Impact of the Numerical Aperture on the Dosimetry Performances of Low‐OH Pure Silica‐Core Optical Fibers

This study investigates the influence of pre‐irradiation and numerical aperture (NA) on radiation‐induced luminescence (RIL) and radiation‐induced attenuation (RIA) of pure silica core (PSC) multimode (MM) optical fibers (OFs) under steady state X‐rays (40 keV mean energy‐fluence). The RIL properties of MM PSC OFs with identical core compositions and geometries but having different NAs (0.12, 0.15, and 0.22) have been characterized as well as the influence of pre‐irradiation doses at 250 kGy, 1 and 2 MGy. RIL were measured under dose rates varying from 40 mGy(SiO 2 )/s to 1.1 Gy/s. RIL spectral analysis shows two main emission bands correlated to Oxygen Deficient Centers (ODC(II), ∼460 nm) and NonBridging Oxygen Hole Centers (NBOHC, ∼650 nm). The spatial distribution of NBOHC, confined in the fiber core, has been measured through confocal photoluminescence microscopy. RIA was carried out up to a total ionizing dose (TID) up to 200 kGy and no major effect of NAs was observed. RIL intensity increases with both NA and pre‐irradiation dose due to defect generation within the PSC MM optical fiber. Based on these results, the potential of these PSC MM fibers to serve as radiation sensitive probes or as transport fibers for dosimetry systems is discussed.