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31.
I. Espe B. Skaali P. O. Tjøm S. M. Lee M. Rozkoš B. Elbek 《Czechoslovak Journal of Physics》1980,30(4):395-416
The experimental data have been compared with the result of extensive compound nucleus calculations based on the statistical theory. The shapes and the absolute cross sections for the high energy parts of the proton- and -spectra are reproduced with a level density parametera 0·11 A MeV–1 and a moment of inertiaJ1·3J
rig. The same parameters fairly well reproduce the angular distributions corresponding to the high energy parts of the spectra whereas deviations between theory and experiment are observed for the lower energies where particles emitted by higher order processes contribute. The observed total cross section for emission of an -particle is 500 mb or 1·7 times calculated value. For protons the corresponding numbers are 2313 mb and 3·0. The increase in cross section is ascribed to the process in which several particles are evaporated. Various methods are discussed for determination of the average orbital angular momentum of the emitted particle or the average spin of the daughter nucleus.On leave fromFaculty of Matematics and Physics, Charles University, Prague, Czechoslovakia. 相似文献
32.
J. W. Petersen G. Weyer S. Damgaard H. L. Nielsen 《Zeitschrift für Physik B Condensed Matter》1980,38(4):313-326
Single crystalline and polycrystalline -tin has been implanted at room temperature with 80-keV ions of radioactive119m
Sn,119Sb, and119m
Te. The radioactive nuclei decay to the Mössbauer level of119Sn. Mössbauer spectra of the emitted 24-keV radiation have been measured for different source temperatures by resonance counting techniques. Five individual lines in the spectra are characterized mainly by their isomer shifts and Debye temperatures. From these parameters the radiogenic119Sn atoms are concluded to be located in regular substitutional and interstitial lattice sites and in defect complexes. Simple models for the defects are proposed: A Sn-vacancy pair consists of Sn atoms on (nearly) substitutional sites with a dangling bond into an adjacent vacancy. In a complex oxygen-containing defect the Sn atoms have approximately a 5s
2 configuration withp-bonds to two nearest neighbour atoms. Sn atoms, having an atomic 5s
2 5p
2 configuration and large vibrational amplitudes, are concluded to be in non-bonding regular interstitial sites. For special implantation conditions minor fractions of SnO2 molecules are formed in the bulk. The interstitial119Sn and the119Sn-vacancy pairs are proposed to represent elementary point defects in -tin. Conclusions are also drawn concerning the lattice location and the defects created in the implantation process of the implanted parent isotopes. 相似文献
33.
The addition of stannylcuprate reagents such as (Bu3Sn)(PhS)CuLi to alkynones has been found to proceed in high yield and with excellent stereoselectivity for the Z isomer of the product (>95%). The behavior of the stannylcuprates is thus very different from that of their "carbocuprate" counterparts such as Me2CuLi or Me2Cu(CN)Li2 which are nonstereoselective. Furthermore, in contrast to the reactions of (R3Sn)(PhS)CuLi with the corresponding alkynoates, the presence of a proton source in the reaction medium has no effect on the stereoselectivity of the reaction of alkynones. 相似文献
34.
The NaF-AlF(3) system with additions of CaF(2) and MgF(2) has been studied with Raman and vapor pressure measurements for 3 >/= CR (NaF/AlF(3) molar ratio) >/= 1 and up to 50 mol % additive. The results show that the binary melt can be described using the two equilibria AlF(6)(3)(-) = AlF(6)(2)(-) + F(-) and AlF(5)(2)(-) = AlF(4)(-) + F(-) with equilibrium constants 0.25 and 0.05, respectively, at 1293 K. Both reactions have positive reaction enthalpies. The first equilibrium is strongly shifted to the right resulting in a melt mixture with very low AlF(6)(3)(-) concentrations even at the Na(3)AlF(6) composition. Evidence for nonideal mixing of anions was found. For the ternaries, models based on Raman data are presented and compared with vapor pressure measurements. Good agreement is observed when association between the additives, CaF(2) or MgF(2), with the AlF(5)(2)(-) ions in the melt was considered. This association could be experimentally observed through a band broadening and a slight shift in the AlF(5)(2)(-) band frequency. Our vapor pressures and Raman data both indicate that MgF(2) clearly acts as an acid when added to NaF-AlF(3) melts of any composition. When CaF(2) is added, a slight decrease of vapor pressure occurs. Raman data indicate a decrease of AlF(4)(-) concentration, corresponding to a dissociation of CaF(2) with liberation of F(-) ions. All these results are, however, very much dependent on the initial melt composition. These data are explained in terms of acid-base, dilution, and association reactions of the solute with the solvent. 相似文献
35.
Crystalline samples of La3Ni2B2N3 were synthesized using solid state metathesis reactions from combinations of La, LaCl3, NiCl2 together with Li3BN2. The structure was determined by single crystal X‐ray diffraction (I4/mmm (No. 139), a = 372.95(2) pm, c = 2056.3(2) pm, R1 = 0.027, wR2 = 0.062) and confirmed earlier results from neutron powder diffraction. La3Ni2B2N3 contains BN units capping square planar Ni layers. Isolated nitrogen atoms reside in La6 octahedra. Magnetic measurements on several bulk samples exhibit superconductivity at temperatures below 14.6 K. 相似文献
36.
Characteristic partial structures of lipidated proteins embodying different lipid groups as well as additional fluorescent tags or a maleimide for coupling to proteins can be synthesized readily by means of a new solid-phase technique employing the oxidative cleavage of the hydrazide linker as well as on-resin farnesylation and palmitoylation after appropriate deprotection of cysteine thiol groups as the key steps. 相似文献
37.
Analyzing a gliadin extract by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) combined with an artificial neural network (ANN) is a suitable method for identification of wheat varieties. However, the ANN can not distinguish between all different wheat varieties. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to three pairs of wheat varieties, which can not be classified correctly by ANN. By 2-D PAGE the varieties in the three pairs can be discriminated and these six wheat varieties can be separated from each other, which could not be separated by MALDI-TOF-MS and NN. 相似文献
38.
Harald Høiland 《Journal of solution chemistry》1977,6(5):291-297
The isentropic coefficients of compressibility of the homologous series of alcohols and diols R
n
CH2OH (n=2–6), CH3CHOHR
n
(n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC. 相似文献
39.
Photomobilization of trapped electrons in 7 M NaClO4- and 9 M NaOH-glass gives rise to trapped hydrogen atoms. This is probably due to the reaction e?m + H2O → H + OH?. Experiments with an electron scavenger indicate that electrons are not precursors to radiolytically produced hydrogen atoms. It seems that the mobile electrons produced during photobleaching are not slowed down to thermal energy before they react to produce hydrogen atoms, since the yield of the latter species is strongly dependent on the wavelength of the bleaching light. 相似文献
40.
Jörn Manz 《Chemical physics》1977,24(1):51-64
Energy stored in vibrational level ν = 1 of several individual dipolar diatomic molecules AB which are trapped in a rare gas matrix M is automatically accumulated in a higher level ν > 1 of a single molecule AB. This remarkable cascade of energy upwards competes with a cascade of energy downwards. the radiative decay. The interplay of both cascades, first observed by Dubost and Charneau, is explained a simple model. The model incorporates three processes into a master equation for the relative populations Pν(t) of levels ν: (a) migration of single quanta by resonance energy transfer, AB(1) + AB(0) ? AB(0) + AB(1); (b) phonon assisted excitation of upper levels, AB(1) + AB(ν) → AB(0) + AB(ν+1); and (c) radiative decay, AB(ν) → AB(ν-1). The model assumes that there is only one isotopic species AB which has a small but nonzero vibrational anharmonicity, that the temperature is low, T → 0 K, the concentration ratio ?M/?AB is large and that, initially, at time t = 0, a small fraction p1 of molecules AB is excited to level ν = 1. The master equation has only two parameters, the radiative lifetime trad and k 2/[?AB?1k(1,1 → 0,2)trad], where k(1,1 → 0,2) is the reference rate constant of process (b). The master equation is solved in closed form for the Pν(t). For trad = 14 ms and k = 0.2, very satisfactory qualitative agreement is found for the theoretical Pν(t) and the experimental time evolution of the relative population of vibrational levels of 12C16O in an argon matrix, for ?M/?AB = 2000 at T = 9 K. In agreement with experimental results it is concluded that the risetime of the fluorescence signals decreases whereas population inversion increases for decreasing values of ?M/?AB. At long times, t > trad, any population inversion should disappear. 相似文献