Radiation Monitoring With Radiosensitive Pure-Silica Core Ultralow Loss Optical Fiber

Abstract

This article presents a new prospect for radiation detection exploiting the high radiation sensitivity of an ultra-low loss pure-silica core optical fiber (ULL-PSCF). This fiber exhibits very high transient X-ray radiation-induced attenuation (RIA) levels from UV to IR during irradiation while its RIA quickly returns to a low permanent level after irradiation. In this work, the RIA kinetics are investigated exposing the ULL-PSCF to multiple short irradiation runs at different dose rates. A pre-irradiation has been demonstrated to stabilize the response of the optical fiber and to make it even more appealing for radiation detection and monitoring. After this pre-irradiation treatment, the RIAs at 620 nm and 1310 nm in particular exhibit an ON/OFF behavior: the permanent RIA is nearly zero in-between irradiation and the transient RIA quickly increases up to dB/m level when the ULL-PSCF is exposed to X-rays. By varying the fiber length and adapting the interrogation setup, large ranges of doses and dose rates can be detected with this new class of optical fibers.

Distributed Optical Fiber-Based Radiation Detection Using an Ultra-Low-Loss Optical Fiber

“…Interestingly enough, this effect does not seem to affect the permanent part of the IR-RIA. Recently, our group also proved that the fiber radiation response changes after X-ray pre-irradiation at 1 MGy [23]. Indeed, considering this first irradiation at 1 MGy as pre-treatment, hence calculating the RIA starting from the losses of the pre-irradiated fiber, greatly reduces the influence of the dose-dependent permanent losses.…”

“…In this case though, a careful choice of light injection source is needed to obtain enough regeneration of the fiber transmission. Recently, multiple publications have been devoted to the study of a particular ultra-low-loss PSC fiber (ULL-PSCF) [19][20][21][22][23]. The RIA response of this OF differs from most other PSC fibers, which are among the most radiation-resistant under steady-state radiation [24,25].…”

“…The RIA sensitivity in the infrared (IR) range of this OF can even be higher than the aforementioned P-doped fiber at high dose rates, and it recovers almost completely once the irradiation has ended. More in detail, it was shown that during irradiation, the RIA in the IR range is composed of a limited permanent contribution, which increases with dose and stabilizes at a certain level, and a huge transient contribution, which quickly reaches a maximum level depending on the dose rate and disappears once the irradiation is over [23]. This transient RIA is typical of a particular defect, known in the literature as self-trapped holes (STHs) [19,[26][27][28][29][30][31].…”

“…The spectral response of this fiber together with th ergy-dispersive X-ray (EDX) spectroscopy measurements of its chemical elements their radial distribution were presented in [19]. Figure 1 reports the RIA kinetics at nm under a 5 min irradiation at 14 Gy/s, obtained with a classical spectral RIA mea ment setup, the same as the one used in [23], composed of a white light source (few of injected power) on one side of the fiber under test and an IR spectrometer on the side. The reported kinetics describe how the RIA increases quickly during irradiatio to a maximum point around 12.3 dB/m, and then decreases toward a slightly lower v ~11.8 dB/m.…”

“…The ULL-PSCF response was investigated at room temperature using the stepped irradiation profile illustrated in Figure 3, the same used in [23]. The dose rate was varied only by adjusting the X-ray tube current, changing neither the distance between the tube and the sample under test nor the voltage of the tube.…”