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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Angular correlations in the ${e^+}{e^-}$ decay of excited states in $\mathrm{^8Be}$

Motivated by the recent observation of anomalous electron-positron angular correlations in the decay of the 18.15-MeV $\mathrm{1^+}$ excited states in $\mathrm{^8Be}$, we reexamine in detail the standard model expectations for these angular correlations. The 18.15-MeV state is above particle threshold, and several multipoles can contribute to its ${e^+}{e^-}$ decay. Here, we present the general theoretical expressions for ${e^+}{e^-}$ angular distributions for nuclear decay by $C0, C1, C2, M1, E1,$ and $E2$ multipoles, and we examine their relative contribution to the ${e^+}{e^-}$ decay of $\mathrm{^8Be}$ at 18.15 MeV. We find that this resonance is dominated by $M1$ to $E1$ decay, and that the ratio of $M1$ to $E1$ strength is a strong function of energy. This is in contrast to the original analysis of the ${e^+}{e^-}$ angular distributions, where the $M1/E1$ ratio was assumed to be a constant over the energy region ${E_p} = 0.8 – 1.2$ MeV. We find that the existence of a “bump” in the measured angular distribution is strongly dependent on the assumed $M1/E1$ ratio, with the present analysis finding the measured large-angle contributions to the ${e^+}{e^-}$ angular distribution to be lower than expectation. Thus, in the current analysis we find no evidence for axion decay in the 18.15-MeV resonance region of $\mathrm{^8Be}$.

6 ≤ A ≤ 19↗
DOE OSTI2025

Nuclear fragmentation at the future electron-ion collider

We explore the potential of conducting low-energy nuclear physics studies, including nuclear structure and decay, at the future Electron-Ion Collider (EIC) at Brookhaven. By comparing the standard theory of electron-nucleus scattering with the equivalent photon method applied to Ultraperipheral Collisions (UPC) at the Large Hadron Collider (LHC) at CERN. In the limit of extremely high beam energies and small energy transfers, very transparent equations emerge. We apply these equations to analyze nuclear fragmentation in UPCs at the LHC and 𝑒𝐴 scattering at the EIC, demonstrating that the EIC could facilitate unique photonuclear physics studies. Furthermore, we have also shown that the fragmentation cross-sections at the EIC are about 1,000 times smaller than those at the LHC. At the LHC, the fragmentation of uranium nuclei displays characteristic double-hump mass distributions from fission events, while at the EIC, fragmentation is dominated by neutron emission and fewer few fission products, about 10,000 smaller number of events.

Bertulani, Carlos A. [East Texas A&M University, C↗
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

In-beam γ-ray spectroscopy of 68 Fe from charge exchange on 68 Co projectiles

Excited states in the neutron-rich nucleus 68 Fe were populated using a 9 Be( 68 Co, 68 Fe + γ)X charge-exchange reaction at 95 MeV/u. The new γ-ray transitions reported here for the first time complement data from β-decay studies and nucleon knockout reactions. In comparison to shell-model calculations with the LNPS effective interaction, two candidate states for the $6$$^{+}_{1}$ level emerge. Here, the distinct population pattern of excited states and the magnitude of the cross section, σ inc = 0.51(6) mb, make this reaction a promising one for future in-beam γ -ray spectroscopy. Reaction calculations with nuclear structure input from a new, locally optimized Hamiltonian, f7j4a, together with general considerations for heavy-ion-induced charge-exchange reactions appear consistent with most of the observations, although challenges remain.

59 ≤ A ≤ 89↗
DOE OSTI2021

Evidence against the Efimov effect in 12 C from spectroscopy and astrophysics

Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body subsystems. A hypothetical state in 12 C at 7.458-MeV excitation energy, comprising a loose structure of three α particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally. Purpose: Using a combination of γ spectroscopy, charged-particle spectroscopy, and astrophysical rate calculations allowing for strict limits on the existence of such a state to been established here. Method: Using the combined data sets from two recent experiments, one with the TexAT (Texas Active Target) TPC (Time Projection Chamber) to measure α decay and the other with Gammasphere to measure γ decay of states in 12 C populated by 12 N and 12 B β decay, respectively, we achieve high sensitivity to states in close proximity to the α threshold in 12 C. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit γ -decay branching ratio is determined as a function of the β-decay feeding strength relative to the Hoyle state. In parallel, calculations of the 3α reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around 5 × 10 7 K. Conclusion: From decay spectroscopy—at the 95% confidence limit, the Efimov state cannot exist at 7.458 MeV with any γ-decay branching ratio unless the β strength is less than 0.7% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in 12 C . Furthermore, the 3α reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Ab initio electroweak corrections to superallowed β decays and their impact on V ud

Radiative corrections are essential for an accurate determination of V ud from superallowed β decays. In view of recent progress in the single-nucleon sector, the uncertainty is dominated by the theoretical description of nucleus-dependent effects, limiting the precision that can currently be achieved for V ud . In this work, we provide a detailed account of the electroweak corrections to superallowed β decays in effective field theory (EFT), including the power counting, potential and ultrasoft contributions, and factorization in the decay rate. Here, we present a first numerical evaluation of the dominant corrections in light nuclei based on quantum Monte Carlo methods, confirming the expectations from the EFT power counting. Finally, we discuss strategies how to extract from data the low-energy constants that parametrize short-distance contributions and whose values are not predicted by the EFT. Combined with advances in ab initio nuclear-structure calculations, this EFT framework allows one to systematically address the dominant uncertainty in V ud , as illustrated in detail for the 14 O → 14 N transition.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Following nuclei through nucleosynthesis: A novel tracing technique

Astrophysical nucleosynthesis is a family of diverse processes by which atomic nuclei undergo nuclear reactions and decay to form new nuclei. The complex nature of nucleosynthesis, which can involve as many as tens of thousands of interactions between thousands of nuclei, makes it difficult to study any one of these interactions in isolation using standard approaches. In this work, we present a new technique, nucleosynthesis tracing, that we use to quantify the relative fraction of nuclear abundances that pass through individual nuclear reaction, decay, and fission processes at any point during nucleosynthesis. Here, we apply this technique to study fission and β – decay as they occur in the rapid neutron capture (r) process of nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Nuclear Data Sheets for A=203

Evaluated nuclear structure and decay data for all nuclei with mass number A=203 ( 203 Os, 203 Ir, 203 Pt, 203 Au, 203 Hg, 203 Tl, 203 Pb, 203 Bi, 203 Po, 203 At, 203 Rn, 203 Fr, 203 Ra) are presented. All available experimental data are compiled and evaluated, and best values for level and γ-ray energies, quantum numbers, lifetimes, γ-ray intensities and transition probabilities, as well as other nuclear properties, are recommended. Inconsistencies and discrepancies that exist in the literature are discussed. A number of computer codes (https://www-nds.iaea.org/public/ensdf_pgm/index.htm) developed by members of the NSDD network were used during the evaluation process. For example, the reported absolute γ-ray emission probabilities and their uncertainties were determined using the GABS code. Here, the γ-ray transition probabilities were determined using the RULER code and the corresponding uncertainties were estimated by means of a Monte-Carlo approach. This work supersedes the earlier evaluation by F.G. Kondev (2005Ko20), published in Nuclear Data Sheets 105, 1 (2005).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Nuclear Data Sheets for A=201

Evaluated nuclear structure and decay data for all nuclei with mass number A=201 ( 201 Os, 201 Ir, 201 Pt, 201 Au, 201 Hg, 201 Tl, 201 Pb, 201 Bi, 201 Po, 201 At, 201 Rn, 201 Fr, 201 Ra) are presented. All available experimental data are compiled and evaluated, and best values for level and γ-ray energies, quantum numbers, lifetimes, γ-ray intensities and transition probabilities, as well as other nuclear properties, are recommended. Inconsistencies and discrepancies that exist in the literature are discussed. A number of computer codes (https://wwwnds.iaea.org/public/ensdf pgm/index.htm) developed by members of the NSDD network were used during the evaluation process. For example, the reported absolute γ-ray emission probabilities and their uncertainties in various decay data sets were determined using the GABS code. The γ-ray transition probabilities were determined using the RULER code and the corresponding uncertainties were determined using a Monte-Carlo approach. In conclusion, this work supersedes the earlier evaluation by F.G. Kondev (2007Ko06), published in Nuclear Data Sheets 108, 365 (2007).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

First β -delayed neutron spectroscopy of 24 O

The β decay of 24 O was investigated at NSCL/MSU using a combination of neutron and γ-ray spectroscopy. For the first time, the β-delayed neutron energy spectrum of 24 O was measured, revealing three intensely populated, isolated neutron-unbound states in 24 F. This allowed for the extraction of the decay strength in 24 F up to 6.2 MeV. A comprehensive comparison of the experimental results with various nuclear theories, ranging from the empirical shell model to the most advanced ab initio calculations, was conducted. While most theoretical predictions align with the experimental data for low-lying states, discrepancies arise at higher excitation energies. Finally, in the transition from 24 O to 24 F, shell model calculations using the empirical USDB interaction predicted the structure of both nuclei without invoking the need for a stronger proton-neutron tensor force, which was postulated for the neighboring isotone 25 F.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Nuclear Data Sheets for A=214

Here, experimental nuclear structure and decay data are evaluated for all of 12 known nuclides of mass 214 (Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa). For each nuclide, detailed evaluated spectroscopic information is presented in each reaction and decay, and the best values combining all available data are recommended for level properties, γ and β radiations, and other spectroscopic properties in the Adopted Levels and Gammas. The present evaluation supersedes the earlier one on A=214 by S.-C. Wu (2009Wu02), published in Nuclear Data Sheets 110, 681 (2009).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Nuclear Data Sheets for A=236

Experimental nuclear structure and decay data are evaluated for all of 10 known nuclides of mass 236 (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf). For each nuclide, detailed evaluated spectroscopic information is presented in each reaction and decay, and the best values combining all available data are recommended for level properties, γ and β radiations, and other spectroscopic properties in the Adopted Levels and Gammas. The present evaluation supersedes the earlier one on A=236 by E. Browne, J. K. Tuli (2006Br20), published in Nuclear Data Sheets 107, 2641 (2006).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Application of an efficient generator-coordinate subspace-selection algorithm to neutrinoless double- β decay

The generator coordinate method begins with the variational construction of a set of nonorthogonal mean-field states that span a subspace of the full many-body Hilbert space. These states are then often projected onto states with good quantum numbers to restore symmetries, leading to a set with members that can be similar to one another, and it is sometimes possible to reduce this set without greatly affecting results. Here, we propose a greedy algorithm that we call the energy-transition-orthogonality procedure (ENTROP) to select subsets of important states. As applied here, the approach selects on the basis of diagonal energy, orthogonality, and contribution to the matrix element that governs neutrinoless double-β decay. We present both shell-model and preliminary ab initio calculations of this matrix element for the decay of 76Ge, with quadrupole deformation parameters and the isoscalar pairing strength as generator coordinates. ENTROP converges quickly, reducing significantly the number of basis states needed for an accurate calculation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

First measurement of proton decay from a transfer reaction to 21 Na

Decay protons from excited states in Na 21 populated through a previously reported Mg 24 ( p , α ) Na 21 transfer reaction [Cha et al. , Phys. Rev. C 96 , 025810 (2017) ] were analyzed to extract the proton branching ratios of the energy levels. Additionally, by utilizing 31-MeV proton beams from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and isotopically enriched Mg 24 solid targets, the decay protons were detected in coincidence with α particles from the ( p , α ) reaction using a silicon strip detector array. Proton decay branching ratios of several Na 21 levels were deduced for the p 0 and p 1 decay channels to the ground and first excited states in Ne 20 , respectively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

New, low-energy excitations in 107 Mo and 109 Mo

New ground-state level with spin-parity 1/2 + is established in 109 Mo, 69.8 keV below the previously reported 5/2(+) ground state in this nucleus, based on precise spectroscopy measurements of gamma radiation following spontaneous fission of 248 Cm performed using the Eurogam2 array of anti-Compton spectrometers. Analogous measurement of gamma radiation following spontaneous fission of 252 Cf, performed using the Gammasphere array, confirms the new 1/2 + ground state of 107 Mo, proposed recently and establishes the isomeric character of the 5/2 + first excited state in 107 Mo. Two beta-decaying isomers are suggested in 111 Mo nucleus based on regular energy systematics, supporting previous predictions. Low-energy excitations in Mo isotopes are interpreted and compared to calculations reported in the literature. The results suggest shape transition from prolate to oblate deformation at N >= 67.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

High-isospin multiplets in 𝐴=15 and 16 nuclei

Isospin quartets (T=3/2) and quintets (T=2) have been investigated for A=15 and A=16 nuclei, respectively. Data from an invariant-mass experiment, with a 17 Ne beam, were reanalyzed and the T=3/2 and T=2 states in 15 O and 16 F, associated with p+ 14 N and 2p+ 14 N exit channels respectively, were found. In some cases, γ-ray gating was used to tag on events that decay to the excited 0 + , T=1 state in 14 N rather than the ground state. With the new states, the lowest-energy 1/2 + and 5/2 + quartets for A=15 and the 0 + and 2 + quintets for A=16 are completed. In addition, members of these multiplets in 15 F and 16 Ne decaying to the p+ 14 O and 2p+ 14 O channels are reevaluated by gating on events where the 14 O fragment recoils perpendicular to beam axis in the parent reference frame. Such transverse-decay events have the best invariant-mass resolution. No evidence for deviations from a quadratic dependence of the mass on the isospin projection was found for the A=15 quartets. However for the A=16 0 + and 2 + quintets, evidence for deviations were found.

Coulomb energies↗
DOE OSTI2022

Isospin-symmetry implications for nuclear two-body distributions and short-range correlations

Here, we study the implications of isospin symmetry in nuclear systems on two-body distributions and derive relations between different densities or momentum distributions of a given nucleus or of different nuclei in the same isospin multiplet. A connection between neutrinoless double beta decay transition of mirror nuclei and two-body densities is also obtained. The relations are numerically verified by means of quantum Monte Carlo calculations. We discuss the relevance of these results to the analysis of nuclear short-range correlations and also show that isospin symmetry allows us to extract information about the spectator nucleons when a short-range correlated pair is formed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Dipole response in Te 128 , 130 below the neutron threshold

Numerous studies of the ground-state decay of the pygmy dipole resonance (PDR) have been carried out in the past. However, data on the decay of the PDR to low-lying excited states is still very scarce due to limitations of the sensitivity to weak branching transitions of experimental setups. Here, we present a detailed examination of the low-energy dipole response of 128 Te and 130 Te below their neutron separation thresholds of 8.8 and 8.5 MeV, respectively. Photonuclear reactions with the subsequent γ-ray spectroscopy of the decay channel with continuous-energy bremsstrahlung at varying endpoint energies and linearly polarized quasimonochromatic γ-ray beams with energies ranging from 2.7 to 8.9 MeV in steps of roughly 250 keV were used for probing the decay behavior of the low-energy dipole response in 128Te and 130Te. In addition, (γ,γ' γ") reactions were used to study the population of low-lying states of 128 Te. Spin-parity quantum numbers and reduced transition probabilities are determined for individual photo-excited states. The analysis of average decay properties for nuclear levels in narrow excitation-energy bins enable the extraction of photoabsorption cross sections, average branching ratios to the $2$$^{+}_{1}$ state, and the distinction between E1 and M1 transitions to the ground state and to the $2$$^{+}_{1}$ state accounting for resolved and unresolved transitions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗