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The time-differential-perturbed γ- γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er 2 O 3 and Gd 2 O 3. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er 2 O 3) and 300-1173 K (in the case of Gd 2 O 3). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were attributed to the electric-field gradients (EFG) acting on 181Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG results are compared with predictions of the point-charge model and discussed together with previous results obtained with the probes 111Cd and 181Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed in terms of dilatometric expansion data. [ABSTRACT FROM AUTHOR]

The perturbed angular correlation (PAC) technique was applied to study the incorporation of the transition metal Hf into GaN after implantation. To this end the PAC probe 181Hf(181Ta) was implanted into epitaxial Wurtzite GaN layers (1.3 μm on sapphire) with an energy of 160 keV and doses of 7× 1012 at/cm2. PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in the 300–1000ºC temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency (QIF) of νQ= 340 MHz for 30% of the probe nuclei. Annealing up to 600ºC reduces the damping of this frequency without an increase of the probe atom fraction fs in these sites. Above 600ºC fs grows rapidly until after the 900ºC RTA step more than 80% of the Hf probes experience a well defined QIF due to the incorporation of Hf on undisturbed sites of the hexagonal GaN wurtzite lattice. An interaction frequency of νQ= 340 MHz is derived. RTA and furnace annealing yield similar results for annealing up to 800ºC, where the undisturbed fraction reaches about 60%. Then RTA at higher temperatures increases this fraction, while furnace annealing leads to a decrease down to 22% after annealing at 1000ºC. To our knowledge this is the first time that a transition metal probe like Hf is incorporated to such a large extent into a semiconductor lattice. [ABSTRACT FROM AUTHOR]

The temperature dependence of the electric-field gradient of 111Cd in single crystalline LiTaO3 was studied from room temperature to 1040 K in the ferroelectric and paraelectric phases. The data taken at room temperature show unambiguously the presence of two quadrupole interaction frequencies, νQ1=230 MHz and νQ2=242 MHz, with nonzero asymmetry parameters, while above the Curie temperature (TC=878 K) the data are well described by a unique frequency. The electric field gradient shows a usual temperature dependence, increasing aproximately in a linear fashion until TC and then decreasing faster. The initial increase is explained mostly by the lattice expansion, while above TC it is necessary to consider Li and O displacements. [ABSTRACT FROM AUTHOR]

The electron-capture decay ofPa to levels inTh has been studied using mass-separated sources and high-resolution γ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2 member of a second excited K=0 band, with the 0 band head at 938.6 keV. The 2 and 3 members of a second excited K=2 band at 1153.5 and 1200.5 keV, which decay by strong E0 transitions to the 969 keV γ-vibrational band, are confirmed. In addition we tentatively propose a K=1 band at 944 keV. The K=0, 1 and 2 members of the octupole quadruplet are confirmed, and the γ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for the E1 transition moments. A total of 29 levels is observed between ∼1.4 and ∼2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear. [ABSTRACT FROM AUTHOR]

Nuclear levels inTh have been investigated in the β decay ofPa, theTh( d, pnγ) reaction and theTh( p, t) reaction. The K=0, 2, and 2 bands with band heads at 635, 781, and 1010 keV were observed up to the 8, 9, and 7 levels, respectively. A second excited 0 level was identified at 1297 keV which might be interpreted as the usual β shape-oscillation. The branching ratios of the E2 transitions from the 0, 2, and 2 bands are explained in the framework of the rotational model by taking into account the coupling of these bands with the ground-state band, and the coupling between the 0 and 2 band. A strong enhancement of E2 transitions from the 2 to the 0 band reported earlier is not confirmed. For the octupole vibrations with K=0, 1, and 2 the E1 branching ratios are analyzed in terms of the Coriolis coupling of these bands. An almost complete experimental set of E1 transition moments from these negative-parity bands to the 0, 0, and 2 bands was obtained. It is suggested that octupole correlations might be important in explaining these E1 moments. [ABSTRACT FROM AUTHOR]

The electron-capture decay of 228Pa to levels in 228Th was studied using mass-separated sources and a γ-ray detection system consisting of five Compton-suppressed Ge detectors. A total of 87 levels were observed up to an excitation energy of 2 MeV which are connected by approximately 500 γ-ray transitions. The complete octupole quadruplet, three excited Kπ=0+ bands and two Kπ=2+ bands were identified below 1.4 MeV. The observed level structure is compared to calculations within the quasiparticle-phonon nuclear model. The surprisingly good agreement indicates that 228Th has less transitional character than hitherto assumed. [ABSTRACT FROM AUTHOR]

RadioactiveHf ions were implanted into polycristalline platinum foils at 293 K. The radiation damage produced during the implantations was detected by subsequent time-differential perturbed-angular-correlation measurements of the γ-radiation emitted by theHf daughterTa. After annealing of the samples between 630 K and 850 K a large fraction of the implanted impurities interacts with well defined nearby lattice defects, which are assumed to be vacancy loops. [ABSTRACT FROM AUTHOR]

By implantation ofHf ions radiation damage is produced in platinum. Subsequent annealing of the samples leads to the trapping of a unique defect at the probe atoms. The temperature dependence of the resulting electric field gradient eq( T) is measured by use of the TDPAC-method. Assuming a relation eq( T)=eq(0)·(1− B·T) one finds B=(1.9±0.7)×10 K. This low value is of the same magnitude as the corresponding values forCd in various locally distorted cubic metals. [ABSTRACT FROM AUTHOR]

Time differential perturbed angular correlation and nuclear orientation studies of the electric quadrupole interaction for Hg in Sb have been performed. The effective field gradients | V(Hg Sb)|=1.43(18)×10V cm at room temperature and V(Hg Sb)=+1.8(2) × 10V cm below 0.05 K have been derived. These two values are no indication for an anomalous temperature dependence of the effective field gradient for Hg in Sb. The value of the electric field gradient fits well into the systematics for Hg in other hosts. It is shown that the electronic enhancements of the field gradients are correlated to the valence of the impurities and are rather insensitive to the host properties. [ABSTRACT FROM AUTHOR]

The magnetic hyperfine field at dilute Hg impurities in Gd has been investigated by the conversion electron ( e)- γ-time differential perturbed angular correlation (TDPAC) technique. The radioactivitiesHg andTl were implanted into Gd foils by means of an isotope separator. TDPAC measurements were performed with the 165 keV- L-conversion electron-134 keV- γ-cascade ofHg at different temperatures and with the 334 keV- γ-158 keV- K-conversion electron cascade ofHg at 200 K. The regular site occupation probabilities were found to be 15(3)% for an annealedHg Gd sample and 29(5)% in unannealedTl Gd samples. From the magnetic hyperfine interaction frequencies measured for the regular sites at 200 K the magnetic hyperfine fields | H(Hg Gd; 200 K)|=256(13) kG and | H(Hg Gd; 200 K)|=267(7) kG were deduced. [ABSTRACT FROM AUTHOR]

Zn have been implanted with an isotope separator on-line into a cold iron host matrix. Nuclear magnetic resonance of the low-temperature oriented isotopes has been observed. The resonance frequencies for zero external magnetic field are v(ZnFe @#@) =36.814(35) MHz and v(Zn Fe)=33.47(19) MHz. From these the magnetic moments of the 9/2 iosmeric states have been derived as μ(Zn)=(−)1.138(18) n.m. and μ(Zn)=(−)1.035(18) n.m. The experimentally known magnetic moments of ( vg)-levels in odd zinc isotopes are compared to theoretical estimates. [ABSTRACT FROM AUTHOR]

Conversion electron measurements with an electrostatic spectrometer proved the existence of the 1,565±6 eV transition inHg. The conversion intensity ratios, N/ N =1.2±0.2, N/ N=1.1±0.2, N/ N=0.92±0.15, N/ N=0.03± 0.02 and N/ N=0.04 ±0.02 were determined. These values agree with our calculations for the M1± E2 multipolarity with the E2/ M1 mixing ratio δ=(l.l±0.3)xl0 and exclude all pure multipolarities with L≦4. The total conversion coefficient for the above M1 + E2 mixture was evaluated to be (4.7±0.7)× 10. The reduced B( M1, 1/2→3/2) probability was derived to be (3.9 ±1.2) × 10 (eℏ/2Mc). The natural widths of the N-subshell conversion lines in mercury were found to be Γ( N)=8.3± 1.5, Γ( N) =5.8±1.5 and Γ( N) =6.5±1.0 eV. Monte Carlo calculations of electron scattering in matter yielded the conversion line shapes in qualitative agreement with the experiment. [ABSTRACT FROM AUTHOR]

Low temperature nuclear orientation experiments have been performed withSb in Sb and Zn single crystals. The ratio of the quadrupole moments ofSb andSb is derived from the data as Q/ Q= +2.17 (11). The sign of the effective electric field gradient at the nuclear site of Sb was found to be negative for host Sb and positive for host Zn. [ABSTRACT FROM AUTHOR]

By γ- e and e -γ TDPAC measurements with the 133 keV-482 keV cascade ofTa in a polycrystalline beryllium matrix the A( e)-coefficient of the 482 keV transition was determined as: A(482 e)=−0.095±0.015. The theoretical value is 6.0 times larger. A remeasurement of the E2/M1 mixing ratio of the same transition by integral γ- γ angular correlation measurements with a system of three 20 ccm Ge(Li)-detectors gave the result: δ(482)=4.96±0.25. The α-coefficient was redetermined as: α(482)=0.0246±0.0018. From these data the penetration parameter: λ=157±11 is derived and compared with previously published values and theoretical estimates. [ABSTRACT FROM AUTHOR]

Lu andLu with half lives of 6.8 d and 161 d, respectively, were implanted into iron foils and oriented at low temperatures. From the temperature dependence of the anisotropies of several γ-rays the magnetic moment of the I=23/2 three quasiparticle isomeric stateLu was determined as μ=3.3±0.3 nm. It is shown that the additivity relation for magnetic moments is well fulfilled for four high spin multiparticle states in this mass region. Using the known magnetic moment of the ground state a value of ¦ H¦=377±15 kG was derived for the internal field of Lu in Fe for our sample. [ABSTRACT FROM AUTHOR]

At external magnetic fields between 1.3 and 22.5 kG the integral αγ-angular correlations of the O(α)2(γ) O cascades from the ground states ofTh andRa respectively implanted into iron and aluminum lattices have been studied. The data were analyzed assuming different additional time dependent and static perturbations. The rotation of the angular correlation for Ra in Al proved independent of these assumptions. Therefore a g-factor of the 84.4 keV 2 state inRa g=0.46 (11) could be derived. Although static electric interactions seem the most probable cause for the attenuations observed for Ra and Rn implanted into Fe it was found that the two parameter Abragam and Pound theory better reproduces the data than the one parameter static perturbations. Therefore the hyperfine fields experienced by Ra and Rn in Fe were derived using Abragam and Pound theory to be H( RaFe)=−127(31) kG and H( RnFe)=1095 kG. [ABSTRACT FROM AUTHOR]

A prospective, randomized study was performed in order to evaluate the effect of cefotiam in the prevention of postoperative infectious morbidity in patients undergoing low-risk elective cesarean section. A total of 146 patients were randomly assigned to receive either intraoperative single-shot prophylaxis with 2 g cefotiam (study group, n=76) or no prophylaxis (control group, n=70). Due to a higher rate of urinary tract infections, the incidence of infectious morbidity after cefotiam prophylaxis was higher in the study group than in the control group (16% vs. 9%, P=0.1). Postoperative infectious morbidity following low-risk elective cesarean section cannot be reduced by intraoperative cefotiam prophylaxis. [ABSTRACT FROM AUTHOR]

The level structure of 228Th was studied using mass-separated 228Pa sources and a γ - γ coincidence setup of 5 Compton suppressed Ge detectors. The complete octupole quadruplet, three excited Kπ = 0+ bands and two excited Kπ = 2+ bands were identified at excitation energies elow 1.4 MeV. [ABSTRACT FROM AUTHOR]

The 48.7 mCd activity was implanted in Zn and Be single crystals which were soldered to the cold finger of a dilution refrigerator and kept below 0.2 K during implantation. Subsequent nuclear orientation experiments allowed the determination of the quadrupole interaction frequency v of the 11/2 isomeric state ofCd in Zn and Be as −139 (15) MHz and +43(16) MHz respectively. With these results we derive the quadrupole moment of the 5/2 245 keV level ofCd including sign as Q = +0.83(13) b and the sign of the electric field gradient for Cd in Be. The half-life ofCd was redetermined as 48.67 (6) m. [ABSTRACT FROM AUTHOR]