L- x-ray fluorescence by a Mo transmission tube operated at 30 kV have been measured. K x-ray excitation efficiencies for 14 elements ranging from A1 to Y and L x-ray excitation efficiencies for 12 elements ranging from Br to U are presented. The K x-ray excitation efficiencies are compared to those predicted from theoretical photoionization cross sections and empirical fluorescence yields, and the L x-ray excitation efficiencies are used in conjunction with theoretical photoionization cross sections to derive average L-shell fluorescence yields.

Fluorescence Yields of theLIIandLIIIShells in Heavy Elements

A method has been developed to measure the fluorescence yields of the ${L}_{\mathrm{III}}$ subshells in many heavy elements. This method is closely related to the $K$ to $L$ x-ray coincidence measurements used to determine ${\ensuremath{\omega}}_{\mathrm{KL}}$, the partial $L$ shell yield following $K$ x-ray emission. The fluorescence yield ${\ensuremath{\omega}}_{\mathrm{KL}}$ is a linear combination of ${\ensuremath{\omega}}_{{L}_{\mathrm{II}}}$ and ${\ensuremath{\omega}}_{{L}_{\mathrm{III}}}$, the fluorescence yields of the ${L}_{\mathrm{II}}$ and ${L}_{\mathrm{III}}$ subshells. The scintillation counters used to perform the coincidence experiments cannot separate the two components (${K}_{\ensuremath{\alpha}1}$ and ${K}_{\ensuremath{\alpha}2}$) of the ${K}_{\ensuremath{\alpha}}$ x rays, and thus the experiment determines only the average fluorescence yield ${\ensuremath{\omega}}_{\mathrm{KL}}$. There are a number of elements possessing $K$ absorption edges between the ${K}_{\ensuremath{\alpha}1}$ and ${K}_{\ensuremath{\alpha}2}$ x rays of the target materials. By using one of these elements as a secondary radiator, it is possible to eliminate all pulses in the $K$ x-ray counter due to ${K}_{\ensuremath{\alpha}2}$ x rays. The only target x rays contributing to the coincidence rate are the ${K}_{\ensuremath{\alpha}1}$ x rays which are caused by ${L}_{\mathrm{III}}\ensuremath{\rightarrow}K$ transitions. The observed coincidence rate is therefore proportional to ${\ensuremath{\omega}}_{{L}_{\mathrm{III}}}$. Values of ${\ensuremath{\omega}}_{{L}_{\mathrm{II}}}$ can then be computed using previous measurements of ${\ensuremath{\omega}}_{\mathrm{KL}}$.