121967474
Shell-model calculation for two-neutrino double beta decay of Ca48
The 2{nu}{beta}{beta} decay matrix element of {sup 48}Ca has been studied in a large basis shell-model space. The theoretical and experimental {beta}{sup {minus}} and {beta}{sup +} spectra and their relation to 2{nu}{beta}{beta} are discussed. A new empirical effective interaction is found to give the best agreement to {beta}{sup {minus}} and {beta}{sup +} spectra with the effective Gamow-Teller operator {tilde {sigma}}{ital t}=0.77{sigma}{ital t}. The predicted {ital T}{sub 1/2}=1.9{times}10{sup 19} yr differs by a factor of 2 from the present experimental limit of {ital T}{sub 1/2}{gt}3.6{times}10{sup 19} yr. We also compare the matrix elements obtained at various levels of the truncation in the shell-model space.
5675751
Level structure of Mg21: Nuclear and astrophysical implications
Resonant elastic scattering of a radioactive $^{20}\mathrm{Na}$ beam incident upon protons in a polyethylene target has been used to probe the level structure of $^{21}\mathrm{Mg}$ above the proton decay threshold. Three states have been observed, and their properties deduced through analysis based on the R-matrix formalism. The results improve and extend previous studies of this nucleus. An estimate of the $^{20}\mathrm{Na}$(p,\ensuremath{\gamma})$^{21}\mathrm{Mg}$ reaction rate, including these new data, suggests this reaction will not play a significant role in explosive hydrogen burning in astrophysical sites such as novae and x-ray bursts.
34139540
Shape of the beta spectra in the A=14 system.
10644949
One-neutron knockout reactions on proton-rich nuclei with N = 16
One-neutron knockout reactions from the deeply bound N=16 isotones with Z=16,17, and 18 have been studied in inverse kinematics with intermediate-energy beams. gamma-ray spectroscopy in coincidence with the detection of knockout residues allowed for an investigation of the one-neutron removal leading to individual excited states. Spectroscopic factors are deduced in the framework of the sudden and eikonal approximations and are compared to USD shell-model predictions. The momentum distributions observed in the experiment are used to identify the angular momentum l carried by the knockedout neutron by comparing with calculations based on a black-disk reaction model. The systematics of reduced single-particle occupancies attributed to the effect of short-range correlations, observed so far for stable and near-magic nuclei in (e,e(')p) and (d,He-3) reactions and in one-nucleon knockout on light deeply bound systems, are extended in this work.
39044560
Neutron halos in the Na isotopes.
The neutron and proton density distributions of the Na isotopes out to the proton and neutron drip lines are calculated in the spherical Hartree-Fock model with a wide variety of density-dependent Skyrme interactions. The results are compared to recent experimental data for the interaction cross sections and for the rms radii. We discuss the role of the deformed intruder states and the problems associated with predicting the location of the neutron drip line for this mass region. {copyright} {ital 1996 The American Physical Society.}
35774621
Many-body approximations in the sd-shell "sandbox"
A new theoretical approach is presented that combines the Hartree-Fock variational scheme with the exact solution of the pairing problem in the finite orbital space. Using this formulation in the sd-space as an example, we show that the exact pairing significantly improves the results for the ground state energy.
118606402
Radial Photon Trajectories Near an Evaporating Black Hole
The radial motion of photons emitted near the horizon of a black hole that evaporates at a steady rate is examined. The space-time of the black hole is generated using non-orthogonal coordinates. It is shown that some photons that are initially drawn towards the singularity can escape falling into the horizon. The behaviors of various outgoing and ingoing photons are clearly demonstrated through the use of a Penrose diagram.
18973653
Construction of a Penrose diagram for a spatially coherent evaporating black hole
A Penrose diagram is constructed for an example black hole that evaporates at a steady rate as measured by a distant observer, until the mass vanishes, yielding a final state Minkowski spacetime. Coordinate dependences of significant features, such as the horizon and coordinate anomalies, are clearly demonstrated on the diagram. The large-scale causal structure of the spacetime is briefly discussed.