Radioactive 26Al in the galaxy: observations versus theory

Prantzos, Nikos; Diehl, R.

doi:10.1016/0370-1573(95)00055-0

Cited by 279 publications

(334 citation statements)

References 96 publications

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“…Up to now, this has been possible for the 1809 keV 26 Al emission. The 26 Al map obtained with the COMPTEL instrument onboard the Compton Gamma-Ray Observatory CGRO (Diehl et al 1995, Oberlack et al 1996, Knödlseder 1997 has posed interesting questions about the origin of the galactic 26 Al (see, e.g., review from Prantzos and Diehl, 1996). It provides a direct and unique insight on the integrated nucleosynthesis during the last 10 6 years.…”

Section: Observational Cluesmentioning

confidence: 99%

Explosive Nucleosynthesis

Hernanz¹

2011

Encyclopedia of Astrobiology

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Many radioactive nuclei relevant for gamma-ray astrophysics are synthesized during explosive events, such as classical novae and supernovae. A review of recent results of explosive nucleosynthesis in these scenarios will be presented, with a special emphasis on the ensuing gamma-ray emission from individual nova and supernova explosions. The influence of the dynamic properties of the ejecta on the gamma-ray emission features, as well as the still remaining uncertainties in nova and supernova modelling will also be reviewed.

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Section: Observational Cluesmentioning

confidence: 99%

Explosive Nucleosynthesis

Hernanz¹

2011

Encyclopedia of Astrobiology

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“…Possible production sites are supernovae, novae or massive stars (in the Asymptotic Giant Branch or in the Wolf Rayet phases). The proton temperature of supernovae or novae is in the order of T = 2×10 8 K, whereas in massive stars hydrogen burning occurs at temperatures around T = 5 × 10 7 K [5]. These temperatures correspond to proton energies of around 200 keV and 100 keV, respectively (see Eq.…”

Section: The 26 Al Radioisotopementioning

confidence: 99%

An alternative method for the measurement of stellar nuclear-reaction rates

Niello¹,

Arazi²,

Knie³

et al. 2003

Braz. J. Phys.

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For charged-particle induced reactions occurring in astrophysical scenarios, projectile energies are usually well below the Coulomb barrier of the reacting system. Hence, extremely small cross section reactions pose a difficult task for laboratory measurements. Most commonly, these energy-dependent cross sections are studied by detecting the emitted prompt gamma rays following the de-excitation of the produced compound nucleus. In this work we propose an alternative way for the measurement of the extremely small cross sections of the 25 Mg(p,γ) 26 Al resonant reaction, namely the use of the Accelerator Mass Spectrometry (AMS) technique. I IntroductionIn the understanding of the nucleosynthesis of the elements in stars, one of the most important quantities is the reaction rate. This quantity must be evaluated in terms of the stellar temperature T, and its determination involves the knowledge of the excitation function σ(E) of the specific nuclear reaction leading to the final nucleus. The particular case of proton capture reactions plays an important role in stellar process of intermediate-mass elements.In several cases, the formation of a compound nucleus is dominated by a resonant process: the entrance channel, formed by a projectile P impinging on a target nucleus A, evolves into an excited state of a compound nucleus B = P + A, which ultimately decays into lower-lying states with the subsequent emission of gamma rays. This process occurs at well-defined center of mass (CM) energies, E CM = E X − Q, where E X is the energy of the excited states of the compound nucleus B and Q is the Q-value of the reaction [1].In a stellar environment, the reaction rate per particle pair is calculated as [2]where σ is the energy-dependent reaction cross section, v the relative velocity between the reacting particles and φ(v) is the velocity distribution of these particles in the stellar plasma. Nuclei participating in thermonuclear reactions can be considered as non-relativistic and non-degenerate ones, therefore, their velocities v (and hence their energies E) follow a Maxwell-Boltzmann distribution,where E = 1 2 mv 2 represents the kinetic energy of the nucleus with mass m, and T refers to the temperature of the gas. This distribution reaches a maximum value at E = kT. The second term defining the reaction rate is the cross section for the compound nucleus formation. This can be described by three factors: a geometrical one, σ = πλ / 2 ∝ E −1 ; a second one resembling the exponential behavior for tunneling through a Coulomb barrier, σ ∝ exp(−Z P Z A e 2 / v); and finally by a nuclear S-factor, S(E), which depicts the specific nuclear characteristics of the particular reaction. Therefore, the reaction rate per particle pair can also be expressed as

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“…Since D is completely destroyed as gas cycles through stars and there are no known sources of substantial production other than BBN (Epstein et al 1976, Prodanović & Fields 2003, its evolution is obtained for free from GCE models. Good models for the solar neighbourhood -i.e., models which satisfy the majority of the observational constraints available for the solar neighbourhood -have always predicted astration factors f D ≡ (D/H) P /(D/H) LISM not in excess of 2-3 for deuterium (Audouze & Tinsley 1974, Steigman & Tosi 1992, Edmunds 1994, Galli et al 1995, Prantzos 1996, Tosi et al 1998, Chiappini et al 2002, Romano et al 2003. Attempts to accommodate larger astration factors (Vangioni-Flam et al 1994, Scully et al 1997 have resulted in models which failed to reproduce important observational constraints.…”

Section: Introductionmentioning

confidence: 99%

Galactic evolution of D, ³He and ⁴He

Romano

2009

Proc. IAU

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Abstract. The uncertainties which still plague our understanding of the evolution of the light nuclides D, 3 He and 4 He in the Galaxy are described. Measurements of the local abundance of deuterium range over a factor of 3. The observed dispersion can be reconciled with the predictions on deuterium evolution from standard Galactic chemical evolution models, if the true local abundance of deuterium proves to be high, but not too high, and lower observed values are due to depletion onto dust grains. The nearly constancy of the 3 He abundance with both time and position within the Galaxy implies a negligible production of this element in stars, at variance with predictions from standard stellar models which, however, do agree with the (few) measurements of 3 He in planetary nebulae. Thermohaline mixing, inhibited by magnetic fields in a small fraction of low-mass stars, could in principle explain the complexity of the overall scenario. However, complete grids of stellar yields taking this mechanism into account are not available for use in chemical evolution models yet. Much effort has been devoted to unravel the origin of the extreme helium-rich stars which seem to inhabit the most massive Galactic globular clusters. Yet, the issue of 4 He evolution is far from being fully settled even in the disc of the Milky Way.

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Radioactive 26Al in the galaxy: observations versus theory

Cited by 279 publications

References 96 publications

Explosive Nucleosynthesis

Explosive Nucleosynthesis

An alternative method for the measurement of stellar nuclear-reaction rates

Galactic evolution of D, ³He and ⁴He

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Radioactive 26Al in the galaxy: observations versus theory

Cited by 279 publications

References 96 publications

Explosive Nucleosynthesis

Explosive Nucleosynthesis

An alternative method for the measurement of stellar nuclear-reaction rates

Galactic evolution of D, 3He and 4He

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Galactic evolution of D, ³He and ⁴He