• Journal of the Korean Society of Radiology
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• v.13 no.1
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• pp.15-20
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• 2019

We developed a novel depth-of-interaction positron emission tomography (PET) detector using wavelength shifting (WLS) fibers and optimized it. The optimization module was designed by using two scintillators and three WLS fibers and attaching a sensor to the end of the WLS fiber. Optimum combinations were obtained through the light collection efficiency and the light collection ratio between sensors depending on coupling materials and reflectors of scintillators, WLS fibers and sensors. The highest light collection efficiency and the light collection ratio between sensors were obtained in the combination of the epoxy (coupling materials)-diffuse reflector (scintillators)-specular reflector (WLS fibers).

• Journal of Sensor Science and Technology
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• v.9 no.1
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• pp.15-21
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• 2000

Optical fiber temperature sensor, using resonance wavelength shifting of single mode fiber-to-planar waveguide coupler by heat, was fabricated. Thermo-optic polymers, have large change of refractive index due to heat, were used for planar waveguide. The device fabrication procedure including fiber polishing steps was illustrated and the device structure with independent polarization was demonstrated experimentally. The resonance wavelength difference of fabricated device was less than 2nm. The resonance wavelength shifting owing to temperature variation, from room temperature($24^{\circ}C$) to $90^{\circ}C$, was showed $-0.54nm/^{\circ}C$, $-3nm/^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.201-207
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• 1999

The fiber-optical confocal scanning interference microscope with a simple configuration was constructed with a 4-port fiber-optic coupler, and the new method based on the phase shifting method was proposed for surface profiling by the system. In the method, the height of a specimen was determined from the phase of confocal beam. It was verified experimentally that the method was applicable to even the confocal interference microscope with a long-wavelength source and a low NA objective, and that the scanning time could be drastically reduced compared with the conventional method. Finally, it was found that our method is less sensitive to the variation of surface reflectivity than the conventional method.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1009-1014
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• 2023

Muon tomography is a useful method for monitoring special nuclear materials (SNMs) such as spent nuclear fuel inside dry cask storage. Multiple Coulomb scattering of muons can be used to provide information about the 3-dimensional structure and atomic number(Z) of the inner materials. Tomography using muons is less affected by the shielding material and less harmful to health than other measurement methods. We developed a muon detector for muon tomography, which consists of a plastic scintillator, 64 long wavelength-shifting (WLS) fibers attached to the top of the plastic scintillator, and silicon photomultipliers (SiPMs) connected to both ends of each WLS fiber. The muon detector can acquire X and Y positions simultaneously using a position determination algorithm. The design parameters of the muon detector were optimized using DETECT2000 and Geant4 simulations, and a muon detector prototype was built based on the results. Spatial resolution measurement was performed using simulations and experiments to evaluate the feasibility of the muon detector. The experimental results were in good agreement with the simulation results. The muon detector has been confirmed for use in a muon tomography system.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.5
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• pp.305-310
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• 2015

We propose a new concept for a depth of interaction (DOI) positron emission tomography (PET) detector based on dual-ended-scintillator (DES) readout for small animal imaging. The detector consists of lutetium yttrium orthosilicate (LYSO) arrays coupled with orthogonal wavelength-shifting (WLS) fibre placed on the top and bottom of the arrays. On every other line, crystals that are 2 mm shorter are arranged to create grooves. WLS fibre is inserted into these grooves. This paper describes the design and performance evaluation of this PET detector using Monte Carlo simulations. To investigate sensitivity by crystal size, five types of PET detectors were simulated. Because the proposed detector is composed of crystals with three different lengths, degradation in sensitivity across the field of view was also explored by simulation. In addition, the effect of DOI resolution on image quality was demonstrated. The simulation results proved that the devised PET detector with excellent DOI resolution is helpful for reducing the channels of sensors/electronics and minimizing gamma ray attenuation and scattering while maintaining good detector performance.

• Journal of Sensor Science and Technology
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• v.10 no.3
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• pp.156-162
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• 2001

Novel pressure sensor using the resonance wavelength shift of single mode fiber-to-planar waveguide coupler, was demonstrated. It is found that the resonance wavelength shift due to refractive index variation of polymers by pressure occurs and its sensitivity depends on materials. We adopted symmetric structure of planar waveguide and remove the polarization dependence which is inevitable with side-polished fiber. AZ4562, AZl512 and THB-30 are used as planar waveguide materials and the resonance wavelength shifting by pressure was shown -0.008um/bar, 0.033nm/bar and 0.16nm/bar, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4C
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• pp.163-174
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• 2009

Mechanical device using the load cell or strain gage sensor can be influenced by tempearute changes because temperature change can cause a shift in the load cell or straing gage output at zero loading. In this paper, micro cone penetrometers with 1~7mm in diameter, are developed by using an optical fiber sensor (FBG: Fiber Bragg Grating) to compensate the continous temperature change during cone penetration test. Note the temperature compensated method using optical fiber sensor which has hair-size in diameter, and is not affected by environmental conditions because the measured data is the wavelength shifting of the light instead of the intensity of the electric voltage. Temperature effect test shows that the output voltage of strain gage changes and increases with an increase in the temperature. A developed FBG cone penetrometer, however, achieves excellent temperature compensation during penetration, and produces continuous change of underground temperature. In addition, the temperature compensated FBG cone shows the excellent sensitivity and detects the interface of the layered soils with higher resolution. This study demonstrates that the fiber optic sensor renders the possibility of the ultra small size cone and the new fiber optic cone may produce more reliable temperature compensated tip resistance.

• Journal of Radiation Protection and Research
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• v.41 no.3
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• pp.185-190
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• 2016

Background: In order to measure neutron energy spectra, the conventional Bonner Sphere Spectrometers (BSS) are widely used. In this spectrometer, several measurements with different size Bonner spheres are required. Operators should, therefore, place these spheres in several times to a measurement point where radiation dose might be relatively high. In order to reduce this effort, novel neutron energy spectrometer using an onion-like single Bonner sphere was proposed in our group. This Bonner sphere has multiple sensitive spherical shell layers in the single sphere. In this spectrometer, a band-shaped thermal neutron detection medium, which consists of a LiF-ZnS mixed powder scintillator sheet and a wavelength-shifting (WLS) fiber readout, was looped to each sphere at equal angular intervals. Amount of LiF neutron converter is reduced near polar region, where the band-shaped detectors are concentrated, in order to uniform the directional sensitivity. The LiF-ZnS mixed powder has an advantage of extremely high light yield. However, since it is opaque, scintillation photons cannot be collect uniformly. This type of detector shows no characteristic shape in the pulse height spectrum. Subsequently, it is difficult to set the pulse height discrimination level. This issue causes sensitivity fluctuation due to gain instability of photodetectors and/or electric modules. Materials and Methods: In order to solve this problem, we propose to replace the LiF-ZnS mixed powder into a flexible and Transparent RUbber SheeT type $LiCaAlF_6$ (TRUST LiCAF) scintillator. TRUST LiCAF scintillator can show a peak shape corresponding to neutron absorption events in the pulse height spectrum. Results and Discussion: We fabricated the prototype detector with five sensitive layers using TRUST LiCAF scintillator and conducted basic experiments to evaluate the directional uniformity of the sensitivity. Conclusion: The fabricated detector shows excellent directional uniformity of the neutron sensitivity.