Results 1 - 10 of 64439
Results 1 - 10 of 64439. Search took: 0.06 seconds
|Sort by: date | relevance|
[en] The distribution of energies of low-lying levels of odd-A nuclei from Ag to Ba is analysed. It is shown that this distribution for most levels considered has a discrete character with parameter of multiplicity lying in the range 20-50 keV which varies from nucleus to nucleus. (author)
[en] We present a detailed Moessbauer study of a series of Au and Pt particles in the size range from 1 to 17 nm. All measured spectra can be explained consistently with a refined model, in which the Moessbauer isomer shift varies in the inner core of a small metallic particle due to size effects. The large surface/volume ratio makes surface effects, like screening of considerable importance and even the so-called quantum-size effect may have an influence. The size evolution of the electronic properties of the particles is also discussed
[en] 197Au Moessbauer spectra from Au/TM (TM = Fe, Co, Ni) multilayers consist mainly of two components. One component shows a large hyperfine magnetic field due to the hybridization at the interface between Au and ferromagnetic layers. The other component is nonmagnetic arising from the middle part of the Au layers. From the fractional area of the magnetic components in each spectrum, the Au atoms in 0.4 nm Au layers are perturbed by the Fe and Ni layers, and Co layers perturb 0.3 nm Au layers at the interface
[en] A low energy negative ion implanter facility had been developed at IUAC. The typical ion energies of this facility are in the range of 30 KeV to 200 KeV. It is capable of delivering ion species having masses "1H to "1"9"7Au. The facility is equipped with a sputter base negative ion source namely MC- SNICS (multi cathode -source of negative ion by cesium sputtering) placed on a high voltage platform (200 kV) for generating negative ion beams. The beam line essentially consists of a negative ion source, an accelerating column, focusing devices such as electrostatic quadruple triplets, an analyzer magnet for selecting the particular ion beam as well as transporting in a particular direction and finally, an ion implantation chamber. The analyzer magnet has a maximum rigidity, R =mE/Z"2 of 34 (where m- mass in a.m.u., E- energy in MeV, Z- charge state) thereby, it restricts the energies of the higher mass ions at 150 keV. The ion beam optics for this facility was calculated using GIOS and GICOSY software codes. The control system used for its operation is indigenously developed. The optimized or minimum ion beam spot size obtained is 5 mm x 5 mm (but, variable with ion energy and mass). An electrostatic scanner placed in front of the implantation chamber allows a uniform ion implantation on the samples of sizes up to 15 mm x 15 mm. The facility is in regular operation for ion implantation purposes especially for material science experiments. (author)
[en] As with the k-capture, γ-emission decay of 57Co, the chemical consequences of the isomeric decay of 119Snm can be investigated by the techniques of Moessbauer spectroscopy. The de-excitation of the 245-d 11/2-state occurs by the emission of 65.3-keV (M4) and 23.8-keV (M1-E2) γ-radiation in cascade. Three major chemical effects of nuclear transformations that can be investigated by Moessbauer techniques are: (a) consequences of the 118Sn(n, γ)119Snm process and effects of the concomitant γ-radiation during pile exposure; (b) recoil effects accompanying the M4 decay; and (c) effects of internal conversion of the M4 decay. These effects have been studied in stannic oxide metallic (grey) tin, and tetraphenyl tin, each labelled with the nuclide 119Sn111
[en] With the aim of calibrating Moessbauer spectroscopic measurements, the electric-field gradient and electron contact density is calculated on the Sn nuclear position in a number of Sn compounds representing all kinds of chemical bonding in solids. The full-potential linear-muffin-tin-orbitals method with the local-density approximation for exchange and correlation effects is used. By comparison with experimental 119Sn Moessbauer data the calibration constants relating measured isomer shifts and quadrupole splittings to the electron contact density and the electric-field gradient, respectively, are derived. The difference between the mean square radius of the 119Sn Moessbauer nucleus in its excited isomeric and ground states is found to be Δ left-angle r2 right-angle=(0.0072±0.0002) fm2, while the quadrupole moment of the excited 119Sn(24 keV,3/2+) nuclear state is obtained as |Q|=(12.8±0.7) fm2. The larger database considered and the use of a more accurate band-structure calculational scheme than in earlier works makes these numbers more accurate and provides improved calibration for Moessbauer spectroscopy. copyright 1997 The American Physical Society
[en] Highlights: • A new nuclear quadrupole moment value is determined for xenon. • Four-component calculations with the recently developed RPF-4Z sets are used. • This is indicated as the reference value based on the high level calculations done. This study provides a new determination of the nuclear electric quadrupole moment (NQM) for 131Xe, which is achieved by the molecular method. Dirac-Coulomb Coupled Cluster calculations with a Gaunt correction (DC+G-CC) of electric field gradients (EFGs) and experimental nuclear quadrupole coupling constants of six molecular systems (XeH+, XeCuF, XeCuCl, XeAgF, XeAgCl and XeAuF) were considered. The best NQM obtained by our DC+G-CCSD-T EFGs was −114.6(1.1) mbarn, which is recommended as the new reference value for this nuclide given the high level electron structure calculations done here.
[en] In this paper the factors which are responsible for precision and reliability of the experimental data are discussed. The detectors of different types are compared with respect to the precision of the final results. It is shown that the use of resonance detectors gives the best results in most cases of the Sn-119m Moessbauer spectroscopy. The estimation of spectral line distortion caused by a short distance between source and detector is presented. Different procedures of velocity scale calibration are discussed. It has to be underlined that Kuprijanov's method of the velocity scale calibration gives the most reliable and fast results.
[en] We report on a 197Au Moessbauer study of several types of supported gold catalysts. Differences in particle size show up in the Moessbauer spectra by a change in the relative weight of the spectral contribution of the surface atoms. The presence of ionic gold in active gold catalysts is not observed. The spectra can be interpreted in terms of bulk-like contributions from the inner-core atoms plus contributions from the outermost atoms at the surface of the particles.