Opto-Mechanical Fiber Sensing of Gamma Radiation

Yosef London,Mikhail Kalina,Hagai Diamandi,Olga Kleinerman,Amnon Zentner,Garry Berkovic,Moshe Mayoni,Kavita Sharma,Andrei Stolov,Mirit Hen,Gil Bashan,Avi Zadok,Elad Zehavi,Shlomi Zilberman,Ehud Shafir

doi:10.1109/jlt.2021.3102698

Abstract

The monitoring of ionizing radiation is critical for the safe operation of nuclear and other high-power plants. Fiber-optic sensing of radiation has been pursued for over 45 years. Most protocols rely on radiation effects on the optical properties of the fiber. Here we propose a new concept, in which the opto-mechanics of standard fibers coated by thin layers of fluoroacrylate polymer are observed instead. The time-of-flight of radial acoustic waves through the coating is evaluated by forward stimulated Brillouin scattering measurements. The time-of-flight is seen to decrease monotonically with the overall dosage of gamma radiation from a cobalt source. Variations reach 15% of the initial value for 180 Mrad dose and remain stable for at least several weeks following exposure. The faster times-of-flight are consistent with a radiation-induced increase in the coating stiffness, observed in offline analysis. The effects on the coating are independent of possible changes in the optical parameters of the fiber. The combination of opto-mechanical analysis together with established fiber sensing protocols may help disambiguate the evaluation of multiple radiation metrics and reduce environmental cross-sensitivities. The technique is suitable for online monitoring and may be extended to spatially distributed measurements.

Highlights

The monitoring of ionizing radiation is essential for the proper and safe operation of nuclear and other high-energy plants, waste disposal sites and research facilities
The results provide the basis for optical fiber sensors of ionizing radiation [10,11,13,14,15,16,17,18,19,20,21]
These changes are manifested in distributed temperature measurements through optical frequency domain reflectometry (OFDR), and may alter their proper calibration [39,40,41,42]

Summary

INTRODUCTION

The monitoring of ionizing radiation is essential for the proper and safe operation of nuclear and other high-energy plants, waste disposal sites and research facilities. Several studies monitored radiation induced changes to the backward Brillouin scattering frequency shift [33,34,35], which depends on both the refractive index and the velocity of dilatational acoustic waves in the core of the fiber [7,8] In another example, changes in the density of silica were observed following exposure to neutron radiation [36]. A series of studies by Rizzolo and coworkers has shown that both temperature and radiation exposure could modify the elastic properties of several types of coating, or the interface between fiber and coating [39,40,41,42] These changes are manifested in distributed temperature measurements through optical frequency domain reflectometry (OFDR), and may alter their proper calibration [39,40,41,42]. The method is suitable for continuous monitoring of fibers within protective cables, and it is scalable to spatially distributed analysis

Principle of operation

Experimental results

Findings

DISCUSSION

CONCLUSIONS