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1.
Coherent neutron scattering lengths and total cross sections have been measured on elemental and oxide samples of ordinary Ge and of isotopically enriched substances. From the experimental results the following values were obtained: the coherent scattering lengths (in fm) of the bound atoms Ge(8.185±0.020);70Ge(10.0±0.1);72Ge(8.51±0.10);73Ge(5.02±0.04);74Ge(7.58±0.10) and76Ge(8.2 ±1.5); the absorption cross sections at 0.0253 eV (in barn) for Ge(2.20±0.04);70Ge(2.9±0.2);72Ge(0.8±0.2);73Ge(14.4±0.4) and74Ge(0.4±0.2); the free cross sections for epithermal neutrons and the zero energy scattering cross sections. On the basis of this data, the isotopic- and spin-incoherent cross sections and thes-wave resonance contributions to the coherent scattering lengths have been determined and discussed. Transmission measurements at 0.57 meV on amorphous and crystalline GeO2 yielded for the amorphous sample an inelastic cross section eight times larger than for the crystalline samples. This effect corresponds to a clearly higher density of low energy states in the amorphous than in the crystalline substances. 相似文献
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Total cross section measurements at various neutron energies were performed on metallic and oxide samples of natural Sc, Ti, V, and Mn. By means of the Christiansen filter technique the coherent scattering lengths were determined on natural and isotopically enriched samples of Ti-, V-, and Mn-compounds. From the measured values we deduced the following data: ? the absorption cross sections (at 0.0253 eV in barn) ofnatTi (6.43±0.06) and ofnatV (5.06±0.04); ? the bound coherent scattering lengths (in fm) ofnatTi (?3.370±0.013),46Ti (4.72±0.05),47Ti (3.53±0.07),48Ti (?5.86±0.02),49Ti (0.98±0.05),50Ti (5.88±0.10),natV (?0.443±0.014), and Mn (?3.750±0.018); ? the free potential radii (in fm) of Sc (3.60 ±0.10),46Ti (3.50±0.10),47Ti (3.60±0.10),48Ti (3.90±0.10),49Ti (4.10 ±0.15),50Ti (4.50±0.15),51V (5.20±0.20), and Mn (6.50±20). On the basis of the well known resonance parameters in combination with new fits of bound levels the spin state scattering lengths, the spin incoherence, and the obtained potential radii are discussed. Total cross section calculations were performed by multi-level formalism and are compared with the measurements. 相似文献
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L. Koester K. Knopf W. Waschkowski A. Klüver 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(4):661-668
Coherent neutron scattering lengths and total cross sections have been measured for elemental Zn,Zn-compounds and on isotopicly enriched samples for neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities were obtained: the coherent scattering lengths (b in fm) of Zn (5.689±0.014);64Zn (5.23±0.04);66Zn (5.98±0.05);67Zn (7.58±0.08;b +=9.4±0.5/5.8±0.5;b ?=5.0±0.7/10.1±0.7);68Zn (6.04 ±0.03); the potential scattering radii (R′ in fm) of Zn (6.2±0.2),64Zn (6.0±0.3) and66Zn (6.2 ±0.3); the absorption cross sections (σ γ at 0.025 eV in barn) of Zn (1.11±0.02);64Zn (1.1 ±0.1) and66Zn (0.62±0.06). Derived quantities are the “zero energy” scattering cross sections (σ 0 in barn) for Zn (4.128±0.010) and67Zn (7.8±0.3) and the incoherent bound cross sections of Zn (0.061 ±0.023) and67Zn (0.6±0.4). In the epithermal region the Zn-cross section can be described by introduction of two strong bound levels of67Zn+n for which estimated parameters are given. 相似文献
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Carolyn J. Koester James F. Blankenship Patrick M. Grant 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):2015-2019
Using cyanoacrylate or “superglue” fuming to develop latent dermatoglyphic prints significantly altered the volatile and semivolatile compounds within the material of polyethylene zip-lock bags. Comparisons of SPME-GC/MS analyses of poly bags obtained before and after application of a glue fuming fingermark-developing technique resulted in markedly different material profiles of the bags. Not only were species added to the chemical composition of a bag, but other compounds that had been initially present were removed. These effects are particularly important for nuclear forensic investigations in the realm of route (pathway) analyses, and may also be of general interest to criminalistics laboratories that examine illicit drugs and their packaging. 相似文献
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In117Te,119Te and121Te isomeric states withJ π=5/2+, 5/2+ and 7/2+ and half-lives of 19.1(9)ns, 2.2(2) ns and 86(6) ns, respectively, have been identified at low excitation energies using (α, 2n) reactions on enriched115–119Sn targets. Positive parityΔJ=1 bands built on these isomeric states have been observed up to 17/2+. The states are interpreted as members of rotational bands built on deformation driving 5/2+ [402] and 7/2+ [404] Nilsson orbitals which overcome theN=64 subshell gap. The irregular level spacings and electromagnetic properties of the bands are well explained in Coriolis calculations. The moment of inertia parameter as function of collective angular momentum has been derived from the doubly even Te cores. The hindrance of the band head deexcitation may be caused by shape fluctuations of these transitional nuclei. 相似文献
10.
Stereocontrolled Synthesis of Vinyl Boronates and Vinyl Silanes via Atom‐Economical Ruthenium‐Catalyzed Alkene–Alkyne Coupling
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Prof. Dr. Barry M. Trost Dr. Dennis C. Koester Alastair N. Herron 《Angewandte Chemie (International ed. in English)》2015,54(52):15863-15866
The synthesis of vinyl boronates and vinyl silanes was achieved by employing a Ru‐catalyzed alkene–alkyne coupling reaction of allyl boronates or allyl silanes with various alkynes. The double bond geometry in the generated vinyl boronates can be remotely controlled by the juxtaposing boron‐ and silicon groups on the alkyne substrate. The synthetic utility of the coupling products has been demonstrated in a variety of synthetic transformations, including iterative cross‐coupling reactions, and a Chan‐Lam‐type allyloxylation followed by a Claisen rearrangement. A sequential one‐pot alkene‐alkyne‐coupling/allylation‐sequence with an aldehyde to deliver a highly complex α‐silyl‐β‐hydroxy olefin with a handle for further functionalization was also realized. 相似文献