Synthesis of luminescent nanoparticle embedded polymer nanocomposites for scintillation applications
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Synthesis of luminescent nanoparticle embedded polymer nanocomposites for scintillation applications Thomas Rogers, Chenlu Han, Brent Wagner, Jason Nadler and Zhitao Kang* Georgia Tech Research Institute, Georgia Institute of Technology, 925 Dalney Street, Atlanta GA 30332-0826, U.S.A. ABSTRACT Detecting gamma-ray emission from radionuclides hidden within containers is a significant concern to national security and can be accomplished with scintillating materials such as NaI:Tl, LaBr3:Ce crystals. However, the use of these high quality crystals limits the functionality of the detectors due to their high cost and scalability issues. Therefore the development of more durable, more easily manufactured, and more cost effective scintillating materials is desired. The incorporation of nanophosphors or Quantum Dots (QDs) into a polymer matrix to produce a transparent nanocomposite could potentially provide an alternative method to fabricate scintillating detectors. Embedded in a suitable polymer matrix, nanocomposite detectors may be easily made suitably large for portal monitors. Also, preparation of suitable particle sizes and/or compositions permits selection of a photon wavelength that optimally matches the photodetector response curve to increase the number of photons collected per pulse. In this paper a series of LaF3:Ce nanophosphors with varying doping concentrations (130mol%Ce) were synthesized using a chemical precipitation method. Photoluminescence and photoluminescence excitation characterizations indicated that the highest luminescent intensity was obtained from the 20%Ce doped sample with a peak emission at 325 nm. The refractive indices of the nanoparticles were identified by index matching measurements. Then an index matched epoxy was selected for incorporation of these nanoparticles to prepare transparent nanocomposite scintillators. In addition, colloidal solutions of CdTe QDs with various emitting colors were synthesized and incorporated into a Polymethyl-methacrylate (PMMA) matrix to make transparent nanocomposites. An initial evaluation of the scintillation behavior of these nanocomposites was evaluated by exposure to gamma rays. INTRODUCTION A specific threat to national security is the detonation of a Radiological Dispersion Device (RDD) in an urban area. These devices can contaminate a large area by emitting high energy radiation via a nonfissile process. Because the resulting radiation from such an explosion can cause extensive and lasting destruction, prevention methods must remain capable of detecting threats quickly and reliably. In order to prevent the entry these types of devices into vulnerable population areas, detection and intervention are critical. The success of the prevention process relies heavily on the material properties of the detectors used. Current radionuclide detectors contain single-crystal scintillators such as LaBr3:Ce and NaI:Tl.[1] However, due to their high cost and scalability issues the functional use of these high quality single crystals is limited.[2] Scintillation de
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