Novel dosimetric study of the sp2 to sp3 hybridisation ratio in free–standing carbon nanotubes buckypaper

Abstract

Over the past several years a great deal of research has focused on the adaptation of carbon nanotubes (CNTs) for a wide range of applications, including as gas detectors, in energy storage, for various photonics purposes, also as radiation sensors. In previous studies by this group, investigating thermoluminescent (TL) properties, the sensitivity of CNTs towards ionising radiations has been observed using beta radiation at dose levels from fractions of a Gy and more. Strain and impurity defects in CNTs give rise to substantial TL yields, the extent to which electron trapping centres exist varying inversely with the quality of CNT, from super-pure to pure to raw. In present study the contribution to TL of beta particle irradiated CNTs has been investigated with respect to changes in the lattice atomic orbitals, pointing to the possibility of a new radiation dosimetry method. The surface-sensitive method, one highly suited to the thin (few tens of µm thick) CNT samples produced in the form of free-standing buckypaper, is based on use of the X-Ray Photoelectron Spectroscopy (XPS) technique, evaluating sp2 to sp3 hybridisation. The CNT samples have been examined subsequent to irradiation using a relatively large activity 90Sr/90Y radionuclide source (Eβ = 0.546 MeV/2.28 MeV), delivering doses in the range 0.2–6 Gy, in all three qualities sp2 to sp3 hybridisation being observed to increase with dose deposition. Considerable advantage is seen in making use of such thin CNTs in dosimetry, rendering them particularly suitable for beta particle soft tissue dosimetry.