共查询到20条相似文献,搜索用时 15 毫秒
1.
The pygmy dipole resonance(PDR) of nickel isotopes is studied using the deformed random phase approximation method. The isoscalar character of the pygmy resonance is confirmed, and the correlation between the pygmy resonance and neutron skin thickness is discussed. Our investigation shows a linear correlation between PDR integral cross section and neutron skin thickness when the excess neutrons lie in pf orbits, with a correlation rate of about 0.27 fm~(-1). However, in more neutron-rich nickel isotopes, the growth of the pygmy dipole resonance is stagnant. Although the neutron skin thickness increases, the whole skin is not active. There is an inertial part in the nuclei~(70-78)Ni which does not participate in the pygmy resonance actively and as a result, contributes little to the photo-absorption cross section. 相似文献
2.
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
3.
Endres J Litvinova E Savran D Butler PA Harakeh MN Harissopulos S Herzberg RD Krücken R Lagoyannis A Pietralla N Ponomarev VY Popescu L Ring P Scheck M Sonnabend K Stoica VI Wörtche HJ Zilges A 《Physical review letters》2010,105(21):212503
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn with the (α, α'γ) coincidence method at Eα=136 MeV. The comparison with results of photon-scattering experiments reveals a splitting into two components with different structure: one group of states which is excited in (α, α'γ) as well as in (γ, γ') reactions and a group of states at higher energies which is only excited in (γ, γ') reactions. Calculations with the self-consistent relativistic quasiparticle time-blocking approximation and the quasiparticle phonon model are in qualitative agreement with the experimental results and predict a low-lying isoscalar component dominated by neutron-skin oscillations and a higher-lying more isovector component on the tail of the giant dipole resonance. 相似文献
4.
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
5.
C. Kohstall D. Belic P. von Brentano C. Fransen R. -D. Herzberg J. Jolie U. Kneissl H. Lehmann A. Linnemann P. Matschinsky A. Nord N. Pietralla H. H. Pitz M. Scheck F. Stedile V. Werner S. W. Yates 《Physics of Atomic Nuclei》2001,64(6):1141-1146
Low-lying dipole excitations in the medium-weight vibrational nuclei of the Cd isotopic chain were investigated by means of nuclear resonance fluorescence experiments performed at the bremsstrahlung beam of the Stuttgart Dynamitron accelerator (endpoint energy 4.1 MeV). Detailed information has been obtained on excitation energies, spins, decay widths, and transition probabilities of numerous excited states in 110–114,116Cd. Additionally, the use of two Compton polarimeters enabled model-independent parity assignments for excitations in the even-even isotopes. Strongly excited J π = 1? states are found in all even-even Cd nuclei at excitation energies near the sumof the energies of the first 2+ and 3? states. These excitations are interpreted as the 1? member of the quadrupole-octupole coupled quintuplet (2+?3?). The fragmented strength observed in the odd isotopes 111,113Cd is compared with the strength distributions in the neighboring even-even Cd isotopes. 相似文献
6.
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
7.
8.
H. -W. Brandt K. Heilig H. Knöckel A. Steudel 《Zeitschrift für Physik A Hadrons and Nuclei》1978,288(3):241-246
The isotope shift of all stable Ca isotopes was studied in the Ca I resonance line. Enriched isotopes were used in an atomic beam, passing through the center of a spherical Fabry-Perot interferometer. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with δ〈r 2〉 values derived from recent muonic x-ray measurements. The results are discussed together with known data on the isotope shift in the Ca I intercombination line and data from Hartree-Fock calculations. The following mean values are obtained for the change in nuclear charge distribution δ〈r 2〉 [fm2]∶ [40, 42] 0.23(3); [40, 43] 0.13(3); [40, 44] 0.28(4); [40, 46] 0.14(7); [40, 48] 0.00(2). 相似文献
9.
N. G. Goncharova Yu. A. Skorodumina 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(10):1085-1088
The structure of the dipole resonance in even-even isotopes of titanium is calculated within the particle-core coupling (PCC) version of the shell model using data from spectroscopy of direct (p, d) reactions. The main features of the E1 resonances in 46Ti, 48Ti, and 50Ti are reproduced. 相似文献
10.
Measurements of the (γ, np) cross sections of 70Ge, 72Ge, 74Ge and 76Ge and the (γ, p) cross section of 74Ge are reported. The (γ, np) reaction is discussed as a channel for the observation of the T = T0 + 1 component of the giant dipole resonance of the nuclear photo effect, and experimental evidence is presented in support of this conjecture in Ge isotopes. 相似文献
11.
The giant dipole resonance at large angular velocities and finite temperatures is studied within the framwork of temperature-dependent linear response theory for superfluid Fermi liquids. The peak energy of the resonance and its splitting is discussed as a function of angular momentum and temperature. The influence of the shape and gap parameters on the fine structure is investigated. 相似文献
12.
We study the nature of the low-lying dipole strength in neutron-rich nuclei, often associated with the pygmy dipole resonance.
The states are described within the Hartree-Fock plus RPA formalism, using different parametrizations of the Skyrme interaction.
We show how the information from combined reaction processes involving the Coulomb and different mixtures of isoscalar and
isovector nuclear interactions can provide a clue to reveal the characteristic features of these states. 相似文献
13.
The isovector giant dipole resonances(IVGDR)in proton-rich Ar and Ca isotopes have been systematic-ally investigated using the resonant continuum Hartree-F ock+BCS(HF+BCS)and quasiparticle random phase ap-proximation(QRPA)methods.The Skyrme SLy5 and density-dependent contact pairing interactions are employed in the calculations.In addition to the giant dipole resonances at energy around 18 MeV,pygmy dipole resonances(PDR)are found to be located in the energy region below 12 MeV.The calculated energy-weighted moments of PDR in nuclei close to the proton drip-line exhaust about 4%of the TRK sum rule.The strengths decrease with in-creasing mass number in each isotopic chain.The transition densities of the PDR states show that motions of pro-tons and neutrons are in phase in the interiors of nuclei,while the protons give the main contribution at the surface.By analyzing the QRPA amplitudes of proton and neutron 2-quasiparticle configurations for a given low-lying state,we find that only a few proton configurations give significant contributions.They contribute about 95%to the total QRPA amplitudes,which indicates that the collectivity of PDR states is not strong in proton-rich nuclei in the present study. 相似文献
14.
We have studied dipole states of oxygen isotopes in large scale shell model calculations. The calculated photoreaction cross sections in 16O, 17O and 18O give reasonable agreement with experimental observations both in the low energy region below ?ω=15 MeV and in the high energy giant resonance region (15 MeV < ?ω ≤ 30 MeV). We found that the transition strength below dipole giant resonance (?ω ≤ 15 MeV) exhausts about 10% of the classical Thomas-Reiche-Kuhn sum rule and more than 40% of the cluster sum rule in heavier oxygen isotopes than 17O. The predicted Pigmy strengths in 20O and 22O are also confirmed by recent Coulomb excitation experiment at GSI. 相似文献
15.
A. Leprêtre H. Beil R. Bergére P. Carlos J. Fagot A. De Miniac A. Veyssiére H. Miyase 《Nuclear Physics A》1976,258(2):350-364
The partial photoneutron cross sections [σ(γ, n) + σ(γ, pn)] and σ (γ, 2n) of 124, 126, 128, 130Te and 140, 142Ce were measured in the giant dipole resonance region by means of the monochromatic photon beam installation at SACLAY. Absolute total photoneutron cross sections, Lorentz line parameters and integrated cross sections are evaluated. The experimental behaviour of the GDR for the above nuclei and in particular its spreading, is then tentatively interpreted in terms of the improved dynamic collective model using the concept of potential energy surfaces. 相似文献
16.
Savran D Babilon M van den Berg AM Harakeh MN Hasper J Matic A Wörtche HJ Zilges A 《Physical review letters》2006,97(17):172502
A concentration of electric-dipole excitations below the particle threshold, which is frequently denoted as the pygmy dipole resonance, has been studied in the semimagic nucleus 140Ce in (alpha, alpha' gamma) experiments at E alpha = 136 MeV. The technique of alpha-gamma coincidence experiments allows the separation of E1 excitations from states of other multipolarities in the same energy region and provides an excellent energy resolution to allow a detailed analysis for each state. The experimental results show that the PDR splits into two parts with different nuclear structure: one part which is excited in (alpha, alpha' gamma) as well as (gamma, gamma') experiments and one part which is excited only in (gamma, gamma'). 相似文献
17.
H. Beil R. Bergère P. Carlos A. Leprêtre A. De Miniac A. Veyssière 《Nuclear Physics A》1974,227(3):427-449
By using a variable monochromatic photon beam, the partial photoneutron cross sections σ(γ, n) + σ(γ, pn), σ(γ, 2n) and σ(γ, 3n) are determined in the region of the giant dipole resonance for the doubly even Mo isotopes 92Mo, 94Mo, 96Mo, 98Mo and 100Mo. Measured integrated photoneutron cross sections are compared with available integrated photoproton cross sections as a function of A. Broadening of the giant dipole resonance as A increases is observed in good agreement with the predictions of the dynamic collective model. A tentative study of some isospin splitting effects is also carried out. 相似文献
18.
Tran Duc Thiep Truong Thi An Phan Viet Cuong Nguyen The Vinh Bui Minh Hue A. G. Belov O. D. Maslov G. V. Mishinsky V. I. Zhemenik 《Physics of Particles and Nuclei Letters》2017,14(1):102-111
We have determined the isomeric ratios of isomeric pairs 97m,gNb, 95m,gNb and 91m,gMo produced in 98Mo(γ, p)97m,gNb, 96Mo(γ, p)95m,gNb and 92Mo(γ, n)91m,gMo photonuclear reactions in the giant dipole resonance (GDR) region by the activation method. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, neutron configuration, channel effect and direct and pre-equilibrium processes in (γ, p) photonuclear reactions. In this work the isomeric ratios for 97m,gNb from 14 to 19 MeV, for 195m,gNb from14 to 24 MeV except 20 and 23.5 MeV and for 91m,gMo at 14 and 15 MeV are the first time measurements. 相似文献
19.
V. Sonnenschein I. D. Moore H. Khan I. Pohjalainen M. Reponen 《Hyperfine Interactions》2014,227(1-3):113-123
Resonance ionization spectroscopy (RIS) inside a buffer gas-filled ion guide is a very sensitive tool for a first determination of nuclear moments and charge radii of radioactive isotopes produced using the IGISOL technique. Currently employed pulsed Ti:sapphire laser systems have a typical laser linewidth of 5 GHz in the fundamental, which in many cases is the dominant line broadening effect. We present results of RIS on stable 63,65Cu using a dual-etalon Ti:sapphire laser with a reduced linewidth of 1 GHz. Determination of hyperfine parameters of 63Cu revealed discrepancies when compared to existing higher resolution data. A study of systematic uncertainties is underway using a homemade scanning Fabry-Pérot interferometer (FPI). A real-time recording of the mode structure of the multi-longitudinal mode Ti:sapphire laser during a scan of the 244.238 nm atomic ground state transition in parallel with the readout from the commercial wavemeter has identified sources of uncertainty. 相似文献
20.
Carlos E. Vargas Víctor Velázquez Sergio Lerma 《The European Physical Journal A - Hadrons and Nuclei》2013,49(1):1-8
Microscopic studies in heavy nuclei are very scarce due to large valence spaces involved. This computational problem can be avoided by means of the use of symmetry-based models. Ground-state, γ and β bands, and their B(E2) transition strengths in 160–168Dy isotopes, are studied in the framework of the pseudo-SU(3) model which includes the preserving symmetry Q · Q term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized. Additionally, three rotor-like terms are considered, whose free parameters, fixed for all members of the chain, are used to fine tune the moment of inertia of rotational bands and the band head of γ and β bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus 170Dy. The results presented show that it is possible to study a full chain of isotopes or isotones in the region with the present model. 相似文献