Localized phonons in Pb—Tl—In and Pb—Tl—Bi—In studied by superconducting tunneling

Superconducting tunneling was used to obtain the phonon density of states ²()F() associated with high frequency localized phonons in (Pb_1–x Tl _x )_0.96In_0.04 (0<x<0.6), (Pb_0.5Tl_0.5)_0.88In_0.12 and (Pb_0.70Tl_0.15Bi_0.15)_0.96In_0.04. ²()F () from impurities can be described as three superimposed peaks. One of the peaks appears only when Tl is present. The main peak has the same width in (Pb_1–x Tl _x )_0.96In_0.04 as in Pb_0.96In_0.04, but is much broader in (Pb_0.70Tl_0.15Bi_0.15)_0.96In_0.04. The electron-phonon coupling _loc ² of the localized phonons is well below the mean ² of the full spectrum for all alloys in general and for (Pb_0.70Tl_0.15Bi_0.15)_0.96In_0.04 in particular.     

Energieverlustmessungen von schnellen Elektronen an Oberflächen von Ga,In, Al und Si

The excitation of surface plasmons on liquid indium, gallium and aluminum surfaces as well as on silicon cleavage faces is studied by reflection of 10 keV electrons at grazing incidence (80° up to 89°). Due to the high excitation probability of surface plasmons at these large angles of incidence multiples of surface plasmons are observed. (Except on Si.) The Poisson distribution of the intensity of these energy losses is verified quantitatively as well as the dependence on (cos)^–1. The value of the excitation probability indicates that at grazing incidence the electrons are reflected just at the surface without penetrating into the volume. This is further demonstrated by the lack of volume plasmons. The surface loss positions in the solid and the liquid state show the calculated differences due to the density difference of both phases     

Mittlere Energien und Driftgeschwindigkeiten von Elektronen in Stickstoff,Argon und Xenon,ermittelt aus Bildverstärkeraufnahmen von Elektronenlawinen

Local and temporal development of electron avalanches in a pulsed discharge gap (d=3,00 cm) are investigated in N₂, Ar, Xe and mixtures of N₂ and CH₄ by simultaneously applying high gain image intensifier- and photomultiplier techniques. Electron drift velocities are obtained from time-of-flight and way-of-flight measurements in these gases. The mean energy of agitation of the electrons is derived both from electron mobility and avalanche image trace profile (diffusion broadening). The results obtained (for 20°C), being in fair agreement with one another, read N₂: (4·6...5·0) eV forE/p=50...200 V/cm Torr; Ar: (9·0...9·5) eV forE/p=24... 45 V/cm Torr; Xe: (4·8...5·0) eV forE/p= 40... 90 V/cm Torr; CH₄(10% N₂): 6·3 eV forE/p= 89 V/cm Torr. The mean energy of agitation does not change very much withE/p in the ranges investigated. Some results concerning the radiation properties of these gases are included such as lifetime of the excited states, quenching pressure etc.     

Halbwertszeit,Elektroneneinfangverhältnis und β-Spektrum des Tl204

Half-life,P _L /P _K -capture ratio andβ-spectrum of Tl²⁰⁴ were studied with a scintillation spectrometer. To avoid source absorption and scattering troubles, the Tl²⁰⁴ source was built in in the lattice of NaJ(Tl)-crystals. The half-life measurements were performed over a period of 2,2 years, and we obtained a half-life of 3.81±0.04 years. TheP _L /P _K -capture ratio was determined at 0.41±0.03. This ratio gives a desintegration energy of 442 _?24 ⁺³⁰ keV for the unique first forbidden electron capture decay of Tl²⁰⁴. For the branching ratio of electron capture toβ ^?-decay we found a value of (2.15±0.06)% and for the ratio ofK-capture toβ ^?-decay a value of (1.53±0.05)%. Theβ ^?-spectrum of Tl²⁰⁴ was measured from 200 down to 6 keV and yields an experimental shape factor which deviates below an energy of ～90 keV from the theoretical shape factorq ² L ₀+9L ₁. Reasons for this deviation which is opposite to the one obtained with magnetic spectrometers are discussed.     

Verzweigungsverhältnisse undβ +-Maximalenergie beim Zerfall von Ag108

The branching ratios of Ag¹⁰⁸ have been remeasured with scintillation spectrometers. There is evidence for a weak 177 keV-β ^?-branch going to the 1473 keV level of Cd¹⁰⁸, followed by aγ-γ-cascade of (841+632)keV. Spin and parity 2+ of this level are supported by logft=4.7 of theβ ^?-branch. Theβ ⁺-spectrum has been measured for the first time yielding an end point energy of (880±25)keV, in agreement with the value derived from theK/β ⁺ratio.     

Production of fragments withA≧16 in interactions of 6.3 GeV deuterons with Th,Bi, Au,and Ag

Polycarbonate track detector Makrofol, sensitive to fragments withA16 was used to register products of interactions of 6.3 GeV deuterons with Th, Bi, Au, and Ag. Cross sections for the production of events with one, two and three fragments have been determined and their variation as a function of theZ ²/A of the target analyzed. Possible mechanisms were proposed and discussed. Geometric characteristics of binary events were used in order to identify those binary events which resulted from the process of fission. The results were compared with corresponding proton data.We are grateful to Profs. A. M. Baldin and I. N. Semenyuskin for the exposure of the detectors and for measurement of the flux. We are also thankful to the technical staff of our Laboratory for accurate measurements.     

Anregung und Schädigung der Lumineszenz von CaWO4 und ZnS/Ag durch Ionen

The luminescence-response of ZnS/Ag and CaWO₄ to ion-bombardement and the deterioration of luminescence under prolonged irradiation was determined as a function of ion-energyE, ion-massM _i and beam-densityI. The variation of lightoutput with ion-energy is of the formJ ₀=C. (E-E ₀) ⁿ withn=2 (ZnS/Ag) or lower values (CaWO₄). The luminescence-response to ions of various mass was found to decrease generally with growing mass, but to be nearly constant to ions of middle atomic weight (ZnS/Ag). The luminescence-efficiency, caused by ions of energy greater than 5 keV, is independent of beam-density within the whole range studied here (maximum 3 · 10^?7 A · cm^?2), but it diminishes in the caseE=5 keV for values ofI above 6 · 10^?8 A · cm^?2. The deterioration-effect grows, except in the case of He⁺-ions, the lightest ions used here, with ion-energy. It also increases by substituting Ne⁺- for He⁺-ions, but remains nearly independent of mass (CaWO₄) or diminishes with growing ion-mass (ZnS/Ag), if the ions are heavier than Ne⁺-ions. Increasing beam-density leads to a reduced deterioration of ZnS/Ag-luminescence, yet has no influence to that of CaWO₄.