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At least 433 records · Page 24

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DOE OSTI2022

First experiment at the Super Heavy Element Factory: High cross section of Mc 288 in the Am 243 + Ca 48 reaction and identification of the new isotope Lr 264

Here, we present results of the first experiment aimed at the synthesis of Mc isotopes in the 243 Am+ 48 Ca reaction performed at the new gas-filled separator DGFRS-2 online to the new cyclotron DC280 at the Super Heavy Element Factory at JINR. Fifty-five new decay chains of 288 Mc and six chains assigned to 289 Mc were detected. The α decay of 268 Db with an energy of 7.6–8.0 MeV, half-life of 16$^{+6}_{-4}$h, and a branch of 55$^{+20}_{-15}$% was registered for the first time, and a new spontaneously fissioning isotope 264 Lr with a half-life of 4.9$^{+2.1}_{-1.3}$h was identified. The cross section for the 243 Am( 48 Ca,3n) 288 Mc reaction was measured to be 17.1$^{+6.3}_{-4.7}$ pb, which is the largest value for the known superheavy nuclei at the island of stability.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of 37,38 Sc, 35 Ca, 34 K

A fast secondary beam of 37 Ca impinged on a 9 Be target resulting in a set of reactions populating proton-rich nuclei including 35 Ca and the first observations of 37,38 Sc and 34 K. Invariant-mass spectroscopy, used to reconstruct proton decays for these nuclei, yielded three new ground-state masses and information on their low-lying structures. The newly measured mass excesses are: ΔM( 37 Sc) = 3500(410) keV, ΔM( 38 Sc) = –4656(14) keV, and ΔM( 34 K) = –1487(17) keV. These nuclei straddle the well-known Z = 20 shell closure as well as the N = 16 subshell closure. Furthermore, trends in separation energies help elucidate how nuclear structure evolves showing a fading of the Z = 20 shell gap for N ≥ 18 and indications of a N = 16 subshell gap.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Gamow-Teller Strength in Ca 48 and Ni 78 with the Charge-Exchange Subtracted Second Random-Phase Approximation

Here, we develop a fully self-consistent subtracted second random-phase approximation for charge-exchange processes with Skyrme energy-density functionals. As a first application, we study Gamow-Teller excitations in the doubly magic nucleus 48 Ca, the lightest double-β emitter that could be used in an experiment, and in 78 Ni, the single-beta-decay rate of which is known. The amount of Gamow-Teller strength below 20 or 30 MeV is considerably smaller than in other energy-density-functional calculations and agrees better with experiment in 48 Ca, as does the beta-decay rate in 78 Ni. These important results, obtained without ad hoc quenching factors, are due to the presence of two-particle–two-hole configurations. Their density progressively increases with excitation energy, leading to a long high-energy tail in the spectrum, a fact that may have implications for the computation of nuclear matrix elements for neutrinoless double-β decay in the same framework.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

High Resolution Study of 40 Ca to Constrain Potassium Nucleosynthesis in NGC 2419

The globular cluster NGC 2419 was the first to exhibit a Mg-K anticorrelation, linked to hydrogen burning at temperatures between 80-260 MK. However, the key K-destroying reaction, 39 K(p,γ) 40 Ca, has a large rate uncertainty in this range. We significantly constrain this rate with a high resolution 39 K( 3 He,d) 40 Ca study. We resolve the $E$$^{c.m.}_{r}$ = 154 keV resonance in 39 K+p for the first time, increasing the previous rate by up to a factor 13 and reducing its 1σ width by up to a factor of 42. As a result, reaction network calculations for NGC 2419 suggest that this could lower temperatures needed to reproduce the Mg-K anticorrelation.

39 ≤ A ≤ 58↗

DOE OSTI2024

Magnetic Dipole Transition in Ca 48

Here, the magnetic dipole transition strength B(M1) of 48 Ca is dominated by a single resonant state at an excitation energy of 10.23 MeV. Experiments disagree about B(M1) and this impacts our understanding of spin flips in nuclei. We performed ab initio computations based on chiral effective field theory and found that B(M1 : 0 + → 1 + ) lies in the range from 7.0 to 10.2 $µ^2_N$. This is consistent with a (γ, n) experiment but larger than results from (e, e') and (p, p') scattering. Two body currents yield no quenching of the B(M1) strength and continuum effects reduce it by about 10%. For a validation of our approach, we computed magnetic moments in 47,49 Ca and performed benchmark calculations in light nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Growth and characterization of large (Y,La)TiO 3 and (Y,Ca)TiO 3 single crystals

The Mott-insulating rare-earth titanates ( R TiO 3 , with R being a rare-earth ion) are an important class of materials that encompasses interesting spin-orbital phases as well as ferromagnet-antiferromagnet and insulator-metal transitions. The growth of these materials has been plagued by difficulties related to overoxidation, which arises from a strong tendency of Ti 3 + to oxidize to Ti 4 + . We describe our efforts to grow sizable single crystals of YTiO 3 , Y 1 - x La x TiO 3 ( x ≤ 0.25 ), and Y 1 - y Ca y TiO 3 ( y ≤ 0.35 ) with the optical traveling-solvent floating-zone technique. Finally, we present sample characterization via chemical composition analysis, magnetometry, charge transport, neutron scattering, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism to understand macroscopic physical property variations associated with overoxidation. Furthermore, we demonstrate a good signal-to-noise ratio in inelastic magnetic neutron scattering measurements of spin-wave excitations. A superconducting impurity phase, found to appear in Ca-doped samples at high doping levels, is identified as TiO.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Structure and equation of state of Bi 2 Sr 2 Ca n-1 Cu n O 2n+4+δ from x-ray diffraction to megabar pressures

Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. In this work we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-T c cuprate superconductors with the nominal composition Bi 2 Sr 2 Ca n-1 Cu n O 2n+4+δ (n=1, 2, 3) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of Bi 2 Sr 2 Ca n-1 Cu n O 2n+4+δ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of T c with pressure, including the increase in T c at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Jeankempite, Ca 5 (AsO 4 ) 2 (AsO 3 OH) 2 (H 2 O) 7 , a new arsenate mineral from the Mohawk Mine, Keweenaw County, Michigan, USA

Abstract Jeankempite, Ca 5 (AsO 4 ) 2 (AsO 3 OH) 2 (H 2 O) 7 , is a new mineral species (IMA2018-090) discovered amongst coatings of arsenate minerals on oxidised copper arsenides from the Mohawk No. 2 mine, Mohawk, Keweenaw County, Michigan, USA. The new mineral occurs as lamellar bundles of colourless to white plates up to 1 mm wide and is visually indistinguishable from guérinite, with which it forms intergrowths. Jeankempite is transparent to translucent with a waxy lustre and white streak, is non-fluorescent under longwave and shortwave ultraviolet illumination, has a Mohs hardness of ~1.5 and brittle tenacity with uneven fracture. Crystals are flattened on {01 $\bar{1}$ } and exhibit perfect cleavage on {01 $\bar{1}$ }. Optically, jeankempite is biaxial (+), α = 1.601(2), β = 1.607(2), γ = 1.619(2) (white light); 2V meas. = 72(2)° and 2V calc. = 71.0°. The empirical formula is (Ca 4.97 Na 0.013 Mg 0.017 )(As 3.99 S 0.01 ) 4 O 23 H 16 , based on 23 O and 16 H atoms per formula unit. Thermogravimetric analysis indicates that jeankempite undergoes four weight losses totalling 16.82%, close to the expected loss of 16.30%, corresponding to eight H 2 O. Jeankempite is triclinic, P $\bar{1}$ , a = 6.710(6), b = 14.901(14), c = 15.940(15) Å, α = 73.583(12)°, β = 81.984(12)°, γ = 82.754(12)°, V = 1507(2) Å 3 and Z = 3. The final structure was refined to R 1 = 0.0591 for 2781 reflections with I obs > 3σ I . The crystal structure of jeankempite is built from a network of edge- and vertex-sharing CaO 6 , CaO 7 and AsO 4 polyhedra, and we hypothesise that the new mineral has formed due to a topotactic reaction brought on by dehydration of preexisting guérinite.

Mineralogy↗

DOE OSTI2020

Biocompatibility of a novel heat-treated and ceramic-coated magnesium alloy (Mg–1.2Zn–0.5Ca–0.5Mn) for resorbable skeletal fixation devices

Our recent exploration into the use of biodegradable metals and surface treatments resulting in sufficient strength for skeletal reconstruction applications has led to the need to test these devices’ cytotoxicity. More specifically, our group has developed a resorbable magnesium alloy, Mg–1.2Zn–0.5Ca–0.5Mn, that can be strengthened by heat treatment and coated with a ceramic layer offering time-certain resorption of a medical device. This in vitro study shows that these treatments do not result in cytotoxicity. Both heat-treated (HT) and HT + ceramic-coated (sol–gel) coupons demonstrated more than 70% viability. Thus, these processing steps are likely to be useful in producing biocompatible, resorbable implants that incorporate our Mg–1.2Zn–0.5Ca–0.5Mn alloy.

36 MATERIALS SCIENCE↗

DOE OSTI2021

AmeriFlux CA-DB2 Delta Burns Bog 2

This is the AmeriFlux version of the carbon flux data for the site CA-DB2 Delta Burns Bog 2. 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 OSTI2021

AmeriFlux FLUXNET-1F CA-ER1 Elora Research Station

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-ER1 Elora Research Station. This is the FLUXNET version of the carbon flux data for the site CA-ER1 Elora Research Station produced by applying the standard ONEFlux (1F) software. Site Description - This is an agricultural site that typically grows corn. It is part of a larger research project on N2O fluxes from different fertilizer treatments. The site is relatively flat and homogenous. The site has been managed as agricultural land since the 1960’s and records exist of the previously-grown crops.

Wagner-Riddle, Claudia↗

DOE OSTI2021

AmeriFlux FLUXNET-1F CA-LP1 British Columbia - Mountain pine beetle-attacked lodgepole pine stand

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-LP1 British Columbia - Mountain pine beetle-attacked lodgepole pine stand . This is the FLUXNET version of the carbon flux data for the site CA-LP1 British Columbia - Mountain pine beetle-attacked lodgepole pine stand produced by applying the standard ONEFlux (1F) software. Site Description - This tower is located at an mountain pine beetle (MPB)-attacked almost pure lodgepole pine stand, 15 tall, approximately 35 km southeast of Mackenzie at Kennedy Siding .

Black, Thomas Andrew↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-Cbo Ontario - Mixed Deciduous, Borden Forest Site

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-Cbo Ontario - Mixed Deciduous, Borden Forest Site. This is the FLUXNET version of the carbon flux data for the site CA-Cbo Ontario - Mixed Deciduous, Borden Forest Site produced by applying the standard ONEFlux (1F) software. Site Description - Mixed deciduous forest from natural regrowth.

Staebler, Ralf↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-DBB Delta Burns Bog

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-DBB Delta Burns Bog. This is the FLUXNET version of the carbon flux data for the site CA-DBB Delta Burns Bog produced by applying the standard ONEFlux (1F) software. Site Description - Disturbed raised bog ecosystem (peat harvesting 1957 to 1963). Site has been restored and rewetted in 2007 by ditch blocking.

Christen, Andreas↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-TP3 Ontario - Turkey Point 1974 Plantation White Pine

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-TP3 Ontario - Turkey Point 1974 Plantation White Pine. This is the FLUXNET version of the carbon flux data for the site CA-TP3 Ontario - Turkey Point 1974 Plantation White Pine produced by applying the standard ONEFlux (1F) software. Site Description - White pine plantation established in 1974 over sandy abandoned land

Arain, M. Altaf↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-TPD Ontario - Turkey Point Mature Deciduous

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-TPD Ontario - Turkey Point Mature Deciduous. This is the FLUXNET version of the carbon flux data for the site CA-TPD Ontario - Turkey Point Mature Deciduous produced by applying the standard ONEFlux (1F) software. Site Description - The forest is approximately 90 years old. Naturally regenerated on sandy terrain and abandoned agricultural land. Predominantly hardwood species with a few scattered conifers. Site has been managed (thinned) in the past. It has a high biodiversity with 573 tree and plant species, 102 bird species, 23 mamal species and 22 reptile and amphibian species (SWALSREP Report, 1999). The dominant tree species is white oak (Quercus alba), with other scattered broadleaf Carolinian species including sugar and red maple (Acer saccharum, A. rubrum), American beech (Fagus grandifolia), black and red oak (Q. velutina, Q. rubra) and white ash (Fraxinus americana) . There are also scattered conifers, mostly white and red pine (Pinus strobes, P. resinosa), comprising about 5% of the trees. Average tree height is 25.7 m with a stand density of 504 ± 18 trees per hectare. Average tree diameter at breast height is 22.3 cm and basal area is 0.06 m2 or approximately 29 square meters per hectare.

Arain, M. Altaf↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-ARB Attawapiskat River Bog

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-ARB Attawapiskat River Bog. This is the FLUXNET version of the carbon flux data for the site CA-ARB Attawapiskat River Bog produced by applying the standard ONEFlux (1F) software. Site Description - Ontario Ministry of Environment and Climate Change's Environmental Monitoring and Reporting Branch has established five carbon flux monitoring towers in Ontario’s Far North as part of its Climate Change Modelling and Monitoring program. These long term monitoring stations measure carbon exchange and a suite of soil and meteorological parameters over peatland ecosystems to better understand carbon cycling in Ontario’s Far North. Information produced by these monitoring stations will assist the province in land use planning and the development of climate change adaptation strategies.

Todd, Aaron↗

DOE OSTI2022

AmeriFlux FLUXNET-1F CA-ARF Attawapiskat River Fen

This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site CA-ARF Attawapiskat River Fen. This is the FLUXNET version of the carbon flux data for the site CA-ARF Attawapiskat River Fen produced by applying the standard ONEFlux (1F) software. Site Description - Ontario Ministry of Environment and Climate Change's Environmental Monitoring and Reporting Branch has established five carbon flux monitoring towers in Ontario’s Far North as part of its Climate Change Modelling and Monitoring program. These long term monitoring stations measure carbon exchange and a suite of soil and meteorological parameters over peatland ecosystems to better understand carbon cycling in Ontario’s Far North. Information produced by these monitoring stations will assist the province in land use planning and the development of climate change adaptation strategies.

Todd, Aaron↗