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1.
The quasiparticle representation of the phonon darnping model (PDM) is developed to include the superfluid pairing correlations
microscopically. The formalism is applied to calculate the photoabsorption and the electromagnetic (EM) differential cross
sections of E1 excitations in neutron-rich oxygen and calcium isotopes. The calculated photoabsorption cross sections agree
reasonably well with the available data for 16,18O and 40,48Ca. The results of calculations show that the change of the fraction of the E1 integrated strength in the region of pygmy
dipole resonance (PDR) as a function of mass number A with increasing neutron number N is in agreement with the recent experimental data, and does not follow the prediction by the simple cluster model. The EM
differential cross sections obtained within PDM in this work show prominent PDR peaks below 15 MeV for 20,22O in agreement with the recent experimental observation. It is also shown that, using low-energy RI beams at around 50–60
MeV/nucleon, one can observe clean and even enhanced PDR peaks without the admixture with the GDR in the EM differential cross
sections of neutron-rich nuclei. 相似文献
2.
《Physics letters. [Part B]》1987,196(4):409-413
A microscopic formulation of the scissors mode, based on the angular-momentum projected Hartree-Fock Bogoljubov approximation, is applied to the Ti and Ne isotopes. Results for M1 transition strengths and form factors are presented and compared to available experimental data and shell model calculations. For 46Ti the B(M1)↑ value obtained is in excellent agreement with the experimental data for the 1+ state at 4.3 MeV. 相似文献
3.
The two-rotor model0 with the Feshbach projection operator method is applied for investigating the properties of the positive parity low-lying collective states in the rare earth nuclei. The calculations of the energy spectra, E2-transition probability and magnetic properties of the states of β- and γ-bands are carried out for the isotopes 164, 166, 168Er. The B(M1) values from 1+ states to the ground band are estimated. 相似文献
4.
R.R. Hilton W. Höhenberger P. Ring 《The European Physical Journal A - Hadrons and Nuclei》1998,1(3):257-260
Experimental observations in certain rare earth nuclei have established the presence of sizeable B(M1) strength of two peak
structure lying in the 5–10 MeV region. The character of the states concerned, studied within a self-consistent Random Phase
Approximation using Skyrme forces, are identified to be that of proton and neutron giant spin-flip resonances.
Received: 14 July 1997 / Revised version: 20 October 1997 相似文献
5.
Theoretical results for giant resonances in the three doubly magic exotic nuclei 78Ni, 100Sn and 132Sn are obtained from Hartree-Fock (HF) plus Random Phase Approximation (RPA) calculations using the D1S parameterization of
the Gogny two-body effective interaction. Special attention is paid to full consistency between the HF field and the RPA particle-hole
residual interaction. The results for the exotic nuclei, on average, appear similar to those of stable ones, especially for
quadrupole and octupole states. More exotic systems have to be studied in order to confirm such a trend. The low energy of
the monopole resonance in 78Ni suggests that the compression modulus in this neutron-rich nucleus is lower than the one of stable ones. 相似文献
6.
After the initial discovery of the so-called “spin crisis in the parton model” in the 1980s, a large set of polarization data in deep inelastic lepton-nucleon scattering was collected at labs like SLAC, DESY and CERN. More recently, new high precision data at large x and in the resonance region have come from experiments at Jefferson Lab. These data, in combination with the earlier ones, allow us to study in detail the polarized parton densities, the Q2 dependence of various moments of spin structure functions, the duality between deep inelastic and resonance data, and the nucleon structure in the valence quark region. Together with complementary data from HERMES, RHIC and COMPASS, we can put new limits on the flavor decomposition and the gluon contribution to the nucleon spin. In this report, we provide an overview of our present knowledge of the nucleon spin structure and give an outlook on future experiments. We focus in particular on the spin structure functions g1 and g2 of the nucleon and their moments. 相似文献
7.
Giorgio Parisi 《Journal of statistical physics》1993,72(5-6):857-878
We review some known results on the nature of the tree of states in spin glasses and we present new results on its topology. We pay particular attention to the so-called continuum limit in which the levels are labeled by a continuous variablex. We also study the dependence on the levelx of the type of branching (bifurcation, trifurcation,...). We show that the statistics of the tree is universal in the continuum limit, i.e., it does not depend on the details of the algorithm used to generate the tree. 相似文献
8.
The boson structure of the low-lying states of A = 44 and A = 60 nuclei is investigated by studying the eigenvalue problem of the boson image of the shell-model Hamiltonian in spaces
expanded in terms of bosons corresponding to the collective nuclear pairs allowed in the 1p0f shell.
The text was submitted by the authors in English. 相似文献
9.
We investigate the electron transport through one double-helical molecule with four terminals, by considering one terminal to be the source and others to be the drains. It is found that notable spin polarizations simultaneously occur during the processes of intra-chain electron tunneling and inter-chain electron reflection. More importantly, in these two processes, the spin polarizations always show similar strengths and opposite directions. Based on these results, we consider that the spin polarization and spin separation can be co-realized in this system. 相似文献
10.
11.
An analogy is presented between periodic persistent currents in mesoscopic rings and staggerings of gamma energy transitions
from some nuclear high-spin states. Various sources of damping of the expected periodic structures in both physical systems
are compared. This discussion provides, in the nuclear case, a tentative explanation of the scarcity of such staggerings,
their appearance near 150Gd and the existence of a spin-window for their observation.
Received: 21 July 1997 / Revised version: 13 October 1997 相似文献
12.
D P Ahalpara 《Pramana》1978,10(4):399-408
Collective bands of the positive parity states in odd-A f
7/2 shell nuclei are described in the framework of deformed Hartree-Fock theory by projecting states from lowest energy intrinsic
states with (d
3
2/−1
f
7
2/n+1
) one hole configurations. In the calculation empirical (d
3/2 −f
7/2)2 effective matrix elements have been used to test the tacit assumptions of the Bansal and French model. 相似文献
13.
We investigate the spin structure of the pion within the framework of the nonlocal chiral quark model from the instanton vacuum. We first evaluate the tensor form factors of the pion for the first and second moment (n=1,2) and compare it with the lattice data. Combining the tensor form factor of the pion with the electromagnetic one, we determine the impact-parameter dependent probability density of transversely polarized quarks inside the pion. It turns out that the present numerical results for the tensor form factor as well as those for the probability density are in good agreement with the lattice data. We also discuss the distortion of the spatial distribution of the quarks in the transverse plane inside the pion. 相似文献
14.
15.
Ultrasonic attenuation was studied in pure In, In + 0.003 at.% Pb, pure Pb and Pb + 0.003 at.% In in the intermediate states
(for the magnetic fields 0.7H
c
and 0.9H
c
) and superconducting states, for frequencies varying from 9.9 to 29.7 MHz, in the temperature range 4.2 to 1.4K. Collective
excitation modes were observed in both the states for all the samples. There exist two distinct phases in the intermediate
state but only one phase in the superconducting state in all the samples. The first phase was dependent on the magnetic field
and independent of the concentration and nature of the dopant. The second phase was independent of the magnetic field and
dependent essentially on the concentration of vacancies and marginally on the concentration of the dopant. The origin of the
two phases has been discussed. 相似文献
16.
P. Arumugam A. Ganga Deb S. K. Patra 《The European Physical Journal A - Hadrons and Nuclei》2005,25(2):199-209
We discuss the shape transitions in few medium heavy-mass nuclei with emphasis on low-temperature behaviour of the giant dipole resonance (GDR) observables. We employ a macroscopic approach towards GDR in which the GDR observables are related to the nuclear shapes. Shape calculations were done using the cranked Nilsson-Strutinsky method (CNSM) extended to finite temperature. Thermal shape fluctuations are computed with free energies calculated employing Landau parameterization as well as those calculated exactly (without using parameterizations) at given spin and temperature. The results obtained are confronted with the experimental data wherever available. Our study reveals that if the fluctuations are treated properly, then, in spite of thermal fluctuations, GDR observables could very well reflect the shape transitions at low temperature. 相似文献
17.
18.
A. Fahmi 《Physica B: Condensed Matter》2009,404(16):2474-2480
In this work, we study the elementary excitations and magnetic properties of the [M/Cu] super-lattices with: M=Fe, Co and Ni, represented by a Heisenberg ferromagnetic system with N atomic planes. The nearest neighbour (NN), next nearest neighbour (NNN) exchange, dipolar interactions and surface anisotropy effects are taken into account and the Hamiltonian is studied in the framework of the linear spin wave theory. In the presence of the exchange alone, the excitation spectrum E(k) and the magnetization 〈Sz〉/S analytical expressions are obtained using the Green's function formalism. The obtained relaxation time of the magnon populations is nearly the same in the Fe and Co-based super-lattices, while these magnetic excitations would last much longer in the Ni-based super lattice. A numerical study of the surface anisotropy and long-ranged dipolar interaction combined effects are also reported. The exchange integral values deduced from a comparison with experience for the three super-lattices are coherent. 相似文献
19.
The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent
approach using the Gogny force. Introducing configuration mixing, 32Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in 44
S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2+ excitation energy Ex = 1.46 MeV and the reduced transition probability B(E2;0+
gs→ 2+
1)= 420 e
2
fm
4 obtained with our approach are in good agreement with experimental data.
Received: 26 July 2000 / Accepted: 30 August 2000 相似文献
20.
R. Ashby J.J. Clarke W.A. van Wijngaarden 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):327-331
6Li 32D
3/2, 5/2
states were studied using a diode laser to first excite the 2P
3/2
state and a dye laser to populate the 32D
3/2, 5/2
states. The dye laser was modulated by an electro-optic modulator and intersected an atomic beam that passed through a field
free region and subsequently through a uniform electric field. A value of 1084.24±0.20 MHz was found for the 32D fine structure splitting. The scalar and tensor polarizabilities were determined to be α
(3D
3/2
) = - 3.753±0.015, α
2
(3D
3/2
) = 2.893±0.017, α
(3D
5/2
) = - 3.772±0.008 and α
2
(3D
5/2
) = 4.058±0.013 MHz/(kV/cm)2.
Received 26 September 2002 / Received in final form 22 January 2003 Published online 11 March 2003
RID="a"
ID="a"e-mail: wlaser@yorku.ca 相似文献