A. Bartos

A compact TDPAC spectrometer

Abstract A fast-fast TDPAC spectrometer consisting of four BaF2 detectors, a simple constant fraction and routing interface module, a TAC, an ADC and a personal computer for data administration has been developed. Four double-window constant fraction discriminators, allowing simultaneous timing- and energy discrimination, a routing unit and an interface to the personal computer are integrated in the double-NIM module. The fast component in the scintillation light of BaF2 make such an exceptionally simple TDPAC spectrometer possible, which has a time resolution of 200(10) ps FWHM for the 1173–1333 keV γ-cascade of 60Co.

Scaling of the electric field gradient of 111Cd impurities in the bixbyite oxides of Y, Sc, Dy and Yb☆

Abstract The quadrupole hyperfine interaction of 111Cd in the cubic C-form sesquioxides of Sc, Y, Dy and Yb has been investigated over the temperature range 295–850 K with perturbed angular correlation (PAC) spectroscopy. The 111Cd probe nuclei were either produced in the EC-decay of 111In or in the γ-decay of the 111Cd isometric state and introduced via ion implantation into the oxide matrices. A simple scaling of the components of the electric field gradient with the lattice constant has been observed on both substitutional octahedral sites.

Electric field gradients of 111Cd in the copper oxides CuO and Cu2O

Abstract Perturbed angular correlation measurements were performed after 111In implantation into CuO and Cu2O powder samples and 1 μm thick Cu2O surface layers. The quadrupole hyperfine interaction of 111Cd was studied in isochronal annealing cycles at 370–1170 K covering the CuO→Cu2O phase transition. The electric field gradients obtained for 111Cd on substitutional Cu lattice sites were associated with the repective oxygen coordinations. Annealing of Cu2O surface layers on copper foils resulted in a texture with the efg pointing preferentially out of the surface plane.

Dynamic Hyperfine Interaction in Cr2O3 Observed via PAC

Perturbed-angular-correlation (PAC) measurements with 111In(EC)111Cd probes, implanted at 400 keV into poly- or mono-crystalline Cr2O3, have been carried out as a function of temperature (290-1370 K). Two different electric-field gradients (e.f.g.s) with identical orientations in the lattice have been found. Their temperature-dependent variations can be well described by a dynamical model which we propose to be connected with a hole trapping at a next-neighbour Cr ion.

Precision PAC measurements in Er2O3 and Ho2O3 single crystals and structure refinement

The structure of C-form Ho2O3 and Er2O3 single crystals and powder samples was investigated by the electric quadrupole hyperfine interaction of111In(EC)111Cd probe ions using the perturbed γ-γ angular correlation method (PAC). The resulting set of refined atomic coordinates is compared to X-ray data and used to calculate the orientations of the electric field gradients (EFG) which are reproduced by the PAC measurements in single crystals. The temperature dependence of the coordinates was measured for both substances.

Surface oxidation of copper observed by perturbed angular correlation and Rutherford backscattering

Abstract The oxidation process of copper was investigated by the Rutherford backscattering spectrometry (RBS) and perturbed angular correlation (PAC) techniques. The variation of the oxygen concentration below the surface was analysed by RBS. The PAC method was applied to obtain a microscopic picture of the oxidation process. Some 10 12 radioactive 111 In + ions were implanted at 400 keV into copper foils, which were oxidized at a fixed oxygen pressure either isothermally or isochronally at increasing temperature ( T ox = 300–1200 K ). The PAC spectra were taken at room temperature. The hyperfine interaction parameters were compared with those found after 111 In implantation into Cu 2 O and CuO pressed powder samples, respectively oxide layers on copper foils. The broad frequency distribution observed during the oxidation process is suggested to be due to a complex formed by indium, oxygen and copper vacancies in the Cu 2 O lattice.

PAC study on111Cd in antiferromagnetic CuO

Abstract400 keV111In+ ions were implanted into CuO powder. After annealing at 570 K, more than 50% of the implants were found on substitutional sites in the monoclinic CuO lattice. PAC-spectra taken below the Néel temperatureTN≈230 K revealed a broadening of the quadrupole spectrum and additional satellite frequencies caused by combined electric and magnetic hyperfine interaction. Assuming that the orientation of the electric field gradient is given by the point charge model and taking the 〈010〉 direction of the supertransferred fieldBtr in CuO from neutron diffraction, we find a Larmor frequency of ωL≈40 MHz corresponding toBtr≈2.7 T at 60 K.

Electric field gradients at 111Cd in M2Cu2O5 cuprates (MSc, Y, In, Lu, Yb, Ho, Tb)

Abstract Perturbed angular correlation spectroscopy has been used to study the hyperfine interaction at 111In(EC)111Cd in several cuprates M2Cu2O5 (MSc, Y, In, Lu, Yb, Ho, Tb) with Ho2Cu2O5 structure. The radioactive 111In probes were either ion implanted or chemically introduced into polycrystalline powder samples. Two electric field gradients, populated with equal fractions by the 111In(EC)111Cd probes, have been attributed to the two octahedral M sites. A smooth variation of the hyperfine parameters with the ion radius of the M elements was observed and traced back to the variation of the position of the oxygen ion connecting the two M sites.

111Cd hyperfine probes in YBaCuO

Different techniques like implantation or in-diffusion have been applied to place the hyperfine probe111Cd at YBaCuO lattice sites. In this paper different experiments are reviewed which show that the standard PAC-probe can be placed at any regular site of YBaCuO. The PAC-parameters of these sites are collected and discussed.

Electric field gradients of111Cd in the hexagonal (A-phase) La2O3 and Nd2O3 sesquioxides

Perturbed angular correlation measurements of111In in hexagonal La2O3 and Nd2O3 yield well defined symmetric electric field gradients with coupling constantvQ=280 MHz (extrapolated) in La2O3 andvQ=269 MHz for Nd2O3 at room temperature. The coupling constant in La2O3 linearly decreases with temperature. The spectra of La2O3, strongly damped at RT, rise to full amplitude at 870 K indicating dynamical interactions.