Shape and Structure of Neutron-Rich from Cf-252 Fission Fragments

<p>The transition quadrupole moments, Q_t, of rotational bands in the neutron-rich, even-mass <super>102-108</super>Mo and <super>108-112</super>Ru nuclei were measured with the Doppler-shift attenuation method. The nuclei were populated as fission fragments from <super>252</super>Cf fission. The detector setup consisted of the Gammasphere spectrometer and the Hercules fast-plastic array. This allowed the measurement of asymmetric DSAM lineshapes at different Gammasphere detector angles with respect to the fission axis. The measurements typically covered the 6 to 16&#1115; spin range of the ground-state band and at least a strong transition in the &#947; band. At moderate spin, the Q_t moments are found to be reduced with respect to the values near the ground states, the latter being reported in the literature.</p><p>An attempt has been made (by Afanasjev) to describe the data in the framework of cranked relativistic Hartree-Bogolyubov theory, and the results are reported in the present work as well as in a Physics Letters paper by Snyder et al. For <super>104</super>Mo reliable predictions can be made. Here an oblate shape and a low-spin triaxial shape (deformation parameter &#947;~-44°), predicted to be favored in other theoretical calculations, are ruled out by the data. There is some indication for a gradual change, at higher spin, from an initially prolate shape to a triaxial shape in <super>104</super>Mo. The Q_t data for <super>106</super>Mo and <super>110,112</super>Ru support this picture. The challenge of theory to describe the Q_t data is addressed, which has to do with the very &#947;-soft potential-energy surfaces.</p><p>As a byproduct of the Q_t analysis (which requires the determination of the intensities of the feeding transitions), the transition intensities of many weak high-spin or non-yrast states have been determined. These previously unknown intensity data are also reported.</p><p>In the appendix, the results of an attenuation-coefficient analysis for &#947;-ray angular distributions (due to recoil-in-vacuum) in heavy Ba isotopes are reported. These results are from a separate project, though from the same data set.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date.available

2014

Author dc:creator

• Snyder, Jason Benjamin

Contributors dc:contributor

• Demetrios G Sarantites

• cranked relativistic Hartree-Bogoliubov Theory
• excited state lifetimes
• fission fragments
• rotational bands
• transition quadrupole moments
• triaxiality

Language dc:language

English (en)

DOI

https://doi.org/10.7936/K7CV4FVC

OAI identifier oai:identifier

oai:openscholarship.wustl.edu:etd-2348