Empirical description of beta-delayed fission partial half-lives

Background: The process of beta-delayed fission (bDF) provides a versatile tool to study low-energy fission in nuclei far away from the beta-stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in bDF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of bDF partial half-lives. Results: The bDF partial half-life appears to exponentially depend on the difference between the Q value for beta decay of the parent nucleus and the fission-barrier energy of the daughter (after beta decay) product. Such dependence was found to arise naturally from some simple theoretical considerations. Conclusions: This systematic trend was confirmed for experimental bDF partial half-lives spanning over 7 orders of magnitudes when using fission barriers calculated from either the Thomas-Fermi or the liquid-drop fission model. The same dependence was also observed, although less pronounced, when comparing to fission barriers from the finite-range liquid-drop model or the Thomas-Fermi plus Strutinsky Integral method.Comment: accepted for publication in Phys. Rev.

Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism

The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely spin-, energy- and time-resolved photoemission and time-resolved magneto-optical Kerr effect. Combining the two methods it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs timescale. Instead we find experimental evidence for the relevance of Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.Comment: 12 pages, 3 figures; accepted by Physical Review Letter

Розрахунок кумулянтів і параметрів функції розподілу методом Монте-Карло та із рівняння для неї

Calculations results of the moments, central moments, cumulants and parameters of the distribution function of a beam of ions implanted in a solid body were analyzed. To analyze the differences between the results of modeling this process by the Monte Carlo method, which is widely used for practically important targets, and the results of the solution of the corresponding integrodifferential equations that describe ions distribution analytically, in the simple case of axial symmetry of the ion beam, when all moments of odd order along the transverse Cartesian coordinate is considered equal to zero due to the symmetry of the problem. It is shown that the same moments obtained by the Monte Carlo method is not exactly equal to zero, but slowly decrease with an increase in the number of ions, as predicted by statistics, and then remain approximately constant. Increasing the number of ions for Monte Carlo simulation reduces the statistical component of this error, but does not affect on the component arising from the application of a simplified model of ion-atom collisions. Pages of the article in the issue: 112 - 115 Language of the article: UkrainianПроаналізовано результати розрахунку моментів, центральних моментів, кумулянтів та параметрів функції розподілу пучка іонів імплантованих у тверде тіло. Для аналізу відмінностей між результатами моделювання цього процесу методом Монте-Карло, який широко використовується для практично важливих мішеней, та результатами розв’язку інтегродиференціальних рівнянь, які його описують аналітично, розглянуто випадок осьової симетрії пучка іонів, коли всі моменти непарного порядку по поперечній декартовій координаті рівні нулю в силу симетрії задачі. Показано, що ці ж самі моменти, отримані методом Монте-Карло повільно спадають до нуля із збільшенням кількості іонів, як і передбачається статистикою, і залишаються приблизно сталими

Abrupt changes in alpha decay systematics as a manifestation of collective nuclear modes

An abrupt change in $\alpha$ decay systematics around the N=126 neutron shell closure is discussed. It is explained as a sudden hindrance of the clustering of the nucleons that eventually form the $\alpha$ particle. This is because the clustering induced by the pairing mode acting upon the four nucleons is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.Comment: 6 pages, 3 figures, submitted to Phys. Rev. C, a few new references adde

Shape Coexistence in Pb186: Beyond-mean-field description by configuration mixing of symmetry restored wave functions

We study shape coexistence in Pb186 using configuration mixing of angular-momentum and particle-number projected self-consistent mean-field states. The same Skyrme interaction SLy6 is used everywhere in connection with a density-dependent zero-range pairing force. The model predicts coexisting spherical, prolate and oblate 0+ states at low energy.Comment: 5 pages REVTEX4, 4 eps figures, accepted by Phys. Lett. B. Revised version with some polishing of the text without changing its conten

Structural evolution in Pt isotopes with the Interacting Boson Model Hamiltonian derived from the Gogny Energy Density Functional

Spectroscopic calculations are carried out, for the description of the shape/phase transition in Pt nuclei in terms of the Interacting Boson Model (IBM) Hamiltonian derived from (constrained) Hartree-Fock-Bogoliubov (HFB) calculations with the finite range and density dependent Gogny-D1S Energy Density Functional. Assuming that the many-nucleon driven dynamics of nuclear surface deformation can be simulated by effective bosonic degrees of freedom, the Gogny-D1S potential energy surface (PES) with quadrupole degrees of freedom is mapped onto the corresponding PES of the IBM. Using this mapping procedure, the parameters of the IBM Hamiltonian, relevant to the low-lying quadrupole collective states, are derived as functions of the number of valence nucleons. Merits of both Gogny-HFB and IBM approaches are utilized so that the spectra and the wave functions in the laboratory system are calculated precisely. The experimental low-lying spectra of both ground-state and side-band levels are well reproduced. From the systematics of the calculated spectra and the reduced E2 transition probabilities $B$(E2), the prolate-to-oblate shape/phase transition is shown to take place quite smoothly as a function of neutron number $N$ in the considered Pt isotopic chain, for which the $\gamma$-softness plays an essential role. All these spectroscopic observables behave consistently with the relevant PESs and the derived parameters of the IBM Hamiltonian as functions of $N$. Spectroscopic predictions are also made for those nuclei which do not have enough experimental E2 data.Comment: 11 pages, 5 figure

Trends of Macroeconomic Models

This article provides an overview and analysis of the ideas of the leading macroeconomists expressed in the issue “Rebuilding Macroeconomic Theory”, Oxford Review of Economic Policy journal. These ideas were expressed in connection with the discussion of the future of macroeconomic models. The motivation for the discussion lies in the poor performance of macroeconomic models before the global economic crisis of 2007–2008 and in the subsequent period of recovery. The main issue considered by economists is the possible changes in the basic neoKeynesian model and DSGE-models as a whole. It was found that there are three directions for the solution of the issue. First, the rejection of the primary role of DSGE-models in the analysis of modern macroeconomics and the use of other types of models. Secondly, the elimination of defciencies of existing models associated with poor justifcation at the micro level, as well as an unsatisfactory description of fnancial frictions. Thirdly, it is possible not to make any targeted efforts, since the class of DSGE-models is still the most efcient. The paper concludes that the second path of development is more preferable