Detail Project and Funding

Abstract: Ionizing radiations are nowadays involved in several physical processes relevant to environmental, industrial and health issues. In this regard, radiation dosimetry plays a fundamental role to quantify the absorbed energy and thus assess radiation effects. A number of physical and chemical devices based on liquids, solids and gases are currently available to detect ionizing radiation and measure the released dose. However, researchers are continually investigating on ways to improve the existing systems and satisfy new demands for sensitivity, real-time measurements, reliability, size and costs. For instance, more accurate determination of dose value and spatial distribution is mandatory in high-precision state-of-the-art radiation therapy procedures. With this in mind, development of novel detection systems, relying on different physical principles, technologies and methodologies, are needed.
Recently, efforts have been made to demonstrate the feasibility of optical fiber sensing for application in radiation environments, although there are only few publications on this subject. So far optical fiber sensors, based on optical telecommunication technology, have been successfully used for temperature, strain, pressure and acceleration monitoring in many different areas of research. Fiber Bragg-grating (FBG) sensors have been the most popular ones in the last decades. Wavelength-encoded information as well as ruggedness and ease of use make them extremely attractive as thermal and mechanical sensors.
The presence of a radiation field significantly affects the fiber physical properties as well, introducing a modification of the optical signal itself. One of the effects of radiation exposure is well known to be an increase in optical transmission loss. Also, a correlated change of average refractive index occurs in the optical waveguide, which can be exploited to extract the desired information. At the same time, immunity to electromagnetic interference, intrinsic safety, mechanical simplicity and small size as well as multiplexing and embedding capability make optical fiber sensors, in principle, ideal dosimeters.
The research proposal on “detection of ionizing radiation by means of intrinsic optical fiber sensors” (DROPS), is intended to devise novel dosimeters for clinical use entirely based on passive optical fibers sensors. Multiple Bragg-grating reflectors and high-quality in-fiber resonators systems will be developed for direct sensing of radiation-induced effects in silica fibers. Refractive-index variation in the optical material will be exploited to measure the absorbed radiation dose by means of high-sensitivity interrogation schemes. The interrogation approach will be based on laser-frequency stabilization and heterodyne detection techniques that lead to high signal-to-noise ratio and enable fast and active reading. Our project will include a thorough investigation on the interaction of gamma-rays and electrons (energy ~ 5-20 MeV) produced from medical accelerators and ultimately heavy particles with optical fibers of various nature. Among them P-doped, Ge-doped, Er-doped, conventional pure-silica-core fibers and highly-birefringent fibers. Transmission and refractive index will be both characterized for all types of fibers as a function of energy, dose and dose rate at different wavelengths, using light sources from the near UV to the near infrared. Based on the obtained results, the best-suited combination of fibers and lasers will be selected in order to optimize detection response, dose linearity and accuracy while minimizing signal fading and dose-rate dependence. As a final step, prototype laser-based intrinsic dosimeters will be tested for real-time and off-line measurements and validated with commercial systems in different radiation therapy applications

INO’s Experiments/Theoretical Study correlated:
Physical sensing with optical-fiber ring, grating-based and coupled resonators