Constraining the Neutron Star Compactness: Extraction of the

The ^{23}Al(p,γ)^{24}Si reaction is among the most important reactions driving the energy generation in type-I x-ray bursts. However, the present reaction-rate uncertainty limits constraints on neutron star properties that can be achieved with burst model-observation comparisons. Here, we present a novel technique for constraining this important reaction by combining the GRETINA array with the neutron detector LENDA coupled to the S800 spectrograph at the National Superconducting Cyclotron Laboratory. The ^{23}Al(d,n) reaction was used to populate the astrophysically important states in ^{24}Si. This enables a measurement in complete kinematics for extracting all relevant inputs necessary to calculate the reaction rate. For the first time, a predicted close-lying doublet of a 2_{2}^{+} and (4_{1}^{+},0_{2}^{+}) state in ^{24}Si was disentangled, finally resolving conflicting results from two previous measurements. Moreover, it was possible to extract spectroscopic factors using GRETINA and LENDA simultaneously. This new technique may be used to constrain other important reaction rates for various astrophysical scenarios.

Proton reaction cross sections as measures of the spatial distibutions of neutrons in exotic nuclei.

Proton and neutron densities from Skyrme-Hartree-Fock calculations of a number of nuclei with masses ranging from 28 to 58 have been used to generate optical potentials for proton elastic scattering. Those potentials, generated by folding the structure functions with effective in-medium nucleon-nucleon (NN) interactions, have been used to evaluate proton total reaction cross sections; cross sections that reveal signatures of the structures.

First observation of 54Zn and its decay by two-proton emission.

The nucleus 54Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasifragmentation of a 58Ni beam at 74.5 MeV/nucleon in a (nat)Ni target. The fragments were analyzed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54Zn implantation events were observed. From the correlated decay events, the half-life of 54Zn is determined to be 3.2(+1.8)(-0.8) ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial half-life are compared to model predictions and allow for a test of these two-proton decay models.

Evaluation of ceramic margins for metal-ceramic restorations.

This study evaluated various techniques for forming ceramic margins on metal-ceramic restorations. Marginal openings were measured using a scanning electron microscope on replicas derived from elastomeric impressions. Ceramic margins formed with a platinum foil backing showed significantly better fit than those formed with direct-lift techniques. With the platinum foil method these ceramic margins displayed a marginal fit comparable to that obtained with cast metal margins.

Fit of three porcelain-fused-to-metal marginal designs in vivo: a scanning electron microscope study.

This study examined the comparative fit in vivo of three types of PFM crown margins. Marginal openings were measured with an SEM on replicas derived from elastomeric impressions. There was no significant difference among beveled metal margins, metal butt margins, or porcelain butt margins either before or after cementation at the 95% confidence level. This study has shown that it is possible under clinical conditions to consistently produce porcelain butt margins with less than 50 micron marginal opening in PFM restorations.