Abstract
We fabricated a small-sized, flexible, and insertable fiber-optic radiation sensor (FORS) that is composed of a sensing probe, a plastic optical fiber (POF), a photomultiplier tube (PMT)-amplifier system, and a multichannel analyzer (MCA) to obtain the energy spectra of radioactive isotopes. As an inorganic scintillator for gamma-ray spectroscopy, a cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) crystal was used and two solid-disc type radioactive isotopes with the same dimensions, cesium-137 (Cs-137) and cobalt-60 (Co-60), were used as gamma-ray emitters. We first determined the length of the LYSO:Ce crystal considering the absorption of charged particle energy and measured the gamma-ray energy spectra using the FORS. The experimental results demonstrated that the proposed FORS can be used to discriminate species of radioactive isotopes by measuring their inherent energy spectra, even when gamma-ray emitters are mixed. The relationship between the measured photon counts of the FORS and the radioactivity of Cs-137 was subsequently obtained. The amount of scintillating light generated from the FORS increased by increasing the radioactivity of Cs-137. Finally, the performance of the fabricated FORS according to the length and diameter of the POF was also evaluated. Based on the results of this study, it is anticipated that a novel FORS can be developed to accurately measure the gamma-ray energy spectrum in inaccessible locations such as narrow areas and holes.
Highlights
Gamma-rays emitted from radioactive sources have specific energies
The main purpose of the present study is to demonstrate that the proposed fiber-optic radiation sensor (FORS) can discriminate different gamma-ray emitters by measuring their inherent energy spectra, even when radioactive isotopes are mixed
In order to obtain photopeaks in the inherent energy spectrum of a radioactive isotope, the sensing volume is very important since the size of the scintillator used in a FORS is normally small
Summary
Gamma-rays emitted from radioactive sources have specific energies. Due to the fact that gamma-rays are uncharged and indirectly ionizing radiation, gamma detection depends on causing the gamma-ray photons to undergo interactions in the absorbing material. When gamma-rays interact with a scintillator, they produce charged electrons mainly by three different interactions, a photoelectric effect, Compton scattering, and pair production. These electrons give rise to scintillating light, making it is possible to analyze and compare radioactive isotopes by measuring the total energy absorbed per interaction (i.e., pulse height) according to the specific energies of gamma-rays [1]. The NaI:Tl crystal must be sealed within an air-tight container, as it has a hygroscopic characteristic [1,2,3,4] To overcome these problems and allow real-time and remote measurements in harsh environments, a newly designed gamma-ray spectrometer with small size, flexibility, and non-hygroscopicity is required
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