Spherical Shell Model description of rotational motion

Exact diagonalizations with a realistic interaction show that configurations with four neutrons in a major shell and four protons in another -or the same- major shell, behave systematically as backbending rotors. The dominance of the $q\cdot q$ component of the interaction is explained by an approximate form of SU3 symmetry. It is suggested that these configurations are associated with the onset of rotational motion in medium and heavy nuclei.Comment: 7 pages, RevTeX 3.0 using psfig, 6 Postscript figures included using uufile

Stringent Numerical Test of the Poisson Distribution for Finite Quantum Integrable Hamiltonians

Using a new class of exactly solvable models based on the pairing interaction, we show that it is possible to construct integrable Hamiltonians with a Wigner distribution of nearest neighbor level spacings. However, these Hamiltonians involve many-body interactions and the addition of a small integrable perturbation very quickly leads the system to a Poisson distribution. Besides this exceptional cases, we show that the accumulated distribution of an ensemble of random integrable two-body pairing hamiltonians is in perfect agreement with the Poisson limit. These numerical results for quantum integrable Hamiltonians provide a further empirical confirmation to the work of the Berry and Tabor in the semiclassical limit.Comment: 5 pages, 4 figures, LaTeX (RevTeX 4) Content changed, References added Accepted for publication in PR

Backbending in 50Cr

The collective yrast band and the high spin states of the nucleus 50Cr are studied using the spherical shell model and the HFB method. The two descriptions lead to nearly the same values for the relevant observables. A first backbending is predicted at I=10\hbar corresponding to a collective to non-collective transition. At I=16\hbar a second backbending occurs, associated to a configuration change that can also be interpreted as an spherical to triaxial transition.Comment: ReVTeX v 3.0 epsf.sty, 5 pages, 5 figures included. Full Postscript version available at http://www.ft.uam.es/~gabriel/Cr50art.ps.g

Ciencia en el aula. una propuesta para el desarrollo, adquisición y evaluación de las competencias

Desde el SXVIII (nacimiento del museo moderno) hasta hoy ha habido un cambio sustancial en las instituciones museísticas. Las funciones de conservación, exhibición e investigación han cedido parte de su protagonismo a la educativa. El Parque de las Ciencias articula esta función desde el Departamento de Educación y Actividades que desde el año 2006 viene desarrollando la actuación Ciencia en el Aula, dentro del programa Asómate a la Ciencia y financiada por la Consejería de Educación de la Junta de Andalucía. En este artículo se presenta Ciencia en el Aula como algo más que un espacio para exponer las actividades de investigación realizadas en los centros educativos andaluces. La presentación y el desarrollo expositivo de las mismas puede constituir una herramienta que permite el desarrollo y adquisición de las competencias básicas , así como la evaluación de todo el proceso

1/f noise in the Two-Body Random Ensemble

We show that the spectral fluctuations of the Two-Body Random Ensemble (TBRE) exhibit 1/f noise. This result supports a recent conjecture stating that chaotic quantum systems are characterized by 1/f noise in their energy level fluctuations. After suitable individual averaging, we also study the distribution of the exponent \alpha in the 1/f^{\alpha} noise for the individual members of the ensemble. Almost all the exponents lie inside a narrow interval around \alpha=1 suggesting that also individual members exhibit 1/f noise, provided they are individually unfoldedComment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.

Full 0ℏω0\hbar\omega shell model calculation of the binding energies of the 1f7/21f_{7/2} nuclei

Binding energies and other global properties of nuclei in the middle of the $pf$ shell, such as M1, E2 and Gamow-Teller sum rules, have been obtained using a new Shell Model code (NATHAN) written in quasi-spin formalism and using a $j-j$-coupled basis. An extensive comparison is made with the recently available Shell Model Monte Carlo results using the effective interaction KB3. The binding energies for -nearly- all the $1f_{7/2}$ nuclei are compared with the measured (and extrapolated) results.Comment: 7 page

Shell Model Study of the Double Beta Decays of 76^{76}Ge, 82^{82}Se and 136^{136}Xe

The lifetimes for the double beta decays of $^{76}$Ge, $^{82}$Se and $^{136}$Xe are calculated using very large shell model spaces. The two neutrino matrix elements obtained are in good agreement with the present experimental data. For $<1$ eV we predict the following upper bounds to the half-lives for the neutrinoless mode: $T^{(0\nu)}_{1/2}(Ge) > 1.85\,10^{25} yr.$, $T^{(0\nu)}_{1/2}(Se) > 2.36\,10^{24} yr.$ and $T^{(0\nu)}_{1/2}(Xe) > 1.21\,10^{25} yr$. These results are the first from a new generation of Shell Model calculations reaching O(10$^{8}$) dimensions

Theoretical derivation of 1/f noise in quantum chaos

It was recently conjectured that 1/f noise is a fundamental characteristic of spectral fluctuations in chaotic quantum systems. This conjecture is based on the behavior of the power spectrum of the excitation energy fluctuations, which is different for chaotic and integrable systems. Using random matrix theory we derive theoretical expressions that explain the power spectrum behavior at all frequencies. These expressions reproduce to a good approximation the power laws of type 1/f (1/f^2) characteristics of chaotic (integrable) systems, observed in almost the whole frequency domain. Although we use random matrix theory to derive these results, they are also valid for semiclassical systems.Comment: 5 pages (Latex), 3 figure

Short-range correlations and neutrinoless double beta decay

In this work we report on the effects of short-range correlations upon the matrix elements of neutrinoless double beta decay. We focus on the calculation of the matrix elements of the neutrino-mass mode of neutrinoless double beta decays of 48Ca and 76Ge. The nuclear-structure components of the calculation, that is the participant nuclear wave functions, have been calculated in the shell-model scheme for 48Ca and in the proton-neutron quasiparticle random-phase approximation (pnQRPA) scheme for 76Ge. We compare the traditional approach of using the Jastrow correlation function with the more complete scheme of the unitary correlation operator method (UCOM). Our results indicate that the Jastrow method vastly exaggerates the effects of short-range correlations on the neutrinoless double beta decay nuclear matrix elements.Comment: 12 pages, 3 figures, to appear in Physics Letters B (2007