Earticle

Background: Boron neutron capture therapy (BNCT) is a potential radiation therapy for treating refractory cancers. Measuring the neutron energy spectrum is important to evaluate the biological effect of BNCT. We have developed a novel low-energy neutron spectrometer with a 3He position-sensitive proportional counter. The effectiveness of this spectrometer remained unvalidated due to the inadequate response function. Materials and Methods: The response function of this spectrometer was evaluated by Monte Carlo simulation to perform the validation experiment of this spectrometer. The 3He(n,p)3H reaction rate for each monochromatic neutron (energy range, 0.5 eV–10 keV) was calculated. Numerical experiments were conducted to investigate the performance of this spectrometer. Several estimated values of the energy spectrum were obtained and compared with a calculated energy spectrum at the exit of the epithermal column by the Monte Carlo simulation by preparing several candidates for signals. The Bayesian estimation algorithm was utilized for the estimation. Results and Discussion: The results indicate that the spectrometer and the evaluated response functions can be utilized to measure the energy spectrum of neutrons in the low-energy range. However, the energy spectrum could not be well represented >4 keV due to the poor response function, including uncertainties in response function calculation as well as the poor energy resolution of this detector in the high-energy region. Conclusion: The response function of the low-energy neutron spectrometer for the epithermal energy region can be assessed by the Monte Carlo simulation. The numerical experiments reveal that the effectiveness of this spectrometer can be shown in the range of 0.5 eV.

We report a simple technique for direct neutron spectroscopy using pure LaCl₃ crystals. Pure LaCl₃ crystals exhibit considerably better pulse shape discrimination (PSD) capabilities with relatively good energy resolution as compared with Ce-doped LaCl₃ crystals. Single crystals of pure and Ce-doped LaCl₃ were grown using an inhouse-developed Bridgman furnace. PSD capabilities of these crystals were investigated using ²⁴¹Am and ¹³⁷Cs sources. Fast neutron detection was tested using a²⁵²Cf source and three separate bands corresponding to electron, proton, and alpha were observed. The proton band induced by the ³⁵Cl(n,p)³⁵S reaction can be used for direct neutron spectroscopy because proton energy is proportional to incident neutron energy. Owing to good scintillation performance and excellent PSD capabilities, pure LaCl₃ is a promising candidate for space detectors and other applications that necessitate gamma/fast neutron discrimination capability.

MeV 영역의 속중성자분광을 위해 재래의 radiator system을 개량하여 ringshaped vertical radiator와 cone-shaped horizontal radiator를 공용한 특수한 recoil proton radiator assembly를 사용함으로서 energy 분해능의 저하없이 검출효율을 높이도록 recoil Proton telescope detector를 설계ㆍ제작하였다. 이 검출기에는 입사중성자속에 대한 Si(ti) 검출기의 직접노출을 피함으로서 background를 줄일수 있도록 입사중성자차폐부도 고안 내장되어 있다. 이 개량된 recoil proton telescope detector의 검출효율 및 energy 분해능을 중성자 energy 1-15 MeV에 대하여 radiator system과 Si(Li) 검출기사이의 거리변화에 따라 이론적인 계산치로 도출ㆍ표시하였으며, 실험적검증의 예로서 이 거리를 29cm로 하고 중성자 energy를 14.1 MeV로 하였을 때의 검출기의 제특성측정결과를 얻어 분석하였다. 측정결과의 분석에 의하면 이론에서 추정된것처럼 혼합형 radiator system을 사용하였을 때의 검출 효율은 단일 radiator system을 사용한 재래식 검출기의 검출효율의 2.2배의 증가를 보인데 반하여 energy 분해능의 저하는 불과 30%, background의 증가는 약40% 말만임을 알수가 있었다. 또한 측정에 의한 14.1 MeV 중성자에 대한 energy 분해능은 3.9% FWHM었는데, 이는 이논적인 3.7% FWHM와 거의 완전한 일치를 보이고 있음도 입증되였다.

For fast neutron spectroscopy in MeV region, a recoil proton telescope detector was designed and constructed so as to increase in detection efficiency without appreciable deterioration in energy resolution by adopting a special type of recoil proton radiator which is a combination of a ring-shaped vertical radiator and a cone-shaped horizontal radiator at a certain geometry. A neutron stopper was built in the detector system to minimize the background due to direct exposure of the Si(Li) detectors to primary incident neutrons. The detection efficiency and the energy resolution calculated at various neutron energies and geometries are given and these characteristics of the detector system were tested by 14.1 MeV neutrons. As the calculation predicted, the relative detection efficiency in case of the combined radiator system is almost 2.2 times of that for a single, ring-shaped vertical radiator system. The calculated energy resolution is 3.7% FWHM, whereas the measured resolution was 3.9% which means resolution broadening of approximately. 30% was resulted by introducing a combined radiator system into the telescope. Increase in background less than 40% was also observed.

최근 Y. Masumoto[1]등에 의하여 Co가 도핑된 anatase 구조의 TiO$_2$ 물질에서 상온 강자성 현상이 보고된 이후, 이에 대한 관심이 고조되면서 다른 연구 그룹들에 의해 실험적으로 상온 강자성을 성공하였다는 보고[2,3]가 있으나 현재 그 메커니즘에 대하여 명확한 해석이 되어있지 않고 있기 때문에 이것이 정말 자성반도체의 성질인지 아니면 clustering에 의한 것인지 아직 확실히 밝혀져 있지는 않다. (중략)

본 연구에서는 중성자-감마 스펙트럼검층 존데 설계를 목적으로 Monte Carlo 시물레이션을 이용하여 열중성자 반응의 우세한 영역 파악 및 포획감마 스펙트럼의 에너지피크 값에 기초한 지층 구성 원소 구분을 수행하였다. 14 MeV 에너지준위의 중성자를 방출하는 중성자발생장치를 선원으로 이용하여 선원으로부터 10 cm 간격으로 12개의 중성자 검출기들을 배열함으로써 거리에 따른 열중성자 양을 측정하였다. 시추공 영향 저감을 위해 존데모형에 차폐재를 적용하여 보다 정확한 열중성자 측정을 수행하여 열중성자 반응이 우세한 위치를 분석한 뒤, 이 위치에서 검출된 포획감마 에너지 스펙트럼을 분석하여 지층을 구성하는 주요 원소 및 그 양을 확인하였다. 본 연구 결과는 중성자-감마 스펙트럼검층 존데의 신호대잡음 비 향상과 포획감마 검출기 최적 위치 선정에 도움이 될 것으로 판단된다.

For efficiently designing neutron induced gamma spectroscopy sonde, Monte Carlo simulation is employed to understand a dominant location of thermal neutron and classify the formation elements from the energy peak of capture gamma spectrum. A pulsed neutron generator emitting 14 MeV neutron particles was used as a source, and flux of thermal neutron was calculated from the twelve detectors arranged at each 10 cm intervals from the source. Design for reducing borehole effects using shielding materials was also applied to numerical sonde model. Moreover, principal elements and quantities of numerical earth models were verified through the energy spectrum analysis of capture gamma detected from a gamma detector. These results can help to enhance the signal-to-noise ratio, and determine an optimal placement of capture gamma detectors of neutron induced gamma spectroscopy sonde.

$^{252}Cf$ 중성자 선원을 이용한 즉발감마선 계측 시스템 (NIPS, Neutron Induced Promp ${\gamma}$-ray Spectroscopy)을 설계 및 구성하기 위하여, 시스템내의 감속제 및 차폐체등의 효과를 시험하고 감마선 바탕값과 Cl을 포함한 시료의 즉발 감마선을 계측하였다. 이를 위한 예비시험으로 한국원자력연구소 내에 있는 TLD 판독용 $^{252}Cf$ 선원을 이용하였으며 즉발감마선은 시스템 내부의 동축형 HPGe (GMX, 60% relative efficiency)과 시스템외부 (약 20m 거리)의 Notebook PC 중성자와 감마선의 바탕값을 측정하고, 바탕값을 최소로 할 수 있는 차폐체의 기하학적 구조를 고안하였다. 감마선 바탕값을 최소화하기 위하여 두 개의 HPGe 검출기를 이용한 감마-감마 동시계측법을 이용하였다. 이 실험 자료를 이용하여 최적의 NIPS 시스템을 구성하였다.

For the design and set-up of neutron induced prompt ${\gamma}$-ray spectroscopy system using $^{252}Cf$ neutron source, the effects of shielding and moderator materials have been examined. The $^{252}Cf$ source being used for TLD badge calibration in Korea Atomic Energy Research Institute was utilized for this preliminary experiment. The ${\gamma}$-ray background and prompt ${\gamma}$-ray spectrum of the sample containing Cl were measured using HPGe (GMX 60% relative efficiency) located at the inside of the system connected to notebook PC at the outside of the system (about 20 meter distance). The background activities of neutron and ${\gamma}$-rays were measured with neutron survey meter as well as ${\gamma}$-ray survey meters, respectively and the system was designed to minimize the activities. Prompt ${\gamma}$-ray spectrum was measured using ${\gamma}$-${\gamma}$ coincident system for reduce the background and the continuum spectrum. The optimum system was designed and set up using the experimental data obtained.

남해연안 갯벌 속에 있는 무기원소들의 정량을 위해 중성자 방사화 분석법과 ICP-AES를 적용하였다. 중성자 방사화 분석법과 ICP=AES에 의하여 얻어진 Al, Ca, Fe, Mg, K, Na의 분석결과들을 상호 비교하였다. 결과적으로 침전물 중의 미량 원소를 분석하는데 ICP-AES보다 중성자 방사화 분석법이 더 우수한 것으로 나타났다. 따라서 중성자 방사화 분석법은 갯벌과 같은 복잡한 모체를 갖는 환결시료들의 분석헤서 중요한 역할을 할 것이다.

Neutron Activation Analysis (NAA) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) have been applied for the determination of inorganic elements in mud flat of south seaside in Korea. The analytical results of Al, Ca, Fe, Mg, K and Na by NAA were compared with those by ICP-AES. The results show that NAA is superior to ICP-AES for the determination of minor elements in sediment. Accordingly, NAA will play an important role in the analysis of environment samples such as mud flat and sediment having complex matrix.