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

Abstract

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....

Recent developments of SOLEROO: Australia’s first high energy radioactive Ion Beam capability

“…The first radioactive ion beam experiment has recently been carried out at the ANU, where the RIB capability SOLEROO [1,2,5] was tested with the tracking detector system integrated with a silicon detector array [BALIN], developed for breakup measurements [11][12][13][14][15][16][17][18][19][20]. In order to test the integrated system as a whole, elastic scattering measurements were carried out using a tagged 8 Figure 5.…”