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Abstract 11

Ⅰ. 서론 13

Ⅱ. 이론 18

Ⅱ-1. 고분해능 반도체 검출기 18

Ⅱ-2. 감마스펙트럼 측정 및 분석 23

Ⅱ-2-1. 전 흡수 peak 면적 산출 방법[13] 24

Ⅱ-2-2. 검출효율 산출 27

Ⅱ-3. In-situ 감마스펙트럼 분석법 31

Ⅱ-3-1. 스펙트럼-방사능 변환 연산자 31

Ⅱ-3-2. 감마선 선속 계산 35

Ⅱ-4. 선량 평가법 50

Ⅱ-4-1. 에너지 띠 이론(Energy Band Theory) 50

Ⅱ-4-2. G(E) 연산법 51

Ⅲ. 측정기기 및 방법 55

Ⅲ-1. 휴대용 HPGe 검출기 55

Ⅲ-1-1. 휴대용 HPGe 검출기의 특성 및 구조 55

Ⅲ-1-2. 휴대용 HPGe 검출기에 대한 pin-hole 검사 방법 56

Ⅲ-2. 교정선원 57

Ⅲ-3. 스펙트럼-방사능 변환 연산자 58

Ⅲ-3-1. Nf/No 측정 방법(이미지참조) 58

Ⅲ-3-2. No/Φ 측정 방법(이미지참조) 58

Ⅲ-3-3. Φ/A 결정 58

Ⅲ-3-4. 스펙트럼-방사능 환산인자 61

Ⅲ-3-5. 스펙트럼-조사선량률 환산인자 61

Ⅲ-4. 에너지 띠 이론에 의한 조사선량 평가 63

Ⅲ-5. G(E) 연산자에 의한 조사선량 평가 63

Ⅳ. 측정 결과 및 논의 66

Ⅳ-1. 휴대용 HPGe 검출기의 pin-hole 검사 결과 68

Ⅳ-2. In-situ 감마스펙트럼 분석을 통한 비방사능 측정 결과 70

Ⅳ-2-1. Nf/No 측정 결과(이미지참조) 70

Ⅳ-2-2. No/Φ 측정 결과(이미지참조) 72

Ⅳ-2-3. 스펙트럼-방사능 환산인자 계산 결과 74

Ⅳ-2-4. 스펙트럼-방사능 환산인자 적용 결과 76

Ⅳ-3. 에너지 띠 이론에 의한 조사선량률 평가 90

Ⅳ-4. G(E)연산자에 의한 조사선량률평가 93

Ⅴ. 결론 100

참고 문헌 103

부록 106

List of Tables

Table 1. Properties of an intrinsic-silicon and a germanium 20

Table 2. Unscattered flux at one meter above ground for the sources distributed exponentially in the soil*(Φ) 41

Table 3. Mass attenuation coefficients of soil without coherent scattering by the moisture content and the soil composition used in the transport calculation on XCOM 42

Table 4. Unscattered flux per mCi/㎢ at one meter above ground for typical fallout isotope in the soil(Φ) 46

Table 5. Unscattered flux per pCi/g at one meter above ground for uniformly distributed 226Ra and ²³²Th sources in the soil(Φ)(이미지참조) 47

Table 6. Specifications of the portable HPGe detector 55

Table 7. Characteristics of standards gamma-ray sources 57

Table 8. Photon fluence rate at the height of 1 m above ground per activity per unit mass of natural radionuclide distributed homogeneously in the ground 60

Table 9. Conversion factor of the specific activity to the exposure(dose) rate 62

Table 10. Relative count of the portable HPGe detector with an angular dependence 70

Table 11. Nf/No as a function of the photon energy(이미지참조) 71

Table 12. Conversion factor Nf/No of the portable HPGe detector for natural and artificial nuclide with α/ρ(이미지참조) 71

Table 13. Peak detection efficiency per unit flux as a function of the photon energy 72

Table 14. Conversion factor of cpm in spectrum to the specific activity for natural nuclide 74

Table 15. Conversion factor of cpm in spectrum to the specific activity for artificial nuclide 75

Table 16. Coordinates and exposure rates of the fifteen sites 76

Table 17. Comparison of soil specific activity for natural nuclide determined by in-situ spectrometry with that by the laboratory spectrometry 78

Table 18. Mean exposure rates on in-situ spectrometry at the fifteen sites 90

Table 19. Conversion factor of cps in the spectrum to exposure rates for the portable HPGe detector 91

Table 20. Comparison of exposure rate determined by means of the portable HPGe and NaI(Tl) detector around the each site 92

Table 21. Exposure rates(C/kg/h) determined by G(E) factor at fifteen sites 95

Table 22. Comparative the exposure rate determined by the energy band theory with that by G(E) factor 99

List of Appendix Tables

Table A. Fluence rate of primary photons at one meter above ground per unit activity per unit area, Φ/A (s-¹ · Bq-¹)(이미지참조) 106

List of Figures

Fig. 1. Comparison of the pulse height spectra recorded using a NaI(Tl) detector with that of a HPGe detector 22

Fig. 2. Linear attenuation coefficients as a function of the photon energy in Ge. 23

Fig. 3. Determination of a peak area on the summation method 25

Fig. 4. Set up of in-situ spectrometry 37

Fig. 5. Mass attenuation coefficients without coherent scattering in the soil with the moisture 44

Fig. 6. Mass attenuation coefficients without coherent scattering in aluminum 45

Fig. 7. Mass attenuation coefficients without coherent scattering in air 45

Fig. 8. 238U-series decay chain(이미지참조) 48

Fig. 9. ²³²Th-series decay chain 49

Fig. 10. Schematic representation of radiation transport in Monte Carlo simulations 54

Fig. 11. Structure dimension of the portable HPGe detector 56

Fig. 12. Geometry for simulating the response function of the portable HPGe detector with the MCNPX 64

Fig. 13. Typical in-suit γ-ray spectrum(이미지참조) 67

Fig. 14. Variation of the total count rates for 137Cs gamma ray front incident into the portable HPGe detector.(이미지참조) 68

Fig. 15. Variation of the total count rates for 137Cs gamma ray side incident into the portable HPGe detector.(이미지참조) 69

Fig. 16. Reciprocal count rate as a function of the distance from the source to the detector for 1333 keV γ-ray of 60Co(이미지참조) 73

Fig. 17. No/Φ as a function of the photon energy(이미지참조) 73

Fig. 18. Site map for in-situ spectrometry 77

Fig. 19. Specific activity ratio of in-situ to Lab. for 238U-series(이미지참조) 85

Fig. 20. Specific activity ratio of in-situ to Lab. for ²³²Th-series 86

Fig. 21. Specific activity ratio of in-situ to Lab. for 40K(이미지참조) 86

Fig. 22. Ratios of exposure rates to in-situ spectrometry gross counts rates 91

Fig. 23. Response function for the portable HPGe detector with the length of 40 mm, the diameter of 61.3 mm and the efficiency of 30% 93

Fig. 24. G(E) factor for the portable HPGe detector 94

초록보기

When an accident of nuclear facilities is occurred, an in-situ spectrometry method with the portable HPGe detector has a merit that can be determined the concentrations of the natural and the artificial nuclide as well as the exposure rate quickly. In fifteen sites, in-suit gamma-ray spectra were measured and the specific activities of U-series, Th-series, 40K, and 137Cs were obtained by the in-suit gamma spectra. The factor to convert the count-per-minute to the specific activity was also obtained. The specific activity of in-situ spectrometry was compared with the value measured in the laboratory after the pre-treatment for soil.

The mean specific activity for 238U series and 232Th series was estimated to be 1.02 and 1.12 to the measured value in laboratory, respectively. For the case of 40K, the mean specific activity was obtained to be 0.77, which is determined less than that of laboratory. In spite of their differences, the technique of the in-situ spectrometry can be applied to measure the environmental radiation in soil because the ratio is almost like 1.0 but, for 137Cs, the mean specific activity was estimated to have large difference than that of laboratory, because the depth distribution of the cesium to happen in nuclear weapon tests in the atmosphere during the 1950 and 1960th had had a large disturbance.

The energy band theory has been generally used to calculate the dose rate for the natural nuclide from the in-suit gamma ray spectrum. But, the method is inadequate for analyzing the component to be largely affected in the spectrum. The G(E) method can be compensative for that method.

For a few gamma ray, G(E) factor was calculated by the MCNPX code that could simulate the interaction of gamma in the portable HPGe detector. The gamma spectrum by the in-situ spectrometry was conversed to the exposure rate by the G(E) factor. When the exposure rate by the G(E) factor are compared with that by energy band theory, two data have agreement with the ratios of 0.87∼ 1.04 in the measured sites.

The in-situ spectrometry with the portable HPGe using G(E) factor will be an available method for analyzing the accident of nuclear facilities.

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