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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.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Structure of odd-mass Ne, Na, and Mg nuclei

The island of inversion is a region of neutron-rich nuclei around 31 Na that are deformed in their ground states. In this region, less is known about the energy levels of odd-mass nuclei, how they evolve with increasing neutron numbers, and how they can be organized into rotational bands. We perform ab initio coupled-cluster calculations of spectra in odd-mass Ne, Na, and Mg nuclei based on an interaction of chiral effective field theory. In conclusion, our results confirm some tentative spin and parity assignments, predict the structure of nuclei near the neutron dripline, and inform us about rotational bands in this region of the nuclear table.

20 ≤ A ≤ 38↗
DOE OSTI2021

Pseudospin-doublet bands and Gallagher Moszkowski doublet bands in 100 Y

New transitions in neutron-rich 100 Y have been identified in a 9 Be + 238 U experiment with mass and Z gates to provide full fragment identification. These transitions and high spin levels of 100 Y have been investigated by analyzing the high statistics γ–γ–γ and γ–γ–γ–γ coincidence data from the spontaneous fission of 252 Cf at the Gammasphere detector array. Two new bands, 14 new levels, and 23 new transitions have been identified. The K π = 4 + new band decaying to a 1s isomeric state is assigned to be the high-K Gallagher-Moszkowski (GM) partner of the known K π = 1 + band, with the π5/2[522]Ⓧν3/2[411] configuration. This 4 + band is also proposed to be the pseudospin partner of the new K π = 5 + band with a 5 + π5/2[422] Ⓧ ν5/2[413] configuration, to form a π5/2[422] Ⓧ ν[3125/2,3/2] neutron pseudospin doublet. Here, constrained triaxial covariant density-functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found to be in good agreement with experimental values.

100Y↗
DOE OSTI2021

Long-lived isomeric states and quasiparticle band structures in neutron-rich 162,164 Gd nuclei from β decay

Neutron-rich nuclei 162,164 Eu were produced by bombarding a proton beam on a 238 U target at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory and mass separating the 162,164 Eu products. New level schemes and new γ-ray transitions of the daughters 162,164 Gd were identified from β-decay spectroscopy studies. Additionally, half-lives of the 162,164 Eu were remeasured to clarify the previous ambiguous results. Two quasiparticle band structures were built and compared with neighboring nuclei. The β and γ bands were extended in 162 Gd and a γ band was extended in 164 Gd. Half-lives of the isomeric states at (6 - ) 1449 keV in 162 Gd and (4 - ) 1096 keV in 164 Gd were measured to be 99(3) μs and 0.56(3) μs, respectively. Projected shell model calculations were performed and found to be in good agreement with all of the experimental data.

150 ≤ A ≤ 189↗
DOE OSTI2026

Isomeric states in the neutron-rich 𝑁 = 108 nuclei 178 Yb and 179 Lu

A multinucleon transfer reaction with a 136 Xe beam and a gold-backed 176 Yb target populated isomers in N = 108 178 Yb and 179 Lu. The single decay from the t 1/2 = 203(16) ns isomer in 178 Yb to the I π = 4 + level in the ground-state band suggests a I π = 4 − assignment, and multiquasiparticle calculations associate this state with the K π = 4 − , ν 2 (1/2[510], 9/2[624]) configuration. At least two isomers were observed in 179 Lu. One likely couples the K π = 4 − configuration found in 178 Yb to the 9/2[514] quasiproton orbital to form a K π = 17/2 + level (t 1/2 = 1.0(4) µs) which primarily decays into the rotational band based on the 9/2[514] state. A second isomer was observed to decay into this same band, but at higher energy and spin. Based on its feeding pattern, its similarity to an isomer found in 181 Ta, and a multiquasiparticle calculation, it is proposed to correspond to a K π = 29/2 − state based on the π9/2[514]ν 2 (9/2[624], 11/2[615]) configuration. As a result, an analysis of the reduced hindrance factors for negative-parity, two-quasineutron isomers in the rare-earth region is presented as well.

150 ≤ A ≤ 189↗
DOE OSTI2020

Fine structure of the isovector giant dipole resonance in Nd 142 – 150 and Sm 152

Inelastic proton scattering at energies of a few hundred MeV and very-forward scattering angles including 0° has been established as a tool for the study of electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the isovector giant dipole resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at the iThemba Laboratory for Accelerator Based Sciences in Cape Town, South Africa. The scattering products were momentum-analyzed by the K600 magnetic spectrometer positioned at θ Lab = 0°. Using dispersion-matching techniques, energy resolutions of ΔE ≈ 40–50 keV (full width at half maximum) were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photoabsorption cross sections using the equivalent virtual-photon method. Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Fine structure of the IVGDR is observed even for the most deformed nuclei studied. Comparisons between the extracted experimental energy scales and those energy scales obtained from the quasiparticle-phonon model (QPM) and Skyrme separable random phase approximation (SSRPA) predictions provide insight into the role of different giant-resonance damping mechanisms. It can be seen that the scales in the spherical and most likely also in the deformed nuclei mainly result from the fragmentation of the one-particle-one-hole (1p1h) strength into several dominant transitions serving as doorway states. In cases where calculations beyond the 1p1h level are available, some impact of the spreading due to coupling of the two-particle-two-hole (2p2h) states to the 1p1h doorway states is observed. New virtual-photon absorption data for the chain of stable Nd isotopes and 152 Sm are presented, with a focus on the phenomenon of nonstatistical cross-section fluctuations, referred to as fine structure, in the energy region of the IVGDR. The wavelet-analysis techniques used allowed for the features of the fine structure to be quantified in the form of characteristic scales. Finally, comparisons between experimental results and model predictions indicate that Landau damping seems to be the main source of the fine structure in both the spherical and deformed nuclei, but calculations including 2p2h degrees of freedom would be beneficial to confirm this for the deformed cases.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Chiral-like doublet band structure and octupole correlations in 104 Ag

The nature of the yrast negative-parity band and its chiral-like partner band in 104 Ag is investigated experimentally and theoretically. Lifetimes of states in the negative-parity yrast band and positive-parity band based on the 4424-keV level are measured using Doppler shift attenuation technique. Lifetimes of three more states have been determined along with the upper limit for the lifetime of the highest observed yrast states. Further, lifetimes known from earlier studies are determined with better precision. The level scheme of 104 Ag has also been extended with the addition of new enhanced E1 transitions linking the positive-parity band based on the 4424-keV levels and the yrast negative-parity and its partner band. B(E1) and/or B(E1)/B(M1) values for the transitions from the positive-parity band to the yrast and its partner band have been determined for the first time; these suggest strong octupole correlation between the positive-parity and the negative-parity bands. Here, calculations based on the triaxial projected shell model (TPSM) and covariant density functional theory (CDFT) have been performed to unravel the intrinsic structures of the partner band and the excited positive-parity band. TPSM calculations predict that doublet bands have significant angular momentum contributions along the three principle axes, suggesting that bands could have chiral symmetry breaking origin. The CDFT calculations predict a π(g 9/2 ) -1 Ⓧν(h 11/2 )(g 7/2 ,d 5/2 ) 2 aligned quasiparticle configuration for the negative-parity doublet bands with deformation parameters β≈0.20 and γ≈5°. The partner band could be interpreted as a chiral vibration mode built on top of the yrast band. The excited positive-parity band is predicted to have aligned four quasiparticle configurations, namely, π(g 9/2 ) -1 Ⓧν(h 11/2 ) 2 (g 7/2 ,d 5/2 ) 1 . Further, these calculations predict significant octupole softness in 104 Ag which could be the reason for enhanced E1 transitions between the four quasiparticle positive-parity bands and the doublet negative-parity bands.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Rotational bands in 249 Md

Rotational structures in 249 Md have been observed for the first time. One set of states forms a pair of strongly coupled bands with relatively strong E2 transitions and no identifiable M1 transitions between the two signature partners. Another set of states suggests a decoupled sequence of E2 transitions. Furthermore, these bands are assigned as based on the 7/2 − [514] and on the favored signature of the 1/2 - [521] Nilsson level, respectively. Based on previous decay studies, these levels are thought to be the ground state and first excited state of 249 Md, which also agrees with theoretical predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Case studies in bias reduction and inference for electronic health record data with selection bias and phenotype misclassification

Electronic health records (EHR) are not designed for population‐based research, but they provide easy and quick access to longitudinal health information for a large number of individuals. Many statistical methods have been proposed to account for selection bias, missing data, phenotyping errors, or other problems that arise in EHR data analysis. However, addressing multiple sources of bias simultaneously is challenging. We developed a methodological framework (R package, SAMBA ) for jointly handling both selection bias and phenotype misclassification in the EHR setting that leverages external data sources. These methods assume factors related to selection and misclassification are fully observed, but these factors may be poorly understood and partially observed in practice. As a follow‐up to the methodological work, we demonstrate how to apply these methods for two real‐world case studies, and we evaluate their performance. In both examples, we use individual patient‐level data collected through the University of Michigan Health System and various external population‐based data sources. In case study (a), we explore the impact of these methods on estimated associations between gender and cancer diagnosis. In case study (b), we compare corrected associations between previously identified genetic loci and age‐related macular degeneration with gold standard external summary estimates. These case studies illustrate how to utilize diverse auxiliary information to achieve less biased inference in EHR‐based research.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

A Typology for Characterizing Human Action in MultiSector Dynamics Models

The role of individual and collective human agency is increasingly recognized as a prominent and arguably paramount determinant in shaping the behavior, trajectory, and vulnerability of multisector systems. This human influence operates at multiple scales: from short-term (hourly to daily) to long-term (annually to centennial) timescales, and from the local to the global, pushing systems towards either desirable or undesirable outcomes. However, the effort to represent human systems in multisector models has been fragmented across philosophical, methodological, and disciplinary lines. To cohere insights across diverse modeling approaches, we present a new typology for classifying how human actors are represented in the broad suite of coupled human-natural system models that are applied in MultiSector Dynamics (MSD) research. The typology conceptualizes a “sector” as a system-of-systems that includes a diverse group of human actors, defined across individual to collective social levels, involved in governing, provisioning, and utilizing products, goods, or services towards some human end. We trace the salient features of modeled representations of human systems by organizing the typology around three key questions: 1) Who are the modeled actors in MSD systems? 2) What are their modeled actions? 3) How and for what purpose are these actors and actions operationalized in a computational model? The typology is used to critically examine existing models and chart the frontier of future human systems modeling for MSD research.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2026

Observing neutron alignment at high angular momenta in heavy deformed actinides

An outstanding puzzle in the structure of very heavy nuclei lies in the rotation response of deformed transuranic isotopes. While the rotation alignment of pairs of 𝑖 13/2 protons is ubiquitous and well understood, observing the analogous alignment of the 𝑗 15/2 neutrons has been elusive. In this work we present a new quantitative analysis approach: from their moments of inertia as a function of frequency, we compare the alignments of rotational bands with both “low” and high-𝑗 intrinsic structures in the 𝑁 = 151 isotones of Pu, Cm, Cf, and No, thereby distinguishing between the alignments of neutron versus proton pairs through “blocking” effects. In this way, the alignment of 𝑗 15/2 neutrons can be clearly identified for the first time. The protons and neutrons begin aligning at a very similar frequency. The contribution of 𝑗 15/2 neutrons to the total alignment is found to grow with increasing 𝑍 compared to 𝑖 13/2 protons. To explain these observations, it is necessary to adopt a self-consistent set of single-particle energies corresponding to the nuclear shape that minimizes the mass. The shape description needs to include high-order deformations up to at least 𝛽 6 .

A ≥ 220↗
DOE OSTI2020

Search for the high-spin members of the α : 2 n : α band in 10 Be

Clustering plays an important role in the structure of 10 Be. Exotic molecular-like configurations, such as α:2n:α, have been suggested at relatively low excitation energies. To search for the high-spin states that may belong to the molecular-like α:2n:α configuration in 10 Be. Measuring excitation functions for 6 He + α scattering, populating states in the excitation energy range from 4.5 MeV to 8 MeV in 10 Be using a 6 He rare-isotope beam and a thick helium gas target. No new excited states in 10 Be have been observed. Stringent limitation on the possible degree of a-clustering of the hypothetical yrast 6 + state has been obtained. Here, the high-spin members of the α:2n:α molecular-like rotational band configuration, that is considered to have a 0 + bandhead at 6.18 MeV, either do not exist or have small overlap with the 6 He(g.s.)+α channel.

6 ≤ A ≤ 19↗
DOE OSTI2020

Rotational excitations in rare-earth nuclei: A comparative study within three cranking models with different mean fields and treatments of pairing correlations

High-spin rotational bands in rare-earth Er (Z = 68), Tm (Z = 69), and Yb (Z = 70) isotopes are investigated by three different nuclear models. These are (i) the cranked relativistic Hartree-Bogoliubov (CRHB) approach with approximate particle number projection by means of the Lipkin-Nogami (LN) method, (ii) the cranking covariant density functional theory (CDFT) with pairing correlations treated by a shell-model-like approach (SLAP) or the so-called particle-number conserving (PNC) method, and (iii) cranked shell model (CSM) based on the Nilsson potential with pairing correlations treated by the PNC method. A detailed comparison between these three models in the description of the ground-state rotational bands of even-even Er and Yb isotopes is performed. The similarities and differences between these models in the description of the moments of inertia, the features of band crossings, and equilibrium deformations and pairing energies of the even-even nuclei under study are discussed. These quantities are considered as a function of rotational frequency and proton and neutron numbers. The changes in the properties of the first band crossings with increasing neutron number in this mass region are investigated. On average, a comparable accuracy of the description of available experimental data is achieved in these models. However, the differences between model predictions become larger above the first band crossings. Because of the time-consuming nature of numerical calculations in the CDFT-based models, a systematic study of the rotational properties of both ground-state and excited-state bands in odd-mass Tm nuclei is carried out only by the PNC-SCM. With few exceptions, the rotational properties of experimental 1-quasiparticle and 3-quasiparticle bands in 165,167,169,171 Tm are reproduced reasonably well. As a result, the appearance of backbendings or upbendings in these nuclei is well understood from the analysis of the variations of the occupation probabilities of the single-particle states and their contributions to total angular momentum alignment with rotational frequency.

150 ≤ A ≤ 189↗
DOE OSTI2020

In-beam γ-ray and electron spectroscopy of 249,251 Md

The odd-Z 251 Md nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the [521]1/2 - configuration, another rotational structure has been identified using γ-γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a [514]7/2 - single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely g K = $0.69$ $^{+0.19}_{-0.16}$ for the ground-state band. The odd-Z 249 Md was studied using γ-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the Δl = Δ j = 3 [521]3/2 - and [633]7/2 + Nilsson orbitals were found in both 249,251 Md. Here, a surprising similarity of the 251 Md ground-state band transition energies with those of the excited band of 255 Lr has been discussed in terms of identical bands. Lastly, Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Landscape of pear-shaped even-even nuclei

The phenomenon of reflection-asymmetric nuclear shapes is relevant to nuclear stability, nuclear spectroscopy, nuclear decays and fission, and the search for new physics beyond the standard model. Global surveys of ground-state octupole deformation, performed with a limited number of models, suggest that the number of pear-shaped isotopes is fairly limited across the nuclear landscape. Here, we carry out a global analysis of ground-state octupole deformations for particle-bound even-even nuclei with Z ≤ 110 and N ≤ 210 using nuclear density functional theory (DFT) with several nonrelativistic and covariant energy density functionals. In this way, we can identify the best candidates for reflection-asymmetric shapes. The calculations are performed in the frameworks of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory and relativistic Hartree-Bogoliubov theory using DFT solvers employing harmonic oscillator basis expansion. We consider five Skyrme and four covariant energy density functionals. We predict several regions of ground-state octupole deformation. In addition to the “traditional” regions of neutron-deficient actinide nuclei around 224 Ra and neutron-rich lanthanides around 146 Ba, we identified vast regions of reflection-asymmetric shapes in very neutron-rich nuclei around 200 Gd and 288 Pu, as well as in several nuclei around 112 Ba. Our analysis suggests several promising candidates with stable ground-state octupole deformation, primarily in the neutron-deficient actinide region, that can be reached experimentally. Detailed comparison between Skyrme and covariant models is performed. Octupole shapes predicted in this study are consistent with the current experimental information. This work can serve as the starting point of a systematic search for parity doublets in odd-mass and odd-odd nuclei, which will be of interest in the context of new physics searches.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

The convergence of quadrupole rotational invariants from the nuclear shell model

Nuclei exhibit both single-particle and collective degrees of freedom, with the latter often subdivided into vibrational and rotational motions. Experimentally identifying the relative roles of these collective modes is extremely challenging, particularly in the face of possible shape coexistence. Model-independent, invariant quantities describing the deformation of a nucleus in the intrinsic frame have long been known but their determination potentially requires a large quantity of experimental data to achieve convergence. Through comparison with the nuclear shell model, the question of convergence is addressed. Shell-model calculations performed in the sd- and pf-shell model spaces are used to determine electric-quadrupole matrix elements for a multitude of low-lying states using the first 40 states of the relevant spins. Relative contributions to the rotationally invariant quantities from multiple states can therefore be determined. It is found that, on average, the inclusion of four intermediate states results in the leading-order invariant, $\langle\hat{Q^2}\rangle$, converging to within 10% of its true value and the triaxiality term, cos (3δ), converging to its true value, though some variance remains. Higher-order quantities relating to the softness of the nuclear shape are found to converge more slowly. The convergence of quadrupole rotationally invariant sum rules was quantified in the sd- and pf-shell model spaces and indicates the challenge inherent in a full determination of nuclear shape. The present study is limited to relatively small valence spaces. Finally, larger spaces, such as the rare-earth region, potentially offer faster convergence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Nuclear structure and band mixing in Pt 194

We introduce a two-particle, two-hole mixed configuration scheme to fit E2 strengths for the 0 ↔ 2, 2 ↔ 4, and 4 ↔ 6 transitions in 194 Pt. The interaction includes two sets of pairing operators, {S ± (t), S 0 (t)} (t = s, d). Solutions within this framework are used to analyze energy spectra, E2 transitions, and band-mixing features of the model. The results confirm that mixing is small and similar for J = 2, 4, and 6, with the calculated energies and transition matrix elements in excellent agreement with experimental data.

190 ≤ A ≤ 219↗
DOE OSTI2021

Properties of isoscalar giant multipole resonances in medium-heavy closed-shell nuclei: A semimicroscopic description

The semimicroscopic particle-hole dispersive optical model (PHDOM) is implemented to describe main properties of Isoscalar Giant Multipole Resonances (up to L=3) in medium-heavy closed-shell nuclei. Here, the main properties are characterized by the strength distribution, transition density, partial and total probabilities of direct one-nucleon decay. Calculation results obtained for the 208 Pb nucleus are compared with available experimental data.

190 ≤ A ≤ 219↗
DOE OSTI2021

Possible quenching of static neutron pairing near the N=98 deformed shell gap: Rotational structures in 160,161 Gd

A 160 Gd beam was accelerated to an energy of 1000 MeV and, separately, bombarded thick targets of 154 Sm and 164 Dy in order to observe neutron-rich, rare-earth nuclei via deep-inelastic collision processes. Gammasphere was utilized to observe g-ray emissions. Here, many new states and transitions were observed in 160 Gd as a result of so-called "unsafe" Coulomb excitation. The ground-state band in 160 Gd has been extended to I π = 20 + and a rotational band based on the K π = 4 + state, previously associated with a hexadecapole vibration, was observed up to 18 + . The quasiparticle configuration of the K π = 4 + band has been determined, and its unusual alignment behavior may result from a possible quenching of static neutron pairing. In addition, the band based on the [523]5/2 quasineutron orbital in 161 Gd was extended from 11/2 – to 33/2 – , and also displays the same unusual alignment behavior.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗