Lattice defects in ion-implanted aluminium studied by means of perturbed angular correlations

Migration and clustering of lattice defects after implantation of¹¹¹In in Al and subsequent annealing at temperatures in the range from 80 to 800 K were investigated applying the DPAC technique. The effects of implantation dose, implantation temperature, laser irradiation, and plastic deformation were studied. The measurements on plastically deformed Al were complemented by positron lifetime measurements. We observed four In-defect clusters that can be flagged by well-defined hyperfine interaction parameters, and we determined their symmetry properties by using single-crystal samples. Important conclusions are: (i) monovacancies are not trapped by In-atoms, (ii) small In-defect clusters are formed by direct trapping of divacancies and/or trivacancies, and (iii) extended In-defect clusters are very stable and anneal in the temperature range 600–700 K. Consequences for the interpretation of other measurements on dilute Al(In) alloys are discussed.On leave from Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India.     

Probing nucleon structure on the lattice

The QCDSF/UKQCD Collaboration has an ongoing program to calculate nucleon matrix elements with two flavours of dynamical O(a) improved Wilson fermions. Here we present recent results on the electromagnetic form factors, the quark momentum fraction 〈x〉 and the first three moments of the nucleon's spin-averaged and spin-dependent generalised parton distributions, including preliminary results with pion masses as low as 320MeV.     

Temperature dependence of the Knight shift for cadmium in palladium

The Knight shift and its temperature dependence for a Cd impurity in palladium metal were measured by means of DPAD- and DPAC-methods utilizing the well known 5/2⁺, 247-keV state in¹¹¹Cd. The shift at 80 K was found to be KS (CdPd, 80 K)=?0.8(2)%. The observed variation of the KS in the temperature range from 80 K up to 1400 K is 0.5%. For calibration purposes an accurate remeasurement of the magnetic moment of the 5/2⁺ state in¹¹¹Cd was necessary and yieldedμ(¹¹¹Cd, 5/2⁺, 247 keV)=?0.7697(20) n.m.     

Magnetic hyperfine field for zinc in nickel

Electron mobility in the narrow band solid with a cellular disorder is investigated by methods of the coherent potential theory. Numerical results for the tight-binding model with the Lorentzian distribution of site potentials are presented. The motion of the electron in the region of extended states is neither a well defined coherent band motion nor a simple Brownian diffusion. The statistical electron-hole correlation proves to be important and increases fast with the potential distribution width to band width ratio. The correlation also increases when approaching the mobility edges.     

The electric field gradient at188Os nuclei in Re metal

The electric quadrupole interaction of the first excited 2⁺ state of¹⁸⁸Os in hexagonal rhenium metal was investigated by means of the time-differential perturbed angular correlation technique. From the observed quadrupole frequencyV _Q=170(7) MHz, we deduce an electric field gradient value of |V_zz|=4.77(23)·10²¹V/m² for the system OsRe. The half-life of the 2⁺ state was measured to be 641(4)ps.