Browsing by Author "Lee, SH"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Application of an SOI microdosimeter for monitoring of neutrons in various mixed radiation field environments
    (Institute of Electrical and Electronics Engineers (IEEE), 2022-03-01) Pan, VA; Vohradsky, J; James, B; Pagani, F; Chartier, L; Debrot, E; Pastuovic, Z; Cutajar, D; Poder, J; Nancarrow, M; Pereloma, E; Bolst, D; Lee, SH; Inaniwa, T; Safavi-Naeini, M; Prokopovich, DA; Guatelli, S; Petasecca, M; Lerch, MLF; Povoli, M; Kok, A; Tran, LT; Rosenfeld, AB
    Radiation monitoring in space radiation is complex due to galactic cosmic rays (GCRs), solar particle events (SPEs), and albedo particles. Thermal neutrons are an important component in the Moon radiation albedo field which can cause single event upset (SEU) in electronics when they interact with the 10 B present in electronic components. In this work, we studied an application of silicon on insulator (SOI) microdosimeters for neutron monitoring in various mixed radiation field environments. A 10- μm SOI microdosimeter was utilized in conjunction with a 10 B 4 C thin-film converter to successfully measure the thermal neutron contribution out of field of a therapeutic proton beam as well as an 18-MV X-ray linear accelerator (LINAC). The microdosimeter was placed downstream of the Bragg peak (BP) as well as laterally out of field of the proton beam and at two positions along the treatment couch of the 18-MV LINAC. It was demonstrated that the 10- μm SOI microdosimeter with 10 B 4 C converter is suitable for detection of thermal neutrons with excellent discrimination of gamma, fast and thermal neutron components in the presence of a gamma-neutron pulsed field of an 18-MV LINAC. To reduce the gamma contribution and further improve detection of neutrons in mixed radiation fields, a new 2 μm Mushroom-planar microdosimeter was fabricated and characterized in detail using an ion beam induced charge collection (IBIC) technique with 1.78 MeV He2+ ions. It was demonstrated that this 2 μm SOI microdosimeter can be operated in a passive mode. The SOI microdosimeter with the 10 B 4 C converter can be recommended for the detection of thermal neutrons for SEU prediction in the mixed gamma-neutron fields during space missions, especially for the Moon mission.© Copyright 2025 IEEE
  • No Thumbnail Available
    Item
    Magnetic-field-induced instability of the cooperative paramagnetic state in ZnxCo(4-x)(OD)6Cl2
    (American Physcical Society, 2012-05-29) Dissanayake, SE; Chan, C; Ji, S; Lee, J; Qiu, Y; Rule, KC; Lake, B; Green, MA; Hagihala, M; Zheng, XG; Ng, TK; Lee, SH
    Using elastic and inelastic neutron scattering techniques with and without application of an external magnetic field H, the magnetic ground states of ZnxCo(4-x)(OD)6Cl2 (x = 0,1) were studied. Our results show that for x = 0, the ground state is a magnetic long-range ordered (LRO) state where each tetrahedron forms an "umbrella"-type structure. On the other hand, for x = 1, no static ordering was observed down to 1.5 K, which resembles the behavior found in the isostructural quantum system ZnxCo(4-x)(OD)6Cl2. When H field is applied, however, the x = 1 system develops the same LRO state as x = 0. This indicates that the x = 1 disordered state is in the vicinity of the x = 0 ordered state. © 2012, American Physical Society.
  • No Thumbnail Available
    Item
    Rational design of Li off-stoichiometric Ni-rich layered cathode materials for Li-ion batteries
    (Elsevier, 2022-11) Song, SH; Hong, S; Cho, M; Yoo, JG; Jin, HM; Lee, SH; Avdeev, M; Ikeda, K; Kim, J; Nam, SC; Yu, SH; Park, I; Kim, H
    The electrification trend in the automotive industry is fueling research on Ni-rich layered NCM cathode materials with high specific capacities. The simplest way to maximize the electrochemical performance of Ni-rich NCM is to tune the crystal structure by controlling the Li content and synthesis temperature. Herein, we demonstrate the critical roles of the Li content and synthesis temperature in determining the crystal structure of Li-excess Ni-rich NCM with enhanced electrochemical performance. The crystal structure of Li-excess Ni-rich NCM was systemically investigated using X-ray diffraction, neutron diffraction, and X-ray absorption spectroscopy, revealing that excess Li can be accommodated in Ni-rich NCM as the synthesis temperature decreases, resulting in stable cycle performance at high working voltage. We believe that our findings provide a rational reason for the excess amount Li required for optimization of the synthesis of Ni-rich NCM and offer insight for the simplest design of Ni-rich cathode materials that are stable under high-voltage operation. © 2022 Elsevier B.V.
  • No Thumbnail Available
    Item
    Ultra-low-level determination of 236U in IAEA marine reference materials by ICPMS and AMS
    (Elsevier, 2008-06) Lee, SH; Povinec, PP; Wyse, E; Hotchkis, MAC
    The development of analytical procedures for the measurement of ultra-low levels of U-236 in marine samples using high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and accelerator mass spectrometry (AMS) techniques are discussed and results are presented for IAEA reference materials-marine sediments (IAEA-135, 306, 384 and 385), marine biota (IAEA-134 and 414) and seawater (IAEA-381), collected in areas affected by nuclear reprocessing plants and nuclear weapons tests. The obtained minimum detection limit of the U-236/U-231 atom ratio was 1 x 10(-8) for AMS and 1 x 10(-6) for HR-ICPMS. © 2008, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Unravelling the nature of the intrinsic complex structure of binary‐phase Na‐layered oxides
    (Wiley, 2022-07) Paidi, AK; Park, WB; Ramakrishnan, P; Lee, SH; Lee, JW; Lee, KS; Ahn, H; Liu, T; Gim, J; Avdeev, M; Pyo, M; Sohn, JI; Amine, K; Sohn, KS; Shin, TJ; Ahn, D; Lu, J
    The layered sodium transition metal oxide, NaTMO2 (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium‐ion batteries (SIBs). Herein, an in‐depth phase analysis of developed Na1−xTMO2 cathode materials, Na0.76Ni0.20Fe0.40Mn0.40O2 with P2‐ and O3‐type phases (NFMO‐P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed‐phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first‐principles calculations support the evidence of the formation of a binary NFMO‐P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O′3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P‐ and O‐type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5–4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high‐voltage cathode materials for SIBs. © 1999-2024 John Wiley & Sons