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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Analytic optical potentials for nucleon-nucleus nucleus-nucleus collisions involving light and medium nuclei

Utilizing an optical model potential approximation to the exact nucleus-nucleus multiple-scattering series, optical potentials for nucleon-nucleus and nucleus-nucleus collisions are analytically derived. These expressions are applicable to light and medium cosmic ray nuclei as their single-particle density distributions are analytically determined, without approximation, from their actual harmonic well charge density distributions. Pauli correlation effects are included through the use of a simple Gaussian function to replace the usual expression obtained in the infinite nuclear matter approximation.

Bidasaria, H. B.↗
DOE OSTI2022

Two-body weak currents in heavy nuclei

In light and medium-mass nuclei, two-body weak currents from chiral effective field theory account for a significant portion of the phenomenological quenching of Gamow-Teller transition matrix elements. Here we examine the systematic effects of two-body axial currents on Gamow-Teller strength and β-decay rates in heavy nuclei within energy-density functional theory. Using a Skyrme functional and the charge-changing finite amplitude method, we add the contributions of two-body currents to the usual one-body linear response in the Gamow-Teller channel, both exactly and though a densitymatrix expansion. The two-body currents, as expected, usually quench both summed Gamow-Teller strength and decay rates, but by an amount that decreases as the neutron excess grows. They can enhance individual low-lying transitions, however, leading to decay rates that are quite different from those that an energy-independent quenching would produce, particularly in neutron-rich nuclei. We show that both these effects are related to changes in the total nucleon density as the number of neutrons increases.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Spin-trap isomers in deformed, odd-odd nuclei in the light rare-earth region near $N=98$

Masses of neutron-rich, odd-odd Pm, Eu, and Tb nuclei near N = 98 were measured using the Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility. High-resolution mass measurements yielded the discovery of spin-trap isomers at N = 97 in Tb 162 , and in the N = 99 isotones of Pm 160 and Tb 164 . Furthermore, no evidence of long-lived isomers were observed at N = 95 in Eu 158 , at N = 97 in Pm 158 , nor at N = 101 in Eu 164 and Tb 166 . Here, these experimental observations are compared to results from multiquasiparticle blocking calculations.

150 ≤ A ≤ 189↗
DOE OSTI2026

A Short-Lived Isotope Counting System (SLICS) to measure reaction cross sections producing light, beta-decaying nuclei on OMEGA

A new activation detector optimized for short-lived isotopes was designed, installed, and tested on OMEGA. The Short-Lived Isotope Counting System (SLICS) can be positioned as close as 35 cm from the OMEGA target chamber center in a ten-inch-manipulator. Stable target samples can be mounted on the front end of the detector assembly to undergo triton-, deuteron-, or neutron-induced reactions that produce short-lived reaction products that beta decay. The emitted betas are detected in a phoswich configuration to eliminate the gamma background. The detector is optimized for isotopes with half-lives from 150 ms to 20 s, filling a gap in OMEGA’s current activation detectors for isotopes with half-lives >5 min. In a pilot study, SLICS achieved an efficiency of 24.5% ± 2.0% for counting 8Li, with a total of 505.8 ± 4.4 qualifying events. Using the existing triton laser-ion acceleration platform on OMEGA, this detector can be used to measure rarely studied tritium-induced reactions on light nuclei with an estimated uncertainty of 12%. As a result, the design of the detector and its performance during a first experiment employing deuterium as a surrogate will be discussed.

Beta spectrometry↗
DOE OSTI2021

Measurement of the EMC effect in light and heavy nuclei

In this work, inclusive electron scattering from nuclear targets has been measured to extract the nuclear dependence of the inelastic cross section in Hall C at the Thomas Jefferson National Accelerator facility. Results are presented for 2 H, 3 He, 4 He, 9 B, 12 C, 63 Cu and 197 Au at an incident electron beam energy of 5.77 GeV for a range of momentum transfer from Q 2 = 2 to 7 (GeV/c) 2 . These data improve the precision of the existing measurements of the EMC effect in the nuclear targets at large x, and allow for more detailed examinations of the A dependence of the EMC effect.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1975

Cosmic ray measurements of light and medium nuclei using a new telescope

Three separate balloon flights provided with a new multielement cosmic ray telescope are used to collect data on the isotopic composition of cosmic rays of Z equals 3 to 10 in the energy range 150-450 MeV/nuc. The discussion covers Li, Be, B, C, N, and O. The data on Ne is a new finding that suggests a possible enhancement of Ne-22 in cosmic rays relative to the normally accepted universal abundances. Other data are presented which directly verify the expected geomagnetic cutoff effects on isotopes characterized by different charge-to-mass ratio.

Preszler, A. M.↗
NASA NTRS1994

A new measurement of the flux of the light cosmic-ray nuclei at high energies

A new cosmic-ray detector utilizing a ring-imaging Cerenkov counter to determine the energy of light cosmic-ray nuclei was flown on high-altitude balloon from Fort Sumner, NM, in 1991 September. We describe the design and performance of this instrument and discuss the data analysis procedures. The measurement provides a new determination of the absolute flux and differential energy spectrum of the primary cosmic-ray species helium between 40 and 320 GeV/nucleon. The experiment also yields the spectra of carbon and oxygen and some information on the intensities of the secondary nuclei Li, Be, and B. A comparison between our results and previous measurements of heavier nuclei (Z greater than or equal to 4) from HEAO 3 and Spacelab 2 indicates good consistency between these measurements. The data set is compared with the results of a leaky box propagation model. We find good agreement with this model if the abundance of helium relative to oxygen at the source is taken to be 25 +/- 6 and if the source spectrum is given by a power law in energy proportional to E(exp -2.15).

Buckley, J.↗
DOE OSTI2025

Response functions and giant monopole resonances for light to medium-mass nuclei from the ab initio symmetry-adapted no-core–shell model

Using the ab initio symmetry-adapted no-core–shell model, we compute sum rules and response functions for light to medium-mass nuclei, starting from interactions that are derived in the chiral effective field theory. Specifically, we investigate electromagnetic transitions of monopole, dipole and quadrupole nature for 4 He, and explore dominant features of giant monopole resonances in symmetric nuclei such as the closed-shell 4 He and 16 O light nuclei, the intermediate-mass open-shell 20 Ne and the medium-mass closed-shell 40 Ca. Furthermore, for the NNLO opt chiral potential, we determine parameter-free monopole sum rules, which can provide information on the incompressibility of symmetric nuclear matter. Here, we report 213(10) MeV as an estimate for the compression modulus for infinite nuclear matter, which overlaps with the lower range of values often used in current astrophysical applications.

ab initio nuclear structure↗
NASA NTRS2001

Characteristic Ultraviolet/Optical Timescales in Active Galactic Nuclei

The UV/optical light curves of active galactic nuclei (AGNs) may be roughly characterized by a periodic fractional flux variations of approx. 10% on timescales of 1 month. The physical mechanism(s) responsible remain ill defined. We present a structure function analysis, i.e., measure the power distribution over a range of timescales tau, of 13 AGNs to constrain the origin of UV/optical emission. On timescales tau approx. 5- 60 days, the mean UV and optical power density spectra (PDS) are equivalent. This may suggest that the underlying energy generating mechanism is identical. The combined W/optical PDS is P(f) proportional to f(sup -alpha)- with alpha = 2.13(sup +0.22, sub -0.06). For sources with measured X-ray PDS indices, we find they are indistinguishable from their UV/optical counterparts. This supports scenarios whereby X-rays are generated via Compton upscattering of UV photons, to later radiatively drive optical variations. At the same time, we present evidence for characteristic variability timescales tau(sub char) of approx. 5-100 days in 10 sources. These variability timescales combined with reverberation based masses M suggest a M - tau(sub char) relationship; higher mass systems have larger characteristic timescales. The UV tau(sub char) may possibly reflect dynamical or accretion disk thermal timescales. We find suggestive evidence for a dichotomy, at tau approx. 30 days and M approx. l0(exp 7) solar mass, between short- and long-time scale optical variations. These optical variations may be attributable to dynamical and accretion disk thermal or starburst activity timescales, respectively.

Collier, Stefan↗
NASA NTRS1993

X-ray light curves of active galactic nuclei are phase incoherent

We compute the Fourier phase spectra for the light curves of five low-luminosity active galactic nuclei observed by EXOSAT. There is no statistically significant phase coherence in any of them. This statement is equivalent, subject to a technical caveat, to a demonstration that their fluctuation statistics are Gaussian. Models in which the X-ray output is controlled wholly by a unitary process undergoing a nonlinear limit cycle are therefore ruled out, while models with either a large number of randomly excited independent oscillation modes or nonlinearly interacting spatially dependent oscillations are favored. We also demonstrate how the degree of phase coherence in light curve fluctuations influences the application of causality bounds on internal length scales.

Krolik, Julian↗
DOE OSTI2025

AI-assisted transport of radioactive ion beams

Beams of radioactive heavy ions allow researchers to study rare and unstable atomic nuclei, shedding light into the internal structure of exotic nuclei and on how chemical elements are formed in stars. However, the extraction and transport of radioactive beams rely on time-consuming expert-driven tuning methods, where hundreds of parameters are manually optimized. Here, in this study, we introduce a system that employs Artificial Intelligence (AI), specifically utilizing Bayesian Optimization, to assist in the transport process of radioactive beams. We apply our methodology to real-life scenarios showing advantages when compared with standard tuning methods. This AI-assisted approach can be extended to other radioactive beam facilities around the world to improve operational efficiency and enhance scientific output.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Observation of deuteron and antideuteron formation from resonance-decay nucleons

High-energy hadronic collisions generate environments characterized by temperatures above 100 MeV (refs.), about 100,000 times hotter than the centre of the Sun. At present, it is therefore unclear how light (anti)nuclei with mass number A of a few units, such as the deuteron, 3 He or 4 He, each bound by only a few MeV, can emerge from these collisions. Here, the ALICE Collaboration reports that deuteron–pion momentum correlations in proton–proton (pp) collisions provide model-independent evidence that about 90% of the observed (anti)deuterons are produced in nuclear reactions following the decay of short-lived resonances, such as the Δ(1232). These findings, obtained by the ALICE Collaboration at the Large Hadron Collider, resolve a gap in our understanding of nucleosynthesis in ultrarelativistic hadronic collisions. Apart from offering insights on how (anti)nuclei are formed in hadronic collisions, the results can be used in the modelling of the production of light and heavy nuclei in cosmic rays and dark-matter decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Study of Nuclear Structure Functions at Jefferson Lab

This thesis presents a study of nuclear modification of quark distributions (the EMC effect) using inclusive electron-scattering data from Jefferson Lab Hall C, with emphasis on experiment E12-10-008 (XEM2). The analysis spans nuclei from light to heavy targets and combines measurements at multiple spectrometer settings to constrain EMC ratios over a broad range in Bjorken-x and Q2. A complete analysis framework was developed to extract charge-normalized and efficiency-corrected yields, including detector calibrations, beam-current calibration, density-loss corrections for cryogenic targets, background subtraction, radiative and Coulomb corrections, and systematic studies. Instrumental cross-checks, including HMS–SHMS comparisons and reconstruction studies, show that residual spectrometer differences are predominantly multiplicative in the kinematic region relevant to the EMC analysis. The extracted EMC ratios are broadly consistent with previous measurements while extending coverage across many nuclei. The EMC slope increases from light to heavy nuclei and shows signs of saturation at large A. After accounting for the dominant A dependence, the results are consistent with no isospin dependence, but also consistent with the predicted modification from the isovector model.

Sharda, Abhyuday [Univ. of Tennessee, Knoxville, T↗
NASA NTRS1996

Study of Analytic Statistical Model for Decay of Light and Medium Mass Nuclei in Nuclear Fragmentation

The angular momentum independent statistical decay model is often applied using a Monte-Carlo simulation to describe the decay of prefragment nuclei in heavy ion reactions. This paper presents an analytical approach to the decay problem of nuclei with mass number less than 60, which is important for galactic cosmic ray (GCR) studies. This decay problem of nuclei with mass number less than 60 incorporates well-known levels of the lightest nuclei (A less than 11) to improve convergence and accuracy. A sensitivity study of the model level density function is used to determine the impact on mass and charge distributions in nuclear fragmentation. This angular momentum independent statistical decay model also describes the momentum and energy distribution of emitted particles (n, p, d, t, h, and a) from a prefragment nucleus.

Cucinotta, Francis A.↗
NASA NTRS1989

Thermal light variations of active galactic nuclei

Thermal limit cycles in accretion disks are a promising explanation of the quasi-periodic outbursts of dwarf novae. A similar mechanism may lead to observable light variations in active galactic nuclei (AGNs) at wavelengths 1-5 microns. The variations should obey a characteristic period-luminosity relation. For low-luminosity AGNs, these variations could have a period of less than about 10 yr.

Clarke, C. J.↗
DOE OSTI2021

Lifetime measurements in the even-even Cd 102 – 108 isotopes

The heaviest T z = 0 doubly-magic nucleus, Sn 100 , and the neighboring nuclei offer unique opportunities to investigate the properties of nuclear interaction. For instance, the structure of light-Sn nuclei has been shown to be affected by the delicate balance between nuclear-interaction components, such as pairing and quadrupole correlations. From Cd to Te, many common features and phenomena have been observed experimentally along the isotopic chains, leading to theoretical studies devoted to a more general and comprehensive study of the region. In this context, having only two proton holes in the Z = 50 shell, the Cd isotopes are expected to present properties similar to those found in the Sn isotopic chain. The aim of this work was to measure lifetimes of excited states in neutron-deficient nuclei in the vicinity of Sn 100 . Here, the neutron-deficient nuclei in the N ≈ Z ≈ 50 region were populated using a multinucleon transfer reaction with a Cd 106 beam and a Mo 92 target. The beamlike products were identified by the VAMOS + + spectrometer, while the γ rays were detected using the AGATA array. Lifetimes of excited states were determined using the recoil distance Doppler-shift method, employing the Cologne differential plunger. Lifetimes of low-lying states were measured in the even-mass Cd 102 – 108 isotopes. In particular, multiple states with excitation energy up to ≈ 3 MeV, belonging to various bands, were populated in Cd 106 via inelastic scattering. The transition strengths corresponding to the measured lifetimes were compared with those resulting from state-of-the-art beyond-mean-field calculations using the symmetry-conserving configuration-mixing approach. Conclusions: Despite the similarities in the electromagnetic properties of the low-lying states, there is a fundamental structural difference between the ground-state bands in the Z = 48 and Z = 50 isotopes. The comparison between experimental and theoretical results revealed a rotational character of the Cd nuclei, which have prolate-deformed ground states with β 2 ≈ 0.2 . At this deformation Z = 48 becomes a closed-shell configuration, which is favored with respect to the spherical one.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗