Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “nuclear shell model”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Theoretical study of band structure of odd-mass {sup 115,117}I isotopes

By using the microscopic approach of Projected Shell Model (PSM), negative-parity band structures of odd mass neutron-rich {sup 115,117}I nuclei have been studied with the deformed single-particle states generated by the standard Nilsson potential. For these isotopes, the band structures have been analyzed in terms of quasi-particles configurations. The phenomenon of back bending in moment of inertia is also studied in the present work.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Ground-state electromagnetic moments of Ca 37

The hyperfine coupling constants of neutron deficient 37 Ca were deduced from the atomic hyperfine spectrum of the 4 s 2 S 1/2 ↔ 4 p 2 P 3/2 transition in Ca II , measured using the collinear laser spectroscopy technique. The ground-state magnetic-dipole and spectroscopic electric-quadrupole moments were observed for the first time as μ=+0.7453(72)μ N and Q = -15(11) e 2 fm 2 , respectively. The experimental values agree well with nuclear shell-model calculations using the universal sd model-space Hamiltonians versions A and B (USDA/B) in the sd -model space with a 95% probability of the canonical nucleon configuration. It is demonstrated that the magnetic moment of 39 Ca requires a larger non- sd -shell component than that of 37 Ca for good agreement with the shell-model calculation, suggests a more robust closed subshell structure of 36 Ca at the neutron number N =16 than 40 Ca. The results are also compared to valence-space in-medium similarity renormalization group calculations based on chiral two- and three-nucleon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

The gallium solar neutrino capture cross section revisited

Solar neutrino flux constraints from the legacy GALLEX/GNO and SAGE experiments continue to influence contemporary global analyses of neutrino properties. The constraints depend on the neutrino absorption cross sections for various solar sources. Following recent work updating the 51 Cr and 37 Ar neutrino source cross sections, we reevaluate the 71 Ga solar neutrino cross sections, focusing on contributions from transitions to 71 Ge excited states, but also revising the ground-state transition to take into account new 71 Ge electron-capture lifetime measurements and various theory corrections. The excited-state contributions have been traditionally taken from forward-angle (𝑝, 𝑛) cross sections. Here we correct this procedure for the ≈ 10%–20% tensor operator contribution that alters the relationship between Gamow-Teller and (𝑝, 𝑛) transition strengths. Using state-of-the-art nuclear shell-model calculations to evaluate this correction, we find that it lowers the 8 B and hep neutrino cross sections. However, the addition of other corrections, including contributions from near-threshold continuum states that radiatively decay, leads to an overall increase in the 8 B and hep cross sections of ≈ 10% relative to the values recommended by Bahcall. Uncertainties are propagated using Monte Carlo simulations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Precision mass measurements of 44 V and 44m V for nucleon-nucleon interaction studies

Here, we discuss the motivation and technique of Penning trap mass spectrometry applied to radioactive 44 V and 44m V, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. A complementary measurement of these nuclides, performed at the CSRe in Lanzhou, China, was recently published, but with errors several times larger than obtainable for a short-lived radionuclide in a Penning trap. Interpretation of the higher precision results is ongoing and a full accounting of this measurement is anticipated in the coming months.

44-vanadium↗
NASA NTRS1998

Transport of Light Ions in Matter

A recent set of light ion experiments are analyzed using the Green's function method of solving the Boltzmann equation for ions of high charge and energy (the GRNTRN transport code) and the NUCFRG2 fragmentation database generator code. Although the NUCFRG2 code reasonably represents the fragmentation of heavy ions, the effects of light ion fragmentation requires a more detailed nuclear model including shell structure and short range correlations appearing as tightly bound clusters in the light ion nucleus. The most recent NTJCFRG2 code is augmented with a quasielastic alpha knockout model and semiempirical adjustments (up to 30 percent in charge removal) in the fragmentation process allowing reasonable agreement with the experiments to be obtained. A final resolution of the appropriate cross sections must await the full development of a coupled channel reaction model in which shell structure and clustering can be accurately evaluated.

Wilson, J. W.↗
DOE OSTI2025

Triaxiality and shape dynamics in 70 Ge

The electromagnetic properties of low-lying states in 70 Ge were investigated via multi-step Coulomb excitation of a 70 Ge beam impinging on a 208 Pb target at the ATLAS facility of the Argonne National Laboratory. A total of 27 transitional elements and six diagonal matrix elements coupling 11 low-lying states, were extracted from the measured cross sections. These were used to calculate reduced transition probabilities, spectroscopic quadrupole moments, and rotational invariant shape parameters, providing enhanced precision and expanding on previous studies. The experimental data were compared within several theoretical frameworks, including the generalized triaxial rotor model, configuration interaction shell-model calculations, and computations within the combined frameworks of relativistic density functional theory and the five-dimensional collective Hamiltonian. The results demonstrate a good agreement with the experimental data and, in conjunction with calculations using a two-state mixing model, support significant triaxiality and strong mixing between the 0$^{+}_{1}$ and 0$^{+}_{2}$ states. This results in the magnitudes of their respective quadrupole deformations [β rms (0$^{+}_{1}$) = 0.228 (3), β rms (0$^{+}_{2}$) = 0.273 (1)] being more similar than previously observed. Furthermore, the implications of these results for understanding the complex shape coexistence phenomena, the role of triaxiality, and shape evolution along the Ge isotopic chain are discussed.

59 ≤ A ≤ 89↗
DOE OSTI2016

Tables of E2 transition probabilities from the first 2 + states in even–even nuclei

Highlights: • Compilation of experimental transition probabilities or B(E2) values for the known first 2{sup +} states in even–even nuclei. • Evaluation of B(E2) values, lifetimes and deformation parameters for 447 even–even nuclei. • Extensive discussion on data evaluation policies and procedures. • Nuclear shell model calculation of the first 2{sup +} states energies and B(E2) values in even–even nuclei. Experimental results of E2 transition probabilities or B(E2) values for the known first 2{sup +} states in 447 even–even nuclei have been compiled and evaluated. The evaluation policies for the analysis of experimental data have been described and new results are discussed. The recommended B(E2) values have been compared with comprehensive shell model calculations for a selected set of nuclei, where such theoretical procedures are amenable. The present work was motivated by a rapid increase in the number of new B(E2) measurements for the first 2{sup +} states since the previous evaluation of such data by S. Raman et al. published in 2001. Future plans to investigate the systematics of B(E2)↑ values, and intercomparison of different experimental techniques to obtain these data are outlined.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Study on Modeling of Nuclear Fuel End Drop during a Hypothetical Accident

It is well known that shell elements have been used to model the cladding of single nuclear fuel pins. These have been used, for example, to analyze the response of a fuel assembly by assuming that all fuel pins in a fuel assembly deform in the same pattern. It is increasingly significant to model the entire fuel assembly in order to capture more realistically the behavior of each individual nuclear fuel during a hypothetical accident in a manner that can account for interactions among single pins. However, modeling each individual fuel pin in an entire fuel assembly using shell elements will result in models with large amount of elements and degrees of freedom that take correspondingly larger amount of computational times to execute. Therefore, modeling the nuclear fuel assembly with beam elements may become an option. This paper presents the results of a set of analysis with the LS-DYNA finite element software that investigated the differences and similarities of modeling nuclear fuel assemblies using either shell elements or beam elements. This study provides additional insights on the appropriateness of using beam element models of the fuel pins in the simulation of a hypothetical accident. In this study, two single pin models, a single pin model using shell elements and a single beam model using beam elements, are constructed to analyze end drop scenarios with the LS-DYNA code. Each model is then analyzed for a 19 ft end drop scenario (linear behavior) and 30 ft end drop scenario (non-linear behavior). Comparisons are made between the results obtained with the single pin shell model and with the single pin beam model to study the differences and similarities resulting from the two modeling approaches. In this study, a B and W 15x15 PWR fuel is analyzed for both 30 ft and 19 ft end hypothetical accident drops using both single pin finite element model with shell elements and beam elements for the fuel cladding. It is found that for the 19 ft end drop, the difference in the Max/Min total axial strains is about 12% between the two models. For the 30 ft end drop, the maximum total axial strains calculated with both models is similar, and a difference of about 12% is observed for the minimum total axial strains calculated by the two models. Advantages of the single pin shell model are that it permits consideration of internal pressures and may capture local buckling. Therefore, use of beam elements to model the fuel cladding needs to take into account the possible significance of local buckling and internal pressurization for the problem being analyzed. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

Toward scalable many-body calculations for nuclear open quantum systems using the Gamow Shell Model

Drip-line nuclei have very different properties from those of the valley of stability, as they are weakly bound and resonant. Therefore, the models devised for stable nuclei can no longer be applied therein. Hence, a new theoretical tool, the Gamow Shell Model (GSM), has been developed to study the many-body states occurring at the limits of the nuclear chart. GSM is a configuration interaction model based on the use of the so-called Berggren basis, which contains bound, resonant and scattering states, so that inter-nucleon correlations are fully taken into account and the asymptotes of extended many-body wave functions are precisely handled. However, large complex symmetric matrices must be diagonalized in this framework, therefore the use of very powerful parallel machines is needed therein. So, in order to fully take advantage of their power, a 2D partitioning scheme using hybrid MPI/OpenMP parallelization has been developed in our GSM code. The specificities of the 2D partitioning scheme in the GSM framework will be described and illustrated with numerical examples. It will then be shown that the introduction of this scheme in the GSM code greatly enhances its capabilities.

2D partitioning↗
DOE OSTI2022

The Gamow shell model with realistic interactions: a theoretical framework for ab initio nuclear structure at drip-lines

Abstract Ab initio approaches are among the most advanced models to solve the nuclear many-body problem. In particular, the no-core–shell model and many-body perturbation theory have been recently extended to the Gamow shell model framework, where the harmonic oscillator basis is replaced by a basis bearing bound, resonance and scattering states, i.e. the Berggren basis. As continuum coupling is included at basis level and as configuration mixing takes care of inter-nucleon correlations, halo and resonance nuclei can be properly described with the Gamow shell model. The development of the no-core Gamow shell model and the introduction of the Q ¯ ˆ -box method in the Gamow shell model, as well as their first ab initio applications, will be reviewed in this paper. Peculiarities compared to models using harmonic oscillator bases will be shortly described. The current power and limitations of ab initio Gamow shell model will also be discussed, as well as its potential for future applications.

Physics↗
DOE OSTI2025

Understanding the Effect of Chiral NN Parametrization on Nuclear Shapes From an Ab Initio Perspective

The ab initio symmetry-adapted no-core shell model naturally describes nuclear deformation and collectivity, and is therefore well-suited to studying the dynamics and coexistence of shapes in atomic nuclei. For the first time, we analyze how these features in low-lying states of 6 Li and 12 C are impacted by the underlying realistic nucleon-nucleon interaction. We find that the interaction parametrization has a notable but limited effect on collective shapes in the lowest 6 Li and 12 C states, while collective structures in the excited 2 + state of 12 C are significantly more sensitive to the interaction parameters and exhibits emergent shape coexistence.

Becker, Kevin S. [Louisiana State University, Bato↗
DOE OSTI2023

First observation of 28 O

Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton ($N/Z$) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric $N/Z$ ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10 -21 s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28 O and 27 O through their decay into 24 O and four and three neutrons, respectively. The 28 O nucleus is of particular interest as, with the $Z$ = 8 and $N$ = 20 magic numbers, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Furthermore, both 27 O and 28 O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28 O from a 29 F beam is consistent with it not exhibiting a closed $N$ = 20 shell structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Nuclear Weak Rates and Detailed Balance in Stellar Conditions

Detailed balance is often invoked in discussions of nuclear weak transitions in astrophysical environments. Satisfaction of detailed balance is rightly touted as a virtue of some methods of computing nuclear transition strengths, but I argue that it need not necessarily be strictly obeyed in astrophysical environments, especially when the environment is far from weak equilibrium. I present the results of shell model calculations of nuclear weak strengths in both charged-current and neutral-current channels at astrophysical temperatures, finding some violation of detailed balance. I show that a slight modification of the technique to strictly obey detailed balance has little effect on the reaction rates associated with these strengths under most conditions, though at high temperature the modified technique in fact misses some important strength. I comment on the relationship between detailed balance and weak equilibrium in astrophysical conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Testing shell-model interactions at high excitation energy and low spin: Nuclear resonance fluorescence in Ge 74

With their complex low-spin structure, the germanium isotopes have accrued a large number of experimental data which challenge nuclear models. The structure of the 74 Ge isotope is investigated here with nuclear resonance fluorescence as part of an extensive campaign of experimental tests of the shell model in the germanium isotopic chain using a number of complementary techniques. Levels were excited with 3.10 – 5.44 MeV photon beams provided by the High Intensity Gamma-Ray Source at TUNL. Many new levels were identified and their spins, parities, branching ratios, and associated scattering cross section values were determined. Large-scale shell-model calculations, which include jj44b and JUN45 effective interactions developed to describe nuclei in this mass region, predict the new data satisfactorily. Herein this study extends the validation of these two interactions, which are candidates for computation of matrix elements to be used in the interpretation of neutrinoless double-β decay experiments in 76 Ge, into the low-spin, high excitation energy domain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Weak entanglement approximation for nuclear structure

The interacting shell model, a configuration-interaction method, is a venerable approach for low-lying nuclear structure calculations, but it is hampered by the exponential growth of its basis dimension as one increases the single-particle space and/or the number of active particles. Recent, quantum-information-inspired work has demonstrated that the proton and neutron sectors of a nuclear wave function are weakly entangled. Furthermore, the entanglement is smaller for nuclides away from N = Z, such as heavy, neutron-rich nuclides. Here, in this study, we implement a weak entanglement approximation to bipartite configuration-interaction wave functions, approximating low-lying levels by coupling a relatively small number of many-proton and many-neutron states. This truncation scheme, which we present in the context of past approaches, reduces the basis dimension by many orders of magnitude while preserving essential features of nuclear spectra.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Nuclear matrix elements for 0νβ{sup −}β{sup −} decays: Comparative analysis of the QRPA, shell model and IBM predictions

In this work we report on general properties of the nuclear matrix elements involved in the neutrinoless double β{sup −} decays (0νβ{sup −}β{sup −} decays) of several nuclei. A summary of the values of the NMEs calculated along the years by the Jyväskylä-La Plata collaboration is presented. These NMEs, calculated in the framework of the quasiparticle random phase approximation (QRPA), are compared with those of the other available calculations, like the Shell Model (ISM) and the interacting boson model (IBA-2)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗