An Experimental and Theoretical Study of the Effective Length of Embedded Scintillator Materials in End-Constructed Optical Fiber Radiation Sensing Probes

Inorganic scintillating material used in optical fibre sensors (OFS) when used as dosimeters for measuring percentage depth dose (PDD) characteristics have exhibited significant differences when compared to those measured using an ionization chamber (IC), which is the clinical gold standard for quality assurance (QA) assessments. The percentage difference between the two measurements is as high as 16.5% for a 10 × 10 cm2 field at 10 cm depth below the surface. Two reasons have been suggested for this: the presence of an energy effect and Cerenkov radiation. These two factors are analysed in detail and evaluated quantitatively. It is established that the influence of the energy effect is only a maximum of 2.5% difference for a beam size 10 × 10 cm2 compared with the measured ionization chamber values. And the influence of the Cerenkov radiation is less than 0.14% in an inorganic scintillating material in the case of OFS when using Gd2O2S:Tb as the luminescent material. Therefore, there must be other mechanisms leading to over-response. The luminescence mechanism of inorganic scintillating material is theoretically analysed and a new model is proposed and validated that helps explain the over-response phenomenon.

This article presents the results of experimental studies of simultaneous transmission of ultrasonic waves and laser signals in optical fibers by the use of both the optical single mode and multimode fiber couplers. This work was aimed, among other things, at the study of the way the acoustic energy affects a laser beam. The light wave was guided into one of the coupler's arms. The optical power applied to one input of the coupler is separated into two coupler outputs according to the rate determined by the coupling coefficient. Only an ultrasonic wave generated by a sandwich type transducer is applied to the other arm of the coupler. In this experiment, as in case of the light wave, the acoustic power is separated into both the outputs. One can observe the interaction of both the waves on the two outputs - a modulation of the light wave by means of the ultrasonic wave is possible. The output signal was detected using a PIN diode and an optical power meter (OPM). Temporary courses were observed on an oscilloscope screen. The simultaneous transmission of ultrasounds and optical radiation in optical fibers can be used in the construction of medical equipment.

This review article considers the latest developments in the field of inorganic scintillation materials. Modern trends in the improvement of inorganic scintillation materials are based on engineering their features at the nanoscale level. The essential challenges to the fundamental steps of the technology of inorganic glass, glass ceramics, and ceramic scintillation materials are discussed. The advantage of co-precipitation over the solid-state synthesis of the raw material compositions, particularly those which include high vapor components is described. Methods to improve the scintillation parameters of the glass to the level of single crystals are considered. The move to crystalline systems with the compositional disorder to improve their scintillation properties is justified both theoretically and practically. A benefit of the implementation of the discussed matters into the technology of well-known glass and crystalline scintillation materials is demonstrated.

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, the Cerenkov light also can be generated due to their dielectric components. Accordingly, the radiation-induced light signals can be obtained using optical fibers without any scintillating material. In this study, to measure the intensities of Cerenkov radiation induced by gamma-rays, we have fabricated the fiber-optic Cerenkov radiation sensor system using silica optical fibers, plastic optical fibers, multi-anode photomultiplier tubes, and a scanning system. To characterize the Cerenkov radiation generated in optical fibers, the spectra of Cerenkov radiation generated in the silica and plastic optical fibers were measured. Also, the intensities of Cerenkov radiation induced by gamma-rays generated from a cylindrical Co-60 source with or without lead shielding were measured using the fiberoptic Cerenkov radiation sensor system.

In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry.

This report gives a review of the radiation damages induced by gammas and energetic hadrons in inorganic scintillating materials. We discuss the creation and recovery of color centers in scintillating materials under gamma and high energy proton irradiation, the two main causes of irradiation in High Luminosity LHC. The induced phosphorescence and the production of radioisotopes in heavy and light inorganic scintillators and in surrounding construction materials, as well as their influence on the possible design of the detector working in a high dose rate environment, are also described.

Scintillator materials convert high-energy radiation into photons in the ultraviolet to visible light region for radiation detection. In this review, advances in X-ray emission dynamics of inorganic scintillators are presented, including inorganic halides (alkali-metal halides, alkaline-earth halides, rare-earth halides, oxy-halides, rare-earth oxyorthosilicates, halide perovskites), oxides (binary oxides, complex oxides, post-transition metal oxides), sulfides, rare-earth doped scintillators, and organic-inorganic hybrid scintillators. The origin of scintillation is strongly correlated to the host material and dopants. Current models are presented describing the scintillation decay lifetime of inorganic materials, with the emphasis on the short-lived scintillation decay component. The whole charge generation and the de-excitation process are analyzed in general, and an essential role of the decay kinetics is the de-excitation process. We highlighted three decay mechanisms in cross luminescence emission, exitonic emission, and dopant-activated emission, respectively. Factors regulating the origin of different luminescence centers controlling the decay process are discussed.

Cerenkov radiation can be observed easily as a shimmer of blue light from the water in boiling- and pressurized-water reactors, or spent fuel storage pools. In this research, we fabricated the fiber-optic Cerenkov radiation sensor using a Gdfoil, rutile crystal and optical fiber for detecting neutrons. Also, the reference sensor for measuring background gammarays was fabricated with the rutile crystal and optical fiber. The neutron fluxes could be obtained by measuring the signal difference between two sensors. To characterize the fiber-optic Cerenkov radiation sensor, we measured neutron fluxes using a Cf-252 neutron source according to depths of polyethylene. As the results, the counts of fiber-optic Cerenkov radiation sensor were higher than those of reference sensor due to additional interactions between Gd-foil and neutrons. Also, the counts of Cerenkov radiation decreased with increasing polyethylene thickness. It is anticipated that the novel and simple fiber-optic Cerenkov radiation sensor using the Cerenkov effect can be widely used to detect the neutrons in hazardous nuclear facilities.

Optical fibers are being widely utilized as radiation sensors and dosimeters. Benefiting from the rapidly growing optical fiber manufacturing and material engineering, advanced optical fibers have evolved significantly by using functional structures and materials, promoting their detection accuracy and usage scenarios as radiation sensors. This paper summarizes the current development of optical fiber-based radiation sensors. The sensing principles of both extrinsic and intrinsic optical fiber radiation sensors, including radiation-induced attenuation (RIA), radiation-induced luminescence (RIL), and fiber grating wavelength shifting (RI-GWS), were analyzed. The relevant advanced fiber materials and structures, including silica glass, doped silica glasses, polymers, fluorescent and scintillator materials, were also categorized and summarized based on their characteristics. The fabrication methods of intrinsic all-fiber radiation sensors were introduced, as well. Moreover, the applicable scenarios from medical dosimetry to industrial environmental monitoring were discussed. In the end, both challenges and perspectives of fiber-based radiation sensors and fiber-shaped radiation dosimeters were presented.

In this study, we characterized the Cerenkov radiation generated from optical fibers as fundamental research for the development of a fiber-optic Cerenkov radiation sensor to verify spent fuel. We measured the amount of Cerenkov radiation according to OH content and numerical aperture of the optical fiber. Also, we measured the Cerenkov radiation as functions of the length and the diameter of the optical fiber. As a result, the silica optical fibers with high numerical aperture and high OH content were efficient and stable for gathering the Cerenkov radiation generated in the optical fiber. Also, the intensity of the Cerenkov radiation generated in the optical fiber was proportional to the irradiated length and to the square of the irradiated diameter.

Remote optical fiber dosimetry

Using a phenomenological approach, the light yield is derived for inorganic scintillators as a function of the rates of linear, bimolecular, and Auger processes occurring in the electron track initiated by an x ray or a γ-ray photon. A relation between the track length and incident energy is also derived. It is found that the nonproportionality in the light yield can be eliminated if either nonlinear processes of interaction among the excited electrons, holes, and excitons can be eliminated from occurring or the high density situation can be relieved by diffusion of carriers from the track at a faster rate than the rate of activation of nonlinear processes. The influence of the track length and radius on the yield nonproportionality is discussed in view of the known experimental results. Inventing new inorganic scintillating materials with high carrier mobility can lead to a class of proportional inorganic scintillators. Results agree qualitatively with experimental results for the dependence of light yield on the incident energy.

To investigate the diffusion characteristics of water of optic nerve and optic radiation in healthy adults and its related factors by diffusion tensor imaging (DTI) at 3T. A total of 107 healthy volunteers performed head conventional MRI and bilateral optic nerve and optic radiation DTI. The primary data of DTI was processed by post-processing software of DTI studio 2.3, obtaining fractional anisotropy value, mean diffusivity value, principal engine value, orthogonal engine value by measuring, and analyzed by the SPSS13.0 statistical software. The bilateral optic nerve and optic radiation fibers presented green color in directional encoded color (DEC) maps and presented high signal in fractional anisotropy (FA) maps. The FA value of the left optic nerve was 0.598±0.069 and the right was 0.593±0.065; the mean diffusivity (MD) value of the left optic nerve was (1.324±0.349)×10(-3)mm(2)/s and the right was (1.312±0.350)×10(-3)mm(2)/s; the principal engine value (λ‖) of the left optic nerve was (2.297±0.522)×10(-3)mm(2)/s and the right was (2.277±0.526)×10(-3)mm(2)/s; the orthogonal engine value (λ⊥) of the left optic nerve was (0.838±0.285)×10(-3)mm(2)/s and the right was (0.830±0.280)×10(-3)mm(2)/s; the FA value of the left optic radiation was 0.636±0.057 and the right was 0.628±0.056; the mean diffusivity (MD) value of the left optic radiation was (0.907±0.103)×10(-3)mm(2)/s and the right was (0.889±0.125)×10(-3)mm(2)/s; the principal eigenvalue (λ‖) of the left optic radiation was (1.655±0.210)×10(-3)mm(2)/s and the right was (1.614±0.171)×10(-3)mm(2)/s; the orthogonal enginvalue (λ⊥) of the left optic radiation was (0.531±0.103)×10(-3)mm(2)/s and the right was (0.524±0.152)×10(-3)mm(2)/s. There was no obvious difference between the FA, MD, λ‖, λ⊥ of the bilateral optic radiation and the bilateral optic nerve (P>0.05) and no obvious difference between male and female group. The FA, MD, λ‖, λ⊥ of the bilateral optic radiation and the bilateral optic nerve had no obvious correlations to the age. DTI is sensitive to the optic nerve and radiation and the relevant DTI parameters of the optic nerve and radiation are established preliminarily in this study.

Fiber-optic radiation sensors have been developed to detect gamma-rays generated from radioisotopes. Recently, many studies on the Cerenkov radiation in optical fibers without scintillator materials have been conducted to experimentally investigate their response characteristics against gamma-rays. The purpose of this study is to develop a Monte Carlo-based computer program in order to simulate the Cerenkov-based Fiber-Optic Radiation Sensor and to investigate the response characteristics of the sensor. In the model, the gamma photon generates an electron by Compton scattering and then the electron with velocity greater than the phase velocity of light generates an optical photon by the Cerenkov principle. Finally, the energy spectrum and number of optical photons are evaluated. The computer program is used to simulate the sensors under an environment with Iridium-192 radioisotope. The simulation results exhibited good agreement with experimental results.

Benchmarking novel optical fibre sensors for applications in radiation therapy