Evidence for boson-mode excitations in the16O(α,n) and20Ne(α,n) excitation functions

Excitation functions for¹⁶O(α,n) and²⁰Ne(α,n) have been measured from threshold to 26 and 31 MeV compound excitation energy, respectively. The dominating compound states are interpreted as boson excitation modes of nuclei with α-particle structure.     

On the computation of molecular auxiliary functions A n and B n

Molecular auxiliary functions A _n (p) and B _n (pt), arising in the Hartree-Fock-Roothaan (HFR) approximation for molecules, Ewald’s crystal lattice theory, electromagnetic stopping theory, and other approximate methods, are evaluated and analysed in the range of 17≤n≤60 and 25≤pt≤60.     

Influence of shell structure and pairing correlations on the nuclear state density

A microscopic calculation of nuclear state densities was performed starting from realistic single-particle levels. Within this concept, a correspondence between microscopic ground state energy corrections and microscopic effects on state densities was deduced. It is shown that the approximations introduced by a simple analytical expression for the nuclear state density are comparable to the uncertainties of microscopically calculated state densities for nuclei in their ground state configuration. Guidelines for the determination of the parameters of this analytical expression were deduced from the microscopic computations.     

Effect of the Fermi motion on nuclear structure functions and the EMC effect

The effect of the Fermi motion on nuclear structure function at largeQ ² (the EMC effect) is discussed in detail. We especially study its dependences on the kinematics of interaction, the 4-momentum transferQ ², the nucleon momentum distribution inside nucleus and the nuclear mass number. Moreover the structure function of¹²C at very largex such asx>1 is evaluated by only the nuclear Fermi motion, and related problems are discussed. We also point out a new dynamical mechanism expected to produce the depletion of valence quark inside nucleus for intermediatex, which does not encroach upon the conventional nuclear physics, and discuss it along the line of scaling hypothesis proposed by Daté et al.     

物质结构在夸克-轻子层次上的动力学规律和研究发展趋势

文章综述了粒子物理中标准模型理论的历史发展、面临挑战以及未来的发展趋势.目前阶段物质结构最小组成单元是夸克和轻子,量子色动力学是描述夸克-胶子之间强相互作用的基本理论,它具有渐近自由和夸克禁闭的特点.量子色动力学和电弱统一理论一起构成粒子物理中标准模型理论.标准模型理论成功同时也面临两大挑战:对称性破缺的本质和夸克禁闭难题,这意味着标准模型理论需要发展和突破.人们期望粒子物理学、天文学和宇宙学交叉发展联手解决物质结构和早期宇宙研究中面临的难题,最终揭示超出标准模型的新物理规律.     

An experimental test on parity violation in nuclear forces studied in113Cd (n, γ)

An oriented compound-state in¹¹⁴Cd was obtained by capture of polarized thermal neutrons. The asymmetry coefficientA in the angular distribution ofγ-rays (8.1–9.5 MeV) was measured to (1.2±1.2) 10^?4, indicating no violation of parity in nuclear forces.     

Theory for the ultrafast dynamics of excited clusters: interplay between elementary excitations and atomic structure

We present a theoretical study of the short-time relaxation of clusters in response to ultrafast excitations using femtosecond laser pulses. We analyze the excitation of different types of clusters (Hg_n, Ag_n, Si_n, C₆₀ and Xe_n) and classify the relaxation dynamics in three different regimes, depending on the intensity of the exciting laser pulse. For low-intensity pulses (I<10¹² W/cm²) we determine the time-dependent structural changes of clusters upon ultrashort ionization and photodetachment. We also study the laser-induced non-equilibrium fragmentation and melting of Si_n and C₆₀ clusters, which occurs for moderate laser intensities, as a function of the pulse duration and energy. As an example for the case of high intensities (I>10¹⁵ W/cm²), the explosion of clusters under the action of very intense ultrashort laser fields is described. Received: 26 November 1999 / Published online: 2 August 2000     

New data on nuclear subshells obtained from the analysis of the information from the international database on nuclear structure ENSDF

In the last decade, a large amount of experimental nuclear spectroscopy data was obtained. This is good progress really, but a new very serious problem appears. Due to significant systematic errors of the data, one is often forced to deal with very discrepant data and often it is difficult to obtain reliable information from them. To solve this problem and to remove the systematic errors, new technologies in working with the data were developed. Using these new technologies, one can obtain information with a high accuracy and reliability, and in many cases, new information has not been or could not be obtained experimentally. Below, an approach of this kind is presented concerning spectroscopic data on Ca and Zr isotopes. It is shown that the behavior of the energy of the first 2⁺ level in Zr isotopes can be explained in the framework of a shell-model approach. A separation of the 2d_5/2 subshell in ⁹⁶Zr (as is for the 1f_7/2 subshell in ⁴⁸Ca) is found, so that the neutron number N=56 becomes like a magic number for Z=40. To explain a similarity in decaying properties of ⁴⁸Ca and ⁹⁶Zr, an additional interaction between closed structures consisting of 20 and 28 nucleons is proposed. Irregularities of the ground-state spin values in the K isotopic chain are explained in the framework of the shell-model approach by the inversion of the proton 1d_3/2 and 2s_1/2 orbitals.     

K(m,n)方程与B(m,n)方程的无穷序列新精确解

进一步研究了辅助方程法,给出了几种常用辅助方程的新解、B(a|¨)cklund变换和解的非线性叠加公式.在此基础上,根据m和n的不同情况,利用变换和直接积分相结合的方法,获得了K(m,n)方程与B(m,n)方程的无穷序列新精确解.这里包括无穷序列光滑孤立子解、无穷序列尖峰孤立子解和无穷序列紧孤立子解.     

Study of nuclear effects in nucleon structure functions up to and beyond the kinematic limit

An experiment on deep inelastic muon nucleon scattering in order to study the x-dependence of nucleon structure functions and their ratios over a range ofQ ²=50–200 GeV² andx= =0·4–2·0 is proposed. Such measurements performed on a number of nuclei with atomic weights from 2 to 207 provide new information for detailed studies of the EMC effect and test models explaining thex-behaviour of the nucleon structure functions and their ratios. The measurements are decisive for the proof that a quark-parton model of the nucleus describes adequately nuclear structure probed at high energies. The upgraded high luminosity BCDMS spectrometer with improved resolution in transferred energy can be used for the measurements.Dedicated to the 30th anniversary of the Joint Institute for Nuclear Research.     

Nonlinear localization of excitations and the dynamics of solitons in self-modulated systems

The nonlinear dynamics of systems with a spatially periodic ground state was studied. The dynamics of kinks against the background of a periodic soliton structure was considered for the example of the sine-Klein-Gordon model that described a fluxon lattice in a long Josephson contact in an external magnetic field and an incommensurate structure of a surface atomic layer or adatom chains on the surface of a crystal. The velocity of moving kinks was shown to be bounded from above and from below if the ground state was spatially periodic.     

Some new leaf normal-angle distribution models and their influence on geometry functions and area scattering phase functions related to radiative transfer problems in vegetative canopies

This note is devoted to the study of some new analytic leaf angle distribution models by a linear combination of idealized models primarily developed to study realistic light scattering processes for radiative transfer in a vegetative canopy medium.