Radiation Detection: Resistivity Responses in Functional Poly(Olefin Sulfone)/Carbon Nanotube Composites

Abstract

Detection and dosimetry of ionizing radiation are crucial in several fields such as energy, national security, biological and nuclear research, and in other advanced applications such as monitoring the attrition of materials in space travel. The most common systems for the detection and dosimetry of ionizing radiation usually have one or several of the following drawbacks: incapability to produce a real-time signal, expensive and/or complicated manufacturing, need for operation at low temperatures, low sensitivity to non-charged radiation, or voluminous size. Although organic materials present the advantages of being easily processed, synthetic versatility, and relatively low cost, deployment of organic systems as small size ionizing radiation detectors and dosimeters has been traditionally limited to the detection of charged particles, owing to the low gamma ray cross sections of elements incorporated in these molecules. We report herein a new sensing scheme that is not based on scintillation or charge generation in semiconductors. Our sensing mechanism (Figure 1) makes use of a polymer/multiwalled carbon nanotube (MWCNT) blend for the detection of gamma rays, capable of producing a real-time signal at room temperature, composed of relatively inexpensive starting materials, with nearly zero cost of operation and a small size. In our system, the conducting MWCNTs form a percolated network and are partially isolated from each other in a non-conductive polymeric matrix. The turn-on detection mechanism is as follows: upon irradiation of the composite, ionization induces depolymerization of the matrix follows, creating a lower resistance connection between the MWCNTs. The depolymerization creates amplification and large changes in the electrical properties of the composite, increasing its conductivity, which can be detected via amperometry (measurement over time of the current intensity, I, between two electrodes at a constant potential, V). For the aforementioned sensing scheme to work, the following requirements need to be met: a) the polymer must degrade rapidly upon ionization, b) the MWCNTs must be initially well dispersed in the polymeric matrix, Figure 1. Sensor design showing a) a low conductance device where the CNTs are wrapped with non-conducting POSs, which upon ionization develops b) interconnected nanocircuitry and a higher conductance.