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991.
Bockhorst M. Burbach G. Burgwinkel R. Empt J. Guse B. Guse B. Haas K. -M. Hannappel J. Heinloth K. Hey T. Hoffmann-Rothe P. Honscheid K. Jahnen T. Jakob H. P. Jöpen N. Jüngst H. Kirch U. Klein F. -J. Kostrewa D. Lindemann L. Link J. Manns J. Menze D. Merkel H. Merkel R. Neuerburg W. Paul E. Plötzke R. Schenk U. Schmidt S. Scholmann J. Schütz P. Schultz-Coulon H. -C. Schweitzer M. Schwille W. J. Tran M. -Q. Umlauf G. Vogl W. Wedemeyer R. Wehnes F. Wißkirchen J. Wolf A. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):37-47
The reactions pK
+ and pK
+ 0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the 0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and 0 is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I 相似文献
992.
P. Abreu W. Adam T. Adye E. Agasi R. Aleksan G. D. Alekseev P. Allport S. Almehed F. M. L. Almeida Junior S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):3-15
The average lifetime ofB hadrons was measured using data collected with the DELPHI detector at the LEP collider during 1991 and 1992. The measurement was performed using two different anayses. The first method was an improvement on a previous technique, which used charged particle impact parameter distributions. This analysis measured an average lifetime forB hadrons of
相似文献
993.
P. Abreu W. Adam T. Adye E. Agasi R. Aleksan G. D. Alekseev A. Algeri S. Almehed S. J. Alvsvaag U. Amaldi et al. 《Zeitschrift fur Physik C Particles and Fields》1994,61(3):407-419
The study of the properties of inclusive production ofD
s
mesons and of events in which a and a muon are present in the same jet provides two independent measurements of the probability,f
s
w
, for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ
0 decays. The combined value of these measurements isf
s
w
=0.19±0.06±0.08. From the flight distance distributions ofD
s and of (-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB
s
0
meson lifetime. Combining these measurements with a previous result based on the study ofD
s- events, theB
s
0
meson lifetime is measured to be: 0.96±0.37 ps. 相似文献
994.
W. D. Wu A. Keren L. P. Le G. M. Luke B. J. Sternlieb Y. J. Uemura D. C. Johnston B. K. Cho P. Gehring 《Hyperfine Interactions》1994,86(1):615-621
Muon spin relaxation (SR) studies have been performed in the normal spinel LiTi2O4 and the A-15 superconductor V3Si to measure the magnetic penetration depth . The relaxation rate(T) 1/2 in field-cooled measurements shows a sharp increase belowT
c
followed by saturation at low temperatures in both systems. This feature implies an isotropic energy gap without anomalous zeros, and most likelys-wave pairing. The low temperature penetration depth (T 0) is determined to be 2100Å for LiTi2O4 and 1300Å for V3Si respectively. Assuming a clean limit relation –2 n
s
/m
*, we derive the Fermi temperatureT
F
n
s/
2/3
m
* from the relaxation rate and the Sommerfeld constant asT
F
3/4–1/4. Unlike conventional superconductors, both LiTi2O4 and V3Si have a large ratio ofT
c
/T
F
0.01, only slightly smaller than those ratios in more exotic superconductors.We thank C. Ballard and K. Hoyle for technical assistance. Work at Columbia University is supported by NSF Grant No. DMR-89-13784 and Packard Foundation (YJU). Ames Laboratory is operated for the U. S. Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. Work at Ames was supported by the Director for Energy Research, Office of Basic Energy Sciences. 相似文献
995.
Reactions of ferrocene (C5H5)2Fe with halogenated fullerenes C60X
n
for X=F, Cl, Br andn = 15–39) yield non-stoichiometric solids with intense singlet Mössbauer spectra characteristic of Cp2Fe+ (where Cp=C5H5). The material isolated from reaction of Cp2Fe with C60Br24 exhibits two different iron environments and magnetic ordering temperatures of 14 K and between 4.6 and 1.32 K. These data are seen to be consistent with loss of bromine from the fullerene and formation of ferricenium tetrahaloferrate salts. 相似文献
996.
R. F. Kiefl J. Sonier D. A. Bonn J. H. Brewer J. F. Carolan K. H. Chow P. Dosanjh W. N. Hardy Ruixing Liang W. A. MacFarlane P. Mendels G. D. Morris T. M. Riseman J. W. Schneider 《Hyperfine Interactions》1994,86(1):537-542
We report precision transverse fieldSR measurements of the internal field distribution in the vortex state of crystalline YBa2Cu3O6.95. A novel low background apparatus was used to study a mosaic sample of three high quality single crystals (Tc=93.3K). The observed frequency spectra in magnetic fields of 5kG and 15 kG applied along the c-axis have the characteristic features expected for a regular vortex lattice with some additional broadening. From a preliminary analysis we find that [(0)/(T)]2 has a linear temperature coefficient forT<30 K. Such a term is inconsistent with simple s-wave pairing in the superconducting state. These results support recent microwave measurements of(T) on similar crystals in zero applied field but differ significantly from previousSR reports on sintered powders and crystals with lower Tc.This research was supported by the Natural Sciences and Engineering Research Council of Canada. 相似文献
997.
Monocationic forms of the symmetric and asymmetric indacene bridged species [(Cp*Fe)2(-s-indacene)],I, and [(Cp*Fe)2(-as-indacene)],II, are fully detrapped and trapped, respectively, over the entire range from 1.5 K to ambient temperature as their BF
4
–
salts. In contrast to [II
+][BF
4
–
], the TCNE.– salt [II
+][TCNE.–] exhibits a transition from fully trapped to a largely detrapped valence state behaviour over the increasing temperature range 100 to 300 K. Mössbauer spectra ofI suggest that while it is relatively insensitive to oxygen as a neat solid, it is strongly oxidized by O2 in dry hexane solution. Similar studies ofII indicate essential insensitivity to O2, both as a solid and in hexane solution. 相似文献
998.
R. L. Lichti K. H. Chow D. W. Cooke S. F. J. Cox E. A. Davis R. C. DuVarney T. L. Estle B. Hitti S. R. Kreitzman R. Macrae C. Schwab A. Singh 《Hyperfine Interactions》1994,86(1):711-716
Longitudinal-field muon-spin depolarization rates in high-purityGe and semiinsulatingGaAs are reported and compared to similar data for intrinsicSi. Depolarization onset temperatures provide a comparison of charge carrier concentrations leading to rapid charge exchange and a shift in the onset, for n-typeGaAs verifies anelectron process. The temperature dependence of the low-field rate constants imply more complicated dynamics inGe than observed earlier inSi. Features near 750K inGaAsTe appear consistent with dissociation of aMu-Te pair.This work was supported by the US National Science Foundation (DMR-8917639 [TLE, BH]), the Science and Engineering Research Council of the UK (EAD, AS, SFJC), the Robert A. Welch Foundation (D-1053 [RLL], and C-1048 [TLE]), and a NATO Collaborative Research Grant (RLL, SFJC, RCD, CS). We wish to thank D.A. Vanderwater of Hewlett Packard for providing theGaAsTe sample. 相似文献
999.
H. Reuther O. Nikolov S. Kruijer R. A. Brand W. Keune D. Liljequist S. Weber S. Scherrer 《Hyperfine Interactions》1994,92(1):1367-1372
-Fe surfaces were implanted with a nominal dose of 5×1017 Al ions/cm2 at 50 keV and a current density of about 3.7 A/cm2. Samples of different shapes and thicknesses have been used in order to test the influence of heat flow from specimen to target holder during implantation. Integral and energy differential (depth-selective)57Fe conversion electron Mössbauer spectroscopy (CEMS and DCEMS) were employed. The spectra indicated a magnetic phase characterised by a broad hyperfine field distributionP(B
hf), a non-magnetic phase, and -Fe. The relative intensity of the non-magnetic phase was enhanced if the thermal contact during implantation became worse. An energy dependence of DCEM spectra in the L-electron range was observed. Model calculations using L-electron weight functions and experimental concentration profiles obtained by secondary neutral mass spectroscopy (SNMS) yielded fair agreement between calculated and experimental phase signals. The results demonstrate that the non-magnetic Fe-Al alloy phase with high Al concentration is located closer to the surface than the magnetic alloy phase, which extends to much larger depth than expected. 相似文献
1000.
Detailed studies have been made of elastic scattering and positronium formation in low energy collisions of positrons with lithium atoms for the two partial wavesl=0,1. For this system, as for all alkali atoms, the positronium formation channel is open even at zero positron energy. A two-channel version of the Kohn variational method is used with trial functions containing many variational parameters, and reasonably well converged results are obtained. The s-wave positronium formation cross section is infinite at zero positron energy but it then falls rapidly to become several orders of magnitude smaller than the elastic scattering cross section which has a maximum value of approximately 100
0
2
at a positron energy of 0.5 eV. For p-wave scattering the positronium formation cross section rises to a value of approximately 10
0
2
at an energy of 0.1 eV, with the elastic scattering cross section rising to a maximum of approximately 60
0
2
just below the first excitation threshold at 1.84 eV. 相似文献
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