Descritpion of Exotic Nuclei Using Continuum Shell Model

In weakly bound exotic nuclei, number of excited bound states or narrow resonances is small and, moreover, they couple strongly to the particle continuum. Hence, these systems should be described in the quantum open system formalism which does not artificially separate the subspaces of (quasi-) bound and scattering states. The Shell Model Embedded in the Continuum provides a novel approach which solves this problem. Examples of application in sd-shell nuclei will be presented.Comment: Presented at the NATO Advanced Research Workshop Brijuni, Pula, Croatia, June 2-5, 200

Partial fiscal decentralization and public-sector heterogeneity: Theory and evidence from Norway

This paper provides an empirical test of a principal tenet of fiscal federalism: that spending discretion, when granted to localities, leads to public-sector heterogeneity, with public-good levels adjusting to suit local demands. The test is based on a simple model of partial fiscal decentralization, under which earmarking of central transfers for particular uses is eliminated, allowing funds to be spent according to local tastes. The model predicts that partial decen- tralization generates dispersion in the levels of public services as spending adjusts to local preferences. But the model also yields the more-general prediction that the characteristics of local jurisdictions should play a bigger role in determining the levels of public goods after a decentralization reform than before. Both predictions are confirmed by the paper's empirical results, which show the effects of the 1986 Norwegian reform

Emergence of influential spreaders in modified rumor models

The burst in the use of online social networks over the last decade has provided evidence that current rumor spreading models miss some fundamental ingredients in order to reproduce how information is disseminated. In particular, recent literature has revealed that these models fail to reproduce the fact that some nodes in a network have an influential role when it comes to spread a piece of information. In this work, we introduce two mechanisms with the aim of filling the gap between theoretical and experimental results. The first model introduces the assumption that spreaders are not always active whereas the second model considers the possibility that an ignorant is not interested in spreading the rumor. In both cases, results from numerical simulations show a higher adhesion to real data than classical rumor spreading models. Our results shed some light on the mechanisms underlying the spreading of information and ideas in large social systems and pave the way for more realistic diffusion models.Comment: 14 Pages, 6 figures, accepted for publication in Journal of Statistical Physic

Evidence of a new state in 11^{11}Be observed in the 11^{11}Li β\beta-decay

Coincidences between charged particles emitted in the $\beta$-decay of $^{11}$Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the $^{11}$Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in $^{11}$Be has been identified selecting the $\alpha$ + $^7$He$\to\alpha$ + $^6$He+n channel. The angular correlations between the $\alpha$ particle and the center of mass of the $^6$He+n system favors spin and parity assignment of 3/2$^-$ for this state as well as for the previously known state at 18 MeV.Comment: 13 pages, 6 figure

Systematic trends in beta-delayed particle emitting nuclei: The case of beta-p-alpha emission from 21Mg

We have observed beta+-delayed alpha and p-alpha emission from the proton-rich nucleus 21Mg produced at the ISOLDE facility at CERN. The assignments were cross-checked with a time distribution analysis. This is the third identified case of beta-p-alpha emission. We discuss the systematic of beta-delayed particle emission decays, show that our observed decays fit naturally into the existing pattern, and argue that the patterns are to a large extent caused by odd-even effects.Comment: 6 pages, 5 figure

Clarification of the low-lying states of Be-9

5 pages, 1 table, 2 figures.-- Presented at the International Conference on Finite Fermionic Systems: Nilsson Model 50 years (Lund University, Sweden, June 14–18, 2005).-- PACS nrs.: 23.40.Hc, 27.20.+n, 24.80.+y.A newly developed technique for dealing with three-body decays of broad isolated levels is extended to deal with the broad, overlapping levels found at 2-9 MeV excitation energy in Be-9. The levels are populated through beta-decay of Li-9. The method gives firm evidence for the existence of several levels. Angular correlation studies allow spin values to be assigned.Peer reviewe

Clarification of the low-lying states of Be-9

5 pages, 1 table, 2 figures.-- Presented at the International Conference on Finite Fermionic Systems: Nilsson Model 50 years (Lund University, Sweden, June 14–18, 2005).-- PACS nrs.: 23.40.Hc, 27.20.+n, 24.80.+y.A newly developed technique for dealing with three-body decays of broad isolated levels is extended to deal with the broad, overlapping levels found at 2-9 MeV excitation energy in Be-9. The levels are populated through beta-decay of Li-9. The method gives firm evidence for the existence of several levels. Angular correlation studies allow spin values to be assigned.Peer reviewe

Nuclear structure of Ac-231

The low-energy structure of 231Ac has been investigated by means of gamma ray spectroscopy following the beta-decay of 231Ra. Multipolarities of 28 transitions have been established by measuring conversion electrons with a mini-orange electron spectrometer. The decay scheme of 231Ra --> 231Ac has been constructed for the first time. The Advanced Time Delayed beta-gamma-gamma(t) method has been used to measure the half-lives of five levels. The moderately fast B(E1) transition rates derived suggest that the octupole effects, albeit weak, are still present in this exotic nucleus

Study of bound states in 12Be through low-energy 11Be(d,p)-transfer reactions

The bound states of 12Be have been studied through a 11Be(d,p)12Be transfer reaction experiment in inverse kinematics. A 2.8 MeV/u beam of 11Be was produced using the REX-ISOLDE facility at CERN. The outgoing protons were detected with the T-REX silicon detector array. The MINIBALL germanium array was used to detect gamma rays from the excited states in 12Be. The gamma-ray detection enabled a clear identification of the four known bound states in 12Be, and each of the states has been studied individually. Differential cross sections over a large angular range have been extracted. Spectroscopic factors for each of the states have been determined from DWBA calculations and have been compared to previous experimental and theoretical results

Beta-delayed deuteron emission from 11Li: decay of the halo

The deuteron-emission channel in the beta-decay of the halo-nucleus 11Li was measured at the ISAC facility at TRIUMF by implanting post-accelerated 11Li ions into a segmented silicon detector. The events of interest were identified by correlating the decays of 11Li with those of the daughter nuclei. This method allowed the energy spectrum of the emitted deuterons to be extracted, free from contributions from other channels, and a precise value for the branching ratio B_d = 1.30(13) x 10-4 to be deduced for E(c.m.) > 200 keV. The results provide the first unambiguous experimental evidence that the decay takes place essentially in the halo of 11Li, and that it proceeds mainly to the 9Li + d continuum, opening up a new means to study of the halo wave function of 11Li.Comment: 4 pages, 3 figure