The giant dipole resonance in 55Co

Recent measurements of the ⁵⁴Fe(p, γ)⁵⁵Co cross section indicate the existence of a splitting between the T_< and T_> components of the giant dipole resonance. We have calculated the (p, γ) cross section in the shell-model formalism. The bound-state interaction was determined by a fit to fp and sd shell nuclei. The calculation predicts the isospin splitting of ≈ 2.4 MeV and is consistent with all data in the energy region E_p = 9–15 MeV as well as the low-lying ⁵⁵Co spectrum.     

Giant dipole resonance in heavy deformed nuclei

Analysis of all the experimental data on nuclear shape deformation and photonuclear reaction cross sections in the energy range of giant dipole resonance is performed. The relationship between the giant resonance width and the nuclear-quadrupole-deformation parameter value is shown.     

Giant dipole resonance parameters from photoabsorption cross-sections

The structural effect is believed to have no influence on the decay properties of medium and heavy-mass nuclei at excitation energies above the pairing gap.These properties can be described by statistical properties using so-called photon strength functions for different multipolarities,and directly related to the photoabsorption cross-section(σ_(abs)).σ_(abs) is dominated by the electric giant dipole resonance at y energy ε_γ≤40 MeV.In this study,we construct two kinds of systematic giant dipole resonance parameters by fitting the experimental photoabsorption crosssections.One is based on the microscopic relativistic quasiparticle random phase approximation approach,whereas the other is estimated by the phenomenological models within the Lorentzian representation.Both of them are demonstrated of efficiently describe the experimental photoabsorption cross-sections available for medium to heavymass nuclei,and they can obtain more reliable predictions for the unknown nuclear system.     

Giant dipole resonance in 4d photo absorption of atomic barium

We calculate the photoabsorption cross section for the 4d¹⁰ and 5p⁶ shells of atomic barium using the random phase approximation (RPAE) including relaxation. For both shells the oscillator strength goes mainly into a collective vibration of the entire shell.     

Giant dipole resonance and shape transitions in warm and rapidly rotating nuclei

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.     

Some properties of 1805 keV resonance in p +55Mn interaction

Rather special behaviour of the 1805 keV resonance in the p +⁵⁵Mn interaction, especially an extremely strong decay into the inelastic channel is discussed.     

Status of the endcap BGO calorimeter of the CMD-3 detector

The electromagnetic endcap BGO calorimeter of the CMD-3 detector is ready for experiments at the new e ⁺ e ^? collider VEPP-2000. Light readout is performed by silicon photodiodes. A thermalcontrol system that is able to maintain the calorimeter temperature at a level of 12 ±1°C was designed and manufactured. All blocks of the endcap calorimeter are assembled, tested, and prepared for installing at the detector.     

Giant dipole resonance in absorption and emission of γ rays by medium and heavy nuclei

Experimental characteristics of total cross sections for γ-ray absorption by medium and heavy nuclei in the energy region of giant dipole resonance are systematized. A variation of parameters of E1 giant resonance are analyzed as a function of mass, excitation energy, and angular momentum of nuclei. Experimental results are interpreted within the relevant theoretical approaches.     

Nature of the pygmy dipole resonance in 140Ce studied in (alpha, alpha' gamma) experiments

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').     

Nuclear magnetic resonance of 55Mn in the antiferromagnet CsMnBr3 in a variable longitudinal magnetic field

The spectrum and intensities of NMR lines are investigated experimentally and theoretically for excitation by an alternating magnetic field h‖ parallel to a static field H in the quasi-one-dimensional, six-sublattice antiferromagnet CsMnBr₃. According to theory, two new NMR lines, which are not excited by a transverse magnetic field h _⊥, are observed near the phase transition from triangular to collinear structure (H=H _c ) [JETP 86, 197 (1998)]. Zh. éksp. Teor. Fiz. 115, 2228–2241 (June 1999)     

Pygmy dipole resonance in nuclei

A brief survey of the state of the modern microscopic theory of the so-called pygmy dipole resonance in nuclei is given—in particular, some unresolved problems are listed. It is emphasized that, in order to explain the pygmy dipole resonance, it is necessary but not sufficient to take into account the coupling of single-particle degrees of freedom to photon degrees of freedom. The results of the calculations performed for the first time for the isovector pygmy dipole resonance and the isovector electric giant dipole resonance in ¹²⁴Sn within a self-consistent approach involving, in addition to the standard quasiparticle random-phase approximation, a single-particle continuum and quasiparticle-phonon coupling of single-particle degrees of freedom to phonon degrees of freedom are presented. The results are found to be in satisfactory agreement with experimental data. The calculation of the isoscalar strength function in the energy region of the pygmy dipole resonance revealed that the nuclear-structure mechanism does not provide the isoscalar-strength suppression observed at energies in excess of 7 MeV in (α, α′γ) reactions; therefore, this suppression may stem from the reaction mechanism.     

Giant dipole resonance in the hot and thermalized 132Ce nucleus: damping of collective modes at finite temperature

The gamma decay of the giant dipole resonance (GDR) in the 132Ce compound nucleus with temperature up to approximately 4 MeV has been measured, using the reaction 64Ni + 68Zn at E(beam) = 300, 400, and 500 MeV. The gamma and charged particles measured in coincidence with recoils are consistent with a fully equilibrated compound nucleus emission. The GDR width, obtained with the statistical model analysis, is found to increase almost linearly with temperature. This increase is rather well reproduced within a model including thermal shape fluctuations and the lifetime of the compound nucleus.     

Stagnancy of the pygmy dipole resonance

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.     

Evolution of the giant dipole resonance properties with excitation energy

The studies of the evolution of the hot Giant Dipole Resonance (GDR) properties as a function of excitation energy are reviewed. The discussion will mainly focus on the A ∼ 100-120 mass region where a large amount of data concerning the width and the strength evolution with excitation energy are available. Models proposed to interpret the main features and trends of the experimental results will be presented and compared to the available data in order to extract a coherent scenario on the limits of the development of the collective motion in nuclei at high excitation energy. Experimental results on the GDR built in hot nuclei in the mass region A ∼ 60-70 will be also shown, allowing to investigate the mass dependence of the main GDR features. The comparison between limiting excitation energies for the collective motion and critical excitation energies extracted from caloric curve studies will suggest a possible link between the disappearance of collective motion and the liquid-gas phase transition.