Search

The nuclear structure for the positive ( 21,2,3+ ) States and negative ( 31− ) states of 36,40Ar nuclei have been studied via electromagnetic transitions within the framework of shell model. The shell model analysis has been performed for the electromagnetic properties, in particular, the excitation energies, occupancies numbers, the transition strengths B(CL) and the elastic and inelastic electron scattering longitudinal form factors. Different model spaces with different appropriate interactions have been considered for all selected states. The deduced results for the (CL) longitudinal form factors and other properties have been discussed and compared with the available experimental data. The inclusion of the effective charges are essential for obtaining a reasonable description for the data. The results of sdpf-model space with sdpfk and sdpfmu-interactions have a good improved for the ground state form factors for 36,40Ar and for excitation properties of 21+ and 31− state of 36Ar nucleus. [ABSTRACT FROM AUTHOR]

The heavy-ion inelastic scattering of the neutron-rich nucleus 29Ne to its excited states was studied using a 100.1 MeV/u 29Ne rare isotope beam on 181Ta and 9Be targets. The combined setup consisting of the GRETINA array, the TRIPLEX device and the S800 Spectrograph facilitates the simultaneous measurements of the two inelastic reactions, providing the first measurement of the transition strengths for this isotope. A sizable E2 strength B(E2↑) which amounts to 163(30) e2fm4 was determined in the excitation to the 931-keV state, demonstrating a large degree of collectivity. The present results of B(E2↑) are compared to various shell-model calculations, confirming the role of intruder configurations in 29Ne at the boundary of the island of inversion.

This brief review presents current experimental evidence on the existence of deformed axially symmetric but reflection asymmetric or pear shapes in nuclei. A summary of the main findings on the properties of nuclear energy levels and electric transition probabilities is given. These experimental investigations have been possible due to the development of high efficiency gamma-detector arrays and production and availability of exotic radioactive ion beams which facilitated in-beam Coulomb excitation. The nuclear structure of odd-mass pear-shaped nuclei has assumed importance as they can be vital in solving some of the fundamental problems in physics. This paper is sequel to the publication of the book by the author on Pear-shaped Nuclei (World Scientific, 2020). [ABSTRACT FROM AUTHOR]

A new high-spin isomer in the neutron-rich nucleus 128Cd was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T1/2=6.3(8) ms was measured for the new state which was tentatively assigned a spin/parity of (15−). The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus 129Cd. In the present experiment no evidence was found for the decay of a 18+ E6 spin-trap isomer, based on the complete alignment of the two-neutron and two-proton holes in the 0h11/2 and the 0g9/2 orbit, respectively, which is predicted to exist by the shell model.

Low-energy dipole excitations in |${}^{10}\textrm{Be}$| were investigated based on the generator coordinate method with |$\alpha + {}^6\textrm{He}$| and |$\alpha + \alpha + 2n$| cluster models. We obtained three |$1^-$| states in |$E_{x}<15$| MeV, which show different characters in the |$E1$|⁠ , compressive dipole, and toroidal dipole transition strengths. We found the strong toroidal dipole transition in the |$1_1^-$| state, remarkable |$E1$| strength in the |$1^-_2$| state, and the strong |$E1$| and compressive dipole strength in the |$1^-_3$| state. The |$1^-_1$| is described by the |$\alpha + {}^6\textrm{He}$| cluster structure, whereas the |$1^-_2$| and |$1^-_3$| states are understood by three-body excitations of the |$\alpha + \alpha + 2n$| clustering. [ABSTRACT FROM AUTHOR]

Abstract Self-conjugate nuclei in the A ≈ 70 – 80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N = Z line. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B (E 2 ; 2 1 + → 0 1 +) transition strength in 74Kr. The method is then applied to determine the B (E 2 ; 2 1 + → 0 1 +) transition strength in 74Rb, the heaviest odd–odd N = Z nucleus for which this quantity has been determined. This result and extended systematics along N = Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in 74Rb. [ABSTRACT FROM AUTHOR]

The dependence of reduced transition probabilities corresponding to electric quadrupole [B(E2)] and magnetic dipole [B(M1)] transition occurring in 1 8 F nucleus on excitation energy and spin parity of the states involved in the transition has been investigated within the framework of simple potential model based on M3Y interaction. It is found that B(E2) increases with increasing excitation energy irrespective of the spin of excited states while B(M1) is very sensitive to the spin of the excited states and is independent of excitation energy. [ABSTRACT FROM AUTHOR]

Proteins have numerous physiological functions in the body. Their most important property is serving as depot carriers and as target molecules for many drugs. Three-dimensional fluorescence spectroscopy, zeta potential analysis, resonance light scattering (RLS), thermodynamic analysis, circular dichroism and fluorescence resonance energy transfer (FRET) measurements were performed to study the interactions between estradiol and human lactoferrin (Hlf). According to the three-dimensional fluorescence spectra, the binding of the drug to Hlf induced a slight destabilization of the protein. Circular dichroism results provided new insight into the course of structural transitions of Hlf after addition of estradiol, and revealed that a molten globule state was intermediate between the native and unfolded states. This is a compact state with a significant amount of native-like secondary structure, but a largely disordered tertiary structure. The experimental results further indicated that the fluorescence quenching mechanism between Hlf and estradiol corresponded to a static quenching procedure. The binding constant and the number of binding sites were obtained from modified Stern-Volmer diagrams. The distance r between donor and acceptor was obtained by FRET and found to be 1.96 nm for estradiol and Hlf. The critical induced aggregation concentrations (CCIAC) of estradiol on Hlf were determined by a non-linear relationship between the enhancement of the RLS intensities and drug concentrations. The zeta potential results were used to verify the existence of complexes and confirmed the CCIAC values obtained by the RLS technique. In addition, molecular modeling showed that estradiol was bound within the domain II of the C-lobe and N-lobe of the Hlf via hydrophobic interactions and hydrogen bonding. [ABSTRACT FROM AUTHOR]

Interfacial morphology evolution in FeCrAl alloys with varying Al content has been investigated by conducting a series of directional solidification experiments. A comparison between the experimental data and the Hunt-Lu model confirms that cellular spacing widens while dendritic spacing narrows as Al content of the alloy increases. The ratio of upper and lower limit cellular/dendritic spacing λ max /λ min is only weakly dependent on growth velocity and Al content. Under the experimental conditions in the present study, cell to dendrite transition (CDT) occurs at a growth velocity between 25 μm/s and 50 μm/s, and dendrite to cell transition (DCT) is observed at a growth velocity less than 100 μm/s. Critical spacing of CDT λ cd and local solidification time (LST) t f are used to discuss the influence of Al content on CDT and DCT respectively. The transition between non-planar and planar interface of the alloy is investigated based on the interface stabilization theory of Mullins and Sekerka. [ABSTRACT FROM AUTHOR]

Thermal unfolding of proteins is used extensively in screening of drug candidates because molecular interactions with ligands and substrates affect strongly protein stability, transition temperature, and cooperativity. We use synchrotron radiation circular dichroism to monitor the thermal evolution of secondary structure in proteins as they approach the melting point and the impact of substrate on their thermal behavior. Using Landau free energy expansion, we quantify transition strength and proximity to a critical point through the relative separation τ+ between the transition temperature Tm and the spinodal T+, obtained from the equation of state. The weakest transition was observed in lysozyme with τ+ = -0.0167 followed by holo albumin with τ+ = -0.0208 with the strongest transition in monomeric apo albumin τ+ = -0.0242. A structural transition at 45 °C in apo albumin leads to a noncooperative melt with τ+ = -0.00532 and amyloidogenic increase in beta content. [ABSTRACT FROM AUTHOR]

We have carried out a detailed study of scaling region using detrended fractal analysis test by applying different forcing likewise noise, sinusoidal, square on the floating potential fluctuations acquired under different pressures in a DC glow discharge plasma. The transition in the dynamics is observed through recurrence plot techniques which is an efficient method to observe the critical regime transitions in dynamics. The complexity of the nonlinear fluctuation has been revealed with the help of recurrence quantification analysis which is a suitable tool for investigating recurrence, an ubiquitous feature providing a deep insight into the dynamics of real dynamical system. An informal test for stationarity which checks for the compatibility of nonlinear approximations to the dynamics made in different segments in a time series has been proposed. In case of sinusoidal, noise, square forcing applied on fluctuation acquired at P = 0.12 mbar only one dominant scaling region is observed whereas the forcing applied on fluctuation (P = 0.04 mbar) two prominent scaling regions have been explored reliably using different forcing amplitudes indicating the signature of crossover phenomena. Furthermore a persistence long range behavior has been observed in one of these scaling regions. A comprehensive study of the quantification of scaling exponents has been carried out with the increase in amplitude and frequency of sinusoidal, square type of forcings. The scalings exponent is envisaged to be the roughness of the time series. The method provides a single quantitative idea of the scaling exponent to quantify the correlation properties of a signal. [ABSTRACT FROM AUTHOR]

Undoped and co-doped zinc oxide thin films were deposited on glass substrates using a chemical spray technique. The experimental Lorentz profiles of co-doped ZnO thin films were measured in the spectral region 720–1750 nm. A single oscillator model of the resulted materials is constructed by calculation of: zero-frequency refractive index ( n o ), average interband oscillator wavelength ( λ o ), oscillator strength ( S o ), dispersion energy ( E d ), single-effective oscillator energy ( E o ), plasma oscillation frequency ( ω p ) and interband transition strength moments ( M −1 , M −3 ). [ABSTRACT FROM AUTHOR]

Recent shell-model advances in the mass region above the doubly closed core 132Sn are reported in the present work. Using an effective interaction based on the N3LO potential, the low-lying spectra, E2 and M1 transition strengths are calculated for the following nuclei: 134,136,138Te, 136,138,140Xe, 138,140,142Ba, 140,142,144Ce and 142,144,146Nd. We focus in the discussion on the collectivity in the N = 86 isotones characterized by development of triaxial γ bands. [ABSTRACT FROM AUTHOR]

I have used a simple two-state model to fit E2 strengths connecting the first two 0 + states to the first two 2 + states in 98 Sr. Results for mixing parameters are in excellent agreement with those from a recent analysis. Perhaps surprisingly, they are also in remarkable agreement with results from 1980, despite the wide variation reported in the intervening years. [ABSTRACT FROM AUTHOR]

Unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, as such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. As an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ∼ 2. [ABSTRACT FROM AUTHOR]

Lineshapes for the electromagnetically induced absorption (EIA) of thermal 85 Rb atoms in a degenerate two-level system have been investigated using matching ( σ ∥ σ , π ∥ π ) and orthogonal ( σ ⊥ σ , π ⊥ π ) polarization configurations of coupling and probe beams. EIA signals, which result from coherence population oscillation and transfer of coherence of the excited state, are obtained in detail theoretically and experimentally. The observed EIA linewidths, which are limited due to the decoherence rate between the magnetic sublevels in the ground state from transit-time relaxation, match well with the calculated ones. Decompositions of the absorption signals analyzed with respect to magnetic sublevels of the ground state show that enhanced or decreased absorption signals for each component of magnetic sublevels in the ground state depend on several factors. These factors include the decay rates and transition strengths, which determine the overall absorption spectral profile. [ABSTRACT FROM AUTHOR]

The rheological characterization of drilling fluids is crucial to ensure an adequate performance of drilling operations. These materials show elastoviscoplastic and thixotropic behaviors simultaneously so that its gel strength is highly affected by the aging time to which the sample is subjected. This work presents experimental evidences of a correlation between the stress overshoot observed in flow start-up rheometric experiments after different aging times and the storage modulus, G′, monitored during a low amplitude oscillatory sweep over the aging time. A comparison of the correlation with the measured data at five different shear rates show that results lie within error bands of 10%. The results also suggest that the stress overshoot for different aging times can be estimated by using only two rheometric tests: an oscillatory sweep and a controlled shear rate experiment. [ABSTRACT FROM AUTHOR]

Excited low-spin states in 96 Mo and 98 Mo have been studied in γγ angular correlation experiments in order to determine spins and multipole mixing ratios. Furthermore, from a Doppler lineshape analysis effective lifetimes τ in the femtosecond range were obtained. The experimental data show a complex spectrum due to configuration mixing, which is confirmed by Interacting Boson Model calculations based on a Skyrme energy density functional. The M 1-transition strengths of transitions depopulating excited 2 + states to the first 2 + state are discussed in terms of the proton–neutron mixed symmetry. [ABSTRACT FROM AUTHOR]

Statistical nuclear spectroscopy (also called spectral distribution method), introduced by J.B. French in late 60's and developed in detail in the later years by his group and many other groups, is based on the Gaussian forms for the state (eigenvalue) and transition strength densities in shell model spaces with their extension to partial densities defined over shell model subspaces. The Gaussian forms have their basis in embedded random matrix ensembles with nuclear Hamiltonians consisting of a mean-field one-body part and a residual two-body part. However, following the recent random matrix results for the so called Sachdev–Ye–Kitaev model due to Verbaarschot et al, embedded random matrix ensembles with k -body interactions are re-examined and it is shown that the density of states, transition strength densities and strength functions (partial densities) in fact follow more closely the q -normal distribution (the parameter q is related to the fourth moment of these distributions with q = 1 giving Gaussian and q = 0 giving semi-circle form). The q -normal has the important property that it is bounded for 0 ≤ q < 1. The q -normal (also its bivariate and general multi-variate extensions) and the associated q -Hermite polynomials are studied for their properties by Bryc, Szablowski and others. Following these, in the present article, developed is statistical nuclear spectroscopy based on q -normal (univariate and bivariate) distributions and the associated q -Hermite polynomials. In particular, formulation is presented for nuclear level densities, shell model orbit occupancies, transition strengths (for electromagnetic and β and double β -decay type operators) and strength sums. [ABSTRACT FROM AUTHOR]

Uncertainties in absolute plunger distances are an often overlooked component in measurements with the Recoil Distance Doppler-shift (RDDS) method when the Differential Decay Curve (DDC) method cannot be used for the analysis. It is shown how these uncertainties arise when the capacitance method is used to determine absolute distances and how they influence the obtained lifetime values of a plunger experiment. Furthermore, a new approach to obtain absolute foil separations for plunger measurements using a high precision optical distance probe is introduced, which can reduce these uncertainties by a large margin. The performance of this method is demonstrated by comparisons to the capacitance method as well as to a precise measurement of absolute distances using known lifetimes in 181Ta. [ABSTRACT FROM AUTHOR]

Shape coexistence between the strongly deformed ground state and the weakly deformed 02+ state in 98Sr has been a major topic of interest due to the energy difference of 215 keV, which is the smallest in all even-even nuclei. The electric monopole transition strength ρ²(E0) is an important quantity that can relate the deformation difference and the shape mixing between the two 0+ states, which are admixtures of the vibrational (S) and the rotational (D) states in a simple mixing model. In a β-decay spectroscopy experiment, the experimental ρ²(E0) was measured. A value of 0.053(5) is consistent with the previous measurement and was combined with known electric quadrupole transition strengths B(E2) in calculations of a two-state mixing model. Based on a systematic study on neighboring Kr, Zr, and Mo isotopes, the mixing of the 0+ and 2+ states in 98Sr was determined to be 8.6% and 1.3%, respectively, corresponding to deformation parameters βD = 0.38(1) and βS = -0.23(2). These parameters reproduce experimental transition strengths well except for the 41+ → 21+ transition, which suggests a smaller D-band deformation for J ⩾ 4. [ABSTRACT FROM AUTHOR]

Lifetimes of the states in the quadrupole structure in 143 Eu have been measured using the Doppler shift attenuation method and the parity of the states in the sequence has been firmly identified from polarization measurements using the Indian National Gamma Array. The decreasing trends of the deduced quadrupole transition strength B ( E 2 ) with spin, along with increasing J ( 2 ) / B ( E 2 ) values before the band crossing, conclusively establish the origin of these states as arising from antimagnetic rotation. The abrupt increase in the B ( E 2 ) values after the band crossing in the quadrupole band, a novel feature observed in the present experiment, may possibly indicate the crossing of different shears configurations resulting in the re-opening of a shears structure. The results are reproduced well by numerical calculations within the framework of a semi-classical geometric model. [ABSTRACT FROM AUTHOR]

Background: In neutron-rich nuclei around N=40 rapid changes in nuclear structure can be observed. While Ni68 exhibits signatures of a doubly magic nucleus, experimental data along the isotopic chains in even more exotic Fe and Cr isotopes-such as excitation energies and transition strengths-suggest a sudden rise in collectivity toward N=40. Purpose: Reduced quadrupole transition strengths for low-lying transitions in neutron-rich 58,60,62Cr are investigated. This gives quantitative new insights into the evolution of quadrupole collectivity in the neutron-rich region close to N=40. Method: The recoil distance Doppler-shift (RDDS) technique was applied to measure lifetimes of low-lying states in Cr58,60,62Cr. The experiment was carried out at the National Superconducting Cyclotron Laboratory (NSCL) with the SeGA array in a plunger configuration coupled to the S800 magnetic spectrograph. The states of interest were populated by means of one-proton knockout reactions. Results: Data reveal a rapid increase in quadrupole collectivity for 58,60,62Cr toward N=40 and point to stronger quadrupole deformations compared to neighboring Fe isotopes. The experimental B(E2) values are reproduced well with state-of-the-art shell-model calculations using the LNPS effective interaction. A consideration of intrinsic quadrupole moments and B42 ratios suggest an evolution toward a rotational nature of the collective structures in 60,62Cr. Compared to 58Cr, experimental B42 and B62 values for 60Cr are in better agreement with the E(5) limit. Conclusion: Our results indicate that collective excitations in neutron-rich Cr isotopes saturate at N=38, which is in agreement with theoretical predictions. More detailed experimental data of excited structures and interband transitions are needed for a comprehensive understanding of quadrupole collectivity close to N=40. This calls for additional measurements in neutron-rich Cr and neighboring Ti and Fe nuclei. [ABSTRACT FROM AUTHOR]

We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric 16O + 208Pb system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric dinuclear system to calculate the transition strength B(E3) as a function of the center-of-mass distance. The obtained B(E3) strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of B(E3) are also strongly correlated with the damping factor, which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions. [ABSTRACT FROM AUTHOR]

Embedded random matrix ensembles are generic models for describing statistical properties of finite isolated interacting quantum many-particle systems. For the simplest spinless fermion (or boson) systems, with say m fermions (or bosons) in N single particle states and interacting via k -body interactions, we have EGUE( k ) [embedded GUE of k -body interactions] with GUE embedding and the embedding algebra is U ( N ) . A finite quantum system, induced by a transition operator, makes transitions from its states to the states of the same system or to those of another system. Examples are electromagnetic transitions (then the initial and final systems are same), nuclear beta and double beta decay (then the initial and final systems are different), particle addition to or removal from a given system and so on. Towards developing a complete statistical theory for transition strength densities (transition strengths multiplied by the density of states at the initial and final energies), we have derived formulas for the lower order bivariate moments of the strength densities generated by a variety of transition operators. Firstly, for a spinless fermion system, using EGUE( k ) representation for a Hamiltonian that is k -body and an independent EGUE( t ) representation for a transition operator that is t -body and employing the embedding U ( N ) algebra, finite- N formulas for moments up to order four are derived, for the first time, for the transition strength densities. Secondly, formulas for the moments up to order four are also derived for systems with two types of spinless fermions and a transition operator similar to beta decay and neutrinoless beta decay operators. In addition, moments formulas are also derived for a transition operator that removes k 0 number of particles from a system of m spinless fermions. In the dilute limit, these formulas are shown to reduce to those for the EGOE version derived using the asymptotic limit theory of Mon and French (1975). Numerical results obtained using the exact formulas for two-body ( k = 2 ) Hamiltonians (in some examples for k = 3 and 4 ) and the asymptotic formulas clearly establish that in general the smoothed (with respect to energy) form of the bivariate transition strength densities take bivariate Gaussian form for isolated finite quantum systems. Extensions of these results to bosonic systems and EGUE ensembles with further symmetries are discussed. [ABSTRACT FROM AUTHOR]

We report the results of a direct search for the 229Th (Iπ = 3/2+← 5/2+) nuclear isomeric transition, performed by exposing 229Th-doped LiSrAlF6 crystals to tunable vacuum-ultraviolet synchrotron radiation and observing any resulting fluorescence. We also use existing nuclear physics data to establish a range of possible transition strengths for the isomeric transition. We find no evidence for the thorium nuclear transition between 7.3 eV and 8.8 eV with transition lifetime (1-2) s ≲ τ ≲ (2000-5600) s. This measurement excludes roughly half of the favored transition search area and can be used to direct future searches. [ABSTRACT FROM AUTHOR]

The possible role of growing static order in the dynamical slowing down toward the glass transition has recently attracted considerable attention. On the basis of random first-order transition theory, a new method to measure the static correlation length of amorphous order, called "point-to-set" (PTS) length, has been proposed and used to show that the dynamic length grows much faster than the static length. Here, we study the nature of the PTS length, using a polydisperse hard-disk system, which is a model that is known to exhibit a growing hexatic order upon densification. We show that the PTS correlation length is decoupled from the steeper increase of the correlation length of hexatic order and dynamic heterogeneity, while closely mirroring the decay length of two-body density correlations. Our results thus provide a clear example that other forms of order can play an important role in the slowing down of the dynamics, casting a serious doubt on the order-agnostic nature of the PTS length and its relevance to slow dynamics, provided that a polydisperse hard-disk system is a typical glass former. [ABSTRACT FROM AUTHOR]

The IR-based method of infrared transition moment orientational analysis (1R-TMOA) is employed to unravel molecular order in thin layers of the semiconducting polymer poly[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) (P(NDI20DT2)). Structure-specific vibrational bands are analyzed in dependence on polarization and inclination of the sample with respect to the optical axis. By that the molecular order parameter tensor for the respective molecular moieties with regard to the sample coordinate system is deduced. Making use of the specificity of the IR spectral range, we are able to determine separately the orientation of atomistic planes defined through the naphthalenediimide (NDI) and bithiophene (T2) units relative to the substrate, and hence, relative to each other. A pronounced solvent effect is observed: While chlorobenzene causes the T2 planes to align preferentially parallel to the substrate at an angle of 29°, using a 1:1 chloronaphthalene:xylene mixture results in a reorientation of the T2 units from a face on into an edge on arrangement. In contrast the NDI unit remains unaffected. Additionally, for both solvents evidence is observed for the aggregation of chains in accord with recently published results obtained by UV--vis absorption spectroscopy. [ABSTRACT FROM AUTHOR]

The electric quadrupole transitions between 0+, 2+, and 4+ states in 12C are investigated in a 3α model. The three-body wave functions are obtained by means of the hyperspherical adiabatic expansion method, and the continuum is discretized by imposing a box boundary condition. Corresponding expressions for the continuum three-body (3α) bremsstrahlung and photon dissociation cross sections are derived and computed for two different a - a potentials. The available experimental energy dependence is reproduced and a series of other cross sections are predicted. The transition strengths are defined and derived from the cross sections, and compared to schematic rotational model predictions. The computed properties of the l2C resonances suggest that the two lowest bands are made, respectively, by the states (O1+,21+,42+} and {O2+, 22+,41+}. The transitions between the states in the first band are consistent with the rotational pattern corresponding to three alphas in an equilateral triangular structure. For the second band, the transitions are also consistent with a rotational pattern, but with the three alphas in an aligned arrangement. [ABSTRACT FROM AUTHOR]

Recent discoveries of highly efficient solar cells based on lead iodide perovskites have led to a surge in research activity on understanding photo carrier generation in these materials, but little is known about trap states that may be detrimental to solar cell performance. Here we provide direct evidence for hole traps on the surfaces of three-dimensional (3D) CH3NH3PbI3 perovskite thin films and excitonic traps below the optical gaps in these materials. The excitonic traps possess weak optical transition strengths, can be populated from the relaxation of above gap excitations, and become more significant as dimensionality decreases from 3D CH3NH3PbI3 to two-dimensional (2D) (C4H9NH3I)2(CH3NH3I)n-1(PbI2)n (n = 1, 2, 3) perovskites and, within the 2D family, as n decreases from 3 to 1. We also show that the density of excitonic traps in CH3NH3PbI3 perovskite thin films grown in the presence of chloride is at least one-order of magnitude lower than that grown in the absence of chloride, thus explaining a widely known mystery on the much better solar cell performance of the former. The trap states are likely caused by electron-phonon coupling and are enhanced at surfaces/interfaces where the perovskite crystal structure is most susceptible to deformation. [ABSTRACT FROM AUTHOR]

The deformed proton–neutron quasiparticle random phase approximation (QRPA) has been developed and applied to evaluate Gamow–Teller (GT) transition strength distributions, including high-lying excited states. The data of high-lying excited states are recently available beyond one or two nucleon threshold by charge exchange reactions using hundreds of MeV projectiles. Our calculations started with single-particle states calculated using a deformed, axially symmetric Woods–Saxon potential. The neutron–neutron and proton–proton pairing correlations are explicitly taken into account at the deformed Bardeen–Cooper–Schriffer theory. Additionally, the ground state correlations and two-particle and two-hole mixing states were included in the deformed QRPA. In this work, we used a realistic two-body interaction, given by the Brueckner G -matrix based on the CD Bonn potential to reduce the ambiguity on the nucleon–nucleon interactions inside nuclei. We applied our formalism to the GT transition strengths for 76 Ge, 76,82 Se, and 90,92 Zr, and compared the results with the available experimental data. The GT strength distributions were sensitive to the deformation parameter as well as its sign, i.e. , oblate or prolate. The Ikeda sum rule, which is usually thought to be satisfied under the one-body current approximation, regardless of nucleon models, was used to test our numerical calculations and shown to be satisfied without introducing the quenching factor, if high-lying GT excited states were properly taken into account. Most of the GT strength distributions of the nuclei considered in this work have the high-lying GT excited states beyond one-nucleon threshold, which are shown to be consistent with the available experimental data. [ABSTRACT FROM AUTHOR]

We have studied the β decay of the Tz = -1, f7/2 shell nuclei 54Ni, 50Fe, 46Cr, and 42Ti produced in fragmentation reactions. The proton separation energies in the daughter Tz = 0 nuclei are relatively large (≈4-5 MeV) so studies of the γ rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision β-decay half-lives, excitation energies, and β branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these β decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths observed in beta decay including a sensitivity limit with the strengths of the Tz = +1 to Tz = 0 transitions derived from high resolution (³He,t) reactions on the mirror target nuclei at RCNP, Osaka. The accumulated B(GT) strength obtained from both experiments looks very similar although the charge exchange reaction provides information on a broader energy range. Using the "merged analysis" one can obtain a full picture of the B(GT) over the full Qβ range. Looking at the individual transitions some differences are observed, especially for the weak transitions. Their possible origins are discussed. [ABSTRACT FROM AUTHOR]

The exact formulation of the correspondence principle and in particular understanding the quantum-to-classical transition remains an open problem in quantum mechanics. In this paper we present our investigation into the quantum-to-classical transition of the most trivial of quantum systems - a particle in a box. Whilst it is perhaps surprising, even this example can produce new physical insight into these fundamental problems. With modern fabrication techniques of nano-mechanical systems we will be able to experimentally investigate these results and directly observe the quantum-to-classical transition. This will enable us to build technologies that probe the fundamental questions of quantum mechanics, such as the maximum size of a quantum object. [ABSTRACT FROM AUTHOR]

The distribution of the total transition strength, i.e. the right hand side of the integral form of Thomas–Reiche–Kuhn sum rule, into individual absorption processes is described for crystalline silicon containing interstitial oxygen. Utilization of the sum rule allows the construction of a dispersion model covering all elementary excitations from phonon absorption to core electron excitations. The dependence of transition strength of individual electronic and phonon contributions on temperature and oxygen content is described. [ABSTRACT FROM AUTHOR]

The decay of an isomeric state in the neutron-rich nucleus 129 Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a 238 U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ -rays and internal conversion electrons, a multipolarity of E 3 was tentatively assigned to the isomeric transition. A half-life of T 1 / 2 = 3.6 ( 2 ) ms was determined for the new state which was assigned a spin of ( 21 / 2 + ) , based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions. [ABSTRACT FROM AUTHOR]

Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ-ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been determined. With these first results the Tz = -3/2 nucleus 33Ar is now, together with 21Na (Tz = -1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way. [ABSTRACT FROM AUTHOR]

To improve the bonding strength and the oxidation resistance of SiC coating by chemical vapor deposition (CVD) for carbon/carbon (C/C) composites, C/C composites were modified by pre-oxidation treatment. It is found that an inlaid transition structure was obtained at the interface between SiC coating and pre-oxidized C/C composites. After pre-oxidation treatment, the interface adhesion strength increases from 23.5±3.2 to 37±2.5N, and the weight loss of the coated C/C samples is only 0.50% after oxidation at 1773K for 12h. The obvious improvement of the bonding strength and the oxidation resistance was mainly attributed to the pre-oxidation of the C/C substrate, forming an inlaid transition layer at the C/C–SiC interface during CVD process. [ABSTRACT FROM AUTHOR]

The article informs about the Gamow-Teller transition strengths from the helium reaction. Topics discussed include that Gamow-Teller (GT) transition strengths being the key inputs for estimating weak reaction rates of a wide variety of astrophysical applications, extracting the Gamow-Teller (GT) transition strength in electron-capture direction, and mediation of reactions by the weak nuclear force.

The Gamow-Teller strength in the β+ direction to 46Sc was extracted via the 46Ti(t, 3He + γ) reaction at 115 MeV/u. The γ-ray coincidences served to precisely measure the very weak Gamow-Teller transition to a final state at 991 keV. Although this transition is weak, it is crucial for accurately estimating electron-capture rates in astrophysical scenarios with relatively low stellar densities and temperatures, such as presupernova stellar evolution. Shell-model calculations with different effective interactions in the pf shell-model space do not reproduce the experimental Gamow-Teller strengths, which is likely due to sd-shell admixtures. Calculations in the quasiparticle random phase approximation that are often used in astrophysical simulations also fail to reproduce the experimental Gamow-Teller strength distribution, leading to strongly overestimated electron-capture rates. Because reliable theoretical predictions of Gamow-Teller strengths are important for providing astrophysical electron-capture reaction rates for a broad set of nuclei in the lower pf shell, we conclude that further theoretical improvements are required to match astrophysical needs. [ABSTRACT FROM AUTHOR]

Abstract: Transition strengths for decays from low-lying states in A ∼ 70 nuclei have been deduced from lifetime measurements using the recoil distance Doppler shift technique. The results confirm the collectivity previously reported for the decay in 68Se and reveal a relative decrease in collectivity in 70Br. This trend is reproduced by shell model calculations using the GXPF1A interaction in an fp model space including the Coulomb, spin-orbit and isospin non-conserving interactions. The decay in 70Br is found to have a very small B(M1) value, which is consistent with the configuration of the state being dominated by the coupling of protons and neutrons. The results suggest that the orbit does not play an important role at low spin in these nuclei. The B(E2) values for the decays of the (T = 1) states in 70Br and 70Se are almost identical, suggesting there is no major shape change between the two nuclei at low spin. [Copyright &y& Elsevier]

The half-lives of the 9/2+, 13/2+, and 15/2+ yrast states in the neutron-rich 67Cu nucleus were determined by using the in-beam fast-timing technique. The experimentally deduced E3 transition strength for the decay of the 9/2+ level to the 3/2- ground state indicates that the wave function of this level might contain a collective component arising from the coupling of the odd proton p3/2 with the 3- state in 66Ni. Theoretical interpretations of the 9/2+ state are presented within the particle-vibration weak-coupling scheme involving the unpaired proton and the 3- state from 66Ni and within shell-model calculations with a56Ni core using the jj44b residual interaction. The shell model also accounts reasonably well for the other measured electromagnetic transition probabilities. [ABSTRACT FROM AUTHOR]

Properties of neutron-rich 22C are studied using the mean-field approach with Skyrme energy density functionals. Its weak binding and large total reaction cross section, which are suggested by recent experiments, are simulated by modifying the central part of Skyrme potential. Calculating E1 strength distribution by using the random-phase approximation, we investigate developments of low-lying electric dipole (E1) strength and the contribution of core excitations of 20C. As the neutron Fermi level approaches the zero-energy threshold (εF≳-1 MeV), we find that the low-lying E1 strength exceeds the energy-weighted cluster sum rule, which indicates the importance of core excitations with the 1d5/2 orbit. [ABSTRACT FROM AUTHOR]

Background: The Gamow-Teller response of 40Ar is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of 1+ states at 2290 and 2730 keV in 40K results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from 40Ar(p, n) charge-exchange data and the transition strengths for the analog transitions studied in the β decay of 40Ti. Purpose: This study was aimed at resolving the ambiguity between the results from the 40 Art p, n) chargeexchange and 40Ti β-decay data. Method: Shell-model calculations in the sd-pf shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from 40Ar and 40Ti. Distorted-wave Bom approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the 40Ar(p,n) data. New high-resolution data for the 40Ar(³He,r) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations. Results: The shell-model calculations showed that interference between amplitudes associated with pf and sd components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for 40Ar and 40Ti, can produce the differences on the scale of those observed between the 40Ar charge-exchange and 40Ti β-decay data. In combination with the difference in nuclear penetrability of the (p, n) and (³He,i) probes, the different contributions from amplitudes associated with transitions in the pf and sd shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying 1+ states in the 40Ar(p, n) and 40Ar(³He,i) data. Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the 40Ar(p, n) data, not the 40Ti, β-decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying 1+ states in 40K and 40Sc and the experimentally observed Gamow-Teller strengths. [ABSTRACT FROM AUTHOR]

The internal-conversion and internal-pair-production decays of the first excited 0+ state in 68Ni are studied following the β decay of 68Co. A novel experimental technique, in which the ions of 68Co were implanted into a planar germanium double-sided strip detector and which required digital pulse processing, is developed. The values for the energy of the first excited 0+ state and the electric monopole transition strength from the first excited 0+ state to the ground state in 68Ni are determined to be 1605(3) keV and 7.6(4)×10-3, respectively. Comparisons of the experimental results to Monte Carlo shell-model calculations suggest the coexistence between a spherical ground state and an oblate first excited 0+ state in 68Ni. [ABSTRACT FROM AUTHOR]

We report on the first three-dimensional numerical simulations of first-order phase transitions in the early Universe to include the cosmic fluid as well as the scalar field order parameter. We calculate the gravitational wave (GW) spectrum resulting from the nucleation, expansion, and collision of bubbles of the low-temperature phase, for phase transition strengths and bubble wall velocities covering many cases of interest. We find that the compression waves in the fluid continue to be a source of GWs long after the bubbles have merged, a new effect not taken properly into account in previous modeling of the GW source. For a wide range of models, the main source of the GWs produced by a phase transition is, therefore, the sound the bubbles make. [ABSTRACT FROM AUTHOR]

Abstract: Details of Gamow–Teller (GT) and Fermi (F) strength extraction from charge-exchange reactions at intermediate energies, as well as the concept of using the phenomenological effective interaction for the description of the reactions are reviewed. The focus lies on high-resolution (3He, t) data, yet new data on (d, 2He) charge-exchange reactions are presented as well to indicate the connection and the similarity of both probes to the elementary , resp. reactions. We show that for the extraction of and strength a proper extrapolation of the charge-exchange cross section to the zero momentum transfer point, , gets to be increasingly important for medium to high-mass target nuclei and at moderate excitation energies of a few MeV. Numerous (3He, t) and spectra are being compared, and, once adjusted for the different momentum transfers, they reveal a remarkable similarity up to the highest measured excitation energies of . Further, we remark that the precision, with which GT and F transition strengths can be extracted, is limited by the relatively poor knowledge of the absorption processes, and a more thorough theoretical understanding of the nuclear structure leading to absorption in charge-exchange reactions, especially in the restricted kinematic region of low-momentum transfers, is warranted. Finally, values for the 136Xe(3He, t) are being re-evaluated in the light of the present discussion. [Copyright &y& Elsevier]

Background: Neutron-deficient krypton isotopes are of particular interest due to the coexistence of oblate and prolate shapes in low-lying states and the transition of the ground state from one dominate shape to another as a function of neutron number. Moreover, the onset of large E2 transition strength around 76Kr indicates the erosion of the N = 40 subshell gap. Purpose: A detailed interpretation of these phenomena in neutron-deficient Kr isotopes requires the use of a method going beyond a mean-field approach that permits the determination of spectra and transition probabilities. The aim of this work is to provide a systematic calculation of low-lying states in the even-even 68-86Rr isotopes and to understand the shape coexistence phenomenon and the onset of large collectivity around N = 40 from beyond relativistic mean-field studies. Method: The starting point of our method is a set of relativistic mean-field plus BCS wave functions generated with a constraint on triaxial deformations (ß, y). The excitation energies and electric multipole transition strengths of low-lying states are calculated by solving a five-dimensional collective Hamiltonian (5DCH) with parameters determined by the mean-field wave functions. To examine the role of triaxiality, a configuration mixing of both particle-number- and angular-momentum-projected axially deformed states is also carried out within the exact generator coordinate method based on the same energy density functional. Results: The energy surfaces, the excitation energies of O+2, 2+1, and 2+2 states, as well as the E0 and E2 transition strengths are compared with the results of similar 5DCH calculations but with parameters determined by the nonrelativistic mean-field wave functions, as well as with the available data. The results show a picture of oblate-triaxial-prolate shape transition. Coexistence of low-lying excited 0+ states is found to be a common feature in the neutron-deficient Kr isotopes. The underlying mechanism responsible for the shape coexistence is discussed. Conclusions: The main features of the low-spin spectra and the systematics of excitation energies and transition strengths in the neutron-deficient Kr isotopes are reproduced very well. The effects of dynamic correlations and triaxiality turn out to have important influences on the balance between the competing oblate and prolate states. An exact treatment of configuration mixing of particle-number- and angular-momentum-projected triaxial states is highly demanded to pin down these effects. [ABSTRACT FROM AUTHOR]

Abstract: Nine lifetimes have been determined for the first time in the and bands of 167Yb by means of Recoil distance Doppler-shift measurements carried out at the Cologne FN tandem. For the data analysis, a dedicated version of the Differential decay curve method was used. The newly deduced transition strengths and the level scheme are reasonably described by the Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the band. The stretched B(E2)ʼs in the favored signature are appreciably larger than those in the unfavored signature. The effect increases with spin. In the PTRM calculations, the wave functions of the favored signature levels contain larger contribution of low-Ω orbitals from parentage than those of the unfavored levels. This could selectively increase the deformation of the favored signature band members. If so, rotation and Coriolis interaction would give rise to a dynamic shape coexistence taking place between the two signatures. [Copyright &y& Elsevier]

We consider the AN → NN weak transition, responsible for a large fraction of the nonmesonic weak decay of hypernuclei. We follow the previously derived effective field theory and compute the next-to-leading one-loop corrections. Explicit expressions for all diagrams are provided, which result in contributions to all relevant partial waves. [ABSTRACT FROM AUTHOR]