Online Gamma Radiation Monitoring Using Few-Mode Polymer CYTOP Fiber Bragg Gratings

Abstract

We investigated the gamma radiation response of fiber Bragg gratings (FBGs) inscribed in a few-mode polymer optical fiber. The fiber had a graded-index CYTOP core of 20 µm and XYLEX overclad of 250 µm in diameter. Four FBGs were exposed to gamma radiation during four irradiation sessions at a 5.3 kGy/h dose rate. The FBGs showed a linear Bragg wavelength shift with the received dose with a mean sensitivity of −3.95 pm/kGy at 43 °C. The increased temperature provides a rise in the sensitivity: it reached −10.6 pm/kGy at 58 °C. After irradiation, the FBGs showed partial recovery, which increased with the received dose. Furthermore, the FBG’s reflection power decreased with the dose. This attenuation is mainly due to insertion losses caused by the radiation induced attenuation in the CYTOP fiber. Linear response to the received dose makes CYTOP FBGs attractive for gamma radiation dosimetry. However, temperature dependence of the sensitivity should be compensated in practical applications.

Temperature and RH response of polymer CYTOP FBG treated by gamma radiation

“…In our previous works [7][8][9], we demonstrated that gamma radiation treatment changes the climatic properties of CYTOP FBGs: we observed a rise of the RH sensitivity with received dose and a decrease of temperature sensitivity with subsequent change of sign from positive to negative. Among irradiation doses, which we applied in the experiment, the dose of 200 kGy provided the closest to zero temperature sensitivity of the irradiated FBGs [7,8]. This case is prospective for RH sensing since temperature cross-sensitivity can be eliminated.…”

“…Performing the second temperature cycle at high RH (89%) straight after the cycle at 40 %RH, we faced a difficulty with temperature sensitivity precise calculation, because the BW slowly increased during the entire experiment. From our previously performed experiments with RH cycles [8], we found that the BW requires longer stabilization time in case of high RH levels and when the FBG was treated by gamma radiation. Taking this into account, we developed a program of the experiment allowing to analyze the FBG response when the RH quickly changes from high value to moderate and back, and allowing to perform the temperature cycle at stable BW (Figure 3).…”

“…However, practical realization of RH sensors requires temperature crosssensitivity elimination. A certain optimal fiber pre-strain [6] and gamma irradiation of FBGs of up to optimal dose [7][8][9] are potential solutions recently proposed for CYTOP ® FBGs.…”

Elimination of temperature cross-sensitivity for polymer FBG-based humidity sensor by gamma radiation treatment

“…Also, the method of gamma radiation dosimetry based on the measurement of the RIA during (or after) irradiation was investigated [19]. Finally, the response of FBGs inscribed in perfluorinated POF was examined during and after irradiation [20,21]. Recently, we tested irradiated FBGs in the environmental chamber and we found that gamma radiation increases the sensitivity of perfluorinated FBGs to relative humidity (RH) and decreases their temperature sensitivity.…”

Feature Papers in Optical Sensors 2022

“…In the first paper, by Chapalo et al [ 1 ], the authors investigated the gamma radiation response of fiber Bragg gratings (FBGs) inscribed in a few-mode polymer optical fiber. The fiber had a graded-index CYTOP core of 20 µm and XYLEX overclad of 250 µm in diameter.…”