L. Ziegeler

Preparation of ion-implanted and sub-monolayer 111In-tracer layers for perturbed angular correlation analysis

Abstract Some 10 12 radioactive 111 In-tracer atoms are routinely implanted at 400 keV into different samples to perform Perturbed Angular Correlation (PAC) measurements. The experimental details and the tricks used during the preparation and implantation are summarized. As an alternative to ion-implantation, a method to deposit submonolayer 111 In-tracer films into metallic multilayers is described. The different applications and benefits of both techniques are compared.

Half-life and α-ray energy of146Sm

Up-to-date α-decay data of the double-even,N=84 isotones are presented, including the presently remeasured values for146Sm. For this nuclide a half-life,T1/2 =1.031 (45) ×108 y, and α-ray energy, Eα=2455(4) keV, were measured. The significance of these data for the subshell closure atZ=64 observed in α-decay is discussed.

Stopping of slow recoil atoms in gases

Nuclear Resonance Fluorescence spectra contain information on the slowing-down behaviour of recoiling atoms in the energy range pertinent to the specific reaction. On the basis of conventional transport theory, measured spectra for arsenic atoms with energies ≲15 eV slowing down in helium are analysed. The assumption of continuous slowing down turns out to be well justified, and the thermal motion of the gas atoms is shown to influence the effective stopping power only slightly. Somewhat surprising in view of uncertainties concerning the charge state of the recoiling atoms, theoretical predictions based on Lenz-Jensen elastic interaction agree well with the measured spectra. At present, the experimental data do not allow direct inversion, but the calculated spectra are shown to depend sensitively on the stopping-power input.

The slowing down of atoms with kinetic energies ofW≲5 eV in Noble Gases: Evidence for inelastic interactions

Profiles of the 264.6 keVγ-line of75As emitted after the electron capture decay of75Se have been measured using nuclear resonance fluorescence in combination withγγ-coincidences as a high resolution, variable-energyγ spectrometer. The sources consisted of gaseous75SeH2 with different amounts of Kr or Xe. From the line profiles information has been obtained about the velocity distribution of the radioactive75As ions after electron capture decay and about the slowing down of the75As ions in the moderator gas. The75As ions obtain kinetic energies of up toW∼5 eV by neutrino recoil and Coulomb fragmentation of the75SeH2 molecules, corresponding to velocities of the order of 105 cm s−1. The slowing down of the75As ions has been interpreted in terms of the model of colliding elastic spheres, taking into account the thermalization in an exact way. No satisfactory agreement has been obtained between measured and calculated line profiles. This result indicates that inelastic processes are of great importance in the interaction of75As ions or atoms with the noble gas moderator atoms.

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.

Photometrische bestimmung von kupfer mit polyäthylenimin

Zusammenfassung Mit Polyathylenimin konnen in Leichtmetall-Legierungen Kupfer-Gehalte von 0,3-10% bei 645 mμ photometrisch bestimmt werden. Reaktionen der Polyimine mit HNO 2 , CS 2 HgJ 2 , As 2 S 3 werden aufgezeigt.

Dependence of the nuclear recoil motion on the phonon spectrum of solids investigated by nuclear resonance fluorescence

The time dependence of the recoil velocity of a140Ce nucleus in a La and a LaF3 lattice after β emission is studied via the Doppler shift of the 1.596 MeV γ transition in140Ce. Evidence is obtained that the nucleus does not leave the lattice site even at a recoil energy of about 20 eV but carries out a damped oscillation. The quantitative comparison of the recoil velocity with the predictions of lattice theory leads to partial agreement.

Selektivierung geringer Mengen Kupfer mit Polyäthylenimin-Zellulose

ZusammenfassungPolyäthyleniminzellulosen sorbieren Cu2+ durch koordinative Bindung als Zentralion des sekundären Stickstoffs des Polyäthylenimins im PH-Bereich 3,5 bis 4,5 selektiv aus verd. Lösungen. 10μg Kupfer können von 105fachen Überschüssen anderer Übergangsmetalle separiert, mit verd. Salzsäure eluiert und mit Diäthyldithiocarbamat photometrisch bestimmt werden. Das Verfahren eignet sich zur Erfassung von 0,001% Kupfer in Zink, Mangan, Kobalt, Nickel, Cadmium und Aluminium sowie aus Lösungen, deren Kupfergehalt 0,02 ppm beträgt.SummaryPolyethyleneimine celluloses selectively sorb Cu2+ from dilute solutions through coordinative bonding as central ion of the secondary nitrogen of polyethyleneimine in the pH-range of 3.5–4.5. 10μg of copper may be separated from 105-fold excesses of other transition metals, then eluted with dilute hydrochloric acid and determined photometrically with diethyldithiocarbamate. The method is suitable for determining 0.001% copper in zinc, manganese, cobalt, nickel, cadmium, and aluminium as well as in solutions whose coppercontent is 0.02 ppm.

On the observation of intrinsic defects in (Co1-xInx)1-δO by PAC

We report on the results of Perturbed Angular Correlation measurements in polycrystalline (Co1-xInx)1-δO samples (x = 0.04 and 0.8 at.%) using ion-implanted 111In tracers. The temperature and the oxygen activity (adjusted via a CO/CO2 mixture) were chosen in such a way as to be able to observe defect trapping and detrapping in thermal equilibrium. The results are compared with those obtained for (Co1-xInx)1-δO (x= 0.04 at.%) rapidly cooled to 350 K and for CoO.

PAC MEASUREMENTS OF THE VERWEY TRANSITION IN MAGNETITE

Perturbed angular correlation (PAC) experiments with implanted 111In tracers have recently been used to investigate magnetic phase transitions in metal oxides. Here we report on PAC measurements for 111Cd in polycrystalline Fe3O4 in the neighborhood of the Verwey phase transition (TV≈ 120 K). Perturbed angular correlation spectra were taken for implanted 111In probes at temperatures between 9 and 850 K. The two observed Larmor frequencies are attributed to the two possible cation sites in the cubic inverse spinel lattice. For T > 120 K, the temperature dependence of both Larmor frequencies follows a Curie–Weiss power law ωL(T)/ ωL(0)=(1-T/TN)β, with the parameters TN=848(2) K and β= 0.392(2). At the Verwey temperature we find a rapid change of both Larmor frequencies, with ωL1 increasing from 178(2) MHz at 120 K to 191(4) MHz at 100 K, and ωL2 decreasing from 173(4) MHz to 151(5) MHz. The Verwey transition also affects the widths of the frequency distributions, which more or less double below TV. This possibly indicates the presence of several components with Larmor frequencies similar to those found in the previous Mössbauer data, or for electronic after-effects correlated with the semiconductivity of magnetite below TV.