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

Perturbative description of nuclear double beta decay transitions

A consistent treatment of intrinsic and collective coordinates is applied to the calculation of matrix elements describing nuclear double beta decay transitions. The method, which was developed for the case of nuclear rotations, is adapted to include isospin and number of particles degrees of freedom. It is shown that the uncertainties found in most models, in dealing with these decay modes, are largely due to the mixing of physical and spurious effects in the treatment of isospin dependent interactions.Comment: 4 pages, 2 figures, RevTe

Double beta decay of 100Mo^{100}Mo: the deformed limit

The double beta decay of $^{100}Mo$ to the ground state and excited states of $^{100}Ru$ is analysed in the context of the pseudo SU(3) scheme. The results of this deformed limit are compared with the vibrational one based on the QRPA formalism. Consistency between the deformed limit and the experimental information is found for various $\beta\beta$ transitions, although, in this approximation some energies and B(E2) intensities cannot reproduced.Comment: 16 pages, revtex, no figures. Submmitted to Phys. Rev.

Light-neutrino mass hierarchies, nuclear matrix elements, and the observability of neutrinoless double-beta decay

Results for neutrino flavor oscillations and neutrino mixing mechanisms, obtained from the analysis of the Sudbury Neutrino Observatory (SNO), the SuperKamiokande (SK), CHOOZ, KamLAND and WMAP data, are used to calculate the effective neutrino mass relevant for the neutrinoless double-beta decay. The observability of the decay of 76Ge is discussed within different light-neutrino mass hierarchies and by presenting a systematics on the available nuclear matrix elements.Comment: 25 pages, 1 figur

Uncertainties in the 0νββ0\nu\beta\beta--decay nuclear matrix elements

The nuclear matrix elements $M^{0\nu}$ of the neutrinoless double beta decay ($0\nu\beta\beta$) of most nuclei with known $2\nu\beta\beta$-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA (RQRPA). The experimental $2\nu\beta\beta$-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. With such procedure the $M^{0\nu}$ values become essentially independent on single-particle basis size, the axial vector quenching factor, etc. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. It is suggested that most of the spread among the published $M^{0\nu}$'s can be ascribed to the choices of implicit and explicit parameters, inherent to the QRPA method.Comment: 9 pages, 1 figure. Contribution to MEDEX'05, Corfu, Greece, September 26 - 29, 2005. A short version of nucl-th/0503063, to be published in Czech. J. Phy

The effect of microstructure on mechanical properties of HVOF sprayed WC-CoCr composite coatings

This study aims for deeper understanding of the composition and phase changes occurring during HVOF spraying of the powder to WC-CoCr coatings. Also, the effect of lamellar microstructure on the mechanical properties is studied. Compositional and microstructural features are studied by means of X-ray diffraction, XRF, FE-SEM and TEM (EDX, EELS). Mechanical properties are mainly studied by different instrumented indentation and nanoindentation techniques. The use of two new fracture parameters, complementing the fracture toughness value of the coating, are proposed and examined. Higher load range indentations are used to measure cross-sectional and surface hardness, elastic modulus and fracture toughness of the coatings. Mechanical properties of individual phases are studied by nanoindentation. To our knowledge this is the first time that the mechanical properties of this amorphous/nanocrystalline matrix are studied. ICP (In-situ Coating Property) sensor, developed for quality control and residual stress evaluation, is also used to measure the elastic modulus and coefficient of thermal expansion (CTE) of the coatings. Abrasion wear resistance of the coatings are studied according to standard ASTM G 65D. Because of the brittle nature of HVOF coatings, the main focus of this study is in the effects of coating microstructure on fracture toughness, and on crack initiation and propagation resistance. It is shown that even when two similar coatings have equal indentation fracture toughness values, the critical crack initiation loads may be very different. This new parameter is expected to be extremely useful in the evaluation of the coating performance under loading conditions

Double beta decay to excited states in Nd150

The pseudo SU(3) model is used to study the double beta decay of Nd150 to the ground and excited states of Sm150 . Low lying collective excitations of Sm150 and its BE(2) intensities are well reproduced. Expressions for the two neutrino double beta decay to excited states are developed and used to describe the decay of Nd150 . The existence of selection rules which strongly restrict the decay is discussed.Comment: 22 pages, LaTeX, 1 figure with Postscript file available under request at [email protected]

Shell model description of Ge isotopes

A shell model study of the low energy region of the spectra in Ge isotopes for $38\leq N\leq 50$ is presented, analyzing the excitation energies, quadrupole moments, $B(E2)$ values and occupation numbers. The theoretical results have been compared with the available experimental data. The shell model calculations have been performed employing three different effective interactions and valence spaces.We have used two effective shell model interactions, JUN45 and jj44b, for the valence space $f_{5/2} \, p \,g_{9/2}$ without truncation. To include the proton subshell $f_{7/2}$ in valence space we have employed the $fpg$ effective interaction due to Sorlin {\it et al.}, with $^{48}$Ca as a core and a truncation in the number of excited particles.Comment: 10 pages, 10 figures, Proc. of the XXXV Nuclear Physics Symposium, January 3-6 2012, Cocoyoc, Morelos, Mexico. IOP Journal of Physics: Conference Series (in press