Reaction cross sections and radii of A=17 and A=20 isobars

Reaction cross sections and root-mean-square (rms) radii of A=17 and A=20 isobars are calculated by using a simplified Glauber model and spherical and deformed Hartree-Fock (HF) wave functions. The small separation energy effect is discussed on the reaction cross sections of A=17 isobars and possible proton halo in ¹⁷Ne by using modified spherical HF wave functions. The calculated rms mass radii of A=20 isobars are increased appreciably by the deformation effect and show a similar irregular pattern as a function of the isospin to that of the observed radii.     

Two-body photodisintegration of 3He with realistic bound-state wave functions

Total and differential cross sections for two-body photodisintegration of ³He have been recalculated using realistic bound-state wave functions. Contrary to previous calculations we find neither any unusual structure in the energy distributions nor any distinct signature of D-state components in the bound-state wave functions for photon energies ω ≦ 35 MeV. Final-state interactions and, possibly, meson exchange currents increase the total cross section substantially, but decrease the E2 contribution from 1 % to 0.5 %. After subtraction of spurious non-orthogonal components in the wave function, the M1 contribution decreases by about one order of magnitude to a value of 1.5 % in agreement with the experimental data.     

The oscillator frequency in resonating-group-method calculations

For the example α-¹⁶O we present simple RGM calculations with equal (ω = ω′) and different (ω ≠ ω′) oscillator frequencies for the two nuclei. In the case ω ≠ ω′ and ω → ω′ the one-channel RGM space for angular momentum zero contains all ²⁰Ne states with four particles in the s-d shell and total spatial symmetry ($\text{[?] = [4]}$). These states form a basis for low-lying excited 0⁺ states of ²⁰Ne. The ω ≠ ω′ calculation (as well for ω → ω′ as for realistic ω, ω') exhibits, therefore, resonances corresponding to these states. We present also the calculation for ω = ω′ where these physically important resonances are missing.     

Theory of the local field correction in an electron gas

The wave-vector- and frequency-dependent dielectric function ?(k,ω) of an electron gas can be expressed in terms of Lindhard's function and a complex local field correctionG(k,ω) which incorporates all the effects of dynamic exchange and correlation in the system. The general properties ofG(k,ω) are discussed, in particular the static and high-frequency limits. It is shown that for smallk, bothG(k, 0) andG(k, ∞) vary ask ², with different coefficients, but both determined by the average kinetic and potential energies per particle. For largek,G(k, ∞) varies again ask ² and it is argued that the same holds true forG(k, 0), with both coefficients (though different) determined by the average kinetic energy per particle. General formulas for the plasma dispersion relation and damping, involving, respectively, the real and imaginary parts ofG(k,ω), are given. The term in the plasma frequency which is proportional tok ² is given directly in terms of the average kinetic and potential energies per particle, a result true at all temperatures. A calculation of the frequency dependence ofG(k,ω), starting from the exact equation of motion for the particle-hole operator and employing a decoupling approximation introduced previously by Toigo and Woodruff, is presented. Explicit results forG(k,ω) are obtained for smallk and allω. The complete expressions forG(k, 0) andG(k, ∞) in this approximation have been obtained and are plotted.     

Electron Green's function in the planar t − J model

The electron Green's functions G(k, ω) within the t ? J model and in the regime of intermediate doping is studied analytically using equations of motion for projected fermionic operators and the decoupling of the self energy into the single-particle and spin fluctuations. It is shown that the assumption of marginal spin dynamics at T = 0 leads to an anomalous quasiparticle damping. Numerical results show also a pronounced asymmetry between the hole (ω < 0) and the electron (ω > 0) part of the spectral function, whereby hole-like quasiparticles are generally overdamped.     

Quantum beats in two-photon resonance fluorescence

The two-photon resonance fluorescence spectrum of a three-level atom is shown to consist of the low frequency modes in addition to the high frequency ones in the limit of high photon densities. The spectral function for the low frequency modes consists of two lorentzian lines describing: the peak occuring at the renormalized beat frequency Δ₊ and that of the zero-photon excitation at the frequency Δ_-, where Δ_±=Δ-3Ω²/2ω_a±Ω²u/2ω_a, u²=1+(2Δω_a/Ω ²)². Here, 2Δ is the energy splitting between the two excited states, ω_a is the photon energy of the pump field and Ω is the Rabi frequency. The peak at the renormalized beat frequency Δ₊ occurs provided that the condition (2Δω_a/Ω²)² > 1 is satisfied. The two-photon laser spectroscopy is expected to be a useful tool for the observation of the low frequency modes in question.     

A study of even-parity states of the nuclei 19F, 21Ne and 23Na with the generator coordinate method and with mixing of projected Hartree-Fock determinants in comparison with complete diagonalization

The energies and electromagnetic properties of the even-parity states of the nuclei ¹⁹F, ²¹Ne and ²³Na are calculated with the generator coordinate method and with mixing of projected HartreeFock determinants, using the Kuo and the Preedom-Wildenthal two-body interactions. The two parameters β and ? of Nilsson's potential are chosen as generator coordinates and the subspace is enlarged with a few different configurations, i.e. one for A = 19 and three for A = 21 and 23 nuclei. Special care is taken in choosing the appropriate Hartree-Fock solution corresponding to possible occupied single-particle states. For both methods six basic functions are enough to obtain a good approximation to complete diagonalization within the same model space. The collective features of these nuclei are also investigated.     

Calculation of the static and dynamic triaxial shapes of 24Mg

The Skyrme interaction is used in a Hartree-Fock calculation of ²⁴Mg with triaxial symmetry. A transition between axial and triaxial shapes is studied as a function of the spin-orbit strength. The effect of the other components of the interaction on the shape of ²⁴Mg is examined. Constrained Hartree-Fock calculations of the energy surface and the cranking mass parameter are used for the calculation of the intrinsic γ-vibration. The main result of the dynamical calculation is that despite the different equilibrium shapes obtained with the two forces SIII and SV, the triaxiality obtained by considering the zero-point γ-oscillation is essentially the same for both forces.     

Evidence for reduced neutron pairing correlations in 165Yb

Three rotational sequences in ¹⁶⁵Yb have been extended to high spins by using the ¹³⁰Te(⁴⁰Ar, 5n) and ¹⁵⁰Nd(²⁰Ne, 5n) reactions. Evidence is presented for a reduction of the neutron pairing correlations at the highest rotational frequencies (hω > 0.40 MeV), but no quantitative measure of this reduction can be made. There appears to be a conflict with the expectations of simple CSM calculations.     

The effect of correlation on the excitation probability Kr 4p 6→Rb+ 4p 5 5p following β-decay

Using a multi-configuration Hartree-Fock (MCHF) approximation for the stationary states, the effect of correlation on the excitation probability, Kr 4p ^{6 1} S→ Rb⁺ 4p ⁵ 5p ¹ S is studied. It is shown that the MCHF approximation equivalent to a nonorthogonal Hartree-Fock approximation, is the most important correction to the Hartree-Fock total wave function, and that the remaining correlation, though significant, has a much smaller effect.     

Stimulated Raman scattering of sub-millimeter waves in bismuth

A high-power sub-millimeter wave propagating through bismuth, a semimetal with non-spherical energy surfaces, parametrically excites a space-charge mode and a back-scattered electromagnetic wave. The free carrier density perturbation associated with the space-charge wave couples with the oscillatory velocity due to the pump to derive the scattered wave. The scattered and pump waves exert a pondermotive force on electrons and holes, driving the space-charge wave. The collisional damping of the decay waves determines the threshold for the parametric instability. The threshold intensity for 20 μm wavelength pump turns out to be ∼2×10¹² W/cm². Above the threshold, the growth rate scales increase with ω_o, attain a maximum around ω_o=6.5ω_p, and, after this, falls off.     

DFT study on addition reaction mechanism of guanine‐cytosine base pair with OH radical

The addition reaction mechanism of OH radical with guanine‐cytosine (G^.C) base pair has been explored at the B3LYP/DZP++ level of density functional theory (DFT). Structures perturbations along the hydroxylation of G^.C base pair cause strain in the pairing and double‐strand breaks in DNA. Seven possible hydroxylation reactions are exothermic, and the reaction energy decreases in the order of G^.C^C4 > G^C5.C > G^C2.C > G^C4.C > G^.C^C5 > G^.C^C6 > G^C8.C. The hydroxylation reactions at G^.C^C5 and G^C8.C sites appear to be barrierless, and the sequence of the barrier energy is G^.C^C4 > G^C4.C > G^C2.C > G^C5.C > G^.C^C6 > G^.C^C5 ~ G^C8.C. The results indicate that hydroxylation at G^C8.C, G^.C^C5 and G^.C^C6 are more thermodynamically and kinetically favorable than other sites in G^.C base pair. Considering the solvent effects by using the polarizable continuum model, the stabilities of all the compounds are increased significantly. Little change is taken place on the data of the reaction energies and barrier energies. Their sequences and the stability order follow the same trends like them in gas phase. The fluctuation of natural bond orbital charge further confirms that the hydroxylation reactions are exothermic. And transient spectra computed with the time‐dependent density functional theory (TD‐DFT) match well with the previous experimental and theoretical reports. Our deduced mechanism is in good agreement with the experimentally observed hydroxylated adducts. Copyright © 2015 John Wiley & Sons, Ltd.     

Wave functions for low-lying states of light deformed nuclei using a “realistic” hamiltonian and their test by inelastic scattering: The case of 20Ne

Nuclear structure wave functions for the ground and low-lying excited states of ²⁰Ne, obtained from the angular momentum projected deformed particle-hole model using a “realistic” many-nucleon hamiltonian (kinetic energy plus a Brueckner G-matrix based on the Hamada-Johnston potential), are used as input to microscopic antisymmetrised DWBA analyses of inelastic proton scattering from ²⁰Ne. This nuclear structure model, which has been previously shown able to describe the essential features of the giant multipole resonances of both ²⁰Ne and ²⁸Si, predicts angular distributions for inelastic proton scattering, exciting a number of states below 9 MeV in ²⁰Ne, in qualitative agreement with the available data; a somewhat surprising result given the nuclear structure model's completely microscopic formulation. Anomalies observed in the assignment of some predicted levels to experimental states suggest some shortcomings in the form adopted for the hamiltonian.     

Nuclear compression moduli and density-dependent forces

Density-dependent zero-range forces of the form of the modified delta interaction (MDI) are generalized (MDI3, MDI4) in order to yield reasonable values of the compression modulus in nuclear matter (K_N = 200 MeV). This low value can be fitted by introducing two terms with different density dependence in the force. The four free parameters of MDI3 are adjusted to reproduce the nuclear matter values of the binding energy, density and compression modulus, and to fulfil the condition that the total energy of ¹⁶O in harmonic oscillator wave functions has a minimum at the oscillator length b = 1.75 fm, corresponding to the correct rms radius. MDI4 contains in addition a two-body spin-orbit interaction. The five parameters of MDI4 are fitted to the above three nuclear matter data and by requiring that Hartree-Fock (HF) calculations in ²⁰⁸Pb yield the experimental charge rms radius and reasonable values of certain single-particle spin-orbit splittings. The quality of MDI4 is checked by comparing calculated rms radii, binding energies, and elastic electron scattering cross sections with available experimental data for doubly closed shell nuclei. As a test the energy levels and the nuclear monopole polarization of muonic ²⁰⁸Pb are calculated self-consistently yielding impressive agreement with experiment.     

Two particle — two hole mixing in Hartree-Fock calculations

The constrained Hartree-Fock theory is used for studying the stability of the solutions against two particle — two hole excitations. Quadropole and hexadecapole deformation are imposed on the Hartree-Fock equations to get the true energy minimum and the equilibrium shape. Energy corrections are calculated using second-order perturbations and complete diagonalization. Applications are made to the ²⁰Ne and ²⁸Si nuclei.     

Multi-state impact parameter approximation for many particle excitations in atomic collisions; Total cross sections for Na-Ne and N-Ne

A multi-state impact parameter treatment of many electron excitations in atomic collisions for the energy rangeE _lab=1 keV–1 MeV is applied to the 3s-3p excitation of Na and to the⁴ S ² D,² P excitations of N by collision with Ne. The Ne-target, for which simultaneous excitations are neglected, is described by a Hartree-Fock frozen-core potential. The calculated cross sections for Na-Ne turn out to be higher by an order of magnitude than the available experiment.     

Angular-momentum-projected cranked hfb approach to the study of nuclear rotations

Employing a pairing-plus-quadrupole interaction hamiltonian and projecting out good angular momentum states from the cranked Hartree-Fock-Bogoliubov (CHFB) intrinsic wave functions the yrast spectra of ¹⁵⁸Dy and ¹⁶⁸Yb are calculated up to moderately high spins (I_max = 16) as to include the backbending region. Then the variation of pairing correlation, g-factor and rotational alignment of neutron spin as a function of total angular momentum is studied. The effect of particle number projection on the spin-projected CHFB wave functions is also investigated and is found to be unimportant for the calculation of g-factors. On the other hand, corrections of the excitation energies for number fluctuations in the CHFB wave functions are essential. Furthermore, looking at the distribution of the total projection quantum number K in various cranking wave functions we are able to throw some light on the K ≠ 0 nature of the aligned s-band.A variation-after-spin projection calculation strictly for the axial shape, without cranking, is also carried out for both the nuclei considered here. In the low-spin region this numerically “cheaper” scheme produces energy spectra similar to that of the CHFB method, and may thus be used to readjust the interaction parameters.     

β delayed emission of a proton by a one-neutron halo nucleus

Some one-neutron halo nuclei can emit a proton in a β decay of the halo neutron. The branching ratio towards this rare decay mode is calculated within a two-body potential model of the initial core + neutron bound state and final core + proton scattering states. The decay probability per second is evaluated for the ¹¹Be, ¹⁹C and ³¹Ne one-neutron halo nuclei. It is very sensitive to the neutron separation energy.     

Adiabatic and non-adiabattc cranking models for the solution of the large amplitude time-dependent Hartree-Fock equations and the calculation of nuclear energy surfaces

An analysis is made of the device of forced vibrations to reduce the difficult large amplitude TDHF (time-dependent Hartree-Fock) problem to a simpler static problem. It is shown that cranking is a perfectly valid technique if the cranking field is defined by the criterion that the constrained static wave function be identical at a given instant of time to the freely oscillating TDHF wave function. On the basis of this criterion an exact general expression is derived for the cranking field and adiabatic and non-adiabatic cranking models are proposed as practical means of solving the large amplitude TDHF equations and calculating energy surfaces for fission and heavy ion reactions. The non-adiabatic model, which is favoured, corresponds to cranking the nucleus to move always in the direction of a local decoupled “normal mode” calculated from its unconstrained time-dependent equations of motion. The familiar Belyaev cranking model and the Baranger-Kumar model are discussed in the context of the new formalism.