Perturbed alpha-gamma angular correlation studies of radon recoils into aluminium

The quadrupole interaction of ²²²Rn and ²²⁰Rn implanted by α-particle-decay in Al metal and Al-oxide has been investigated. The experimental results indicate an electrical interaction in cubic Al metal not in agreement with earlier measurements using isotope implanted sources.     

Perturbed angular correlation study of radiation-induced defects in Rh metal

Radiation-induced defects are studied in cubic rhodium metal, using the local probe technique ‘Time differential perturbed angular correlation’ (TDPAC) at liquid N₂ temperature. Isochronal annealing was done at 300, 1073 and 1473 K temperatures. The irradiated sample showed two quadrupole interaction frequencies at 1150 and 93 MHz. The low frequency disappeared at room-temperature annealing, which was assigned to In trapped at a vacancy, whereas the higher frequency remained up to high temperatures and was attributed to In trapped at Rh–C complexes in the Rh matrix.     

Perturbed angular correlation study of a nanostructured HfO2 film

The hyperfine field at ¹⁸¹Ta lattice sites in a nanostructured HfO₂ thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive ¹⁸¹Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction ¹⁸⁰Hf(n,γ)¹⁸¹Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the ¹⁸¹Ta probe sites. The ¹⁸¹Ta isotopes appear in the sample as disintegration product of ¹⁸¹Hf.     

Perturbed angular correlation study of surface magnetization in iron single crystals

The behaviour of closure domains at the surface of iron single crystals in an external magnetic field was studied by DPAC on samples implanted with¹¹¹In. It is observed that the surface magnetization does not follow that of the bulk. The movement of both the 90 and 180 walls of the closure domains is blocked up to a certain starting value H_s of the external field that is related to the demagnetization factor D of the sample and also depends on the precise orientation of the crystal axes and on the implanted indium dose.On leave from the Institue of Nuclear Physics, Cracow, PolandOn leave from the Institue of Physics, Jagiellonian University, Cracow, PolandThis work forms part of the research program of the Foundation for Fundamental Research of Matter (FOM) subsidized through the Netherlands Organization for Pure Research (ZWO).     

Perturbed angular correlation experiments on the rehydration of ZnTiF6

The rehydration process at room temperature, after the dehydration of ZnTiF₆· 6H₂O to ZnTiF₆, was studied by means of the Time Differential Perturbed Angular Correlations technique. The time evolution of the hyperfine parameters related to the hyperfine interaction observed is reported and interpreted in terms of a simple model for the growth of the phases. In the framework of this model, the time evolution of the relative fractions of each interaction is interpreted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Perturbed angular correlation study of order– disorder transition in HfW2O8

The perturbed angular correlation (PAC) technique has been used to characterize the degree of atomic order in the neighbourhood of radioactive ¹⁸¹Hf isotopes in HfW₂O₈. PAC measurements were carried out at temperatures between 14 and 723 K. The compound was synthesized starting with the oxides HfO₂ and WO₃, using a method involving ball milling, high temperature annealing and quenching in liquid nitrogen. Fast cooling allows to have the compound at temperatures below 1050 K. The compound has a high degree of stability below such temperature and around 430 K atomic ordering occurs. This transition order–disorder is reversible. ^aAlso at Comisión de Investigasiones Científicas de la Provincia de Buenos Aires, Argentina.     

Perturbed angular correlation experiments on111In in oxidized AgCd alloy

The hyperfine interaction of¹¹¹Cd probes in preoxidized and α-irradiated Ag_0.94Cd_0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of¹¹¹Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very similar to the ones observed after α-irradiation.     

Perturbed angular correlation measurement of theg-factor of the 668keV state in132Xe

A valueg=0.38±0.06 was obtained for theg-factor of the 668 keV state of¹³²Xe (τ=7.3±0.6 psec) from time-integral perturbed angular correlation measurements on gamma cascades in¹³²Xe. Sources of¹³²Te implanted in iron were used to obtain a magnetic hyperfine field of 1510±100 kG at the¹³²Xe nuclei.     

Perturbed angular correlation measurements on the 40.9 keV level of62Cu. A preliminary study of 2Zn-insulin

Time-differential PAC measurements have been made using⁶²Zn, both in aqueous solution at pH 6.0 and also incorporated into crystalline 2Zn-insulin. Three Nal(Tl) detectors were used — a 2.54 cm thick scintillator detecting the stop 41 keV gamma ray and two 5.0 cm thick scintillators at 90 and 135 detecting the start 597 keV gamma rays. The need to separate the 597 keV line from the 511 keV background was found to require very careful setting-up conditions in the case of a fixed-detector spectrometer. The solution data produced a fast relaxation time of (75±25) ns, while the three 2Zn-insulin batches gave data which were analyzed using a static interaction with an assumed axial symmetry to give an electric quadrupole frequency of (77±8) MHz.     

Perturbed angular correlation studies of Ta hyperfine interactions in Hf-Ni and Zr-Ni compounds

The hyperfine interaction experienced by ¹⁸¹Ta nuclei in the intermetallic compounds ZrNi₅, HfNi₅, and Hf₂Ni₇ has been investigated by perturbed angular correlation (PAC) spectroscopy. At temperatures T≥15 K the ¹⁸¹Ta angular correlation of appropriately annealed ZrNi₅ and HfNi₅ is unperturbed, indicating the absence of a magnetic hyperfine interaction. This observation rules out the possibility of spontaneous magnetic order of ZrNi₅ and HfNi₅ recently proposed in the literature. The temperature dependence of the electric quadrupole interaction of ¹⁸¹Ta in Hf₂Ni₇ suggests the existence of a reversible phase transformation at T≥500 K.     

Oxidation of indium implanted aluminium studied by the Rutherford backscattering and perturbed angular correlation methods

Aluminium foils oversaturated with 5.10¹⁵/cm² implanted¹¹⁵In⁺ ions were oxidized in 200 mbar oxygen or vacuum annealed at 370–870 K. The samples were analyzed by the Rutherford backscattering (RBS) and perturbed angular correlation (PAC) techniques, using some 10¹¹/cm² implanted radioactive¹¹¹In tracers. Furthermore, the oxygen surface profiles were also scanned with high resolution by using the nuclear resonance technique (NRA). The formation of passivating Al₂O₃ surface layers, preventing deeper oxygen diffusion and the indium diffusion into these oxidized surface layers and into the bulk, were studied. Several quadrupole interaction frequencies previously attributed to strained cubic indium precipitates and indium (-vacancy) clusters were observed. When the samples were oxidized above 750 K, the formation of In-O complexes and of substitutional¹¹¹In in Al₂O₃ was observed.     

Perturbed angular correlations of187Re in nickel

The internal field at¹⁸⁷Re in Ni has been measured by the TDPAC technique to beH _int=?105±3 kG at 293 °K.     

Mass exchange and angular distribution in a dynamical treatment of heavy ion collisions

We present a first numerical computation of the absolute value of the double differential cross section as a function of mass asymmetry and detection angle including a dynamical coupling between relative motion and mass asymmetry. We apply it to the⁶³Cu+¹⁹⁷Au experiment at two different energies. The equation of motion used is a Fokker Planck equation for the distribution function in classical phase space. The coefficients needed are those known from classical model calculations, besides a friction coefficient introduced for the mass asymmetry degree. We find encouraging agreement between the calculated and experimental curves.     

Perturbed angular distributions in the presence of isotropic paramagnetic relaxation

The effect of paramagnetic relaxation on perturbed angular distributions is treated for nuclei interacting with their electronic shells via isotropic hyperfine interaction. The conditions are given under which Blume's analytical stochastic-model result for the nuclear perturbation factorsG _k (t) can be derived quantum mechanically. Systems with arbitrary nuclear spin, but electronic spinS=1/2 may be calculated without resorting to the assumption necessary forS>1/2. Explicit closed expressions forG _k (t) can be found for this particular case.     

Perturbed angular correlation study of Ta-doped PbTi1−xHfxO3 compounds

In this work, the hyperfine quadrupole interaction at Ta-doped PbTi_1−xHf_xO₃ polycrystalline samples is studied for the first time. Powders with x=0.25, 0.50 and 0.75 were prepared and characterized by X-ray diffraction analysis. Perturbed Angular Correlation (PAC) analyses were done as a function of temperature, using low concentration ¹⁸¹Ta nuclei as probes. In the ferroelectric and paraelectric phases of these compounds two sites were occupied by the probes. For each site the quadrupole frequency, asymmetry and relative distribution width parameters were obtained as a function of temperature above and below the Curie temperature (T_C). One of these sites was assigned to the regular Ti–Hf site, while the other one was assigned to some kind of defect. The behavior of the hyperfine parameters as a function of temperature was analyzed in terms of a recent published phase diagram and the presence of disorder below and above T_C. For the three compositions measured, the obtained hyperfine parameters present discontinuities which correspond to the ferroelectric–paraelectric phase transition. In both phases it was found broad frequency distributed interactions. The disorder in the electronic distribution would be responsible for the broad line width of the hyperfine interaction.     

Time-dependent perturbed angular correlation study of181Ta in Mg

The quadrupole interaction of¹⁸¹Ta in Mg metal has been investigated at room temperature by time differential perturbed angular correlation method yieldingv _Q=127±7 MHz. The observed EFG is calculated to be 20.8×10¹⁶ V/cm².     

Gamma-gamma angular correlation study of oxygen motion in yttria-stabilized zirconia

The nuclear quadrupole relaxation of ¹⁸¹Ta in ZrO₂9 mole% Y₂O₃ has been measured by time differential angular correlations between 350 and 1150°C. The results are consistent with a distribution of the activation energy controlling the local motion of oxygen vacancies.