A. Weidinger

Defect configurations in irradiated molybdenum

Abstract Irradiated molybdenum has been investigated by the pertubed angular correlation technique using 111 In as radioactive source. It is observed that defects become trapped at the probe atom in annealing stage III around 500 K. By the quadrupole interaction three different defect configurations are identified; they are characterized by: (1) ν Q = eQV zz / h = 125 MHz, η = ( V yy − V xx )/ V zz = 0, symmetry axis [111]; (2) ν Q = 155 MHz, η = 1 and (3) ν Q = 98 MHz, η = 0, symmetry axis [100]. The defects are assigned to simple defect configurations.

Annealing behaviour of particle irradiated molybdenum foils

Abstract Radioactive 111 In atoms were implanted with an energy of 350 keV in annealed mono- and polycrystalline molybdenum foils. The radiation damage produced by the implantation itself or - after annealing at 1300 K - by a subsequent proton or electron bombardment was studied by the perturbed angular correlation method. Three distinct detect configurations are found in recovery stage III around 500 K. The symmetry of the measured electric field gradients suggests that these configurations consist of one, two and three vacancies, respectively, trapped at the 111 In atom. Two further configurations which are stable up to ≈1300 K are attributed to vacancy clusters.

μSR in ferromagnetic and antiferromagnetic dysprosium

Abstract The muon spin rotation (μSR) technique has been used to measure the local magnetic field at the site of a positive muon in Dy. In both the ferromagnetic and antiferromagnetic phases a single precession frequency is observed, demonstrating that the muon is localized.

Systematically weak temperature dependence of electric field gradients in distorted cubic metals

Abstract The temperature dependence of the electric field gradient for radiation-damaged copper and for the dilute alloy Zn Ag has been measured using the perturbed angular correlation technique. A systematically weak temperature dependence is found for distorted cubic metals compared to non-cubic metals. The strong temperature dependence for the Zn Ag , In Ag and Sn Ag alloys as reported in literature has not been confirmed in the present experiment.

Impurity-defect configurations in ion-irradiated copper studied by the DPAC-technique with111In

The structure and dynamics of lattice defects in copper are investigated. The defects have been produced by irradiation with heavy ions of 350 keV between 85 K and 300 K. Three different defect configurations are distinguished by the time differential perturbed angular correlation technique (DPAC) with111In as radioactive probe. Their electric quadrupole coupling constantsνQ=e2Qqzz/h areνQ1=116(2)MHz,νQ2=181(3)MHz andνQ3=52(1)MHz. The defects characterized byνQ1 andνQ2 are observed in the temperature range of recovery stage III. The appearance ofνQ3 is closely correlated with recovery stage V. The symmetry axis of the electric field gradient associated with this defect-111In configuration points along a crystallographic 〈111〉 direction. We attribute this defect to a planar faulted loop, presumably of vacancy type. The influence of irradiating particles and dose on the defect configurations is analyzed.

Diffusion of positive mouns in nickel and iron

The depolarization rate for spin polarized μ+ particles implanted into high purity polycrystalline nickel and iron samples were studied as a function of temperature in zero external field. In nickel a rapid decrease of the depolarization rate above 300 K was found. Assuming an Arrhenius behaviour, an activation energy of Ea=173 meV was determined. In iron it was not possible to fit the data with a simple Arrhenius law. At least two different slopes can be observed in an Arrhenius plot with Ea=(124±35) meV and Ea=(19±2) meV, respectively.

μSR study of proton-irradiated aluminum and copper at low temperatures

Abstract A search for muon trapping at lattice defects in proton-irradiated aluminum and copper in a μSR-experiment is reported. Thin foils have been irradiated at 77 K with 4 MeV protons to a total dose of 2 × 10 15 particles cm −2 resulting in a defect concentration of approximately 80 ppm for Cu and 30 ppm for Al. No trapping of muons is observed below 300 K in both targets. An upper limit for the trapping rate of 0.5 μs −1 is derived.

Application of μ SR to radiation damage in metals

Proton-irradiated Al, Cu and Ni foils have been investigated by the μSR technique. No trapping of μ+ has been observed in the temperature range investigated (<300 K). In Ni a temperature-independent increase of the depolarisation rate by a factor of three is found for the irradiated target. This change is attributed to field inhomogeneities produced by defects.