Excited states were investigated in 21 F and 25 Na using the 9 Be( 14 C,pnγ) reaction at 30, 35, and 45 MeV and the 9 Be( 18 O,pnγ) reaction at 35 MeV. Protons were detected and identified in an E-∆E telescope at 0 o in coincidence with one or more γ radiations in the FSU Compton-suppressed Ge detector array. Many new levels and electromagnetic decays were observed, especially among the higher spin states. Angular distributions and mean lifetimes were measured wherever possible in both nuclei. The energy levels of the positive-parity states in the two nuclei agree rather well with shell model calculations using both the USDA and WBP interactions up to the highest spins observed of 13/2h. Both a weak coupling approximation and shell model calculations using the WBP interaction generally reproduce the negative-parity states in 21 F. The shell model calculations reproduce relatively well the measured M1 and E2 transitions in both nuclei, but overpredict the parity-changing E1 transitions in 21 F, the only nucleus in which negative-parity states were observed in the present experiment.

The observation that Type Ia supernovae (SNe Ia) are fainter than expected given their red shifts has led to the conclusion that the expansion of the universe is accelerating. The widely accepted hypothesis is that this acceleration is caused by a cosmological constant or, more generally, some dark energy field that pervades the universe. In this paper, we explore what, on their own, the supernovae data tell us about this hypothesis. We do so by answering the following question: can these data be explained with a model in which the strength of gravity varies on a cosmic timescale?We conclude that they can. Consequently, the supernovae data alone are insufficient to distinguish between a model with a cosmological constant and one in which G varies. However, the varying-G models prove not to be viable when other data are taken into account. This topic is an ideal one for investigation by an undergraduate physics major because the entire chain of reasoning from models to data analysis is well within the mathematical and conceptual sophistication of a motivated undergraduate. arXiv:0909.5416v2 [astro-ph.CO]

Low-spin states in the neutron-rich, N = 90 nuclide 146 Ba were populated following β-decay of 146 Cs, with the goal of clarifying the development of deformation in Ba isotopes through delineation of their non-yrast structures. Fission fragments of 146 Cs were extracted from a 1.7-Ci 252 Cf source and mass-selected using the CARIBU facility. Low-energy ions were deposited at the center of a box of thin β detectors, surrounded by a high-efficiency HPGe array. The new 146 Ba decay scheme now contains 31 excited levels extending up to ∼2.5 MeV excitation energy, double what was previously known. These data are compared to predictions from the Interacting Boson Approximation (IBA) model. It appears that the abrupt shape change found at N = 90 in Sm and Gd is much more gradual in Ba and Ce, due to an enhanced role of the γ degree of freedom.

The structure of 29 Al and 27 Mg was investigated using the reactions 18 O( 14 C,p2n) and 18 O( 14 C,α n) at 40 MeV. The charged particles were detected and identified with a ∆E-E telescope in coincidence with γ radiation detected in the Florida State University (FSU) Compton suppressed γ detector array. The level and decay schemes of both nuclei have been expanded at higher spins and excitation energies. The positive-parity states up to 3.5 to 4.5 MeV agree well with shell model calculations using the USDA interaction. The negative-parity states in 27 Mg are reproduced relatively well by one-particle-hole calculations with the WBP-a interaction. Three 27 Mg states unbound by 0.4 to 1.4 MeV to neutron decay were observed to decay radiatively. One of these states had been previously observed to γ decay in a (d,pγ) experiment along with a surprising 16 other neutron unbound states. The competition between neutron and gamma decay in these states is discussed in terms of angular momentum barriers and spectroscopic factors.

High-spin states in 39 Ar were populated using the 27 Al(14 C, pn) reaction at 25.6 MeV. The deexciting γ rays were measured with the FSU γ detector array along with evaporation protons in a Si E-∆E telescope. The known high-spin level scheme was extended up to over 11 MeV with a dozen new levels above the neutron decay threshold. The decay pattern appears somewhat atypical for heavy-ion fusion-evaporation reactions. The structure of 39 Ar is discussed in terms of the new FSU cross-shell spsdpf interaction fitted to a wide range of nuclei. This interaction has proved quite successful in accounting for the level scheme of 39 Ar, including the previously suggested fully aligned πf 7/2 ⊗ νf 7/2 17/2 + state and previously discovered analogs of the lowest states in 39 Cl.