共查询到20条相似文献,搜索用时 0 毫秒
1.
Reiner Neuhausen 《Nuclear Physics A》1977,282(1):125-152
The inelastic electron scattering cross sections for the quadrupole transitions to the 21+ and 22+ states in the even Zn isotopes 64Zn, 66Zn and 68Zn and for the hexadecapole transition to the 4+1 state in 64Zn have been measured in a momentum transfer range up to q = 2.2 fm?1. In the frame-work of the vibrational model these states are considered as one- and two-quadrupole-phonon states. The measurements are characterized by high statistical accuracy and by an overall resolution of δE/E0 = 10?3 which permitted separation of almost all members of the two-phonon triplet. The measured cross sections are analyzed with phenomenological models as well as with a Fourier-Bessel expansion of the transition charge density. The latter analysis yields realistic error bands for the transition charge densities and model-independent values for the reduced transition probabilities and transition radii. 相似文献
2.
The effect of two-body nature of the nuclear shell model potential on the recent numerical calculations of the nucleai level
density has been examined. For the two most widely used single particle energy level schemes based on harmonic oscillator
and Woods-Saxon potential, this effect is shown to significantly modify the excitation energy dependence of the level densisties. 相似文献
3.
A new method to calculate level densities for non-interacting Fermions within the constant-spacing model with a finite number of states is developed. We show that asymptotically (for large numbers of particles or holes) the densities have Gaussian form. We improve on the Gaussian distribution by using analytical expressions for moments higher than the second. Comparison with numerical results shows that the resulting sixth-moment approximation is excellent except near the boundaries of the spectra and works globally for all particle/hole numbers and all excitation energies. 相似文献
4.
The Hill-Wheeler equation is used to derive a collective Hamiltonian from an energy surface. Two simple ansatz are proposed for the collective Hamiltonian, which is then calculated explicitly in a hierarchy of approximations. The consistency of the method is verified in an illustrative example. 相似文献
5.
The particle-X-ray coincidence method is applied in (p, p0) and (p, p′) reactions on 112 Sn at 7.138, 10 and 12 MeV proton energy to measure the width of compound nuclear states in 113Sb. The united-atom K X-ray intensities observed in coincidence with inelastic proton scattering (35+78?35, 80 ± 50 and 250 ± 80 counts at the respective energies) yield mean level widths for 113Sb of ?3.9 eV, 16.6 ± 15.1 eV, and 19.1 ± 11.1 eV at the excitation energies 10.1, 13 and 15 MeV, respectively. From X-ray coincidences with elastic proton scattering, upper limits for the compound elastic component are derived. No united-atom X-rays were detected in short runs at 7 MeV on 92Mo and 106Cd. A comparison of nuclear state widths from X-ray method, crystal blocking technique and fluctuation averaging is given. 相似文献
6.
Giant resonances are understood as superposition of particle-hole excitations. The empirical systematics indicates that the associated spreading widths are considerably smaller than the sum of typical widths of single-particle and single-hole states, and that the centroid energy is in good agreement with the RPA predictions. These results imply a destructive interference between the different contributions to the mass operator associated with collective vibrations. We study the properties of the mechanism responsible for this quenching by inspecting contributions to the mass operator in the semiclassical limit of large single-particle angular momenta. 相似文献
7.
The Inglis cranking model is generalized to take into account effects of any velocity dependence present in the single-particle potential and the reaction of the pairing field to the collective motion. The generalized model is applied to translations, rotations and some special types of vibrations. Some of our results and our numerical calculations are obtained with a harmonic-oscillator single-particle potential. Unlike the inertia calculated with the Inglis cranking model, the inertia calculated with the generalized cranking model is independent of the effective mass and approaches the irrotational value in the limit of large pairing. 相似文献
8.
J. Broeckhove E. Kesteloot P. Van Leuven 《Zeitschrift für Physik A Hadrons and Nuclei》1988,331(3):255-264
Coherent state dynamics is used to study the time evolution of the quadrupole parameters and to determine the energy spectrum for the two dimensional analogue of the Elliott rotational model. The results are compared in great detail to the exact Schrödinger dynamics. 相似文献
9.
10.
H. Reinhardt 《Nuclear Physics A》1978,298(1):77-92
By using path integral techniques nuclear field theory (NFT) is developed for Fermi systems interacting via a general two-body force. The NFT Lagrangian is strictly derived. As a by-product, the corresponding graphical rules are obtained. The relation between the NFT and the conventional Feynman diagrammatic many-body perturbation theory is established for processes connecting initial and final states, too. 相似文献
11.
A new method is used to analyze recent experiments on electron scattering on 3He in the high momentum transfer region. The accuracy of the new measurements is very high so that the charge density can be determined with much higher accuracy than before. We find that further reduction of the error in charge density can only be achieved by a more accurate measurement of the region 3 < q < 6 fm?1. Continuing the previous work of Hetherington and Borysowicz, a very useful approximate relation is derived between the error of charge density and the error of measurements of form factor. We find that linear expansion methods lead to similar results as the present method. They require, however, stronger asymptotic assumptions about ?(r). 相似文献
12.
The propagation of single-particle and small-amplitude collective excitations in a heavy nucleus is considered. We calculate perturbatively corrections to the mean-field approximation induced by the coupling of one-particle and collective motion via the residual particle-hole interaction. Special attention is paid to the energy variation of the quasiparticle effective mass near Fermi energy. We conclude from the calculation that particles and holes excited in low multipolarity giant resonances have average effective masses of the order of 0.8 m rather than m. The mechanism for the decrease is provided by the enforced decoupling of the quasiparticles from surface oscillations due to the high frequency of the giant resonances. We also study the role of surface modes in the decay of giant resonances. Considerable reduction of the damping into 2p-2h states expected from the absorptive part of the optical potential is found. The correlated particle-hole pairs interact with each other by exchanging surface oscillations which adds a destructive interference term to the decay widths of giant resonances. The reduction depends on the multipolarity of the mode and is only large for low angular momenta. 相似文献
13.
Thomas D. Cohen 《Nuclear Physics A》1984,431(1):45-74
The time-dependent variation principle is used to obtain generally non-canonical equations of motion from any class of quantum states which are parameterized by a set of continuous complex quantities. A class of states is presented whose associated classical dynamics is described by the five collective quadrupole degrees of freedom. Information about the classical dynamics of the system can be obtained from the non-canonical equations by finding physically interesting quantities which are coordinate independent and which characterize the low-energy collective motion. Approximate collective hamiltonians, of either a Bohr-Mottelson or an IBM type, can be found by insisting that the interesting physical quantities which describe the low-energy classical behavior of the many-body system are the same as those describing the classical behavior of the system given by the collective hamiltonian. The method is applied to two simple schematic models, one vibrational and one rotational, and IBM hamiltonians are obtained. 相似文献
14.
S. Ayik 《Nuclear Physics A》1981,370(2):317-328
The dissipation mechanism in slow nuclear collective motion is studied in the frame of the extended mean-field theory. The collective motion is treated explicitly by employing a travelling single-particle representation in the semi-classical approximation. The rate of change of the collective kinetic energy is determined by: (i) one-body dissipation, which reflects uncorrelated particle-hole excitations as a result of the collisions of particles with the mean field, (ii) two-body dissipation, which consists of simultaneous 2 particle-2 hole excitations via direct coupling of the residual two-body interactions, and (iii) potential dissipation due to the redistribution of the single-particle energies as a result of the random two-body collisions. In contrast to the first two processes the potential dissipation exhibits memory effects due to the large values of the local equilibration times. 相似文献
15.
16.
The inelastic electron scattering cross sections for the excitation of the low-lying collective states in the even Zn isotopes 64Zn, 66Zn, 68Zn and 70Zn have been measured in the momentum transfer region q = 0.3–1.1 fm?1. Strong transitions to the first 2+ and 3? states have been observed and the modified Tassie model with a two parameter Fermi charge distribution for the ground state was used to extract the values for the reduced transition probability B↑ (Eλ). Besides the investigation of these states, which in the framework of the vibrational model are considered as one-phonon states, special effort was made to measure the transition to the 2+ two-phonon states in 64Zn (ε = 1.80 MeV) and 70Zn (ε = 1.76 MeV). We have applied the anharmonic vibrator model to these two nuclei and have extracted values for the static quadrupole moment of the first excited state. 相似文献
17.
Elastic and inelastic cross sections have been measured for the system 16O + 17O at c.m. energies from 12.5 to 15.5 MeV, and for 16O + 18O at c.m. energies from 12 to 20 MeV, at angles between 60° and 125°. Position-sensitive detectors were employed, using the kinematic coincidence technique. The data have been analyzed with particular attention to the contributions of multiple-exchange processes. 相似文献
18.
19.
V.A. Ionescu Jean Kern R.F. Casten W.R. Kane I. Ahmad J. Erskine A.M. Friedman K. Katori 《Nuclear Physics A》1979,313(3):283-306
Low and high energy spectra from thermal neutron capture in 237Np have been studied over the energy ranges 25 to 650 keV and 2600 to 5500 keV. Primary transitions from neutron capture in four resonances have been observed between about 4800 and 5400 keV. Using 12 MeV deuterons, (d, p) spectra at three angles have been observed with a magnetic spectrograph. A nuclear level scheme for 238Np has been constructed by combining the results of the above measurements with previous data from a study of the 242mAm α-decay. The Nilsson model has been used to interpret the level structure. Including results from the previous α-decay study, nine rotational bands can be assigned. The Nilsson configurations (Kπ [Nn3ΛΣ]) and band-head energies are: 2+π[642↑]?ν[631↓], 0.0 keV; 3+π[642↑]+ν[631↓], 86.6 keV; 3?π[523↓]+ν[631↓], 136.0 keV; 2?π[523↓]?ν[631↓], 182.8 keV; 5+π[642↑]+ν[622↑], 278.1 keV; 0+π[642↑]?ν[622↑], 332.5 keV; 5?π[523↓]+ν[622↑], 342.6 keV; 0?π[523↓]?ν[622↑], 286.0 keV; 6?π[642↑]+ν[743↑], 301 keV. The measured (d, p) reaction cross sections are compared with theoretical calculations based on these assignments. The Gallagher-Moszkowski rule is found to be valid in the four cases where we have observed both parallel and antiparallel coupled bands with and . The lowest levels of the two K = 0 bands have spin I = 1; Newby odd-even shifts can be determined in both cases. 相似文献
20.
G. Leander 《Nuclear Physics A》1976,273(2):286-300
A numerically feasible method, based on the use of deformed phonons, is developed for the diagonalization of the collective quadrupole Hamiltonian for a system with an odd particle coupled to an anharmonic even core. Examples: the transition from prolate to oblate via γ-unstable shapes and furthermore the spectra of the nuclei 187Ir and 197Tl. 相似文献