The anisotropic emission of the K-X-radiation of boron and nit'rogen in hexagonal boron nitride BN permits the determination of the x -and a-subbands of the two X-ray spectra. Together with the X-ray photoelectron spectrum a consistent picture of the valence band of BN is obtained. Position and width of the s-, o-, and x-bands are determined. None of the band structure and density-of-states calculations known so far is in satisfactory agreement with the experimental observations. Die anisotrope Emission der K-Rontgenstrahlung von Bor und Stickstoff in hexagonalem Bornitrid BPU' erlaubt die Bestimmung der x -und a-Teilbanden der beiden Ront,genspektren. Zusammen mit dem Rontgen-Photoelektronenspektrum ergibt sich daraus ein konsistentes Bild des Valenzbandes von BN. Breite und Lage der s-, a-und x-Bande werden bestimmt. Keine der vorliegenden Bandstruktur-und Zustandsdichteberechnungen zeigt eine zufriedenstellende Ubereinstimmung mit den experimenbellen Beobachtnngen.
Differential cross sections and polarizations for 17.8-MeV protons scattered by nickel isotopes have been calculated by solving the coupled equations. The nuclear states were described in terms of their microscopic composition in the two-quasiparticle approximation. Two such model calculations were used. The effect of the presence of pure "two-phonon" states was investigated by generating them from the collective operator for the 2i + state. The effects of the spin-flip term in the direct interaction were included. Comparison of the results with experiments suggests that, except for the collective 2i + state, the two-quasiparticle method is inadequate for treating nuclear states. The vibrational treatment also fails. A much more elaborate structure calculation which treats the mixing between the two-quasiparticle and the "two-phonon" configurations is suggested.
Das S Kfl-Spek~rum von rhombischem Schwefcl, CaS, $rS, c~-MnS, K2S() ~ und CaSO, wird mit Rbntgenstrahlell erregt nnd mit eillcm Vakuumspektrographen t)hotographisch registriert, l)as Spektrum, das dutch l~:berg~inge vorl Valcnzelektronen zustandc kommt, besteht beim Element ulld bei den Su]fidell aus einer breiten Bande, bei den Sulfaten aus einer auifallend scharfen Linic. Die Ergebnisse zeigen, dab (tie VerS~nderungen des Kfl-SpeMrulns mit dem Billdungszllstand nicht wie die des Kc~-Dubletts als lAnienverschiebungerl behandeltwerden kSnnen. --Im I iinblick anf die geringe Intensit/it der sekund~ren l~61atgenstrahlcn wird die I"rage gepriift, wieweit sich bei dcr Prim~irmcthode die st6rende VvSrkung der Kathodenstrahlcn durch kleine Brenllfleckbelastung vermeiden l~il3t. Dabei werden ~Beobachtungen gemacht, die darauf'hindcllten, dab die illi~ Kathodenstrahlen erregten Spektren gcgeniiber den mit R6ntgenstrahleI1 erregten t)rinzipielle, nicht auf chemische Ver~nderungen zurfickftihrbare Untcrschiede aufweiscll.Einleilung.
The intensity distribution of the N K-emission band of hexagonal boron nitride samples with partially oriented crystallites is found to be strongly dependent upon the take-off angle of the emitted radiation. The observed emission bands can be separated unambiguously into a cr-and a n-subband. On the basis of the directional characteristic of radiating dipoles within the layers (o-bondings) and perpendicular t o the layers (x-bonding) the angular dependence of the intensity of the subbands is quantitatively explained. I n addition, the degree of orientation of the crystallites in t'he sample can be determined. The intensity distributions of the emission bands t o be expected for single crystals and for samples without any texture are determined; in the latter case the results are found to be in good agreement with experiment.Die Intensitatsverteilung der K K-Emissionsbande von Proben hexagonalen Bornitrids mit teilweise orientierten Kristalliten zeigt eine starke Abhangigkeit vom Abnahmewinkcl der emittierten Strahlung. Die gemessenen Emissionsbanden konnen eindeut'ig in eine cr-undeinex-Teilbande zerlegt werden. Auf der Basis der Richtungscharakteristik von strahlenden Dipolen in der Schicht (cr-Bindung) nnd senkrecht zur Schicht (x-Bindung) wird die Winkelabhangigkeit der Intensitat der Teilbanden quantitativ erklart. Zusatzlich kann der Orientierungsgrad der Kristallite in der Probe bestimmt werden. Die Intensitatsverteilungen der Emissionsbande, wie man sie fur Einkristalle und Proben ohne Textur erwartet, werden ermittelt; im letzteren Fall befinden sich die Ergebnisse in guter ifbereinstimmung mit experimentellen Ergebnissen.
The relaxation of hot nuclear matter to an equilibrated state in the central zone of heavy-ion collisions at energies from AGS to RHIC is studied within the microscopic UrQMD model. It is found that the system reaches the (quasi)equilibrium stage for the period of 10-15 fm/c. Within this time the matter in the cell expands nearly isentropically with the entropy to baryon ratio S/A = 150 − 170. Thermodynamic characteristics of the system at AGS and at SPS energies at the endpoints of this stage are very close to the parameters of chemical and thermal freeze-out extracted from the thermal fit to experimental data. Predictions are made for the full RHIC energy √ s = 200 AGeV. The formation of a resonance-rich state at RHIC energies is discussed.Thermalization and chemical equilibration of hot and dense nuclear matter produced in ultrarelativistic heavy-ion collisions is a topic of great importance for the interpretation of current SPS and RHIC results. In our investigation we study the relaxation process in central Au+Au collisions at √ s = 200 AGeV within the microscopic transport UrQMD model [1]. Earlier studies at AGS and SPS energies revealed that the central reaction volume defined by a cubic cell of volume V = 125 fm 3 is well suited for this kind of study [2]. It contains enough particles to be treated as a statistical system, and its macroscopic characteristics become isotropic after some time. Figure 1 depicts the velocity distributions of hadrons in the cell in transverse (x and y) and in longitudinal (z) directions. At t = 3 fm/c the longitudinal velocity distribution differs considerably from the distributions in the transverse plane, while at t = 5 fm/c the magnitudes and widths of all three distributions become very close to each other. Isotropy of the velocity distributions results in the isotropy of pressure in the cell. Pressure in longitudinal and in transverse direction is shown in Fig. 2(a) for AGS, SPS, and RHIC energies. It is widely believed that the thermalization at RHIC sets in quite early. Indeed, at RHIC the pressure in the cell becomes isotropic at t ≈ 5 fm/c compared with t ≈ 8 fm/c (SPS) and t ≈ 10 fm/c (AGS). Starting from t = 5 fm/c the results of the microscopic calculations are compared with the predictions of the statistical model (SM) of an ideal hadron gas [3]. The values of the energy density ε, baryon density ρ B , and strangeness density ρ S , determined
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