Development of Virtual Gamma-ray Energy Spectrum Database for KHNP Detectors by MCNP Simulation

Yoomi Choi,Young-yong Ji,Sungyeop Joung 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

To obtain the gamma-ray energy spectrum of artificial radionuclides which is difficult to obtain practically, virtual gamma-ray energy spectrum simulator program was developed. It can be applied for the predetermined measurement condition for which the database was developed through computational simulation and actual measurement of background radiation. For gamma spectrometry training for KHNP HPGe detectors using this program, the database for KNPG HPGe detectors was developed. First, the geometry of the detector in the simulation was adjusted to resemble the real structure by comparing the actually measured net counts rate at the main gamma peak with the value simulated by MCNP6. The Certified Reference material (CRM) of 137Cs and 60Co were used for verification. The comparison was made with respect to the situation where CRM was attached to the top and side of the detection part of the considered detector. The geometry structures of detectors were simulated by reflecting the design drawing of the products, and the simulation was performed for several thicknesses of the Ge/Li dead layer in consideration of the change in the thickness over time. As the results, the simulation geometry was tuned so that the results for 137Cs showed a difference within 10% for all detectors. At this time, in some detectors, the result for 60Co shows a 10% higher error, which is estimated to be due to the random summing. It was not considered in tuning the simulation geometry, but it was found that improvements were needed to reflect the coincidence summing when construction the virtual spectrum in the future. The determined simulation geometry was applied to generate theoretical gamma-ray energy spectra of representative artificial radionuclides. In order to create a virtual spectrum similar to the real one, the background spectrum was measured for each detector without a source, and the simulation results were calculated in the form of having the same energy channel as the background spectrum. The background spectrum and theoretical spectra of artificial radionuclides for each detector were databased so that virtual spectra could be generated under desired conditions. The virtual spectrum was generated by adding a background spectrum and a spectrum obtained by multiplying the spectrum of the desired nuclide by the concentration of the nuclide. The validity of generated virtual spectra was verified using the pre-developed gamma spectrometry program. As a results of gamma spectrometry of virtual spectra, the virtual spectra was verified by showing a difference within 20% from the radioactivity value input when generating the virtual spectra.

A Study on the Comparison of HPGe Detector Response Data for Low Energy Photons Using MCNP, EGS, and ITS Codes

Kim,Jong-Oh,Kim,Jong-Kyung,Kim,Bong-Hwan,Kim,Soon-Young 대한방사선 방어학회 1996 방사선방어학회지 Vol.21 No.2

저에너지 광자에 대한 고순도 게르마늄 검출기의 에너지 반응데이타를, 3개의 몬테칼로 코드(MCNP4A, EGS4, ITS3의CYLTRAN)를 사용하여 계산하였다. 본 연구에서는, bare고순도 게르마늄 검출기(100 mm²×10 mm)가 사용되었고, 측정기표면의 중아에 pencil beam을 수직으로 입사시켰다. 관전효과 효율, Kα, 및 Kβ 이탈률을, 12 KeV 부터 60 KeV 범위까지 2 KeV 간격으로 입사된 X-선네너지의 함수로 나타내었다. 이 에너지범위에서 컴프턴산란률, 탄성산란률 및 투과율은 매우 작기 때문에 본 계산에서는 제외되었다. 비록 MCNP, EGS, CYLTRAN 코드의 저에너지 광자에 대한 고순도 게르마늄 검출기 에너지 반응데이터값은 약간의 차이를 나타내지만, 세가지 몬테칼로 코드는 검출기내의 저네너지 광자산란을 정확히 예측하고 있음을 알 수 있다. 또한 EGS나 ITS의 결과에 비해 저에너지 영역에서 정확성이 떨어진다고 여겨지는 MCNP의 결과도 EGS나 ITS의 결과에 상당하는 정확성을 보여주고 있으며, 제에너지 광자에 대한 검출기 반응데이타 계산에 응용될 수 있다. The energy response of HPGe detector for low energy photons was determined by using three Monte "Carlo codes. MCNP4A EGS4, and CYLTRAN in ITS3. In this study, bare HPGe detector (100 mm²×10 mm) was used and a pencil beam was incident perpendicularly on the center of the4 detector surface. The photopeak efficiency, Kαand Kβ escape fractions were calculated as a function of incident X-ray energies ranging from 12 to 60 KeV in 2-KeV increments. Since the Compton, elastic, and penetration fraction were negligible in this energy range, they were ignored in the calculation. Although MCNP, EGS and CYLTRAN codes calculated slightly different energy response of HPGe detector for low energy photons, it appears that the three Monte Carlo codes can predict the low energy photon scattering processes accurately. The MCNP results, which are generally known as to be less accurate at low energy ranges than the EGS and ITS results, are comparable to the results of EGS and ITS and are applicable to the calculation of the low energy response data of a detector.

Improvement of accuracy in radioactivity assessment of medical linear accelerator through self-absorption correction in HPGe detector

유수아,권나혜,김상록,원영진,김금배,이세병,백철하,최상현 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.6

Medical linear accelerators with an energy of 8 MV or higher are radiated owing to photonuclear reactions and neutron capture reactions. It is necessary to quantitatively evaluate the concentration of radioactive isotopes when replacing or disposing them. HPGe detectors are commonly used to identify isotopes and measure radioactivity. However, because the detection efficiency is generally calibrated using a standard material with a density of 1.0 g/cm3, a self-absorption effect occurs if the density of the measured material is high. In this study, self-absorption correction factors were calculated for tungsten, lead, copper, and SUS-303, which are the main materials of medical linear accelerator head parts, for each gamma-ray energy using MCNP 6.2 code. The selfabsorption effect was more pronounced as the energy of the emitted gamma rays decreased and the density of the measured materials increased. These correction factors were applied to the radioactivity measurements of the in-built and portable HPGe detectors. Furthermore, compared to the surface dose rate measured by the survey meter, the accuracy of the measurements of radioactivity improved by an average of 124.31 and 100.53 % for inbuilt and portable HPGe detectors, respectively. The results showed a good agreement, with an average difference of 3.70 and 5.24 %.

Experimental and Simulated Efficiency of a HPGe Detector in the Energy Range of $0.06{\sim}11$ MeV

Park Chang Su,Sun Gwang Min,Choi H.D. Korean Nuclear Society 2003 Nuclear Engineering and Technology Vol.35 No.3

The full energy peak efficiency of a hyper pure germanium (HPGe) detector was calibrated in a wide energy range from 0.06 to 11 MeV. Both the experimental technique and the Monte Carlo method were used for the efficiency calibration. The measurement was performed using the standard radioisotopes in the low energy region of $60{\sim}1408$ keV, which was further extended up to 11 MeV by using the $^{14}N(n,r)\;and\;^{35}Cl(n,r)$ reactions. The GEANT Monte Carlo code was used for efficiency calculation. The calculated efficiency had the same dependency on the r-ray energy with the measurement, and the discrepancy between the calculation and the measurement was minimized by fine-tuning of the detector geometry. From the calculated result, the efficiency curve of the HPGe detector was reliably determined particularly in the high energy region above several MeV, where the number of measured efficiency points is relatively small despite the wide energy region. The calculated efficiency agreed with the measurement within about $7\%$. In addition to the efficiency calculation, the origin of the local minimum near 600 keV on the efficiency curve was analyzed as a general characteristics of a HPGe detector.

p-type HPGe 검출기 특성에 따른 밀도 보정인자 의존도 평가

장미,지영용,김창종,이완로,강문자 한국방사성폐기물학회 2015 방사성폐기물학회지 Vol.13 No.4

HPGe 검출기를 이용하여 밀도가 다양한 환경시료에 대한 정밀 분석시 정확한 분석을 위해서는 밀도보정인자가 필요하다. 밀도에 대한 보정인자를 구하기 위해서 본 연구에서는 몬테카를로 코드인 MCNPX 코드를 사용하여 크리스털의 높이, 지름및 코어의 크기와 같은 특성이 다른 세 대의 p-type HPGe 검출기를 모사하고 밀도 1 g/cm3의 교정용 표준시료를 이용하여 모델링을 검증하였다. 검증을 통하여 모델링을 확정한 후 0.3, 0.6, 0.9, 1.0, 1.2, 1.5 g/cm3 밀도를 가진 샘플에 대한 효율을 시뮬레이션하고 밀도보정인자를 도출하였다. 도출된 각 검출기에 대한 밀도보정인자를 비교하였을 때 전 에너지 범위에서 그차이가 거의 없음을 확인하였으며 이는 검출기의 크리스털과 같은 주요 특성에 대해 밀도보정인자가 독립적임을 의미한다. The precise determination of the activity for each radionuclide in environmental samples requires the self-absorption correction factor. In this research, we derived the self-absorption correction factor for three p-type high purity germanium detectors using the Monte Carlo code MCNPX. These detectors have different characteristics such as crystal diameter, height and size of the core. We compared the calculated full-energy peak efficiency with the experimental value using a standard sample with 1 g/cm3 density and verified the modeling. We simulated the dependency of the full-energy peak efficiency on the 0.3, 0.6, 0.9, 1.0, 1.2 and 1.5 g/cm3 samples and obtained the corresponding self-absorption correction factor. The self-absorption correction factors calculated for the three detectors differ by less than 1% over most of the energy range and sample densities considered. This indicates that the self-absorption correction factors are independent of the crystal characteristics of HPGe detector.

Development of a HPGe Shielding System for Radioactivity Measurements at Cheongpyeong Underground Radiation Laboratory

임선인,J. Y. Huh,E. K. Lee,S. H. Choi,I. S. Hahn,W. G. Kang,A. Kim,D. H. Kim,Y. D. Kim,Y. J. Kim,K. W. Kim,S. Y. Park,J. S. Yoo 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.11

We constructed an underground laboratory called Cheongpyeong Underground Radiation Laboratory (CURL) for measuring the radioactivity levels of various samples by using HPGe detectors. CURL is located underground at a depth of 1000-m water equivalent in the Cheongpyeong Pumped Storage Power Plant. We developed a shielding system, which consists of 15-cm-thick Pb blocks and 5-cm-thick Cu blocks and completely surrounds a 100% HPGe detector. We measured the background radiations and the gamma peaks from sources with and without the shield. The shielding efficiencies were also estimated using MCNP5 simulations, and they were compared to our measured data. The shielding system blocked more than 99.99% of gamma rays with energies up to 3.0 MeV. The HPGe detector with the shielding system at CURL blocked both high-energy cosmic rays and background radiation from surrounding rocks and materials. Our CURL detector system was optimized for gamma-ray measurements of meterials with ultra-low radioactivity.

고순도 Ge 검출기의 전기적 노이즈 감소를 통한 감마선 에너지 스펙트럼의 분해능 향상에 관한 연구

이삼열(Samyol Lee) 한국방사선학회 2020 한국방사선학회 논문지 Vol.14 No.7

감마선 에너지 스펙트럼 연구에서 에너지 분석을 통한 핵종 분석은 매우 중요하다. 감마선 에너지 측정에 일반적으로 사용되는 고순도 Ge 검출기는 높은 에너지 분해능과 상대적으로 높은 검출 효율 때문에 일반적으로 사용된다. 그러나 반도체 검출기는 높은 에너지 분해능을 유지하기 위해 주변 환경에서 발생하는 노이즈를 효과적으로 차단하지 않으면 원래의 성능을 유지하기 어렵고 고가의 장치의 효과를 얻지 못하는 문제점이 있. 따라서 본 연구에서는 검출기에서 발생하는 전기적 노이즈를 제거하기 위해 접지 루프 아이솔레이터 (NEXT-001HDGL)를 사용했다. 에너지 분해능 향상 효과를 테스트하기 위해 양성자 가속기 KOMAC에 새로 설치된 HPGe 검출 장치를 사용했다. 감마선 에너지 2614 keV의 경우 에너지 분해능이 (0.16 ± 0.02) %에서 (0.11 ± 0.01) %로 개선되었고, 감마선 에너지 662 keV의 경우 에너지 분해능이 (0.72 ± 0.07) %에서 0.27 ± 0.03 %로 향상되었다. 이 결과는 KOMAC (Korea Multi-Purpose Accelerator Complex)의 HPGe 검출 장비를 이용한 감마선 스펙트럼 연구에 매우 유용한 것으로 판단된다. In the gamma-ray energy spectrum study, nuclide analysis through energy analysis is very important. High-purity Ge detectors, which are commonly used for gamma-ray energy measurements, are commonly used because of their high energy resolution and relatively high detection efficiency. However, in order to maintain a high energy resolution, the semiconductor detector has a problem in that it is difficult to maintain the original performance if the noise generated from the surrounding environment is not effectively blocked, and the effect of the expensive device is not achieved. Therefore, in this study, ground loop isolator (NEXT-001HDGL) was used to remove the electrical noise generated from the detector. In order to test the effect of improving energy resolution, HPGe detection device newly installed in the proton accelerator KOMAC was used. In the case of gamma-ray energy 2614 keV, the energy resolution was improved from (0.16 ± 0.02) % to (0.11 ± 0.01) %, and in the case of gamma-ray energy 662 keV of 137Cs isotope, the energy resolution was improved from (0.72 ± 0.07) % to (0.27 ± 0.03) %. This result is considered to be very useful for the gamma ray spectrum study using the HPGe detection equipment of KOMAC(Korea Multi-Purpose Accelerator Complex).

Efficiency Application of Monte Carlo Simulation and HPGe Detector Using Mapping Method

Eun-Sung Jang,Bo-Seok Chang 한국자기학회 2024 Journal of Magnetics Vol.29 No.2

In order to obtain the detection efficiency according to the distance around the detector, the total energy peak efficiency was used, and the grid mapping method was used to investigate axis-symmetry. The detector was measured at 0.5 cm intervals up to 5 cm in the x, z, direction, and 5.5 cm in the y direction. The efficiency of the cylinder beaker and marinelli beakers at the center of the 134Cs 604 keV detector was compared with the efficiency of the mapping method. For cylinder beakers, the efficiency was 0.0412 ± 0.002, and the efficiency by mapping was 0.040 ± 0.001, which was consistent within 3 % of the uncertainty range. For Marinelli beakers, the efficiency was 0.0242 ± 0.002 mapping efficiency was 0.0248 ± 0.0013. It was confirmed that precise measurement of radioactive sources with volume was possible when measured at each point around the detector.

¹⁸F Half-life measurement using 2-γ coincidence method

Kang, Y.S.,Ahn, J.K.,Kim, S.H.,Byun, J.I.,Han, J.B.,Lee, K.B. Elsevier 2015 Nuclear Instruments & Methods in Physics Research. Vol.801 No.-

<P><B>Abstract</B></P> <P>The accuracy of the half-life measurement of short-lived radioisotopes such as positron-emitting <SUP>18</SUP>F ( <SUB> τ 1 / 2 </SUB> ≈ 100 min ) is limited mainly by inaccuracies in the detector counting statistics. Gamma-ray measurement with a high-activity <SUP>18</SUP>F source requires counting-loss corrections to compensate for random summing effects and the detector׳s dead time. In this study, we measure the half-life of <SUP>18</SUP>F with two 511-keV γ-rays using two high-purity germanium (HPGe) detectors. The counting-loss corrections are performed via two approaches to address the problems of random coincidence summing and dead time: a half-life measurement with a <SUP>22</SUP>Na source and a Geant4 simulation of the detector response. Variations in the full-width at half maximum (FWHM) of the 511-keV peak are found to show good correlation with the random summing effect. The half-life of <SUP>18</SUP>F is estimated as 109.73 ± 0.14 min .</P>

방사성동위원소(60Co,133Ba)를 사용하여 mapping method에 의한 HPGe detector의 효율성 결정.

장은성,강연수,안정근,김성현,변종인,윤주영 대한방사선방어학회 2011 대한방사선방어학회 학술발표회 논문요약집 Vol.2011 No.11