• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2640-2645
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• 2021

We report the development of a gamma-ray imaging device, named Large-Area Hybrid Gamma Imager (LAHGI), featuring high imaging sensitivity and good imaging resolution over a broad energy range. A hybrid collimation method, which combines mechanical and electronic collimation, is employed for a stable imaging performance based on large-area scintillation detectors for high imaging sensitivity. The system comprises two monolithic position-sensitive NaI(Tl) scintillation detectors with a crystal area of 27 × 27 cm² and a tungsten coded aperture mask with a modified uniformly redundant array (MURA) pattern. The performance of the system was evaluated under several source conditions. The system showed good imaging resolution (i.e., 6.0-8.9° FWHM) for the entire energy range of 59.5-1330 keV considered in the present study. It also showed very high imaging sensitivity, successfully imaging a 253 µCi ¹³⁷Cs source located 15 m away in 1 min; this performance is notable considering that the dose rate at the front surface of the system, due to the existence of the ¹³⁷Cs source, was only 0.003 µSv/h, which corresponds to ~3% of the background level.

• Journal of Radiation Protection and Research
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• v.34 no.1
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• pp.9-14
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• 2009

High density polyethylene (HDPE) is degraded due to a radiation-induced oxidation when it is used as a neutron moderator in a neutron counter for a nuclear material accounting of spent fuels. The HDPE exposed to the gamma-ray emitted from the fission products in a spent nuclear fuel results in a radiation-induced degradation which changes its original molecular structure to others. So a neutron moderating power variation of HDPE, irradiated by a gamma radiation, was investigated in this work. Five HDPE moderator structures were exposed to the gamma radiation emitted from a $^{60}Co$ source to a level of $10^5-10^9$ rad to compare their post-irradiation properties. As a result of the neutron measurement test with 5 irradiated HDPE structures and a neutron measuring system, it was confirmed that the neutron moderating power for the $10^5$ rad irradiated HDPE moderator revealed the largest decrease when the un-irradiated pure one was used as a reference. It implies that a neutron moderating power variation of HDPE is not directly proportional to the integrated gamma dose rate. To clarify the cause of these changes, some techniques such as a FTIR, an element analysis and a densitometry were employed. As a result of these analyses, it was confirmed that the molecular structure of the gamma irradiated HDPEs had partially changed to others, and the contents of hydrogen and oxygen had varied during the process of a radiation-induced degradation. The mechanism of these changes cannot be explained in detail at present, and thus need further study.

• Progress in Medical Physics
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• v.5 no.2
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• pp.3-12
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• 1994

$\^$137/Cs gamma ray induced thermoluminescenc(TL) from Na$\^$+/ ion implanted Al$_2$O$_3$ and unimplanted Al$_2$O$_3$ and the TL from Na$\^$+/ ion implanted Al$_2$O$_3$ are measured over the temperature range of 340K～620K. The TL curve of Na$\^$+/ ion implanted Al$_2$O$_3$ induced by $\^$137/Cs gamma ray is split into iolated TL peak located at 415K, 452K, 508K, and 568K. Because that the concentration of trapped char he carries of $\^$137/Cs gamma ray induced Al$_2$O$_3$ implanted with Na$\^$+/ ion is larger than that of Na$\^$+/ ion only implanted Al$_2$O$_3$, and the trap concentration of Na$\^$+/ ion implanted Al$_2$O$_3$ is much than that of $\^$137/Cs gamma ray only irradiated Al$_2$O$_3$, the TL intensity of Na$\^$+/ ion implanted Al$_2$O$_3$ induced by $\^$137/Cs gamma ray is about 20 times and 5 times higher than that of Al$_2$O$_3$ only implanted with Na$\^$+/ ion and Al$_2$O$_3$ only irradiated with $\^$137/Cs gamma ray, respectively. In proportion as ion implantation does and energy are incresed, the number of generated defects and the rate of defect creation are incresed, respectively. Therefore the TL intensity of ion implanted Al$_2$O$_3$ is depend on ion dose and energy. Acccrding to increse of incident ion mass, the TL intensity of ion implanted Al$_2$O$_3$ is abruptly decresce. This result showes that the TL intensity of ion implanted Al$_2$O$_3$ is closely related to ion depth range as wll as rate of defect creatin. The TL intensity of ion implanted Al$_2$O$_3$ is found to be related with defects generated by ion implantation. Table Caption

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3898-3903
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• 2024

There is a lack of available data on the radioactivity levels of these materials, despite the potential risks they may pose to patients, dental technicians, and dentists. A total of forty samples were collected from different dental markets in Egypt. Using an NaI(Tl) detector, the gamma-ray spectrometer measured the activity levels of uranium-238, radium-226, thorium-232, and potassium-40. The findings revealed that the mean concentration of ²³⁸U (below the minimum detectable activity, MDA), ²²⁶Ra (135 ± 5 and 132 ± 5 Bq/kg), ²³²Th (187 ± 4 and 243 ± 8 Bq/kg), and ⁴⁰K (1560 ± 52 and 2501 ± 89 Bq/kg) in feldspar and zirconia (ZrO₂) dental ceramic samples, respectively, were all within the limits established by the International Organization for Standardization (ISO) and the European Commission (EC). The use of feldspar and zirconia dental ceramics to restore all teeth would result in an estimated maximum beta dose of 1.5 mGy/year to the oral tissue. The results suggest that there is no cause for concern regarding any additional beta dose to the oral cavity from the use of feldspar and zirconia dental ceramics.

• Journal of radiological science and technology
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• v.43 no.4
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• pp.259-264
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• 2020

Radiation causes radiation hazards in the human body. In Korea, a case of radiation necrosis occurred in 2014. In this study, the scatter and shielding efficiency according to lead shielding were classified into epidermis and dermis for 0.511 MeV used in nuclear medicine. In this study, experiments were conducted using the slab phantom that represents calibration and the dose of human trunk. Experimental results showed that the shielding rate of 0.25 mmPb was 180% in the epidermis and 96% in the dermis. Shielding at 0.5mmPb showed shielding rates of 158%in the epidermis and 82% in the dermis. As a result of measuring the absorbed dose by subdividing the thickness of the dermis into 0.5 mm intervals, when the shielding was carried out at 0.25 mmPb, the dose appeared to be about 120% at 0.5 mm of the dermis surface, and the dose was decreased at the subsequent depth. Shielding at 0.5 mmPb, the dose appeared to be about 101% at the surface 0.5 mm, and the dose was measured to decrease at the subsequent depth. This result suggests that when lead aprons are actually used, the scattering rays would be sufficiently removed due to the spaces generated by the clothes and air, Therefore, the scattered ray generated from lead will not reach the human body. The ICRU defines the epidermis (0.07), in which the radiation-induced damage of the skin occurs, as the dose equivalent. If the radiation dose of the dermis is considered in addition, it will be helpful for the evaluation of the prognosis for radiation hazard of the skin.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.12
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• pp.2310-2316
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• 2016

We studied the effect of $Co^{60}$ gamma-radiation on the fiber Bragg gratings (FBGs) by irradiation time of UV Krypton fluoride (KrF) excimer laser among grating processing parameters. The FBGs were fabricated in a different UV laser irradiation time at 30, 60, 90, and 120 seconds using the same commercial Ge-doped silica core fiber (SMF-28e). It was exposed to gamma-radiation up to a high dose of 34.3 kGy at the dose rate of 106 Gy/min, and then it was analyzed radiation effects by measuring the radiation-induced change in the temperature sensitivity coefficient and Bragg wavelength shift. According to the experimental results, We confirmed that the UV laser irradiation period for grating inscription has a highly effect on the radiation sensitivity of the FBGs. The radiation-induced Bragg wavelength shift by the change of laser irradiation conditions showed a difference more than about 50 %.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.10
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• pp.1980-1986
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• 2016

In this study, we studied the gamma-radiation effect of fiber Bragg gratings (FBGs) on the high temperature annealing condition after grating inscription using a KrF UV laser (248 nm). The FBGs were fabricated in a different annealing temperature using the same commercial Ge-doped silica core fiber (SMF-28e) and exposed to gamma-radiation up to a dose of 31 kGy at the dose rate of 115 Gy/min. The high temperature annealing procedure for grating stabilization was applied to change the radiation sensitivity of the FBGs. According to the experimental data and analysis results, the gratings that were stabilized at different temperatures at 100, 150 and $200^{\circ}C$ have clearly shown that exposure to higher temperatures increases their radiation sensitivity. The radiation-induced Bragg wavelength shift (BWS) was shown a difference of up to about a factor of two depending on the annealing temperature conditions of the gratings.

• Journal of the Korean Society of Radiology
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• v.17 no.3
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• pp.367-373
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• 2023

Aircrews and passengers are exposed to radiation from cosmic rays and secondary scattered rays generated by reactions with air or aircraft. For aircrews, radiation safety management is based on the exposure dose calculated using a space-weather environment simulation. However, the exposure dose varies depending on solar activity, altitude, flight path, etc., so measuring by route is more suggestive than the calculation. In this study, we developed an instrument to measure the cosmic radiation dose using a general-purpose Si sensor and a multichannel analyzer. The dose calculation applied the algorithm of CRaTER (Cosmic Ray Telescope for the Effects of Radiation), a space radiation measuring device of NASA. Energy and dose calibration was performed with Cs-137 662 keV gamma rays at a standard calibration facility, and good dose rate dependence was confirmed in the experimental range. Using the instrument, the dose was directly measured on the international line between Dubai and Incheon in May 2023, and it was similar to the result calculated by KREAM (Korean Radiation Exposure Assessment Model for Aviation Route Dose) within 12%. It was confirmed that the dose increased as the altitude and latitude increased, consistent with the calculation results by KREAM. Some limitations require more verification experiments. However, we confirmed it has sufficient utilization potential as a cost-effective measuring instrument for monitoring exposure dose inside or on personal aircraft.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1925-1931
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• 2024

The study conducted in the northwest region of Jordan aimed to assess the levels of natural radioactivity in soil and olive mill pomace (OMP) samples. The researchers used Nal (TI) gamma-ray spectrometry to measure the activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs in the samples. The average activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs in the soil samples were found to be 18.624 ± 5.82, 12.276 ± 5.728, 518.33 ± 212.57, and 0.140 ± 0.09 (Bq, kg^-1), respectively. In the OMP samples, the average activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were 7.272 ± 4.386, 3.454 ± 1.503, and 169.997 ± 81.873 (Bq kg^-1), respectively, and no ¹³⁷Cs was detected. The study also investigated fundamental parameters associated with radon, specifically the radon emanation coefficient (Rn_EC) and radon mass exhalation rate (E_x). The Rn_EC values ranged from 0.621 to 0.78 (Bq kg^-1), with an average value of 0.71 ± 0.06 (Bq kg^-1). The estimated E_x from the soil samples ranged from 65.83 to 124.86 (mBq kg^-1h^-1), with an average value of 99.74 ± 21.73 (mBq kg^-1h^-1). Regarding radiological hazards, the study examined various parameters, including radium equivalent activity, external and internal hazard indices, gamma and alpha indices, absorbed gamma dose rate, and excess lifetime cancer risk. All of these assessed values were found to be below the worldwide recommended limits for radiological safety. Additionally, the study analyzed the concentrations of gross alpha and gross beta radioactivities in soil and OMP samples. The soil samples had an average gross alpha activity of 4.642 ± 1.04 (Bq kg^-1) and an average gross beta activity of 48.13 ± 14.50 (Bq kg^-1). The OMP samples showed an average gross alpha activity of 0.32 ± 0.27 (Bq kg^-1) and an average gross beta activity of 59.19 ± 12.94 (Bq kg^-1). Overall, the obtained results are crucial for evaluating the radiological risks associated with natural radioactivity in the northwest region of Jordan. The findings establish baseline data for comparison and reference for radioactivity levels in the environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.124-129
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• 2018

This study was conducted to investigate the penetration dose and shielding rates of tungsten shields used in apron material by changing the type of source used in the nuclear medicine department, thickness of shielding material and distance between the source and detector. For the experiment, the source, shield, and detector were arranged in a straight line and measured with an inspector at a height of 100 cm. The highest shielding effect of tungsten was measured for $^{201}Tl$, while $^{123}I$ showed a higher shielding effect than $^{99m}Tc$. For the sources used in the experiment, the penetration dose decreased with distance and the shielding rate was measured with thicker thickness. However, the shielding rate of $^{13}1I$ and $^{18}F$ sources was found to be lower than when there was no shielding at 0.25 mmPb shield. Therefore, even if the radiation shielding effect of tungsten is high, considering the characteristics according to the type of source and the thickness of the shielding material, it may be helpful to reduce the exposure.