The tilted-multifoil hyperfine interaction and nuclear spectroscopy

Ions emerging from a stretched foil with their velocity vectorv at an oblique angle to the normaln (tilted foil geometry) are known to be polarized along the axisv×n. The electronic polarization of atomic configurations can influence the nucleus during flight in vacuum via the hyperfine interaction. For a large number of polarizing foils and for very short interaction times, the resulting effects resemble a pure precession in an external magnetic field and have been used to measureg-factors of short-lived nuclear high-spin levels. For long interaction times, a net nuclear polarization is induced and has so far been utilized to determine signs of nuclear quadrupole moments of high-spin isomers and to investigate parity nonconservation effects in⁹³Tc.     

Construction of conducting and photoconducting 3D structures with submicron resolution in electrooptical substrates

It is shown that the implantation of protons in electrooptical substrates enables the construction of 3D structures with submicron features that are both conductive and photoconductive embedded in amorphized regions that possess reduced refractive index. The conductivity and photoconductivity are attributed to the transformation of the material into a degenerate semiconductor due to the formation of high concentration of OH⁻ complexes that are created by the bonding of the implanted H⁺ ions to the O⁻² ions of the lattice. It is argued that these results extend significantly the capabilities of integrated photonic circuits and devices fabricated by Refractive Index Engineering by ion implantations.     

Density functional theory of transition metal phthalocyanines,I: electronic structure of NiPc and CoPc—self-interaction effects

We present a two-part systematic density functional theory study of the electronic structure of selected transition metal phthalocyanines. We use a semi-local generalized gradient approximation (GGA) functional, as well as several hybrid exchange-correlation functionals, and compare the results to experimental photoemission data. Here, we study the low-spin systems NiPc and CoPc. We show that hybrid functionals provide computed photoemission spectra in excellent agreement with experimental data, whereas the GGA functional fails qualitatively. This failure is primarily because of under-binding of localized orbitals due to self-interaction errors.     

Magnetic moments of mirror nuclei with tilted-foil polarization

We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions. The nuclei are polarized by the tilted foil technique and the resulting 0–180^○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in this program was the measurement of the βasymmetry and the NMR resonance for the ground state of ²³Mg (I=3/2, T_1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique is also contemplated. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Maximum Number of Edges in Geometric Graphs with Pairwise Virtually Avoiding Edges

Let G be a geometric graph on n vertices that are not necessarily in general position. Assume that no line passing through one edge of G meets the relative interior of another edge. We show that in this case the number of edges in G is at most 2n?3.     

A Planar 3-Convex Set is Indeed a Union of Six Convex Sets

Suppose S is a planar set. Two points $a,b$ in S  see each other via S if $[a,b]$ is included in S . F. Valentine proved in 1957 that if S is closed, and if for every three points of S, at least two see each other via S, then S is a union of three convex sets. The pentagonal star shows that the number three is the best possible. We drop the condition that S is closed and show that S is a union of (at most) six convex sets. The number six is best possible.     

Parity violation in the 17/2− isomer of93Tc

The parity-violating mixing of the 17/2^? and 17/2⁺ levels in⁹³Tc nuclei, polarized by the tilted multifoil interaction, was measured by the observation of the forwardbackwardγ-ray asymmetry. The asymmetry was determined to beA _γ=1.18(48)×10^?3. The nuclear polarization was determined in a measurement of the quadrupole interaction in a⁹²Mo isomer and the parity violation matrix element 〈H _PV〉 is found to be ¦〈H _PV〉¦ =0.8(4) meV.     

Magnetic excitations in Cu6 and Mn6 hexagons embedded in D3d-symmetric polyoxotungstates

In this article we reconsider the discussion of the magnetic measurements for the two novel polyoxotungstates, (n-BuNH(3))(12)[(CuCl)(6)(AsW(9)O(33))(2)].6H(2)O and (n-BuNH(3))(12)[(MnCl)(6)(SbW(9)O(33))(2)].6H(2)O, which have been synthesized and characterized by Yamase et al. (Inorg.Chem. 2006, 45, 7698). Analysis of the magnetic susceptibility and magnetization for Cu(6)(12+) and Mn(6)(12+) hexagons based on the exact diagonalization of isotropic exchange Hamiltonian shows that the best-fit first-neighbor coupling parameters are J = 35 and 0.55 cm(-1), respectively, while the second-neighbor interactions are very small. These values exceed considerably those obtained by Yamase et al. (J = 8.82 and 0.14 cm(-1)) on the basis of the Kambe-Van Vleck formula that is inappropriate for six-membered rings. We also got perfect fits to the experimental data for the field dependence of magnetization at 1.8 K. The results imply the importance of axial anisotropy, which is shown to be especially pronounced for the Mn(6)(12+) cluster. We discuss also the symmetry assignments of exchange multiplets to the exact SGamma terms (full spin, S, and irreducible representation, Gamma, of the point group) and correlate the results with the selection rules for the anisotropic magnetic contributions. The antisymmetric exchange is shown to appear in orbitally degenerate multiplets as a first-order perturbation and gives rise to an easy axis of magnetization along the C(6) axis. Evaluation of the Zeeman levels shows that the field applied in the plane of the hexagon fully reduces the effect of the antisymmetric exchange.