Investigation of 6 Li Enriched Particle Dispersion in Fluorescent Electrospun Polymer Nanofibers to be Used as Thermal Neutron Scintillators

[+] Author and Article Information
Stephen A. Young

Graduate Student Department of Engineering Science and Mechanics,  University of Tennessee TN, 37996 syoung13@utk.edu

Indraneel Sen

Post-Doctoral Researcherisen@utk.edu

Dayakar Penumadu

Fred Peebles Professor and Head JIAM Chair of Excellence, Department of Civil and Environmental Engineering,  University of Tennessee, Knoxville, TN, 37996dpenumad@utk.edu

J. Eng. Mater. Technol 134(1), 010908 (Dec 19, 2011) (7 pages) doi:10.1115/1.4005412 History: Received April 17, 2011; Accepted September 09, 2011; Published December 19, 2011; Online December 19, 2011

Electrospun polymer nanofibers are attractive due to their unique volume-to-surface area, chemical, electrical, and optical properties. Department of Homeland security has interest in applications with polymeric scintillation detectors that directly discriminate between neutron and gamma radiations using manufacturing techniques that are inexpensive and which can be effectively implemented to produce large area detectors. Lithium-6 (6 Li) isotope has a significant thermal neutron cross-section and produces high energy charged particles upon thermal neutron absorption. In this research, 6 Li loaded polymer composite was successfully spun onto a stationary stainless steel target creating a thermal neutron scintillator made of randomly oriented fibers. Fiber mats thus obtained were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for morphology, and fluorospectroscopy for optical properties. Additionally, the fiber mats were characterized for polymeric properties including microstructure evaluation and response to thermal neutrons, alpha, beta, and gamma radiation using suitable radiation facilities. Fiber matrix was made out of an aryl vinyl polymer and a wavelength shifting fluor with efficient resonant energy transfer characteristics. The mats produced had scintillation fibers having diameters from 200 nm to 3.2 μm.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Optical micrograph showing 4.2 μm equivalent diameter of 6 Li-Salicylate (6 LiSal) domains separated within P2VN matrix [5]

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Figure 2

(a) Scanning electron microscope (SEM) micrograph of electrospun nanofibers and (b) illustration of nanophases uniformly dispersed within the nanofiber

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Figure 3

(a) Spectral narrowing in the case of poly[(p-phenylenevinylene)- alt-(m-phenylenevinylene) PPV (polymer 7 a) copolymer (15 wt. %) blend in PS electrospun nanofibers with average fiber diameter of 480 nm [38]. Emission spectra recorded at different excitation pulse energies, λexc  = 365 nm and (b) corresponding laser confocal micrograph showing excited nanofiber.

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Figure 4

(a) Optical image of electrospun 6 Li based scintillator and (b) its exposure to UV radiation. (Note: The fluorescence of the scintillator can be clearly observed in color image.)

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Figure 5

Schematic diagram of electrospinning setup

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Figure 6

SEM micrographs of (a) PS (20 wt. %), 6 LiF (20 wt. % in PS), and PPO/POPOP (8 wt. % in PS) electrospun with CHCl3 /DMF (17:3) and (b) PS(3 wt. %)/P2VN (2 wt. %), 6 LiSal (13.5 wt. % in PS/P2VN), and anthracene (7 wt. % in PS/P2VN) electrospun with THF/DMF (4:1) fibers

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Figure 7

Fiber size diameter distribution of (a) PS (20 wt. %), 6 LiF (20 wt. % in PS), and PPO/POPOP (8 wt. % in PS) electrospun with CHCl3 /DMF (17:3) and (b) PS(3 wt. %)/P2VN (2 wt. %), 6 LiSal (13.5 wt. % in PS/P2VN), and anthracene (7 wt. % in PS/P2VN) electrospun with THF/DMF (4:1) fibers

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Figure 8

SEM micrograph of 6 LiF crystals trapped in polystyrene fiber

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Figure 9

(a) SEM micrograph and (b) elemental mapping of 6 LiF crystal showing distribution of fluorine inside electrospun fiber (LiF/PS) (c) EDS spectrum from area shown in (b). The fluorine peak is derived from the micron size 6 LiF crystal and from the nanophase surrounding the crystal, where oxygen and carbon peaks correspond to the polystyrene polymer matrix. The gold peaks come from the sputter coating on nanofibers and copper peak from a copper SEM substrate.

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Figure 10

6 LiF/PS electrospun nanofiber mat has excitation peak (280 nm) and emission peak (420 nm) with Stokes shift (140 nm). 6 LiSal/PS/P2VN electrospun nanofiber mat has excitation peak (313 nm) and emission peak (432 nm) with Stokes shift (119 nm).

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Figure 11

6 LiSal/PS/P2VN electrospun scintillation and GS20 net thermal neutron response using 252 Cf source. The electrospun scintillator as maximum neutron response around the 4000 channel number and GS20 has a maximum response at approximately 25,000 channel number.



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