共查询到20条相似文献,搜索用时 15 毫秒
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Ever since it was proposed more than three decades ago, the nuclear optical model has been very successful in interpreting
a large body of nucleon-induced nuclear reaction data in terms of a complex nucleon-nucleus potential. Rapid progress both
in the experimental measurements and the theoretical developments in the last two decades has led to a better understanding
of this nucleon-nucleus optical potential. From the parameter-fitting phenomenological stage, the optical model has come a
long way and it is now possible to calculate the nucleon-nucleus optical potential in a reasonable way starting from the fundamental
nucleon-nucleon interaction. Excellent reviews on various aspects of the optical model exist in the literature for proton
energies above 10 MeV. The present article is an attempt to review comprehensively the status of the proton-nucleus optical
potential at low proton energies, below the Coulomb-barrier, for target nuclei with mass numbers lying between 40 and 130.
The sets of phenomenological optical potential derived mostly from (p, n) reaction data are reviewed and their applicabilities discussed. The neutron-nucleus optical model is referred to wherever
it is relevant. Microscopic calculations for one case is carried out and compared with the corresponding phenomenological
values. 相似文献
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All presently available experimental data on deuteron photodisintegration below 40 MeV (i.e., total and differential cross sections, photon asymmetry and neutron polarization) are collected and carefully compared with the present status of the conventional theory (i.e., in the framework of mesontheoretical or semi-phenomenologicalN-N potentials including subnuclear degrees of freedom and relativistic corrections). No significant evidence for a failure of the conventional theory is found within the present experimental accuracy.Partially supported by the Deutsche Forschungsgemeinschaft (SFB 201) 相似文献
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Recent experimental data obtained by the OBELIX collaboration on ˉpD and ˉp4 He total annihilation cross sections are analyzed. The combined analysis of these data with existing antiprotonic atom data
allows, for the first time, the imaginary parts of the S-wave scattering lengths for the two nuclei to be extracted.
The obtained values are: Im asc
0= [−0.62 ± 0.02 stat) ± 0.04 (sys)] fm for ˉpD and Im asc
0= [−0.36 ± 0.03 (stat)+0.19
−0.11 (sys)] fm for ˉp 4He. This analysis indicates an unexpected behaviour of the imaginary part of the ˉp-nucleus S-wave scattering length as a
function of the atomic weight A:
|Im asc
0| (macr;pp) > |Im asc
0| (ˉpD) > |Im asc
0 (ˉp4 He).
Received: 3 November 1999 / Revised version: 15 December 1999 相似文献
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H. Gao 《The European physical journal. Special topics》2011,198(1):3-17
Understanding how quantum chromodynamics, the theory of strong interaction, works in the low-energy region, the so-called
confinement region is one of the major challenges facing physicists. Low energy hadron physics, particularly the structure
of hadron is one of the most active areas of research in nuclear physics addressing this challenge. In this talk, I will review
advances made in this area on a few selected topics in the last decade or so and also provide outlook for the future. 相似文献
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Neil Rowley 《Pramana》1999,53(3):495-504
Through precision measurements of fusion cross sections at energies close to the Coulomb barrier and through the application
of the method of “experimental barrier distributions” which these permit, many recent advances have been made in our understanding
of the dynamical processes occurring during a heavy-ion collision. It is now clear that the target and projectile reach one
another in superpositions of states which correspond to different orientations for rotational nuclei or to different induced
deformations for vibrational nuclei. The creation of a neck of neutron matter has also long been postulated and by studying
the isotopic dependence of the fusion reaction, some recent results in the 10Ca+90,96Zr systems appear to confirm this result. For large Z
1
Z
2 a type of extra-push effect can arise from the same inelastic entrance-channel effects which enhance the fusion of lighter
systems, though this will be absent in cases where the enhancement arises from neutron transfers.
The existence of different barriers will of course influence all other reaction channels. Fusion simply allows one to visualise
the barriers most easily, since for this process, the total cross section is an incoherent sum of the contributions from all relevant eigenchannels. Some effects in other channels have already been observed. Other
possible effects will be discussed. These include; the exploitation of the lowest-energy barrier to produce exotic evaporation
residues and strongly deformed high-spin states at low excitation energy. 相似文献
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H. Leutwyler 《Czechoslovak Journal of Physics》2002,52(2):B9-B27
The lectures review some of the basic concepts relevant for an understanding of the low energy properties of the strong interactions: chiral symmetry, spontaneous symmetry breakdown, Goldstone bosons, quark condensate. The effective field theory used to analyze the low energy structure is briefly sketched. As an illustration, I discuss the implications of the recent data on the decay K→ππeν for the magnitude of the quark condensate. 相似文献
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The main cause of loss of trapped AH is due to collisions with H2 and He. As a first step towards treating these reactions we are studying the interaction of AH with H. We have carried out
variational calculations to determine an upper bound to the smallest internuclear distance at which the light particles are
still bound to the nuclei. We are currently in the process of taking into account the motion of the nuclei. This will enable
us to calculate cross-sections for low energy H-AH scattering.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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H. H. Brouwer J. W. de Maag L. P. Kok 《Zeitschrift für Physik A Hadrons and Nuclei》1984,318(2):199-204
We consider a simple coupled-channel model for the¯KN system at low energies. For the strong interaction separable potentials are used. The Coulomb potential is included rigorously. The model is completely solvable. Our results suggest that a slight reinterpretation of the measured spectra will solve the existing discrepancy between boundstate data and scattering data. 相似文献
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Gravitational scattering in the ADD model is considered at both sub- and transplanckian energies using a common formalism.
By keeping a physical cut-off in the KK tower associated with virtual KK exchange, such as the cut-off implied by a finite
brane width, troublesome divergences are removed from the calculations in both energy ranges. The scattering behavior depends
on three different energy scales: the fundamental Planck mass, the collision energy and the inverse brane width. The result
for energies low compared to the effective cut-off (inverse brane width) is a contact-like interaction. At high energies the
gravitational scattering associated with the extra dimensional version of Newton’s law is recovered. 相似文献
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The cross sections for neutron inelastic scattering by niobium at 20 MeV and for the charge-exchange (p,n) reaction on copper at 27 MeV have been calculated using the multistep direct reaction theory of Feshbach, Kerman and Koonin [1]. The theory was modified to include the non-DWBA matrix elements and the collective vibrations. The results show enhanced contributions from two-, three- and four-step direct reactions in agreement with experiment. 相似文献
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We complete the analysis of meson resonance contributions to chiral low-energy constants of O(p4) by including all quark–antiquark bound states with orbital angular momentum ≤1. Different tensor meson Lagrangians used
in previous work are shown to produce the same final results for the low-energy constants, once QCD short-distance constraints
are properly implemented. We also discuss the possible relevance of axial-vector mesons with odd C-parity (JPC=1+-). 相似文献
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Acta physica Academiae Scientiarum Hungaricae - The cluster transfer processes below the Coulomb barrier are investigated for arbitrary charges and angular momentum transfer, taking into account... 相似文献
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P.H. Dawson 《Surface science》1976,57(1):229-240
The adsorption of oxygen by aluminum was studied using secondary ion mass spectrometry at low primary ion energies (? 500 eV) and low primary ion fluxes (? 5 × 1010ions/cm2/sec) in an ultrahigh vacuum system. The SIMS characteristics of a cleaned aluminum surface were measured and yield changes of positive and negative ions were measured as a function of oxygen exposure. The results strongly support a model of oxygen uptake in two stages, the first monolayer equivalent being mostly incorporated into the aluminum, probably in the second layer and the next half-monolayer equivalent being superficially chemisorbed. Selection of the correct model is important in calculations of the resonances in the electronic (valence band) structure of free-electron-like metals caused by oxygen adsorption. 相似文献
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Granados Carlos Leupold Stefan Perotti Elisabetta 《The European Physical Journal A - Hadrons and Nuclei》2017,53(6):1-82
The European Physical Journal A - The experimental hadronic physics programme at the COoler SYnchrotron of the Forschungszentrum Jülich terminated at the end of 2014. After describing the... 相似文献