Light nuclei as distinct probes for transient magnetic fields

Salient features of transient magnetic fields are brought out from nuclear spin precession measurements on light ions penetrating polarized Fe-, Ni- and Gd-hosts. At low velocities ion fractions with singleK-shell vacancies, at high velocities H-like charge state fractions, can account for the observed precessions. The data suggest a sharp reduction of theK-shell field at a velocityv _ion?0.5v ₀. Large degrees ofK-shell polarization have been derived for C- and O-ions. Measurements in different ferromagnets show that the transient fields scale with the polarized electron density of the host.     

On the assignment of the carbon K-shell spectra of the methyl halides

Electron energy loss spectra of the methyl halides in the region of carbon K-shell excitation have been obtained at higher resolution than those previously reported. The existence of two electronic transitions between 288 and 290 eV in CH₃F is demonstrated. This result conflicts with a recent SCF calculation which suggests that the σ* (C–F) level in CH₃F is unbound and thus predicts the existence of only one electronic transition in this spectral region. Studies of the carbon K-shell spectra of CH₃Br and CD₃Br demonstrate the vibrational origin of some spectral features. These new results support our earlier tentative assignments for the carbon K-shell spectra of the methyl halides.     

Inner shell excitation of CH 3F,CH 3Cl,CH 3Br and CH 3I by 2.5 keV electron impact

Small angle inelastic scattering of 2.5 keV electrons was used to study inner shell excitation in the methyl halides at energy transfers between 50 and 700 eV. Discrete peaks due to the excitation of carbon K, fluorine K, chlorine L, bromine M_{4, 5} and iodine N _{4, 5} electrons were observed. Correlations through the methyl halide series were used to aid in the assignment of features in the carbon K-shell spectra. A comparison of halogen inner-shell excitation structures with the carbon K-shell excitation structure in the same molecule allowed a complete assignment of all spectral features. The assignments proposed involve promotions of inner shell electrons to unoccupied valence and Rydberg orbitals. On the basis of our assignments of the chlorine L- and carbon K-shell electron energy loss spectra of CH ₃Cl we propose an alternate assignment of the previously reported CH ₃Cl chlorine K-shell photoabsorption spectrum.     

Fragment-ion appearance-potential spectroscopy

Nitrogen K-shell excitation in NH₃, NO, N₂, N₂O and NF₃ has been measured. The excitation thresholds were identified by mass-spectroscopic detection of positive ions produced in the course of decay of the highly excited species. The threshold energies for the N1s core level show a pattern similar to ESCA chemical shifts. In the N₂O data, the abundances of fragment ions having m/e = 14 and m/e = 16 correlate with the location of the primary K-shell vacancy. This may indicate a new approach to molecular structure determinations.     

Study of high energetic electrons emitted during heavy ion collisions

Double differential cross sectionsd ² σ/dΩdE were measured for high energetic electrons emitted in heavy ion collisions. Electrons were detected in the energy range of 60 keV-500 keV for various target projectile combinations 66≦Z _u =Z _t +Z _p ≦145 and projectile velocities between 7 % and 10 % of the speed of light. Clear evidence was found that these electrons stem from the united atom formed during the collision. Slope and height of the spectra are discussed with respect to the momentum distribution of strongly bound states (i.e. theL-shell) at momenta far above the mean value. In addition for the systems S, Ni, Br→Pb electrons were detected in coincidence withK x-rays of Pb. By this method the contribution of theK-shell of the combined system to the total spectrum could be separated. Binding energies of theK-shell were estimated by a slope comparison between the coincident and single spectrum. The resulting values are close to the united atom limit.     

TheK-shell fluorescence yield of germanium

TheK-shell fluorescence yield of germanium has been determined asω _K=0.570±0.003 by the modified proportional counter technique using a special wall-less proportional counter filled with methane and small admixture of germanium hydride GeH₄. The required ratio of the total photoabsorption to the absorption in theK-shell has been obtained from the separate study of the energy dependence of the X-ray absorption in germanium.     

Determination of theK-shell electron capture probabilityP K in the decay of139Ce

A new coincidence procedure for the determination of theK-shell electron capture probability in simpleEC decays is described. By measuringγ-rays andK-shell conversion electrons separately and in coincidence with theK X-rays theK capture probability can be deduced only from counting rates. The method has been applied to¹³⁹Ce. The result ofP _K = 0.726±0.010 is in fairly good agreement with other experimental values reported previously.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

K-shell excitation spectra of CO,N2 and O2

Electron energy loss spectra of CO, N₂ and O₂ have been recorded in the regions of carbon, nitrogen and oxygen K-shell excitation and ionisation. These results are compared to previous energy loss, photoabsorption and theoretical studies of the same spectral regions. Several inconsistencies in the published spectra are clarified in the present work. Comparisons with recent calculations of the K-shell continua of these molecules are presented. Vibrational structure in the K → π * transitions of CO (C 1s) and N₂ (N 1s) has been resolved in high-resolution studies (< 0.1 eV FWHM) of these species.     

Electronic excitations in phosphorus-containing molecules. I. Inner shell electron energy loss spectra of PH3, P(CH3)3, PF3 and PCL3

Electron energy loss Spectroscopy has been used to obtain the inner shell electronic excitation spectra of PH₃, PF₃, PCl₃ and P(CH₃)₃ in the phosphorus L-shell (P 2p, 2s) region as well as the respective ligand K -shells (F 1s, C 1s) and L-shell (Cl 2p and 2s) regions. The spectra were obtained under small momentum transfer conditions so that dipole-allowed transitions dominate. An impact energy of 2.5 ke V was used and inelastically scattered electrons were detected at a typical scattering angle of about 1°. A dipoleforbidden transition of unusual character is observed at 135.11 eV in the P 2p spectrum of PCl₃. Although optically forbidden, as indicated by its absence in a soft X-ray absorption spectrum, the intensity of this transition rises very rapidly with increase in momentum transfer.     

TheK-shell fluorescence yield of gallium

TheK-shell fluorescence yield of gallium has been determined asω _K =0.529± 0.002 from the study of theK-capture in germanium 71 by the use of GeH₄ as gaseous source in a multiwire proportional counter system.     

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 C₂H₂ 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 C₂H₂ 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.     

s-Shell Λ-Hypernuclei Taking into Account Λ N–ΣN Coupling Explicitly with TOSM

The Λ N–ΣN coupling is one of the open questions in strangeness physics. We studied the Λ N–ΣN coupling explicitly in light s-shell hypernuclei using Tensor Optimized Shell Model, which is ab initio like approach starting from the realistic interaction. We show the obtained results of s-shell Λ-hypernuclei, _Λ ⁴ H and _Λ ⁵ He, and investigate the roles of the Λ N–ΣN coupling interaction in those hypernuclei.     

Carbon K-shell excitation spectra of linear and branched alkanes

The electron energy loss spectra of ethane, propane, n-butane, n-pentane, n-hexane, isobutane, isopentane and neopentane in the region of carbon K-shell excitation have been recorded under dipole-dominated conditions (2.8 ke V impact energy, small angle). The spectra are dominated by transitions to unoccupied valence π¹(CH₂, CH₃) and σ¹(C-C) levels. Additional weak features are assigned to Rydberg transitions. The position of the main continuum feature in each spectrum is consistent with the predictions of an empirical relationship with bond length. Systematic variations of spectral intensities are observed which support our assignments. The dominant feature in the K-shell spectrum of ethane, which was previously assigned to C 1s → 3p Rydberg transitions, is reassigned to excitation to a 3p/π¹(CH₃ ), mixed Rydberg/valence orbital (of antibonding σ-¹(C-H) character), in comparison to the other alkane spectra. An improved calibration value of 290.74(5) eV for the energy of the C 1s → π¹ transition in CO₂ is also obtained.     

The determination of theK-shell fluorescence yield of antimony using the proportional counter techniques

From the spectra of electrons emitted in photoelectric absorption of europiumKα radiation in antimony, theK-shell fluorescence yield was determined asω _K =0.873±0.010. A multiwire proportional counter filled with methane and a small admixture of stibine, SbH₃, was employed as a spectrometer.     

Reevaluation of the conversion coefficient of the 14.4 keV transition in57Fe

Existing values of the conversion coefficient of the 14.4 keV transition in⁵⁷Fe have been reevaluated using newK-shell fluorescence yields and recent decay scheme information. Previous disagreements are removed and the mean values found are α _T =8.26±0.19, α _K =7.37±0.17.     

Transport properties of single crystals of CeCu2Si2 and CeNi2Ge2

The resistivity, thermopower and thermal conductivity were measured on single crystals of CeCu₂Si₂ and CeNi₂Ge₂ between 60mK and 300 K. All transport anomalies associated with the unstable 4f-shell in Ce are strongly anisotropic in these noncubic systems.     

On the possibility of superconductivity in a MgB2 compound

A concept of strong interaction in a single unit cell is used to predict Cooper instability in a system with hopping between main-group cations and anions. A phase diagram of ferromagnetic ordering is constructed for different degrees of (n _p )p ⁶-and (n _s )s ²-shell filling in main-group elements.     

Determination of the K-shell internal conversion coefficient for the 37.2 keV transition in the decay of121mSn

TheK-shell internal conversion coefficientα _K for the 37.2 keV transition (7/2⁺→5/2⁺) occuring in¹²¹Sb afterβ ^? decay of¹²¹ mSn has been redetermined applying theX- toγ-peak method (XPG). Measurements of photon spectra from thin sources have been performed at various source-detector distances with a high resolution, efficiency calibrated Si(Li) detector. Values ofα _K have been deduced from the number of emittedKX rays compared to that of the emittedγ rays. TheK-shell fluorescence yield for antimony has been taken from the literature. From in total 14 experimental runs a mean result ofα _K =9.52±0.27 has been obtained. The quoted uncertainty comprising statistical and systematic parts is discussed in detail. The present result is compared with the few existing earlier experimental values and with the theoretical value interpolated from the most recent tabulations.     

Positron impact inner shell ionization

The positron impact ionization cross section for theK-shell was determined in the case of Ni, Y and Ag at 670 and 490 keV as well as for theL-shell in the case of Yb, Ta, Au and Pb at 490 keV using a beta-ray spectrometer as a source of monoenergetic electrons and anX-e ⁺ coincidence arrangement. The results for theK-shell are compared with the theoretical calculations according to Kolbenstvedt and with the earlier experimental values.