K-shell Electrons Research Articles

Impact-parameter dependence of K-shell ionization

The impact-parameter-dependent probability of K-shell ionization by protons has been measured in the energy range 0.5–2.5 MeV for copper, silver, and gold targets. The data are used to test the scaling relations predicted from semiclassical calculations in first Born approximation, with unperturbed projectile trajectory and nonrelativistic hydrogenic electron wave functions. A systematic procedure is described for correcting such calculations for the inadequacy of these approximations, and the correction scheme is tested by comparison partly with experiments, partly with more complete theoretical treatments. The relation between ionization by scattered particles and by particles emitted in nuclear decays or absorbed in compound-nucleus reactions is discussed, and quantitative estimates are derived for the monopole term, which dominates for projectile velocities much lower than the K-shell electron velocity.

Atomic (p,n)-threshold cross sections

The (p,n)-threshold cross section is calculated for a light atom wherein the role of an active K-shell electron is included a priori. We find that the usual nuclear threshold law is covered asymptotically well above threshold on the atomic scale.

Compton scattering of 145 keV photons from bound electrons of tin and molybdenum

Differential cross sections for Compton scattering of 145 keV gamma rays from K-shell electrons of tin and molybdenum at scattering angles in the range 30 to 150 degrees . Measurements are made employing NaI(Tl) detectors and a coincidence set up with resolving time approximately=30 ns. The experimental results are compared with the available theoretical data. The total cross section is estimated to be about 0.43 sigma F for tin and 0.41 sigma F for molybdenum.

On the two-state approximation for capture

The two-state version of the two-centre, travelling atomic states approximation for capture of K-shell electrons by fast light ions is examined and an unphysical element which may lead to a spurious dip in the differential cross section is isolated.

Theoretical Incoherent Scattering Functions for Photons Scattered by Atoms and K-Shell Electrons

Theoretical Incoherent Scattering Functions for Photons Scattered by Atoms and K-Shell Electrons

Compton Scattering of 279.1 and 661.6 keV Photons by K-shell Electrons

The spectral distributions of 279?1 and 661? 6 keY photons incoherently scattered by the K electrons of U, Pb, Ta and Sm are calculated for a point-Coulomb potential using a theory previously developed by the author which accounts completely for electron binding and relativistic effects. WKB treatments of the regular and irregular continuum Dirac wavefunctions have been developed and used to mprove the computation of the 'absorption-first' radial matrix elements. The scattered photon spectra for the four elements and scattering angles for which the free electron Compton energy lies below the high energy cutoff due to conservation of energy have broad peaks shifted by 3 to 18 and by 30 to 50 keY, for 279?1 and 661? 6 keY photons respectively, from the free electron Compton energy towards higher scattered photon energies. An infrared divergence, whose magnitude increases strongly with atomic number, commences at ~ 56 keV and is present in those spectra where there is no peak or where the peak lies significantly above 56 keY. Differential cross sections daK' computed using a low energy cutoff, are nonzero for zero-angle scattering and are lower than the Klein-Nishina cross section daF for scattering angles ~ 50� for 661?6 keV photons and for all scattering angles for 279?1 keY photons (with the exception of 80�-130� in the case of Sm). The cross section ratio daK/daF increases with increasing scattering angle until about 100� and 80� for 279?1 and 661? 6 keY photons respectively and then subsequently decreases slowly.

An investigation into allegations of double scattering in the carbon K-shell electron energy loss spectrum of acetylene

In several recent publications (R. G. Cavell and D. A. Allison, J. Chem. Phys., 69 (1978) 159; A. Barth et al., Chem. Phys., 46 (1980) 149) it has been suggested that the feature at 295.6 eV energy loss in the carbon K-shell spectrum of C 2H 2 may arise from double scattering (i.e., collisions of one electron with two acetylene molecules). The pressure-dependence of the carbon K-shell excitation spectrum of C 2H 2 has been examined by inelastic scattering of 2.5-keV electrons to investigate this possibility. The intensity of all features, including that at 295.6 eV, was observed to vary linearly with pressure, indicating that the spectral features arise only from single collisions.

Compton Scattering of 145 keV Gamma Rays by K-Shell Electrons of Silver

Differential cross-sections for the incoherent scattering of 145 keV photons from K-shell electrons of silver are measured at scattering angles ranging from 30° to 150° to investigate the effect of electron binding on the scattering process in the low energy region. Measurements are made employing two NaI (T1) scintillation spectrometers and a slow-fast coincidence circuit of resolving time 30 ns. The experimental results are compared with the available theoretical data. The total K-shell scattering cross-section is also estimated and is about 45% of the free electron cross-section.

Impulse approximation calculations for capture of K-shell electrons by fast light nuclei

A succession of peaking approximations is used to study the structure of the impulse approximation in its impact parameter form. The results of numerical calculations are compared with experimental results.

The binding change effect on the K-shell ionization by 0.3–0.7 [formula omitted] deuterons and alpha particles

The ratios of the K-shell ionization cross sections induced by deuterons to those induced by α-particles for Cu, Ag and Tb targets were measured in the energy range of 0.3–0.7 MeV amu at equal velocities of the deuterons and α-particles. The observed ratios are found to be 15–20% lower than those predicted by the CPSS theory of Basbas et al. The predicted rise of the ratios with decreasing velocities is consistent with our Cu data but not with our Ag and Tb data. The importance of the relativistic effect of the K-shell electrons is discussed.

Charge transfer in asymmetric heavy-ion collisions

The impact parameter dependence of the capture of a target K-shell electron by a light projectile is calculated within the impulse approximation. Using a peaking approximation the authors show that the capture probability decreases monotonically with impact parameter. They evaluate the transfer probability in collisions of protons with C, Ne and Ar and compare with experiments.

Iron K photons from weakly magnetized neutron stars in X-ray binaries

The emission of iron K photons by the continuum X-ray source and the neutron star surface is considered. It is shown that the continuum sources of X-ray binaries produce negligible amounts of iron K photons because nearly all iron atoms in the continuum source are fully stripped due to the intense X-ray fluxes. In contrast, the atmosphere of the neutron star in an X-ray binary might be an important source of iron K photons (photon energy about 6.5 keV) because it is bombarded by a large number of hard X-rays capable of photo-ejecting K-shell electrons from iron atoms. Information is discussed concerning the magnetic field strength, the gravitational potential at the neutron star surface, and the direction of the magnetic dipole axis which are obtainable from the observations of K photons of the neutron star atmosphere.

The influence of the static potential in high-energy K-shell electron capture collisions

A theoretical model based on the CDW approximation of Cheshire (1964) for K-shell electron capture by stripped nuclei from multi-electronic atoms at high energies has been derived. The influence of the projectile-passive-electron interaction has been properly taken into account in addition to the well known nucleus-nucleus interaction. As an application of this model, differential cross sections for H++He(1s2) to H(1s)+He+(1s) are calculated and compared with other recent theoretical and experimental data.

X-ray absorption in polymers

We report on the results of a series of X-ray absorption experiments utilizing synchrotron radiation on the polymeric conductors, brominated (SN) x , and (CH) x doped with AsF 5. These experiments employ the K-edges of bromine and arsenic at 13.47 keV and 11.89 keV, respectively, for the study of the short range order in the vicinity of the source atom. This information is supplied by the backscattering effect of the surrounding coordination shells on the ejected K-shell electron (EXAFS). In addition, the edge region fine structure is studied to deduce information on the molecular species present (Br 2 orBr 3 − in (SN) x , AsF 5 orAsF 6 − in (CH) x ). Experiments were performed over a range of temperatures between 5 K and room temperature to check the relevant distance parameters and charge transfer for their temperature dependence. Nearest and second nearest neighbor distances are given for the bromine species in (SN) x , while an average AsF distance for the arsenic species in (CH) x is found to be somewhat larger than for AsF 5 gas molecules. The advantages of X-ray absorption spectroscopy over other methods such as XPS and UPS for the resolution of chemical questions in partially disordered systems are stressed, particularly, the bulk sensitivity of X-ray absorption vis-à-vis the surface escape depth problems of the other techniques.

K-shell autoionization accompanying the beta decays ofTc99,Pm147,Sm151, andTl204

The K-shell autoionization probabilities of /sup 99/Tc, /sup 147/Pm, /sup 151/Sm, and /sup 204/Tl have been determined to be (3.52 +- 0.20) x 10/sup -4/, (0.936 +- 0.063) x 10/sup -4/, (0.024 +- 0.003) x 10/sup -4/, and (1.22 +- 0.16) x 10/sup -4/, per decay, respectively. The first excited state branching ratios for /sup 147/Pm and /sup 151/Sm are (6.48 +- 0.56) x 10/sup -5/ and (0.94 +- 0.06) x 10/sup -2/, respectively. The K-shell electron capture to beta decay ratio for /sup 204/Tl is (1.22 +- 0.06) x 10/sup -2/. The autoionization probabilities are compared to the theory of Law and Campbell as modified by Isozumi, Shimizu, and Mukoyama.

K-shell photoionization of multielectron atomic systems

A simplified procedure is proposed for calculating the cross section for photoionization from the K-shell for a general atomic system that contains an arbitrary number of outer-shell electrons. The procedure retains the formalism of the one-electron atom case (pure Coulomb-field problem) by determining the effective nuclear charge reduced from Z by 'screening parameters' associated with the other K-shell electron and the outer-bound electrons. The parameters are determined essentially by fitting the atom's radial electric field to Coulomb form at the distance from the nucleus where the integrand of the dipole radial integral is peaked.

The influence of finite lifetime of electronic states on the vibrational structure of molecular electronic spectra

A general theory describing the effect of finite lifetime of electronic states on the vibrational structure of electronic spectra is developed. A proper description of the decay of the excited state involved in the transition is achieved by summing the perturbation series for the T matrix to infinite order in the interaction responsible for the decay. An effective non-hermitian hamiltonian is obtained which describes the vibrational motion in the short-lived electronic state. The finite lifetime influences the spectra in a different way, depending whether the shoft-lived state is the final or the initial state of the electronic transition. In the former case the spectrum is given by an incoherent superposition to lorentzian lines, while in the latter case there are interferences between the vibrational levels of the short-lived electronic state which modify the vibrational structure is a characteristic manner. The theory is applied to various spectra of CO and N 2 involving the excitation of K-shell electrons. Interferences effects are predicted and identified in the experimental spectra.

The early radiation spectrum, cooling, and escape of supernova shock-accelerated cosmic rays

view Abstract Citations (17) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The early radiation spectrum, cooling, and escape of supernova shock-accelerated cosmic rays. Colgate, S. A. ; Petschek, A. G. Abstract The early radiation spectrum emitted by the expanded and cooling shock-ejected outer layers of a Type I supernova is derived for a model in which the presupernova star is a minimum-mass highly compact white dwarf. It is found that the outer electrons of matter ejected with energies less than 5 GeV/n will recombine before again becoming ionized by interaction with the interstellar medium, that the K-shell electrons high-Z matter up to an energy of 50,000 GeV/n will recombine before stripping about 1000 yr later in the interstellar medium, and that the formation of relativistic grains is unlikely. The results indicate that a compact presupernova star without an extended envelope should produce both cosmic rays and a burst of radiation, after which the supernova should not be visible until heating at a later time causes a slow rise to maximum luminosity. It is concluded that an observable X-ray burst of several times 10 to the 43rd erg should occur in a few tenths of a second and have a flat spectrum. Publication: The Astrophysical Journal Pub Date: April 1979 DOI: 10.1086/157003 Bibcode: 1979ApJ...229..682C Keywords: Cosmic Rays; Particle Acceleration; Radiation Spectra; Shock Waves; Stellar Mass Ejection; Supernovae; X Ray Sources; Doppler Effect; Electron Recombination; Energy Dissipation; Interstellar Gas; Stellar Envelopes; Stellar Luminosity; Surface Cooling; Temperature Distribution; Space Radiation; Cosmic Rays:Supernovae full text sources ADS |

Inner shell electron energy loss studies of HCN and C 2N 2

Small angle inelastic scattering of electrons with several kilovolts impact energy has been used to study carbon and nitrogen K-shell excitation and ionization of HCN and C 2N 2. The observed energy loss structures are assigned to promotions of K-shell electrons to valence and Rydberg orbitals. High resolution spectra (<100 meV fwhm) of the most intense inner shell transitions in HCN are reported. Excitation and ionization energies of the radicals HN 2 and HCO are derived from the HCN inner shell spectra using the equivalent core analogy.

Energy loss of relativistic electrons and its fluctuation in gas proportional counters

Absolute measurements of the energy loss and its fluctuation of relativistic electrons in this gas layer over the momentum region of 50–800 MeV/ c have been extensively achieved with high accuracy using a 100 cm proportional counter, operated with a conventional mode or a special mode (the central wire is divided by a small glass bead into two sensitive lengths of 10 cm and 90 cm). The counter is filled with Ar + 10% CH 4 mixture at various pressures between 0.1 and 2.0 atm. The experimental distributions of the energy losses are compared with those predicted by the Landau theory, the Blunck-Leisegang theory, the Chechin-Ermilova theory and the Monte Carlo method (Ispiryan et al., Cobb et al. and Ermilova et al.). The observed fractional widths agree relatively well with those of the Monte Carlo calculations. The observed values of the most probable energy losses for small thickness (≤3 × 10 −2 g/cm 2) of gas layer are 10–25% smaller than those predicted by the Landau-Sternheimer theory and they approach to the theoretical ones with increase of the thickness. A part of such a discrepancy between the theory and the experiment may be explained by the fact that the inner shell electrons of argon atoms in the absorber material do not contribute to the most probable energy loss, when the energy loss is not larger than the binding energy of K-shell electrons. The explanation, however, does not give an understanding for the fact that even when the thickness of gas layer is equal for the short and long counters, the difference in the most probable value between both counters is larger than that predicted by the Landau-Sternheimer theory. This suggests that the density effect correction given by Sternheimer may be insufficient to the thin gas layer. The observed most probable values are also compared with those predicted by the Chechin-Ermilova theory and the Monte Carlo method (Cobb et al. and Ermilova et al.). These predictions do not give a satisfactory explanation for the decrease of the observed values. However, the Monte Carlo results calculated by Ermilova et al. show the tendency close to the observed data.