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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Structure of high-lying excited states in 47 Ca with ℓ ≥ 3 populated in fast-beam 𝛾-ray-tagged one-neutron pickup reactions

Located just one neutron removed from doubly magic, stable 48 Ca, the adjacent isotope 47 Ca has been studied extensively with neutron-removing transfer reactions and interpreted within a shell-model picture. Neutron-adding transfer reactions onto the stable 46 Ca, however, have not been performed in nearly 60 years and never with the aid of high-resolution 𝛾-ray spectroscopy. Here, we report on the 12 C⁡( 46 , Ca 47 Ca+𝛾)⁢𝑋 one-neutron pickup reaction from 12 C onto 46 Ca at more than 50 MeV/nucleon, a regime of orbital angular momentum mismatch that selectively populates 47 Ca final states based on ℓ ≥ 3 neutron configurations. Newly observed excited states and 𝛾-ray transitions are discussed in comparison to 𝑓⁡𝑝 shell-model calculations in a variety of configuration spaces. Furthermore, it is shown that the nature of the observed spectrum of final states can be well interpreted, albeit with a significant fragmentation of the 𝜈⁢0⁢𝑓 5/2 strength observed in the measurement that is not borne out in the structure calculations.

39 ≤ A ≤ 58↗
DOE OSTI2026

Halo Nuclei from Ab Initio Nuclear Theory

A realistic description of halo nuclei, characterized by low-lying breakup thresholds, requires a proper treatment of continuum effects. We have developed an ab initio approach, the No-Core Shell Model with Continuum (NCSMC), capable of describing both bound and unbound states in light nuclei in a unified way. With chiral two- and three-nucleon interactions as the only input, we can predict the structure and dynamics of halo and other light nuclei and, by comparing to available experimental data, test the quality of chiral nuclear forces. We review NCSMC calculations of weakly bound states and resonances of the exotic halo nuclei 6He, 8B, 11Be, and 15C. For the latter, we discuss its production in the capture reaction 14C(n,𝛾 )15C. We highlight the challenges of a description of 6He as a Borromean n-n-4He system. Finally, we present our calculations of excited states in 10Be exhibiting a one-neutron halo structure and a large scale No-Core Shell Model investigation of 11Li as a precursor of a full n-n-9Li NCSMC study.

Navrátil, Petr↗
DOE OSTI2021

Wigner SU(4) symmetry, clustering, and the spectrum of $$^{12}$$C

Abstract We present lattice calculations of the low-lying spectrum of $$^{12}$$ 12 C using a simple nucleon–nucleon interaction that is independent of spin and isospin and therefore invariant under Wigner’s SU(4) symmetry. We find strong signals for all excited states up to $$\sim 15$$ ∼ 15 MeV above the ground state, and explore the structure of each state using a large variety of $$\alpha $$ α cluster and harmonic oscillator trial states, projected onto given irreducible representations of the cubic group. We are able to verify earlier findings for the $$\alpha $$ α clustering in the Hoyle state and the second $$2^+$$ 2 + state of $$^{12}$$ 12 C. The success of these calculations to describe the full low-lying energy spectrum using spin-independent interactions suggest that either the spin-orbit interactions are somewhat weak in the $$^{12}$$ 12 C system, or the effects of $$\alpha $$ α clustering are diminishing their influence. This is in agreement with previous findings from ab initio shell model calculations.

Shen, Shihang (ORCID:0000000280516466)↗
DOE OSTI2017

Ab initio calculation of the potential bubble nucleus Si 34

Background: The possibility that an unconventional depletion (referred to as a “bubble”) happens in the middle of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which Si 34 appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable Si 34 is currently out of reach, ($d, p$) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1/2 – –3/2 – splitting in the spectrum of Si 35 as compared to S 37 . Purpose: We study the potential bubble structure of Si 34 on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of Si 34 and S 36 . In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in S 36 . The next observable of interest is the low-lying spectroscopy of Si 35 and S 37 obtained from ($d, p$) experiments along with the spectroscopy of Al 33 and P 35 obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in Si 34 varies significantly with the nuclear Hamiltonian used. Yet, demanding that the experimental charge density distribution and the root-mean-square radius of S 36 be well reproduced, along with Si 34 and S 36 binding energies, only leaves the NNLO sat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of Si 34 , is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2 – –3/2 – splitting in the spectrum of Si 35 as compared to S 37 . Conclusions: The occurrence of a bubble structure in the charge distribution of Si 34 is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of Si 34 in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on Si 34 and S 36 in order to further test our theoretical spectral strength distributions over a wide energy range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Intruder configurations of excited states in the neutron-rich isotopes P 33 and P 34

Here, excited states in the neutron-rich isotopes P 33 and P 34 were populated by the O 18 + O 18 fusion-evaporation reaction at E lab = 24 MeV. The Gammasphere array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus S 36 . The use of Microball enabled the selection of the proton emission channel. It also helped in determining the exact position and energy of the emitted proton; this was later employed in kinematic Doppler corrections. 16 new transitions and 13 new states were observed in P 33 and 21 γ rays and 20 energy levels were observed in P 34 for the first time. The nearly 4 π geometry of Gammasphere allowed the measurement of γ -ray angular distributions leading to spin assignments for many states. The experimental observations for both isotopes were interpreted with the help of shell-model calculations using the (0+1) ℏ ω PSDPF interaction. The calculations accounted for both the 0p-0h and 1p-1h states reasonably well and indicated that 2p-2h excitations might dominate the higher-spin configurations in both P 33 and P 34 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2000

On the Modeling of Shells in Multibody Dynamics

Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the, constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.

Bauchau, Olivier A.↗
DOE OSTI2020

Toroidal States of the 12 C Nucleus

Among the states of 12 C, there is an important subset of $K$ = 0 and $K$ = I planar intrinsic states in which the intrinsic motion of the nucleons are confined in the planar region defined by the three-alpha cluster or by their generated toroid. The intrinsic nuclear densities of these states are toroidal in nature. In this work we study these 12 C toroidal states from the generator-coordinate viewpoints in both the alpha cluster model and the toroidal shell model. Numerical solutions in the toroidal mean field approximation are examined to pave the way for future extensions and refinements.

12C Hoyle state↗
DOE OSTI2017

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

Core@shell design represents an important class of architectures because of its capability to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend towards the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive x-ray spectroscopy (EDXS) and x-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe the local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultra-small (4.8 ± 0.5 nm) optically active cores (β-NaGd0.78Yb0.2Er0.02F4) surrounded by an optically inert shell (NaYF4) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the inter-diffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a non-homogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step towards the comprehensive understanding of the “structure - property” relationship of upconverting core@shell architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1994

Influence of an asymmetric ring on the modeling of an orthogonally stiffened cylindrical shell

Structural models are examined for the influence of a ring with an asymmetrical cross section on the linear elastic response of an orthogonally stiffened cylindrical shell subjected to internal pressure. The first structural model employs classical theory for the shell and stiffeners. The second model employs transverse shear deformation theories for the shell and stringer and classical theory for the ring. Closed-end pressure vessel effects are included. Interacting line load intensities are computed in the stiffener-to-skin joints for an example problem having the dimensions of the fuselage of a large transport aircraft. Classical structural theory is found to exaggerate the asymmetric response compared to the transverse shear deformation theory.

Rastogi, Naveen↗
DOE OSTI2025

In-beam 𝛾-ray spectroscopy toward the proton dripline: The curious case of 32 Ar

High-resolution in-beam 𝛾-ray spectroscopy was used to study excited states of the neutron-deficient nucleus 32 Ar populated in fast-beam induced four- and six-nucleon removal reactions from 36,38 Ca. One new 𝛾-ray transition and indications for an additional two were found, allowing for a glimpse at the level scheme beyond the 2$^{+}_{1}$ state. The nature of the new 1900⁢(4)-keV transition is discussed in the context of the known energy spectrum of the mirror nucleus 32 Si and shell-model calculations using the FSU and SDPF-M cross-shell effective interactions. Its resulting parent state at 3767⁢(5)⁢keV, more than 1.3 MeV above the proton separation energy, is tentatively assigned to have mixed 𝑠⁢𝑑-shell and 2p-2h character. It might either be the mirror of the 𝐽 𝜋 = 2$^{+}_{2}$ state of 32 Si at 4230.8⁢(8)⁢keV, but with a decay branch favoring a transition to the 2$^{+}_{2}$ over the ground state, or the mirror of the 4983.9⁢(11)-keV state with quantum numbers 0 + . Furthermore, the resulting mirror-energy differences of −473⁢(5) and −1218⁢(5)⁢keV are both sizable when compared to systematics; in the latter case the result would, in fact, be among the largest reported to date in the nuclear chart or suggest the potential existence of an additional, hitherto unidentified, low-lying 0 + state of 32 Si.

20 ≤ A ≤ 38↗
DOE OSTI2018

Low-spin structure of the N = 82 nucleus Cs 137

Excited states in 137 Cs have been studied by using the near-barrier, single-proton transfer reaction 10 B( 136 Xe, 9 Beγ) 137 Cs in inverse kinematics and performing particle-γ and particle-γγ coincidence measurements. The low-spin level scheme of 137 Cs has been augmented: (i) The expected set of single-proton, seniority ν = 1 states has been delineated in its entirety; (ii) Another member of the v = 3 proton 0g 7/2 multiplet, a low-lying 9/2 + level, has been identified and this set of states now approaches completion; (iii) A second 9/2 + and a candidate 13/2 + level have been observed. Furthermore, the results are discussed in the framework of shell-model calculations in the proton 2s1 d 0 g 0 h shell.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Active Cryovolcanism on Europa?

Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al. found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Hierarchic models for laminated plates

Structural plates and shells are three-dimensional bodies, one dimension of which happens to be much smaller than the other two. Thus, the quality of a plate or shell model must be judged on the basis of how well its exact solution approximates the corresponding three-dimensional problem. Of course, the exact solution depends not only on the choice of the model but also on the topology, material properties, loading and constraints. The desired degree of approximation depends on the analyst's goals in performing the analysis. For these reasons models have to be chosen adaptively. Hierarchic sequences of models make adaptive selection of the model which is best suited for the purposes of a particular analysis possible. The principles governing the formulation of hierarchic models for laminated plates are presented. The essential features of the hierarchic models described models are: (1) the exact solutions corresponding to the hierarchic sequence of models converge to the exact solution of the corresponding problem of elasticity for a fixed laminate thickness; and (2) the exact solution of each model converges to the same limit as the exact solution of the corresponding problem of elasticity with respect to the laminate thickness approaching zero. The formulation is based on one parameter (beta) which characterizes the hierarchic sequence of models, and a set of constants whose influence was assessed by a numerical sensitivity study. The recommended selection of these constants results in the number of fields increasing by three for each increment in the power of beta. Numerical examples analyzed with the proposed sequence of models are included and good correlation with the reference solutions was found. Results were obtained for laminated strips (plates in cylindrical bending) and for square and rectangular plates with uniform loading and with homogeneous boundary conditions. Cross-ply and angle-ply laminates were evaluated and the results compared with those of MSC/PROBE. Hierarchic models make the computation of any engineering data possible to an arbitrary level of precision within the framework of the theory of elasticity.

Actis, Ricardo Luis↗
DOE OSTI2022

Isomers in Tl 203 and core excitations built on a five-nucleon-hole structure

Isomers with three- and five-nucleon-hole configurations have been established in 203 Tl These include newly identified levels with a three-nucleon-hole structure: I π = (15/2 – ) with T 1/2 = 7.9(5) ns and I π = (35/2 – ) with T 1/2 = 4.0(5) ns. In addition, five-nucleon-hole states have also been established: I π = (39/2 – ) with T 1/2 = 1.9(2) ns and I π = (49/2 + ) with T 1/2 = 3.4(4) ns. The previously determined long-lived decay, T 1/2 = 6.6(3) μs from this work, is associated with isomerism of the I π = (29/2 + ) state. Levels above this long-lived isomer have been identified through a delayed-prompt γ–γ coincidence measurement. Five-nucleon-hole states with excitation energies E x ≈ 7 MeV have been established as well as possible octupole excitations of the 208Pb core built on these levels. Furthermore, the level scheme of 203 Tl is extended up to E x ≈ 11 MeV with the inclusion of 25 new transitions. Empirical and shell-model calculations have been performed to aid in the description of the observed states which are found to be of intrinsic character.

190 ≤ A ≤ 219↗
DOE OSTI2022

β − decay of exotic P and S isotopes with neutron number near 28

β - decay of very neutron-rich isotopes of P and S, studied at the National Superconducting Cyclotron Laboratory (NSCL) using the Beta Counting Station (BCS) consisting of a Double Sided Strip Detector surrounded by clovers detectors for observing delayed γ transitions is reported here. β-decay half-lifes and delayed neutron emission probabilities were extracted for 42,43,44 P and 44,46 S by analyzing spatial and temporal correlations between implants and decay events in the Si detector with further coincidence with γ transitions. Detection of delayed γ rays allowed for the identification of negative parity 1p1h states in 42 S for the first time, also constraining the parent ( 42 P) spin/parity to 2 - or 3 - . For the most exotic isotope studied, 46 S, no strong γ transition was observed unlike lighter even-even S isotopes, thus implying the shift of Gamow Teller (GT) strength distribution to higher energies. In conclusion, comparison of experimental observations to detailed shell-model calculations using the SDPFSDG-MU interaction allowed us to infer the importance and role of First Forbidden (FF) β transitions as the neutron number approaches and then exceeds N = 28.

39 ≤ A ≤ 58↗
NASA NTRS1978

Five micron limb-darkening and the structure of the Jovian atmosphere

A combined radiative, dynamical, and chemical model of the Jovian atmosphere is presented which reproduces the observed IR limb-darkening curves for several regions on the disk of Jupiter. Two approaches are used to perform the inversion required for determination of the source function, and a power-series-expansion model is examined, along with a convective-equilibrium model, cloud and intermediate-zone models, and a thin-shell model. The statistical methods used in the analysis are outlined, and model fits to the observations are discussed. The chemistry of phase transitions in the hot spots of Jupiter's equatorial belt is briefly investigated.

Newman, W. I.↗
DOE OSTI2023

Nuclear-level effective theory of 𝜇→𝑒 conversion: Formalism and applications

Over the next decade new 𝜇→𝑒 conversion searches at Fermilab (Mu2e) and J-PARC (COMET, DeeMe) are expected to advance limits on charged lepton flavor violation (CLFV) by more than four orders of magnitude. Here, by considering the consequence of 𝑃 and 𝐶⁢𝑃 on elastic 𝜇→𝑒 conversion and the structure of possible charge and current densities, we show that rates are governed by six nuclear responses and a single scale, 𝑞/𝑚 𝑁 , where 𝑞 ≈ 𝑚 𝜇 is the momentum transferred from the leptons to the nucleus. To relate this result to microscopic formulations of CLFV, we construct in nonrelativistic effective theory (NRET) the CLFV nucleon-level interaction, pointing out the relevance of the dimensionless scales 𝑦=($^{𝑞⁢𝑏}_2$) 2 ⁢ > |$\overrightarrow{𝑣}_N$⁢|>|$\overrightarrow{𝑣}_μ$⁢|>|$\overrightarrow{𝑣}_T$| , where 𝑏 is the nuclear size, $\overrightarrow{𝑣}_N$ and $\overrightarrow{𝑣}_μ$ are the nucleon and muon intrinsic velocities, and $\overrightarrow{𝑣}_T$ is the target recoil velocity. We discuss previous work, noting the lack of a systematic treatment of the various small parameters. Because the parameter 𝑦 is not small, a proper calculation of 𝜇→𝑒 conversion requires a full multipole expansion of the nuclear response functions, an apparently daunting task with Coulomb-distorted electron partial waves. We demonstrate that the multipole expansion can be carried out to high precision by introducing a simplifying local momentum 𝑞 eff for the electron. Previous work has been limited to simple charge or spin interactions, thereby treating the nucleus effectively as a point particle. We show that such formulations are not compatible with the general form of the 𝜇→𝑒 conversion rate, failing to generate three of the six allowed nuclear response functions. The inclusion of the nucleon velocity $\overrightarrow{𝑣}_N$ yields an NRET with 16 operators and a rate of the general form. Consequently, in the current discovery era for CLFV, it provides the most sensible starting point for experimental analysis, defining what can and cannot be determined about CLFV from the highly exclusive process of 𝜇→𝑒 conversion. Finally, we expand the NRET operator basis to account for the effects of $\overrightarrow{𝑣}_μ$, associated with the muon's lower component, generating corrections to the CLFV coefficients of the point-nucleus response functions. Using advanced shell-model methods, we compute 𝜇→𝑒 conversion rates for a series of experimental targets, deriving bounds on the coefficients of the CLFV operators. These calculations are the first to include a general basis of CLFV operators, full evaluation of the associated nuclear response functions, and an accurate treatment of electron and muon Coulomb effects. We discuss target selection as an experimental “knob” that can be turned to probe the microscopic origins of CLFV. We describe two types of coherence that enhance certain CLFV operators and selection rules that blind elastic 𝜇→𝑒 conversion to others. We discuss the matching of the NRET onto higher level effective field theories, such as those constructed at the light quark level, noting opportunities to build on existing work in direct detection of dark matter. We discuss the relation of 𝜇→𝑒 conversion to 𝜇→𝑒+𝛾 and 𝜇→3⁢𝑒, showing how MEG II and Mu3e results will complement those of Mu2e and COMET. Finally we describe a accompanying script—in Mathematica and Python versions—that can be used to compute 𝜇→𝑒 conversion rates in various nuclear targets for the full set of NRET operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Onset of band structure in 70 Ga

Excited states in the odd-odd nucleus 70 Ga were studied using the 62 Ni( 14 C, αpn) fusion-evaporation reaction at the John D. Fox Superconducting Accelerator Laboratory at Florida State University with a 50 MeV beam. Depopulating γ rays were measured in coincidence with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. Analysis of γ–γ coincidences led to the addition of 16 new transitions to the 70 Ga level scheme, including transitions associated with the onset of a new positive-parity band structure likely based on the πg 9/2 ⊗ νg 9/2 configuration. Spins and parities were assigned using directional correlation of oriented nuclei (DCO) ratios and linear polarization measurements. Shell-model calculations with the JUN45 effective interaction reproduce the excitation energies of the positive-parity states reasonably well but predict negative-parity states that are typically 400–500 keV lower than observed. Furthermore, total Routhian surface calculations for the lowest positive-parity configuration with signature α = 0 indicate significant triaxiality (γ ≈ −20°) and the development of competing non-collective excitations at J = 8, corresponding to the experimentally observed onset of the positive-parity band. Similar features are found in the calculated surfaces for the lowest negative-parity states with α = 0.

59 ≤ A ≤ 89↗