3D-ORAM Dosimeter (March 2000)

Research staff in the Biochemistry and Biophysics and Assessment Technology Sections of the Life Sciences Division have demonstrated the feasibility of a new energy-independent neutron dosimeter based on fluorescence changes in three-dimensional optical random access memory materials (3D-ORAMs). These 3D-ORAM dosimeter materials use photochromic dyes, such as spirobenzopyran and anthracene, that can be converted from a non-fluorescent state to a fluorescent state by irradiation with specific wavelengths of light or certain types of ionizing radiation. A stable 3D material in which fluorescence images can be monitored is fabricated by doping these dyes into a poly(methylmethacrylate) (PMMA) support. It is possible to interrogate specific locations within the dosimeter material, determining the spatial distribution of ‘tracks’ left behind by the radiation, by exciting the sample in a 2-photon absorption process using two orthogonal laser beams. The total fluorescence and distribution of fluorescence changes in the sample are functions of radiation fluence, energy, and linear energy transfer (LET), which determine radiation dose and dose equivalent. Collaborators at Georgetown University and the Naval Research Laboratory have already demonstrated that 3D ORAMs respond to heavy charged particles, but are totally insensitive to photons and beta particles. The ORNL results, using PMMA doped with anthracene and irradiated with neutrons from a Cf-252 source, confirms the predicted 3D ORAM response to energetic neutrons. The optical readout system used to analyze the samples was developed by the Advanced Monitoring Development Group. (Contact: Tuan Vo-Dinh, 574-6249, vodinht@ornl.gov; Funding Source: DOE NN-20) – March 2000