Doppler-broadened Lineshapes Research Articles

Microstructure and defects of 0.1P2O5–0.65ZnO–0.25(xTeO2–(1-x)MoO3) quaternary glass nanocomposites using positron annihilation and correlated experimental methods

This study reports the spectroscopic examination of positron annihilation to characterize structural defects in glass nanocomposite systems of 0.1P2O5–0.65ZnO–0.25(xTeO2–(1-x)MoO3), consisting of two ternary (x = 0.0 and 1.0) and several intermediate quaternary (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, and 0.8) samples prepared by the melt quenching process. The lifetimes of the positrons, the relative intensities, and the parameters of the Doppler-broadened lineshape of the positron annihilation gamma ray spectra indicated porous-type defects inside the amorphous glassy matrices formed in samples of x = 0.05–0.2 and free volume defects in interfaces of the newer nanocrystallites at higher stages of modification (x ≥ 0.3). The results of X-ray diffraction confirmed the amorphous character of the samples and transmission electron micrographs confirmed the formation of the nanocrystallites. Selected area electron diffraction patterns revealed that the nanocrystallites were superimposed on the amorphous glass matrices. The spectra of energy-dispersive X-ray analysis revealed the presence of elemental constituents of the nanocomposites according to the required stoichiometries. A detailed Rietveld analysis of the X-ray diffraction patterns was used to identify the dispersed nanocrystallites and ascertain their stoichiometries. The work here is important in the context of developing technologically relevant glass nanocomposites from metal oxides with suitable physical characteristics. However, defects like vacancies that are formed during preparation may play a crucial role in determining their physical properties as well as the formation of free volumes and new nanocrystallites, where the latter were adequately dispersed over the glassy network. This can help transform the material into novel archetypes.

Lifetimes of core-excited states in semi-magic ^{95}mathrm {Rh}

Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus ^{95}mathrm {Rh}. The fusion-evaporation reaction ^{58}Ni(^{40}Ca, 3p) was used to populate high-spin states in ^{95}mathrm {Rh} at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6;mathrm {mg/cm}^2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.

Vacancy defects and their influence on mechanical properties in as-dealloyed and Fe+ ion irradiated nanoporous Au

Continuous depth sensing nano-indentation hardness measurements coupled with low-energy positron beam Doppler broadening line shape measurements were performed to investigate the influence of vacancy defects on mechanical properties in as-dealloyed and Fe+ ion irradiated nanoporous Au. A linear relationship has been obtained from the actual data between the nano-indentation hardness and square root of the concentration of defects. It suggests that the vacancy-type defects that evolved in the ligaments play a significant role in the modification of mechanical properties in both as-dealloyed and Fe+ ion irradiated nanoporous Au. The results have been also compared with those obtained on bulk Au.

Defect characterization of slow-cooled and quenched samples of calcium-copper-titanate through positron annihilation spectroscopy

Positron annihilation lifetime and Doppler-broadened gamma-ray spectra have been analyzed for slow-cooled and thermally quenched polycrystalline samples of calcium-copper-titanate. Two positron lifetimes revealing the characteristic defects in the respective samples were carefully analyzed to compare and contrast the significance of their origin and implication. A third component arising from positronium formation at the powdered particle surfaces has been considered in the analysis although its significance is lost in its very small intensity (∼ 1.1–1.2%). In the quenched sample, the defect-specific long positron lifetime (τ2) is found to larger and the mean lifetime smaller while its intensity I2 is found drastically smaller and the concentration of defects less by an order of magnitude as compared to the slow-cooled sample. The observed changes in electrical parameters of slow-cooled and quenched samples were found to have correlations with the positron annihilation lifetime and Doppler-broadened lineshape parameters.

Spectroscopy and excited-state g factors in weakly collective Cd111 : Confronting collective and microscopic models

The even cadmium isotopes near the neutron midshell have long been considered good examples of vibrational nuclei. However, the vibrational nature of these nuclei has been questioned based on E2 transition rates that are not consistent with vibrational excitations. In the neighbouring odd-mass nuclei, the g factors of the low-excitation collective states have been shown to be more consistent with a deformed rotational core than a vibrational core. Beyond the comparison of vibrational versus rotational models, recent advances in computational power have made shell-model calculations feasible for Cd isotopes, which may give insights into the emergence and nature of collectivity in the Cd isotopes. Collective excitations in the A ~ 100 region were studied through magnetic moments and electromagnetic transitions in 111Cd. The spectroscopy of 111Cd has been studied following Coulomb excitation. Angular correlation measurements, transient-field g-factor measurements and lifetime measurements by the Doppler-broadened line shape method were performed. The structure of the nucleus was explored in relation to particle-vibration versus particle-rotor interpretations. Large-scale shell-model calculations were performed with the SR88MHJM Hamiltonian. Excited-state g factors have been measured, spin assignments examined and lifetimes determined. Attention was given to the reported $5/2^{+}$ 753-keV and $3/2^{+}$ 755-keV states. The $3/2^{+}$ 755-keV level was not observed; evidence is presented that the reported $3/2^+$ state was a misidentification of the $5/2^{+}$ 753-keV state. It is shown that the g factors and level structure of 111Cd are not readily explained by the particle-vibration model. A particle-rotor approach has both successes and limitations. The shell-model approach successfully reproduces much of the known low-excitation structure in 111Cd.

Determination of isotope ratio in the divertor of JET-ILW by high-resolution Hα spectroscopy: H–D experiment and implications for D–T experiment

The data of the Hα high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertor is found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertor than that in the outer divertor by the values of 0.15–0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertor in the upcoming deuterium–tritium experiments. Also, separation of the overlapped Tα and Dα spectral lines is shown to be a challenging task especially when the local Doppler-broadened (Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium–tritium experiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic’s measurements. This model is shown to increase the accuracy of tritium concentration measurements in the divertor.

M1 and E2 transition rates from core-excited states in semi-magic 94Ru

Lifetimes of high-spin states have been measured in the semi-magic $(N=50)$ nucleus 94Ru. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru* fusion-evaporation reaction at the Grand Accelerateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from $\gamma$ -rays emitted while the residual nuclei were slowing down in a thick 6mg/cm^2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range $I = (13-20)\hbar$ have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

Neutron-resonance capture analysis on the VESUVIO spectrometer: Towards high-throughput material characterisation

We discuss the possibility to characterise nuclear quantum effects on the dynamics of heavy nuclei by means of neutron-resonance capture analysis on the VESUVIO spectrometer at ISIS. VESUVIO is equipped with yttrium-aluminium-perovskite gamma-sensitive detectors that can be used to record the Doppler-broadened line shape from a neutron-induced resonance in the neutron-energy range between 1 and 100 eV. The measurement of nuclear momentum distributions for heavy atoms using deep inelastic neutron scattering, the traditional technique for light-weight nuclei from hydrogen to fluorine, is currently severely limited by the resolution of the instrument. On the other hand, gamma-Dopplerimetry studies as the one presented here on gold allow for exquisite precision and short data-collection measurements, of the order of one hour, for the measurements, rendering the technique ideal for high-throughput investigations.

Intermediate-spin states of 92Zr and a large B(E2) value between the 101+ and 81+ states

This study investigated intermediate-spin states of $^{92}\mathrm{Zr}$ via the inverse reaction $^{9}\mathrm{Be}(^{86}\mathrm{Kr},3\mathrm{n})\phantom{\rule{0.16em}{0ex}}^{92}\mathrm{Zr}$. Seven transitions were newly observed, and a lifetime was extracted for the ${10}_{1}^{+}$ state by analysis of Doppler-broadened line shapes of decay $\ensuremath{\gamma}$ rays. A large $B(E2)$ value was obtained for the transition from ${10}_{1}^{+}$ to ${8}_{1}^{+}$, and the magnitude was comparable to that for the deformed excited configurations in $^{94}\mathrm{Zr}$ that have recently been established. A possible origin for such collectivity is discussed qualitatively based on a phenomenological deformed rotor model. Moreover, a multipletlike structure that fits into the systematics for $N=52$ even-$A$ isotones is revealed for the negative-parity yrast states.

First-principles calculations of momentum distributions of annihilating electron–positron pairs in defects in UO2

We performed first-principles calculations of the momentum distributions of annihilating electron–positron pairs in vacancies in uranium dioxide. Full atomic relaxation effects (due to both electronic and positronic forces) were taken into account and self-consistent two-component density functional theory schemes were used. We present one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) along with line-shape parameters S and W. We studied the effect of the charge state of the defect on the Doppler spectra. The effect of krypton incorporation in the vacancy was also considered and it was shown that it should be possible to observe the fission gas incorporation in defects in UO2 using positron annihilation spectroscopy. We suggest that the Doppler broadening measurements can be especially useful for studying impurities and dopants in UO2 and of mixed actinide oxides.

Fully self-consistent calculations of momentum distributions of annihilating electron-positron pairs in SiC

We performed calculations of momentum distributions of annihilating electron-positron pairs in various fully relaxed vacancy defects in SiC. We used self-consistent two-component density functional theory schemes to find the electronic and positronic densities and wave functions in the considered systems. Using the one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) we calculated the line-shape parameters $S$ and $W$. We emphasize the effect of the experimental resolution and the choice of the integration ranges for the $S$ and $W$ parameters on the distributions of the points corresponding to different defects in the $S(W)$ plot. We performed calculation for two polytypes of SiC, $3C$, and $6H$ and showed that for silicon vacancies and clusters containing this defect there were no significant differences between the Doppler spectra. The results of the Doppler spectra calculations were compared with experimental data obtained for $n$-type $6H$-SiC samples irradiated with 4-MeV Au ions. We observed a good general agreement between the measured and calculated points.

Dispersion corrections to the Gaussian profile describing the Doppler broadening of spectral lines

A dispersionally corrected Gaussian profile describing Doppler-broadened spectral line shapes is presented. Proposed corrections include the frequency dependence of the Doppler shifting caused by dispersion as well as by light frequency variation over the whole spectral line shape. It is shown that the frequency dependence of the Doppler shifting can have a non-negligible influence on the line-shape model and can affect the line shape even at the relative level of ${10}^{\ensuremath{-}5}$. Moreover, this effect also influences the determination of the line position at the level of kilohertz. Finally, the impact of the presented results on the Doppler width thermometry and precise molecular spectroscopy for fundamental studies is emphasized.

Lifetime measurement for the possible antimagnetic rotation band inPd101

Lifetime measurements were made for the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$, which had been interpreted as a possible antimagnetic rotation band based on the comparison of $I\ensuremath{-}\ensuremath{\omega}$ behavior with the calculation of a semiclassical particle-rotor model in our previous study. Doppler broadened line shapes were analyzed for the decaying $\ensuremath{\gamma}$ rays in the band following the reaction $^{68}\mathrm{Zn}(^{37}\mathrm{Cl},\phantom{\rule{0.16em}{0ex}}\text{1p3n})^{101}\mathrm{Pd}$. The semiclassical particle-rotor model was modified to reproduce both the $I\ensuremath{-}\ensuremath{\omega}$ plot and the $B(E2)$ behavior simultaneously for the antimagnetic rotation bands in Pd and Cd nuclei, for which $B(E2)$ values had been measured so far. Reasonable agreements between the experiment and the calculation were obtained. It is concluded that the lower part of the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$ can be interpreted as an antimagnetic rotor.

The use of positron annihilation Doppler broadening spectroscopy in the characterization of radiochromic dosimetry films

The positron annihilation Doppler broadening (PADB) spectroscopy has been employed to probe the defects and structural changes of various types of materials. In this work, an investigation was carried out for the first time to use PADB spectroscopy in probing the γ irradiated radiochromic films. The GafChromic MD–55 and HD–V2 radiochromic films irradiated with absorbed doses ranges of 0–80 and 0–2000 Gy, respectively, were subjected to Doppler broadening measurements employing a HPGe γ–ray spectrometer. The Doppler broadening line–shape parameters (S and W) of 511 keV annihilation radiations were discussed in terms of the polymerization degree of the active components of these dosimetry films. The S- and W-parameters were found to be dependent on the active component structures of both films. A reasonable correlation was also found between the values of the S–parameter and the optical density of these radiochromic films. In addition, the Doppler broadening line–shape parameters were successfully used to provide explanation of the observed nonlinearity of these films at the end of their dynamic dose ranges. The results demonstrate the applicability of the PADB technique to probe the physical and chemical changes occurred in the active layer of the studied radiochromic films during the solid–state polymerization reaction caused by γ irradiation of different absorbed doses.

Vibrational and rotational excitation of CO2 in the collisional quenching of H2(v = 1)

Energy transfer in H2 (1,1) +CO2 collisions was investigated using high resolution transient laser spectroscopy. Rotational state selective excitation of v = 1 for rotational level J = 1 was achieved by stimulated Raman pumping. Energy gain into CO2 resulting from collisions with H2 (1,1) was probed using transient absorption techniques, Distributions of nascent CO2 rotational populations in both the ground (00 degrees 0) state and the vibrationally excited (00 degrees 1) state were determined from overtone absorption measurements. Translational energy distributions of the recoiling CO2 in individual rovibrational states were determined through measurement of Doppler-broadened transient line shapes. A kinetic model was developed to describe rates for appearance of CO2 states resulting from collisions with H2(1,1). From scanned CARS (coherent anti-stokes Raman scattering) the spectral peaks population ratio n0/n1 was obtained, where n0 and n1 represent the number densities of H2 at the levels (0,1) and (1,1), respectively. Using rotational Boltzmann distribution of H2 (v = 0) at 300 K, n1 was yielded. Values for rate coefficients were obtained using data for CO2 (00 degrees 0) J = 48 to 76 and CO2 (00 degrees 1) J = 5 to 33. The rate coefficients derived from appearance of the (00 degrees 0) state have values of K(tr) = (3.9 ± 0.8) x 10(-11) cm3 x molecule(-1) x s(-1) for J = 48 and k(tr) = (1.4 ± 0.3) x 10(-10) cm3 x molecule(-1) x s(-1) for J = 76, with a monotonic increase for the higher J states. For the (00 degrees 1) state, values of k(tr) remain fairly constant at k(tr) = (4.3 ± 0.9) x 10(-12) cm3 x molecule(-1) x s(-1). Rotational populations for the nascent CO2 states were measured at 0. 5 μs following excitation of H2. The transient population for each state was fit using a Boltzmann rotational distribution. The CO2 (00 degrees 0) J = 48-76 rotational states were populated substantially relative to the initial 300 K CO2 distributions, and the distribution is described by Trot. The excited (00 degrees 1) state has T(rot), 310 K. The center-of-mass translational temperatures for the (00 degrees 0) state are all much greater than 300 K, with T(rel) = 1 532 K for J = 76. In contrast, transient line profiles for the J = 5 - 33 levels of excited (00 degrees 1) state do not show any broadening above the initial 300 K distributions, indicating that excitation to the (00 degrees 1) state is not accompanied by translational energy change.

Positron annihilation study on CuInSe2 solar cell thin films

Positron annihilation spectroscopy has been used to investigate CuInSe2 solar cell thin films. The films were grown on Mo-coated soda lime glass substrates by the electrochemical deposition processing technique. As-grown samples are found to contain large concentration of vacancy defects. The selenium (Se) atmosphere and sulfur (S) atmosphere annealing of as-grown samples at 800K can dramatically reduce the number of vacancy defects and the film becomes crystalline. In addition, a defect layer of about 50nm thickness was observed at the surface of the CuInSe2 thin film. This layer results from the electrochemical deposition method, but the defect concentration in the defect layer can be greatly reduced by annealing in selenium atmosphere. The Doppler broadening line shape parameter correlation plot provided evidence that the positron trapping defect states where in three samples.

Lifetime measurements and nuclear deformation in theA≈100region

The EUROGAM-2 array has been used to study $\ensuremath{\gamma}$ rays emitted following the spontaneous fission of a ${}^{248}$Cm source. Analysis of Doppler-broadened lineshapes corresponding to transitions from excited rotational states in neutron-rich Sr, Zr, Mo, Ru, and Pd fission fragments has enabled measurements of state lifetimes in these nuclei at nuclear spins of $I\ensuremath{\sim}10$. Extracted transition quadrupole moments are compared with various recent theoretical approaches, as well as with measurements at lower spin, and an interpretation of the data is made within the context of prolate-oblate shape competition in this region.

Lifetime measurements by the Doppler-shift attenuation method in theSn115(α,nγ)Te118reaction

$\ensuremath{\gamma}$ rays were measured at several angles in both singles and coincidence modes in the $^{115}\mathrm{Sn}$$(\ensuremath{\alpha},n\ensuremath{\gamma}){}^{118}$Te reaction at 15 MeV on a thick target. Multipolarities and mixing ratios were determined from the $\ensuremath{\gamma}$-ray angular distribution analysis. Lifetimes of 11 low- and medium-spin excited states in $^{118}\mathrm{Te}$ were determined from a Monte Carlo Doppler-shift attenuation method analysis of the Doppler broadened line shapes of $\ensuremath{\gamma}$ rays deexciting the levels. The results are discussed in comparison with the predictions of the interacting boson model.

Thickness Impacts of Vacancy Defects in Epitaxial La0.7Sr0.3MnO3 Thin Films Using Slow Positron Beam

Thickness effects of thin La0.7Sr0.3MnO3 (LSMO) films on (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates were examined by a slow positron beam technique. Doppler-broadening line shape parameter S was measured as a function of thickness and differnt annealing conditions. Results reveal there could be more than one mechanism to induce vacancy-like defects. It was found that strain-induced defects mainly influence the S value of the in situ oxygen-ambience annealing LSMO thin films and the strain could vanish still faster along with the increase of thickness, and the oxygen-deficient induced defects mainly affect the S value of post-annealing LSMO films.

Optimization of three-dimensional positron annihilation spectroscopy system (3DPASS) for three-dimensional momentum measurements

A three-dimensional positron annihilation spectroscopy system (3DPASS) was characterized. 3DPASS permits determination of three-dimensional electron–positron ( e −– e + ) momentum distributions by simultaneously measuring angles and energies for coincident two-gamma annihilation photons. 3DPASS collects a single dataset of correlated energies and positions for two coincident annihilation photons from a pair of solid-state double-sided strip detectors (DSSDs). Subpixel-interpolated positions are determined by transient charge analysis. 3DPASS performs simultaneous two-dimensional angular correlation of annihilation radiation (2D ACAR) and two-detector coincidence Doppler-broadening of annihilation radiation (CDBAR) measurements, which are typically collected independently. The 2D ACAR response of 3DPASS was measured for single-crystal Cu and 6H-SiC, with and without compensation for subpixel detection efficiency. Variation of efficiency across the width of DSSD charge collection electrodes was dominated by the event selection criteria required by the subpixel interpolation method. The DBAR resolution was optimized by adjusting the energy range of CDBAR events included in the Doppler-broadening (DB) lineshape. 2D ACAR and DBAR spectra from 3DPASS were compared to previously published results for single-crystal Cu and 6H-SiC. Detailed analysis of the ACAR spectra and the DB lineshapes highlighted momentum features not previously reported.