Search results for "nuclear astrophysic"
showing 10 items of 63 documents
Solar and Atmospheric Four-Neutrino Oscillations
2001
We present an analysis of the neutrino oscillation solutions of the solar and atmospheric neutrino problems in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones and the mass spectra presents two separated doublets. Such scenarios allow for simultaneous transitions of solar $\nu_e$, as well as atmospheric $\nu_\mu$, into active and sterile neutrinos controlled by the additional mixing angles $\vartheta_{23}$ and $\vartheta_{24}$, and they contain as limiting cases the pure solar $\nu_e$-active and $\nu_e$-sterile neutrino oscillations, and the pure atmospheric $\nu_\mu\to\nu_s$ and $\nu_\mu\to\nu_\tau$ oscillations, respectively. We evaluate t…
If sterile neutrinos exist, how can one determine the total solar neutrino fluxes?
2002
The 8B solar neutrino flux inferred from a global analysis of solar neutrino experiments is within 11% (1 sigma) of the predicted standard solar model value if only active neutrinos exist, but could be as large as 1.7 times the standard prediction if sterile neutrinos exist. We show that the total 8B neutrino flux (active plus sterile neutrinos) can be determined experimentally to about 10% (1 sigma) by combining charged current measurements made with the KamLAND reactor experiment and with the SNO CC solar neutrino experiment, provided the LMA neutrino oscillation solution is correct and the simulated performance of KamLAND is valid. Including also SNO NC data, the sterile component of the…
Four-neutrino oscillation solutions of the solar neutrino problem
2000
We present an analysis of the neutrino oscillation solutions of the solar neutrino problem in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones. We perform a fit to the full data set corresponding to the 825-day Super-Kamiokande data sample as well as to Chlorine, GALLEX and SAGE and Kamiokande experiments. In our analysis we use all measured total event rates as well as all Super-Kamiokande data on the zenith angle dependence and the recoil electron energy spectrum. We consider both transitions via the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism as well as oscillations in vacuum (just-so) and find the allowed solutions for different values …
Decay of the key 92-keV resonance in the 25Mg(p,γ) reaction to the ground and isomeric states of the cosmic γ-ray emitter 26Al
2021
Abstract The 92-keV resonance in the 25Mg ( p , γ ) 26 Al reaction plays a key role in the production of 26Al at astrophysical burning temperatures of ≈100 MK in the Mg-Al cycle. However, the state can decay to feed either the ground, 26 g Al, or isomeric state, 26 m Al. It is the ground state that is critical as the source of cosmic γ rays. It is therefore important to precisely determine the ground-state branching fraction f 0 of this resonance. Here we report on the identification of four γ-ray transitions from the 92-keV resonance, and determine the spin of the state and its ground-state branching fraction f 0 = 0.52 ( 2 ) s t a t ( 6 ) s y s t . The f 0 value is the most precise report…
Beta-decay half-lives of very neutron-rich nuclei and their consequences for the astrophysical r-process
2005
Half-lives for Gamow-Teller β-decay of very neutron-rich nuclei have been calculated using the RPA shell-model code of Krumlinde and Muller. For the examples of the isotope sequences of 27Co and 37Rb, and of nuclei around 132Sn it is demonstrated that close agreement between experiment and theory can be obtained, provided an appropriate choice of model parameters is made for each mass region. On the basis of this agreement, T1/2 predictions for isotopes up to the r-process path are made and compared to earlier model calculations. Possible implications of the results on the site and the cycle time of the r-process are discussed.
Relevance of β-delayed neutron data for reactor, nuclear physics and astrophysics applications
2023
Initially, yields (or abundances) and branching ratios of β-delayed neutrons (βdn) from fission products (Pn-values) have had their main importance in nuclear reactor control. At that time, the six-group mathematical approximation of the time-dependence of βdn-data in terms of the so-called "Keepin groups" was generally accepted. Later, with the development of high-resolution neutron spectroscopy, βdn data have provided important information on nuclear-structure properties at intermediate excitation energy in nuclei far from stability, as well as in nuclear astrophysics. In this paper, I will present some examples of the βdn-studies performed by the Kernchemie Mainz group during the past th…
Influences on the triple alpha process beyond the Hoyle state
2010
7 pags., 3 figs. -- International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX, 25-30 June 2006, CERN
Decay Spectroscopy for Nuclear Astrophysics: β-delayed Proton Decay
2011
In several radiative proton capture reactions important in novae and XRBs, the resonant parts play the capital role. We use decay spectroscopy techniques to find these resonances and study their properties. We have developed techniques to measure beta- and beta-delayed proton decay of sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A&M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. This allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. At the same time we measu…
The Nuclear astrophysics program at n_TOF (CERN)
2017
An important experimental program on Nuclear Astrophysics is being carried out at the n_TOF since several years, in order to address the still open issues in stellar and primordial nucleosynthesis. Several neutron capture reactions relevant to s-process nucleosynthesis have been measured so far, some of which on important branching point radioisotopes. Furthermore, the construction of a second experimental area has recently opened the way to challenging measurements of (n, charged particle) reactions on isotopes of short half-life. The Nuclear Astrophysics program of the n_TOF Collaboration is here described, with emphasis on recent results relevant for stellar nucleosynthesis, stellar neut…
High-precision mass measurements of 25Al and 30P at JYFLTRAP
2016
The masses of the astrophysically relevant nuclei 25Al and 30P have been measured with a Penning trap for the first time. The mass-excess values for 25Al ( $\Delta = -8915.962(63)$ keV) and 30P ( $\Delta = -20200.854(64)$ keV) obtained with the JYFLTRAP double Penning trap mass spectrometer are in good agreement with the Atomic Mass Evaluation 2012 values but $ \approx$ 5-10 times more precise. A high precision is required for calculating resonant proton-capture rates of astrophysically important reactions 25Al (p, $ \gamma$ )26Si and 30P(p, $ \gamma$ )31S . In this work, $ Q_{(p,\gamma)} = 5513.99(13)$ keV and $ Q_{(p,\gamma)} = 6130.64(24)$ keV were obtained for 25Al and 30P , respectivel…