Polymer Composites for Radiation Detection: Diiodobenzene and light emitting polymer molecular solutions for gamma detec
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1038-O03-03
Polymer Composites for Radiation Detection: Diiodobenzene and light emitting polymer molecular solutions for gamma detection Qibing Pei1, Yongsheng Zhao2, and Haizheng Zhong2 1 Department of Materials Science and Engineering, University of California, Los Angeles, Engineering V Bldg, Room 3121H, 420 Westwood Plaza, Los Angeles, CA, 90095-1595 2 Department of Materials Science and Engineering, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA, 90095-1595 ABSTRACT Conjugated polymers are largely intact by gamma exposure but can be energized in the presence of high-Z compounds. The resulting alteration of the polymer’s high optical density and photoluminescence efficiency can be exploited for the detection of gamma radiation with high sensitivity. Diiodobenzene and conjugated polymers mix on the molecular level in solid thin films. Composite films of various thicknesses were conveniently cast from solution and exposed to gamma radiation. The responses of the films to gamma dosage were observed with dramatic changes in ultraviolet-visible absorption and photoluminescence.
INTRODUCTION Gamma detection is generally based on scintillation or photoelectron generation. Because of the requirement of high-Z for high stopping power, inorganic compounds containing high-Z atoms are often used.[1-3] Synthetic polymers, composed primarily of low-Z carbon, hydrogen and oxygen atoms are not particularly sensitive to gamma exposure. On the other hand conjugated polymers exhibit high photoluminescence efficiency and moderate carrier mobility. They have been studied for the detection of charged particles, such as electrons,[4] protons,[6] and α particles.[7] For high-energy photons such as X and gamma rays, the changes in polymer properties were observed only at high dosages, higher than 1 kGy.[8,9] Borin et al.[10] observed that the sensitivity of poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) to gamma photons can be substantially increased when the polymer is dissolved in chloroform. The formation of Cl radicals due to gamma irradiation accelerates the degradation of the polymer. Campbell and Crone[11] showed that the addition of core-shell quantum dots of CdSeZnSe increases the scintillation efficiency of MEH-PPV. This method is limited by photoluminescence quenching and scattering loss at high volume fraction of the high-Z quantum dots. We are exploiting two unique properties of conjugated polymers for gamma radiation: high-sensitivity photoluminescence quenching by charge transfer[12,13] and fluorescence resonance energy transfer[14]. The conjugated polymers are mixed with high-Z compounds on the molecular or nanometer scale. The high-Z compounds absorb gamma photons. The resulting charged species and/or exitons cause dramatic change of the polymer’s photophysical properties through charge or energy transfer. Below we report the preparation of polymer-diiodobenzene molecular solutions and their response to gamma radiation.
EXPERIMENT MEH-PPV and diiodobenzene were first d
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