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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Energy dependence of light hypernuclei production in heavy-ion collisions from a coalescence and statistical-thermal model perspective

A comparison of light hypernuclei production, from Ultra-relativistic Quantum Molecular Dynamics (UrQMD)+coalescence and the thermal model, in heavy ion collisions over a wide range of beam energies and system sizes is presented. We find that both approaches provide generally similar results, with differences in specific details. Especially the ratios of hypertriton to Λ are affected by both the source radius Δr of the coalescence procedure as well as canonical effects. On the other hand, the double ratio S 3 is almost independent of canonical effects, which is in contrast to coalescence. Thus, both the beam energy dependence and centrality dependence of S 3 can be used to constrain the hypertriton source radius. To do so the currently available data are not yet sufficient. Elliptic flow is shown to be unaffected by the source size of the nuclei and an almost perfect mass scaling of the elliptic flow is observed. Furthermore, our predictions further suggest that the existence of the H-dibaryon(ΛΛ) seems ruled out by ALICE data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Angular distribution of 𝛾 rays from a neutron-induced 𝑝-wave resonance of 132 Xe

A neutron-energy dependent angular distribution was measured for individual 𝛾 rays from the 3.2 eV 𝑝-wave resonance of 131 Xe+⁢𝑛, that shows enhanced parity violation owing to a mixing between 𝑠- and 𝑝-wave amplitudes. The 𝛾-ray transitions from the 𝑝-wave resonance were identified, and the angular distribution with respect to the neutron momentum was evaluated as a function of the neutron energy for 7132 keV 𝛾 rays, which correspond to a transition to the 1807 keV excited state of 132 Xe. The angular distribution is considered to originate from the interference between 𝑠- and 𝑝-wave amplitudes, and will provide a basis for a quantitative understanding of the enhancement mechanism of the fundamental parity violation in compound nuclei.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Search for an s -wave resonance in Li 7 just above the proton-decay threshold

Near-threshold resonances play an important role in nucleosynthesis and applied nuclear science. The study of nuclei removed from stability has greatly extended the list of resonances close to decay thresholds. The no core shell model with continuum (NCSMC) recently predicted an s-wave resonance just above the proton-decay threshold of 7 Li at an excitation energy of 10.2 MeV. This potential case of a near-threshold resonance is dependent on the quantum mechanics of the p + 6 He fragments extended into the continuum. Further, the 6 He(d,n) 7 Li* reaction was employed in an attempt to populate this resonance and search for its proton decay via the invariant-mass method. No evidence of this resonance was found. However, the data collected in this search led to better constraints on the energy and width of the isobaric analog state (IAS) with (J π ,T) = (3/2 - , 3/2) and revealed a new weak resonance just above the IAS in energy, predicted by the NCSMC as a (J π , T ) = (3/2 – , 1/2) state and potentially a part of the antianalog structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurements of H Λ 3 and H Λ 4 Lifetimes and Yields in Au + Au Collisions in the High Baryon Density Region

We report precision measurements of hypernuclei $^3_ΛH$ and $^4_ΛH$ lifetimes obtained from Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV and 7.2 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider, and the first measurement of $^3_ΛH$ and $^4_ΛH$ midrapidity yields in Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV. $^3_ΛH$ and $^4_ΛH$, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221 ± 15 (stat) ± 19 (syst) ps for $^3_ΛH$ and 218 ± 6 (stat) ± 13 (syst) ps for $^4_ΛH$. The p T -integrated yields of $^3_ΛH$ and $^4_ΛH$ are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of $4_ΛH$ is different for 0%–10% and 10%–50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the $^3_ΛH$ yield well, while underestimating the $^4_ΛH$ yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured $^3_ΛH$ and $^4_ΛH$ yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Removal of trace gases can both increase and decrease cloud droplet formation

Aerosols consist of liquid or solid particles dispersed in a gas. Aerosol measurements generally rely on drying the particles before quantifying their physicochemical properties. This drying can potentially remove semivolatile compounds from the particles. Here, we show size-resolved cloud condensation nuclei (CCN) measurements quantifying the hygroscopicity parameter in the presence and absence of a denuder. The denuder efficiently removed alkanes and weakly functionalized acids, aldehydes, and alcohols with fewer than 10 carbon atoms from the gas phase. Denuding organic compounds perturbed the CCN-derived hygroscopicity parameter by up to 50%. Denuding either rendered the particles more or less CCN active, and the direction of the effect depended on sample relative humidity and trace gas concentration. The effect was weakest in early spring and strongest in late spring and summer. The measurements demonstrate an unexpectedly strong coupling between the particle and gas phase, influencing CCN activity through either volatilization or surface adsorption, or both.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

A Vision for the Science of Rare Isotopes

The field of nuclear science has considerably advanced since its beginning just over a century ago. Today, the science of rare isotopes is on the cusp of a new era with theoretical and computing advances complementing experimental capabilities at new facilities internationally. In this article we present a vision for the science of rare isotope beams (RIBs). We do not attempt to cover the full breadth of the field; rather, we provide a perspective and address a selection of topics that reflect our own interests and expertise. We focus in particular on systems near the drip lines, where one often finds nuclei that are referred to as exotic and where the role of the nuclear continuum is only just starting to be explored. An important aspect of this article is its attempt to highlight the crucial connections between nuclear structure and the nuclear reactions required to fully interpret and leverage the rich data to be collected in the next years at RIB facilities. Further, we connect the efforts in structure and reactions to key questions of nuclear astrophysics.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2026

Toward the Limits of Nuclear Existence: First Science with FRIB

The opportunity to explore the properties of short-lived atomic nuclei—or rare isotopes—in laboratories has enabled discoveries across the sciences related to the nature of the nuclear force and the limits of nuclear existence, the origin of the elements in the Universe, the cosmic matter–antimatter asymmetry, and the application of rare isotopes for society and the nation. The newest-generation Facility for Rare Isotope Beams (FRIB) on the campus of Michigan State University commenced operations in May 2022 as a user facility for the US Department of Energy, Office of Science, Office of Nuclear Physics. FRIB provides fast, stopped, and reaccelerated beams of rare isotopes for measurements, serving a 1,800-member-strong community of scientists from around the world. Here, this article reviews some of the first results from FRIB, showcasing the breadth of the science discoveries that have already occurred while the facility is ramping up to full capability.

FRIB↗
DOE OSTI2020

Complex radius in the R-matrix algorithm for inclusion of direct capture component [Slides]

In the low-energy range there are two possible physical mechanisms for γ-ray emissions. While both mechanisms emit γ-rays, the compound radiative capture (CRC) process is generated by the formation of a compound nucleus state before γ-emission. CRC has a characteristic resonance structure in the cross section, The direct radiative capture (DRC) process goes to the final state by the electromagnetic radiation of the incident neutron. DRC has a smooth behavior in the cross section. For light nuclei, a non-negligible component of the neutron capture process can be often associated to DRC process. Although these two mechanisms should be described by a unified theoretical formalism, in the nuclear data libraries, the CRC and DRC components are evaluated and reported separately. The updated R-matrix algorithm will allow the ability to implicitly include correlations between CRC and DRC mechanisms, to improve the quality of nuclear data evaluations, and to facilitate simple large-scale applicability to current nuclear data evaluations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

First Experimental Test of the Ratio Method

The ratio is a new reaction observable suggested to extract accurately structure information on halo nuclei. It corresponds to the ratio of differential cross sections for scattering and breakup, which is predicted to remove the uncertainty related to the reaction dynamics. We present here the first experimental test of the method for the 11 Be + 12 C collision at E Lab = 20A MeV performed at Texas A&M University. Differential cross sections for scattering and inclusive one-neutron breakup have been measured with the new detector array BlueSTEAl. The ratio of cross sections is very smooth and independent of the projectile-target interaction, which demonstrates the validity of the ratio method. We extend our analysis to existing 11 Be + 208 Pb data, confirming that the method works well on any target.

11Be↗
DOE OSTI2022

Particle configurations in the $NN\bar K$ system

Three-body AAB model for the $NN\bar K$(s NN = 0) kaonic cluster is considered based on the configuration space Faddeev equations. Within a single channel approach, the difference between masses of nucleons and kaons and the charge independence breaking of nucleon-nucleon interaction are taken into consideration. We definite the particle configurations in the system according to the particle masses and pair potentials. There are two sets of the particle configurations, ppK¯, npK¯ 0 and nnK¯ 0 , npK¯, charged and neutral. The three-body calculations are performed by applying NN and NK¯ phenomenological isospin-dependent potentials. The mass and energy spectra related to the particle configurations are presented. We evaluate the mass and energy uncertainties for the NNK¯ model. As a result, an analogy to NNN model for the 3 H and 3 He nuclei is proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

The Intrinsic Scatter of the Broad Lines–Narrow Line Correlation in Type I AGN

A correlation between the FWHM of the broad Balmer lines and the narrow [O iii]/H{sub β} line ratio was recently applied to the black hole (BH) mass estimation in type II active galactic nuclei (AGN), where only the narrow lines are visible to the observer. The correlation was initially quantified with type I AGN using stacked spectra, in groups automatically created using a machine-learning algorithm. Such an analysis does not provide information about the intrinsic scatter of the correlation. In addition, it does not necessarily reproduce the true underlying correlation, for example, due to the stacking of spectra with different properties. Testing these two issues requires measurements of individual objects. In this work, we perform such a test by fitting the broad and narrow lines for 8302 type I AGN from the Sloan Digital Sky Survey. Due to the difficulty in reliably measuring the narrow Balmer lines in such objects, which are, in many cases, a small contribution on top of the broad lines, we visually inspect all of the fits and identify 1561 objects with robust measurements. Using these measurements, we find that while a correlation does exist, it shows a large scatter and is not well described by a linear relation. This should be taken into account when using the broad H{sub β} FWHM versus narrow [O iii]/H{sub β} correlation for type II AGN BH mass estimation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Dust Reverberation of 3C 273: Torus Structure and Lag–Luminosity Relation

We monitored the z = 0.158 quasar 3C 273 between 2015 and 2019 in the optical (BVrz) and near-infrared (JHK) with the aim to perform dust reverberation mapping. Accounting for host galaxy and accretion disk contributions, we obtained pure dust light curves in JHK. Cross correlations between the V band and the dust light curves yield an average rest-frame delay for the hot dust of τ {sub cent} ∼ 410 days. This is a factor of two shorter than that expected from the the dust ring radius R {sub x} ∼ 900 lt-day reported from interferometric studies. The dust covering factor (CF) is about 8%, much smaller than that predicted from the half covering angle of 45° found for active galactic nuclei (AGNs). We analyze the asymmetric shape of the correlation functions and explore whether an inclined biconical bowl-shaped dust torus geometry could bring these findings (τ {sub cent}, R {sub x} and CF) into a consistent picture. The hot varying dust emission originates from the edge of the bowl rim with a small covering angle 40° < θ < 45°, and we see only the near side of the biconus. Such a dust gloriole with R {sub x} = 900 ± 200 lt-day and an inclination 12° matches the data remarkably well. Comparing the results of 3C 273 with literature for less luminous AGN, we find a lag–luminosity relation τ ∝ L {sup α} with α = 0.33–0.40, flatter than the widely adopted relation with α ∼ 0.5. We address several explanations for the new lag–luminosity relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Alert Classification for the ALeRCE Broker System: The Light Curve Classifier

We present the first version of the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker light curve classifier. ALeRCE is currently processing the Zwicky Transient Facility (ZTF) alert stream, in preparation for the Vera C. Rubin Observatory. The ALeRCE light curve classifier uses variability features computed from the ZTF alert stream and colors obtained from AllWISE and ZTF photometry. We apply a balanced random forest algorithm with a two-level scheme where the top level classifies each source as periodic, stochastic, or transient, and the bottom level further resolves each of these hierarchical classes among 15 total classes. This classifier corresponds to the first attempt to classify multiple classes of stochastic variables (including core- and host-dominated active galactic nuclei, blazars, young stellar objects, and cataclysmic variables) in addition to different classes of periodic and transient sources, using real data. We created a labeled set using various public catalogs (such as the Catalina Surveys and Gaia DR2 variable stars catalogs, and the Million Quasars catalog), and we classify all objects with ≥6 g-band or ≥6 r-band detections in ZTF (868,371 sources as of 2020 June 9), providing updated classifications for sources with new alerts every day. For the top level we obtain macro-averaged precision and recall scores of 0.96 and 0.99, respectively, and for the bottom level we obtain macro-averaged precision and recall scores of 0.57 and 0.76, respectively. Updated classifications from the light curve classifier can be found at the ALeRCE Explorer website (http://alerce.online).

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

GLEAM: Galaxy Line Emission & Absorption Modeling

We present Galaxy Line Emission & Absorption Modeling (gleam), a Python tool for fitting Gaussian models to emission and absorption lines in large samples of 1D extragalactic spectra. gleam is tailored to work well in batch mode without much human interaction. With gleam, users can uniformly process a variety of spectra, including galaxies and active galactic nuclei, in a wide range of instrument setups and signal-to-noise regimes. gleam also takes advantage of multiprocessing capabilities to process spectra in parallel. With the goal of enabling reproducible workflows for its users, gleam employs a small number of input files, including a central, user-friendly configuration in which fitting constraints can be defined for groups of spectra and overrides can be specified for edge cases. For each spectrum, gleam produces a table containing measurements and error bars for the detected spectral lines and continuum and upper limits for nondetections. For visual inspection and publishing, gleam can also produce plots of the data with fitted lines overlaid. In the present paper, we describe gleam’s main features, the necessary inputs, expected outputs, and some example applications, including thorough tests on a large sample of optical/infrared multi-object spectroscopic observations and integral field spectroscopic data. gleam is developed as an open-source project hosted at https://github.com/multiwavelength/gleam and welcomes community contributions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Functional Principal Component Analysis of Radio–Optical Reference Frame Tie

The Gaia optical reference frame is intrinsically undefined with respect to global orientation and spin, so it needs to be anchored in the radio-based International Celestial Reference Frame (ICRF) to provide a referenced and quasi-inertial celestial coordinate system. The link between the two fundamental frames is realized through two samples of distant extragalactic sources, mostly active galactic nuclei and quasars, but only the smaller sample of radio-loud ICRF sources with optical counterparts is available to determine the mutual orientation. The robustness of this link can be mathematically formulated in the framework of functional principal component analysis using a set of vector spherical harmonics to represent the differences in celestial positions of the common objects. The weakest eigenvectors are computed, which describe the greatest deficiency of the link. The deficient or poorly determined terms are specific vector fields on the sphere that carry the largest errors of absolute astrometry using Gaia in reference to the ICRF. This analysis provides guidelines for the future development of the ICRF maximizing the accuracy of the link over the entire celestial sphere. A measure of the robustness of a least-squares solution, which can be applied to any linear model fitting problem, is introduced to help discriminate between reference frame tie models of different degrees.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Analysis of Hybrid Gas–Dust Outbursts Observed at 67P/Churyumov–Gerasimenko

Cometary outbursts offer a valuable window into the composition of comet nuclei with their forceful ejection of dust and volatiles in explosive events, revealing the interior components of the comet. Understanding how different types of outbursts influence the dust properties and volatile abundances, to better interpret what signatures can be attributed to primordial composition and what features are the result of processing, is an important task best undertaken with a multi-instrument approach. The European Space Agency Rosetta mission to 67P/Churyumov–Gerasimenko carried a suite of instruments capable of carrying out this task in the near-nucleus coma with unprecedented spatial and spectral resolution. In this work, we discuss two outbursts that occurred 2015 November 7 and were observed by three instruments on board: the Alice ultraviolet spectrograph, the Visual Infrared and Thermal Imaging Spectrometer, and the Optical, Spectroscopic, and Infrared Remote Imaging System. Together, the observations show that mixed gas and dust outbursts can have different spectral signatures representative of their initiating mechanisms, with the first outburst showing indicators of a cliff collapse origin and the second more representative of fresh volatiles being exposed via a deepening fracture. This analysis opens up the possibility of remote spectral classification of cometary outbursts with future work.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Investigation of the Origins of Comets as Revealed through Infrared High-resolution Spectroscopy I. Molecular Abundances

We report and analyze updated molecular abundances in 20 comets obtained by employing modern data reduction procedures and molecular models. Using box and scatter plots, we examine how the different molecular species are distributed among the comet population, while by means of pie charts, we investigate the relative proportions of these molecular species in each comet. We compare these results with the orbital parameters of the selected comets to identify trends related to their dynamical history. With these analyses, we tentatively identify at least three chemical classes based mainly on relative abundances of CO, CH{sub 3}OH, CH{sub 4}, C{sub 2}H{sub 6}, HCN, and NH{sub 3}. The combination of relative abundances and orbital parameters is then compared with recent chemical models of planetary system formation. This approach may help in investigating the origins and evolution of the material in cometary nuclei. Among other aspects, we underline the need to increase our sample size, especially for hypervolatiles (i.e., CH{sub 4} and CO) in Jupiter family comets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Where Do Obscured AGN Fit in a Galaxy’s Timeline?

Many X-ray bright active galactic nuclei (AGNs) are predicted to follow an extended stage of obscured black hole growth. In support of this picture we examine the X-ray undetected AGNs in the COSMOS field and compare their host galaxies with X-ray bright AGNs. We examine galaxies with M {sub *} > 10{sup 9.5} M {sub ⊙} for the presence of AGNs at redshifts z = 0.5–3. We select AGNs in the infrared using Spitzer and Herschel detections and use color selection techniques to select AGNs within strongly star-forming hosts. We stack Chandra X-ray data of galaxies with an infrared (IR) detection but lacking an X-ray detection to obtain soft and hard fluxes, allowing us to measure the energetics of these AGNs. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. We also find that X-ray undetected AGNs all lie on the main sequence—the tight correlation between the star formation rate and M {sub *} that holds for the majority of galaxies, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGNs than previously thought.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗