• Journal of Sensor Science and Technology
• /
• v.21 no.4
• /
• pp.287-292
• /
• 2012

A fiber-optic radiation sensor was fabricated using a sensing probe, a plastic optical fiber, a photomultiplier tube, and a multichannel analyzer for gamma-ray spectroscopy. As an inorganic scintillator of the sensing probe, a LYSO crystal was used. In this study, we obtained the relationship between the photon counts of the fiber-optic radiation sensor and the activity of the radioactive isotope. In addition, the gamma-ray energy spectra were also measured using a fiber-optic radiation sensor to discriminate species of gamma-ray emitters.

• Journal of Biomedical Engineering Research
• /
• v.37 no.1
• /
• pp.7-14
• /
• 2016

Radiopharmaceutical agents for positron emission tomography (PET), such as $^{18}F$-FDG and $^{68}Ga$, have been used not only for whole-body PET imaging but also for intraoperative radionuclide-guided surgery due to their quantitative and sensitive imaging characteristics. Current intraoperative probes detect gamma or beta particles, but not both of them. Gamma probes have low sensitivities since a collimator has to be used to reduce backgrounds. Positron probes have a high tumor-to-background ratio, but they have a 1-2 mm depth limitation from the body surface. Most of current intraoperative probes produce only audible sounds proportional to count rates without providing tumor images. This research aims to detect both positrons and annihilation photons from $^{18}F$ using plastic scintillators and a GAGG scintillation crystal attached to silicon photomultiplier (SiPM). The depth-of-interaction (DOI) along the plastic scintillator can be used to obtain the 2-D images of tumors near the body surface. The front and rear part of the intraoperative probe consists of $4{\times}1$ plastic scintillators ($2.9{\times}2.0{\times}12.0mm^3$) for positron detection and a Ce:GAGG scintillation crystal ($12.0{\times}12.0{\times}9.0mm^3$) for annihilation photon detection, respectively. The DOI resolution of $4.4{\pm}1.6mm$ along the plastic scintillator was obtained by using the 3M enhanced specular reflector (ESR) with rectangular holes between the plastic scintillators, which showed the feasibility of a 2-D image pixel size of $2.9{\times}4.4mm^2$ (X-direction ${\times}$ Y-direction).

• Nuclear Engineering and Technology
• /
• v.32 no.5
• /
• pp.457-464
• /
• 2000

In this paper, we describe the results of various calculations performed for a design of the thickness gauges that use the gamma-ray backscattering method. The radiation source is assumed to be the $_{24}$1Am(60keV gamma-ray) and the detector is a single crystal scintillator in a cylindrical form. The source is located at the center of the detector with the collimator of a cylindrical shape. First, when gamma-rays are incident on a material with a constant angle, we compute the variations of the spectrum for the photons scattered into different angular intervals. Next, we compute for an optimal size for the collimator cylinder for a fixed detector size and an optimal distance from the detector to the material. Finally, we compute the number of observed photons for different thickness of two different materials, a plastic film and an Al foil.

• Journal of Radiation Protection and Research
• /
• v.29 no.4
• /
• pp.263-268
• /
• 2004

Using the Monte Carlo simulation, a study on the lion-proportionality of the prototype phoswich detector with $2'{\times}2'$ CSI(Tl) and plastic scintillator, which was made by KAERI, has been carried. The defector response functions (DRFs) calculated by simulations were compared with the experimental measurement on the $^{137}Cs\;and\;^{60}Co$. To precisely simulate the DRF for the phoswich, the CSI(Tl) non-proportionality was calculated using the electron response and the simplified electron cascade sequence for treating the photoelectric absorption event. The resulting DRFs of $^{137}Cs\;and\;^{60}Co$ sources obtained by simulations were compared with experiments for verification. For $^{137}Cs$, gamma-ray responses simulated by MCNP5 are generally good agreement with the measured ones. But the DRF of $^{60}Co$ does not match well with the results of experiment in the energy region below second peak due to the coincidence effect of two gamma-rays (1.17 MeV and 1.33 MeV). Through the analysis of the non-proportionality of CsI(Tl) in the prototype phoswich, the improved DRFs considering non-proportionality were produced and the simulation results were verified using the experimental measurements. However, to more precisely reproduce the DRF for the phoswich, further studies in relation to the electron channeling effect and the Doppler broadening effect of a scintillator are still needed as well as considering that effect of the transfer contribution.

• Nuclear Engineering and Technology
• /
• v.55 no.2
• /
• pp.681-689
• /
• 2023

Purpose: Muons are characterized by a strong penetrating ability and can travel through thousands of meters of rock, making them ideal to image large volumes and substances typically impenetrable to, for example, electrons and photons. The feasibility of 3D image reconstruction and material identification based on a cosmic ray muons tomography (MT) system with triangular bar plastic scintillator detectors has been verified in this paper. Our prototype shows potential application value and the authors wish to apply this prototype system to 3D imaging. In addition, an MT experiment with the same detector system is also in progress. Methods: A simulation based on GEANT4 was developed to study cosmic ray muons' physical processes and motion trails. The yield and transportation of optical photons scintillated in each triangular bar of the detector system were reproduced. An image reconstruction algorithm and correction method based on muon scattering, which differs from the conventional PoCA algorithm, has been developed based on simulation data and verified by experimental data. Results: According to the simulation result, the detector system's position resolution is below 1 ~ mm in simulation and 2 mm in the experiment. A relatively legible 3D image of lead bricks in size of 20 cm × 5 cm × 10 cm used our inversion algorithm can be presented below 1× 10⁴ effective events, which takes 16 h of acquisition time experimentally. Conclusion: The proposed method is a potential candidate to monitor the cosmic ray MT accurately. Monte Carlo simulations have been performed to discuss the application of the detector and the simulation results have indicated that the detector can be used in cosmic ray MT. The cosmic ray MT experiment is currently underway. Furthermore, the proposal also has the potential to scan the earth, buildings, and other structures of interest including for instance computerized imaging in an archaeological framework.

• Journal of Radiation Protection and Research
• /
• v.45 no.3
• /
• pp.117-129
• /
• 2020

Background: Radiation portal monitors (RPMs) involving plastic scintillators installed at the border inspection sites can detect illicit trafficking of radioactive sources in cargo containers within seconds. However, RPMs may generate false alarms because of the naturally occurring radioactive materials. To manage these false alarms, we previously suggested an energy-weighted algorithm that emphasizes the Compton-edge area as an outstanding peak. This study intends to evaluate the identification of radioactive sources using an improved energy-weighted algorithm. Materials and Methods: The algorithm was modified by increasing the energy weighting factor, and different peak combinations of the energy-weighted spectra were tested for source identification. A commercialized RPM system was used to measure the energy-weighted spectra. The RPM comprised two large plastic scintillators with dimensions of 174 × 29 × 7 ㎤ facing each other at a distance of 4.6 m. In addition, the in-house-fabricated signal processing boards were connected to collect the signal converted into a spectrum. Further, the spectra from eight radioactive sources, including special nuclear materials (SNMs), which were set in motion using a linear motion system (LMS) and a cargo truck, were estimated to identify the source identification rate. Results and Discussion: Each energy-weighted spectrum exhibited a specific peak location, although high statistical fluctuation errors could be observed in the spectrum with the increasing source speed. In particular, ¹³⁷Cs and ⁶⁰Co in motion were identified completely (100%) at speeds of 5 and 10 km/hr. Further, SNMs, which trigger the RPM alarm, were identified approximately 80% of the time at both the aforementioned speeds. Conclusion: Using the modified energy-weighted algorithm, several characteristics of the energy weighted spectra could be observed when the used sources were in motion and when the geometric efficiency was low. In particular, the discrimination between ⁶⁰Co and ⁴⁰K, which triggers false alarms at the primary inspection sites, can be improved using the proposed algorithm.

• Progress in Medical Physics
• /
• v.19 no.4
• /
• pp.285-290
• /
• 2008

In this study, we have fabricated a one-dimensional fiber-optic dosimeter for electron beam therapy dosimetry. Each fiber-optic dosimeter has an organic scintillator with a plastic optical fiber and it is embedded and arrayed in the plastic phantom to measure one-dimensional high energy electron beam profile of clinical linear accelerator. The scintillating lights generated from each sensor probe are guided by plastic optical fibers to the multi-channel photodiode amplifier system. We have measured one-dimensional electron beam profiles in a PMMA phantom according to different field sizes and energies of electron beam. Also, the isodose and three-dimensional percent depth dose curves in a PMMA phantom are obtained using a one-dimensional fiber-optic dosimeter with different electron beam energies.

• Journal of Sensor Science and Technology
• /
• v.18 no.5
• /
• pp.402-407
• /
• 2009

In this study, plastic optical fiber sensors which can measure thermal neutron dose in a mixed neutron-gamma field are developed and characterized. Using $^{252}Cf$ and $^{60}Co$ sources, the scintillators suitable for thermal neutron detection, are tested and the scintillating lights generated from a plastic optical fiber sensor in the Kyoto University Critical Assembly (kuca) core are measured. Also, the distributions of thermal neutron and gamma-ray are measured in a mixed field as a function of the distance from the center of the reactor core at KUCA and the distribution of thermal neutron is obtained using a subtraction method. Sensitivity of the fiber-optic radiation sensor system is about 0.49 V/mW according to power of the KUCA core and its relative error is about 1.2 %.

• Journal of Radiation Protection and Research
• /
• v.41 no.2
• /
• pp.105-109
• /
• 2016

Background: For an accelerator-based BNCT, we have fabricated a new detector consisting of quartz optical fibers that have excellent radiation-resistant characteristics. Materials and Methods: The developed detectors were irradiated at Kyoto University Research Reactor. Results and Discussion: The experimental results showed that the new detector had good output linearity for the neutron intensity, and the response of the new detector did not decrease during the irradiation. Conclusion: The new detector consisting of quartz optical fibers can be applied to measurement of neutron field of an accelerator-based BNCT.

• Nuclear Engineering and Technology
• /
• v.51 no.4
• /
• pp.1169-1175
• /
• 2019

The minimum detectable activity (MDA) value was derived according to the flow rate of the sample and degree of amplification of the device by sending the sample directly from the collection site to the detection part through a pump. This method can lead to reduction in time and cost compared to the existing measurement method that uses a pre-treatment process. In this study, experiments were conducted on $^3H$ and $^{90}Sr$, which are the major pure beta-emitting radionuclides, by setting the sample flow rate and the amplification gain as factors. The MDA values were derived according to the flow rates, considering that the flow rate can affect the MDA values. There were no change in the MDA under different flow rates of 0, 600, 800, and 1000 mL/min. Therefore, it was confirmed that the flow rate may not be considered when collecting samples for monitoring in actual field. As the degree of amplification of the amplifier increased, the time required to reach the target MDA decreased. When the amplification was quadrupled, the detection efficiency increased by approximately 23.4 times, and the time to reach the MDA decreased to approximately 1/550 times. This method offers the advantage of real-time on-site monitoring.