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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
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↗
NASA NTRS1982

Calculation of a mirror asymmetric effect in electron scattering from chiral targets

A dynamical calculation is presented of the helicity induced in an initially unpolarized electron beam after elastic scattering from an optically active medium, a process analogous to the circular polarization induced in unpolarized light following Rayleigh scattering from chiral targets. The calculation is based on the bound helical electron model of a chiral molecule, according to which the major contribution to the helicity is provided by the perturbation of the electron bound state by the spin-orbit interaction of the bound electrons moving in the electric field of the molecular core. The net helicity acquired is found to depend directly on a molecular asymmetry factor and the square of the atomic number of the heaviest atom in an asymmetric environment. For the case of carbon, the induced helicity is on the order of 0.00001, which would account for its lack of observation in a recent experiment. Results may have implications for the origin of optical activity in biological molecules by the differential ionization of D and L isomers by beta-decay electrons.

Rich, A.↗
DOE OSTI2022

New collective structures in Au 179 and their implications for the triaxial deformation of the Pt 178 core

The extremely neutron-deficient isotope 179 Au has been studied by a combination of in-beam γ-ray and isomeric-decay spectroscopy. For in-beam spectroscopy, the recoil-isomer tagging technique was employed, using the known 3/2 – , T 1/2 = 328 ns isomer. A new rotational band, associated with the unfavored signature band of the 1⁢ℎ 9/2 ⊕2f⁢ 7/2 proton-intruder configuration, was revealed. A previously unknown, high-spin isomeric state with an excitation energy of 1743(17) keV and T 1/2 = 2.16⁢(8) ⁢µs was discovered. Five decay paths were identified, some of them feeding previously unknown non-yrast excited states, associated with the 1⁢i 13/2 proton-intruder configuration. Calculations based on the particle-plus-triaxial-rotor model were performed to interpret the data. On the basis of these calculations, the new 1⁢ℎ 9/2 ⊕2f 7/2 rotational band is interpreted as due to triaxial deformation of the underlying configuration with β 2 ≈ 0.26 and γ ≈ 27°. In conclusion, observed non-yrast states of the positive-parity 1i 13/2 intruder configuration are interpreted as due to triaxial deformation with β 2 ≈ 0.26 and γ ≈ 20°.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Levels in 125 Cd populated by the β decay of 125 m Ag and 125 Ag

Here, the β decay of 125 m, 125 Ag into levels in 125 Cd was investigated at the Holifield Radioactive Ion Beam Facility (HRIBF). Uranium-238 targets were bombarded with 50-MeV protons with an intensity of 15 μ A, and the induced fission products were mass separated and deposited on a moving tape in the center of the VANDLE array consisting of γ detectors and plastic scintillators. A partial decay scheme has been assigned for both β decay of the (9/2 + ) ground state of 125 Ag and its low-lying (1/2 - ) isomer, with the energy of the low-lying (11/2 - ) isomeric state in 125 Cd assigned as 188.5 keV. In addition, β -delayed neutron emission probabilities were also determined to be 1.2(2)% for the (9/2 + ) 125 Ag ground state and 4.6(10)% for the (1/2 - ) isomer, which are substantially lower than the previously reported value.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

First Observation of Multiphonon 𝛾-Vibrations in an Odd-Odd Nuclear System

Here, the identification of the first multiphonon 𝛾-vibrational bands in an odd-odd neutron-rich nucleus of the nuclear chart is presented. These high-spin structures of hard to access $^{104}_{41}\textrm{Nb}_{63}$, produced in fission, were studied by combining a spectrometer with isotopic resolution coupled to a 𝛾-ray tracking array and independently from high-fold 𝛾 coincidence measurements. Triaxial projected shell model calculations for the high-spin states are in good agreement with the measured observables for the yrast, one-phonon, and two-phonon 𝛾 bands. The possibility of an oblate shape of an isomeric state and coexistence of triaxial and oblate configurations is investigated from the decay of the 141 keV isomer. The present Letter illustrates the robustness of vibration excitations in the presence of an odd valence proton and neutron as well as the possibly coexisting shapes beyond the 𝑁 = 60 transitional region.

Wang, E. H. [Shandong Univ., Jinan (China); Vander↗
DOE OSTI2020

Intrinsic electric quadrupole moment of the K π = 8 - isomeric state in Hf 178

The lifetime of the 9 - state in the rotational band based on the 4.0 s, K π = 8 - , isomeric state ( 178 Hf m 1 ) from the decay of the 31-yr isomer ( 178 Hf m 2 ) was determined to be 99(2) ps by means of the fast-timing technique using two LaBr 3 (Ce) scintillators. The δ (E2/M1) mixing ratios of the ΔI = 1 γ rays depopulating levels in this band were deduced from γ-γ angular correlations by using a 178 Hf m 2 radioactive source located at the center of the Gammasphere HPGe detector array. The new results, together with previous spectroscopic information, provide a different way to extract the intrinsic quadrupole moment of Q 0 = 6.45 (14) eb for the 178 Hf m 1 band. A possible explanation for the reduction of the 178 Hf m 1 nuclear charge radius is presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Decay spectroscopy at the two-proton drip line: Radioactivity of the new nuclides 160 Os and 156 W

The radioactivity of $^{160}_{76}$Os 84 and $^{156}_{74}$W 82 that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160 Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58 Ni ions bombarding a 106 Cd target. The 160 Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160 Os (Ε α = 7092(15) keV, t 1/2 = 97$^{+97}_{-32}$ μs) and its isomeric state (Ε α = 8890(10) keV, t 1/2 = 41$^{+15}_{-9}$ μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of 156 W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, 156 Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in $^{156}_{73}$Ta 83 of 333$^{+25}_{-22}$ ms was obtained in a separate experiment using the same experimental systems with a 102 Pd target. This result was employed to improve the precision of the half-life determined for 156 W, which was measured as 157$^{+57}_{-34}$ ms.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Measurement of the Isolated Nuclear Two-Photon Decay in Ge 72

The nuclear two-photon or double-gamma (2 γ ) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the 2⁢ γ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to ~100 keV and half-lives as short as ~10 ms. The half-life for the 2⁢ γ decay of the first-excited 0 + state in bare 72 Ge ions was determined to be 23.9(6) ms, which strongly deviates from expectations.

59 ≤ A ≤ 89↗
DOE OSTI2020

High- K , two-quasiparticle states in Gd 160

Excited states in Gd 160 were populated via β decay from the low- and high-spin isomers in Eu 160 . The high-spin, K π = 5 - state feeds several two-quasiparticle levels, as well as a sequence associated with a γ vibration and a K π = 4 + , hexadecapole vibrational structure. The decay scheme was significantly improved with the observation of new transitions and states when compared with the two competing level schemes from over four decades ago. Configuration assignments for some of the multiquasiparticle levels have been suggested, based upon decay properties, systematics from neighboring nuclei, and comparisons with theoretical calculations. Finally, in addition, 15 new low-spin states and approximately 60 new transitions were observed resulting from the decay of the low-spin Eu 160 isomer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Sensitivity of Neutron-Rich Nuclear Isomer Behavior to Uncertainties in Direct Transitions

Nuclear isomers are populated in the rapid neutron capture process (r process) of nucleosynthesis. The r process may cover a wide range of temperatures, potentially starting from several tens of GK (several MeV) and then cooling as material is ejected from the event. As the r-process environment cools, isomers can freeze out of thermal equilibrium or be directly populated as astrophysically metastable isomers (astromers). Astromers can undergo reactions and decays at rates very different from the ground state, so they may need to be treated independently in nucleosythesis simulations. Two key behaviors of astromers—ground state ↔ isomer transition rates and thermalization temperatures—are determined by direct transition rates between pairs of nuclear states. We perform a sensitivity study to constrain the effects of unknown transitions on astromer behavior. Detailed balance ensures that ground → isomer and isomer → ground transitions are symmetric, so unknown transitions are equally impactful in both directions. We also introduce a categorization of astromers that describes their potential effects in hot environments. We provide a table of neutron-rich isomers that includes the astromer type, thermalization temperature, and key unmeasured transition rates.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm −1 (∼10–20 kcal mol −1 ) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2ν OH ) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Decay spectroscopy of an isomeric state in Md251

Excited states in Md251 have been populated by decay of an isomeric state at Ex≈1174 keV and studied via delayed γ-ray spectroscopy. We observe the population of two rotational bands, one of which we identify as the Nilsson π72[514] ground-state band and the other we propose is based on the π92[624] configuration. From the observed decay pattern, we suggest that the isomer spin parity is 232+, with the three-quasiparticle configuration π72[514]⊗{ν72[624]⊗ν92[734]}Kπ=8−. We compare our results to theoretical predictions of the single- and multi-quasiparticle structure of Md251.

Morse, C↗
NASA NTRS1985

Development of tungsten-tantalum generator

The purpose of this project was to develop a useable tungsten (W)/tantalum (Ta) generator. Ta-178 is formed following the decay of its parent, W-178 (half-life: 21.7d) and has a half life of 9.3 minutes in turn yielding stable Hf-178. The decay of the parent isotope (W-178) occurs entirely by electron capture to the 9.3 minute Ta-178 state, without feeding the high spin Ta-178 isomer (half life 2.2 hours). In Ta-178 decay, 99.2% of the disintegrations proceed by electron capture and 0.18% by positron emission. Electron capture results in a 61.2% branch to the ground state of Hf-178 and 33.7% to the first excited state at 93 1KeV. The most prominent features of the radionuclide's energy spectrum are the hafnium characteristic radiation peaks with energies between 54.6 and 65.0 KeV. The radiation exposure dose of Ta-118 was calculated to be approximately one-twentieth that of Tc-99m on a per millicurie basis. A twenty-fold reduction in radiation exposure from Ta-178 compared with Tc-99m means that the usual administered dose can be increased three or four times, greatly increasing statistical accuracy while reducing radiation exposure by a factor of five.

Leblanc, A.↗
DOE OSTI2026

Quantum enabled precision measurements of the 229Th nuclear isomer transition (final report)

The existence of the nuclear isomer transition in thorium-229 was first inferred from keV lines in the gamma spectrum of uranium-233 decay more than 40 years ago. Over the years, the value of the transition energy has been refined with indirect measurements using nuclear physics techniques, and the current evidence points to transition energy in the laser-accessible vacuum ultra-violet region of the spectrum. At the start of this project, the two best measurements of the transition energy were 7.8±0.5 eV and 8.28±0.17 eV from high precision gamma ray spectroscopy and kinetic energy of internal conversion electrons, respectively. This project aimed to reduce the uncertainty in the transition energy to 10 meV using direct calorimetric measurements of the decay energy with superconducting nanowire single photon detectors (SNSPDs). Specifically, the method that was pursued was to generate thorium-229 in the excited isomer state by the alpha decay of uranium-233, embed the excited state thorium into an SNSPD, then detect the energy released when the isomer deexcites.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Nuclear Data Sheets for A=123

Experimental nuclear structure and decay data are evaluated for all of 15 known nuclides of mass 123 (Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce). 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. No excited states have been identified in 123 Ru, 123 Rh and 123 Pd. For 123 Ag, the long-predicted 1/2 – β-emitting isomer has been identified at 60-keV by 2019Ch24 recently, resolving unknown excitation energies in the level scheme that was previously available only from isomeric decays of two isomers (202 ns and 393 ns) with the position and spin-parity of the former remaining unknown. Significant discrepancies exist between data on high-spin sequences based on 11/2 (–) isomer in 123 Cd (2002Hw01 and 2016Re05), which needs to be resolved with further experimental investigation. In 123 Cs, the 114-ns isomer as the πg 9/2 bandhead proposed at 231.6+x by 2000Gi12 has been resolved by 2004Si26 and 2004Si27 to be the 328-keV level that is proposed by 2000Gi12 as a separate level. Excited states in 123 La and 123 Ce have only been studied via (HI, xnγ) reactions, with their base levels and thus excitation energies remaining unknown. The β– decay schemes for daughter nuclide 123 Cd, 123 In and 123 Sn and the ε decay schemes for 123 Xe, 123 Cs and 123 Ba are considered incomplete due to large gaps between the highest observed excited levels and the Q-values. 123 Sn, 123 Sb, 123 Te and 123 I are the most extensively studied nuclides via various reactions and decays. Furthermore, this work supersedes earlier full evaluations of A=123 by 2004Oh11, 1993Oh12, 1980Ta02 and 1972Au10.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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 OSTI2023

OH Roaming and Beyond in the Unimolecular Decay of the Methyl-Ethyl-Substituted Criegee Intermediate: Observations and Predictions

Alkene ozonolysis generates short-lived Criegee intermediates that are a significant source of hydroxyl (OH) radicals. Here this study demonstrates that roaming of the separating OH radicals can yield alternate hydroxycarbonyl products, thereby reducing the OH yield. Specifically, hydroxybutanone has been detected as a stable product arising from roaming in the unimolecular decay of the methyl-ethyl-substituted Criegee intermediate (MECI) under thermal flow cell conditions. The dynamical features of this novel multistage dissociation plus a roaming unimolecular decay process have also been examined with ab initio kinetics calculations. Experimentally, hydroxybutanone isomers are distinguished from the isomeric MECI by their higher ionization threshold and distinctive photoionization spectra. Moreover, the exponential rise of the hydroxybutanone kinetic time profile matches that for the unimolecular decay of MECI. A weaker methyl vinyl ketone (MVK) photoionization signal is also attributed to OH roaming. Complementary multireference electronic structure calculations have been utilized to map the unimolecular decay pathways for MECI, starting with 1,4 H atom transfer from a methyl or methylene group to the terminal oxygen, followed by roaming of the separating OH and butanonyl radicals in the long-range region of the potential. Roaming via reorientation and the addition of OH to the vinyl group of butanonyl is shown to yield hydroxybutanone, and subsequent C–O elongation and H-transfer can lead to MVK. A comprehensive theoretical kinetic analysis has been conducted to evaluate rate constants and branching yields (ca. 10–11%) for thermal unimolecular decay of MECI to conventional and roaming products under laboratory and atmospheric conditions, consistent with the estimated experimental yield (ca. 7%).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Infrared Fingerprint and Unimolecular Decay Dynamics of the Hydroperoxyalkyl Intermediate (•QOOH) in Cyclopentane Oxidation

A transient carbon-centered hydroperoxyalkyl intermediate (•QOOH) in the oxidation of cyclopentane is identified by IR action spectroscopy with time-resolved unimolecular decay to hydroxyl (OH) radical products that are detected by UV laser-induced fluorescence. Two nearly degenerate •QOOH isomers, β- and γ-QOOH, are generated by H atom abstraction of the cyclopentyl hydroperoxide precursor. Fundamental and first overtone OH stretch transitions and combination bands of •QOOH are observed and compared with anharmonic frequencies computed by second-order vibrational perturbation theory. An OH stretch transition is also observed for a conformer arising from torsion about a low-energy CCOO barrier. Definitive identification of the β-QOOH isomer relies on its significantly lower transition state (TS) barrier to OH products, which results in rapid unimolecular decay and near unity branching to OH products. A benchmarking approach is utilized to compute high-accuracy stationary point energies, most importantly TS barriers, for cyclopentane oxidation (C 5 H 9 O 2 ), building on higher level reference calculations for ethane oxidation (C 2 H 5 O 2 ). The experimental OH product appearance rates are compared with computed statistical microcanonical rates using RRKM theory, including heavy-atom tunneling, thereby validating the computed TS barrier. The results are extended to thermal unimolecular decay rate constants at temperatures and pressures relevant to cyclopentane combustion via master-equation modeling. Furthermore, the various torsional and ring puckering states of the wells and transition states are explicitly considered in these calculations.

Chemical calculations↗