Damage Effects of Ionizing Radiation in Polymer Film Electrets
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0929-II04-19
Damage Effects of Ionizing Radiation in Polymer Film Electrets Marco Aurélio Parada1, Renato Amaral Minamisawa1,2, Marcos Vasques Moreira3, Adelaide de Almeida1, Iulia Muntele4, and Daryush Ila5 1 1Departamento de Física e Matemática, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto, São Paulo, 14040-901, Brazil 2 2Center for Irradiation of Materials, Alabama A&M University, P.O.Box 1447, Normal AL, Huntsville, Alabama, 35762-1447 3 Instituto de Radioterapia e Megavoltagem de Ribeirão Preto (IRMEV), Rua Sete de Setembro 1150, Ribeirão Preto, São Paulo, 14010-180, Brazil 4 Physics, Alabama A&M University, 4900 Meridian Street, Normal, AL, 35762 5 2Center for Irradiation of Materials, Alabama A&M University, P.O. Box 1447, Normal AL, Hunstsville, Alabama, 35762-1447
ABSTRACT Electret sensors or dosimeters can be used to quantify the ionizing radiation dose from charged particles or waves beams (α, β, -e, p etc... γ, X), and with appropriate converters, from fast and slow neutrons. The electret state is reached, by some insulating materials (electrical conductivity lower than 10-8 (Ω m)-1), when once charged, the incorporated charge is quasi-permanent ≈ 109 s. The charge densities are read (before and after the irradiations) and the radiation dose inferred from the difference between them. PFA (Tetrafluoroethylene-per-fluoromethoxyethylene) and FEP (Tetrafluoroethylene-hexa-fluoropropylene) damage mechanisms were studied bombarding these fluoropolymers with: 1 MeV protons at constant current and fluences from 1x1011 tower 1x1016 ions/cm2, 60Co gamma and X-rays, respectively of 1.25 and 0.106 MeV for absorbed doses of 0.5, 1.0, 8,0 and 100 Gy. The emission of chemical species was monitored with a Residual Gas Analyzer (RGA), during proton bombardment and techniques of Optical Absorption Photospectrometry (OAP), Fourier Transform Infrared (FTIR) and Micro-Raman spectroscopy were used to analyze the virgin, exposed and irradiated films. INTRODUCTION Fluorocarbons present high mechanical and electrical resistance, also are resistent to high temperatures. The combination of these characteristics is suitable for: aerospace engineering applications (once they resist damages from the ionizing radiation met in space) [1,2], replacement for some human body tissues, pharmaceutical packing and also as radiation dosimeters [3,4]. Electret dosimeters can be produced with FEP and PFA films, initially charged by corona process [4].After charging, their external electrical fields attract the ions resulting from the radiation interaction with the air, near to their surfaces, and these ions compensate charges initially incorporated. The compensated charge differential is proportional to the radiation dose and a linear behavior (calibration curve) of charge versus radiation absorbed dose
can be obtained for the dosimetry of several types, geometry, energy and intensities radiation [3]. The film remaining charge can be measured, through induction process, with an appropriate reader system composed of a
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