Angular Correlation Technique Research Articles

Direct Measurement of the Internal Pressure of Ultrafine Bubbles Using Radioactive Nuclei

Direct Measurement of the Internal Pressure of Ultrafine Bubbles Using Radioactive Nuclei

Local Crystalline Structure of Doped Semiconductor Oxides Characterized by Perturbed Angular Correlations: Experimental and Theoretical Insights

Doping semiconductor oxides with trace amounts of non-native elements can improve their properties such as bandgap and conductivity. The lack of local techniques makes the precise characterization of these materials difficult. Among the few techniques capable of providing local characterization, those based on hyperfine interactions at probe nuclei have the advantage of being well established, probing the material homogeneously and completely, thus investigating different regions of material. Some of these techniques are also quite sensitive even at extremely low dopant concentrations. The perturbed angular correlation technique, combined with first-principles calculations, has recently been shown to be a powerful method for characterizing doped semiconductor oxides. In this paper, we present a brief review of the unique information extracted from the semiconductor investigation with such a complex approach, including semiconductor oxides doped with cadmium and other elements. A strong relationship between the local environment, including electronic structure, and the nature of the dopant and the native element of the doped oxides is also shown.

Room-Temperature 181Ta(TiO2): An e-γ TDPAC Study

In this work, we report on the hyperfine parameters of the foreign 181Ta probe in the rutile structure of the single crystal TiO2 using the e−γ and γ−γ time differential perturbed angular correlation (TDPAC) technique. We implanted 181Hf ions into a sample of single crystal rutile TiO2 in the Bonn Isotope Separator. The implanted sample was then thermally annealed at a temperature of 873 K for 315 min in a vacuum. The 181Hf radioisotopes decayed by β− emission, followed by a cascade to the ground of γ rays or conversion electrons into a stable state 181Ta. The 181Ta probe substitutes the Ti lattice site with a unique nuclear quadrupole interaction, allowing for the precise measurement of the largest electric field gradient (Vzz) and asymmetry parameter (η). The hyperfine parameters obtained from the e−γ TDPAC spectroscopy agree with those of the γ−γ TDPAC spectroscopy at room temperature, apart from a calibration factor, both from our experiments and the literature. This suggests that the electronic recombination following the internal conversion of the L shell electron takes less time (ps) than the intermediate lifetime of the metastable 181Ta state (ns).

Perturbed Angular Correlation Technique at ISOLDE/CERN Applied for Studies of Hydrogenated Titanium Dioxide (TiO2): Observation of Cd-H Pairs

Profound understanding of the local electronic and defect structure in semiconductors always plays a vital role in the further developing of applications of such materials. In the present work an investigation of the electronic structure in hydrogenated TiO2 (rutile) thin films is conducted by virtue of Time-Differential γ-γ Perturbed Angular Correlation spectroscopy (TDPAC or PAC) with 111mCd/Cd isotope, produced and implanted at ISOLDE/CERN. The measurements were performed at 581 K as a function of the temperature of the samples during hydrogenation. Despite the fact, that rutile single crystals usually show the presence of two local environments, when are studies with Cd/In isotopes, the current pristine thin films sample had a single electric field gradient. Upon various degrees of hydrogenation, Cd probe atoms showed underwent alterations, resulting in up to 3 different local surroundings, generally with high electric field gradients. Broad EFG distributions are likely due to randomly distributed point defects in the neighbourhood of Cd acceptors. Observed results suggest that hydrogenations performed at RT and 423 K are not able to promote unique defect configurations, while in the range of 473-573 K the formation of such configurations is observed. Therefore, one may assume that the formation of Cd-defect complexes (Cd-H pairs) is temperature enhanced. At higher levels of hydrogenation (663 K), the samples become partly amorphous that further hinders any atomistic studies with strong damped PAC spectra. Cd-H complexes seem to be stable up to annealing up to 581 K annealing. The obtained results give a deep insight into complex hydrogen defects, their interactions and bond formations with Cd acceptor.

The Local Exploration of Magnetic Field Effects in Semiconductors

This study reports on the local exploration of magnetic field effects in semiconductors, including silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium phosphide (InP) using the time differential perturbed angular correlation (TDPAC) technique. TDPAC measurements were carried out under external magnetic fields with strengths of 0.48 T and 2.1 T at room temperature, and 77 K following the implantation of 111In (111Cd) probes. Defects caused by ion implantation could be easily removed by thermal annealing at an appropriate temperature. The agreement between the measured Larmor frequencies and the theoretical values confirms that almost no intrinsic point defects are present in the semiconductors. At low temperatures, an electric interaction sets in. It stems from the electron capture after-effect. In the case of germanium and silicon, this effect is well visible. It is associated with a double charge state of the defect ion. No such effects arise in GaAs and InP where Cd contributes only a single electronic defect state. The Larmor frequencies correspond to the external magnetic field also at low temperatures.

Crystalline and magnetic properties of CoO nanoparticles locally investigated by using radioactive indium tracer

We herein report a comprehensive investigation on the magnetic, structural, and electric properties of CoO nanoparticles with different sizes by local inspection through hyperfine interactions measured in a wide range of temperatures (10–670 K) by using radioactive ^{111}In(^{111}Cd) tracers with the perturbed angular correlations technique. Small cobalt oxide nanoparticles with the characteristic size of 6.5 nm have been prepared by the wet chemical route that turned out to be essential to incorporate radioactivity tracers during nucleation and growth of the particles. Nanocrystalline samples with 22.1 nm size were obtained by thermal treatments under low pressure of helium at 670 K. The hyperfine data were correlated with X-ray diffraction, ZFC–FC magnetic measurements, and transmission electron microscopy to describe the structure, magnetic properties, size, and shape of samples. An analysis of the temperature evolution of hyperfine parameters revealed that the structural distortion and the magnetic disorder in the core and on the surface layer play an important role in the magnetic behavior of CoO nanoparticles.

Local inspection of magnetic properties in GdMnIn by measuring hyperfine interactions

GdMnIn is reported to crystallize in the hexagonal MgNi2-type structure presenting a spin-glass behavior with no magnetic order attributed to the triangular spin frustration of magnetic ions. In the present work, FC-ZFC magnetization, specific heat and AC susceptibility measurements along with the local magnetic exchange measured by hyperfine interactions at In sites are used to investigate the magnetic behavior in GdMnIn compound. The ZFC-FC magnetization curves exhibit an inflection which was ascribed to the antiferromagnetic transition at TN= 145 K. These curves also give an indication of thermomagnetic irreversibility at 118 K, which along with the absence of inflection in specific heat results might be associated to spin-glass behavior. Results of AC susceptibility and magnetic hyperfine field measured using 111In(111Cd) probe nuclei carried out by perturbed angular correlations (PAC) technique did not show evidence of spin-glass behavior. The thermomagnetic irreversibility in FC-ZFC curves along with results of hyerfine interactions suggest the presence of magneto-crystalline anisotropy effects and a weak long-range coupling in GdMnIn.

Pharmacoscintigraphy: Techniques for Studying Drug Release And Absorption in Humans

In vivo drug release and absorption in the gastrointestinal tract are governed by a complex process subject to many variables. Extensive efforts were spent in studying the durg and manipulating the excipient and mechanical design of the formulation but little is known regarding the physiological factors that influence the release and absorptive processes. Understanding of the behavior of formulation inside the GI tract has been made by gamma scintigraphy using a single isotope. However, the technique is suffering from several limitations : (1) anatomical location of the object is difficult to determine; (2) quantification of radioactivity is difficult due to tissue attenuation and movement of isotope; (3) cannot distinguish between a radionuclide present as a solid or as a solute; (4) preparation of the radiolabeled dosage forms are problematic; and (5) neither the drug nor the excipients can be labeled with nuclide. These problems can be partly alleviated by using dual isotopic, geometric mean measurement, perturbed angular correlation, neutron activation, and pharmacokinetic techniques. Combining several scintigraphic techniques with pharmacokinetics can drastically improve the quality of the data. Thus, the term pharmacoscintigraphy was coined. The application of pharmacoscintigraphy can be further supplemented by other techniques such as stable isotope with gas chromatography-mass spectrometry, pH monitoring and gastrointestinal intubation. Those techniques can be used either independently or simultaneously with pharmacoscintigraphy to provide us with a full picture of durg release and absorption in humans.

Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3

LaMnO3+δ is a complex oxide, which, depending on the oxygen excess concentration, presents different crystalline structure and interesting magnetic and electric properties such as colossal magnetoresistance, polaron dynamics, multiferroic behavior, and charge-orbital ordering. This complexity requires different characterization techniques to draw a picture as complete as possible allowing a good understanding of these phenomena. Here, we have used the perturbed angular correlation (PAC) technique to measure hyperfine interactions at La and Mn sites of LaMnO3+δ(δ ∼0.15) using 140Ce and 111Cd at La sites as probe nuclei in order to investigate within an atomic scale the magnetic and electric interactions in this compound. The results show that 111Cd nuclei occupy highly symmetric local sites in agreement with a rhombohedral structure. The magnetic hyperfine field (Bhf) measured with 111Cd at La sites is very small (Bhf = 0.40 T) due to the supertransferred magnetic field from Mn neighbors through oxygen orbitals. On the other hand, 140Ce nuclei at La sites present a saturation field of around 3.7 T much higher than that expected for La sites (due to the weak transfer field by superexchange mechanism). In addition, for temperature range above the magnetic ordering (200-300 K) a dynamic hyperfine interaction was observed characterized by the attenuation parameter λ(T) whose temperature dependence allowed to determine the activation energy (Ea) associated to charge transfer. The polarization of the 4f-electron of Ce impurities affects the local magnetic field at impurity sites as well as the Ea.

Apparatus for in-beam hyperfine interactions and [formula omitted]-factor measurements: Design and operation

The design and operation of apparatus for measurements of in-beam hyperfine interactions and nuclear excited-state g factors is described. This apparatus enables a magnetic field of about 0.1 tesla to be applied to the target and the target temperature to be set between ∼4 K and room temperature. Design concepts are developed mainly in terms of transient-field g-factor measurements following Coulomb excitation by the implantation perturbed angular correlation (IMPAC) technique. The formalism for perturbed angular correlations is outlined and a figure of merit for optimizing these measurements is derived to inform design. Particle detection is based on the use of silicon photodiodes of rectangular shape. The particle-γ angular correlation formalism for this case is described. The experimental program to date includes temperature-dependent studies of hyperfine fields, transient-field g-factor measurements, and time-dependent perturbed angular distribution (TDPAD) studies.

High temperature ferromagnetism in NbCo2 nanoparticles – Bulk magnetization and hyperfine field measurements

Abstract We report the observation of high temperature ferromagnetism in nanoparticles of NbCo2, prepared by high speed ball milling. The magnetic properties of the bulk and noncrystalline samples have been studied through measurements of bulk magnetization and hyperfine field of 100Rh, implanted into the sample. Compared to the low, temperature independent magnetic susceptibility ( χ ∼ 10 - 5 emu/gm) observed for bulk NbCo2, the nanoparticle samples exhibit very high value of magnetic susceptibility ( χ ∼ 10 - 3 emu/gm), whose temperature dependence indicates possible ferromagnetic ordering near or above 300 K. The saturation magnetic moment obtained from isothermal magnetization (M vs H) data, however, turns out to be quite small (0.10 μ B ). On the other hand, hyperfine field measurements performed for 100Rh probe using time differential perturbed angular correlation technique indicate strong paramagnetic behavior of nano-NbCo2. We believe that ferromagnetism observed in nano-NbCo2 most probably arise from a small fraction of surface atoms, while the bulk of the material remains paramagnetic.

Mixed-ligand complexes of N-vinylpyrrolidone/N-vinylformamide/N-vinyl iminodiacedic acid copolymers and diethyldithiocarbamate as a co-ligand with indium/indium-111

ABSTRACTMixed-ligand metal-polymer complexes (MPC) of N-vinylpyrrolidone-N-vinylformamide-N-vinyl iminodiacedic acid (VP-VFA-VIDA) copolymers and diethyldithiocarbamate (DEDTC) as a co-ligand with indium were synthesized under mild conditions and pH close to physiological values. Isolated MPC were characterized by UV, IR, 1H NMR, atomic absorption spectrophotometry, and HPLC. The obtained data implied that the MPC contain 8–10 wt% of (IDA)In(DEDTC) fragments. The optimal conditions for radiochemical synthesis of VP-VFA-VIDA-111In-(DEDTC) metal-polymer complex with mixed ligands were defined. The closest coordination environment of 111In was studied by perturbed angular correlation technique. The obtained data are in good agreement with the information about weight amounts of the corresponding indium MPC.

Magnetic interactions at Ce impurities in REMn2Ge2 (RE = La, Ce, Pr, Nd) compounds

In the work reported in this paper, the temperature dependence of the magnetic hyperfine field (Bhf) at 140Ce nuclei replacing Pr atoms in PrMn2Ge2 compound was measured by the perturbed angular correlation technique to complete the sequence of measurements in REMn2Ge2 (RE = La, Ce, Pr, Nd). Results show an anomalous behavior different from the expected Brillouin curve. A model was used to fit the data showing that the Ce impurity contribution (Bhfimp) to Bhf is negative for NdMn2Ge2 below 210 K. The impurity contribution (Bhfimp) at 0 K for all compounds is much smaller than that for the free Ce3+, showing that the 4f band of Ce is more likely highly hybridized with 5d band of the host. Results show that direction of the localized magnetic moment at Mn atoms strongly affects the exchange interaction at Ce impurities.

The influence of 1,2-alkanediol on the crystallinity of magnetite nanoparticles

Magnetic nanoparticles of magnetite have been synthesized by thermal decomposition and investigated by measuring the magnetic hyperfine field. Preformed Fe3O4 nanoparticles were used as seeds to produce a series of magnetic nanoparticles, with different sizes and shapes. Samples were characterized by X-ray diffraction, transmission electron microscopy, and magnetization measurements. The perturbed angular correlation (PAC) technique was used to study the influence of 1,2-octanediol on the seeding growth of the Fe3O4 by measuring hyperfine interactions. The nuclear probes 111In →111Cd were introduced into the samples through the synthesis of first core of Fe3O4, remained in the samples after the consecutive growth. The PAC results show the presence of two probe site fractions, one characterized by a well-defined magnetic dipole frequency with population fI and another characterized with a broad distributed electric quadrupole frequency with population fO, which were, respectively, assigned to probes at substitutional Fe sites in crystalline Fe3O4 formed at inner region of the nanoparticles and probes at non-crystalline iron oxide in the outer region of nanoparticles. A mathematical model was proposed to fit the behavior of fO with the particle size.

TDPAC and first-principles study of electronic and structural properties of a Pd-vacancy complex in undoped germanium

Pd is one of the metals suitable for inducing low-temperature crystallization in Ge. However, it is not clear how residual Pd atoms are integrated into the Ge lattice. Therefore, time-differential γ–γ perturbed angular correlations (TDPAC) technique using the 100Pd(→100Rh) nuclear probe produced by recoil implantation has been applied to study the hyperfine interactions of this probe in single-crystalline undoped Ge. A Pd-vacancy complex aligned along the <111> crystallographic direction with a unique interaction frequency of 8.4(5) Mrad/s has been identified. This complex was measured to have a maximum relative fraction of about 76(4)% following annealing at 350 °C. Further annealing at higher temperatures reduced this fraction, possibly via dissociation of the complex. Calculations suggest dissociation energy of 1.94(5) eV for the complex. DFT calculations performed in this work are in reasonable good agreement with the experimental values for the electric-field gradient of the defect complex in Ge and Si for comparison. The calculations predict a split-vacancy configuration with the Pd on a bond-centred interstitial site having a nearest-neighbour semi-vacancy on both sides (V-PdBI-V) in Ge and Si.

A newly observed state in 12C – characterisation and consequences

Measurements of the 12C(4He,4He)12C* reaction at 40 MeV were performed using a charged-particle detector array composed of four double-sided silicon strip detectors. Resonances in 12 C were reconstructed with the requirement that the a-decay proceeded first via the 8 Be ground state. Of primary significance was the population of the 13.3 and 22.4 MeV resonances, the latter, observed for the first time in this measurement. By using the angular correlation technique the spins of the resonances, have been established as Jπ 4+ and Jπ=5− respectively.

Atomic-level observation of Ag-ion hopping motion in AgI

Applicability of the 111mCd(→111Cd) and 111In(→111Cd) probes to the study of dynamics in polycrystalline silver iodide (AgI) was examined by means of the time-differential perturbed angular correlation technique. It was found that the 111mCd(→111Cd) probe occupies a unique site in γ-AgI and exhibits nuclear relaxation caused by dynamic perturbation arising from Ag + hopping motion in α-AgI; while the residential sites of 111In(→111Cd) vary, suggesting that 111In ions can not settle themselves in a fixed site in the AgI crystal structure. We here demonstrate that 111mCd(→111Cd) can be a potential nucleus to probe the Ag +-ion dynamic motion in α-AgI.

Extranuclear dynamics of 111Ag(→111Cd) doped in AgI nanoparticles

Dynamic behavior of the extranuclear field relative to the 111Ag(→111Cd) probe nucleus introduced in a superionic conductor silver iodide (AgI) was investigated by means of the time-differential perturbed angular correlation technique. For poly-N-vinyl-2-pyrrolidone (PVP)-coated AgI nanoparticles, we observed nuclear spin relaxation of the probe at room temperature. This result signifies that Ag+ ions in the polymer-coated sample make hopping motion from site to site at this low temperature. The activation energy for the dynamic motion was successfully estimated to be 46(10)meV. The first atomic-level observation of the temperature-dependent dynamic behavior of Ag+ ions in the polymer-coated AgI is reported.

Thermal behaviour of hafnium diethylenetriaminepentaacetate studied using the Perturbed Angular Correlation Technique

Abstract Polyaminecarboxilic ligands like diethylenetriaminepentaacetic acid form stable complexes with many heavy metal ions, excelling as cation chelants especially in the field of radiopharmacy. The aim of this work is to characterize, by using the Time Differential Perturbed Angular Correlations (TDPAC) technique, the hyperfine interactions at hafnium sites in hafnium diethylenetriaminepentaacetate and to investigate their evolution as temperature increases. TDPAC results for KHfDTPA · 3H2O obtained by chemical synthesis yield a well defined and highly asymmetric interaction of quadrupole frequency ω Q = 141 Mrad/s, which is consistent with the existence of a unique site for the metal in the crystal lattice. The thermal behaviour of the chelate is investigated by means of differential scanning calorimetry and thermogravimetrical analyses revealing that an endothermic dehydration of KHfDTPA · 3H2O takes place in one step between 80 ℃ and 180 ℃. The anhydrous KHfDTPA thus arising is characterized by a fully asymmetric and well defined interaction of quadrupole frequency ω Q = 168 Mrad/s.

J/ψ and Ψ Polarization in Hadronic Production Processes

Both charm and bottom quarks form nonrelativistic bound states analogous to positronium. The J/ψ and ψ(2S) charmonium states and the first three Ψ(nS) bottomonium states, all spin-triplet S-wave quarkonium states below open heavy-flavor thresholds, have relatively large branching ratios to e−e+ or μ−μ+ pairs. In hadron collisions, experiments measuring lepton pairs can determine polarization by using angular correlation techniques. The polarization, in turn, can be related theoretically to the production mechanism for the bound state. This review summarizes experimental studies with proton beams at fixed-target and colliding-beam accelerators, covering a center-of-mass energy range from 39 to 7,000 GeV for nucleon and antiproton targets. Analyses using various polarization frames and spin-quantization axes are described and results compared. A pattern emerges that connects experimental results over the whole energy span. The theoretical implications of the pattern are presented, and a set of new measurements is proposed.