Directional Correlation Measurements Research Articles

Experimental evidences of shape co-existence in 154Ho

The excited states of odd-odd 154Ho nucleus have been studied by the 141Pr(16O, 3n)154Ho reaction at Elab= 82 MeV utilizing the Indian National Gamma Array (INGA) setup at BARC-TIFR Pelletron facility, Tata Institute of Fundamental Research, Mumbai. Data from γ−γ coincidence, directional correlation (DCO), and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. The reported level scheme of 154Ho has been improved by including new levels and transitions. Mixing ratios for the mixed transitions extracted from DCO ratios and parity assignments from polarisation data are reported for the first time. The low-lying states in H154o, which are mostly collective, characterized by regularity in the excitation spectra, are proposed to be arising from neutron excitation. At higher excitation, there is a transition from collective to single-particle character, accompanied by the appearance of irregular and complex structure caused by proton excitation. The newly identified E1 gamma transitions connecting the low-lying positive and negative parity bands indicate octupole correlation in 154Ho. These new connections also support the phenomenological analysis to interpret the observed experimental features from a different perspective.

Measuring enzymatic degradation of degradable starch microspheres using confocal laser scanning microscopy

Degradable starch microspheres (DSM) have long been used for topical haemostasis, temporary vascular occlusion and as drug delivery systems. When used for the latter, exact degradation rates of DSM have high importance, as this ensures a controlled and timed drug delivery. Current methods of analysing degradation rates are based on whole batch measurements, which does not yield information regarding individual times of degradation nor does it provide direct correlation measurements between sphere diameter and specific degradation time.In this paper we present an alternative method for measuring degradation rates of biodegradable starch microspheres using confocal laser scanning microscopy (CLSM). We succeeded in visualizing the degradation by staining the DSM and then following the spheres over time in a confocal microscope, after the addition of α-amylase.Individual degradation rates of single spheres could be followed, allowing a precise correlation measure between sphere size and degradation time. Furthermore, physical abnormalities such as internal cavities were detected within some spheres. These physical differences also had a measurable effect on the rate of degradation. Finally, complete degradation rates could be determined very accurately.To our knowledge, this is the first paper in which DSM degradation is visualized and measured using CLSM. Statement of significanceUsing degradable starch microspheres as a drug delivery system, is a continuously evolving field which shows promise in several different areas of illnesses. This paper presents a new method which visualizes enzymatic degradation of starch microspheres in real-time using confocal microscopy. The method is simple, yet the versatility of it suggests that it could be broadly applied within the field of biodegradation. Here, it illuminates a previously uninvestigated parameter: the effect of physical sphere deformities on the rate of degradation. It also provides precise correlation measures between initial sphere size and time of complete degradation.

First Observation of Multiple Transverse Wobbling Bands of Different Kinds in ^{183}Au.

We report the first observation of two wobbling bands in ^{183}Au, both of which were interpreted as the transverse wobbling (TW) band but with different behavior of their wobbling energies as a function of spin. It increases (decreases) with spin for the positive (negative) parity configuration. The crucial evidence for the wobbling nature of the bands, dominance of the E2 component in the ΔI=1 transitions between the partner bands, is provided by the simultaneous measurements of directional correlation from the oriented states ratio and the linear polarization of the γ rays. Particle rotor model calculations with triaxial deformation reproduce the experimental data well. A value of spin, I_{m}, has been determined for the observed TW bands below which the wobbling energy increases and above which it decreases with spin. The nucleus ^{183}Au is, so far, the only nucleus in which both the increasing and the decreasing parts are observed and thus gives the experimental evidence of the complete transverse wobbling phenomenon.

Direct optical-structure correlation in atomically thin dichalcogenides and heterostructures

Atomically thin transition metal dichalcogenides (TMDs) have distinct opto-electronic properties including enhanced luminescence and high on-off current ratios, which can be further modulated by making more complex TMD heterostructures. However, resolution limits of conventional optical methods do not allow for direct optical-structural correlation measurements in these materials, particularly of buried interfaces in TMD heterostructures. Here we use, for the first time, electron beam induced cathodoluminescence in a scanning transmission electron microscope (CL-STEM) to measure optical properties of monolayer TMDs (WS2, MoS2 and WSSe alloy) encapsulated between layers of hBN. We observe dark areas resulting from localized (~ 100 nm) imperfect interfaces and monolayer folding, which shows that the intimate contact between layers in this application-relevant heterostructure is required for proper inter layer coupling. We also realize a suitable imaging method that minimizes electron-beam induced changes and provides measurement of intrinsic properties. To overcome the limitation of small electron interaction volume in TMD monolayer (and hence low photon yield), we find that encapsulation of TMD monolayers with hBN and subsequent annealing is important. CL-STEM offers to be a powerful method to directly measure structure-optical correspondence in lateral or vertical heterostructures and alloys.

Kinetic Range Spectral Features of Cross Helicity Using the Magnetospheric Multiscale Spacecraft.

We study spectral features of ion velocity and magnetic field correlations in the magnetosheath and in the solar wind using data from the Magnetospheric Multiscale (MMS) spacecraft. High-resolution MMS observations enable the study of the transition of these correlations between their magnetofluid character at larger scales into the subproton kinetic range, previously unstudied in spacecraft data. Cross-helicity, angular alignment, and energy partitioning is examined over a suitable range of scales, employing measurements based on the Taylor frozen-in approximation as well as direct two-spacecraft correlation measurements. The results demonstrate signatures of alignment at large scales. As kinetic scales are approached, the alignment between v and b is destroyed by demagnetization of protons.

Shape coexistence inHo153

The high-spin states in 153Ho, have been studied by 139 57 La(20Ne, 6n) reaction at a projectile energy of 139 MeV at Variable Energy Cyclotron Centre (VECC), Kolkata, India, utilizing an earlier campaign of Indian National Gamma Array (INGA) setup. Data from gamma-gamma coincidence, directional correlation and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. We have suggested a few additions and revisions of the reported level scheme of 153Ho. The RF-gamma time difference spectra have been useful to confirm the half-life of an isomer in this nucleus. From the comparison of experimental and theoretical results, it is found that there are definite indications of shape coexistence in this nucleus. The experimental and calculated lifetimes of several isomers have been compared to follow the coexistence and evolution of shape with increasing spin.

Negative-parity high-spin states and a possible magnetic rotation band inPr7659135

Excited states in $^{135}\mathrm{Pr}$ have been investigated using the reaction $^{123}\mathrm{Sb}(^{16}\mathrm{O},4n)^{135}\mathrm{Pr}$ at an incident beam energy of 82 MeV. The partial level scheme has been established for negative-parity states with addition of new $\ensuremath{\gamma}$-ray transitions. The directional correlation and polarization measurements have been performed to assign spin parity for most of the reported $\ensuremath{\gamma}$-ray transitions. At high spin, a negative-parity dipole band $(\mathrm{\ensuremath{\Delta}}I=1)$ has been reported along with the observation of new crossover $E2$ transitions. Tilted Axis Cranking (TAC) calculations have been performed by considering a three-quasiparticle (3qp) configuration $\ensuremath{\pi}{({h}_{11/2})}^{1}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{\ensuremath{-}2}$ and a five-quasiparticle (5qp) configuration $\ensuremath{\pi}{({h}_{11/2})}^{1}{({g}_{7/2})}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{\ensuremath{-}2}$ for the lower and upper parts of the band, respectively. The observed results are compared with the results of the theoretical (TAC) calculations.

High-pT direct photon azimuthal correlation measurements

The azimuthal correlations of direct photons ($\gamma_{_{dir}}$) with high transverse momentum ($p_{_{T}}$), produced at mid-rapidity ($|\eta^{\gamma_{_{dir}}}|<1$) in Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV, are measured and compared to those of neutral pions ($\pi^{0}$) in the same kinematic range. The measured azimuthal elliptic anisotropy of direct photon, $v_{_{2}}^{\gamma_{_{dir}}}(p_{_{T}})$, at high $p_{_{T}}$ ($8< p_{_{T}}^{\gamma_{_{dir}}}<20$~GeV/$c$) is found to be smaller than that of $\pi^{0}$ and consistent with zero when using the forward detectors ($2.4 <|\eta|< 4.0$) in reconstructing the event plane. The associated charged hadron spectra recoiled from $\gamma_{_{dir}}$ show more suppression than those recoiled from $\pi^{0}$ $(I_{AA}^{\gamma_{_{dir}}-h^{\pm}} < I_{AA}^{\pi^{0}-h^{\pm}})$ in the new measured kinematic range $12< p_{_{T}}^{\gamma_{_{dir}},\pi^{0}}<24$~GeV/$c$ and $3< p_{_{T}}^{assoc}<24$~GeV/$c$.

Collective excitations inS33

High spin states of $^{33}\mathrm{S}$ populated through ${}^{27}\mathrm{Al}{(}^{12}\mathrm{C},\ensuremath{\alpha}\mathrm{pn})^{33}\mathrm{S}$ reaction at E$(^{12}\mathrm{C})\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}40$ MeV have been studied using the Indian National Gamma Array (INGA) facility. The level scheme was extended and modified utilizing data from the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence, directional correlation, and linear polarization measurements. Three levels of the negative parity yrast sequence were found to be connected by strong E2 transitions. The lifetimes of these states determined by the Doppler shift attenuation method have been utilized to study the evolution of collectivity with spin. Large basis shell model calculations have been performed to understand the microscopic origin of these levels.

Investigation of the high spin structure ofZr88

High spin states of $^{88}\mathrm{Zr}$ were populated with $^{80}\mathrm{Se}$($^{13}\mathrm{C}$, $5n$) fusion evaporation reaction. A thin target as well as Au backed target were used in two different experiments for the present study. Excited levels of $^{88}\mathrm{Zr}$ have been observed up to spin $\ensuremath{\sim}20\ensuremath{\hbar}$ and an excitation energy of $\ensuremath{\sim}10$ MeV. Spin and parity of most of the states have been determined from directional correlation and polarization measurements. The level scheme was substantially extended with the addition of a number of high spin states and transitions. The comparison of the measured levels of $^{88}\mathrm{Zr}$ with large shell model calculations based on the full unrestricted ${f}_{5/2}p{g}_{9/2}$ model space established the dominance of shell-model excitation up to the highest observed spin.

High spin spectroscopy in34Cl

High spin states of ${}^{34}\text{Cl}$ populated through ${}^{27}\text{Al}$(${}^{12}\text{C}$,$\ensuremath{\alpha}n$)${}^{34}\text{Cl}$ reaction at $E{(}^{12}\text{C})=40$ MeV, have been studied using the Indian National Gamma Array facility. The level scheme has been extended up to 10.6 MeV utilizing the results of intensity, directional correlation, and linear polarization measurements. Lifetimes of a few excited states have been estimated for the first time using the Doppler shift attenuation method. Large-basis shell-model calculations within the $sd\text{\ensuremath{-}}pf$ space have been done to understand the microscopic origin of the excited states. Involvement of $pf$ orbitals have been found to be essential to reproduce the negative-parity as well as high spin positive-parity states. Onset of collectivity manifested through short half-lives and large $B(E2)$ values have been reproduced well in the calculations.

Nuclear structure of30S and its implications for nucleosynthesis in classical novae

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.

Experimental investigation of shell-model excitations of89Zr up to high spin

Near yrast states in ${}^{89}$Zr were investigated up to high spin using the fusion evaporation reaction ${}^{80}$Se(${}^{13}$C, 4$n$) at an incident beam energy of 50 MeV. Excited levels of ${}^{89}$Zr have been observed up to $\ensuremath{\sim}$10 MeV excitation energy and spin $\ensuremath{\sim}$37/2$\ensuremath{\hbar}$ using the prompt gamma spectroscopy technique with the Indian National Gamma Array (INGA). The angular distribution, directional correlation, and polarization measurements were carried out to assign the spin and parity of the newly reported states. The structures of both the positive and negative parity states up to highest spin observed in the present experiment have been compared with shell-model calculations using two recently developed residual interactions, JUN45 and jj44b. The role of proton excitations from ${p}_{3/2}$ and ${f}_{5/2}$ orbitals to the ${g}_{9/2}$ orbital for the higher spin states has been discussed.

Exploration of jet energy loss via direct γ-charged particle azimuthal correlation measurements

The multiplicities of charged particles azimuthally associated with direct photons and π 0 have been measured for Au+Au, p+p, and d+Au collisions at s N N = 200 GeV in the STAR experiment. Charged particles with transverse momentum 0.5 < p T h ± < 16 GeV/c for p+p and d+Au, and 3 < p T h ± < 16 GeV/c for Au+Au and pseudorapidity | η | ⩽ 1.5 in coincidence with direct photons and π 0 of high transverse momentum 8 < p T γ , π 0 < 16 GeV/c at | η | ⩽ 0.9 have been used for this analysis. Within the considered range of kinematics, the observed suppressions of the associated yields per direct γ in central Au+Au relative to p+p and d+Au are similar and constant with direct photon fractional energy z T ( z T = p T h ± / p T γ ) . The measured suppressions of the associated yields with direct γ are comparable to those with π 0 . The data are compared to theoretical predictions.

Analysis of γγ directional correlation data taken with a multi-detector system

When performed with a multi-detector system, γγ directional correlation measurements need to be corrected differently for each independent detector pair, especially when those detectors have different active volumes and subtend different solid angles with respect to the radioactive source. We show here a method, which is suitable for setups containing dissimilar detectors. Successful tests were made for four γγ cascades, from Co60, Ba133 and Eu152.

Observation of magnetic rotation in odd-oddAg104

The high spin level structure of $^{104}\text{Ag}$ has been extended to ${I}^{\ensuremath{\pi}}={20}^{+}$ and excitation energy of $7.159\phantom{\rule{0.3em}{0ex}}\text{MeV}$ through the discrete line $\ensuremath{\gamma}$-ray spectroscopy. The negative parity ground state band has been confirmed and extended to ${I}^{\ensuremath{\pi}}={18}^{\ensuremath{-}}$. Two new nonyrast dipole bands, one with positive and the other with negative parity, have been observed. The parities of the two bands have been established through polarization directional correlation measurement of the feed-out transitions from these bands. The level lifetimes have been measured in the ground state band and the positive parity dipole band. The measured total angular momenta and the $B(M1)$ rates have been compared with the predictions of hybrid version of the tilted axis cranking. The $B(M1)$ rates have also been compared with the values obtained from D\onau's geometric formula. The tilted axis calculations give good overall agreement which suggests that all the three bands of $^{104}\text{Ag}$ exhibits magnetic rotation.

Level structure ofSe69

Excited levels in $^{69}\mathrm{Se}$ have been studied using the $^{40}\mathrm{Ca}(^{32}\text{S},2pn)^{69}\mathrm{Se}$ reaction at 95- and $105\text{\ensuremath{-}}\text{MeV}$ beam energy. $\ensuremath{\gamma}$ rays have been detected with the EUROBALL spectrometer operated in conjunction with the neutron wall and the charged-particle detector array EUCLIDES. New level sequences with positive and negative parities have been identified from $n\text{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}$ and $n\text{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences. Spins have been assigned to many of the levels on the basis of angular distribution and directional correlation measurements. Excitation energies of the positive-parity yrast band and the branching ratios of its decay are compared with the predictions of the rigid triaxial rotor plus particle model.

Optical intersubband transitions and femtosecond dynamics in Ag/Fe(100) quantum wells.

The optical intersubband transitions and femtosecond dynamics of electrons in quantum well states in Ag/Fe(100) are investigated by interferometric time-resolved two-photon photoemission. The quantum well wave functions and transition probabilities are evaluated from the two-photon photoemission resonance energies and intensities using an extended phase accumulation model. Direct femtosecond pump-probe correlation measurements elucidate the importance of interfaces in confined structures.

The detector system for measurement of multiple cosmic muons in the central detector of KASCADE

A detector system for directional and time correlation measurements of multiple cosmic muons has been set up within the extensive air shower experiment KASCADE. The system consists of two layers (129 m 2 area each) of position-sensitive multiwire proportional chambers (MWPC) triggered by a layer of segmented plastic scintillation counters placed upon an iron/concrete shielding above the MWPCs. Operation conditions and performance of the MWPCs have been studied by means of a prototype arrangement consisting of a stack of four detectors and two trigger layers. Results of the detailed prototype studies are presented and discussed. In particular, it has been found that for the present purposes an operation with a commonly used argon–methane gas mixture instead of previously used argon–isobutane leads to an excellent performance. The chambers are integrated into the KASCADE experiment as described and are in continuous operation since 1996. Some typical measurements with the full detector assembly are used to illustrate which features of extensive air showers can be studied.

Analysis of direct correlation measurements from adsorbed atom fluctuations

Despite its importance in theoretical studies of surface diffusion there has been limited experimental progress in developing methods to measure the dynamic structure factor S(q,t). In this work we study gases adsorbed on single-crystal surfaces and show that their equilibrium dynamics is measurable in a diffraction experiment through density fluctuations described by the dynamic correlation function . Using a lattice-gas model with nearest-neighbor repulsive interaction, we demonstrate how to separate out the microscopic dynamics caused by diffusion and adsorption-desorption from the form of . Our analytical results show that decays as an exponential with a time constant {tau}(q). Significant deviations from the hydrodynamic dependence of 1/{tau}(q)=D{sub c}q{sup 2} are found with and without desorption. These deviations have important consequences in extracting diffusion constants from experiments. (c) 2000 The American Physical Society.