568 research outputs found
Imaginary-time method for radiative capture reaction rate
We propose a new computational method for astrophysical reaction rate of
radiative capture process. In the method, an evolution of a wave function is
calculated along the imaginary-time axis which is identified as the inverse
temperature. It enables direct evaluation of reaction rate as a function of
temperature without solving any scattering problem. The method is tested for
two-body radiative capture reaction, , showing that it gives identical results to that calculated by the
ordinary procedure. The new method will be suited for calculation of
triple-alpha radiative capture rate for which an explicit construction of the
scattering solution is difficult.Comment: 8 pages, 7 figure
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
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
Energy Loss, Electron Screening, and the Astrophysical 3He(d,p)4He cross section
We reanalyze the low-energy 3He(d,p)4He cross section measurements of
Engstler et al. using recently measured energy loss data for proton and
deuteron beams in a helium gas. Although the new 3He(d,p)4He S-factors are
significantly lower than those reported by Engstler et al. they clearly show
the presence of electron screening effects. From the new S-factors we find an
electron screening energy in agreement with the adiabatic limit.Comment: 8 Page RevTeX document, two postscript figures, now in a
self-extracting uufile type archiv
Functional Characterisation of Alpha-Galactosidase A Mutations as a Basis for a New Classification System in Fabry Disease
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.The study has been supported partially by an unrestricted scientific grant from Shire Human Genetic Therapies (Germany
Large-scale prediction of the parity distribution in the nuclear level density and application to astrophysical reaction rates
A generalized method to calculate the excitation-energy dependent parity
ratio in the nuclear level density is presented, using the assumption of
Poisson distributed independent quasi particles combined with BCS occupation
numbers. It is found that it is crucial to employ a sufficiently large model
space to allow excitations both from low-lying shells and to higher shells
beyond a single major shell. Parity ratios are only found to equilibrate above
at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect
close to major shells is found where the parity opposite to the ground state
parity may dominate across a range of several MeV before the parity ratio
finally equilibrates. The method is suited for large-scale calculations as
needed, for example, in astrophysical applications. Parity distributions were
computed for all nuclei from the proton dripline to the neutron dripline and
from Ne up to Bi. These results were then used to recalculate astrophysical
reaction rates in a Hauser-Feshbach statistical model. Although certain
transitions can be considerably enhanced or suppressed, the impact on
astrophysically relevant reactions remains limited, mainly due to the thermal
population of target states in stellar reaction rates.Comment: 15 pages, 17 figures; corrected/updated references in v2; additional
material can be found at http://nucastro.org/adndt.html#parit
Coulomb dissociation of 9Li and the rate of the 8Li(n,g)9Li reaction
We calculate the Coulomb dissociation of 9Li on Pb and U targets at 28.5
MeV/A beam energy within a finite range distorted wave Born approximation
formalism of the breakup reactions. Invoking the principle of detailed balance,
these cross sections are used to determine the excitation function and
subsequently the rate of the radiative capture reaction 8Li(n,g)9Li at
astrophysical energies. Our method is free from the uncertainties associated
with the multipole strength distributions of the 9Li nucleus. The rate of this
reaction at a temperature of 10^9K is found to be about 2900 cm^3 mole^{-1}
s^{-1}.Comment: 13 pages Revtex, 2 figures, title and abstract changed on referee's
suggestions, figures modified and discussions extended, results remain the
same; version to appear in Phys. Rev.
Atomic effects in astrophysical nuclear reactions
Two models are presented for the description of the electron screening
effects that appear in laboratory nuclear reactions at astrophysical energies.
The two-electron screening energy of the first model agrees very well with the
recent LUNA experimental result for the break-up reaction , which so far defies all available theoretical models.
Moreover, multi-electron effects that enhance laboratory reactions of the CNO
cycle and other advanced nuclear burning stages, are also studied by means of
the Thomas-Fermi model, deriving analytical formulae that establish a lower and
upper limit for the associated screening energy. The results of the second
model, which show a very satisfactory compatibility with the adiabatic
approximation ones, are expected to be particularly useful in future
experiments for a more accurate determination of the CNO astrophysical factors.Comment: 14 RevTex pages + 2 ps (revised) figures. Phys.Rev.C (in production
Enhancement of the Deuteron-Fusion Reactions in Metals and its Experimental Implications
Recent measurements of the reaction d(d,p)t in metallic environments at very
low energies performed by different experimental groups point to an enhanced
electron screening effect. However, the resulting screening energies differ
strongly for divers host metals and different experiments. Here, we present new
experimental results and investigations of interfering processes in the
irradiated targets. These measurements inside metals set special challenges and
pitfalls which make them and the data analysis particularly error-prone. There
are multi-parameter collateral effects which are crucial for the correct
interpretation of the observed experimental yields. They mainly originate from
target surface contaminations due to residual gases in the vacuum as well as
from inhomogeneities and instabilities in the deuteron density distribution in
the targets. In order to address these problems an improved differential
analysis method beyond the standard procedures has been implemented. Profound
scrutiny of the other experiments demonstrates that the observed unusual
changes in the reaction yields are mainly due to deuteron density dynamics
simulating the alleged screening energy values. The experimental results are
compared with different theoretical models of the electron screening in metals.
The Debye-H\"{u}ckel model that has been previously proposed to explain the
influence of the electron screening on both nuclear reactions and radioactive
decays could be clearly excluded.Comment: 22 pages, 12 figures, REVTeX4, 2-column format. Submitted to Phys.
Rev. C; accepte
Nuclear masses set bounds on quantum chaos
It has been suggested that chaotic motion inside the nucleus may
significantly limit the accuracy with which nuclear masses can be calculated.
Using a power spectrum analysis we show that the inclusion of additional
physical contributions in mass calculations, through many-body interactions or
local information, removes the chaotic signal in the discrepancies between
calculated and measured masses. Furthermore, a systematic application of global
mass formulas and of a set of relationships among neighboring nuclei to more
than 2000 nuclear masses allows to set an unambiguous upper bound for the
average errors in calculated masses which turn out to be almost an order of
magnitude smaller than estimated chaotic components.Comment: 4 pages, Accepted for publication in Physical Review Letter
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