Session E9: SPS and Undergraduate Research II

Probing the structure of $^{25}$Na with $\gamma$-ray spectroscopy

Excited states in the neutron-rich, $T = 3/2$ nucleus $^{25}$Na have been populated with the $^{14}$C($^{14}$C,t) and $^9$Be($^{18}$O,d) reactions in two separate experiments. The $t$-$\gamma$, $t$-$\gamma$-$\gamma$, and $\gamma$-$\gamma$ coincidence data were analyzed to study the structure of $^{25}$Na. Nine new $\gamma$-ray transitions have been added to the level scheme, and the decay modes of six states previously known only from charged particle measurements have been determined. The results will be discussed in terms of the shell model using the USD, USDA, and USDB interactions.   

Magnetic Field Reduction in Photomultipliers with the use of Bucking Coil

Three segmented aerogel Cerenkov detectors are employed in the Jefferson Lab High Resolution Kaon Spectrometer (HKS). Cerenkov light is detected with 5'' PMTs. At the detector location a stray field from the magnet of $\sim$5 gauss significantly reduces the photoelectron collection efficiency of the PMTs, despite the use of magnetic shielding. Therefore, we propose to compensate the stray field with bucking coils. In a test setup, a Helmholtz Coil was used to generate external magnetic fields up to 15 gauss. In order to counteract this \textbf{B} field 20 turns of bucking coil (gauge: 12 AWG) were mounted around the cathode sides of the PMT. A recovery of roughly 87.5{\%} was determined for an external \textbf{B} field of 5 Gauss. The experimental procedure and results of both this and new studies will be presented in detail.   

Theoretical and experimental analysis of two different pendula whose common oscillating point is forced periodically

The behavior of a non-linear dynamical system is characterized both experimentally and theoretically. The system consists of two different pendula coupled through a low friction car that oscillates in response to a periodical force. This system is studied theoretically and experimentally in order to compare the results of each approach. All the system's parameters are fixed except the forcing frequency, which is changed within an interval that causes the system to respond. Theoretically, the system's equations have been settled and solved using numerical methods. Experimentally, the system was mounted and data was acquired by computer motion sensors. The three bodies of the system are studied: Lyapunov's exponents are used to identify chaos and stability regions for the forcing frequency changes; phase planes and spaces are plotted to identify periodical and erratic behaviors; Poincare mappings and Fourier transforms are used to identify frequencies in which remarkable behaviors arise. The similarities and differences between theoretical and experimental results are discussed.   

Determining the Onset of Turbulent Flow Using Video Based Motion Analysis

Recent advancements in computing technology have drastically improved the interface between computers and video equipment, thus allowing for the improvement of video-based motion analysis. However, analysis of video data remains susceptible to errors caused by lens distortion, angular distortion, descaling, and discretization. In previous work, methods were developed to correct for some of these errors. This paper presents several improvements to these corrections, as well as additional methods to increase accuracy, including: 1) improvement of the measurement of lens distortion, 2) automation of the lens distortion correction technique, 3) a simulation method to test the correction of lens distortion error, 4) creation of an algorithm to correct for angular distortion, and 5) refinement of a two camera system to correct for descaling error. The methods were tested in the context of the measurement of the air resistance force on a high-speed projectile. This allowed for the determination of the onset of turbulent flow. These significant improvements in accuracy have made video-based analysis an even more powerful tool for the study of motion.   

Optical Spectroscopy of Defects in Yttrium Orthovanadate (YVO4) Crystals

Yttrium orthovanadate (YVO4) is an insulating crystal used in several important and emerging optical technologies such as a solid-state laser host material and in fiber optic components for telecommunications. We are engaged in a study of the growth-related and radiation-related point defects that result in discoloration of commercial quality YVO4. These defects can reduce the usefulness of the material. Alternatively, these same defects may actually play a beneficial role in the use of YVO4 for other applications, such as the observed Anti-Stokes Luminescence (light which is converted to a higher energy due to a two-photon process in the crystal) which could make the YVO4 a candidate for blue lasers. It has been surmised [1] that some of these ``useful'' defects are related to oxygen vacancies in the crystal, so we are exploring the effects on defects after annealing the YVO4 in Oxygen and other gas atmospheres. [1] Anti-Stokes emission in undoped YVO4, W. Ryba-Romanowksi, S. Golab, P. Solarz, and G. Dominiak-Dzik, Applied Physics Letters, 80, 1183 (2002).   

Hamiltonian Constraint Analysis of Vector Theories with Spontaneous Lorentz Violation

A Hamiltonian constraint analysis is performed on a class of field theories in which Lorentz symmetry is spontaneously broken by a vector field. Such symmetry breaking is of interest because it may occur in the context of quantum theories of gravity. For a class of such models, the vector field emerges with properties similar to the photon. The Hamiltonian constraint analysis is used to compare this class of vector theories to conventional electrodynamics.