• Nuclear Engineering and Technology
• /
• v.49 no.7
• /
• pp.1483-1488
• /
• 2017

In order to predict and control the environmental and health impacts of ionizing radiation in environmental sources such as groundwater, it is necessary to identify the radionuclides present. Beta-emitting radionuclides are frequently identified by measuring their characteristic energy spectra. The present work shows that self-attenuation effects from volume sources result in a geometry-dependent shift in the characteristic spectra, which needs to be taken into account in order to correctly identify the radionuclides present. These effects are shown to be compounded due to the subsequent shift in the photon spectra produced by the detector, in this case an inorganic solid scintillator ($CaF_2:Eu$) monitored using a silicon photomultiplier. Using tritiated water as an environmentally relevant, and notoriously difficult to monitor case study, analytical predictions for the shift in the energy spectra as a function of depth of source have been derived. These predictions have been validated using Geant4 simulations and experimental results measured using bespoke instrumentation.

• Journal of radiological science and technology
• /
• v.42 no.1
• /
• pp.67-75
• /
• 2019

Grating interferometry based imaging technology is a kind of radiation imaging system, which can acquire not only absorption image but also phase difference and dark field image using the Talbot pattern. However, because of the technological difficulties and high cost of fabricating the gratings that make up the system, much efforts are being made to look for ways to replace them. The is a preliminary study to see how the Talbot pattern transfer through various kinds of scintillators and if the optical grating can be a way to replace the conventional absorption gratings. The geometry of the interferometer, the scintillator model, and the scintillator thickness are the main inputs for our simulation. We have used the concept of modulation for quantitative analysis of the contrast ratio of the Talbot pattern. This research is expected to provide very useful information on the design of optical gratings, which is an alternative way to analyze the Talbot pattern, which we have filed a patent on.

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

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.3 no.3
• /
• pp.159-165
• /
• 2005

The characterization of radiological contamination inside pipes generated during the decommission of a nuclear facility is necessary before pipes can be recycled or disposed. But, existing direct measurements of radioactive contamination level using the survey-meter can not estimate the characteristic of contamination on a local area such as the pipe inside. Moreover, the measurement of surface contamination level using the indirect methods has many problems of an application because of the difficulty of collecting sample and contamination possibility of a worker when collecting sample. In this work, plastic scintillator was simulated by using Monte Carlo simulation method for detection of beta radiation emitted from internal surfaces of small diameter pipe. Simulation results predicted the optimum thickness and geometry of plastic scintillator at which energy absorption for beta radiation was maximized. In addition, the problem of scintillator processing and transferring the detector into the pipe inside was considered when fabricating the plastic detector on the basis of simulation results. The characteristic of detector fabricated was also estimated. As a result, it was confirmed that detector capability was suitable for the measurement of contamination level. Also, the development of a detector for estimating the radiological characteristic of contamination on a local area such as the pipe inside was proven to be feasible.

• Korean Journal of Materials Research
• /
• v.26 no.4
• /
• pp.212-215
• /
• 2016

In this paper, cerium doped lutetium pyrosilicate (LPS) powders with cerium content (0.05 and 0.07 mol%) were prepared by sol-gel process. The formation of lutetium pyrosilicate (LPS) phase was confirmed by XRD analysis for the powders heated at $1,200^{\circ}C$; in these powders, a single phase of $Lu_2Si_2O_7$ (LPS) was observed. Cerium doped lutetium pyrosilicate (LPS) powder was agglomerated and constituted of small spherical particles with diameters of about 300 nm. The photoluminescence spectra of the $Lu_2Si_2O_7:Ce^{3+}$ powders showed the characteristic of excitation and there was an emission spectrum for $Ce^{3+}$ in the host of $Lu_2Si_2O_7$. The emission spectrum shows a broad band in the range of 350-525 nm; the broad wavelength on the right side of the spectra should be ascribed to the same 5d-4f transitions of $Ce^{3+}$, as in the case of cerium doped $Lu_2Si_2O_7$ single crystals.

• Journal of Radiation Protection and Research
• /
• v.28 no.3
• /
• pp.173-182
• /
• 2003

A prototype liquid scillatillator system for measurement of multiple beta-labeled mixtures was developed and its characteristic was investigated. The signal processing system consists of two photomultiplier tubes and the coincident count circuit. The characteristic of the system was analyzed using 4 beta-labeled samples $(^3H,\;^{14}C,\;^{36}Cl\;and\;^{90}Sr)$. Beta spectra from the samples were obtained without radiation shielding, and the detection limits for each nuclides were estimated based on the spectra. The estimated detection limits were compared to the legal regulation values. It is found that the liquid radioactive nuclides are detectable well below the legal regulation values.

• Journal of the Korean Society of Radiology
• /
• v.16 no.5
• /
• pp.499-504
• /
• 2022

Positron emission tomography (PET) uses a very small scintillator to achieve exellent spatial resolution. Therefore, in this study, a PET system using a scintillator to 0.8 mm size was designed and the performance was evaluated. Anihilation radiation was generated from the center of the field of view (FOV) to the outskirts at intervals of 10 mm, and counted simultaneously. The image was reconstructed using the coincidence data, and the spatial resolution was calculated by acquiring the full width at half maximum through the profile. The spatial resolution at the center of the FOV was 1.02 mm, showing a very good result, and the spatial resolution decreased as it was located at the outer edge. To evaluate the phantom image, the Derenzo phantom was constructed to acquire the image, and the degree of classification between radiation sources was evaluated through profile analysis. The result showed that the distance between the radiation sources was larger than the spatial resolution of the radiation sources at each location, and it was confirmed that the radiation sources were distinguished through this. When the PET system designed in this study is applied to PET for small animals, it is considered that excellent performance can be secured through the characteristic of very good spatial resolution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05b
• /
• pp.35-38
• /
• 2002

In this paper, for digital x-ray conversion receptor development studied by hybrid technology of based on CdZnTe. For this study, First searched fabricate method of CdZnTe x-ray receptor. Second, search the phosphor material & fabricate method for scintillator layer. Fabricated sample is analyzed with physical & electric measurement. This result is showed good SNR ratio hybrid thechnology with direct method & indirect method. In this paper offer the method can reduce the dark-current in the hybrid X-ray detector.

• Progress in Medical Physics
• /
• v.11 no.2
• /
• pp.147-155
• /
• 2000

Patient dose verification is one of the most important parts in quality assurance of the treatment delivery for radiation therapy. The dose distributions may be meaningfully improved by modulating two dimensional intensity profile of the individual high energy radiation beams In this study, a new method is presented for the pre-treatment dosimetric verification of these two dimensional distributions of beam intensity by means of a charge coupled device video camera-based fluoroscopic device (henceforth called as CCD-VCFD) as a radiation detecter with a custom-made software for dose calculation from fluorescence signals. This system of dosimeter (CCD-VCFD) could reproduce three dimensional (3D) relative dose distribution from the digitized fluoroscopic signals for small (1.0$\times$1.0 cm$^2$ square, ø 1.0 cm circular ) and large (30$\times$30cm$^2$) field sizes used in intensity modulated radiation therapy (IMRT). For the small beam sizes of photon and electron, the calculations are performed In absolute beam fluence profiles which are usually used for calculation of the patient dose distribution. The good linearity with respect to the absorbed dose, independence of dose rate, and three dimensional profiles of small beams using the CCD-VCFD were demonstrated by relative measurements in high energy Photon (15 MV) and electron (9 MeV) beams. These measurements of beam profiles with CCD-VCFD show good agreement with those with other dosimeters such as utramicro-cylindrical (UC) ionization chamber and radiographic film. The study of the radiation dosimetric technique using CCD-VCFD may provide a fast and accurate pre-treatment verification tool for the small beam used in stereotactic radiosurgery (SRS) and can be used for verification of dose distribution from dynamic multi-leaf collimation system (DMLC).

• Journal of Radiation Protection and Research
• /
• v.41 no.3
• /
• pp.282-285
• /
• 2016

Background: To optimize the photon transmission efficiency of light guides used in scintillation detectors, LightTools code, which can construct and track light, was used to analyze photon transmission effectiveness with respect to light guides thickness. Materials and Methods: This analysis was carried out using the commercial light guide, N-BK 7 Optical Glass by SCHOTT, as a model for this study. The luminous exitance characteristic of the LYSO scintillator was used to analyze the photon transmission effectiveness according to the thickness of the light guide. Results and Discussion: The results of the simulations showed the effectiveness of the photon transmission according to the thickness of the light guide, which was found to be distributed from 13.38% to 33.57%. In addition, the photon transmission efficiency was found to be the highest for light guides of 4 mm of thickness and a receiving angle of $49^{\circ}$. Conclusion: Through such simulations, it is confirmed that photon transmission efficiency depends on light guide thickness and subsequent changes in the internal angle of reflection. The aim is to produce an actual light guide based on these results and to evaluate its performance.