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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Search for Dark Matter Induced Deexcitation of 180 Ta m

Weak-scale dark matter particles, in collisions with nuclei, can mediate transitions between different nuclear energy levels. In particular, owing to sizeable momentum exchange, dark matter particles can enable de-excitation of nuclear isomers that are extremely long lived with respect to regular radioactive decays. In this paper, we utilize data from a past experiment with 180 Ta m to search for γ-lines that would accompany dark matter induced de-excitation of this isomer. Non-observation of such transitions above background yields the first direct constraint on the lifetime of 180 Ta m against DM-initiated transitions: T 1/2 > 1.3 × 10 14 a at 90% C.I. Using this result, we derive novel constraints on dark matter models with strongly interacting relics, and on models with inelastic dark matter particles. Existing constraints are strengthened by this independent new method. As a result, the obtained limits are also valid for the Standard Model γ-decay of 180 Ta m .

150 ≤ A ≤ 189↗
DOE OSTI2026

Exploration for astromers near 132 Sn with the Canadian Penning Trap

Nuclear isomers can have significant impacts on astrophysical nucleosynthesis processes, with recent efforts demonstrating that the population of isomeric states with different half-lives may require separate treatment in reaction networks to accurately capture the differences in heating or in identifiable electromagnetic signals. Several potential so-called “astromers” in tin and antimony isotopes near doubly magic 132 Sn were identified and direct mass measurements of their ground and isomeric states were performed with the Canadian Penning Trap at Argonne National Laboratory's CARIBU facility, and their impact on astrophysical reaction rates and in reaction networks was calculated. Finally, it was found that 129⁢𝑔,𝑚 Sn , with measured mass excesses of −80593.2⁢(25) and −80557.4⁢(25) keV, respectively, and an excitation energy of 35.8(35) keV, behaves as an astromer during neutron capture in the 𝑖-process and in the 𝑟-process.

isomer decays↗
DOE OSTI2021

The NUBASE2020 evaluation of nuclear physics properties *

The NUBASE2020 evaluation contains the recommended values of the main nuclear physics properties for all nuclei in their ground and excited, isomeric (T-1/2 >= 100 ns) states. It encompasses all experimental data published in primary (journal articles) and secondary (mainly laboratory reports and conference proceedings) references, together with the corresponding bibliographical information. In cases where no experimental data were available for a particular nuclide, trends in the behavior of specific properties in neighboring nuclei were examined and estimated values are proposed. Evaluation procedures and policies that were used during the development of this evaluated nuclear data library are presented, together with a detailed table of recommended values and their uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Rate of Para-Orthohydrogen Conversion in Cryogenic Vortex Tube

Raising efficiency of the cooling process for cryogenic hydrogen and minimizing hydrogen boil-off during storage and transportation of liquid hydrogen are critically important factors for widening implementation of hydrogen-based clean energy systems. One novel approach involves utilization of relatively simple catalyzed vortex tubes, where hydrogen in the primarily para- nuclear spin isomer form is converted into the ortho- form while consuming a significant amount of heat. To design such systems effectively, better understanding is required about catalyst-assisted para-orthohydrogen conversion rates in high-speed vortical flows. In this study, a computational fluid dynamics simulation has been set up to model an experimental system with cryogenic hydrogen vortex tubes. Mesh-verification and a validation study has been conducted first for a non-catalyzed tube. Then, the rate coefficient of the para-orthohydrogen conversion of cryogenic hydrogen has been determined by matching numerical results with experimental data available for a catalyzed vortex tube. Furthermore, the presented information can help design and optimize cryogenic hydrogen cooling within vortex tubes.

08 HYDROGEN↗
DOE OSTI2022

Neutron transfer reactions on the ground state and isomeric state of a 130 Sn beam

The structure of nuclei around the neutron-rich nucleus 132 Sn is of particular interest due to the vicinity of the Z = 50 and N = 82 shell closures and the r-process nucleosynthetic path. Four states in 131 Sn with a strong single-particle-like component have previously been studied via the (d,p) reaction, with limited excitation energy resolution. Here, the 130 Sn( 9 Be, 8 Be) 131 Sn and 130 Sn( 13 C, 12 C) 131 Sn single-neutron transfer reactions were performed in inverse kinematics at the Holifield Radioactive Ion Beam Facility using particle-γ coincidence spectroscopy. The uncertainties in the energies of the single-particle-like states have been reduced by more than an order of magnitude using the energies of γ rays. The previous tentative J π values have been confirmed. Decays from high-spin states in 131 Sn have been observed following transfer on the isomeric component of the 130 Sn beam. The improved energies and confirmed spin-parities of the p-wave states important to the r-process lead to direct-semidirect cross-sections for neutron capture on the ground state of 130 Sn at 30 keV that are in agreement with previous analyses. A similar assessment of the impact of neutron-transfer on the isomer would require significant nuclear structure and reaction theory input. There are few measurements of transfer reaction on isomers, and this is the first on an isomer in the 132 Sn region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Reduction in Nuclear Size and Quadrupole Deformation of High-Spin Isomers of 127,129 In

We employed laser spectroscopy of atomic transitions to measure the nuclear charge radii and electromagnetic properties of the high-spin isomeric states in neutron-rich indium isotopes (𝑍 =49) near the closed proton and neutron shells at 𝑍 = 50 and 𝑁 = 82. Our data reveal a reduction in the nuclear charge radius and intrinsic quadrupole moment when protons and neutrons are fully aligned in 129 In ⁢(𝑁 = 80), to form the high spin isomer. Such a reduction is not observed in 127 In ⁢(𝑁 = 78), where more complex configurations can be formed by the existence of four neutron holes. These observations are not consistently described by nuclear theory.

high spin states↗
DOE OSTI2025

Core-excited microsecond isomer in 207 Pb

An isomeric state with T 1/2 = 1.46(10) μs and E x = 8835 keV has been established in 207 Pb. Here, this state likely arises from the occupation of neutron holes in the high-j i 13/2 and j 15/2 subshells following the excitation of the 208 Pb core. The high-spin excited level structure of 207 Pb has been extended beyond the previously known states up to E x ≈ 6 MeV. Additionally, a more precise value of the half-life of the I π = 10 + isomer in 208 Pb has been obtained. Shell-model calculations provide a good account of the structure up to the 31/2 + level in 207 Pb, while the energies of higher-spin states built from exclusively high-j nucleons are considerably underestimated.

190 ≤ A ≤ 219↗
DOE OSTI2022

First observation of isomeric states in 111 Zr, 113 Nb, and 115 Mo

Isomeric states in the neutron-rich nuclei 111 Zr [T 1/2 =0.10 (7) μs] , 113 Nb [T 1/2 =0.7 (4) μs], 115 Mo [T 1/2 =46 (3) μs] were first identified at the Radioactive Ion Beam Factory (RIBF) of RIKEN by using in-flight fission and fragmentation of a 238 U beam at an energy of 345 MeV/u. Here is a brief report of the γ transitions de-exciting from isomeric states and half-lives measurements, which provides the first spectroscopy in the nuclear region of prolate-to-oblate shape-phase transition around mass A ≈110.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Isomeric and beta-decay spectroscopy of 173,174 Ho

β-decay spectroscopy of 173,174 Ho (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u 238 U primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2 + ) is identified in 173 Ho. Moreover, a new state with a spin and parity of 9 - was discovered in 174 Er. The experimental log ft values of 5.84(20) and 5.25(18) suggest an allowed-hindered β decay from the ground state of 174 Ho to the K π = 8 - isomeric state in 174 Er. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.

150 ≤ A ≤ 189↗
DOE OSTI2024

Cross-shell excited configurations in the structure of 34 Si

The cross-shell excited states of 34 Si have been investigated via β decays of the 4 − ground state and the 1 + isomeric state of 34 Al. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder 1 + isomeric state of 34 Al, intruder levels of 34 Si are populated via allowed β decays. Spin assignments to such intruder levels of 34 Si were established through γ-γ angular correlation analysis for the negative-parity states. The configurations of such intruder states play crucial roles in our understanding of the N = 20 shell gap evolution. A configuration interaction model derived from the FSU Hamiltonian was utilized in order to interpret the intruder states in 34 Si. Furthermore, shell model interaction derived from a more fundamental theory with the valence space in medium similarity renormalization group method was also employed to interpret the structure of 34 Si.

20 ≤ A ≤ 38↗
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 OSTI2021

Measurements of Short-Lived Isomers from Photofission as a Method of Active Interrogation for Special Nuclear Materials

Isomeric fission products, such as 134m Te (T 1/2 = 164 ns) and 136m Xe (T 1/2 = 2.95 μs), are proposed as a signature of special nuclear materials in active interrogation applications. To test this conjecture, monoenergetic 9, 11, and 13 MeV photons from the HIγS facility are used to induce fission of 235 U, 238 U, and 239 Pu targets. The de-excitation γ rays of the isomers are measured using time-gated spectroscopy with high-purity germanium detectors. The 134m Te and 136m Xe isomers are detected and identified by the energy and decay half-life of their characteristic γ-ray transitions. The ratio of yields for these two signature γ rays, corresponding to 134m Te/( 136m Xe + 136 I), is found to be strongly correlated with the identity of the fissioning nuclei. These results show that fission-product isomers may be used in active interrogation to detect and identify special nuclear materials, even providing information on the isotopic enrichment. In conclusion, the feasibility of an active interrogation scenario using a bremsstrahlung beam is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

First observation of the decay of the 13/2 + isomer in 183 Hg and B(M 2) systematics of neutron transitions across the nuclear chart

The decay of the 13/2 + isomeric state in 183 Hg was observed for the first time following the a decay of the 13/2 + isomer in 187 Pb produced in the 142 Nd( 50 Cr, 2p3n) reaction. Using $\alpha - \gamma$ delayed coincidence measurements, the half-life of this isomer was measured to be 290(30) μs. This isomer is proposed to deexcite by an unobserved low-energy M2 transition to the known 9/2 - member of a strongly prolate-deformed 7/2 - [514] band, followed by a 105-keV M1 transition to the bandhead. A lower limit of B(M2) >= 0.018 W.u. was deduced for the unobserved transition. The presumed retardation is proposed to be due to the notable shape change between the initial, nearly spherical, and the final, strongly deformed, states. A similar scenario is also considered for the 13/2 + isomer in 181 Hg, suggesting both are cases of shape isomers. The B(M2) systematics of neutron transitions across the nuclear chart is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

First observation of a high-𝐾 band structure in 162 Er and implications in the context of the identical bands phenomenon

The first ever identification of a high-𝐾 band structure in 162 Er is reported. Based on a 𝐾 𝜋 = 7 (−) isomer, it is found to be identical in nature to the corresponding 𝐾 𝜋 = 7 − sequence in 164 Er up to its highest observed spin. Furthermore, the phenomenon of identical high-K bands built on a two-quasiparticle configuration in an isotopic chain is reported here for the first time. While this is a notable addition to the systematics of known identical bands in nuclei at normal deformation, a satisfactory global understanding of the phenomenon remains elusive.

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↗