Resonant Enhancement of Nuclear Reactions as a Possible Solution to the Cosmological Lithium Problem

Direct measurements of nuclear reactions of astrophysical interest can be challenging. Alternative experimental techniques such as transfer reactions and inelastic scattering reactions offer the possibility to study these reactions by using stable beams. In this context, I will present recent results that were obtained in Orsay using indirect techniques. The examples will concern various astrophysical sites, from the Big-Bang nucleosynthesis to the production of radioisotopes in massive stars.The main characteristics of the nuclear reactions involved in stellar nucleosynthesis is the low energy where they generally occur, between few keV to few MeV and at these energies the cross sections of these reactions are very small ranging from fbarn to hundreds of pbarn especially when it involves charged particles. This makes the direct measurements at stellar energies very difficult and often impossible. Hence direct measurement are usually performed at higher energies and then extrapolated down to stellar energies where the reactions occur. However the extrapolations can lead sometimes to wrong results when a possible very low energy resonance or the tail of a possible sub-threshold resonance are not taken into account. 201, 0 0 EPJ Web of Conferences

Section: The 7 LI Cosmological Problemmentioning

confidence: 99%

Indirect techniques for astrophysical reaction rates determinations

Hammache¹,

Oulebsir²,

Benamara³

et al. 2016

“…In particular, near the 3 He− 6 Li and d− 7 Be thresholds, the TUNL-NDG table lists a resonance of unknown J π at 16.024 MeV above the 9 B ground state, the state considered a possible candidate in Ref. [10] for resonant destruction of 7 Be. The current analysis has a 1/2 − weak subthreshold resonance with a width of several hundred keV, much too large to satisfy the desired parameters of Ref.…”

Section: Epj Web Of Conferencesmentioning

confidence: 99%

“…Recent attention has focused on the role of reactions that destroy A = 7 nuclei at early times 1 s in the big-bang environment [10,11]. The authors of Ref.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Paris

Brown

Hale

et al. 2014

Abstract. Unitarity, the mathematical expression of the conservation of probability in multichannel reactions, is an essential ingredient in the development of accurate nuclear reaction networks appropriate for nucleosynthesis in a variety of environments. We describe our ongoing program to develop a "unitary reaction network" for the big-bang nucleosynthesis environment and look at an example of the need and power of unitary parametrizations of nuclear scattering and reaction data. Recent attention has been focused on the possible role of the 9 B compound nuclear system in the resonant destruction of 7 Li during primordial nucleosynthesis. We have studied reactions in the 9 B compound system with a multichannel, two-body unitary R-matrix code (EDA) using the known elastic and reaction data, in a four-channel treatment. The data include elastic 6 Li( 3 He, 3 He) 6 Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction cross sections for energies from 0.7 to 5.0 MeV for 6 Li( 3 He,p) 8 Be* and from 0.4 to 5.0 MeV for the 6 Li( 3 He,d) 7 Be reaction. Capture data have been added to the previous analysis with integrated cross section measurements from 0.7 to 0.825 MeV for 6 Li( 3 He,γ) 9 B. The resulting resonance parameters are compared with tabulated values from TUNL Nuclear Data Group analyses. Previously unidentified resonances are noted and the relevance of this analysis and a unitary reaction network for big-bang nucleosynthesis are emphasized.

“…Possible solutions to this discrepancy have come from many areas of physics: i) investigating stellar models [3,4], ii) improved observations of lithium in metal-poor stars [5], iii) low metallicity gases in the Small Magellanic Cloud [6], iv) non-standard cosmologies and physics beyond the standard model [7][8][9][10][11], and v) nuclear physics input into models. The lack of a satisfactory explanation to this discrepancy has reignited the search for a nuclear physics solution to the primordial lithium problem [12][13][14][15].…”

Section: The 7 LI Problemmentioning

confidence: 99%

Developing new methods to investigate nuclear physics input to the cosmological lithium problem

Cook

Luong

Williams

et al. 2013

Abstract.A significant challenge to nuclear astrophysics is the cosmological lithium problem, where models of Big Bang nucleosynthesis indicate abundances of 7 Li two to four times larger than what is inferred via spectroscopic measurements of metal-poor stars. Recent experimental techniques developed for nuclear reaction studies at energies near the fusion barrier, if extended to reactions of astrophysical interest, may help understand nuclear reactions that can affect the production of 7 Li during the Big Bang. Experiments at the ANU, using new experimental techniques, have provided complete pictures of the breakup mechanisms of light nuclei in collisions with heavy targets, such as 208 Pb and 209 Bi [1]. These experiments revealed dominant breakup mechanisms which had not even been considered in theoretical models. The study of the breakup of 6 Li and 7 Li following interactions with 58,64 Ni and 27 Al acts as a stepping stone from this previous work towards future experimental studies of breakup reactions of astrophysical relevance. In all cases studied, breakup is dominantly triggered by nucleon transfer between the colliding partners, but the transfer mechanisms are different. The findings of these experiments and experimental considerations for extensions to reactions of light nuclei, such as d + 7 Be, will be presented. The 7 Li problemThere is a significant discrepancy between the abundance of 7 Li observed in metal-poor halo stars and that predicted by Big Bang Nucleosynthesis (BBN) calculations. On the order of 3-4 times more 7 Li is predicted to be present in the primordial universe than is inferred via observation. This disagreement, known as the primordial lithium problem, has posed a significant challenge to astrophysics since its discovery in 1982 [2]. Possible solutions to this discrepancy have come from many areas of physics: i) investigating stellar models [3,4], ii) improved observations of lithium in metal-poor stars [5], iii) low metallicity gases in the Small Magellanic Cloud [6], iv) non-standard cosmologies and physics beyond the standard model [7][8][9][10][11], and v) nuclear physics input into models. The lack of a satisfactory explanation to this discrepancy has reignited the search for a nuclear physics solution to the primordial lithium problem [12][13][14][15].The search for a nuclear physics solution takes the form of re-examining nuclear physics input into models of BBN. Modern models of BBN are such that they are considered parameter free, depending only on experimentally determined nuclear reaction rates. Shown in figure 1 a e-mail: kaitlin.cook@anu.edu.au b Permanent Address: Nuclear Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India is a simplified nuclear reaction network showing the most significant reactions producing 7 Li during BBN. Crucially, the dominant production mode for 7 Li in BBN conditions is not direct production through the reaction 3 H(α,γ) 7 Li but through the production of 7 Be and its subsequent decay through electron capture....