• Journal of Radiation Protection and Research
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• v.44 no.2
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• pp.72-78
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• 2019

Background: In the calibration and testing laboratory of Korea Atomic Energy Research Institute, the old X-ray generator used for the production of reference X-ray fields was replaced with a new one. For this newly installed X-ray irradiation system, beam alignment as well as the verification of beam qualities was conducted. Materials and Methods: The existing X-ray generator, Phillips MG325, was replaced with YXLON Y.TU 320-D03 in order to generate reference X-ray fields. Theoretical calculations and Monte Carlo simulations were used to determine initial filter thickness. Beam alignment was performed in three steps to deliver a homogeneous radiation dosage to the target at different distances. Finally, the half-value layers were measured for different X-ray fields to verify beam qualities by using an ion chamber. Results and Discussion: Beam alignment was performed in three steps, and collimators and other components were arranged to maintain the uniformity of the mean air kerma rate within ${\pm}2.5%$ at the effective beam diameter of 28 cm. The beam quality was verified by using half-value layer measurement methods specified by American National Standard Institute (ANSI) N13.11-2009 and International Organization for Standardization (ISO)-4037. For each of the nine beams than can be generated by the new X-ray irradiation system, air kerma rates for X-ray fields of different beam qualifies were measured. The results showed that each air kerma rate and homogeneity coefficient of the first and second half-value layers were within ${\pm}5%$ of the recommended values in the standard documents. Conclusion: The results showed that the new X-ray irradiation system provides beam qualities that are as high as moderate beam qualities offered by National Institute of Standards and Technology in ANSI N13.11-2009 and those for narrow-spectrum series of ISO-4037.

• Journal of Preventive Medicine and Public Health
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• v.57 no.1
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• pp.55-64
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• 2024

Objectives: This study investigated the prevalence and characteristics of comorbid conditions in patients exposed to ionizing radiation and those who were involved in the Soviet-Afghan war. Methods: This study analyzed the frequency and spectrum of morbidity and comorbidity in patients over a long-term period (30-35 years) following exposure to ionizing radiation at the Semipalatinsk nuclear test site or the Chornobyl nuclear power plant, and among participants of the Soviet-Afghan war. A cohort study, both prospective and retrospective, was conducted on 675 patients who underwent comprehensive examinations. Results: Numerical data were analyzed using the Statistica 6 program. The results are presented as the mean±standard deviation, median, and interquartile range (25-75th percentiles). The statistical significance of between-group differences was assessed using the Student t-test and Pearson chi-square test. A p-value of less than 0.05 was considered statistically significant. We found a high prevalence of cardiovascular diseases, including hypertension (55.0%) and cardiac ischemia (32.9%); these rates exceeded the average for this age group in the general population. Conclusions: The cumulative impact of causal occupational, environmental, and ultra-high stress factors in the combat zone in participants of the Soviet-Afghan war, along with common conventional factors, contributed to the formation of a specific comorbidity structure. This necessitates a rational approach to identifying early predictors of cardiovascular events and central nervous system disorders, as well as pathognomonic clinical symptoms in this patient cohort. It also underscores the importance of selecting suitable methods and strategies for implementing treatment and prevention measures.

• The Journal of Korean Society for Radiation Therapy
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• v.11 no.1
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• pp.16-21
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• 1999

Purpose : The aim of this study is to conform the possibility of the liquid type EPID as a QC tools to clinical indication and of replacement of the film dosimetry. Aditional aim is to describe a procedure for the use of a EPID as a physics calibration tool in the measurements of radiation beam parameters which are typically carried out with film. Method & Materials : In this study we used the Clinac 2100c/d with EPID. This system contains 65536 liquid-filled ion chambers arranged in a $256{\times}256$ matrix and the imaging area is $32.5{\times}32.5cm$ with liquid layer thickness of 1mm. The EPID was tested for different field sizes under typical clinical conditions and pixel values were calibrated against dose by producing images using various thickness of lead attenuators(lead step wedge) using 6 & 10MV x-ray. We placed various thickness of lead on the table of linear accelerator and set the portal vision an SDD of 100cm. To acquire portal image we change the field size and energy, and we recorded the average pixel value in a $3{\times}3$ pixel region of interest(ROI) at field center was recorded. The pixel values were also measured for different field sizes in order to evaluate the dependence of pixel value on x-ray energy spectrum and various scatter components. Result : The EPID, as a whole, was useful as a QA tool and dosimetry device. In mechanical check, cross-hair centering was well matched and the error was less than ?2mm and light/radiation field coincidence was less than 1mm also. In portal dosimetry the wider the field size the the higher the pixel value and as the lead thickness increase, the pixel value was exponentially decreased. Conclusions : The EPID was very suitable for QA tools and it can be used to measure exit dose during patients treatment with reasonable accuracy. But when indicate the EPID to clincal study deep consideration required

• Journal of radiological science and technology
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• v.38 no.4
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• pp.451-461
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• 2015

In megavoltage (MV) radiotherapy, delivering the dose to the target volume is important while protecting the surrounding normal tissue. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) using an edge block in megavoltage X-ray imaging (MVI). We used an edge block, which consists of tungsten with dimensions of 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$ and measured the pre-sampling MTF at 6 MV energy. Various radiation therapy (RT) devices such as TrueBeam$^{TM}$ (Varian), BEAMVIEW$^{PLUS}$ (Siemens), iViewGT (Elekta) and Clinac$^{(R)}$iX (Varian) were used. As for MTF results, TrueBeam$^{TM}$(Varian) flattening filter free(FFF) showed the highest values of $0.46mm^{-1}$ and $1.40mm^{-1}$ for MTF 0.5 and 0.1. In NPS, iViewGT (Elekta) showed the lowest noise distribution. In DQE, iViewGT (Elekta) showed the best efficiency at a peak DQE and $1mm^{-1}DQE$ of 0.0026 and 0.00014, respectively. This study could be used not only for traditional QA imaging but also for quantitative MTF, NPS, and DQE measurement for development of an electronic portal imaging device (EPID).

• Journal of The Korean Astronomical Society
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• v.46 no.1
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• pp.49-63
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• 2013

Nonthermal radiation from supernova remnants (SNRs) provides observational evidence and constraints on the diffusive shock acceleration (DSA) hypothesis for the origins of Galactic cosmic rays (CRs). Recently it has been recognized that a variety of plasma wave-particle interactions operate at astrophysical shocks and the detailed outcomes of DSA are governed by their complex and nonlinear interrelationships. Here we calculate the energy spectra of CR protons and electrons accelerated at Type Ia SNRs, using time-dependent, DSA simulations with phenomenological models for magnetic field amplification due to CR streaming instabilities, Alf$\acute{e}$enic drift, and free escape boundary. We show that, if scattering centers drift with the Alf$\acute{e}$en speed in the amplified magnetic fields, the CR energy spectrum is steepened and the acceleration efficiency is significantly reduced at strong CR modified SNR shocks. Even with fast Afv$\acute{e}$nic drift, DSA can still be efficient enough to develop a substantial shock precursor due to CR pressure feedback and convert about 20-30% of the SN explosion energy into CRs. Since the high energy end of the CR proton spectrum is composed of the particles that are injected in the early stages, in order to predict nonthermal emissions, especially in X-ray and ${\gamma}-ray$ bands, it is important to follow the time dependent evolution of the shock dynamics, CR injection process, magnetic field amplification, and particle escape. Thus it is crucial to understand the details of these plasma interactions associated with collisionless shocks in successful modeling of nonlinear DSA.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.125-128
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• 2005

In this paper, we argue that the gigahertz peaked spectrum (GPS) quasars are special blazars, blazars in dense and dusty gas enviornment. The ROSAT detection rate of GPS quasars is similar to that of flat spectrum radio quasars (FSRQs), suggesting that the relativistic jets in GPS quasars are oriented at small angle to the line of sight. Due to strong inverse Compton scattering off infrared photons from dense and dusty nuclear interstellar media in GPS quasars, most of them may have significant soft gamma-ray and X-ray emission, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than that in FSRQs, synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust, hence most GPS quasars show low optical polarization and small variability, consistent with observations. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. Whether GPS quasars are special blazars can be tested by gamma-ray observations with GLAST in the near future, with the detection rate of GPS quasars being similar to that of FSRQs.

• Nuclear Engineering and Technology
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• v.35 no.5
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• pp.497-505
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• 2003

This paper describes a computational approach to the quantification of primary damage under irradiation and demonstrates the effect of neutron energy spectra on the formation of the displacement cascade. The development of displacement cascades in ${\alpha}-Iron$ has been simulated using the MOLDY code - a molecular dynamics code for simulating radiation damage. The primary knock-on atom energy, key input to the MOLDY code, was determined from the SPECTER code calculation on two neutron spectra. The two neutron spectra include; (i) neutron spectrum in the instrumented irradiation capsule of the high-flux advanced neutron application reactor (HANARO), and (ii) neutron spectrum at the inner surface of the reactor pressure vessel steel for the Younggwang nuclear power plant No.5 (YG 5). Minor differences in the normalized neutron spectra between the two spectra produce similar values of PKA energy, which are 4.7 keV for HANARO and 5.3 keV for YG 5. This similarity implies that primary damage to the components of the commercial nuclear reactors should be well simulated by irradiation in the HANARO. Moreover, the application of the MD calculations corroborates this statement by comparing cascades simulation results.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1174-1180
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• 2015

We investigate in this paper the radiated electromagnetic waves together with the discharge characteristics of Trichel pulse of negative DC corona discharge in air in pin-to-plate and wire-to-plate configurations. The feature of the current pulse and the frequency spectrum of the electromagnetic radiations were measured under various pressures and gas gaps. The results show that the repetition frequency and the amplitude of Trichel pulse current depend on the discharge conditions, but the rising time of the pulse relates only to the radius of needle or wire and keeps constant even if the other conditions (including the discharge current, the gas gap and the gas pressure) change. There exists the characterized spectrum of electromagnetic waves from negative corona discharge in Trichel pulse regime. These characterized radiations do not change their frequency at a given cathode geometry even if the averaged current, the gas gap or the air pressure changes, but the amplitude of radiations changes accordingly. The characterized electromagnetic radiations from Trichel pulse corona relate to the formation or the rising edge of current pulse. It confirms that the characterized radiations from Trichel pulse supply information of discharge system and provide a potential method for detecting charged targets.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.11a
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• pp.637-640
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• 2023

This paper presents multimodal image fusion with human pose for detecting abnormal human behaviors in low illumination conditions. Detecting human behaviors in low illumination conditions is challenging due to its limited visibility of the objects of interest in the scene. Multimodal image fusion simultaneously combines visual information in the visible spectrum and thermal radiation information in the long-wave infrared spectrum. We propose an abnormal event detection scheme based on the multimodal fused image and the human poses using the keypoints to characterize the action of the human body. Our method assumes that human behaviors are well correlated to body keypoints such as shoulders, elbows, wrists, hips. In detail, we extracted the human keypoint coordinates from human targets in multimodal fused videos. The coordinate values are used as inputs to train a multilayer perceptron network to classify human behaviors as normal or abnormal. Our experiment demonstrates a significant result on multimodal imaging dataset. The proposed model can capture the complex distribution pattern for both normal and abnormal behaviors.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.215-223
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• 1999

Characteristics of radiation field in the steam generator(S/G) water chamber of a PWR were investigated and the anticipated effective dose rates to the worker in the S/G chamber were evaluated by Monte Carlo simulation. The results of crud analysis in the S/G of the Kori nuclear power plant unit 1 were adopted for the source term. The MCNP4A code was used with the MIRD type anthropomorphic sex-specific mathematical phantoms for the calculation of effective doses. The radiation field intensity is dominated by downward rays, from the U-tube region, having approximate cosine distribution with respect to the polar angle. The effective dose rates to adults of nominal body size and of small body size(The phantom for a 15 year-old person was applied for this purpose) appeared to be 36.22 and 37.06 $mSvh^{-1}$) respectively, which implies that the body size effect is negligible. Meanwhile, the equivalent dose rates at three representative positions corresponding to head, chest and lower abdomen of the phantom, calculated using the estimated exposure rates, the energy spectrum and the conversion coefficients given in ICRU47, were 118, 71 and 57 $mSvh^{-1}$, respectively. This implies that the deep dose equivalent or the effective dose obtained from the personal dosimeter reading would be the over-estimate the effective dose by about two times. This justifies, with possible under- or over- response of the dosimeters to radiation of slant incidence, necessity of very careful planning and interpretation for the dosimetry of workers exposed to a non-regular radiation field of high intensity.