Dynamical Synthesis of

In the exothermic process of fission decay, an atomic nucleus splits into two or more independent fragments. Several aspects of nuclear fission are not properly understood, in particular the formation of the neck between the nascent fragments, and the subsequent mechanism of scission into two or more independent fragments. Using an implementation of time-dependent density functional theory, based on a relativistic energy density functional and including pairing correlations, we analyze the final phase of the process of induced fission of ^{240}Pu, and show that the timescale of neck formation coincides with the assembly of two α-like clusters. Because of its much larger binding energy, the dynamical synthesis of ^{4}He in the neck predominates over other light clusters, e.g., ^{3}H and ^{6}He. At the instant of scission the neck ruptures exactly between the two α-like clusters, which separate because of the Coulomb repulsion and are eventually absorbed by the two emerging fragments. The mechanism of light charged clusters formation at scission could also be linked to ternary fission.

Microscopic Description of 2α Decay in

A microscopic calculation of half-lives for both the α and 2α decays of ^{212}Po and ^{224}Ra is performed, using a self-consistent framework based on energy density functionals. A relativistic density functional and a separable pairing interaction of finite range are used to compute axially symmetric deformation energy surfaces as functions of quadrupole, octupole, and hexadecapole collective coordinates. Dynamical least-action paths are determined, that trace the α and 2α emission from the equilibrium deformation to the point of scission. The calculated half-lives for the α decay of ^{212}Po and ^{224}Ra are in good agreement with data. A new decay mode, the symmetric 2α emission, is predicted with half-lives of the order of those observed for cluster emission.

Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the

Lifetime measurements of excited states of the light N=52 isotones ^{88}Kr, ^{86}Se, and ^{84}Ge have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2;2^{+}→0^{+}) and B(E2;4^{+}→2^{+}) were obtained for the first time for the hard-to-reach ^{84}Ge. While the B(E2;2^{+}→0^{+}) values of ^{88}Kr, ^{86}Se saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g_{7/2}, 1h_{11/2}) space of an inert ^{78}Ni core, the value obtained for ^{84}Ge largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N≲49, extend beyond N=50. The onset of collectivity at Z=32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector ρ field in shell-structure evolution.

How atomic nuclei cluster.

Nucleonic matter displays a quantum-liquid structure, but in some cases finite nuclei behave like molecules composed of clusters of protons and neutrons. Clustering is a recurrent feature in light nuclei, from beryllium to nickel. Cluster structures are typically observed as excited states close to the corresponding decay threshold; the origin of this phenomenon lies in the effective nuclear interaction, but the detailed mechanism of clustering in nuclei has not yet been fully understood. Here we use the theoretical framework of energy-density functionals, encompassing both cluster and quantum liquid-drop aspects of nuclei, to show that conditions for cluster formation can in part be traced back to the depth of the confining nuclear potential. For the illustrative example of neon-20, we show that the depth of the potential determines the energy spacings between single-nucleon orbitals in deformed nuclei, the localization of the corresponding wavefunctions and, therefore, the degree of nucleonic density clustering. Relativistic functionals, in particular, are characterized by deep single-nucleon potentials. When compared to non-relativistic functionals that yield similar ground-state properties (binding energy, deformation, radii), they predict the occurrence of much more pronounced cluster structures. More generally, clustering is considered as a transitional phenomenon between crystalline and quantum-liquid phases of fermionic systems.

Robust regularity in γ-soft nuclei and its microscopic realization.

γ softness in atomic nuclei is investigated in the framework of energy density functionals. By mapping constrained microscopic energy surfaces for a set of representative nonaxial medium-heavy and heavy nuclei to a Hamiltonian of the proton-neutron interacting boson model (IBM-2) containing up to three-body interactions, low-lying collective spectra and transition rates are calculated. Observables are analyzed that distinguish between the two limiting geometrical pictures of nonaxial nuclei: the rigid-triaxial rotor and the γ-unstable rotor. It is shown that neither of these pictures is realized in actual nuclei, and that a microscopic description leads to results that are almost exactly in between the two geometrical limits. This finding points to the optimal choice of the IBM Hamiltonian for γ-soft nuclei.

Isoscalar and isovector splitting of pygmy dipole structures.

The electric-dipole response of 140Ce is investigated using the fully consistent relativistic quasiparticle random phase approximation. By analyzing the isospin structure of the E1 response, it is shown that the low-energy (pygmy) strength separates into two segments with different isospin character. The more pronounced pygmy structure at lower energy is composed of predominantly isoscalar states with surface-peaked transition densities. At somewhat higher energy the calculated E1 strength is primarily of isovector character, as expected for the low-energy tail of the giant dipole resonance. The results are in qualitative agreement with those obtained in recent (gamma, gamma') and (alpha, alpha'gamma) experiments, and provide a simple explanation for the splitting of low-energy E1 strength into two groups of states with different isospin structure and radial dependence of the corresponding transition densities.

Microscopic description of nuclear quantum phase transitions.

The relativistic mean-field framework, extended to include correlations related to restoration of broken symmetries and to fluctuations of the quadrupole deformation, is applied to a study of shape transitions in Nd isotopes. It is demonstrated that the microscopic self-consistent approach, based on global effective interactions, can describe not only general features of transitions between spherical and deformed nuclei, but also the singular properties of excitation spectra and transition rates at the critical point of quantum shape phase transition.

Proton electric pygmy dipole resonance.

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.

Spin-isospin resonances and the neutron skin of nuclei.

The Gamow-Teller resonances (GTR) and isobaric analog states (IAS) of a sequence of even-even Sn target nuclei are calculated by using the framework of the relativistic Hartree-Bogoliubov model plus proton-neutron quasiparticle random-phase approximation. The calculation reproduces the experimental data on ground-state properties, as well as the excitation energies of the isovector excitations. It is shown that the isotopic dependence of the energy spacings between the GTR and IAS provides direct information on the evolution of neutron-skin thickness along the Sn isotopic chain. A new method is suggested for determining the difference between the radii of the neutron and proton density distributions along an isotopic chain, based on measurement of the excitation energies of the GTR relative to the IAS.

Nonlinear dynamics of giant resonances in atomic nuclei.

The dynamics of monopole giant resonances in nuclei is analyzed in the time-dependent relativistic mean-field model. The phase spaces of isoscalar and isovector collective oscillations are reconstructed from the time series of dynamical variables that characterize the proton and neutron density distributions. The analysis of the resulting recurrence plots and correlation dimensions indicates regular motion for the isoscalar mode, and chaotic dynamics for the isovector oscillations. Information-theoretic functionals identify and quantify the nonlinear dynamics of giant resonances in quantum systems that have spatial as well as temporal structure.

Cardiopulmonary bypass resuscitation for accidental hypothermia.

Many victims of accidental hypothermia have been successfully resuscitated with cardiopulmonary bypass, but questions remain regarding treatment indications and efficacy. To assess the role of cardiopulmonary bypass in resuscitation from hypothermia, a collective literature review was performed. Data on 68 hypothermic patients resuscitated with cardiopulmonary bypass were analyzed. Impairment from alcohol, drug abuse, or mental illness was the most common predisposing factor for accidental hypothermia. Mean initial core temperature was 21 degrees C. Sixty-one patients (90%) were in cardiac arrest. Femoral-femoral bypass was used in 72% of patients. Overall survival was 60%. Eighty percent of survivors returned to their previous level of function. Sixty-seven percent of nonsurvivors died because of inability to establish a cardiac rhythm or wean from bypass. Patient age, type of cardiopulmonary bypass (femoral-femoral or atrial-aortic), and initial core temperature were not significant prognostic indicators. There were no survivors among the 6 patients with a core temperature less than 15 degrees C. Patients in cardiac arrest had a higher mortality than patients who were not (p = 0.02). Climbing and avalanche victims had a higher mortality than other hypothermic patients (p = 0.003). The possibility of publication bias must be considered before firm conclusions can be drawn from this collective literature review. Controlled studies comparing the efficacy of cardiopulmonary bypass and alternative warming techniques have not been done. Nevertheless, cardiopulmonary bypass has several advantages over other warming methods for profoundly hypothermic patients. Tissue perfusion and oxygenation are maintained while rapid warming occurs. Cardiopulmonary bypass resuscitation is recommended for hypothermic patients in arrest and for patients with core temperatures lower than 25 degrees C, irrespective of rhythm. Patients in stable condition with temperatures between 25 degrees and 28 degrees C can be treated with cardiopulmonary bypass or conventional warming methods.

Benign mucous membrane pemphigoid: treatment of esophageal stricture.

The authors describe a 35-year-old man who has had benign mucous membrane pemphigoid from the age of 12 years. Upper esophageal stricture, a rare complication of the syndrome, developed when he was 24 years old. This recurrent condition has been followed for 11 years. It was treated initially, for 6 years, with esophagoscopy and bougie dilatation. Balloon dilatation under fluoroscopic guidance was then substituted for bougienage; this procedure has been performed successfully 10 times over the last 5 years and remains the patient's preferred treatment. The mean period for recurrence of symptoms has been 5 months. Several previous reports of this condition describe treatment with esophagoscopy and bougie dilatation, but there has been no previous report of interventional radiology with balloon dilatation.

Cerebrovascular accident complicating extended cervical mediastinoscopy.

The safety and efficacy of staging cervical mediastinoscopy is well established. Extended cervical mediastinoscopy has been proposed as a safe and effective method of staging left upper lobe lung cancers. We report a case of cerebrovascular accident complicating extended cervical mediastinoscopy.