Nuclear Fusion in the Sun (original) (raw)
Related papers
Further direct approaches to the nuclear reactions in the Sun
Nuclear Physics A, 1997
Nuclear fusion reactions play a key role in the understanding of energy production, neutrino emission and nucleosynthesis of the elements in stars. The direct measurement of the cross section of these reactions at the relevant energies is usually hampered by cosmic radiation, beam induced background and/or the radioactivity of the nuclei involved. *Supported in part by INFN, BMBF, DFG, DAAD-VIGONI and NSF/NATO. 0375-9474/97/$17.00 © 1997 -Elsevier Science B.V. All rights reserved. PII: S0375-9474(97)00312-6 604c U Greife et al./Nuclear Physics A621 (1997) 603c-606c
Screening of nuclear reactions in the Sun and solar neutrinos
Physical Review C, 1995
We quantitatively determine the effect and the uncertainty on solar neutrino production arising from the screening process. We present predictions for the solar neutrino fluxes and signals obtained with different screening models available in the literature and by using our stellar evolution code. We explain these numerical results in terms of simple laws relating the screening factors with the neutrino fluxes. Futhermore we explore a wider range of models for screening, obtained from the Mitler model by introducing and varying two phenomenological parameters, taking into account effects not included in the Mitler prescription. Screening implies, with respect to a no-screening case, a central temperat reduction of 0.5%, a 2% (8%) increase of Beryllium (Boron)-neutrino flux and a 2% (12%) increase of the Gallium (Chlorine) signal. We also find that uncertainties due to the screening effect ar at the level of 1% for the predicted Beryllium-neutrino flux and Gallium signal, not exceeding 3% for the Boron-neutrino flux and the Chlorine signal.
Solar neutrinos, helioseismology and the solar internal dynamics
Reports on Progress in Physics, 2011
Neutrinos are fundamental particles ubiquitous in the Universe and whose properties remain elusive despite more than 50 years of intense research activity. This review illustrates the importance of solar neutrinos in Astrophysics, Nuclear Physics, and Particle Physics. After a description of the historical context, we remind the reader of the noticeable properties of these particles and of the stakes of the solar neutrino puzzle. The Standard Solar Model triggered persistent efforts in fundamental Physics to predict the solar neutrino fluxes, and its constantly evolving predictions have been regularly compared to the detected neutrino signals. Anticipating that this standard model could not reproduce the internal solar dynamics, a Seismic Solar Model was developed which enriched theoretical neutrino flux predictions with in situ observation of acoustic and gravity waves propagating in the Sun. This seismic model contributed to the stabilization of the neutrino flux predictions. This review reminds the main historical steps, from the pioneering Homestake mine experiment and the GALLEX-SAGE experiments capturing the first pp neutrinos. It emphasizes the importance of the Superkamiokande and SNO detectors. Both experiments demonstrated that the solar-emitted electronic neutrinos are partially transformed into other neutrino flavors before reaching the Earth. This sustained experimental effort opens the door to Neutrino Astronomy, with long-base lines and underground detectors. The success of BOREXINO in detecting the 7 Be neutrino signal alone instills confidence in the physicists ability to detect each neutrino source separately. It justifies the building of a new generation of detectors to measure the entire solar neutrino spectrum with greater detail, as well as supernova neutrinos. A coherent picture emerged from neutrino physics and helioseismology. Today, new paradigms take shape in these two fields: the neutrinos are massive particles, but their masses are still unknown, and the research on the solar interior is focusing on the dynamical aspects and on signature of dark matter. The magnetic moment of the neutrino begins to be an actor of stellar evolution. The third part of the review is dedicated to this prospect. The understanding of the crucial role of both rotation and magnetism in solar physics benefit from SoHO, SDO, and PICARD space observations, and from new prototype like GOLF-NG. The magnetohydrodynamical view of the solar interior is a new way of understanding the impact of the Sun on the Earth environment and climate. For now, the particle and stellar challenges seem decoupled, but this is only a superficial appearance. The development of asteroseismology-with the COROT and KEPLER spacecrafts-and of neutrino physics will both contribute to improvements in our understanding of, for instance, supernova explosions. This shows the far-reaching impact of Neutrino and Stellar Astronomy.
Helioseismology and solar neutrinos: an update
Nuclear Physics B - Proceedings Supplements, 2001
We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we address the following points: i) helioseismic tests of recent SSMs; ii) predictions of the Beryllium neutrino flux based on helioseismology; iii) helioseismic tests regarding the screening of nuclear reactions in the Sun.
Helioseismology and screening of nuclear reactions in the Sun
Physics Letters B, 2001
We show that models for screening of nuclear reactions in the Sun can be tested by means of helioseismology. As well known, solar models using the weak screening factors are in agreement with data. We find that the solar model calculated with the anti screening factors of Tsytovitch is not consistent with helioseismology, both for the sound speed profile and for the depth of the convective envelope. Moreover, the difference between the no-screening and weak screening model is significant in comparison with helioseismic uncertainty. In other words, the existence of screening can be proved by means of helioseismology.
Physics of Particles and Nuclei, 2016
Neutrino produced in a chain of nuclear reactions in the Sun starting from the fusion of two protons, for the first time has been detected in a realtime detector in spectrometric mode. The unique properties of the Borexino detector provided an oppurtunity to disentangle pp-neutrino spectrum from the background components. A comparison of the total neutrino flux from the Sun with Solar luminosity in photons provides a test of the stability of the Sun on the 10 5 years time scale, and sets a strong limit on the power production in the unknown energy sources in the Sun of no more than 4% of the total energy production at 90% C.L.
Helioseismology, solar models and neutrino fluxes
Nuclear Physics B - Proceedings Supplements, 1999
We present our results concerning a systematical analysis of helioseismic implications on solar structure and neutrino production. We find Y ph = 0.238 − 0.259, R b /R = 0.708 − 0.714 and ρ b = (0.185 − 0.199) gr/cm 3 . In the interval 0.2 < R/R < 0.65, the quantity U = P/ρ is determined with and accuracy of ±5 • /•• or better. At the solar center still one has remarkable accuracy, ∆U/U < 4%. We compare the predictions of recent solar models (standard and non-standard) with the helioseismic results. By constructing helioseismically constrained solar models, the central solar temperature is found to be T = 1.58 × 10 7 K with a conservatively estimated accuracy of 1.4%, so that the major unceratainty on neutrino fluxes is due to nuclear cross section and not to solar inputs.
Comprehensive measurement of pp-chain solar neutrinos
Nature, 2018
About 99% of the energy of the Sun is produced through sequences of nuclear reactions, initiated by proton-proton (pp) fusion, in which hydrogen is converted into helium. Neutrinos emitted by this nuclear fusion chain represent a unique tool for solar and neutrino physics. Here we report the first complete study of all components of the pp-chain as performed by the Borexino collaboration: we measure the interaction rates of pp, 7 Be, and pep neutrinos with the highest precision to date, and of 8 B neutrinos with the lowest-threshold. We also set a limit on the hep neutrino flux. These measurements provide a direct determination of the pp-II/pp-I branching ratio and a first indication that the temperature profile in the Sun is more compatible with solar models assuming high surface metallicity. At the same time, we determine the survival probability P ee of solar electron neutrinos at different energies, thus probing simultaneously and with high precision the MSW-LMA flavor conversion paradigm in the vacuum and in the matter dominated regimes. In 1937, G. Gamow and C. F. von Weizsäcker 1,2 suggested that the Sun is powered by a chain of nuclear reactions initiated by proton-proton fusion and leading to the production of 4 He. This idea was further developed by H.Bethe and C.Critchfield 3. In the same years, C. F. von Weizsäcker and independently Bethe proposed an alternative mechanism, namely, the carbon-nitrogen-oxygen cycle (CNO cycle) 4 , a closed-loop chain of nuclear reactions catalyzed by 12 C, 14 N, and 16 O nuclei in which four protons are converted into 4 He. Although Bethe incorrectly considered the CNO cycle as the main source of energy in the Sun (mainly because of the overestimation of the Sun's central temperature available at that time), the debate on the role of the CNO cycle in the Sun is still relevant today. Indeed, a direct measure of its importance is missing, although theory predicts that it cannot contribute more than about 1% of the solar luminosity. Conversely, it is now understood to be the main source of energy in stars heavier than the Sun. More historical details can be found in 5. The Sun and lower mass stars are predominantly powered by the proton-proton (pp) chain (see Fig. 1), which was thoroughly studied by W. Fowler and co-workers in the 1950s 6. He and A. Cameron also pointed out that the detection of solar neutrinos (νs) could be a direct way of testing theoretical solar models. The following decades proved them right by elevating neutrinos to be the sole direct probes of the Sun's core and of solar energy generation. Neutrinos are copiously emitted in the primary proton-proton fusion reaction of the chain (pp * Lists of participants and their affiliations appear at the end of the paper.
Solar neutrinos: beyond standard solar models
Physics Reports, 1997
After a short survey of the physics of solar neutrinos, giving an overview of hydrogen burning reactions, predictions of standard solar models and results of solar neutrino experiments, we discuss the solar-model-independent indications in favour of non-standard neutrino properties. The experimental results look to be in contradiction with each other, even disregarding some experiment: unless electron neutrinos disappear in their trip from the sun to the earth, the fluxes of intermediate energy neutrinos (those from 7 Be electron capture and from the CNO cycle) result to be unphysically negative, or anyway extremely reduced with respect to standard solar model predictions. Next we review extensively non-standard solar models built as attempts to solve the solar neutrino puzzle. The dependence of the central solar temperature on chemical composition, opacity, age and on the values of the astrophysical S-factors for hydrogen-burning reactions is carefully investigated. Also, possible modifications of the branching among the various pp-chains in view of nuclear physics uncertainties are examined. Assuming standard neutrinos, all solar models examined fail in reconciling theory with experiments, even when the physical and chemical inputs are radically changed with respect to present knowledge and even if some of the experimental results are discarded.