Effect of 150 MeV protons on carbon nanotubes for fabrication of a radiation detector

Abstract

High energy and high flux protons are used in proton therapy and the impact of proton radiation is a major reliability concern for electronics and solar cells in low earth orbit as well as in the trapped belts. Carbon nanotubes (CNTs), due to their unique characteristics, have been considered for the construction of proton and other radiation sensors. Here, a single wall CNT based proton sensor was fabricated on FR4 substrate and its response to 150 MeV proton irradiation was studied. The change in the resistance of the nanotubes upon irradiation is exploited as the sensing mechanism and the sensor shows good sensitivity to proton radiation. Proton radiation induces dissociation of ambient oxygen, followed by the adsorption of oxygen species on the nanotube surface, which influences its electrical characteristics. Since the nanotube film is thin and the 150 MeV protons are expected to penetrate into and interact with the substrate, control experiments were conducted to study the impact on FR4 substrate without the nanotubes. The dielectric loss tangent or dissipation factor of FR4 increases after irradiation due to an increase in the cross-linking of the resin arising from the degradation of the polymer network.

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“…However, for irradiated samples, situation is quite different because samples suffer many chemical and physical changes because of radiation-induced free radicals. These free radicals act in various ways, e.g., they can react to form crosslinks, further breakage of PE chains, and to react with diffused oxygen with the polyethylene matrix following the well-established oxidation chain reactions of polyethylene [ 39 , 40 , 41 , 42 , 43 ]. Furthermore, the amount of free radicals is linearly correlated with the absorbed gamma dose, therefore, modifications in all above-mentioned regions, i.e., –CH 2 bending vibrations, absorption due –CH 2 units in amorphous region, –C=O absorptions, –CH 2 stretching vibrations, and peroxides bonded regions are higher for 65 kGy and 100 kGy.…”

“…Moreover, gamma rays are also responsible for enhancing the hydrogen adsorption capacity of MWCNTs and the amount of functional-groups attached to the surface of MWCNTs. This is because of an increase in imperfections at MWCNTs surface by gamma radiations [ 38 , 39 , 40 ].…”