Der Beugungseffekt bei der elastischen Streuung von Ionenstrahlen an Atomen

For the elastic scattering of ion beams at atoms the diffraction of the matter wave at the atom can be observed in the region of small scattering angles and high energies. The diffraction causes undulations in the differential scattering cross section. In this paper a general solution of the diffraction effect is given. The solution holds for the Yukawa type screened Coulomb potential which is well suited for the small angle scattering of-ions at atoms and which contains two parameters. The computations have been made using the partial wave method and the Jeffreys-Born-approximation for the scattering phase shifts. The solution is presented in a form in which the amplitudes and characteristic constants of the first four undulation maxima and minima are given in dependence of a product which contains one of the potential parameters. The characteristic constants are correlated in a characteristic equation with the second potential parameter and the positions of the diffraction extrema. The conditions for the appearance of the diffraction effect are discussed.     

Bestimmung der statischen Strukturfunktion von Natrium bei 102 und 149°C

X-ray measurements of the structure functionS(q) on high purity sodium (99.99%) are reported. Data were taken at 102 and 149 °C. An analysis of that part of the curve, in the regionq≦2k _F shows some deviations from the neutron measurements of Gingrich and Heaton. Better agreement is obtained with the experimental values of Orton, Shaw and Williams and with the theoretical “hard core” curve of Ashcroft and Lekner. Using two temperature-dependent pseudopotentials (Schneider and Stoll, Ashcroft) the electrical resistivity is calculated using the conductivity formula of Ziman. These results are generally about 2/3 of the experimental value. This is attributed either to an incorrect atomic form factor of sodium or to an inaccurately known pseudopotential. The measurements confirm Greenfield's determination of the ratio Γ_{146°c/102°c}(q). As a test of the general form ofS(q) curves the radial distribution function is calculated and discussed.     

Elastische und unelastische Streuung von Deuteronen an Aluminium bei 11,8 MeV

Using the 11.8 MeV deuteron beam of a cyclotron, a study has been made of the angular dependence of the deuteron spectrum from interactions on Al²⁷. Separation of the deuterons from other products of the deuteron reactions was accomplished by recordingdE/dx, measured by a three fold proportional counter, andE, measured by a CsI-counter, on an oscilloscope screen. The experimental inelastic angular distributions have the shape of a direct interaction process. The elastic angular distribution shows pronounced diffraction maxima.     

Zur Berechnung von Geometriefaktoren bei der Kernstrahlungsmessung

Der Geometriefaktor von radioaktiven umschlossenen oder offenen Strahlenquellen hängt bei der Messung mittels einer Kernstrahlungsmeßsonde von der räumlichen Anordnung der Strahlenquelle zu der strahlenexponierten wirksamen Fläche des Detektors und von der Geometrie der Strahlenquelle selbst ab. Fūr punktförmige Strahler in verschiedenen Positionen, Geraden, Kreisflächen und Zylinder wurde in möglichst einheitlicher Vorgehensweise die Berechnung der Geometriefaktoren bezüglich kreisförmiger ebener Detektionsflächen vorgenommen und rechentechnisch in Form von BESM 6-Algolprogrammen realisiert. Die Berechnungsergebnisse sind untereinander konsistent und wurden möglichst durch unabhängige Verfahren oder experimentelle Werte kontrolliert. Die Rechengenauigkeit kann gemäß den vorliegenden Anforderungen frei gewählt werden.     

Streuung von Licht an rauhen Oberflächen bei der Anregung von Oberflächenplasmonen

The electromagnetic theory, which explains the scattering of light from a rough surface of a metal foil by means of normale surface currents, is extended to the case of arbitrary directions of this currents. This allows to calculate the scattered intensity ofp ands polarised light in all directions. It is shown that the excitation of surface plasmons (“radiative” and “non radiative”) can produce a characteristic maximum in the scattered light. Detailed calculations for silver foils deposited on a quartz hemisphere are presented and compared with experiments. Furthermore the theory is applied to calculate the decrease in the reflection at frequences near the surface plasma frequenceΩ _s .     

Berechnung der Besetzungsdichte und Ausgangsleistung von Ionenlasern

Rate equations for the density of excited ions in noble gas discharges are solved for the steady state. The atomistic parameters in the theoretical treatment are replaced by experimental values. Hence inversion density and single pass gain can be calculated as a function of gas pressure, discharge current and geometry of the discharge tube. Conditions for maximum inversion density and power output are calculated and compared with experimentally determined values. The calculation is pointing out large bored tubes to be advantageous for high power operation. Numerical evaluations are particularily given for theA ⁺ line 4880 AU.     

Untersuchung der Gammastrahlung aus der unelastischen Streuung von 2,75 MeV-Neutronen an203Tl und205Tl

γ-spectra from the (n, n′ γ) reaction of 2.75 MeV neutrons of natural Tl and enriched²⁰³Tl were measured with Ge(Li) detectors. By means of these measurements about 120γ-lines could be assigned to either of the two isotopes. About half of the lines — however accounting for more than 80% of the totalγ-intensity — could be incorporated into the respective decay schemes, which could be extended in this way. Additionally, for a number of levels already known more accurate level energies could be determined. Comparison of the results with Hauser-Feshbach calculations leads to discrepancies which cannot be removed completely by variation of the model parameters within acceptable limits.     

Die Polarisation der von 0,5, 1 und 2 MeV-Elektronen erzeugten Čerenkov-Strahlung

The theory of ?erenkov radiation predicts a virtually complete linear polarisation of the emitted radiation. In disagreement to this results measurements have always given a large amount of unpolarized light. With an improved geometry that avoids the influence of light quanta resulting from scattered electrons it was possible to show that the ?erenkov radiation is practically complete linear polarized. The contribution of szintillation quanta to the remaining rest of unpolarised light has been estimated.     

Elastische Streuung von Deuteronen an10B bei niedrigen Energien

The excitation curve for the elastic scattering of deuterons from¹⁰B in the energy range from 1.0 to 2.0 MeV has been measured atθ _L =135°. Strong indications for compound nucleus resonances in¹²C at bombarding energies of approximately 1.0 and 1.9 MeV were observed. Angular distributions from 80 to 175° were determined in 200 keV steps from 1.0 to 2.0 MeV. Optical model analysis were made both for volume absorption and surface absorption potentials. Reasonable fits were obtained at energies up to 1.6 MeV with one set of parameters in both cases, whilst for the higher energies strong deviations were found with the same parameters.     

Theorie der galvanomagnetischen Erscheinungen bei beliebigen Energieflächen und anisotroper Streuung der Leitungselektronen

A theory of the galvano-magnetic phenomena of conduction electrons is presented for the case of weak magnetic fields, allowing any energy band structure and any anisotropic scattering mechanism. In order to solve the Boltzmann transport equation an iteration — variation —procedure is developed. It is shown that the variety of trial functions can be restricted considerably by taking into account the point symmetry of the problem. Equations for the phenomenological constants are derived for crystals of octahedral symmetry. The theory, simplified for spherical energy surfaces, is used to calculate the temperature dependence of the galvano-magnetic constants of Na and K.     

Elastische und unelastische Streuung von Deuteronen an Sr,Zr, Nb,Pd und Ag bei 11,8 MeV

Continuing previous experiments on the elastic and inelastic scattering of 11·8MeV deuterons on medium weight nuclei, Sr, Zr, Nb, Pd, and Ag targets have been studied. In addition to elastically scattered deuterons, angular distributions of inelastically scattered deuterons have been obtained for one group in Sr, and three groups in Zr and Nb, respectively, between 20° and 165°. The correlation between the diffraction maxima is discussed in terms ofBlair's phase rule. As in our previous results, this rule works poorly in the comparison between elastic and inelastic angular distributions. However the strongly excited inelastic groups which are interpreted as collective vibrational states do follow this rule. In the case of Pd and Ag, energy spectra at several scattering angles have been measured. The integrated differential cross sections of the inelastically scattered deuterons atΘ=90° of all investigated elements are compared with those of previous measurements. They show the influence of closed shells but no systematic decrease or increase with increasing atomic weight.     

Radiometrische Bestimmung der optimalen Bsdingungen bei der Absorption von Ameisensäure und Methanol am Rieselfilm aus einem Stickstoffstrom

Es wurde eine Methodik zur Bestimmung des Absorptions-koeffizienten β = C_flüssig/C _gas (C bedeuten die Konzentrationen des Absorbats) für den Stoffübergang in einer Rieselfilmkolonne ausgearbeitet, die mit Hilfe der Messung von ¹⁴C-markierten Substanzen die Unterschung kleinster Konzentrationsbereiche gestattet. Die Abhängigkeit von β vom Gas- und Flüssigkeitsdurchsatz, von der Temperatur and von der Konzentration der an Glykolhalbacetal zu sorbierenden Stoffe Methanol und Ameisensäure wurde in orientierenden Experimenten bestimmt.