68 research outputs found
Longitudinal response functions of 3H and 3He
Trinucleon longitudinal response functions R_L(q,omega) are calculated for q
values up to 500 MeV/c. These are the first calculations beyond the threshold
region in which both three-nucleon (3N) and Coulomb forces are fully included.
We employ two realistic NN potentials (configuration space BonnA, AV18) and two
3N potentials (UrbanaIX, Tucson-Melbourne). Complete final state interactions
are taken into account via the Lorentz integral transform technique. We study
relativistic corrections arising from first order corrections to the nuclear
charge operator. In addition the reference frame dependence due to our
non-relativistic framework is investigated. For q less equal 350 MeV/c we find
a 3N force effect between 5 and 15 %, while the dependence on other theoretical
ingredients is small. At q greater equal 400 MeV/c relativistic corrections to
the charge operator and effects of frame dependence, especially for large
omega, become more important. In comparison with experimental data there is
generally a rather good agreement. Exceptions are the responses at excitation
energies close to threshold, where there exists a large discrepancy with
experiment at higher q. Concerning the effect of 3N forces there are a few
cases, in particular for the R_L of 3He, where one finds a much improved
agreement with experiment if 3N forces are included.Comment: 26 pages, 9 figure
Benchmark Calculation of the Three-Nucleon Photodisintegration
A benchmark is set on the three-nucleon photodisintegration calculating the total cross section with modern realistic two- and three-nucleon forces (AV18, UrbIX) using both the Faddeev equations and the Lorentz Integral Transform method. This test shows that the precision of three-body calculations involving continuum states is considerably higher than experimental uncertainties. Effects due to retardations, higher multipoles, meson exchange currents and Coulomb force are studied
Is there a Pronounced Giant Dipole Resonance in ^4He?
A four-nucleon calculation of the total ^4He photodisintegration cross
section is performed. The full final-state interaction is taken into account
for the first time. This is achieved via the method of the Lorentz integral
transform. Semi-realistic NN interactions are employed. Different from the
known partial two-body ^4He(\gamma,n)^3He and ^4He(\gamma,p)^3H cross sections
our total cross section exhibits a pronounced giant resonance. Thus, in
contrast to older data, we predict quite a strong contribution of
the channel at the giant resonance peak energy.Comment: 10 pages, Latex (REVTEX), 4 Postscript figures, to appear in Phys.
Rev. Let
Nuclear muon capture by 3He: meson exchange currents for the triton channel
Exchange current corrections are calculated using currents found from the
hard-pion model and AV14+3BF wavefunctions. Results are given for the rate and
spin observables. Their sensitivity to g_P, the nucleon pseudoscalar form
factor, is reported.Comment: 35 pages, uuencoded gz-compressed tar file 42 Kbyte
On the Accuracy of Hyperspherical Harmonics Approaches to Photonuclear Reactions
Using the Lorentz Integral Transform (LIT) method we compare the results for
the triton total photodisintegration cross section obtained using the
Correlated Hyperspherical Harmonics (CHH) and the Effective Interaction
Hyperspherical Harmonics (EIHH) techniques. We show that these two approaches,
while rather different both conceptually and computationally, lead to results
which coincide within high accuracy. The calculations which include two- and
three-body forces are of the same high quality in both cases. We also discuss
the comparison of the two approaches in terms of computational efficiency.
These results are of major importance in view of applications to the much
debated case of the four-nucleon photoabsorption.Comment: 12 pages, 3 figure
Higher-Order Nuclear-Polarizability Corrections in Atomic Hydrogen
Nuclear-polarizability corrections that go beyond unretarded-dipole
approximation are calculated analytically for hydrogenic (atomic) S-states.
These retardation corrections are evaluated numerically for deuterium and
contribute -0.68 kHz, for a total polarization correction of 18.58(7) kHz. Our
results are in agreement with one previous numerical calculation, and the
retardation corrections completely account for the difference between two
previous calculations. The uncertainty in the deuterium polarizability
correction is substantially reduced. At the level of 0.01 kHz for deuterium,
only three primary nuclear observables contribute: the electric polarizability,
, the paramagnetic susceptibility, , and the third Zemach
moment, . Cartesian multipole decomposition of the virtual
Compton amplitude and its concomitant gauge sum rules are used in the analysis.Comment: 26 pages, latex, 1 figure -- Submitted to Phys. Rev. C -- epsfig.sty
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Electromagnetic response functions of few-nucleon systems
Inclusive electromagnetic reactions in few-nucleon systems are studied basing
on accurate three- and four-body calculations. The longitudinal 4He(e,e')
response function obtained at q\le 600 MeV/c completely agrees with experiment.
The exact 4He spectral function obtained in a semirealistic potential model is
presented, and the accuracy of the quasielastic response calculated with its
help is assessed, as well as the accuracy of some simpler approximations for
the response. The photodisintegration cross section of 3He obtained with the
realistic AV14 NN force plus UrbanaVIII NNN force agrees with experiment. It is
shown that this cross section is very sensitive to underlying nuclear dynamics
in the E_\gamma\simeq 70-100 MeV region. In particular, the NNN nuclear force
clearly manifests itself in this region.Comment: 10 pages, Latex, style file is included, 7 ps figures, to appear in
Proc. of the 2nd Int. Conf. on Perspectives in Hadronic Physics, ITCP,
Triest, May 1999, World Sci., Singapor
Threshold 3He and 3H Transverse Electron Scattering Response Functions
The threshold transverse response functions R_T(q,omega) for 3He and 3H are
calculated using the AV18 nucleon-nucleon potential, the UrbanaIX three-body
force, and the Coulomb potential. Final states are completely taken into
account via the Lorentz integral transform technique. Consistent two-body pi-
and rho-meson exchange currents as deduced using the Arenh\"ovel-Schwamb
technique are included. The convergence of the method is shown and a comparison
of the corresponding MEC contribution is made to that of a consistent MEC for
the meson theoretical r-space BonnA potential. The response R_T is calculated
in the threshold region at q=174, 324, and 487 MeV/c and compared with
available data. The strong MEC contributions in the threshold region are nicely
confirmed by the data at q=324 and 487 MeV/c although some differences between
theoretical and experimental results remain. A comparison is also made with
other calculations, where the same theoretical input is used. The agreement is
generally rather good, but leaves also some space for further improvement.Comment: 16 pages, 5 figure
No systematic effects of sampling direction on climate-growth relationships in a large-scale, multi-species tree-ring data set
Ring-width series are important for diverse fields of research such as the study of past climate, forest ecology, forest genetics, and the determination of origin (dendro-provenancing) or dating of archaeological objects. Recent research suggests diverging climate-growth relationships in tree-rings due to the cardinal direction of extracting the tree cores (i.e. direction-specific effect). This presents an understudied source of bias that potentially affects many data sets in tree-ring research. In this study, we investigated possible direction-specific growth variability based on an international (10 countries), multi-species (8 species) tree-ring width network encompassing 22 sites. To estimate the effect of direction-specific growth variability on climate-growth relationships, we applied a combination of three methods: An analysis of signal strength differences, a Principal Component Gradient Analysis and a test on the direction-specific differences in correlations between indexed ring-widths series and climate variables. We found no evidence for systematic direction-specific effects on tree radial growth variability in high-pass filtered ring-width series. In addition, direction-specific growth showed only marginal effects on climate-growth correlations. These findings therefore indicate that there is no consistent bias caused by coring direction in data sets used for diverse dendrochronological applications on relatively mesic sites within forests in flat terrain, as were studied here. However, in extremely dry, warm or cold environments, or on steep slopes, and for different life-forms such as shrubs, further research is advisable.</p
Impact of meteorological factors on the radial growth of Weymouth pine growing on the Rybnik Plateau
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