121936592
Signature splitting and quasiparticle alignment in the yrast band of Ta-165
Excited states in Ta-165 were populated in the Nd-142(Al-27,4n)Ta-165 and Pr-141(Si-28,4n)Ta-165 reactions and investigated using the AFRODITE array. The yrast rotational decay sequence up to spin 53/2(-) is identified and assigned to the [514]9/2(-) configuration. The nuclear shape is investigated using total Routhian surface calculations. The experimental results are discussed in relation to existing data in the neighboring Ta isotopes and results from cranked shell model calculations. Unexpectedly large signature splitting, for a high-Omega configuration, is observed in the yrast band. Further discrepancies are observed between theoretical and experimental values for the band crossing frequency and signature splitting of the B(M1)/B(E2) ratios. The possibility that these discrepancies are a consequence of a large deviation from an axially symmetric nuclear shape is investigated.
118470901
Signature inversion in the yrast band of Ta-164
Excited states in Ta-164 were populated in the Nd-142(Al-27,5n)Ta-164 reaction and investigated using the AFRODITE spectrometer Arran. The yrast rotational decay sequence Lip to spin 21(-) is identified for the first time and assigned to the pi[514]9/2(-) x nu[660]1/2(+) configuration. A less intense. excited hand is also identified. Low-spin signature inversion is observed in the yrast band, and is compared with the extended total Routhian surface calculations. It is likely that quadrupole pairing plays a role in generating the anomalous signature splitting, but an additional mechanism apart front the assumed mean field and quadrupole pairing interaction may be required to account for the experimental data.
119979477
Possible chirality in the doubly-odd Tl-198 nucleus: Residual interaction at play
A candidate for chiral bands was found in Tl-198 for the first time in a mass region of oblate (or nonaxial with gamma >= 30 degrees) deformed nuclei. Two bands show very similar quasiparticle alignments, moments of inertia, and B(M1)/B(E2) ratios. They have a relative excitation energy of about 500 keV and different patterns of energy staggering. Calculations using the two-quasiparticle-plus-triaxial-rotor model with residual proton-neutron interaction included show that a triaxial deformation with gamma similar to 44 degrees agrees very well with all the experimental observations. Furthennore, considerable energy staggering for both partner bands was calculated for this pi h(9/2) circle times vi(13/2)(-1) configuration at gamma - 30 degrees, suggesting that chiral bands may have substantial energy staggering. (Less)
122046656
Close near-degeneracy in a pair of four-quasiparticle bands in Tl-194
A pair of rotational bands associated with the pi h(9/2) circle times nu i(13/2)(-1) configuration at lower spins and with the pi h(9/2) circle times nu i(13/2)(-3) configuration at higher spins is found in Tl-194. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. Such close near-degeneracy probably indicates chiral geometry in the angular momentum space. (c) 2013 Elsevier B.V. All rights reserved.
121631668
A high energy-resolution zero degree facility for (p,p′) and (p,t) reactions
Medium-energy hadronic scattering and reactions at zero degrees are very selective to excitations with low angular momentum transfer. Only a few facilities exist worldwide where high energy-resolution measurements of this nature can be performed. The K600 Zero-Degree Facility at iThemba LABS, South Africa, was recently successfully developed. Measurements were performed for inelastic proton scattering at an incident energy of 200 MeV for targets ranging from 27Al to 208Pb. Excitation energy-resolution of 50 keV (FWHM) was achieved. A reasonable background subtraction procedure allows for the extraction of excitation energy spectra with low background. Measurements of the (p,t) reaction at 100 MeV benefit from a large difference in magnetic rigidity between the reaction products and primary particles, resulting in almost background-free spectra with excitation energy-resolution of 32 keV (FWHM).
55476809
Evidence for Partial Taylor Relaxation from Changes in Magnetic Geometry and Energy during a Solar Flare
Context. Solar flares are powered by energy stored in the coronal magne tic field, a portion of which is released when the field reconfigures into a lower energy state. Investigation of sun spot magnetic field topology during flare activity is useful t o improve our understanding of flaring processes. Aims. Here we investigate the deviation of the non-linear field con figuration from that of the linear and potential configuratio ns, and study the free energy available leading up to and after a flare . Methods. The evolution of the magnetic field in NOAA region 10953 was ex amined using data from Hinode/SOT-SP, over a period of 12 hours leading up to and after a GOES B1.0 flare. Previous w ork on this region found pre- and post-flare changes in photos pheric vector magnetic field parameters of flux elements outside the primary sunspot. 3D geometry was thus investigated using potential, linear force-free, and non-linear force-free field extrapo lations in order to fully understand the evolution of the fiel d lines. Results. Traced field line geometrical and footpoint orientation di fferences show that the field does not completely relax to a full y potential or linear force-free state after the flare. Magnet ic and free magnetic energies increase significantly ∼ 6.5‐2.5 hours before the flare by ∼ 10 31 erg. After the flare, the non-linear force-free magnetic ene rgy and free magnetic energies decrease but do not return to pre-flare ‘quiet’ values. Conclusions. The post-flare non-linear force-free field configuration is c loser (but not equal) to that of the linear force-free field configuration than a potential one. However, the small degre e of similarity suggests that partial Taylor relaxation has occurred over a time scale of∼ 3‐4 hours.
118373762
Fields and flares : understanding the complex magnetic topologies of solar active regions
Sunspots are regions of decreased brightness on the visible surface of the Sun (photosphere) that are associated with strong magnetic fields. They have been found to be locations associated with solar flares, which occur when energy stored in sunspot magnetic fields is suddenly released. The processes involved in flaring and the link between sunspot magnetic fields and flares is still not fully understood, and this thesis aims to gain a better understanding of these topics. The magnetic field evolution of a number of sunspot regions is examined using high spatial resolution data from the Hinode spacecraft. The research presented in this thesis gives insight into both photospheric and coronal magnetic field evolution of flaring regions. Significant increases in vertical field strength, current density, and field inclination angle towards the vertical are observed in the photosphere just hours before a flare occurs, which is on much shorter timescales than previously studied. First observations of spatial changes in field inclination across a magnetic neutral line (generally believed to be a typical source region of flares) are also discovered. 3D magnetic field extrapolation methods are used to study the coronal magnetic field, using the photospheric magnetic field data as a boundary condition. Magnetic energy and free magnetic energy are observed to increase significantly a few hours before a flare, and decrease afterwards, which is a similar trend to the photospheric field parameter changes observed. Evidence of partial Taylor relaxation is also detected after a flare, as predicted by several previous studies. The results outlined in this thesis show that this particular field of research is vital in furthering our understanding of the magnetic nature of sunspots and its link to flare processes.
119683797
Noncommutative Spherically Symmetric Space
We examine some noncommutative spherically symmetric spaces in three space dimensions. A generalization of Snyder’s noncommutative (Euclidean) space allows the inclusion of the generator of dilations into the defining algebra of the coordinate and rotation operators. We then construct a spherically symmetric noncommutative Laplacian on this space having the correct limiting spectrum. This is presented via a creation and annihilation operator realization of the algebra, which may lend itself to a truncation of the Hilbert space.