692 research outputs found
The reaction 13C(alpha,n)16O: a background for the observation of geo-neutrinos
The absolute cross section of the C(,n)O reaction has
been measured at E = 0.8 to 8.0 MeV with an overall accuracy of 4%.
The precision is needed to subtract reliably a background in the observation of
geo-neutrinos, e.g. in the KamLAND detector.Comment: LaTex file, 13 pages including 3 ps figures. Any request to
[email protected]. Phys. Rev . C, to appea
Study of the 12C+12C fusion reactions near the Gamow energy
The fusion reactions 12C(12C,a)20Ne and 12C(12C,p)23Na have been studied from
E = 2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultra-low
hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new
resonances at E <= 3.0 MeV, in particular a strong resonance at E = 2.14 MeV,
which lies at the high-energy tail of the Gamow peak. The resonance increases
the present non-resonant reaction rate of the alpha channel by a factor of 5
near T = 8x10^8 K. Due to the resonance structure, extrapolation to the Gamow
energy E_G = 1.5 MeV is quite uncertain. An experimental approach based on an
underground accelerator placed in a salt mine in combination with a high
efficiency detection setup could provide data over the full E_G energy range.Comment: 4 Pages, 4 figures, accepted for publication in Phys. Rev. Let
Time-dependent correlations in quantum magnets at finite temperature
In this article we investigate the time dependence of the gap mode of copper
nitrate at various temperatures. We combine state-of-the-art theoretical
calculations with high precision neutron resonance spin-echo measurements to
understand the anomalous decoherence effects found previously in this material.
It is shown that the time domain offers a complementary view on this
phenomenon, which allows us to directly compare experimental data and
theoretical predictions without the need of further intensive data analysis,
such as (de)convolution.Comment: 6 pages, 5 figure
Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas
We study the dependence of the CNO nuclear reaction rates on temperature, in
the range of K, the typical range of temperature evolution from
a Sun-like star towards a white dwarf. We show that the temperature dependence
of the CNO nuclear reaction rates is strongly affected by the presence of
non-extensive statistical effects in the dense stellar core. A very small
deviation from the Maxwell-Boltzmann particle distribution implies a relevant
enhancement of the CNO reaction rate and could explain the presence of heavier
elements (e.g. Fe, Mg) in the final composition of a white dwarf core. Such a
behavior is consistent with the recent experimental upper limit to the fraction
of energy that the Sun produces via the CNO fusion cycle.Comment: Presented at NEXT2003 (Second International Conference on "News and
Expectations in Thermostatistics"), Villasimius (Cagliari)- Italy in 21-28
September 2003. 7 pages including 3 figure
Two important cotton diseases and their control
The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-6311
Correspondence between W. J. Kerr, A. E. Stene, F. M. Rolfs, L. H. Bailey, and Charles F. Curtiss
Correspondence concerning a position in Horticulture Botany at Utah Agricultural College
Nuclear masses, deformations and shell effects
We show that the Liquid Drop Model is best suited to describe the masses of
prolate deformed nuclei than of spherical nuclei. To this end three Liquid Drop
Mass formulas are employed to describe nuclear masses of eight sets of nuclei
with similar quadrupole deformations. It is shown that they are able to fit the
measured masses of prolate deformed nuclei with an RMS smaller than 750 keV,
while for the spherical nuclei the RMS is, in the three cases, larger than 2000
keV. The RMS of the best fit of the masses of semi-magic nuclei is also larger
than 2000 keV. The parameters of the three models are studied, showing that the
surface symmetry term is the one which varies the most from one group of nuclei
to another. In one model, isospin dependent terms are also found to exhibit
strong changes. The inclusion of shell effects allows for better fits, which
continue to be better in the prolate deformed nuclei regionComment: 10 pages, 8 tables, Proc. of the XXXIV Nuclear Physics Symposium,
January 4-7 2011, Cocoyoc, Morelos, Mexico. IOP Journal of Physics:
Conference Series (in press
Microscopic mass estimations
The quest to build a mass formula which have in it the most relevant
microscopic contributions is analyzed. Inspired in the successful Duflo-Zuker
mass description, the challenges to describe the shell closures in a more
transparent but equally powerful formalism are discussed.Comment: 14 pages, 6 figures, submitted to Journal of Physics G, Focus issue
on Open Problems in Nuclear Structure Theor
Luttinger-Liquid Behavior in the Alternating Spin-Chain System Copper Nitrate
We determine the phase diagram of copper nitrate Cu(NO)2.5DO
in the context of quantum phase transitions and novel states of matter. We
establish this compound as an ideal candidate to study quasi-1D Luttinger
liquids, 3D Bose-Einstein-Condensation of triplons, and the crossover between
1D and 3D physics. Magnetocaloric effect, magnetization, and neutron scattering
data provide clear evidence for transitions into a Luttinger liquid regime and
a 3D long-range ordered phase as function of field and temperature. Theoretical
simulations of this model material allow us to fully establish the phase
diagram and to discuss it in the context of dimerized spin systems.Comment: 5 pages, 4 figure
Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy
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
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