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51.
L. Monz R. Hohmann H.-J. Kluge S. Kunze J. Lantzsch E.W. Otten G. Passler P. Senne J. Stenner K. Stratmann K. Swendt K. Zimmer G. Herrmann N. Trautmann K. Walter 《Spectrochimica Acta Part B: Atomic Spectroscopy》1993,48(14):1655-1671
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples. 相似文献
52.
It was investigated, how a chemical reaction was affected by diffusion processes. The analytical solution of the problem is presented for three sample geometries (plate, cylinder, sphere). Furthermore we perform an analysis of the dimensions and get the result, that four dimensionless parameters are essential for the reaction rate. The influence of these parameters on the thermogravimetric curves is discussed and the results are compared with experimental findings. 相似文献
53.
M. Della Negra D. Drijard H.G. Fischer G. Fontaine H. Frehse P. Frenkiel C. Chesquiere R. Gokieli P. Hanke W. Hofmann W. Isenbeck E.E. Kluge V. Korbel D. Linglin A. Minten A. Norton A. Putzer R. Sosnowski D. Wegener 《Physics letters. [Part B]》1976,65(4):394-396
The reaction pp→ppπ+π? at √s=31GeV was studied at the Split Field Magnet Facility of the CERN-ISR. Selecting events with two leading protons of x>0.9 and a rapidity gap Δy>2 between the protons and both pions a sample of 720 events is obtained representing a cross section of 25±10μb. The mass distribution of the dipion system, x and pT distributions for the protons are presented and analyzed for the presence of double pomeron exchange. 相似文献
54.
55.
The polarization of neutrons produced in the reaction12C(d, n 0)13N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV. 相似文献
56.
We report scanning tunneling microscopy observations of Ge deposited on the Si(111)-(7 x 7) surface for a sequence of submonolayer coverages. We demonstrate that Ge atoms replace so-called Si adatoms. Initially, the replacements are random, but distinct patterns emerge and evolve with increasing coverage, until small islands begin to form. Corner adatom sites in the faulted half unit cells are preferred. First-principles density functional calculations find that adatom substitution competes energetically with a high-coordination bridge site, but atoms occupying the latter sites are highly mobile. Thus, the observed structures are indeed more thermodynamically stable. 相似文献
57.
Mukherjee M Kellerbauer A Beck D Blaum K Bollen G Carrel F Delahaye P Dilling J George S Guénaut C Herfurth F Herlert A Kluge HJ Köster U Lunney D Schwarz S Schweikhard L Yazidjian C 《Physical review letters》2004,93(15):150801
Mass measurements with a relative precision of better than 1.5 x 10(-8) were performed on 22Mg and its reaction partners 21Na and 22Na with the ISOLTRAP Penning trap mass spectrometer at CERN, yielding the mass excesses D(22Mg)=-399.92(27) keV, D(21Na)=-2184.71(21) keV, and D(22Na)=-5181.56(16) keV. The importance of these results is twofold. First, a comparative half-life (Ft value) has been obtained for the superallowed beta decay of 22Mg to further test the conserved-vector-current hypothesis. Second, the resonance energy for the 21Na proton capture reaction has been independently determined, allowing direct comparisons of observable gamma radiation in nova explosions with the yield expected from models. 相似文献
58.
We show that thresholds for fault-tolerant quantum computation are solely determined by the quality of single-system operations if one allows for d-dimensional systems with 8 < or = d < or = 32. Each system serves to store one logical qubit and additional auxiliary dimensions are used to create and purify entanglement between systems. Physical, possibly probabilistic two-system operations with error rates up to 2/3 are still tolerable to realize deterministic high-quality two-qubit gates on the logical qubits. The achievable error rate is of the same order of magnitude as of the single-system operations. We investigate possible implementations of our scheme for several physical setups. 相似文献
59.
Line defects of a thin alumina film on NiAl(110) have been studied on the atomic level with scanning tunneling microscopy at 4 K. While boundaries between two reflection domains do not expose a characteristic structure, antiphase domain boundaries are well ordered. The latter boundaries result from the insertion of a row of O atoms, as atomically resolved images of the topmost oxygen layer show. The insertion occurs only in two of the three characteristic directions of the quasihexagonal O lattice. Depending on the direction, either straight or zigzagged boundaries form. An atomic characterization of line defects on the oxide surface is a first step to correlate their topographic structure and chemical activity. 相似文献
60.
Shaikhutdinov ShK Meyer R Lahav D Bäumer M Klüner T Freund HJ 《Physical review letters》2003,91(7):076102
Palladium was vapor deposited on a thin FeO(111) film grown on a Pt(111) substrate. Scanning tunneling microscopy study has revealed that Pd wets the FeO substrate and at elevated temperatures forms extended Pd(111) monolayer islands in contrast to other oxide supports previously studied. For the first time, we have imaged the metal-oxide interface structure with atomic resolution and explained the results on the basis of ab initio calculations. 相似文献