Shell-model half-lives for the N=82 nuclei and their implications for the r-process

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilties of the r-process waiting point nuclei at the magic neutron number N=82. We find good agreement with the measured half-lives of 129Ag and 130Cd. Our shell-model half-lives are noticeably shorter than those currently adopted in r-process simulations. Our calculation suggests that 130Cd is not produced in beta-flow equilibrium with the other N=82 isotones on the r-process path.Comment: 4 pages, 3 figure

The Beta Decay of 44V

We have calculated the $\beta^+$ decay of the proton rich nuclei $^{44}$V in a full fp-shell valence space. We obtain a theoretical half-life of 71~ms compared with the experimental value t$_{1/2}$ = 90 $\pm$ 25 ms. Besides, we make predictions for the Gamow-Teller strength functions corresponding to the decays of the 2$^+$ ground state and 6$^+$ isomer state.Comment: 8 pages, REVTEX 3.0 with epsf.sty, 4 figures Postscrip included and compressed using uufiles, FTUAM-92/0

Magnetoplasmons excitations in graphene for filling factors ν≤6\nu \leq 6

In the frame of the Hartree-Fock approximation, the dispersion of magnetoplasmons in Graphene is derived for all types of transitions for filling factors $\nu\leq 6$. The optical conductivity components of the magnetoplasmon curves are calculated. It is shown that the electron-electron interactions lead to a strong re-normalization of the apparent Fermi velocity of Graphene which is different for different types of transitions.Comment: 15 pages, 7 figure

Shell-model calculations of stellar weak interaction rates: II. Weak rates for nuclei in the mass range A=45-65 in supernovae environment

Based on large-scale shell model calculations we have determined the electron capture, positron capture and beta-decay rates on more than 100 nuclei in the mass range A=45-65. The rates are given for densities \rho Y_e =10^7-10^{10} mol/cm^3 and temperatures T=10^9-10^{10} K and hence are relevant for both types of supernovae (Type Ia and Type II). The shell model electron capture rates are significantly smaller than currently assumed. For proton-to-baryon ratios Y_e=0.42-0.46 mol/g, the beta-decay rates are faster than the electron capture rates during the core collapse of a massive star.Comment: 16 pages, 10 figure

Dynamical r-process studies within the neutrino-driven wind scenario and its sensitivity to the nuclear physics input

We use results from long-time core-collapse supernovae simulations to investigate the impact of the late time evolution of the ejecta and of the nuclear physics input on the calculated r-process abundances. Based on the latest hydrodynamical simulations, heavy r-process elements cannot be synthesized in the neutrino-driven winds that follow the supernova explosion. However, by artificially increasing the wind entropy, elements up to A=195 can be made. In this way one can reproduce the typical behavior of high-entropy ejecta where the r-process is expected to occur. We identify which nuclear physics input is more important depending on the dynamical evolution of the ejecta. When the evolution proceeds at high temperatures (hot r-process), an (n,g)-(g,n) equilibrium is reached. While at low temperature (cold r-process) there is a competition between neutron captures and beta decays. In the first phase of the r-process, while enough neutrons are available, the most relevant nuclear physics input are the nuclear masses for the hot r-process and the neutron capture and beta-decay rates for the cold r-process. At the end of this phase, the abundances follow a steady beta flow for the hot r-process and a steady flow of neutron captures and beta decays for the cold r-process. After neutrons are almost exhausted, matter decays to stability and our results show that in both cases neutron captures are key for determining the final abundances, the position of the r-process peaks, and the formation of the rare-earth peak. In all the cases studied, we find that the freeze out occurs in a timescale of several seconds.Comment: 20 pages, 12 figures, submitted to Phys. Rev. C (improved version

Reflectance Transformation Imaging (RTI) System for Ancient Documentary Artefacts

This tutorial summarises our uses of reflectance transformation imaging in archaeological contexts. It introduces the UK AHRC funded project reflectance Transformation Imaging for Anciant Documentary Artefacts and demonstrates imaging methodologies