The inorganic scintillator used in gamma spectroscopy must have good efficiency in converting the kinetic energy of charged particles into light as well as high light output and high light detection efficiency. Accordingly, various studies have been conducted to enhance the net-efficiency. One way to improve the light yield has been studied by coating scintillators with various nanoparticles, so that the scintillation light can undergo resonance on surface between scintillators and nanoparticles resulting in higher light yield. In this study, an inorganic scintillator coated with CsPbBr3 perovskite nanocrystals using dip coating technique was proposed to improve scintillation light yield. The experiment was carried out by measuring scintillation light output, as the result of interaction between inorganic scintillator coated with CsPbBr3 perovskite nanocrystals and gamma-ray emitted from Cs-137 gamma source. The experimental results show that the channel corresponding to 662 keV full energy peak in the Cs-137 spectrum shifted to the right by 14.37%. Further study will be conducted to investigate the detailed relationships between the scintillation light yield and the characteristics of coated perovskite nanoparticles, such as diameter of nanoparticles, coated area ratio and width of coated region.

In-situ gamma spectrometer with mobile equipment can be used for rapid determination of radioactivity in the environment within a very short interval. 2”×2” NaI(Tl) scintillator are used to build a mobile radiation measurement system (called as Monitoring of Ambient Radiations of KAERI for Backpack, MARK-B3) with a signal processing unit, and GPS and interface units to a PC for wireless controlling system. Development of the survey system is to measure ambient gamma-ray spectrometry for estimating ground radioactivity and radiation dose in the environment. The ambient dose rate is estimated using G-factor method. For determination of G-factor, we conducted MCNP simulations in assumptions of various incident photons into the detector system. And the scintillator was exposed to Cs-137 source in the range of 1- 300 mGy/hr. Calculated dose rates for different simulation results were compared to the irradiated dose rate to derive correction factor of G-factor. To evaluate performance of the MARK-B3, in-situ gamma spectrometry was conducted in Jeju island.

Plastic scintillators can be used to find radioactive sources for portal monitoring due to their advantages such as faster decay time, non-hygroscopicity, relatively low manufacturing cost, robustness, and easy processing. However, plastic scintillators have too low density and effective atomic number, and they are not appropriate to be used to identify radionuclides directly. In this study, we devise the radiation sensor using a plastic scintillator with holes filled with bismuth nanoparticles to make up for the limitations of plastic materials. We use MCNP (Monte Carlo N-particle) simulating program to confirm the performance of bismuth nanoparticles in the plastic scintillators. The photoelectric peak is found in the bismuth-loaded plastic scintillator by subtracting the energy spectrum from that of the standard plastic scintillator. The height and diameter of the simulated plastic scintillator are 3 and 5 cm, respectively, and it has 19 holes whose depth and diameter are 2.5 and 0.2 cm, respectively. As a gamma-ray source, Cs-137 which emits 662 keV energy is used. The clear energy peak is observed in the subtracted spectrum, the full width at half maximum (FWHM) and the energy resolution are calculated to evaluate the performance of the proposed radiation sensor. The FWHM of the peak and the energy resolution are 61.18 keV and 9.242% at 662 keV, respectively.

In this paper, cerium doped lutetium pyrosilicate (LPS) powders with cerium content (0.05 and 0.07 mol%) were prepared by sol-gel process. The formation of lutetium pyrosilicate (LPS) phase was confirmed by XRD analysis for the powders heated at 1,200 oC; in these powders, a single phase of Lu2Si2O7 (LPS) was observed. Cerium doped lutetium pyrosilicate (LPS) powder was agglomerated and constituted of small spherical particles with diameters of about 300 nm. The photoluminescence spectra of the Lu2Si2O7:Ce3+ powders showed the characteristic of excitation and there was an emission spectrum for Ce3+ in the host of Lu2Si2O7. The emission spectrum shows a broad band in the range of 350-525 nm; the broad wavelength on the right side of the spectra should be ascribed to the same 5d-4f transitions of Ce3+, as in the case of cerium doped Lu2Si2O7 single crystals.

민감도 향상을 위해 블록형 섬광체를 사용한 검출기를 개발하였다. 픽셀형 섬광체는 섬광체에서 발생된 빛을 최대한 광센서로 이동시키기 위해 픽셀 사이에 반사체가 위치하며, 반사체 부분으로 민감도 손실이 발생한다. 민감도를 향상시키고 픽셀형 섬광체의 특징을 가지게 하기 위해 블록형 섬광체를 레이저 각인을 통해 픽셀 형태의 섬광체로 가공하였다. 본 섬광체를 위치민감형 광전증배관과 결합하여 평면 영상을 획득 하였고, 각 픽셀별 에너지 스펙트럼과, 에너지 분해능을 측정하였으며, GATE 시뮬레이션을 통해 블록형 섬광체와 픽셀 섬광체의 민감도 분석을 수행하였다. 측정된 전체 에너지 분해능은 20.7%를 보였으며, 민감도는 픽셀 섬광체에 비해 18.5% 높은 결과를 나타내었다. 본 검출기를 감마카메라 및 양전자방출단층촬영 기기 등의 영상화 기기에 활용할 경우 높은 민감도 향상을 통해 촬영시간의 단축 및 적은 방사선원 사용으로 환자의 피폭선량 감소를 이룰 수 있을 것이다.

본 연구는 고해상도 디지털 X선 영상 검출기 적용을 위해 미세 Gd2O2S:Tb 형광체 분말을 저온 액상법을 이용하여 합성하였다. 제조된 형광체 분말을 이용하여 입자침전법을 이용하여 형광체 필름을 제작하여 발광특성을 조사하였다. 측정결과, Tb 첨가농도에 따른 상대적인 발광량 측정결과 5 wt%의 첨가농도에서 가장 높은 발광효율을 보였으며, 첨 가농도가 증가할수록 소광현상에 의한 발광강도가 급격히 감소하는 경향을 보였다. 또한 270 ㎛ 두께의 Gd2O2S:Tb에 서 2945 pC/cm2/mR의 발광 강도를 가졌으며, 발광 강도가 거의 포화되는 것을 관찰할 수 있었다. 끝으로 제조된 형광 체의 영상획득 성능을 평가하기 위해 상용화된 CMOS 센서를 이용하여 X선 영상을 획득하여 MTF, NPS를 측정하여 DQE 평가를 수행하였다. 측정결과, DQE(0)의 값은 37%로 다소 낮은 값을 보였다. 향후 필름 제조 공정상의 문제점 을 해결한다면, DQE를 개선할 수 있을 것으며, 고해상도 의료 방사선 영상 시스템 적용에 유용하게 적용 가능할 것으 로 판단된다.