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1.
The dependence between neutron skin thickness and neutron abrasion cross section (σnabr) for neutron-rich nuclei is investigated within the framework of the statistical abrasion ablation model. Assuming that the density distributions for proton and neutron are of Fermi-type, and adjusting the diffuseness parameter of neutron density distribution in the droplet model, we find out the good linear correlation between the neutron skin thickness and the abrasion cross section σnabr for neutron-rich nuclei. The uncertainty of neutron skin thickness determined from σnabr is very small. It is suggested that σnabr can be used as a new experimental observable to extract the neutron skin thickness for neutronrich nucleus. The scaling behaviours between neutron skin thickness and σnabr, separately, for isotopes of ^26-35Na, ^44-56Ar, ^48-60Ca, ^67-78Ni are also investigated. 相似文献
2.
The cross sections of the fragments produced in the projectile fragmentation reactions of the even calcium isotopes from A=36 to A=52 are calculated using the statistical abrasion ablation model.The neutron skin thickness are studied by investigating the fragments isotopic cross section distributions.The neutron-skin thicknesses of the calcium isotopes have a good linear correlation to the peak positions of their fragment isotopic cross section distributions.The correlation between the neutron skin thickness and the neutron density distributions of 48Ca is investigated by introducing a parameter to adjust the diffuseness parameter in the fermi-type density distribution. 相似文献
3.
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
4.
《中国物理快报》2017,(8)
The pygmy and giant dipole resonances in proton-rich nuclei~(17,18)Ne are investigated with a fully self-consistent approach. The properties of ground states are calculated in the Skyrme Hartree-Fock with the Bardeen-CooperSchrieffer approximation to take into account the pairing correlation. The quasiparticle random phase approximation(QRPA) method is used to explore the properties of excited dipole states. In the calculations the SLy5 Skyrme interaction is employed. In addition to the giant dipole resonances, pygmy dipole resonances(PDR) are found to be located in the energy region below 10 MeV in both 17,18 Ne. The strength and transition density show that the low-lying states are typical PDR states. However, analyzing the QRPA amplitudes of proton and neutron 2 quasiparticle(2 qp) configurations for a given low-lying state in ~(17,18)Ne, we find that the PDR state is less collective, more like a single 2 qp excitation. 相似文献
5.
6.
Hartmann T Babilon M Kamerdzhiev S Litvinova E Savran D Volz S Zilges A 《Physical review letters》2004,93(19):192501
The electric dipole strength distribution in 44Ca has been measured up to 10 MeV in high resolution photon scattering experiments for the first time. The data obtained have been compared to earlier measurements on (40,48)Ca in order to view the evolution of the electric pygmy dipole resonance (PDR). Calculations that were performed within the framework of the microscopic extended theory of finite Fermi systems, which adds contributions of the quasiparticle-phonon coupling to random phase approximation calculations, give a qualitative agreement with the experimental data for all three isotopes. We have shown that it is necessary to include this coupling to describe the PDR. 相似文献
7.
N. N. Arsenyev A. P. Severyukhin V. V. Voronov Nguyen Van Giai 《Physics of Particles and Nuclei》2017,48(6):876-878
Starting from the Skyrme interaction SLy4 we study the effects of 2 particle–2 hole configurations on the low-energy electric dipole response in 130–134Sn. It is shown that the pygmy dipole resonance properties are correlated with the neutron skin thickness. The two-phonon configurations give a considerable contribution to the low-lying E1 strength. 相似文献
8.
A search of the pygmy resonance in 68Ni was made using the virtual photon technique. The experiment was carried out using the radioactive beam 68Ni at 600 A MeV, produced with fragmentation of 86Kr at 900 A MeV on a 9Be target. The 68Ni beam was separated by a fragment separator, and the γ-rays produced at the interaction with the Au target were detected with the RISING and FRS set-up at the GSI laboratory in Germany, also including the HECTOR array. The measured γ-ray spectra show a peak centered at approximately 11 MeV, whose intensity can be explained in term of an enhanced strength of the dipole response function (pygmy resonance). A pygmy structure of this type was also predicted by different models for this unstable neutron-rich nucleus. Correlations between the behavior of the nuclear symmetry energy, the neutron skins, and the percentage of energy-weighted sum rule (EWSR) exhausted by the pygmy dipole resonance (PDR) are investigated by using different random phase approximation (RPA) models. 相似文献
9.
The evolution of the low-lying E1 strength in proton-rich nuclei is analyzed in the framework of the self-consistent relativistic Hartree-Bogoliubov model and the relativistic quasiparticle random-phase approximation (RQRPA). Model calculations are performed for a series of N=20 isotones and Z=18 isotopes. For nuclei close to the proton drip line, the occurrence of pronounced dipole peaks is predicted in the low-energy region below 10 MeV excitation energy. From the analysis of the proton and neutron transition densities and the structure of the RQRPA amplitudes, it is shown that these states correspond to the proton pygmy dipole resonance. 相似文献
10.
Disentangling the Effects of Thickness of the Neutron Skin and Symmetry Potential in Nucleon Induced Reactions on Sn Isotopes
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The effects of density dependence of symmetry energy and the thickness of the neutron skin in proton (neutron) induced reactions on Sn isotopes are investigated by means of the improved molecular dynamics model. The investigation shows that the target size dependence of the reaction cross sections for proton induced reactions on Sn isotopes is sensitive to the density dependence of the symmetry energy and less sensitive to the thickness of the neutron skin of the target nuclei, but that, for neutron induced reactions on Sn isotopes, it is less sensitive to the density dependence of the symmetry energy and sensitive to the thickness of the neutron skin of the target nucleus. 相似文献
11.
A nuclear structuremodel based on a finite rank approximation of Skyrme interaction is applied to calculate the distribution
of dipole strength in tin isotopes. The model is based on the quasiparticle random phase approximation. The results obtained
with the three types of parametrizations of the Skyrme forces (SLy4, SkM*, and SIII) are compared. The low-lying part of dipole
strength distribution reveals the existence of a group of slightly collective states, and the corresponding E1 transition strength increases with the enlargement of neutron excess. The group is associated with the pygmy resonance.
The text was submitted by the authors in English. 相似文献
12.
The photoneutron cross section of 29Si has been measured over the energy range 8 to 28 MeV using the bremsstrahlung yield curve technique. The giant dipole resonance is observed to be centered at 21.2 MeV and is 5.5 MeV wide. In addition, a pygmy resonance containing much fine structure is observed below 17 MeV. An attempt is made to interpret these observations in terms of the weak coupling of the extra neutron to a 28Si core. However, detailed comparisons of the structure and relative strengths of the 28Si and 29Si cross sections reveal that the coupling of the extra-core nucleon is large and significantly modifies the core wave function. 相似文献
13.
The structure of the isovector dipole resonance in neutron-rich calcium isotope, 60Ca, has been investigated by implementing a careful treatment of the differences of neutron and proton radii in the continuum random phase approximation (RPA). The calculations have taken into account the current estimates of the neutron skin. The estimates of the escape widths for direct neutron decay from the pygmy-dipole resonance (PDR) were shown rather wide, implicating a strong coupling to the continuum. The width of the giant-dipole resonance (GDR) was evaluated, bringing on a detailed discussion about its microscopic structure.Received: 22 September 2003, Revised: 9 February 2004, Published online: 7 September 2004PACS:
21.10.Pc Single-particle levels and strength functions - 21.60.-n Nuclear structure models and methods - 24.30.Cz Giant resonances - 24.30.Gd Other resonances 相似文献
14.
Inclusion of the coupling of quasiparticle degrees of freedom with phonon degrees is a natural extention of the standard QRPA
approach. The paper presents the quantitative impact of this phonon coupling on the dipole strength and radiative neutron
capture for the stable 124Sn and very exotic 150Sn isotopes, as an illustration, using the self-consistent version of the Extended Theory of Finite Fermi Systems. It was
found that the phonon contribution to the pygmy-dipole resonance and radiative neutron capture cross section is increased
with the (N − Z) difference growth. The results show that the self-consistent nuclear structure calculations are important for unstable nuclei,
where phenomenological approaches do not work. 相似文献
15.
Ilievski S Aumann T Boretzky K Elze TW Emling H Grünschloss A Holeczek J Holzmann R Kozhuharov C Kratz JV Kulessa R Leistenschneider A Lubkiewicz E Ohtsuki T Reiter P Simon H Stelzer K Stroth J Sümmerer K Wajda E Waluś W;LAND Collaboration 《Physical review letters》2004,92(11):112502
Differential cross sections for electromagnetic fission of 238U projectiles (500 MeV/u) in C, Sn, and Pb targets are measured and analyzed in terms of single- and multiphonon giant resonance excitations as doorway states to fission. A novel experimental method exploits the linear relationship between neutron multiplicity and the primary 238U excitation energy. Multiphonon states contribute up to 20% of the cross section; a component at high excitation energies is indicated that may arise from three-phonon dipole and two-phonon GDR x GQRiv giant resonance excitations. 相似文献
16.
Savran D Fritzsche M Hasper J Lindenberg K Müller S Ponomarev VY Sonnabend K Zilges A 《Physical review letters》2008,100(23):232501
The photoresponse of the semimagic N=82 nucleus (136)Xe was measured up to the neutron separation energy S(n) using the (gamma, gamma') reaction. A concentration of strong dipole excitations is observed well below S(n) showing a fragmented resonancelike structure. Microscopic calculations in the quasiparticle phonon model including complex configurations of up to three phonons agree well with the experimental data in the total integrated strength, in the shape and the fragmentation of the resonance, which allows us to draw conclusions on the damping mechanism of the pygmy dipole resonance. 相似文献
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18.
The isovector giant dipole resonance in Ca isotopes is investigated in the framework of the fully consistent relativistic random phase approximation.The calculations are performed in an effective Lagrangian with a parameter set NL3,which was proposed for satisfactorily describing nuclear ground state properties.It is found that a soft isovector dipole mode for Ca isotopes near drip lines exists at energy around 6-7MeV.The soft dipole states are mainly due to the excitation of the weakly bound and pure neutron (proton)states near Fermi surface as well as the correlation of isoscalar and isovector operators.For nuclei with the extreme value of N/Z,the contributions of isoscalar mesons in the isovector mode play a non-negligible role. 相似文献
19.
Asymmetric s-wave resonances observed in the neutron capture cross section of 54Fe can be explained by interference between resonance valence components. An upper limit is obtained for the background capture cross section which is much smaller than that expected from the large correlation observed between s-wave reduced neutron widths and radiative widths. 相似文献
20.
The photonuclear cross section for the isovector electric dipole in 18O is calculated using the open-shell linear response method. The model accounts for the pygmy resonance and provides a simple interpretation for the main peak at 23.7 MeV observed in photoabsorption cross sections. The model reproduces qualitatively the main differences and common features of the 16O and 18O photoabsorption cross sections. The strength distributions of the isoscalar quadrupole and octupole states in 18O are also presented. 相似文献