New Effective Organic Scintillators for Fast Neutron and Short-Range Radiation Detection

Budakovsky, S.V.,Galunov, N.Z.,Karavaeva, N.L.,Jong Kyung Kim,Yong Kyun Kim,Tarasenko, O.A.,Martynenko, E.V. Professional Technical Group on Nuclear Science 2007 IEEE transactions on nuclear science Vol.54 No.6

<P>This paper describes the techniques used for making new organic scintillators and detectors based on these scintillators. Research has focused on designing large dimension organic scintillators to increase the efficiency of detecting ionizing radiation. The techniques described here have allowed us to produce (1) organic crystals of stilbene and p-terphenyl with diameters up to 120 mm and heights up to 100 mm; (2) p-terphenyl polycrystals doped with diphenylbutadiene molecules, as well stilbene polycrystals up to 250 mm in diameter and 5 mm in height; (3) the first prototypes of a composite scintillation material based on stilbene grains added to a silicone glue base, achieving a high efficiency of fast neutron detection.</P>

Calculation of Thermal Fluence from Extremely High-Energy Emission in Air

Heesoo Jung,Woosup Shim Professional Technical Group on Nuclear Science 2015 IEEE transactions on nuclear science Vol.62 No.3

<P>Thermal radiation from high-energy emission event, such as nuclear explosion, is characterized by a wide energetic spectrum in air. Black body assumption for the fireball associated with this radiation serves as a reasonable approximation for interpreting the thermal radiation emission characteristics. In this study, the time-integrated thermal flux received by a target on the ground and facing a nuclear burst, was calculated as a function of yield, burst elevation, ground range, and visibility. Results of our calculations were compared with previously reported results for different conditions.</P>

An SEU-Tolerant DICE Latch Design With Feedback Transistors

Wang, H.-B,Li, Y.-Q,Chen, L.,Li, L.-X,Liu, R.,Baeg, S.,Mahatme, N.,Bhuva, B. L.,Wen, S.-J,Wong, R.,Fung, R. Professional Technical Group on Nuclear Science 2015 IEEE transactions on nuclear science Vol.62 No.2

<P>This paper presents an SEU-tolerant Dual Interlocked Storage Cell (DICE) latch design with both PMOS and NMOS transistors in the feedback paths. The feedback transistors improve the SEU tolerance by increasing the feedback loop delay during the hold mode. The latch design was implemented in a shift register fashion at a 130-nm bulk CMOS process node. Exposures to heavy-ions exhibited a significantly higher upset LET threshold and lower cross-section compared with the traditional DICE latch design. Performance penalties in terms of write delay, power, and area are non-significant compared to traditional DICE design.</P>

Improvement of Real-Time Tritium Monitor for Low-Level Measurement at HANARO

Professional Technical Group on Nuclear Science 2015 IEEE transactions on nuclear science Vol.62 No.4

<P>Two real-time tritium monitors are installed at the stack of HANARO, a 30 MW research reactor, to measure the tritium concentrations in the discharged air from the reactor hall and reactor concrete island region. The tritium monitor adopts coincidence and anticoincidence coupling to detect the very low energy beta particles from tritium. Since the tritium level in the air released from the reactor hall is very low during normal operation of HANARO, tritium concentration measurements are easily affected by the noble gas signal contribution and background. Thus, a method to remove the noble gas contribution and the tritium background is established. The noble gas contribution is verified and removed using reliable noble gas measurements by a third detection method. The tritium background is deduced using the bubbling method. The tritium concentration is determined using the newly established method, and it is compared with bubbling data. The two measurement methods produce mutually consistent data. Thus it can be concluded that our evaluation method provides useful data processing for the real-time measurement of extremely low tritium levels.</P>

An Effective Post-Filtering Framework for 3-D PET Image Denoising Based on Noise and Sensitivity Characteristics

Ji Hye Kim,Il Jun Ahn,Woo Hyun Nam,Jong Beom Ra Professional Technical Group on Nuclear Science 2015 IEEE transactions on nuclear science Vol.62 No.1

<P>Positron emission tomography (PET) images usually suffer from a noticeable amount of statistical noise. In order to reduce this noise, a post-filtering process is usually adopted. However, the performance of this approach is limited because the denoising process is mostly performed on the basis of the Gaussian random noise. It has been reported that in a PET image reconstructed by the expectation-maximization (EM), the noise variance of each voxel depends on its mean value, unlike in the case of Gaussian noise. In addition, we observe that the variance also varies with the spatial sensitivity distribution in a PET system, which reflects both the solid angle determined by a given scanner geometry and the attenuation information of a scanned object. Thus, if a post-filtering process based on the Gaussian random noise is applied to PET images without consideration of the noise characteristics along with the spatial sensitivity distribution, the spatially variant non-Gaussian noise cannot be reduced effectively. In the proposed framework, to effectively reduce the noise in PET images reconstructed by the 3-D ordinary Poisson ordered subset EM (3-D OP-OSEM), we first denormalize an image according to the sensitivity of each voxel so that the voxel mean value can represent its statistical properties reliably. Based on our observation that each noisy denormalized voxel has a linear relationship between the mean and variance, we try to convert this non-Gaussian noise image to a Gaussian noise image. We then apply a block matching 4-D algorithm that is optimized for noise reduction of the Gaussian noise image, and reconvert and renormalize the result to obtain a final denoised image. Using simulated phantom data and clinical patient data, we demonstrate that the proposed framework can effectively suppress the noise over the whole region of a PET image while minimizing degradation of the image resolution.</P>

Continuously Deforming 4D Voxel Phantom for Realistic Representation of Respiratory Motion in Monte Carlo Dose Calculation

Han, Min Cheol,Seo, Jeong Min,Lee, Se Hyung,Kim, Chan Hyeong,Yeom, Yeon Soo,Nguyen, Thang Tat,Choi, Chansoo,Kim, Seonghoon,Jeong, Jong Hwi,Sohn, Jason W. Professional Technical Group on Nuclear Science 2016 IEEE transactions on nuclear science Vol.63 No.6

<P>We propose a new type of computational phantom, the '4D voxel phantom,' for realistic modeling of continuous respiratory motion in Monte Carlo dose calculation. In this phantom, continuous respiratory motion is realized by linear interpolation of the deformation vector fields (DVFs) between the neighboring original phases in the 4D CT data of a patient and by subsequent application of the DVFs to the phase images or to the reference image to produce multiple inter-phase images between the neighboring original phase images. A 4D voxel phantom is a combination of high-temporal-resolution voxel phantoms and on-the-fly dose registration to the reference phase image. In the course of particle transport simulation, the dose or deposited energy is directly registered to the reference phase image on-the-fly (i.e., after each event) using a DVF for dose registration. In the present study, we investigated two methods-DRP (DIR [deformable image registration] with respect to Reference Phase image) and DNP (DIR with respect to Neighboring original Phase image) - for production of multiple inter-phase images or high-temporal-resolution voxel phantoms. Utilizing these two methods, two 4D voxel phantoms each with 100 phases were produced from the original 10-phase images of the 4D CT data of a real patient in order to compare the two methods and to test the feasibility of the 4D voxel phantom methodology in general. We found that it is possible to produce a 4D voxel phantom very rapidly (i.e., <40 min on a 4-core personal computer for a 100-phase phantom) in a fully automated process. The dose calculation results showed that the constructed 100-phase 4D voxel phantoms provide cumulative-dose distributions very similar to those of the conventional 10-phase approach for stationary proton-beam irradiation. The passing rates of the dose distributions of the 4D voxel phantoms were higher than 99.9% according to the 3% and 3 mm gamma criteria, which results validate the 4D voxel phantom methodology. The point- and dose-tracking analysis data showed that the DRP method, which uses the minimal number of DIR operations but uses inverse DVFs, provides significantly better results than those of the DNP method, which uses only DIR to generate the DVFs for inter-phase image generation and dose registration. The present study also showed that the computation time does not significantly increase when the number of phases in the 4D voxel phantom is increased for more realistic representation of continuous respiratory motion; the only significant increase is in the memory occupancy, which grows almost linearly with the number of phases.</P>

Tl₂GdCl₅ (Ce³⁺): A New Efficient Scintillator for X-and <tex> $\gamma$</tex>-Ray Detection

Rooh, Gul,Khan, Arshad,Kim, H. J.,Park, H.,Kim, Sunghwan Professional Technical Group on Nuclear Science 2018 IEEE transactions on nuclear science Vol.65 No.8

<P>We are in the process of developing novel thallium-based inorganic halide compounds for X- and <TEX>$\gamma $</TEX>-ray radiation detections. In this paper, novel cerium-activated single crystals of Tl<SUB>2</SUB>GdCl<SUB>5</SUB> are reported along with a pure Tl<SUB>2</SUB>GdCl<SUB>5</SUB>. The two-zone vertical Bridgman method is used to grow this scintillator from its melt. Luminescence studies are performed under ultraviolet and X-ray excitations at room temperature. All of the Ce-activated samples exhibit similar emission bands in the range of 350–430 nm, with a peak around 388 nm, attributed to the <TEX>$5d~\to ~4f$</TEX> radiative transition of the Ce<SUP>3+</SUP> ion. In the pure sample, an intense luminescence band appeared owing to the presence of the Tl<SUP>+</SUP> ion in the host lattice, along with the typical Gd<SUP>3+</SUP> emission (~310 nm). Scintillation properties, such as energy resolution, light yield, and decay time, are evaluated under the <TEX>$\gamma $</TEX>-ray excitation. The scintillation properties vary with the Ce<SUP>3+</SUP>-concentration. The best performances are obtained for the 5-mol% Ce-activated crystal, which, under a 662-keV <TEX>$\gamma $</TEX>-ray excitation, exhibited an energy resolution of 5% (full-width at half-maximum) and light yield of 53 000 ± 5300 ph/MeV. Fast scintillation decay components followed by slow components are observed for all grown samples. The measured scintillation properties of Tl<SUB>2</SUB>GdCl<SUB>5</SUB>, which has high density and effective Z-number, reveal its large potentials as a radiation detector in medical imaging techniques.</P>

Programmable High Voltage Distribution for Photodetectors in a 1?mm Resolution Clinical PET System

Lau, Frances W. Y.,Vandenbroucke, Arne,Jung-Yeol Yeom,Reynolds, Paul D.,Hsu, David,Innes, Derek,Levin, Craig S. Professional Technical Group on Nuclear Science 2015 IEEE transactions on nuclear science Vol.62 No.5

<P>We present a scalable, cost-effective, and compact high voltage (HV) distribution design for a system that requires many HV channels for photodetector biasing. A digital-to-analog converter (DAC) with a 100 V output range is floated with its reference at -1800 V, providing outputs between -1800 V and -1700 V. As a consequence, the DAC control and power signals are referenced to -1800 V. This design was implemented in our 1 mm resolution clinical PET imaging system with detectors comprised of LYSO scintillation crystals coupled to position-sensitive avalanche photodiodes (PSAPDs). The programmable bias voltage outputs have only 20 m V<SUB>pp</SUB> of bias ripple. This design enables all PSAPDs to be biased at their optimal bias voltage, allowing us to achieve a standard deviation of only 2.3% in the energy resolution measured across all 512 PSAPDs in the subsystem.</P>

Influence of Total Ionizing Dose on Sub-100 nm Gate-All-Around MOSFETs

Joon-Bae Moon,Dong-Il Moon,Yang-Kyu Choi Professional Technical Group on Nuclear Science 2014 IEEE transactions on nuclear science Vol.61 No.3

<P>The influence of the total ionizing dose (TID) on sub-100 nm gate-all-around (GAA) MOSFETs is investigated through experiments and numerical simulations. Particularly, the TID effect is explored for various gate lengths and radiation doses. The radiation-induced charges and traps under the gate spacer result in changes of the device characteristics and is a dominant factor to cause the device degradation. This phenomenon is experimentally examined by the junction modification of GAA MOSFETs and supported by three-dimensional numerical simulations.</P>

Burnup Measurement of Spent Fuel Assembly by CZT-based Gamma-Ray Spectroscopy for Input Nuclear Material Accountability of Pyroprocessing

Hee Seo,Jong-Myeong Oh,Hee-Sung Shin,Ho-Dong Kim,Seung Kyu Lee,Hyun Su Lee,Se-Hwan Park Professional Technical Group on Nuclear Science 2014 IEEE transactions on nuclear science Vol.61 No.4

<P>Input nuclear material accountability is crucial for a pyroprocessing facility safeguards. Until a direct Pu measurement technique is established, an indirect method based on code calculations with burnup measurement and neutron counting for Cm-244 could be a practical option. Burnup can be determined by destructive analysis (DA) for final dispositive accuracy or by nondestructive assay (NDA) for near-real time accountancy. In the present study, an underwater burnup measurement system based on gamma-ray spectroscopy with the CZT detector was developed and tested on a spent fuel assembly. Burnup was determined according to the Cs-134/Cs-137 activity ratio with efficiency correction by Geant4 Monte Carlo simulations. The activity ratio as a function of burnup was obtained by ORIGEN calculations. The measured burnup error was 8.6%, which was within the measurement uncertainty. It is expected that the underwater burnup measurement system could fulfill an important role as a means of near-real time accountancy at a future pyroprocessing facility.</P>