Cosmology and Nuclear Physics

There are important aspects of Cosmology, the scientific study of the large scale properties of the universe as a whole, for which nuclear physics can provide insights. Here, we will focus on the properties of early universe (Big-Bang nucleosynthesis during the first 20 mn) and on the variation of constants over the age of the universe

Lifetimes of 26Al and 34Cl in an astrophysical plasma

We study here the onset of thermal equilibrium affecting the lifetimes of 26Al and 34Cl nuclei within a hot astrophysical photon gas. The 26Al isotope is of prime interest for gamma ray astronomy with the observation of its delayed (t_1\2=0.74 My) 1.809MeV gamma-ray line. Its nucleosynthesis is complicated by the presence of a short lived (t_1\2=6.34s) spin isomer. A similar configuration is found in 34Cl where the decay of its isomer (34mCl, t_1\2=32m) is followed by delayed gamma-ray emission with characteristic energies. The lifetimes of such nuclei are reduced at high temperature by the thermal population of shorter lived levels. However, thermal equilibrium within 26Al and 34Cl levels is delayed by the presence of the isomer. We study here the transition to thermal equilibrium where branching ratios for radiative transitions are needed in order to calculate lifetimes. Since some of these very small branching ratios are not known experimentally, we use results of shell model calculations.Comment: 11 pages, 5 figures, Latex, accepted for publication in Phys. Rev.

Prospects for detectability of classical novae with INTEGRAL

Classical novae are potential gamma-ray emitters, both in lines and in a continuum. Continuum emission (at energies between 20-30 and 511 keV) and line emission at 511 keV are related to positron annihilation and its Comptonization in the expanding shell; 18F is the main responsible of positron production. The lines at 478 and 1275 keV have their origin in the decay of the radioactive nuclei 7Be and 22Na. Updated models of nova explosions have been adopted for the computation of the gamma-ray emission. New yields of some radioactive isotopes directly translate into new detectability distances of classical novae with INTEGRAL.Comment: Contributed paper at the 4th INTEGRAL Workshop, 4-8 September 2000, Alicante (Spain). To be published in the ESA-SP series: 4 pages, 4 figure

The 18F(p,a)15O reaction rate for application to nova gamma-ray emission

The 18F(p,a)15O reaction is recognized as one of the most important reaction for nova gamma-ray astronomy as it governs the early <= 511 keV emission. However, its rate remains largely uncertain at nova temperatures due to unknown low-energy resonance strengths. We report here on our last results concerning the study of the D(18F,pa)15N reaction, as well as on the determination of the 18F(p,a)15O reaction rate using the R-matrix theory. Remaining uncertainties are discussed.Comment: Contribution to the Eighth International Symposium on Nuclei in the Cosmos, Vancouver july 19-23. 4 pages and 2 figure

Gamma-ray emission of classical novae and its detectability by INTEGRAL

A lot of information concerning the mechanism of nova explosions will be extracted from the possible future observations with INTEGRAL. In order to be prepared for this task, we are performing detailed models of the gamma-ray emission of classical novae, for a wide range of possible initial conditions. Spectra at different epochs after the explosion and light curves for the different lines (511, 478 and 1275 keV) and the continuum are presented, as well as the detectability distances with INTEGRAL spectrometer SPI. New results related to 18F synthesis related to very recent data of nuclear physics are advanced as preliminary.Comment: 4 pages, 2 figures, to appear in "3rd INTEGRAL Workshop: The Extreme Universe", Taormina (Italy

Gamma-ray emission from novae related to positron annihilation: constraints on its observability posed by new experimental nuclear data

Classical novae emit gamma-ray radiation at 511 keV and below, with a cut-off at around (20-30) keV, related to positron annihilation and its Comptonization in the expanding envelope. This emission has been elusive up to now, because it occurs at epochs well before the maximum in optical luminosity, but it could be detected by some sensitive intrument on board a satellite, provided that the nova is close enough and that it is observed at the right moment. The detection of this emission, which is a challenge for the now available and for the future gamma-ray instruments, would shed light into the physical processes occurring in the early phases of the explosion, which are invisible in other lower energy ranges. A good prediction of the emitted fluxes and of the corresponding detectability distances with different instruments relies critically on a good knowledge of reaction rates relevant to f18 destruction, which have been subject to a strong revision after recent nuclear spectroscopy measurements. With respect to previous results, smaller ejected masses of f18 are predicted, leading to smaller emitted fluxes in the (20-511) keV range and shorter detectability distances.Comment: 9 pages, 2 figures, accepted for publication in Astrophys. J. Letter

The variation of fundamental constants and the role of A=5 and A=8 nuclei on primordial nucleosynthesis

We investigate the effect of a variation of fundamental constants on primordial element production in big bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (Li-5 and He-5) and A=8 (Be-8) unstable nuclei and complement earlier work on its effect on the binding energy of deuterium. The reaction rates for He3(d,p)He4 and H3(d,n)He4 are dominated by the properties of broad analog resonances in He-5 and Li-5 compound nuclei respectively. While the triple alpha process is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if Be-8 were stable during BBN. The nuclear properties (resonance energies in He-5 and Li-5 nuclei, and the binding energies of Be-8 and D) are all computed in a consistent way using a microscopic cluster model. The n(p,gamma)d, He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates are subsequently calculated as a function of the nucleon-nucleon interaction that can be related to the fundamental constants. We found that the effect of the variation of constants on the He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates is not sufficient to induce a significant effect on BBN, even if Be-8 was stable. In particular, no significant production of carbon by the triple alpha reaction is found when compared to standard BBN. We also update our previous analysis on the effect of a variation of constants on the n(p,gamma)d reaction rate.Comment: 14 pages, 12 figure

On the 21Na(p,gamma)22Mg thermonuclear rate for 22Na production in novae

Classical novae are potential sources of gamma-rays, like the 1.275 MeV gamma emission following 22Na beta decay, that could be detected by appropriate instruments on board of future satellites like INTEGRAL. It has been shown that the production of 22Na by novae is affected by the uncertainty on the 21Na(p,gamma)22Mg rate and in particular by the unknown partial widths of the Ex = 5.714 MeV, J^pi = 2^+, 22Mg level. To reduce these uncertainties, we performed shell model calculations with the OXBASH code, compared the results with available spectroscopic data and calculated the missing partial widths. Finally, we discuss the influence of these results on the 21Na(p,gamma)22Mg reaction rate and 22Na synthesis.Comment: To appear in Phys. Rev. C, 6 pages with 3 figure

Primordial Nucleosynthesis

Primordial nucleosynthesis, or Big-Bang Nucleosynthesis (BBN), is one of the three evidences for the Big-Bang model, together with the expansion of the Universe and the Cosmic Microwave Background. There is a good global agreement over a range of nine orders of magnitude between abundances of 4He, D, 3He and 7Li deduced from observations, and calculated in primordial nucleosynthesis. This comparison was used to determine the baryonic density of the Universe. For this purpose, it is now superseded by the analysis of the Cosmic Microwave Background (CMB) radiation anisotropies. However, there remain, a yet unexplained, discrepancy of a factor 3-5, between the calculated and observed lithium primordial abundances, that has not been reduced, neither by recent nuclear physics experiments, nor by new observations. We review here the nuclear physics aspects of BBN for the production of 4He, D, 3He and 7Li, but also 6Li, 9Be, 11B and up to CNO isotopes. These are, for instance, important for the initial composition of the matter at the origin of the first stars. Big-Bang nucleosynthesis, that has been used, to first constrain the baryonic density, and the number of neutrino families, remains, a valuable tool to probe the physics of the early Universe, like variation of "constants" or alternative theories of gravity.Comment: Invited Plenary Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS