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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Quenching of the octupole rotational band in 71 Ge

The main goal of this study was to enhance the knowledge of the properties of the known octupole rotational band in 71 Ge, including transition rates, and to investigate whether the band persists to higher spin. An experiment at Florida State University using the 62 Ni ( 14 C, 𝛼⁢𝑛) reaction at 50 MeV was used to produce 71 Ge at high spin. An array of ten Compton-suppressed Ge detectors, consisting of three Clover detectors and seven single-crystal detectors, was used to measure the 𝛾 decays in coincidence. An analysis of the resulting coincidence spectra resulted in the placement of 13 additional transitions in the 71 Ge level scheme, one of which (1092 keV) extends the octupole band to a (35/2 − ) state at 8206 keV. However, calculations of the kinematic moment of inertia show that the 1092-keV transition disrupts the rigid rotational pattern and is likely associated with a band crossing, potentially quenching the octupole deformation. Transition strengths inferred from lifetime measurements in the octupole band are not well reproduced by either shell-model calculations using the JUN45 interaction or a semimicroscopic cluster model, while those for the 𝜈⁢𝑔 9/2 band are in good agreement with the corresponding shell-model predictions. Comparisons between the octupole band in 71 Ge and negative-parity bands based on 3 − octupole states in some neighboring even-even nuclei show both similarities and differences. Systematic trends within the 𝜈⁢𝑔 9/2 bands among odd-𝐴 Ge isotopes point to increased collectivity near 𝑁 = 40.

59 ≤ A ≤ 89↗
DOE OSTI2025

Reaching the prolate-oblate boundary at 𝑁=116 via first fragmentation of a 198 Pt beam: Sharp transition to triaxiality in 189 Ta

High-spin isomers in very-neutron-rich 𝐴≈190 Hf-Ta-W nuclei were populated via the pioneering fragmentation of a 198 Pt primary beam at the National Superconducting Cyclotron Laboratory. The nuclei were implanted in a Si detector stack surrounded by the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to detect delayed 𝛾 rays, providing first level schemes using 𝛾−𝛾 coincidence data from isomeric decays in this previously inaccessible region of the nuclear chart. Here, a sudden transition to a strong triaxial shape is observed in the very-neutron-rich 189 Ta (𝑁 = 116) nucleus from axially prolate shapes in lighter Ta isotopes, providing a critical experimental benchmark for competing theoretical predictions of nuclear-shape evolution.

150 ≤ A ≤ 189↗
DOE OSTI2025

3 𝑃 0 model revisited

We revisit the phenomenological 3 𝑃 0 model for the decay of quarkonium ($Q\bar{Q}$) into two open flavor mesons ($\bar{𝔐}⁢𝔐$). We take the heavy-quark limit and derive a transition rate between $Q\bar{Q}$ and $\bar{𝔐}⁢𝔐$ to be compared with the one calculated in studies of string breaking using lattice QCD. This comparison allows us to fit the creation amplitude of a light quark-antiquark pair in the 3 𝑃 0 model to the string-breaking transition rate in QCD.

lifetimes & widths↗
DOE OSTI2025

Observation of Exotic 𝐽/𝜓⁢𝜙 Resonant Structure in Diffractive Processes in Proton-Proton Collisions

The first study of 𝐽/𝜓⁢𝜙 production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb −1 . The data disfavor a nonresonant 𝐽/𝜓⁢𝜙 production but are consistent with a resonant model including several resonant states observed previously only in 𝐵 + →𝐽/𝜓⁢𝜙⁢𝐾 + decays. The 𝜒 𝑐⁢0⁡ (4500) state is observed with a significance over 6⁢𝜎 and the 𝜒 𝑐⁢1 ⁡(4274) is confirmed with a significance of more than 4⁢𝜎.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Large-scale calculations of 𝛽-decay rates and implications for 𝑟-process nucleosynthesis

Nuclear 𝛽 decay is a key element of the astrophysical rapid neutron capture process (𝑟 process). In this work, we present state-of-the-art global 𝛽-decay calculations based on the quantified relativistic nuclear energy density functional theory and the deformed proton-neutron quasiparticle random-phase approximation. Our analysis considers contributions from allowed and first-forbidden transitions. We used two point-coupling functionals with carefully calibrated time-odd terms and isoscalar pairing strength. The new calculations display consistent results for both employed functionals, especially near the neutron drip line, suggesting slower 𝛽 decays past the 𝑁=126 neutron shell closure than in commonly used 𝛽-decay models. The new rates, along with the existing rates based on the recent nonrelativistic global calculations, are found to slow down the synthesis of heavy elements in the 𝑟 process and significantly reduce the contribution of neutron-induced fission.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Collapse of Nuclear Collectivity along the 𝑁 = 𝑍 Line

The lifetime of the 𝐽 𝜋 = 2 + state in the self-conjugate 88 Ru nucleus has been determined in an experiment performed using rare-isotope beams provided by the new Facility for Rare Isotope Beams. This is the heaviest 𝑁 = 𝑍 nucleus for which such a measurement has been achieved. 88 Ru was populated by both one-neutron knockout and charge-exchange reactions, and the lifetime of 14.3$^{+2.5}_{−3.4}$ ps was determined using the triple-foil plunger technique. The extracted electromagnetic transition strength shows that the quadrupole collectivity has dropped significantly compared with the highly deformed 𝑁 = 𝑍 region around 𝐴 ∼ 80. These results are compared with state-of-the-art large-scale shell-model and discrete nonorthogonal shell-model calculations. The theoretical calculations indicate a moderate triaxial deformation and suggest that low-lying states in this nucleus are no longer dominated by strong many-particle many-hole excitations, unlike the lighter, highly deformed 𝑁 = 𝑍 nuclei nearby.

59 ≤ A ≤ 89↗
DOE OSTI2025

Picosecond lifetime measurements of resonances using a thick-target invariant-mass technique

Here, a new technique is presented for measuring the half-lives of resonances in the picosecond range using presently available invariant-mass apparatus and a thick target. For short-lived resonances, the energy losses of the decay fragments in the target material change their relative velocities giving rise to a poor invariant-mass resolution. However, for longer-lived resonances that travel through the remaining target material before decaying outside of the target, this dominant contribution to the resolution is eliminated. The measured invariant-mass peak will then display a narrow peak from these events which sits on a wider structure associated with the remaining events that decay in the target. The fraction of the events in the narrow peak is related to the probability that the resonance leaves the target before decaying and hence is related to the lifetime. This technique is exercised for the 2.685-MeV resonance in 33 Cl which decays by emitting an f -wave proton. A half-life of T 1/2 =5.7$^{+4.1}_{-2.5}$ ps was measured which is consistent with values inferred from other known properties of this resonance.

lifetimes & widths↗
DOE OSTI2026

Nuclear Radii of Proton-Unbound Systems

Nuclear radius is a fundamental structural observable that informs many properties of atomic nuclei and nuclear matter. Experimental studies of radii in drip line nuclei are in the forefront of research with radioactive ion beams. Of particular interest are charge radii of proton-unbound nuclei that will soon be approached in laser spectroscopy. In this Letter, using the complex-energy approach and direct time propagation, we investigate the radius of the proton resonance whose size is ill defined in the standard stationary quantum-mechanical description. An early-time plateau is identified during which the radius of the Gamow resonance coincides with the real-energy radius accessible experimentally. We demonstrate a nonmonotonic dependence of the complex radius on decay energy and a local increase of the charge radius across the threshold (a halolike enhancement).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1979

An atomic model for neutral and singly ionized uranium

A model for the atomic levels above ground state in neutral, U(0), and singly ionized, U(+), uranium is described based on identified atomic transitions. Some 168 states in U(0) and 95 in U(+) are found. A total of 1581 atomic transitions are used to complete this process. Also discussed are the atomic inverse lifetimes and line widths for the radiative transitions as well as the electron collisional cross sections.

Maceda, E. L.↗
DOE OSTI2025

Precision measurement of the B0 meson lifetime using B0→J/ψK∗0 decays with the ATLAS detector

A measurement of the B0$$B^{0}$$ meson lifetime using B0→J/ψK∗0$$ B^{0} \rightarrow J/\psi K^{*0} $$ decays in data from 13 TeV$$\text {TeV}$$ proton–proton collisions with an integrated luminosity of 140fb-1$$ 140~\mathrm {fb^{-1}} $$ recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is τ=1.5053±0.0012(stat.)±0.0035(syst.)ps.$$ \tau = 1.5053\pm 0.0012~\mathrm {(stat.)} \pm 0.0035~\mathrm {(syst.)~ps}. $$The average decay width extracted from the effective lifetime, using parameters from external sources, is Γd=0.6639±0.0005(stat.)±0.0016(syst.)±0.0038(ext.)ps-1,$$\begin{aligned} \Gamma _d = 0.6639\pm 0.0005~\mathrm {(stat.)} \pm 0.0016~\mathrm {(syst.)}\\ \pm 0.0038~\text {(ext.)} \text {~ps}^{-1}, \end{aligned}$$where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of Γs$$\Gamma _s$$ in the Bs0→J/ψϕ$$B^{0}_{s} \rightarrow J/\psi \phi $$ decay was used to derive a value for the ratio of the average decay widths Γd$$\Gamma _d$$ and Γs$$\Gamma _s$$ for B0$$B^{0} $$ and Bs0$$B^{0}_{s} $$ mesons respectively, of ΓdΓs=0.9905±0.0022(stat.)±0.0036(syst.)±0.0057(ext.).$$ \frac{\Gamma _d }{\Gamma _s } = 0.9905\pm 0.0022~\text {(stat.)} \pm 0.0036~\text {(syst.)} \pm 0.0057~\text {(ext.)}. $$The measured lifetime, average decay width and decay width ratio are in agreement with theoretical predictions and with measurements by other experiments. This measurement provides the most precise result of the effective lifetime of the B0$$B^{0}$$ meson to date.

Aad, G↗
DOE OSTI2025

Total absorption spectroscopy for the 𝛽 + decay strength distribution of 60 Ga

𝛽-decay properties play an important role in most astrophysical processes. In the absence of experimental data, astrophysical models rely on global theoretical calculations to provide the relevant properties. It is therefore important to provide strong experimental constraints when possible. In the case of 𝛽-decay, the most sensitive probe is the 𝛽-decay strength distribution. We report here on the first measurement of the latter quantity for the 𝛽 + decay of 60 Ga using the total absorption spectroscopy technique. The experimental results are compared to theoretical calculations often used in astrophysical models, namely the shell model and the quasiparticle random phase approximation (QRPA), as well as an extension of QRPA that includes higher-order nucleonic calculations. Both models are in reasonable agreement with the experimental results.

59 ≤ A ≤ 89↗
DOE OSTI2025

Carrier Lifetime Control Through the Quantum Confined Stark Effect

This study explores how the quantum confined Stark effect (QCSE) influences minority carrier lifetimes in III-N quantum wells (QWs) by varying the well width. It is found that increasing QW width from zero (bulk material) increases radiative lifetime due to charge separation until charge screening effects reduce and rectify the QCSE for large well widths.

Loveless, James Terrell [Sandia National Laborator↗
DOE OSTI2025

Molecular Engineering of Emissive Molecular Qubits Based on Spin-Correlated Radical Pairs

Spin chemistry of photogenerated spin-correlated radical pairs (SCRPs) offers a practical approach to control chemical reactions and molecular emissions by using weak magnetic fields. This capability to harness magnetic field effects (MFEs) paves the way for developing SCRPs-based molecular qubits. Here, in this work, we introduce a new series of donor–chiral bridge–acceptor (D–χ–A) molecules that demonstrate significant MFEs on fluorescence intensity and lifetime in solution at room temperature—critical for quantum sensing. By precisely tuning the donor site through torsional locking, distance extension, and planarization, we achieved remarkable control over key quantum properties, including field-response range and line width. In the most responsive systems, emission lifetimes increased by over 200%, and the total emission intensity was modulated by up to 30%. This level of tunability shows the power of synthetic spin chemistry. The rational design principle of optically addressable SCRP-based molecular systems, presented in this work, represents a major leap toward functional synthetic molecular qubits, advancing the field of molecular quantum technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

A theoretical analysis of the current-voltage characteristics of solar cells

The current-voltage characteristics and efficiencies of solar cells are discussed. For one solar cell structure detailed curves are presented which include carrier densities, current densities, potential, and quasi-Fermi levels at different voltage levels both with and without optically generated carriers (AMO conditions). In addition some results are presented concerning the influence of various parameter variations such as lifetime, cell thickness, and high-low junction width on solar cell performance.

Hauser, J. R.↗
DOE OSTI2026

Gallium Arsenide Semiconductor Opening Switches: Enabling Nanosecond High Powering Pulsed Systems

The goal of this work awas to investigate design manufacturing semiconductor opening switches (SOS) in both silicon and gallium arsenide (GaAs). Solid-state opening switches are critical components for pulsed power systems and applications in directed energy, dielectric wall accelerators, and novel semiconductor manufacturing techniques. Under this funding, we have developed silicon SOS designs that suppresses an unwanted prepulse, increases the peak output voltage by about 10 percent, and reduces the pulse rise time by ~ 4x compared with more conventional profiles. Through this effort we have improved device fabrication and bonding techniques. Additionally, work on this the GaAs opening switch has defined a unique application space that these devices are suited for. GaAs opening switches have short risetimes and pulse widths compared to silicon devices, however the short carrier lifetime of GaAs makes the circuit design more challenging than in silicon. For high PRF operation, the lifetime of the GaAs is an advantage compared to silicon. TCAD simulations of GaAs devices have been used to optimize a GaAs profile. Additionally, we have designed pulsers with sub 50ns reserve pump times and tested GaAs COTs PIN diodes in them.

42 ENGINEERING↗
NASA NTRS1975

A newly observed solar feature - Macrospicules in He II 304 A

He II 304 A spectroheliograms, obtained with the NRL extreme-ultraviolet slitless spectrograph during the Skylab mission, show spikelike structures at the sun's polar limb which resemble the familiar H-alpha spicules. However, the relatively large size and long life of these He II features has led to distinguishing them by the name 'macrospicules'. The macrospicules appear as protuberances or jets, ranging from 5 to over 60 sec in length, from 5 to 30 sec in width, and from 5 to over 40 minutes in lifetime. Perhaps the most radical departure from H-alpha spicules is that macrospicules occur only within the chromospheric boundaries of coronal holes. Thus macrospicules are most easily visible over the solar poles due to the coronal holes normally present there, and much less frequently at lower latitudes during limb passage of relatively rare, low-latitude coronal holes.

Bohlin, J. D.↗
NASA NTRS1977

Automated array assembly task, phase 1

Various aspects of a sensitivity analysis, in particular, the impact of variations in metal sheet resistivity, metal line width, diffused layer sheet resistance, junction depth, base layer lifetime, optical coating thickness and optical coating refractive index and on process reproducibility for A's diffusion from a polymer dopant source and on module fabrication were studied. Model calculations show that acceptable process windows exist for each of these parameters.

Carbajal, B. G.↗
NASA NTRS1975

Widths of atomic 4s and 4p vacancy states, 46 less than or equal to Z less than or equal to 50

Auger and X-ray photoelectron spectra involving N1, N2, and N3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics with regard to widths and structure were found in the Ag and Cd M4-N4,5N4,5 and M5-N4,5N4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory however predicts wider N2 than N3 vacancy states (as observed for Xe), while the measured N2 and N3 widths are nearly equal to each other and to the average of the calculated N2 and N3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation, to the transition energy and to the fine details of the atomic potential.

Hsiungchen, M.↗