Masters Theses

Date of Award

5-2014

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Mariya Zhuravleva

Committee Members

Charles L. Melcher, Claudia J. Rawn

Abstract

The detection and identification of sources of nuclear radiation is an integral tool in defending our nation from threats of nuclear terrorism as well as enforcement of nuclear non-proliferation agreements around the globe. To improve the capabilities in this application, new detection materials surpassing the performance of existing technology utilizing sodium iodide [NaI:Tl] scintillator crystals must be developed and their production cost lowered to meet the demand for the large volumes required. A recently discovered intrinsic scintillation material in the form of crystalline cesium cerium chloride (CsCe2Cl7) has demonstrated promising performance in the detection of X-ray and gamma ray radiation. In order to assess the potential of this material to be developed into larger scale growth of crystals greater than one cubic inch in volume, research into optimizing the growth processes at smaller volumes is necessary.

Single crystalline boules of CsCe2Cl7 were grown from the melt in sealed fused silica ampoules using the Bridgman method of crystal growth. A transparent growth furnace along with continuous observation apparatus were developed to aid in the investigation of the growth processes. A comparison of growth and cracking behavior under varied conditions was produced and growth protocols identified which improve crystal boule quality. Crystal quality benefits from controlling the self-seeding process through manipulation and control of critical freezing point isotherms during growth. Cracking appears to originate from aggressive detachment of the crystal from the fused silica ampoule wall while inclusions formed during growth by constitutional supercooling of the melt introduce additional crack nucleation sites through action as stress intensifiers within the bulk matrix. Reducing ampoule volume has a minor effect on cracking severity while additions of excess cesium chloride to the initial mixture produce a greater reduction in cracking. The anisotropic coefficients of thermal expansion as well as the refined crystal structure of cesium cerium chloride have been determined through single crystal Laue and temperature dependent powder X-ray diffraction pattern analyses respectively.

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