Abstract. The astrophysical S(E) factor of14 N(p, γ) 15 O has been measured for effective center-of-mass energies between E ef f = 119 and 367 keV at the LUNA facility using TiN solid targets and Ge detectors. The data are in good agreement with previous and recent work at overlapping energies. R-matrix analysis reveals that due to the complex level structure of 15 O the extrapolated S(0) value is model dependent and calls for additional experimental efforts to reduce the present uncertainty in S(0) to a level of a few percent as required by astrophysical calculations. .KvX -and γ ray spectroscopy -97.10.CvStellar structure and evolution PACS
The nuclear physics input from the 3 He(α, γ) 7 Be cross section is a major uncertainty in the fluxes of 7 Be and 8 B neutrinos from the Sun predicted by solar models and in the 7 Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-γ technique and with inferior precision. Using a windowless gas target, high beam intensity and low background γ-counting facilities, the 3 He(α, γ) 7 Be cross section has been determined at 127, 148 and 169 keV center-of-mass energy with a total uncertainty of 4 %. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3 He(α, γ) 7 Be astrophysical S-factor to solar energies. The 3 He(α, γ) 7 Be reaction is a critical link in the 7 Be and 8 B branches of the proton-proton (p-p) chain of solar hydrogen burning [1]. At low energies its cross section σ(E) (E denotes the center of mass energy, E α the 4 He beam energy in the laboratory system) can be parameterized by the astrophysical S-factor S(E) defined as. The 9.4 % uncertainty [3] in the Sfactor extrapolation to the solar Gamow energy (23 keV) contributes 8 % to the uncertainty in the predicted fluxes of solar neutrinos from the decays of 7 Be and 8 B [4]. The interior of the Sun, in turn, can be studied [4,5] by comparing this prediction with the data from neutrino detectors [6,7], which determine the 8 B neutrino flux with a total uncertainty as low as 3.5 % [7].Furthermore, the production of 7 Li in big-bang nucleosynthesis (BBN) is highly sensitive to the 3 He(α, γ) 7 Be cross section in the energy range E ≈ 160-380 keV [8], with an adopted uncertainty of 8 % [9]. Based on the baryon-to-photon ratio from observed anisotropies in the cosmic microwave background [10], network calculations predict primordial 7 Li abundances [11] that are significantly higher than observations [12,13]. A lower 3 He(α,γ)7 Be cross section at relevant energies may explain part of this discrepancy. The3 He(α,γ) 7 Be (Q-value: 1.586 MeV) reaction leads to the emission of prompt γ-rays, and the final 7 Be nucleus decays with a half-life of 53.22 ± 0.06 days, emitting a 478 keV γ-ray in 10.44 ± 0.04 % of the cases [14]. The cross section can be measured by detecting either the induced 7 Be activity (activation method) or the prompt γ-rays from the reaction (prompt-γ method). Previous activation studies [15,16,17,18] cover the energy range E = 420-2000 keV. Prompt γ-ray measurements [15,19,20,21,22,23,24] cover E = 107-2500 keV, although with limited precision at low energies.The global shape of the S-factor curve is well reproduced by theoretical calculations [25,26]. However, the slope has been questioned [26] for E ≤ 300 keV, where there are no high-precision data. Furthermore, a global analysis [3] ind...
Publisher's Note: Astrophysical S factor of the 3 He(α, γ ) 7 Be reaction measured at low energy via detection of prompt and delayed γ rays [Phys. Rev. C 75, 065803 (2007)]
The flux of 7 Be and 8 B neutrinos from the Sun and the production of 7 Li via primordial nucleosynthesis depend on the rate of the 3 He(α,γ) 7 Be 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 3 He(α,γ) 7 Be cross section at 106 keV performed at Italy's Gran Sasso underground laboratory by the activation method. This energy is closer to the solar Gamow energy than ever reached before. The result is σ = 0.567±0.029stat ±0.016syst nbarn. The data are compared with previous activation studies at high energy, and a recommended S(0) value for all 3 He(α,γ) 7 Be activation studies, including the present work, is given.PACS numbers: 25.55.-e, 26.20.+f, 26.35.+c, 26.65.+t
Ultra-sensitive in-beam γ-ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy's Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory γ-ray background for Eγ < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground γ-counting setups. The γ-ray background induced by an incident α-beam has been studied. The data are used to evaluate the feasibility of sensitive in-beam experiments at LUNA and, by extension, at similar proposed facilities.PACS. 25.40.Lw Radiative capture -25.55.-e 3 H-, 3 He-, and 4 He-induced reactions -29.20.Ba Electrostatic accelerators -29.30.Kv X-and gamma-ray spectroscopy
The 3 He(α,γ) 7 Be process is a key reaction in both Big-Bang nucleosynthesis and p-p chain of Hydrogen Burning in Stars. A new measurement of the 3 He(α,γ) 7 Be cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt γ detection methods. The present work reports full details of the prompt γ detection experiment, focusing on the determi-nation of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments and two different theoretical models are used to obtain the S-factor at solar energies.
The 15 N(p,γ) 16 O reaction controls the passage of nucleosynthetic material from the first to the second carbon-nitrogen-oxygen (CNO) cycle.A direct measurement of the total 15 N(p,γ) 16 O cross section at energies corresponding to hydrogen burning in novae is presented here. Data have been taken at 90 -230 keV center-of-mass energy using a windowless gas target filled with nitrogen of natural isotopic composition and a bismuth germanate summing detector. The cross section is found to be a factor two lower than previously believed.
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