Constraints on the Huygens landing site topography from the Surface Science Package Acoustic Properties Instrument

We present analysis of the results from the Huygens acoustic sounder instrument. The sounder sees a relatively smooth terrain, with specular reflectance characteristics

Isospin-mixing corrections for fp-shell Fermi transitions

Isospin-mixing corrections for superallowed Fermi transitions in {\it fp}-shell nuclei are computed within the framework of the shell model. The study includes three nuclei that are part of the set of nine accurately measured transitions as well as five cases that are expected to be measured in the future at radioactive-beam facilities. We also include some new calculations for $^{10}$C. With the isospin-mixing corrections applied to the nine accurately measured $ft$ values, the conserved-vector-current hypothesis and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are tested.Comment: 13 pages plus five tables. revtex macro

Shell model calculation of the beta- and beta+ partial halflifes of 54Mn and other unique second forbidden beta decays

The nucleus 54Mn has been observed in cosmic rays. In astrophysical environments it is fully stripped of its atomic electrons and its decay is dominated by the beta- branch to the 54Fe ground state. Application of 54Mn based chronometer to study the confinement of the iron group cosmic rays requires knowledge of the corresponding halflife, but its measurement is impossible at the present time. However, the branching ratio for the related beta+ decay of 54Mn was determined recently. We use the shell model with only a minimal truncation and calculate both beta+ and beta- decay rates of 54Mn. Good agreement for the beta+ branch suggests that the calculated partial halflife of the beta- decay, (4.94 \pm 0.06) x 10^5 years, should be reliable. However, this halflife is noticeably shorter than the range 1-2 x 10^6 y indicated by the fit based on the 54Mn abundance in cosmic rays. We also evaluate other known unique second forbidden beta decays from the nuclear p and sd shells (10Be, 22Na, and two decay branches of 26Al) and show that the shell model can describe them with reasonable accuracy as well.Comment: 4 pages, RevTeX, 2 figure

Nuclear Structure Calculations and Modern Nucleon-Nucleon Potentials

We study ground-state properties of the doubly magic nuclei 4He, 16O, and 40Ca employing the Goldstone expansion and using as input four different high-quality nucleon-nucleon (NN) potentials. The short-range repulsion of these potentials is renormalized by constructing a smooth low-momentum potential V-low-k. This is used directly in a Hartree-Fock approach and corrections up to third order in the Goldstone expansion are evaluated. Comparison of the results shows that they are only slightly dependent on the choice of the NN potential.Comment: 5 pages, submitted to Physical Review

Semileptonic Hyperon Decays and CKM Unitarity

Using a technique that is not subject to first-order SU(3) symmetry breaking effects, we determine the $V_{us}$ element of the CKM matrix from data on semileptonic hyperon decays. We obtain $V_{us}$ =0.2250(27). This value is of similar precision to the one derived from $K_{l3}$, but higher and in better agreement with the unitarity requirement, $|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2=1$.Comment: 3 pages, 1 tabl

A Conserved Vector Current test using low energy beta-beams

We discuss the possibility of testing the weak currents and, in particular, the weak magnetism term through the measurement of the electron anti-neutrinos capture by protons at a low energy beta-beam facility. We analyze the sensitivity using both the total number of events and the angular distribution of the positrons emitted in a water Cerenkov detector. We show that the weak magnetism form factor might be determined with better than several percent accuracy using the angular distribution. This offers a new way of testing the Conserved Vector Current hypothesis.Comment: 8 pages, 5 figure

Branching ratios for the beta decay of 21Na

We have measured the beta-decay branching ratio for the transition from 21Na to the first excited state of 21Ne. A recently published test of the standard model, which was based on a measurement of the beta-nu correlation in the decay of 21Na, depended on this branching ratio. However, until now only relatively imprecise (and, in some cases, contradictory) values existed for it. Our new result, 4.74(4)%, reduces but does not remove the reported discrepancy with the standard model.Comment: Revtex4, 2 fig

Large-basis shell-model calculation of 10C->10B Fermi matrix element

We use a $4\hbar\Omega$ shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the 10C->10B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence of T=1 partial waves. Our results suggest the isospin- mixing correction $\delta_{C}\approx 0.1$, which is compatible with previous calculations. The correction obtained in those calculations, performed in a $0\hbar\Omega$ space, was dominated by deviation from unity of the radial overlap between the converted proton and the corresponding neutron. In the present calculation this effect is accommodated by the large model space. The obtained $\delta_{C}$ correction is about a factor of four too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data.Comment: 14 pages. REVTEX. 3 PostScript figure