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Search Results: 1 - 10 of 322224 matches for " H. P. Trautvetter "
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Lifetime measurement of the 6792 keV state in 15O, important for the astrophysical S factor extrapolation in 14N(p,g)15O
D. Schuermann,R. Kunz,I. Lingner,C. Rolfs,F. Schuemann,F. Strieder,H. -P. Trautvetter
Physics , 2008, DOI: 10.1103/PhysRevC.77.055803
Abstract: We report on a new lifetime measurement of the E_x=6792 keV state in 15O via the Doppler-shift attenuation method at the E=259 keV resonance in the reaction 14N(p,g)15O. This subthreshold state is of particular importance for the determination of the ground state astrophysical S factor of 14N(p,g)15O at stellar energies. The measurement technique has been significantly improved compared with previous work. The conclusion of a finite lifetime drawn there cannot be confirmed with the present data. In addition, the lifetime of the two states at E_x=5181 and 6172 keV have been measured with the same technique in order to verify the experimental method. We observe an attenuation factor F(tau)>0.98 for the E_x =6172 and 6792 keV states, respectively, corresponding to tau<0.77 fs. The attenuation factor for the E_x=5181 keV state results in F(tau)=0.78+/-0.02 corresponding to tau=8.4+/-1.0 fs in excellent agreement with literature.
First direct measurement of the total cross section of 12C(alpha,gamma)16O
D. Schuermann,A. Di Leva,L. Gialanella,D. Rogalla,F. Strieder,N. De Cesare,A. D'Onofrio,G. Imbriani,R. Kunz,C. Lubritto,A. Ordine,V. Roca,C. Rolfs,M. Romano,F. Schuemann,F. Terrasi,H. -P. Trautvetter
Physics , 2005, DOI: 10.1140/epja/i2005-10175-2
Abstract: The total cross section of 12C(alpha,gamma)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E=1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.
Comparison of the LUNA 3He(alpha,gamma)7Be activation results with earlier measurements and model calculations
Gy. Gyurky,D. Bemmerer,F. Confortola,H. Costantini,A. Formicola,R. Bonetti,C. Broggini,P. Corvisiero,Z. Elekes,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,G. Imbriani,M. Junker,M. Laubenstein,A. Lemut,B. Limata,V. Lozza,M. Marta,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter
Physics , 2007, DOI: 10.1088/0954-3899/35/1/014002
Abstract: Recently, the LUNA collaboration has carried out a high precision measurement on the 3He(alpha,gamma)7Be reaction cross section with both activation and on-line gamma-detection methods at unprecedented low energies. In this paper the results obtained with the activation method are summarized. The results are compared with previous activation experiments and the zero energy extrapolated astrophysical S factor is determined using different theoretical models.
Measurement of 25Mg(p; gamma)26Al resonance strengths via gamma spectrometry
A. Formicola,A. Best,G. Imbriani,M. Junker,D. Bemmerer,R. Bonetti,C. Broggini,A. Caciolli,F. Confortola,P. Corvisiero,H. Costantini,Z. Elekes,Zs Fulop,G. Gervino,A. Guglielmetti,Gy Gyurky,C. Gustavino,A. Lemut,B. Limata,M. Marta,C. Mazzocchi,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter
Physics , 2007, DOI: 10.1088/0954-3899/35/1/014013
Abstract: The COMPTEL instrument performed the first mapping of the 1.809 MeV photons in the Galaxy, triggering considerable interest in determing the sources of interstellar 26Al. The predicted 26Al is too low compared to the observation, for a better understanding more accurate rates for the 25Mg(p; gamma)26Al reaction are required. The 25Mg(p;gamma)26Al reaction has been investigated at the resonances at Er= 745; 418; 374; 304 keV at Ruhr-Universitat-Bochum using a Tandem accelerator and a 4piNaI detector. In addition the resonance at Er = 189 keV has been measured deep underground laboratory at Laboratori Nazionali del Gran Sasso, exploiting the strong suppression of cosmic background. This low resonance has been studied with the 400 kV LUNA accelerator and a HPGe detector. The preliminary results of the resonance strengths will be reported.
Precision study of ground state capture in the 14N(p,gamma)15O reaction
M. Marta,A. Formicola,Gy. Gyurky,D. Bemmerer,C. Broggini,A. Caciolli,P. Corvisiero,H. Costantini,Z. Elekes,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,G. Imbriani,M. Junker,R. Kunz,A. Lemut,B. Limata,C. Mazzocchi,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,M. Romano,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter,A. Vomiero
Physics , 2008, DOI: 10.1103/PhysRevC.78.022802
Abstract: The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV center-of-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor.
Revision of the 15N(p,γ)16O reaction rate and oxygen abundance in H-burning zones
A. Caciolli,C. Mazzocchi,V. Capogrosso,D. Bemmerer,C. Broggini,P. Corvisiero,H. Costantini,Z. Elekes,A. Formicola,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,Gy. Gyurky,G. Imbriani,M. Junker,A. Lemut,M. Marta,R. Menegazzo,S. Palmerini,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter,A. Vomiero
Physics , 2011, DOI: 10.1051/0004-6361/201117475
Abstract: The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T {\simeq} 30 {\cdot} 106 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 RGB (red giant branch) phase of the star or to the pollution of the primordial gas by an early population of massive AGB (asymptotic giant branch) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. The activation of this cycle depends on the rate of the 15N(p,{\gamma})16O 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. We present a new measurement of the 15N(p,{\gamma})16O 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 {\cdot} 106 K and 780 {\cdot}106 K. This range includes the 15N(p,{\gamma})16O 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. 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.
Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy
D. Bemmerer,F. Confortola,H. Costantini,A. Formicola,Gy. Gyurky,R. Bonetti,C. Broggini,P. Corvisiero,Z. Elekes,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,G. Imbriani,M. Junker,M. Laubenstein,A. Lemut,B. Limata,V. Lozza,M. Marta,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter
Physics , 2006, DOI: 10.1103/PhysRevLett.97.122502
Abstract: The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li 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-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity and low background gamma-counting facilities, the 3He(alpha,gamma)7Be 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 3He(alpha,gamma)7Be astrophysical S-factor to solar energies.
The 14N(p,gamma)15O reaction studied with a composite germanium detector
M. Marta,A. Formicola,D. Bemmerer,C. Broggini,A. Caciolli,P. Corvisiero,H. Costantini,Z. Elekes,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,Gy. Gyurky,G. Imbriani,M. Junker,A. Lemut,B. Limata,C. Mazzocchi,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter,A. Vomiero
Physics , 2011, DOI: 10.1103/PhysRevC.83.045804
Abstract: 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.
3He(alpha,gamma)7Be cross section at low energies
Gy. Gyurky,F. Confortola,H. Costantini,A. Formicola,D. Bemmerer,R. Bonetti,C. Broggini,P. Corvisiero,Z. Elekes,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,G. Imbriani,M. Junker,M. Laubenstein,A. Lemut,B. Limata,V. Lozza,M. Marta,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter
Statistics , 2007, DOI: 10.1103/PhysRevC.75.035805
Abstract: The flux of 7Be and 8B neutrinos from the Sun and the production of 7Li via primordial nucleosynthesis depend on the rate of the 3He(alpha,gamma)7Be 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 3He(alpha,gamma)7Be 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 sigma = 0.567 +- 0.029(stat) +- 0.016(syst) nbarn. The data are compared with previous activation studies at high energy, and a recommended S(0) value for all 3He(alpha,gamma)7Be activation studies, including the present work, is given.
An actively vetoed Clover gamma-detector for nuclear astrophysics at LUNA
LUNA collaboration,T. Szucs,D. Bemmerer,C. Broggini,A. Caciolli,F. Confortola,P. Corvisiero,Z. Elekes,A. Formicola,Zs. Fulop,G. Gervino,A. Guglielmetti,C. Gustavino,Gy. Gyurky,G. Imbriani,M. Junker,A. Lemut,M. Marta,C. Mazzocchi,R. Menegazzo,P. Prati,V. Roca,C. Rolfs,C. Rossi Alvarez,E. Somorjai,O. Straniero,F. Strieder,F. Terrasi,H. P. Trautvetter
Physics , 2010, DOI: 10.1140/epja/i2010-10967-1
Abstract: An escape-suppressed, composite high-purity germanium detector of the Clover type has been installed at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility, deep underground in the Gran Sasso Laboratory, Italy. The laboratory gamma-ray background of the Clover detector has been studied underground at LUNA and, for comparison, also in an overground laboratory. Spectra have been recorded both for the single segments and for the virtual detector formed by online addition of all four segments. The effect of the escape-suppression shield has been studied as well. Despite their generally higher intrinsic background, escape-suppressed detectors are found to be well suited for underground nuclear astrophysics studies. As an example for the advantage of using a composite detector deep underground, the weak ground state branching of the Ep = 223 keV resonance in the 24Mg(p,gamma)25Al reaction is determined with improved precision.
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