Symmetry energy dependence of the pygmy and giant dipole resonances in an isospin dependent quantum molecular dynamics model

Isospin-dependent Quantum Molecular Dynamics model (IQMD) has been applied to investigate the Pygmy Dipole Resonance (PDR) and Giant Dipole Resonance (GDR) in Ni isotopes by Coulomb excitation. By Gaussian fitting to the photon emission spectra, the peak energies and strengths of PDR and GDR are extracted. Their sensitivities to impact parameter, incident energy and the symmetry energy are discussed. By the comparison of energy-weighted sum rule (EWSR) with the data and other calculations for 68 Ni, the parameters of density-dependence of symmetry energy in the IQMD are constrained. In addition, the N/Z dependence of PDR and GDR parameters of Ni isotopes are investigated, and the results that the EWSR increases linearly with the N/Z are obtained.     

Integral cross sections of photonuclear reactions near the giant dipole resonance

The total cross sections of (γ, n) reactions were measured for 12 nuclei from⁴⁵Sc to²⁰⁸Pb using an activational method on bremsstrahlung from a microtron with maximum energy 25 MeV. Calculations of the total cross sections were performed on the basis of a modified preequilibrium decay model. Good agreement was obtained between the experimental and computed cross sections in the mass number range 100–208. 1 figure, 3 tables, 13 references. Translated from Atomnaya énergiya, Vol. 88, No. 5, pp. 391–396, May, 2000     

Two-proton sequential decay from excited states of 18Ne

Two-proton radioactivity from 18Ne is discussed in terms of sequential decay. The branch ratios for one- proton emission from excited states are calculated, which including spectroscopic factors, obtained from a Shell- model calculation with realistic interactions. The branch ratios show that the two-proton emission from the 1 state of 16Ne at 7.94 MeV is most likely to go through the sequential decay. The same mechanism is discussed for other excited states at higher energy by different interactions.     

Compilation of directly measured nuclear spins of ground states and long-lived isomers

A compilation of the nuclear spins of ground and isomeric states measured by direct methods is presented. The first compilation of direct measurements of nuclear spins and moments was published in 1976 (G. H. Fuller, J. Phys. Chem. Ref. Data 5, 835, (1976)) with literature covered up to 1974. To our knowledge, the present work is the first such compilation since then. It is anticipated that the area of direct spin measurement will continue to expand using the state-of-the-art radioactive ion-beam and laser techniques. Literature cutoff date for the present compilation is February 2013. It is intended that the present compilation will be kept updated in a timely manner.     

束箔方法测量激发态寿命及其误差

本文阐述了束-箔方法测量原子、分子离子激发态寿命的原理和优点,阐述了我们的实验过程和得到的一些结果。 对于实验误差进行了分析、讨论,提出了我们实验中的三个误差来源。     

Spectral data for doubly excited states of helium with non-zero total angular momentum

A spectral approach is used to evaluate energies and widths for a wide range of singlet and triplet resonance states of helium. Data for total angular momentum L=1,…,4 is presented for resonances up to below the fifth single ionization threshold. In addition, the expectation value of cos(θ₁₂) is given for the calculated resonances.     

Two-proton radioactivity from excited states of proton-rich nuclei within Coulomb and Proximity Potential Model

In the present work, we extend the Coulomb and Proximity Potential Model(CPPM) to study two-proton(2p) radioactivity from excited states while the proximity potential is chosen as AW95 proposed by Aage Withner in 1995. Demonstration reveals that the theoretical results acquired by CPPM exhibit a high level of consistency with prior theoretical models such as the unified fission model(UFM), generalized liquid-drop model(GLDM) and effective liquid-drop model(ELDM).Furthermore, within the CPPM, we ...     

Investigation of excited states of 7Li by means of thermal neutron capture

Capture of unpolarized thermal neutrons has been used to gain information on the ⁷Li level scheme. Two reactions have been investigated. Firstly, a study has been made of the decay scheme of ⁷Li through the ⁶Li(n, γ)⁷Li reaction. Three γ-transitions were observed and placed. The binding energy value of this reaction turned out to be Q = 7251.02(9) keV. Secondly, investigation of radiation from excited Li produced by the ¹⁰B(n,α)⁷Li reaction, made it possible to deduce a more precise lifetime of the 478 keV level of ⁷Li; namely τ = 102 ± 5 fs. This value is compared with existing data; it agrees with previous less accurate independent values and an average could be made in order to reduce the error further. As a byproduct the analysis of the peak shape of the 478 keV transition offered a new method for estimating the size of boron grains embedded in other materials.     

Influence of the Coulomb exchange term on nuclear single-proton resonances

Nuclear single-proton resonances are sensitive to the Coulomb field,while the exchange term of Coulomb field is usually neglected due to its nonlocality.By combining the complex scaling method with the relativistic mean-field model,the influence of the Coulomb exchange term on the single-proton resonances is investigated by taking Sn isotopes and N=82 isotones as examples.It is found that the Coulomb exchange term reduces the singleproton resonance energy within the range of 0.4-0.6 MeV and leads to similar isotopic and isotonic trends of the resonance energy as those without the Coulomb exchange term.Moreover,the single-proton resonance width is also reduced by the Coulomb exchange term,whose influence generally decreases with the increasing neutron number and increases with the increasing proton number.However,the influence of the Coulomb exchange term cannot change the trend of the resonance width with respect to the neutron number and proton number.Furthermore,the influence of the Coulomb exchange term on the resonance width is investigated for the doubly magic nuclei ~(40)Ca,~(56,78)Ni,~(100,132)Sn,and ~(208)Pb.It is found that the Coulomb exchange term reduces the proton resonance width within 0.2 MeV,whose magnitude depends on the specific nucleus and the quantum numbers of resonant states.     

The decay of autoionizing states in electric field formed during collisions of multiply charged ions with metal surface

When a multicharged ion approaches the metal surface, a strong electric field occurs due to interaction between the ion and the charge induced in the metal. During ion-surface scattering, double excited autoionizing states can be formed, and their decay occurs in the presence of strong electric field. The Auger transition rates for such states are higher than those in the absence of the electric field; this is connected with the increase in the wave functions overlap and also with mixing of states with different orbital momentums. This effect changes our view on the population scheme of states with the lowest principal quantum numbers for the collisions considered.     

Band transition moments between excited singlet states of the H2 molecule,nonadiabatic eigenvectors,and probabilities for spontaneous emission

The electronic dipole transition moments of Wolniewicz are used to calculate the vibrational-electronic band transition moments and probabilities for spontaneous emission in the adiabatic and nonadiabatic approximations for the H₂ molecule in the ($\text{EF, GK, H}\text{H}$) ¹Σ_g⁺-(B, B′)¹Σ_u⁺, C¹Π_u systems. The electronic integrals over the nuclear-momentum operators which describe the nonadiabatic coupling within the J = 0 states of EF, GK, and $\text{H}\text{H}{}^1\text{Σ}{}_{\mathrm{<mtext>g</mtext>}}{}^{\mathrm{+}}$, computed by Wolniewicz, are used to obtain nonadiabatic vibrational-electronic ¹Σ_g⁺ eigenfunctions.     

Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Na-like W from Ne-like W

Energy levels, radiative transition probabilities, and autoionization rates for and states in Na-like tungsten (W⁶³⁺) are calculated. Cowan’s relativistic Hartree-Fock method, the relativistic multiconfiguration method implemented in the Hebrew University Lawrence Livermore Atomic Code, and the relativistic many-body perturbation theory method, are used. Autoionizing levels above the threshold 1s²2s²2p⁶ are considered. It is found that configuration mixing plays an important role for all atomic characteristics. Also strong mixing between states with 2s and 2p holes (1s²2s²2p⁵3l₁nl₂+1s²2s2p⁶3l₃nl₄) occurs. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the excited states. It is shown that the contribution of the highly excited states is very important for calculation of total DR rates. Contributions from the autoionizing states and to the DR rate coefficients are estimated by extrapolation of all atomic parameters. The orbital angular momentum (l) distribution of the rate coefficients shows a peak at l=2. The total DR rate coefficient is derived as a function of electron temperature. The dielectronic satellite spectra of W⁶³⁺ are important for L-shell diagnostics of very high-temperature laboratory plasmas such as future ITER fusion plasmas.     

The shielding effect of U238 resonances on the resonance absorption of U235

This paper discusses the question of the mutual effect of resonance neutron absorption by U²³⁸ and U²³⁵ inside a slug, where the resonance absorption is due mainly to volume absorption. As shown by the theoretical calculations and experiments given in the paper, the resonance absorption of neutrons by U²³⁵ in the epithermal region of energies for natural metallic and 10% uranium depends on the effect of the U²³⁸ resonance levels.Calculations may be made in a similar way for other elements.In conclusion the authors epress their gratitude to V. V. Orlov, G. Ya. Rumyantsev, and B. G. Dubovskii for their discussion of the present work. The authors also thank Pen-fan, A. P. Dolgolenko, A. P. Korneev, M.M. Kuzichkin, K. N. Mokhnatkin, and Yu. I. Starykh, who participated in the experiments and calculations.