• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.229-236
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• 2016

Background: In order to manage the patient exposure dose in X-ray diagnosis, it is preferred to evaluate the entrance skin dose; although there are some evaluations about entrance skin dose, a small number of report has been published for direct measurement of patient. We think that a small-type optically stimulated luminescence (OSL) dosimeter, named nanoDot, can achieve a direct measurement. For evaluations, the corrections of angular and energy dependences play an important role. In this study, we aimed to evaluate the angular and the energy dependences of nanoDot. Materials and Methods: We used commercially available X-ray diagnostic equipment. For angular dependence measurement, a relative response of every 15 degrees of nanoDot was measured in 40-140 kV X-ray. And for energy dependence measurement, mono-energetic characteristic X-rays were generated using several materials by irradiating the diagnostic X-rays, and the nanoDot was irradiated by the characteristic X-rays. We evaluated the measured response in an energy range of 8.1-75.5 keV. In addition, we performed Monte-Carlo simulation to compare experimental results. Results and Discussion: The experimental results were in good agreement with those of Monte-Carlo simulation. The angular dependence of nanoDot was almost steady with the response of 0 degrees except for 90 and 270 degrees. Furthermore, we found that difference of the response of nanoDot, where the nanoDot was irradiated from the randomly set directions, was estimated to be at most 5%. On the other hand, the response of nanoDot varies with the energy of incident X-rays; slightly increased to 20 keV and gradually decreased to 80 keV. These results are valuable to perform the precise evaluation of entrance skin dose with nanoDot in X-ray diagnosis. Conclusion: The influence of angular dependence and energy dependence in X-ray diagnosis is not so large, and the nanoDot OSL dosimeter is considered to be suitable dosimeter for direct measurement of entrance surface dose of patient.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1377-1384
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• 2018

Accurate measurement of the absorbed dose and the effective dose is required in dental panoramic radiography involving relatively low energy with a rotational X-ray tube system using long exposures. To determine the effectiveness of measuring the irradiation by using passive dosimetry, we compared the entrance skin doses by using a radiophotoluminescent glass dosimeter (RPL) and an optically stimulated luminescence detector (OSL) in a phantom model consisting of nine and 31 transverse sections. The parameters of the panoramic device were set to 80 kV, 4 mA, and 12 s in the standard program mode. The X-ray spectrum was applied in the same manner as the panoramic dose by using the SpekCalc Software. The results indicated a mass attenuation coefficient of $0.008226cm^2/g$, and an effective energy of 34 keV. The equivalent dose between the RPL and the OSL was calculated based on a product of the absorbed doses. The density of the aluminum attenuators was $2.699g/cm^3$. During the panoramic examination, tissue absorption doses with regard to the RPL were a surface dose of $75.33{\mu}Gy$ and a depth dose of $71.77{\mu}Gy$, those with regard to the OSL were surface dose of $9.2{\mu}Gy$ a depth dose of $70.39{\mu}Gy$ and a mean dose of $74.79{\mu}Gy$. The effective dose based on the International Commission on Radiological Protection Publication 103 tissue weighting factor for the RPL were $0.742{\mu}Sv$, $8.9{\mu}Sv$, $2.96{\mu}Sv$ and those for the OSL were $0.754{\mu}Sv$, $9.05{\mu}Sv$, and $3.018{\mu}Sv$ in the parotid and sublingual glands, orbit, and thyroid gland, respectively. The RPL was more effective than the OSL for measuring the absorbed radiation dose in low-energy systems with a rotational X-ray tube.

• 분석과학
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• 제32권4호
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• pp.131-138
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• 2019

This paper reports results on the physical properties of a powder type of $Al_2O_3:C$ commonly used as a luminescence dosimeter using the LM-OSL technique. On the analysis with the general order kinetics model, the LM-OSL signal measured appeared to be composed of three components (fast, medium, slow) showing the largest area in the medium component. The photoionization cross sections of three components were distributed between $10^{-19}{\sim}10^{-21}cm^2$. The values of the thermal assistance energy were evaluated the largest in slow component and the smallest in fast component, which indicates the electrons trapped in defects attributed to slow component should be the most sensitive to thermal vibration among three components. In illumination to blue light, the fast component showed a rapid linear decay and completely disappeared after light exposure time of about 5 s. The medium component decayed with two exponential elements but the slow component did not observed any noticeable change until light exposure time of 40 s. In a dose response study, all components exhibited a linear behaviour up to approximately 10 Gy.

• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.222-228
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• 2016

Background: We are developing a small size dosimeter for dose estimation in particle therapies. The developed dosimeter is an optical fiber based dosimeter mounting an radiation induced luminescence material, such as an OSL or a scintillator, at a tip. These materials generally suffer from the quenching effect under high LET particle irradiation. Materials and Methods: We fabricated two types of the small size dosimeters. They used an OSL material Eu:BaFBr and a BGO scintillator. Carbon ions were irradiated into the fabricated dosimeters at Heavy Ion Medical Accelerator in Chiba (HIMAC). The small size dosimeters were set behind the water equivalent acrylic phantom. Bragg peak was observed by changing the phantom thickness. An ion chamber was also placed near the small size dosimeters as a reference. Results and Discussion: Eu:BaFBr and BGO dosimeters showed a Bragg peak at the same thickness as the ion chamber. Under high LET particle irradiation, the response of the luminescence-based small size dosimeters deteriorated compared with that of the ion chamber due to the quenching effect. We confirmed the luminescence efficiency of Eu:BaFBr and BGO decrease with the LET. The reduction coefficient of luminescence efficiency was different between the BGO and the Eu:BaFBr. The LET can be determined from the luminescence ratio between Eu:BaFBr and BGO, and the dosimeter response can be corrected. Conclusion: We evaluated the LET dependence of the luminescence efficiency of the BGO and Eu:BaFBr as the quenching effect. We propose and discuss the correction of the quenching effect using the signal intensity ratio of the both materials. Although the correction precision is not sufficient, feasibility of the proposed correction method is proved through basic experiments.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.717-724
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• 2023

An essential step in evaluating and comparing the performance of two passive radiation dosimeter types, thermosluminescent (TLD) and optically stimulated luminescence (OSL), used by workers in environments with ionizing radiation for individual radiological monitoring and control of external exposure at various times (cumulative dose for 1 month), is to compare the measured dose accuracy, energy response, and coefficient of variation. In fact this performance study consists in determining the accuracy of both R(10) and R(0.07) which are considered as the ratios of the measured dose (Hp(10) or Hp(0.07)) to the delivered dose (Hp(10) or Hp(0.07)) for each photon energy. The validity of the results of this test is based on the acceptance limits of the ICRP and the international standard IEC-62387. The relative energy response used is normalized to the ¹³⁷Cs 662 keV energy to find which energy response is closest to the ideal case, and the coefficient of variation that allows to determine the statistical fluctuation of the Hp(10) and Hp(0.07) doses. The results of the accuracy test for the OSL and TLD dosimeters are acceptable because they fall within the ICRP limits. For the energy response, the OSL performs better than the TLD for Hp(10) and Hp(0.07), and for the coefficient of variation, the OSL satisfies the requirements of ISO 62387 for both Hp(10) and Hp(0.07), while the TLD satisfies these requirements only for the measurement of Hp (0.07).

• 대한방사선기술학회지:방사선기술과학
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• 제42권5호
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• pp.379-385
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• 2019

Radiation is used for various purposes such as cancer therapy, research of industrial and drugs. However, in case of radiation accidents such as terrorism, collapsing nuclear plant by natural disasters like Fukushima in 2011, very high radiation does expose to human and could lead to death. For this reason, many people are concerning about radiation exposures. Therefore, assessment and research of retrospective radiation dose to human by various path is an necessary task to be continuously developed. Radiation exposure for workers in radiation fields can be generally measured using a personal exposure dosimeter such as TLD, OSLD. However, general people can't be measured radiation doses when they are exposed to radiation. And even if radiation fields workers, when they do not in possession personal dosimeter, they also can't be measured exposure dose immediately. In this study, we conduct retrospective research on reconstruction of dose after exposure by using smart chip card of personal items through Optically Stimulated Luminescence (OSL). The OSL signal of smart chip card shows linear response from 0.06 Gy to 15 Gy and results of fading rate 45 %, 48% for 24 and 48 hours due to the natural emission of radiation in sample, respectively. The minimum detectable limit (MDD) was 0.38 mGy. This values are expected to use as correction values for reconstruction of exposure dose.

• 대한방사선기술학회지:방사선기술과학
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• 제33권2호
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• pp.149-154
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• 2010

고용량 방사성요오드 $^{131}I$ 투여환자의 퇴원 이후 환자 가족이나 간병인, 가옥에 대한 외부피폭 방사선량을 개인선량계인 OSL(Optically Stimulated Luminescence dosimeter) 선량계를 사용하여 평가하였다. 3.37~5.55 GBq(100~150 mCi)의 $^{131}I$을 투여한 환자가 2박3일 또는 3박4일의 입원 기간이 지난 후 요양을 위하여 가정으로 귀가 한 후부터 5일에서 8일 동안 간병을 담당한 사람이 피폭한 방사선량과 집안 내 주요 지점에서의 누적 공간방사선량인 주변선량을 OSL 선량계를 이용하여 측정하였다. 고용량 치료 환자의 가족이나 간병인, 집안내 주요 지점에서의 누적피폭방사선량은 1 mSv의 1/10 수준인 0.1 mSv 내외로 측정되어 원자력법에서 정하고 있는 일반인에 대한 선량한도를 초과하지 않는 것으로 평가되었다. 소수의 표본임에도 불구하고 환자 주변인에 대한 측정값의 표준편차가 0.087 mSv로 크지 않았음을 볼 때 모집단인 전체 환자가족의 피폭 방사선량도 표본집단의 결과와 큰 차이를 보이지 않을 것으로 유추할 수 있어 환자의 입원 치료기간을 현재보다 단축하는 방안을 추가로 검토하거나 연구할 필요가 있을 것으로 보인다.

• 한국방사선학회논문지
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• 제12권1호
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• pp.79-83
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• 2018

본 논문에서는 OSL 도트 선량계의 교정인자, 흡수선량 선형성, 피크전압 선형성, 각도 변화에 의한 흡수선량 변화를 측정하고 분석했다. 의료용 X 선발생 장치를 사용하여 조사에 노출 선량 보정 계수, 흡수선량 선형성, 피크 전압 선형성은 모두 IEC-62387-1 (2007) 기준을 만족하였다. 기준 방사선 노출과 관련하여 0도, 30도 및 60도에서 선량계 방향에 대한 기준은 -29 % (${\pm}30^{\circ}$) 및 + 67 % (${\pm}60^{\circ}$)이었다. 30도에서 측정된 값은 기준보다 -8 % 낮고 60도에서 기준보다 -18 % 낮게 나타났다. 그러므로 OSL 도트 선량계 사용 시 방향에 따른 영향을 보정하여야 한다.

• Journal of Radiation Protection and Research
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• 제40권1호
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• pp.46-54
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• 2015

열이나 빛의 자극에 의한 물질의 발광현상, 즉 열자극발광(thermoluminescence, TL)과 광자극발광(optically stimulated luminescence, OSL)의 메커니즘을 규명하고, 이 현상을 방사선량의 측정에 활용할 수 있는 새로운 발광물질을 개발하는데 활용할 수 있는 측정장치를 개발하였다. 이는 열자극과 광자극을 동시에 가할 수 있는 장치로서, 열자극에 필요한 온도제어를 위하여 35 kHz의 정현파 전원으로 변환하여 스트립 형태의 발열부에 걸어주게 되며, 최대 $20K{\cdot}s^{-1}$의 온도상승률로 약 1K의 정밀도로 온도를 제어할 수 있었다. 광자극을 위한 광원으로 중심파장이 470 nm인 Luxeon V형 고휘도 LED 등 여러 파장영역의 LED나 레이저를 사용할 수 있도록 하였다. 대표적으로 470 nm의 LED로 $Al_2O_3$:C의 OSL을 측정하는 경우, 시료의 발광에서 자극광을 분리시키기 위하여 LED의 자극광은 단파장차단필터인 GG420을 통과시켜서 시료에 걸리게 하고, 시료의 발광은 대역통과필터인 UG11를 통과하여 광증배관에 걸리게 하였다. 아울러 시료에 따라 LED나 필터들을 다르게 조합할 수 있도록 하여 시료의 발광특성에 맞는 최적의 측정을 수행할 수 있다. PC로 측정장치의 전체적인 제어가 이루어지며 LabView로 개발한 제어프로그램은 그래픽사용자환경(GUI)으로 되어 있다. 이 연구를 통해서 개발한 장치로 LiF:Mg,Cu,Si와 $Al_2O_3$:C를 표준시료로 하여 TL과 OSL을 측정하였고, 이들의 발광특성이 기존에 알려진 특성을 재현하여 이 장치가 신뢰할 수 있는 성능을 내는 것을 확인할 수 있었다.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.429-436
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• 2022

Investigations of retrospective dosimetry have shown that components of mobile phones are suitable as emergency dosimeters in case of radiological incidents. For physical dosimetry, components can be read out using optically stimulated luminescence (OSL), thermoluminescence (TL) and phototransferred thermoluminescence (PTTL) methods to determine the absorbed dose. This paper deals with a feasibility study of display glass from modern mobile phones that are measured by thermally assisted (Ta) optically stimulated luminescence. Violet (VSL, 405 nm) and infrared (IRSL, 850 nm) LEDs were used for optical stimulation and two protocols (Ta-VSL and Ta-IRSL) were tested. The aim was to systematically investigate the luminescence properties, compare the results to blue stimulated Ta-BSL protocol (458 nm) and to develop a robust measurement protocol for the usage as an emergency dosimeter after an incident with ionizing radiation. First, the native signals were measured to calculate the zero dose signal. Next, the reproducibility and dose response of the luminescence signals were analyzed. Finally, the signal stability was tested after the storage of irradiated samples at room temperature. In general, the developed Ta-IRSL and Ta-VSL protocols indicate usability, however, further research is needed to test the potential of a new protocol for physical retrospective dosimetry.