감마분광분석법을 이용한 천연방사성물질 분석 연구 = A Study on the Analysis of Naturally Occurring Radioactive Materials(NORM) Using Gamma-Ray Spectrometry

다국어 초록 (Multilingual Abstract)

This study was conducted to optimize the analytical conditions required for the quantitative determination of the major radionuclides of interest in naturally occurring radioactive materials(NORM), namely 226Ra, 232Th, and 40K, using γ-ray spectrometry. In NORM analysis, factors such as background radiation, sample sealing, self-absorption, coincidence summing effects, and γ-ray energy selection can significantly affect the analytical results; therefore, their systematic evaluation is essential.
To assess the laboratory environment, radon concentration was measured using RAD7. In cases where the background level was high, evaporated nitrogen gas from the cooling of the HPGe detector was injected into the lead shielding. As a result, the background counts of 214Pb and 214Bi were reduced by approximately 80%. In addition, the equilibrium process under different sample sealing conditions was examined. Measurements performed with a Marinelli beaker in its basic state, as well as with sealing using Teflon tape, insulating tape, and epoxy, demonstrated that aluminum tape combined with insulating tape provided a reasonable sealing method when both performance and practicality were considered.

Furthermore, the coincidence summing correction factor (Kcs) for summing peaks generated by simultaneously emitted γ-rays, and the self-absorption correction factor (Ksc) for differences between calibration standards and real samples, were derived using Mirion software. To verify the effectiveness of these corrections, comparative experiments were performed with IAEA-RGU and RGTh reference materials under identical environmental and sealing conditions. In addition, representative γ-rays were selected for each radionuclide by comparing the analysis results across energies. Final validation with the IAEA-412 certified reference material confirmed that the proposed analytical conditions yielded results within the uncertainty range, with deviations of up to 6%.
In addition, measurement-time optimization was performed by classifying approximately 1,600 domestic soil samples into groups based on radionuclide concentrations and Compton background conditions. By comparing measurement results from 1,800 to 172,800 s, the study identified distinct characteristics in uncertainty and MDA behavior across groups, and determined optimal measurement times ranging from 7,200 s for high- and medium-activity samples to 21,600–43,200 s for low-activity or Compton-dominated samples.
The optimized analytical conditions proposed in this study are expected to improve the reliability and accuracy of NORM γ-ray spectrometry, reduce inter-laboratory discrepancies, and enhance the consistency of measurement conditions. Furthermore, these results may support the future refinement of analytical guidelines and contribute to more coherent practices in environmental radioactivity assessment.

목차 (Table of Contents)

• (Abstract)
• Ⅰ. 서 론 1
• 1.1 연구 배경 1
• 1.2 국내·외 이슈 및 현황 2
• 1.3 연구 목적 및 구성 3
• Ⅱ. 이론적 배경 4
• 2.1 감마분광분석 시스템 4
• 2.1.1 시스템 구성 4
• 2.1.2 감마선 검출기 5
• 2.2 교정 및 분석 8
• 2.2.1 스펙트럼 8
• 2.2.2 계수 통계 및 피크 면적 계산 9
• 2.2.3 에너지 및 효율 교정 12
• 2.2.4 방사능 분석 14
• 2.2.5 붕괴 보정인자 및 배경 면적 보정 16
• 2.2.6 측정불확도 17
• 2.2.7 최소검출방사능 18
• 2.3 천연방사성물질 19
• 2.3.1 40K 19
• 2.3.2 232Th 19
• 2.3.3 226Ra 20
• 2.3.4 방사평형 21
• 2.4 분석 영향인자 및 소프트웨어 24
• 2.4.1 분석 영향인자 24
• 2.4.2 소프트웨어 26
• Ⅲ. 재료 및 방법 28
• 3.1 실험 장비 및 교정 28
• 3.1.1 에너지 교정 29
• 3.1.2 효율 교정 30
• 3.1.3 동시합산 보정 31
• 3.2 사전 분석 요인 및 실험 방법 34
• 3.2.1 사전 분석 요인 34
• 3.2.2 실험실 내부 배경준위 34
• 3.2.3 라돈 밀봉 36
• 3.3 분석 영향 요인 및 실험 방법 37
• 3.3.1 분석 영향 요인 37
• 3.3.2 동시합산 보정 계수 산출 방법 38
• 3.3.3 자체흡수 보정 계수 산출 방법 40
• 3.3.4 다른 방사성 핵종의 기여 42
• 3.3 측정시간 최적화 실험 방법 47
• Ⅳ. 결과 51
• 4.1 사전 분석 요인 실험 결과 51
• 4.1.1 실험실 내부 배경준위 실험 결과 51
• 4.1.2 라돈 밀봉 실험 결과 53
• 4.2 분석 영향 요인 실험 결과 54
• 4.2.1 동시합산 보정 후 분석 결과 54
• 4.2.2 자체흡수 보정 후 분석 결과 56
• 4.2.3 다른 방사성 핵종의 기여 분석 결과 60
• 4.2.4 최종 평가 62
• 4.3 측정시간 최적화 실험 결과 64
• Ⅴ. 고찰 74
• Ⅵ. 결론 77
• 참고 문헌 80