General constraints on the age and chemical evolution of the Galaxy

Meyer, B. S.; Schramm, David N.

doi:10.1086/164781

Cited by 34 publications

(15 citation statements)

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“…There are a few other works which investigated the same quantities from radiative cross sections [3]. The (n, γ) cross sections can also be used in the study of nuclear cosmochronology to determine the age of the Galaxy [10][11][12]. Though the neutron capture cross sections, in gen-3 eral, have 1/v dependence, this can significantly differ when the p-wave capture is superimposed on pure swave contribution, thus resulting in an increase in the cross-section values with incident neutron energy.…”

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confidence: 99%

Neutron capture reactions relevant to thesandpprocesses in the region of theN=50shell closure

2016

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Radiative thermal neutron capture cross sections for nuclei participating in s-process and pprocess nucleosynthesis in and around N = 50 closed neutron shell have been calculated in statistical semi-microscopic Hauser-Feshbach approach for the energy range of astrophysical interest. A folded optical-model potential is constructed utilizing the standard DDM3Y real nucleon-nucleon interaction. The folding of the interaction with target radial matter densities, obtained from the relativistic-mean-field approach, is done in coordinate space using the spherical approximation. The standard nuclear reaction code TALYS1.8 is used for cross-section calculation. The cross sections are compared with experimental results and reasonable agreements are found for almost all cases. Maxwellian-averaged cross sections (MACS) for the nuclei are presented at a single thermal energy of 30 keV relevant to s-process. We have also presented the MACS values over a range of energy from 5 to 100 keV for neutron magic nuclei with (N = 50).PACS numbers: I. INTRODUCTIONElements heavier than iron are produced via two principle processes, namely, the slow neutron capture process (s-process) and the rapid neutron capture process (r-process), differing in the respective neutron capture timescales with respect to the β-decay half-lives. There is a minor contribution from another process, namely, pprocess, producing a subset of proton-rich isotopes. The detailed study of the heavy element nucleosynthesis was done in the fundamental work of Burbidge et al. [1] and also of Cameron [2]. Recently Käppeler et al. [3] presented a review of progress on the studies of s-process nucleosynthesis with advanced nuclear physics inputs, observational data, and stellar models.While the majority of the theory of the s-process is well-developed, uncertainty still remains in constraining the neutron capture rates of nuclei involved in nucleosynthesis chain. The capture cross sections are highly scattered and uncertain in the energy range appropriate for astrophysical applications. These uncertainties lead to significant errors in determining exact abundances of elements involved in different processes. Many works * Electronic address: saumidutta89@gmail.com † Electronic address: ggphy@caluniv.ac.in ‡ Electronic address: abhattacharyyacu@gmail.com have been devoted to this respect in order to measure the thermal neutron capture cross sections relevant to s-process temperature. However, reactions on some important nuclei are still not available due to their unavailability in the terrestrial laboratory. Käppeler et al. [4] showed the present status of the uncertainty of stellar (n, γ) cross sections and commented that improvements are certainly necessary especially in the mass region below A=120 and above A=180. Some reactions are of significant importance, basically those with closed neutron shells acting as bottlenecks to the s-process reaction flow. They have very low cross-sections and in some scenarios, the s-process reaction flow cannot overcome these bottlen...

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confidence: 99%

Neutron capture reactions relevant to thesandpprocesses in the region of theN=50shell closure

2016

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“…Typical estimates for the Galaxy's (and Universe's) age as determined from cosmochronology are of the order of 9.6 Gyr (e.g. Meyer and Schramm 1986). In recent years questions about the role of &delayed fis-sion in estimating actinide production ratios 89 well as uncertainties in is7Re decay due to thermal enhancement and the discussion of Th/Nd abundances in stars have obfuscated some of the limits one can obtain.…”

Section: Nucleocosmochronologymentioning

confidence: 99%

“…To extend these mean age limits to a total age limit requires some galactic evolution input. However, as Peeves and Johns (1976) first showed, and as Meyer and Schramm (1986) developed further, one can use chronometers to constrain Galactic evolution models and thereby further restrict the age from the simple mean age limits of Schramm and Wasserburg. To try to push further on such ranges and give ages to fl Gyr accuracy, as some authors have done, always necessitates making some very explicit assumptions about Galactic evolution beyond the pure chronometric arguments.…”

Section: Nucleocosmochronologymentioning

confidence: 99%

The age of the universe

Schramm¹

1996

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“…Meyer and Schramm (25), extending the early work by Schramm and Wasserburg (26), sought to provide a modelindependent age determination. In the limit of long-lived chronometers (T Ͻ Ͻ 1), they derive a simple expression for the age that is approximately independent of galactic evolution effects.…”

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“…The history of star formation and nucleosynthesis activity thus becomes a significant consideration. It was the recognition of this constraint that led Meyer and Schramm (25) to the determination of a lower bound (T ϩ SS ) Ͼ 9.6 Gyr. These authors also concluded that ''the effective nucleosynthesis rate was relatively constant over most of the duration of nucleosynthesis.…”

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The age of the universe from nuclear chronometers

Truran

1998

Proc. Natl. Acad. Sci. U.S.A.

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An overview is presented of the current situation regarding radioactive dating of the matter of which our Galaxy is comprised. A firm lower bound on the age from nuclear chronometers of Ϸ9-10 Gyr is entirely consistent with age determinations from globular clusters and white dwarf cooling histories. The reasonable assumption of an approximately uniform nucleosynthesis rate yields an age for the Galaxy of 12.8 ؎ 3 Gyr, which again is consistent with current determinations from other methods.Estimates of the age of the Galaxy, and thereby limits on the age of the Universe, can be obtained by three independent means: (i) the age of the elements by radioactive dating (nucleocosmochronology); (ii) the ages of the globular clusters (the oldest stars in the halo of our Galaxy); and (iii) the ages of white dwarfs from cooling calculations (the age of the Galactic disk?). This paper will focus on radioactive dating, an approach that has played a particularly important role historically.The presence of naturally occurring radioactive nuclei in Galactic matter testifies to the fact that the age of the elements is finite. To the extent that the long-lived nuclear species of interest are the products of nuclear transformations proceeding in stars and supernovae over the course of our own Galaxy's history, they can be used to provide a measure of the duration of star formation activity and concomitant nucleosynthesis in the Galaxy. The use of long-lived radioactivities as a mechanism for the determination of a lower limit on the age of the Galaxy has a history that spans much of the 20th century. An early paper by Rutherford (1) outlined the essential features of this science. Subsequently, the defining works in nucleosynthesis theory by Burbidge et al. (2) and Cameron (3) U are synthesized. The task, since then, has been to identify the astrophysical site for the operation of this nucleosynthesis process and to calculate the appropriate rates of production as a function of time over the course of galactic evolution. The early developments of the use of the uraniumthorium chronometers by Fowler and Hoyle (4) and Cameron (5) were based necessarily on rather simple prescriptions for the history of galactic nucleosynthesis. As our understanding of the processes of stellar and supernova nucleosynthesis improved, it became possible to address the problem of nuclear chronology in the context of increasingly realistic models of the chemical evolution of the Galaxy (6-10).In this paper, we will be concerned with the determination of realistic age constraints from nucleocosmochronology. We will restrict ourselves to the Os chronometer pair an attractive choice for dating galactic nucleosynthesis (11). A major difficulty here, however, is the fact that 187 Os is also produced in the s-process. The uncertainties introduced by the subtraction of the s-process contribution to isolate the cosmoradiogenic component are significant. Further complications are associated with the fact that the ␤ decay rate of 187 Re in stellar env...

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General constraints on the age and chemical evolution of the Galaxy

Cited by 34 publications

References 13 publications

Neutron capture reactions relevant to thesandpprocesses in the region of theN=50shell closure

Neutron capture reactions relevant to thesandpprocesses in the region of theN=50shell closure

The age of the universe

The age of the universe from nuclear chronometers

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