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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Investigation of B 11 and Ca 40 levels at 8–9 MeV by nuclear resonance fluorescence

Here, we report on the measurement of 11 B and 40 Ca levels between excitation energies of 8 and 9 MeV using nuclear resonance fluorescence (NRF). The experiment was carried out with nearly monoenergetic and linearly polarized photon beams provided by the High-Intensity γ-ray Source (HIγS) facility at the Triangle Universities Nuclear Laboratory (TUNL). States in 11 B are important for calibrations of NRF measurements, while the properties of 40 Ca levels impact potassium nucleosynthesis in globular clusters. For 40 Ca, we report on improved excitation energies and an unambiguous 2¯ assignment for the state at 8425 keV. For 11 B, we obtained improved values for γ-ray multipolarity mixing ratios and branching ratios of the 8920-keV level.

39 ≤ A ≤ 58↗
DOE OSTI2022

Investigation of 48 Ca-induced reactions with 242 Pu and 238 U targets at the JINR Superheavy Element Factory

Experiments using a 48 Ca beam on 238 U and 242 Pu targets to produce superheavy nuclei were performed at the gas-filled separator DGFRS-2 online to the new cyclotron DC280 at the SHE Factory at JINR. The decay properties of 286 Fl and 287 Fl, as well as their α-decay products, were refined after the detection of 25 and 69 new decay chains, respectively. In addition, 16 decay chains of 283 Cn were observed in the 238 U+ 48 Ca reaction. The possibility of existing of isomeric states in the 287 Fl consecutive α decays is discussed. A new α line with an energy of 100–200 keV lower than the main one at 10.19 MeV was observed for the first time for even-even 286 Fl decay. A maximum cross section of $10.4^{+3.5}_{-2.1}$pb was measured for the 242 Pu( 48 Ca,3n) 287 Fl reaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

New isotope 286 Mc produced in the 243 Am + 48 Ca reaction

In this paper, we present results of the second experiment on the synthesis of Mc isotopes in the 243 Am + 48 Ca reaction performed at the gas-filled separator DGFRS-2 of the SHE Factory at JINR. Here, the new isotope 286 Mc was synthesized, and its half-life of $20^{+98}_{–9}$ ms and α-particle energy of 10.71 ± 0.02 MeV were determined. A 286 Mc α–decay chain was recorded down to the spontaneous fission of 266 Db. The spontaneous fission of 279 Rg was observed for the first time in one of four new decay chains of 287 Mc. The excitation function of the reaction was measured at three 48 Ca energies of 242, 250, and 259 MeV; the latter resulted in the first observation of the 5$\textit{n}$–evaporation channel with a cross section of $0.5^{+1.3}_{–0.4}$ pb. The decay properties of 21 previously known odd–$\textit{Z}$ isotopes were improved. The potential for an electron-capture decay mode is discussed for 288 Mc and 284 Nh isotopes. The half-lives of spontaneously fissioning nuclei produced in the 48 Ca–induced reactions with actinide targets are compared with several theoretical predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Ab Initio Computation of the Longitudinal Response Function in 40 Ca

In this work, we present a consistent ab initio computation of the longitudinal response function RL in 40 Ca using the coupled-cluster and Lorentz integral transform methods starting from chiral nucleon-nucleon and three-nucleon interactions. We validate our approach by comparing our results for R L in 4 He and the Coulomb sum rule in 40 Ca against experimental data and other calculations. For R L in 40 Ca we obtain a very good agreement with experiment in the quasielastic peak up to intermediate momentum transfers, and we find that final state interactions are essential for an accurate description of the data. This work presents a milestone towards ab initio computations of neutrino-nucleus cross sections relevant for experimental long-baseline neutrino programs.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Combined Theoretical Analysis of the Parity-Violating Asymmetry for 48 Ca and 208 Pb

The recent experimental determination of the parity violating asymmetry A PV in 48 Ca and 208 Pb at Jefferson Lab is important for our understanding on how neutrons and protons arrange themselves inside the atomic nucleus. To better understand the impact of these measurements, we present a rigorous theoretical investigation of A PV in 48 Ca and 208 Pb and assess the associated uncertainties. Here, we complement our study by inspecting the static electric dipole polarizability in these nuclei. The analysis is carried out within nuclear energy density functional theory with quantified input. We conclude that the simultaneous accurate description of A PV in 48 Ca and 208 Pb cannot be achieved by our models that accommodate a pool of global nuclear properties, such as masses and charge radii, throughout the nuclear chart, and describe—within one standard deviation—the experimental dipole polarizabilities in these nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Iridium valence variation and carrier sign tuning in ( Ca , Ba ) x La 2 – x CuIrO 6 double perovskites

Here, we report the structure and properties of ( Ca , Ba ) x La 2 – x CuIrO 6 . The rock-salt double perovskite structure goes through a P 1 ¯ to P 2 1 / n phase transition with increasing Ba content but not with Ca content. In both cases, the Ir ion is oxidized from 4 + to 5 + with increasing substitution. Transport and magnetic properties measurements reveal that all compositions are insulating with hysteretic spin-freezing magnetic behavior. Seebeck coefficient measurements reveal a large thermopower change from + 176 μ V /K in La 2 CuIrO 6 to – 223 μ V /K with increasing Ba content in Ba x La 2 – x CuIrO 6 . This behavior is modeled well by the Heikes formula for correlated hopping conduction. ( Ca , Ba ) x La 2 – x CuIrO 6 provides a model system for investigations of other systems with similar carrier sign tuning, with applications toward semiconductors and thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Metadynamics simulations reveal mechanisms of Na + and Ca 2+ transport in two open states of the channelrhodopsin chimera, C1C2

Cation conducting channelrhodopsins (ChRs) are a popular tool used in optogenetics to control the activity of excitable cells and tissues using light. ChRs with altered ion selectivity are in high demand for use in different cell types and for other specialized applications. However, a detailed mechanism of ion permeation in ChRs is not fully resolved. Here, we use complementary experimental and computational methods to uncover the mechanisms of cation transport and valence selectivity through the channelrhodopsin chimera, C1C2, in the high- and low-conducting open states. Electrophysiology measurements identified a single-residue substitution within the central gate, N297D, that increased Ca 2+ permeability vs. Na + by nearly two-fold at peak current, but less so at stationary current. We then developed molecular models of dimeric wild-type C1C2 and N297D mutant channels in both open states and calculated the PMF profiles for Na + and Ca 2+ permeation through each protein using well-tempered/multiple-walker metadynamics. Results of these studies agree well with experimental measurements and demonstrate that the pore entrance on the extracellular side differs from original predictions and is actually located in a gap between helices I and II. Cation transport occurs via a relay mechanism where cations are passed between flexible carboxylate sidechains lining the full length of the pore by sidechain swinging, like a monkey swinging on vines. In the mutant channel, residue D297 enhances Ca 2+ permeability by mediating the handoff between the central and cytosolic binding sites via direct coordination and sidechain swinging. We also found that altered cation binding affinities at both the extracellular entrance and central binding sites underly the distinct transport properties of the low-conducting open state. This work significantly advances our understanding of ion selectivity and permeation in cation channelrhodopsins and provides the insights needed for successful development of new ion-selective optogenetic tools.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

AmeriFlux FLUXNET-1F CA-DB2 Delta Burns Bog 2

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-DB2 Delta Burns Bog 2. This is the FLUXNET version of the carbon flux data for the site CA-DB2 Delta Burns Bog 2 produced by applying the standard ONEFlux (1F) software. Site Description - The Burns Bog Ecological Conservancy Area (BBECA) in the metro Vancouver area presents a unique opportunity for insight into greenhouse gas dynamics post restoration. The bog was significantly disturbed for peat mining, development and agriculture over the last century, however since 2005 there has been both active restoration and natural regeneration occurring within the bog. Hence areas of bog are at varying stages of ecological recovery. This site is a Pine-Sphagnum low shrub site characteristic of a later successional stage. Conversely, CA-DBB, another AmeriFlux site in BBECA, is a Beakrush-Sphagnum site characteristic of an earlier successional stage.

Knox, Sara↗
DOE OSTI2024

AmeriFlux FLUXNET-1F CA-SCC Scotty Creek Landscape

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-SCC Scotty Creek Landscape. This is the FLUXNET version of the carbon flux data for the site CA-SCC Scotty Creek Landscape produced by applying the standard ONEFlux (1F) software. Site Description - The Scotty Creek flux tower is located in an organic-rich boreal forest-wetland landscape about 50 km south of Fort Simpson in the Taiga Plains of the Mackenzie watershed. The tower was installed in 2013 and operates an open-path EC system year-round running on solar power only. Flux footprints contain about 50 % forested peat plateaus and 50 % wetlands (i.e., collapse-scar bogs). The forests are underlain by permafrost, while the treeless wetlands are permafrost-free. The tower itself is located on a forested peat plateau. Black spruce tree density on plateaus is sparse and the mean canopy height is ca. 5 m.

Sonnentag, Oliver↗
DOE OSTI2021

Uranium (VI) Adsorbate Structures on Portlandite [Ca(OH)2] Type Surfaces Determined by Computational Modelling and X-ray Absorption Spectroscopy

Portlandite [Ca(OH) 2 ] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically important radionuclide (U) will be adsorbed onto this phase under conditions relevant to a GDF environment. Such data are fundamental for predicting radionuclide mass transfer. Surface coordination chemistry and speciation of uranium with portlandite [Ca(OH) 2 ] under alkaline groundwater conditions (ca. pH 12) were determined by both in situ and ex situ grazing incidence extended X-ray absorption fine structure analysis (EXAFS) and by computational modelling at the atomic level. Free energies of sorption of aqueous uranyl hydroxides, [UO 2 (OH) n ] 2–n (n = 0–5) with the (001), (100) and (203) or (101) surfaces of portlandite are predicted from the potential of mean force using classical molecular umbrella sampling simulation methods and the structural interactions are further explored using fully periodic density functional theory computations. Although uranyl is predicted to only weakly adsorb to the (001) and (100) clean surfaces, there should be significantly stronger interactions with the (203/101) surface or at hydroxyl vacancies, both prevalent under groundwater conditions. The uranyl surface complex is typically found to include four equatorially coordinated hydroxyl ligands, forming an inner-sphere sorbate by direct interaction of a uranyl oxygen with surface calcium ions in both the (001) and (203/101) cases. In contrast, on the (100) surface, uranyl is sorbed with its axis more parallel to the surface plane. The EXAFS data are largely consistent with a surface structural layer or film similar to calcium uranate, but also show distinct uranyl characteristics, with the uranyl ion exhibiting the classic dioxygenyl oxygens at 1.8 Å and between four and five equatorial oxygen atoms at distances between 2.28 and 2.35 Å from the central U absorber. These experimental data are wholly consistent with the adsorbate configuration predicted by the computational models. These findings suggest that, under the strongly alkaline conditions of a cementitious backfill engineered barrier, there would be significant uptake of uranyl by portlandite to inhibit the mobility of U(VI) from the near field of a geological disposal facility.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(ScS2)2 by Materials Project

Ca(ScS2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Ca–S bond distances ranging from 2.92–3.22 Å. There are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–61°. There are a spread of Sc–S bond distances ranging from 2.54–2.65 Å. In the second Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–61°. There are a spread of Sc–S bond distances ranging from 2.56–2.63 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Ca2+ and three equivalent Sc3+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Ca2+ and three Sc3+ atoms. In the third S2- site, S2- is bonded to two equivalent Ca2+ and three equivalent Sc3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Sc3 square pyramids. In the fourth S2- site, S2- is bonded to two equivalent Ca2+ and three Sc3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Sc3 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BeN)2 by Materials Project

Ca(BeN)2 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight equivalent N3- atoms. All Ca–N bond lengths are 2.69 Å. Be2+ is bonded in a trigonal planar geometry to three equivalent N3- atoms. There is one shorter (1.61 Å) and two longer (1.66 Å) Be–N bond length. N3- is bonded in a 7-coordinate geometry to four equivalent Ca2+ and three equivalent Be2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BO2)2 by Materials Project

CaB2O4 crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.61 Å. In the second Ca2+ site, Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with twelve equivalent BO4 tetrahedra and edges with six equivalent BO4 tetrahedra. There are six shorter (2.70 Å) and six longer (2.82 Å) Ca–O bond lengths. B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share corners with two equivalent CaO12 cuboctahedra, corners with four equivalent BO4 tetrahedra, and an edgeedge with one CaO12 cuboctahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Ca2+ and two equivalent B3+ atoms. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to three Ca2+ and two equivalent B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(NiO2)4 by Materials Project

Ca(NiO2)4 is beta indium sulfide-derived structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded in a distorted hexagonal planar geometry to six equivalent O2- atoms. All Ca–O bond lengths are 2.36 Å. There are two inequivalent Ni+3.50+ sites. In the first Ni+3.50+ site, Ni+3.50+ is bonded to six O2- atoms to form edge-sharing NiO6 octahedra. There is four shorter (1.89 Å) and two longer (1.91 Å) Ni–O bond length. In the second Ni+3.50+ site, Ni+3.50+ is bonded to six equivalent O2- atoms to form edge-sharing NiO6 octahedra. All Ni–O bond lengths are 2.03 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ca2+ and three Ni+3.50+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Ni+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(Ni2B)6 by Materials Project

Ca(Ni2B)6 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded in a hexagonal planar geometry to six equivalent B3- atoms. All Ca–B bond lengths are 3.15 Å. There are two inequivalent Ni+1.33+ sites. In the first Ni+1.33+ site, Ni+1.33+ is bonded to four equivalent B3- atoms to form a mixture of distorted edge and corner-sharing NiB4 tetrahedra. There are two shorter (2.04 Å) and two longer (2.09 Å) Ni–B bond lengths. In the second Ni+1.33+ site, Ni+1.33+ is bonded in a T-shaped geometry to three equivalent B3- atoms. There are two shorter (2.07 Å) and one longer (2.08 Å) Ni–B bond lengths. B3- is bonded in a 7-coordinate geometry to one Ca2+ and seven Ni+1.33+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(IO3)2 by Materials Project

Ca(IO3)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.38–2.53 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ca2+ and one I5+ atom. The O–I bond length is 1.83 Å. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Ca2+ and one I5+ atom. The O–I bond length is 1.83 Å. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+ and one I5+ atom. The O–I bond length is 1.84 Å. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+ and one I5+ atom. The O–I bond length is 1.86 Å. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+ and one I5+ atom. The O–I bond length is 1.82 Å. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ca2+ and one I5+ atom. The O–I bond length is 1.83 Å. There are two inequivalent I5+ sites. In the first I5+ site, I5+ is bonded in a 3-coordinate geometry to three O2- atoms. In the second I5+ site, I5+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(Cu2As)2 by Materials Project

Ca(Cu2As)2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent As3- atoms to form edge-sharing CaAs6 octahedra. All Ca–As bond lengths are 3.01 Å. There are two inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded in a distorted single-bond geometry to four equivalent As3- atoms. There are one shorter (2.46 Å) and three longer (2.81 Å) Cu–As bond lengths. In the second Cu1+ site, Cu1+ is bonded in a distorted trigonal non-coplanar geometry to three equivalent As3- atoms. All Cu–As bond lengths are 2.46 Å. As3- is bonded in a 10-coordinate geometry to three equivalent Ca2+ and seven Cu1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(AuO2)2 by Materials Project

Ca(AuO2)2 crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight equivalent O2- atoms. There are four shorter (2.48 Å) and four longer (2.59 Å) Ca–O bond lengths. Au3+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Au–O bond lengths are 2.04 Å. O2- is bonded to two equivalent Ca2+ and two equivalent Au3+ atoms to form a mixture of edge and corner-sharing OCa2Au2 tetrahedra.

36 MATERIALS SCIENCE↗