The Big Bang Nucleosynthesis (BBN) theory allows to calculate the abundance of isotopes createdin the early universe. Interestingly, the primordial abundance of deuterium deduced from observations of pristine gas at high redshifts is more accurate with respect to the computed value because the BBN calculation is affected by the paucity of data for the deuterium-burning reaction D(p,g)3He. In fact, only a single dataset is currently available in the BBN energy range, in which the authors state systematic error of 9%. The concern for the D(p; g)3He cross section error is made worse by the fact that the theoretical and experimental values do not agree at the level of 20%. A new measurement is presently in progress at the LUNA (Laboratory for Underground Nuclear astrophysics) accelerator, operating deep underground at the Gran Sasso Laboratory, Italy. The main goal is the study of the D(p; g)3He cross section in the BBN energy range with accuracy. The LUNA measurement is described and preliminary results are discussed and compared with ab-initio calculations. The impact of this measurement in cosmology and particle physics is also highlighted. In particular, a precision measurement allows to derive the universal baryon density Wb with accuracy comparable to the one obtained by the PLANCK experiment. Finally, the accurate knowledge of the D(p; g)3He cross section increases the sensitivity to probe the existence of relativistic particles (e.g. sterile neutrinos, hot axions etc.) not foreseen in the standard model.

Recent observations of (6)Li in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the (2)H(α,γ)(6)Li reaction dominates (6)Li production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles (2)H and α at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of (6)Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the (2)H(α,γ)(6)Li cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial (6)Li/(7)Li isotopic abundance ratio has been determined to be (1.5 ± 0.3) × 10(-5), from our experimental data and standard BBN theory. The much higher (6)Li/(7)Li values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.

. The production of the stable isotope 6 Li in standard Big Bang nucleosynthesis has recently attracted much interest. Recent observations in metal-poor stars suggest that a cosmological 6 Li plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of 7 Li abundances and would point to a predominantly primordial origin of 6 Li , contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang 6 Li production must be revisited. The main production channel for 6 Li in the Big Bang is the 2 H(α,γ) 6 Li reaction. The present work reports on neutron-induced effects in a high-purity germanium detector that were encountered in a new study of this reaction. In the experiment, an α-beam from the underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2 H(d,n) 3 He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3MeV neutrons on well-shielded high-purity germanium detectors has been studied in detail. Data have been taken at 280 and 400keV α-beam energy and for comparison also using an americium-beryllium neutron source.

Proton captures on Mg isotopes play an important role in the Mg–Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the 25Mg(p, γ)26Al reaction affect the production of radioactive 26Algs as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at the Laboratory for Underground Nuclear Astrophysics, we provide revised rates of the 25Mg(p, γ)26Algs and the 25Mg(p, γ)26Alm reactions with corresponding uncertainties. In the temperature range 50–150 MK, the new recommended rate of 26Alm production is up to five times higher than previously assumed. In addition, at T = 100 MK, the revised total reaction rate is a factor of two higher. Note that this is the range of temperature at which the Mg–Al cycle operates in a H-burning zone. The effects of this revision are discussed. Due to the significantly larger 25Mg(p, γ)26Alm rate, the estimated production of 26Algs in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf–Rayet stars to the galactic 26Al budget. Similarly, we show that the asymptotic giant branch (AGB) extra-mixing scenario does not appear able to explain the most extreme values of 26Al/27Al, i.e., >10−2, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of self-pollution by massive AGBs a more robust explanation for the Mg–Al anticorrelation observed in globular-cluster stars.

With the development of new radioactive ion beam (RIB) facilities such as FRIB, which will push measurements further away from stability, the need for improved RIB targets is more crucial than ever. Important scattering, transfer and capture reaction measurements of rare, exotic, and unstable nuclei on hydrogen and helium require targets that are dense, highly localized, and pure. To this end, the JENSA Collaboration led by the Colorado School of Mines (CSM) is designing, building and testing a supersonic gas jet target for use at existing and future RIB facilities. The gas jet target allows for a high density and purity of target nuclei (such as He-3) within a highly confined region, without the use of windows or backing materials, and will also enable the use of state-of-the-art detection systems. The motivation, specifications and status of the CSM gas jet target system is discussed.

Background Themain energy productionmechanism for massive stars during hydrogen burning is the CNO cycle. The reactions N-15(p,gamma)O-16 and N-15(p,alpha(0))C-12 form a branch point in this cycle. The ratio of the corresponding reaction rates determines the CNO abundances evolving during this early stage of the star's life which affects the subsequent nucleosynthesis in later phases of stellar evolution. Determining the cross sections for these reactions at stellar energies is often very difficult. Measurements of other reactions that populate the same compound nucleus can often be used to indirectly determine the cross section of interest. Purpose The nuclear level properties of broad resonances in O-16 which characterize the cross section of the reactions N-15(p,gamma)O-16 and N-15(p,alpha(0))C-12 must be well known in order to accurately extrapolate the measured cross sections to the stellar energy range. The R-matrix formalism is a powerful technique for interpreting these cross sections and is greatly enhanced by additional data in other reaction channels. In a previous publication, measurements were reported for the cross section of the reaction N-15(p,gamma)O-16 for the ground state transition only. Concurrently, gamma-ray measurements were recorded for the cascade transitions to the E-x = 6.050, 6.130, and 7.117 MeV bound states of O-16 as well as from the reaction N-15(p,alpha(1)gamma)C-12. Excitation curves for the cascade transitions have never been measured and the excitation curve data for the N-15(p,alpha(1)gamma)C-12 reaction found in the literature may suffer from substantial errors due to target contamination. Methods Angle integrated cross sections are measured over the proton energy range from E-p = 0.14 to 1.80 MeV for the gamma-ray cascade transitions and for the reaction N-15(p,alpha(1)gamma)C-12. Results De-excitations associated with several compound nucleus states in O-16 are observed in both the gamma-ray and alpha(1) channels. An R-matrix analysis is performed and partial decay widths are deduced for several previously unobserved decay branchings from these states. Conclusion For the first time, excitation curves for the cascade transitions to the O-16 bound states at E-x = 6.050, 6.130, and 7.117 MeV are reported over the energy range from E-p = 0.14 to 1.80 MeV. In addition, an improved measurement of the N-15(p,alpha(1)gamma)C-12 excitation curve has been made over a similar energy range.

Background The main energy production mechanism for massive stars during hydrogen burning is the CNO cycle. The reactions ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma})}^{16}$O and ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{0})}^{12}$C form a branch point in this cycle. The ratio of the corresponding reaction rates determines the CNO abundances evolving during this early stage of the star's life which affects the subsequent nucleosynthesis in later phases of stellar evolution. Determining the cross sections for these reactions at stellar energies is often very difficult. Measurements of other reactions that populate the same compound nucleus can often be used to indirectly determine the cross section of interest.Purpose The nuclear level properties of broad resonances in ${}^{16}$O which characterize the cross section of the reactions ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma})}^{16}$O and ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{0})}^{12}$C must be well known in order to accurately extrapolate the measured cross sections to the stellar energy range. The $R$-matrix formalism is a powerful technique for interpreting these cross sections and is greatly enhanced by additional data in other reaction channels. In a previous publication, measurements were reported for the cross section of the reaction ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma})}^{16}$O for the ground state transition only. Concurrently, $\ensuremath{\gamma}$-ray measurements were recorded for the cascade transitions to the ${E}_{x}$ $=$ 6.050, 6.130, and 7.117 MeV bound states of ${}^{16}$O as well as from the reaction ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})}^{12}$C. Excitation curves for the cascade transitions have never been measured and the excitation curve data for the ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})}^{12}$C reaction found in the literature may suffer from substantial errors due to target contamination.Methods Angle integrated cross sections are measured over the proton energy range from ${E}_{p}$ $=$ 0.14 to 1.80 MeV for the $\ensuremath{\gamma}$-ray cascade transitions and for the reaction ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})}^{12}$C.Results De-excitations associated with several compound nucleus states in ${}^{16}$O are observed in both the $\ensuremath{\gamma}$-ray and ${\ensuremath{\alpha}}_{1}$ channels. An $R$-matrix analysis is performed and partial decay widths are deduced for several previously unobserved decay branchings from these states.Conclusion For the first time, excitation curves for the cascade transitions to the ${}^{16}$O bound states at ${E}_{x}$ $=$ 6.050, 6.130, and 7.117 MeV are reported over the energy range from ${E}_{p}$ $=$ 0.14 to 1.80 MeV. In addition, an improved measurement of the ${}^{15}$N${(p,\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})}^{12}$C excitation curve has been made over a similar energy range.

In the present work we report on a new measurement of resonance strengths omega gamma in the reaction Mg-25(p, gamma)Al-26 at E-cm = 92 and 189 key. This study was performed at the LUNA facility in the Gran Sasso underground laboratory using a 4 pi BGO summing crystal. For the first time the 92 keV resonance was directly observed and a resonance strength omega gamma = (2.9 +/- 0.6) x 10(-10) eV was determined. Additionally, the gamma-ray branchings and strength of the 189 key resonance were studied with a high resolution HPGe detector yielding an omega gamma value in agreement with the BGO measurement, but 20% larger compared to previous works. (C) 2011 Elsevier B.V. All rights reserved.

The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the 14N(p,gamma)15O reaction. The reaction proceeds by capture to the ground states and several excited states in O-15. In order to obtain a reliable extrapolation of the excitation curve to astrophysical energy, fits in the R-matrix framework are needed. In an energy range that sensitively tests such fits, new cross section data are reported here for the four major transitions in the 14N(p,gamma)15O reaction. The experiment has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy. Using a composite germanium detector, summing corrections have been considerably reduced with respect to previous studies. The cross sections for capture to the ground state and to the 5181, 6172, and 6792 keV excited states in O-15 have been determined at 359, 380, and 399 keV beam energy. In addition, the branching ratios for the decay of the 278 keV resonance have been remeasured.

Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T similar or equal to 30 x 10(6) K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion.Aims. The activation of this cycle depends on the rate of the N-15(p, gamma)O-16 reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances.Methods. We present a new measurement of the N-15(p, gamma)O-16 reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 x 10(6) K and 780 x 10(6) K. This range includes the N-15(p, gamma)O-16 Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars.Results. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the N-14(rho,gamma)O-15 reaction. The reaction proceeds by capture to the ground states and several excited states in O-15. In order to obtain a reliable extrapolation of the excitation curve to astrophysical energy, fits in the R-matrix framework are needed. In an energy range that sensitively tests such fits, new cross-section data are reported here for the four major transitions in the N-14(rho,gamma)O-15 reaction. The experiment has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400-kV accelerator placed deep underground in the Gran Sasso facility in Italy. Using a composite germanium detector, summing corrections have been considerably reduced with respect to previous studies. The cross sections for capture to the ground state and to the 5181, 6172, and 6792 keV excited states in O-15 have been determined at 359, 380, and 399 keV beam energy. In addition, the branching ratios for the decay of the 278-keV resonance have been remeasured.

The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the {sup 14}N(p,{gamma}){sup 15}O reaction. The reaction proceeds by capture to the ground states and several excited states in {sup 15}O. In order to obtain a reliable extrapolation of the excitation curve to astrophysical energy, fits in the R-matrix framework are needed. In an energy range that sensitively tests such fits, new cross-section data are reported here for the four major transitions in the {sup 14}N(p,{gamma}){sup 15}O reaction. The experiment has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400-kV accelerator placed deep underground in the Gran Sasso facility in Italy. Using a composite germanium detector, summing corrections have been considerably reduced with respect to previous studies. The cross sections for capture to the ground state and to the 5181, 6172, and 6792 keV excited states in {sup 15}O have been determined at 359, 380, and 399 keV beam energy. In addition, the branching ratios for the decay of the 278-keV resonance have been remeasured.

Thermonuclear reaction cross sections of astrophysical interest decrease exponentially with energy, approaching the level of femtobarn or less at the Gamow window. Experimental investigations of such small reaction rates in laboratories at the earth's surface are hampered by the cosmic-ray background into detectors. For such studies, Dakota Ion Accelerator for Nuclear Astrophysics, a deep underground, high detector efficiency, high target density, high beam intensity accelerator facility is being designed. We report on a 100 mA, 400 kV accelerator design. To take into account the beam space-charge effects, advanced three-dimensional transportation calculations have been performed. These highly realistic beam calculations demonstrate that high beam currents can be transported to a gas-jet target with a diameter of few millimeters.