Award Date

1-1-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Committee Member

Kenneth Czerwinski

Number of Pages

104

Abstract

Radiation detection is often is hampered by signal losses and noise. Conversion of decay particle energy to photons by scintillation, or induction of emissions from fluorescent materials by laser excitation, offers improved signal-to-noise ratios and the possibility of remote detection. This dissertation investigates the enhancement of induced fluorescence afforded by the application of scintillator-loaded polymer films to a radioactive material and of silanol ligand solutions to a fluorescent material; Prompt ultraviolet fluorescence from barium fluoride (BaF2)-loaded polymer films was induced by exposure to a 99Tc source and measured by scintillation counting. Scintillation photons suffer less attenuation in media than do the 99Tc beta particles and occur in a region of negligible solar background. Films with BaF2 loaded between 0 and 80% were drawn to thicknesses between 508 and 1270 mum. BaF2 crystals, from 0.25 and 5 mum diameter as determined by scanning electron microscopy (SEM), are significantly likely to scatter ultraviolet scintillations, thereby increasing the potential for photon absorption by EVA with a resulting decrease in detectable yield. Scintillation intensity was maximized in thin films (102 mum dry thickness) with high loading (80% by mass); Visible fluorescence from uranyl perchlorate solids contacted with Fe(III) or functionalized polyhedral oligomeric silsesquioxanes (POSSRTM ) is induced by light from a 414-nm pulsed laser, and the time-resolved intensities and lifetimes measured by intensified charge-coupled device (CCD) camera at 23 °C. Uranyl lifetimes were 4.08 +/- 0.02 mus for a 4.8 +/- 0.2 mM UO2(ClO4)2 (aq) solution and 225 +/- 2 mus for a 0.048 mumol UO2(ClO4) 2 solid. With 8.85 times molar excess Fe(III) added, dynamically quenched lifetimes were 3.73 +/- 0.03 micros for the 4.8 +/- 0.2 mM UO 2(ClO4)2 (aq) solution and 124 +/- 5 mus for the 0.048 mumol UO2(ClO4)2 solid. Fluorescence spectra of solids were red-shifted by 6 nm for each maximum due to increased hydrolysis of the uranyl ion; The effects of ligands in 4.2 times molar excess to UO2 2+ were determined by dissolution in buffered ethanol and deposition onto solid UO2(ClO4)2. Uranyl fluorescence intensity was quenched by both ligand solutions by more than ten fold. The lifetimes were reduced from tauo = 225 +/- 2 is to tau = 66 micros for TriSilanolEthyl POSSRTM SO1444 and to tau = 77 micros for TetraSilanolPhenyl POSSRTM SO1460Na, indicating increased shielding of uranyl from ethanol quenching by POSSRTM SO1460Na. The additional effects of Fe 3+ in 8.85 times molar excess to UO22+ were determined by deposition of these ligand solutions onto solids containing UO2(ClO4)2 and Fe(ClO4)3 . Fluorescence intensity was further quenched to by more than twenty five fold. Lifetimes of tau = 13 micros for POSSRTM SO1444 and tau = 46 micros for POSSRTM SO1460Na were measured; The feasibility of enhanced detection of surface radioactive materials using induced fluorescence measurements is demonstrated, and improved methods, including the use of nanoparticle scintillators, phosphate-based solutions, and ion imprinted polymers are recommended.

Keywords

Detection; Enhanced; Fluorescence; Induced; Materials; Radiation Detection; Radioactive; Radioactive Materials; Remote Detection; Residual; Solar-blind; Scintillation; Uranyl Fluorescence

Controlled Subject

Nuclear chemistry; Radiation chemistry; Chemistry, Inorganic

File Format

pdf

File Size

2181.12 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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