<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">Mg</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>24</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi>γ</mml:mi></mml:mrow></mml:math>)<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="

Strandberg, E.; Beard, M.; Couder, M.; Couture, A.; Falahat, S.; LeBlanc, P. J.; Lee, Hye Young; O’Brien, S.; Palumbo, A.; Stech, E.; Tan, Wanpeng; Ugalde, C.; Wiescher, M.; Costantini, H.; Scheller, K.; Pignatari, M.; Azuma, R.E.; Buchmann, L.

doi:10.1103/physrevc.77.055801

Cited by 19 publications

(35 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The 16 O(α,γ) 20 Ne reaction rate on the other hand is determined by a constant non-resonant S-factor term and by the narrow 3 − and 1 − resonances at 1.1 MeV and 1.3 MeV respectively, which dominate the reaction rate above temperatures of T ∼ 10 9 K (Costantini et al 2010). Concerning the reaction rates of the subsequent α-capture reactions 20 Ne(α,γ) 24 Mg (Schmalbrock et al 1983) and 24 Mg(α,γ) 28 Si (Strandberg et al 2008), the non-resonant S-factor terms are larger and the critical energy range above 0.3 MeV is characterized by narrow resonances which cause a further enhance-ment in the reaction rate, as demonstrated for 20 Ne(α,γ) 24 Mg in Fig. 1.…”

Section: Stellar Model Calculations and Nucleosynthesismentioning

confidence: 99%

Production of Carbon-Rich Presolar Grains From Massive Stars

Pignatari

Wiescher

Timmes

et al. 2013

ApJ

Self Cite

View full text Add to dashboard Cite

About a year after core collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events, according to the anomalous isotopic abundances. Several features of these abundances remain unexplained and challenge the understanding of core-collapse supernovae explosions and nucleosynthesis. We show, for the first time, that most of the measured C-rich grain abundances can be accounted for in the C-rich material from explosive He burning in core-collapse supernovae with high shock velocities and consequent high temperatures. The inefficiency of the 12 C(α,γ) 16 O reaction relative to the rest of the α-capture chain at T > 3.5×10 8 K causes the deepest He-shell material to be carbon rich and silicon rich, and depleted in oxygen. The isotopic ratio predictions in part of this material, defined here as the C/Si zone, are in agreement with the grain data. The high-temperature explosive conditions that our models reach at the bottom of the He shell, can also be representative of the nucleosynthesis in hypernovae or in the high-temperature tail of a distribution of conditions in asymmetric supernovae. Finally, our predictions are consistent with the observation of large 44 Ca/ 40 Ca observed in the grains. This is due to the production of 44 Ti together with 40 Ca in the C/Si zone, and/or to the strong depletion of 40 Ca by neutron captures.

show abstract

Section: Stellar Model Calculations and Nucleosynthesismentioning

confidence: 99%

Production of Carbon-Rich Presolar Grains From Massive Stars

Pignatari

Wiescher

Timmes

et al. 2013

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…The presented data were obtained using the generalized gradient approximation (GGA) with a parameterized exchange-correlation functional according to Co dimers have singly occupied two-fold degenerate 3d-δ orbitals which are responsible for the large dimer MAE. 6,7 This degeneracy is not lifted in a hexagonal environment. Thus, we have chosen to investigate the interaction between Co 2 and benzene (Bz, C 6 H 6 ).…”

mentioning

confidence: 94%

“…5 More recently, the magnetic properties of transition metal dimers came into the focus of interest. 6,7,8,9 Isolated magnetic dimers are the smallest chemical objects that possess a magnetic anisotropy as their energy depends on the relative orientation between dimer axis and magnetic moment. Huge MAE values of up to 100 meV per atom were predicted by density functional (DFT) calculations for the cobalt dimer.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits

et al. 2009

View full text Add to dashboard Cite

It is demonstrated by means of density functional and ab-initio quantum chemical calculations, that transition metal -carbon systems have the potential to enhance the presently achievable area density of magnetic recording by three orders of magnitude. As a model system, Co 2 -benzene with a diameter of 0.5 nm is investigated. It shows a magnetic anisotropy in the order of 0.1 eV per molecule, large enough to store permanently one bit of information at temperatures considerably larger than 4 K. A similar performance can be expected, if cobalt dimers are deposited on graphene or on graphite. It is suggested that the subnanometer bits can be written by simultaneous application of a moderate magnetic and a strong electric field. PACS numbers: 31.15.es, 75.30.Gw, 75.75.+a Keywords: applications of density functional theory, magnetic anisotropy, magnetic properties of nanostructures 1 Long-term magnetic data storage requires that spontaneous magnetization reversals should occur significantly less often than once in ten years. This implies that the total magnetic anisotropy energy (MAE) of each magnetic particle should exceed 40 kT , 1 where k is the Boltzmann constant and T is the temperature. Among the elemental ferromagnets (Fe, Co, Ni, and Gd), cobalt metal shows the highest MAE, about 0.06 meV per atom in the hexagonal close packed structure. Thus, Co is the main ingredient of magnetic data storage materials at present. At room temperature, data loss due to fluctuations is avoided, if a Co grain contains not less than 40 k · 300 K/0.06 meV ≈ 15,000 atoms. In fact, the grain diameter of contemporary Co(Cr,Pt,SiO 2 ) recording media is close to 8 nm, each grain containing about 50,000 atoms and each bit being composed of some dozen grains.2 The grain size could be considerably reduced by using the intermetallic compounds FePt or CoPt with record MAE of almost 1 meV per atom in their structurally ordered L1 0 bulk phase. It is, however, hard to achieve the required ordered structure in nano-particles. 3Obviously, a further reduction of the bit size is primarily limited by the value of MAE per atom. Recent efforts to enhance this value were focused on single atoms or small clusters deposited on the surface of heavy metals. This approach combines two ideas: 4 Firstly, the magnitude of MAE is related to the size of the orbital moments. The latter are quenched for highly coordinated atoms but can be large if the coordination is low. Secondly, the magnitude of MAE is related to the strength of spin-orbit coupling which grows with atomic number. Considerable progress was achieved in this way by deposition of single Co atoms on a Pt surface, yielding a record MAE of 9 meV per Co atom. 5 Unfortunately, clusters of several Co atoms on Pt show a much smaller MAE per atom, roughly inversely proportional to the number of atoms. 5More recently, the magnetic properties of transition metal dimers came into the focus of interest. 6,7,8,9 Isolated magnetic dimers are the smallest chemical objects that possess a magnetic a...

show abstract

“…Details of the detector arrangement were described earlier [13]. The 1.3 MeV resonance decays primarily to the first excited state [15] with a γ transition of 4.156 MeV (R → 1 st ).…”

Section: A the Experimental Setupmentioning

confidence: 99%

O16(α,γ)
Costantini
¹
,
deBoer
²
,
Azuma
³

et al. 2010
Phys. Rev. C
Self Cite

View full text Add to dashboard Cite

The article presents new measurements of low-energy resonances in the 16 O(α,γ ) 20 Ne reaction, which represents the endpoint for the reaction sequence responsible for energy production in stellar helium burning in massive red giant stars. The present data and previous unpublished data are analyzed in the framework of R-matrix theory to derive a reaction rate for the temperature regime of stellar helium burning.

show abstract

Mg24(α,γ)
E. Strandberg
¹
,
M. Beard
²
,
M. Couder
³

et al.

Cited by 19 publications

References 20 publications

Production of Carbon-Rich Presolar Grains From Massive Stars

Production of Carbon-Rich Presolar Grains From Massive Stars

Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits

O16(α,γ)
Costantini
¹
,
deBoer
²
,
Azuma
³

et al. 2010
Phys. Rev. C
Self Cite

Contact Info

Product

Resources

About

Mg24(α,γ)E. Strandberg1, M. Beard2, M. Couder3 et al.

Cited by 19 publications

References 20 publications

Production of Carbon-Rich Presolar Grains From Massive Stars

Production of Carbon-Rich Presolar Grains From Massive Stars

Co Dimers on Hexagonal Carbon Rings Proposed as Subnanometer Magnetic Storage Bits

O16(α,γ)Costantini1, deBoer2, Azuma3 et al. 2010Phys. Rev. CSelf Cite

Contact Info

Product

Resources

About

Mg24(α,γ)
E. Strandberg
¹
,
M. Beard
²
,
M. Couder
³

et al.

O16(α,γ)
Costantini
¹
,
deBoer
²
,
Azuma
³

et al. 2010
Phys. Rev. C
Self Cite