141.
Measurement of the 197-Au(n,gamma) cross section at n TOF: towards a new standard - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
Two different detectors and techniques are employed at n TOF facility, at CERN, to improve the accuracyof the neutron capture cross section of 197Au(n,γ): a total absorption calorimeter and a set of C6D6. The accurateknowledge of this cross section is of great importance for all the (n,γ) reactions study. The neutron capture crosssection and nuclear resonce parameters of the 197Au have been measured in the energy range of 1 eV to 1 kev. Thepresent work shows in average a good agreement with evaluated data libraries, although sizeable differences havebeen observed for some resonances. Two new resonances have also been discovered....
142.
Simultaneous measurement of the neutron capture and fission yields of 233-U - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
We have measured the neutron capture and fission cross section of 233U at the neutron time-of-flightfacility n TOF at CERN in the energy range from 1 eV to 1 MeV with high accuracy by using a high performance4π BaF2 Total Absorption Calorimeter (TAC) as a detection device. The method, based on the TAC energy responsestudy, allowing to disentangle between γ’s originating from fission and capture will be presented as well as the firstvery preliminary results.
143.
Neutron resonance spectroscopy at n TOF at CERN - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
Neutron resonance spectroscopy plays an important role in the investigation of neutron induced reactioncross sections and nuclear structure in the MeV excitation range. Neutron time-of-flight facilities are the mostused installations to explore neutron resonances. In this paper we describe the basic features of neutron resonancespectroscopy together with recent results from the time-of-flight facility n TOF at CERN.
144.
Measurements of the 90,91,92,94,96-Zr(n, gamma) cross-sections at n TOF - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
Neutron capture cross sections of the 90,91,92,94,96Zr have been measured over the energyrange from 1 eV to 1 MeV at the spallation neutron facility n TOF at CERN in 2003. The innovative features of the neutron beam, in particular the high instantaneous flux, thehigh energy resolution and low background, together with improvements of the neutronsensitivity of the capture detectors make this facility unique for neutron-induced reactioncross section measurements with much improved accuracy. The preliminary results of theZr measurements show capture resonance strengths generally smaller than in previousmeasurements.
145.
Commissionning of the n_TOF-Ph2 facility - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Gómez Hornillos, María Belén
The white spectrum neutron time-of-flight facility n_TOF is operating at CERN since 2001. Theneutron beam has a very high instantaneous flux and high resolution in energy and it is deliveredin the experimental area located 187 m downstream from the spallation target. The intense neutronfluence per proton burst results in a much enhanced signal to background ratio for neutron captureand fission reactions on radioactive isotopes, thus making the facility well suited for accuratemeasurement of neutron-induced reaction cross-sections. This is especially true to highlyradioactive targets which are of major importance in new nuclear energy system such as Gen-IVreactors, especially those with fast...
146.
Neutron Capture cross section of 90Zr: Bottleneck in the s-process reaction flow - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
The neutron capture cross sections of the Zr isotopes have important implications in nuclear astrophysics andfor reactor design. The small cross section of the neutron magic nucleus 90Zr, which accounts for more than 50%of natural zirconium represents one of the key isotopes for the stellar s-process, because it acts as a bottleneckin the neutron capture chain between the Fe seed and the heavier isotopes. The same element, Zr, also is animportant component of the structural materials used in traditional and advanced nuclear reactors. The (n, γ )cross section has been measured at CERN, using the n TOF spallation neutron source....
147.
Measurements of the 90,91,92,94,96Zr neutron capture cross-section at n_TOF - Cortés Rossell, Guillem Pere; Calviño Tavares, Francisco; Poch Parés, Agustí; Pretel Sánchez, Carme
The neutron capture cross sections of 90,91,92,94,96Zr, which play a key role for the determinationof the neutron density in the He burning zone of the Red Giant stars, were measured over theenergy range from 1 eV to 1 MeV at the spallation neutron facility n_TOF at CERN. Based onthese data the capture resonance strength and the Maxwellian-averaged cross section at 30 keVwere calculated.
150.
Neutron physics of the Re/Os clock. III. Resonance analyses and stellar (n,gamma) cross sections of 186,187,188-Os - Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
Neutron resonance analyses have been performed for the capture cross sections of 186Os, 187Os, and 188Osmeasured at the n TOF facility at CERN. Resonance parameters have been extracted up to 5, 3, and 8 keV,respectively, using the SAMMY code for a full R-matrix fit of the capture yields. From these results averageresonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis formodeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model.Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellarenhancement factors to correct...
151.
New cooling sequences for old white dwarfs - Renedo Rouco, Isabel; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; Romero, A.D.; Córsico, Alejandro Hugo; Rohrmann, Rene Daniel; García-Berro Montilla, Enrique
We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This isdone by evolving white dwarf progenitors from the zero-age main sequence, through the core hydrogen-burningphase, the helium-burning phase, and the thermally pulsing asymptotic giant branch phase to the white dwarf stage.Complete evolutionary sequences are computed for a wide range of stellarmasses and for two different metallicities,Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of oldstellar systems, like globular clusters. During the white dwarf cooling stage, we self-consistently compute the phasein which nuclear reactions...
152.
Revisiting the theoretical DBV (V777 Her) instability strip: The MLT theory of convection - Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; García-Berro Montilla, Enrique
We reexamine the theoretical instability domain of pulsating DB white dwarfs (DBV or V777 Her variables). We performed an extensive g-mode nonadiabatic pulsation analysis of DB evolutionary models considering a wide range of stellar masses, for which the complete evolutionary stages of their progenitors from the ZAMS, through the thermally pulsing AGB and born-again phases, the domain of the PG1159 stars, the hot phase of DO white dwarfs, and then the DB white dwarf stage have been considered. We explicitly account for the evolution of the chemical abundance distribution due to time-dependent chemical diffusion processes. We examine the impact of...
153.
Seismological constraints on the high-gravity DOV stars PG 2131+066 and PG 1707+427 - Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; García-Berro Montilla, Enrique
A seismological study of the pulsating PG1159 stars PG2131+066 and PG 1707+427 is presented. We perform extensive adiabatic computations of g-mode pulsation periods of PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741M⊙. We constrain the stellar mass of PG2131+066 and PG 1707+427 by comparing the observed period spacing of each star with the theoretical asymptotic period spacings and with the average of the computed period spacings. We also employ the individual observed periods to find representative seismological models for both stars.
154.
Divulgació científica per a dames: L'Astronomie des dames de Jérome Lalande - Barca i Salom, Francesc Xavier
Recent studies have focused on the women who were engaged in scientificresearch, an area traditionally considered a male preserve. The fact that astronomy inthe XVII and XVIII centuries was often a family activity meant that the women in thefamily (wives, mothers, sisters and even neighbours) participated in observations andcalculations. This is the case of Lalande, who was assisted by women. In his bookl’Astronomie des dames, which was written to educate women, Lalande reported hislast astronomical discoveries in which he had taken part directly.
155.
Antisymmetric polar modes of thermal convection in rotating spherical fluid shells at high Taylor numbers - García González, Fernando; Net Marcé, Marta; Sánchez Umbría, Juan
The onset of thermal convection in a rotating spherical shell of intermediate radius ratio ¼ 0:4 isstudied numerically for Taylor numbers Ta 1011 and the Prandtl number of the liquid sodium ( ¼0:01). For the first time, it is shown that at very high Taylor numbers the first unstable mode can beantisymmetric with respect to the equator and confined inside a cylinder tangent to the inner sphere at theequator (polar mode). The exponent of the power law determined from the asymptotic dependence of thecritical Rayleigh number for very high Ta is 0.57, lower than 2=3, given theoretically for the spiralingcolumnar...
157.
Particle injection in the LSI+61º303 radio outbursts - Paredes, J. M.; Marti, J; Estalella Boadella, Robert; Sarrate Ramos, Josep
The binary radio, X-ray and gamma-ray star LSI+ 61 °303 presents periodic radio outbursts, of variable amplitude, with a period of 26.5 d. We propose a description of the radio outbursts using the adiabatic expansion model of a synchrotron emitting source, modified to incorporate a prolongedinjection of energetic particles, and including the synchrotron and inverse Compton losses in the energy loss equation. We examine the two-frequency simultaneous radio observations of the 1981 August-September radio outburst. The agreement obtained between the observed and the calculated radio outburst is satisfactory and seems to indicate the important role played by particle injection in...
158.
New chemical profiles for the asteroseismolofy of ZZ Ceti stars - Althaus, Leandro Gabriel; Córsico, Alejandro Hugo; Bischoff-Kim, A.; Romero, A.D.; Renedo Rouco, Isabel; García-Berro Montilla, Enrique; Miller Bertolami, Marcelo M
We compute new chemical profiles for the core and envelope of white dwarfs appropriate for pulsational studies of ZZ Ceti stars. These profiles are extracted from the complete evolution of progenitor stars, evolved through the main sequence and the thermally pulsing asymptotic giant branch (AGB) stages, and from time-dependentelement diffusion during white dwarf evolution. We discuss the importance of the initial–final mass relationship for the white dwarf carbon–oxygen composition. In particular, we find that the central oxygen abundance may be underestimated by about 15% if the white dwarf mass is assumed to be the hydrogen-free core mass before the first...
141.
