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Register a new userThe 7Be(d,p)2alpha cross section at Big Bang energies and the primordial 7Li abundance
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The WMAP satellite, devoted to the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, has recently provided a determination of the baryonic density of the Universe with unprecedented precision. Using this, Big Bang Nucleosynthesis (BBN) calculations predict a primordial 7Li abundance which is a factor 2-3 higher than that observed in galactic halo dwarf stars. It has been argued that this discrepancy could be resolved if the 7Be(d,p)2alpha reaction rate is around a factor of 100 larger than has previously been considered. We have now studied this reaction, for the first time at energies appropriate to the Big Bang environment, at the CYCLONE radioactive beam facility at Louvain-la-Neuve. The cross section was found to be a factor of 10 smaller than derived from earlier measurements. It is concluded therefore that nuclear uncertainties cannot explain the discrepancy between observed and predicted primordial 7Li abundances, and an alternative astrophysical solution must be investigated.
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Among the reactions involved in the production and destruction of deuterium during Big Bang Nucleosynthesis, the deuterium-burning D(p,gamma)3He reaction has the largest uncertainty and limits the precision of theoretical estimates of primordial deuterium abundance. Here we report the results of a careful commissioning of the experimental setup used to measure the cross-section of the D(p,gamma)3He reaction at the Laboratory for Underground Nuclear Astrophysics of the Gran Sasso Laboratory (Italy). The commissioning was aimed at minimising all sources of systematic uncertainty in the measured cross sections. The overall systematic error achieved (< 3 %) will enable improved predictions of BBN deuterium abundance.
Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have determined the baryon density of the Universe $Omega_b$ with a precision of about 4%. With $Omega_b$ tightly constrained, comparisons of Big Bang Nucleosynthesis (BBN) abundance predictions to primordial abundance observations can be made and used to test BBN models and/or to further constrain abundances of isotopes with weak observational limits. To push the limits and improve constraints on BBN models, uncertainties in key nuclear reaction rates must be minimized. To this end, we made new precise measurements of the d(d,p)t and d(d,n)^3He total cross sections at lab energies from 110 keV to 650 keV. A complete fit was performed in energy and angle to both angular distribution and normalization data for both reactions simultaneously. By including parameters for experimental variables in the fit, error correlations between detectors, reactions, and reaction energies were accurately tabulated by computational methods. With uncertainties around 2% +/- 1% scale error, these new measurements significantly improve on the existing data set. At relevant temperatures, using the data of the present work, both reaction rates are found to be about 7% higher than those in the widely used Nuclear Astrophysics Compilation of Reaction Rates (NACRE). These data will thus lead not only to reduced uncertainties, but also to modifications in the BBN abundance predictions.
The flux of 7Be and 8B neutrinos from the Sun and the production of 7Li via primordial nucleosynthesis depend on the rate of the 3He(alpha,gamma)7Be reaction. In extension of a previous study showing cross section data at 127 - 167 keV center of mass energy, the present work reports on a measurement of the 3He(alpha,gamma)7Be cross section at 106 keV performed at Italys Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is sigma = 0.567 +- 0.029(stat) +- 0.016(syst) nbarn. The data are compared with previous activation studies at high energy, and a recommended S(0) value for all 3He(alpha,gamma)7Be activation studies, including the present work, is given.
Rijal, et al. in their recent publication [Phys. Rev. Lett {bf 122}, 182701 (2019), arXiv:1808.07893], on Measurement of d + $^7$Be Cross Sections for Big-Bang Nucleosynthesis (BBN), misrepresent their result, they misrepresent previous work of Parker (72) and of Caughlan and Fowler (88), and quite possibly, contradicts the very BBN theory that has been established over the last few decades. This comment is intended to correct these misrepresentations and critically review their claims on BBN.
The interpretation of the most recent solar neutrinos experiments requires a good knowledge of the cross section of the reaction 7Be(p,gamma)8B at very small energy (Ecm=18 keV). We have recently measured this cross section for Ecm=0.35-1.4 MeV and for Ecm=0.112-0.190 MeV. We report here on the description of the preparation of the radioactive targets of 7Be used in these experiments.
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