49 research outputs found
Strength of the =1.842 MeV resonance in the Ca(p,)Sc reaction revisited
The strength of the MeV resonance in the
Ca(p,)Sc reaction is determined with two different
methods: First, by an absolute strength measurement using calcium hydroxide
targets, and second, relative to the well-determined strength of the resonance
triplet at = 4.5 MeV in the Ca(,)Ti
reaction. The present new value of eV is 37%
(equivalent to ) higher than the evaluated literature value. In
addition, the ratio of the strengths of the 1.842 MeV
Ca(p,)Sc and 4.5 MeV
Ca(,)Ti resonances has been determined to be
. The newly corrected strength of the 1.842-MeV resonance can
be used in the future as a normalization point for experiments with calcium
targets.Comment: Submitted to Phys. Rev.
Effusion Cooling Plates for Combustor Liners: Experimental and Numerical Investigations on the Effect of Density Ratio
AbstractEffusion cooling represents the state-of-the-art of liner cooling technology for modern combustors. The present paper describes experimental tests aiming at evaluating the cooling performance of a multi-perforated plate in real engine representative fluid- dynamic conditions. Adiabatic effectiveness maps were obtained following the mass transfer analogy by the use of Pressure Sensitive Paint. In addition, a CFD campaign was performed in order to benchmark the reliability in estimating the cooling performance of effusion cooling liners. In order to include anisotropic diffusion effects, the k â Ï SST turbulence model was corrected considering a tensorial definition of the eddy viscosity with an algebraic correction to dope its stream-span components
The resonance triplet at E_alpha = 4.5 MeV in the 40Ca(alpha,gamma)44Ti reaction
The 40Ca(alpha,gamma)44Ti reaction is believed to be the main production
channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation
from decaying 44Ti has been observed so far for two supernova remnants, and a
precise knowledge of the 44Ti production rate may help improve supernova
models. The 40Ca(alpha,gamma)44Ti astrophysical reaction rate is determined by
a number of narrow resonances. Here, the resonance triplet at E_alpha = 4497,
4510, and 4523 keV is studied both by activation, using an underground
laboratory for the gamma counting, and by in-beam gamma spectrometry. The
target properties are determined by elastic recoil detection analysis and by
nuclear reactions. The strengths of the three resonances are determined to
omega gamma = (0.92+-0.20), (6.2+-0.5), and (1.32+-0.24) eV, respectively, a
factor of two more precise than before. The strengths of this resonance triplet
may be used in future works as a point of reference. In addition, the present
new data directly affect the astrophysical reaction rate at relatively high
temperatures, above 3.5 GK.Comment: 12 pages, 11 figures; submitted to Phys. Rev.
New direct measurement of the 10 B(p,α) 7 Be reaction with the activation technique
Boron plays an important role in astrophysics and, together with lithium and beryllium, is a probe of stellar structure during the pre-main sequence and main-sequence phases. In this context, the 10 B(p, α ) 7 Be reaction is of particular interest.The literature data show discrepancies in the energy range between 100 keV and 2 MeV. This also poses a normalization problem for indirect data obtained with the Trojan Horse Method.A new measurement of the 10 B(p, α ) 7 Be reaction cross section was performed at Legnaro National Laboratories (LNL). At LNL, the cross section was determined with the activation technique by measuring the activated samples at a low-background counting facility. The analysis of that experiment is now complete and the results are here presented
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
Resonance strengths in the 14N(p, \gamma)15O and 15N(p, \alpha \gamma)12C reactions
The 14N(p, \gamma)15O reaction is the slowest reaction of the
carbon-nitrogen-oxygen cycle of hydrogen burning in stars. As a consequence, it
determines the rate of the cycle. The 15N(p, \alpha \gamma)12C reaction is
frequently used in inverse kinematics for hydrogen depth profiling in
materials. The 14N(p, \gamma)15O and 15N(p, \alpha \gamma)12C reactions have
been studied simultaneously, using titanium nitride targets of natural isotopic
composition and a proton beam. The strengths of the resonances at Ep = 1058 keV
in 14N(p, \gamma)15O and at Ep = 897 and 430 keV in 15N(p, \alpha \gamma)12C
have been determined with improved precision, relative to the well-known
resonance at Ep = 278 keV in 14N(p, \gamma)15O. The new recommended values are
\omega \gamma = 0.3530.018, 36220, and 21.91.0 eV for their
respective strengths. In addition, the branching ratios for the decay of the Ep
= 1058 keV resonance in 14N(p, \gamma)15O have been redetermined. The data
reported here should facilitate future studies of off-resonant capture in the
14N(p, \gamma)15O reaction that are needed for an improved R-matrix
extrapolation of the cross section. In addition, the data on the 430 keV
resonance in 15N(p, \alpha \gamma)12C may be useful for hydrogen depth
profiling.Comment: 10 pages, 8 figures. Corrected typos in the abstract, table IV made
more comprehensible. As accepted in Phys.Rev.
First characterisation of natural radioactivity in building materials manufactured in Albania
This study focuses on the radiological characterisation of building materials manufactured in Albania by using a high-resolution gamma-ray spectrometer. The average activity concentrations of (40)K, (226)Ra and (232)Th were, respectively, 644.1±64.2, 33.4 ± 6.4 and 42.2 ± 7.6 Bq kg(-1) in the clay brick samples and 179.7 ± 48.9, 55.0 ± 5.8 and 17.0 ± 3.3 Bq kg(-1) in the cement samples. The calculated activity concentration index (ACI), varied from 0.48±0.02 to 0.63±0.04 in the clay brick samples and from 0.29±0.03 to 0.37±0.02 in the cement samples. Based on the ACI, all of the clay brick and cement samples were categorised as A1 materials. The authors can exclude (at 3Ï level) any restriction of their use as bulk materials