Characterization of a Fiber Optic Radiation Sensor Prototype for Nuclear Dismantling

Abstract

The use of an active measurement system to localize contamination in concrete structures of nuclear facilities offers advantages like an easy on-site analysis within short measurement time. A measuring system based on a scintillation crystal connected to a long optical fiber with a large diameter could satisfy the demands of a measuring system for gamma-ray spectroscopy in boreholes. This work describes the developement of a gammaray spectroscopy system using a fiber optic radiation sensor. A prototype was built with a GAGG scintillation crystal, that could reach an energy resolution of 33 % at the 662 keV gamma-ray emission energy of 137 Cs. A minimal time for the detection of a contamination of a 137 Cs source with an activity of 21 kBq and a layer of 6 cm concrete between sensor and radiation source was determined to under one minute with three different evaluation methods. They were based on the decision threshold and the Kolmogorov-Smirnov test corresponding to the energy distribution and the distribution of time differences between detector events. Additionally, it was possible to estimate the distance of a point like source from the sensor by establishing a further analysis parameter comparing different energy regions of a spectrum.

An extendable optical fibre probe survey meter for naturally occurring radioactive material (NORM) and other weak emitters

“…The mean dose-rates at distances of 12, 10, 8, 5, 3, 1, and 0.2-cm were found to be 1.19, 1.47, 1.98, 2.72, 4.37, 6.44, and 7.59 µSv/h, respectively. As observed in several previous studies 1 , 7 , at extremely low radiation levels, discrimination between different dose rates requires longer integration time, in the range of tens of seconds. Results for the present arrangement shows effective discrimination at the level of ~ 0.5 µSv/h for data acquired over a period of 30–40 s. A more elaborate discussion regarding responses at low dose rates will be presented in a subsequent subsection.…”

“…Based on these results, the study suggests that an inorganic scintillator with a high light yield and emission wavelength close to 535 nm would perform well in gamma-ray spectroscopy after RGO coating. Dohler et al 7 made note of signal integration time capability for FORS in applications intended to measure for contamination, also in estimating shielding parameters, low-activity sources taking longer to be detected for a source and detector separated by thick concrete material.…”