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MCNPX 코드를 이용한 감마선 조사실의 방사선량 분포 계산

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Author(s)
김용호
Issued Date
2008
URI
http://dcoll.jejunu.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000004230
Abstract
^(60)Co-gamma irradiators have long been used for foods sterilization, plant mutation and development of radio-protective agents, radio-sensitizers and other purposes. The Applied Radiological Science Research Institute of Cheju National University has a multipurpose gamma irradiation facility loaded with a MDS Nordin standard ^(60)Co source (C188), of which the initial activity was 400 TBq (10,800 Ci) on February 19, 2004. This panoramic gamma irradiator is designed to irradiate in all directions various samples such as plants, cultured cells and mice to administer given radiation doses. In order to give accurate doses to irradiation samples, appropriate methods of evaluating, both by calculation and measurement, the radiation doses delivered to the samples should be set up.
Computational models have been developed to evaluate the radiation dose distributions inside the irradiation chamber and the radiation doses delivered to typical biolological samples which are frequently irradiated in the facility. The computational models are based on using the MCNPX code. The horizontal and vertical dose distributions has been calculated inside the irradiation chamber and compared the calculated results with measured data obtained with radiation dosimeters to verify the computational models. The radiation dosimeters employed are a Famer's type ion chamber and MOSFET dosimeters. Radiation doses were calculated by computational models, which were delivered to cultured cell samples contained in test tubes and to a mouse fixed in a irradiation cage, and compared the calculated results with the measured data. The computation models are also tested to see if they can accurately simulate the case where a thick lead shield is placed between the source and detector. Three tally options of the MCNPX code, F4, F5 and F6, are alternately used to see which option produces optimum results. The computation models are also used to calculate gamma ray energy spectra of a BGO scintillator at several points of the irradiation chamber.
It is found that the calculated horizontal dose distribution agrees with the measured data within 5% deviation. The calculated vertical dose distribution generally agrees well with the measured data, but there exist large discrepancies between the calculated and measured data at some points. It is found that these discrepancies have originated from the MOSFET dosimeters used rather than from the computation models. The computed results show a smooth pattern of the dose distribution while the measured data show a very irregular pattern which seems very unnatural. It is deemed that the some of the dosimeters have been inaccurately calibrated. The calculated doses behind a thick lead shield agree with the data measured with ion chamber within 4% deviation. The calculated absorbed doses delivered to the biological samples agrees with the measured data within 5% deviation. The effect of different tally options dose not show a consistent pattern. In some points one tally option agrees better with the measured data while in other points another tally option agrees better.
The gamma ray energy spectra for a BGO scintillator calculated with the MCNPX computation model show the full energy peaks more prominent as the detector is closer to the source. The heights of full energy peaks become lower behind the lead shield due to the interference of the scattered gammas.
Alternative Title
Dose Distribution Calculation Using MCNPX Code in the Gamma-ray Irradiation Cell
Affiliation
제주대학교 대학원
Department
대학원 에너지공학과
Advisor
박재우
Awarded Date
2008. 2
Table Of Contents
Ⅰ. 서론 = 1
Ⅱ. 이론적 배경 = 3
1. 방사선량의 정의 = 3
1) 공기커마 (Air Kerma) = 3
2) 조사선량 = 3
2) 흡수선량 = 4
2. MCNPX 코드 개요 = 5
1) Monte-Carlo Method = 5
2) MCNP(Monte-Carlo N Particle) = 7
3) MCNPX 계산 알고리즘 = 7
4) MCNPX 통계적 고찰 = 10
Ⅲ. 실험 및 계산 방법 = 12
1. 감마선 조사시설 = 12
2. 방사선량 측정 = 14
1) 방사선량계 = 14
2) 선량측정 위치 = 19
3) 선량 측정 = 21
3. 선량 분포 계산모델 = 25
1) Geometry Cards = 25
2) Data Cards = 27
3) Tally Cards = 28
4) Tally normalization = 37
Ⅳ. 결과 및 고찰 = 39
1. 선원에서 거리에 변화에 따른 선량 분포(수평방향 선량계산) = 39
2. 높이 변화에 따른 선량 분포(수직방향 선량 계산) = 42
3. 조사 시료의 흡수선량 = 46
4. 차폐체의 영향 = 48
5. 감마선 에너지 스펙트럼 계산 = 50
6. 선량편차에 따른 조사시간 변화 = 52
Ⅴ. 결론 = 56
참고문헌 = 58
Degree
Master
Publisher
제주대학교 대학원
Citation
김용호. (2008). MCNPX 코드를 이용한 감마선 조사실의 방사선량 분포 계산
Type
Dissertation
Appears in Collections:
Faculty of Applied Energy System > Energy and Chemical Engineering
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