kiwhan chung

Los Alamos National Laboratory, Nuclear Nonproliferation, Faculty Member

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Address: Los Alamos, New Mexico, United States

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Papers by kiwhan chung

Application of lanthanum halide scintillators and low-resolution dense plastics for modern MC&A needs

Recent developments in lanthanum halide scintillators and low-resolution dense plastics give brea... more Recent developments in lanthanum halide scintillators and low-resolution dense plastics give breadth to gamma-ray methods of nuclear material detection suitable for modern MC and A needs. Demanding goals for modernization of MC and A cover both portable and continuous on-line measurement applications that are quantitative for inventory/verification, and that serve those quantitative measurement needs plant-wide. Improved performance (sensitivity and reoslution) is important for portable applications in which a single detector must measure many types of materials. Budget is a major issue for continuous inventory measurements with hundreds or even thousands of detectors placed throughout a facility. Experimentally proven resolution of under 4% for 662 keV ¹³Cs gamma rays measured with large cerium-doped LaCl (lanthanum chloride) crystals set a new performance standard for versatile, efficient portable applications comparable in price to NaI(Tl), which has been dominant for decades. Wh...

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Mitigation of Outgas Effects in the Neutron-Capture /sup 6/Li Pulse-Mode Ionization Chamber Operation

IEEE Nuclear Science Symposium Conference Record, 2005, 2005

ABSTRACT When a novel neutron-capture lithium pulse-mode ionization chamber (LiPMIC) was designed... more ABSTRACT When a novel neutron-capture lithium pulse-mode ionization chamber (LiPMIC) was designed to replace He proportional counters as a more economical solution for some homeland security and counter-terrorism applications for large-scale, long-term remote sensors, this brought on a fundamental disadvantage of possibly exposing the ionization chamber to outgas effects from plastic detector components. The design of LiPMIC intends to reduce the outgas effects to a specified level for continuous operation by selecting the fill-gas mixtures where the electron dynamics do not vary within the range of outgas concentration. For example, Garfield simulation of electron transport properties inside LiPMIC indicates the convergence of electron drift velocity for a different concentration of methane between 0.06 and 0.09 V/cm/Torr. The sufficiently high drift velocity in this low electric field strength is characteristic of the Ar-CH4 mixture, since mixtures of argon and other hydrocarbon gas indicate a higher target range of electric field strength for stable drift velocity. The electron drift velocity between 4% and 15% of methane concentration remains within 20% in the said field strength range. The Garfield simulation data of LiPMIC of analytic geometry have shown that when this criterion is met, the outgas effect from HDPE and other outgassing detector parts inside the detector can be mitigated for continuous operation.

Large area neutron detector based on 6li ionization chamber with integrated bodymoderator of high density polyethylene

IEEE Symposium Conference Record Nuclear Science 2004., 2004

We describe the development of a large area neutron detector based on a pulse-mode ionization cha... more We describe the development of a large area neutron detector based on a pulse-mode ionization chamber lined with 6 Li foil in a low-cost housing of HDPE (High Density Polyethylene) that serves as the moderator. The use of inexpensive materials, technology for mass production and simple construction, which integrates the basic components of the sensor together, results in a substantial cost reduction. For a given sensor size, detection efficiency, or counting time, the proposed detector is expected to provide an order-of magnitude cost reduction compared to current neutron detection technology. This paper describes the detection concept including the optimization of the design using neutron transport calculations. It also gives experimental results on some prototype units using neutron and gamma sources. The properties affecting long term counting stability are discussed. An approach to reduce the effect of outgassing from the HDPE body is suggested.

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Large-Area Neutron Detector based on Li6 Pulse Mode Ionization Chamber

Prototypes of a Li-6 Pulse Mode Ionization Chamber (LiPMIC) have been in development for the past... more Prototypes of a Li-6 Pulse Mode Ionization Chamber (LiPMIC) have been in development for the past two years for the purpose of providing large-area neutron detector. this system would be suitable for remote deployment for homeland security and counterterrorism needs at borders, ports, and nuclear facilities. A prototype of LiPMIC is expected to provide a similar level of performance to the current industry-standard, He-3 proportional counters, while keeping the initial cost of procurement down by an order of magnitude, especially where large numbers of detectors are required. The overall design aspect and the efficiency optimization process is discussed. Specifically, the MCNP simulations of a single-cell prototype were performed and benchmarked with the experimental results. MCNP simulations of a three dimensional array design show intrinsic efficiency comparable to that of an array of He-3 proportional counters. LiPMIC has shown steady progress toward fulfilling the design expecta...

6Li foil scintillation sandwich thermal neutron detector

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011

Increasing needs for neutron detection and limited supply of 3He have led to the need for replace... more Increasing needs for neutron detection and limited supply of 3He have led to the need for replacement neutron detection technology. This paper presents the design and initial results for a neutron detector (6Li foil scintillator sandwich) that uses lithium metal foil to detect thermal neutrons. The reaction products, primarily triton, deposit most of their energy in thin scintillator films and

Measurement of Proton-Induced Delayed Neutron Cross-Sections at 800 and 4000 MeV

by kiwhan chung and Laurie Waters

Energetic proton beams are being used to explore delayed neutron emissions from a variety of mate... more Energetic proton beams are being used to explore delayed neutron emissions from a variety of materials in support of national security goals. To accomplish these goals it is necessary to have a firm understanding of the time structure of delayed neutrons emitted from the daughter nuclei of spallation, fragmentation, and fission interactions in structural and shielding materials as well as fissionable isotopes. Results of experiments conducted at Los Alamos National Laboratory (LANL) at 800-MeV and Brookhaven National Laboratory (BNL) at 4-GeV are presented. )

Progress Toward a Radon Detector Using Pulse-mode and Current-mode Ion Collection

Measurement Capabilities Matrices

Commercial Equipment Evaluation & Liason with Industry

Modern Analog Electronics for Safeguards Application

Muon Tomography for the Detection of Conventional Threats in Mass Transit

Muon Accelerator Study at Los Alamos

advanced charged Particle Radiography for SNM Detection

Pulse Shape Discrimination Properties of Neutron Sensitive Organic Scintillators

Development of a Reliable Fuel Depletion Methodology for the HTR-10 Spent Fuel Analysis

ABSTRACT

A range muon tomography performance study

Soft cosmic ray tomography has been shown to successfully discriminate materials with various den... more Soft cosmic ray tomography has been shown to successfully discriminate materials with various density levels due to their ability to deeply penetrate matter, allowing sensitivity to atomic number, radiation length and density. Because the multiple muon scattering signal from high Z-materials is very strong, the technology is well suited to the detection of the illicit transportation of special and radiololgical nuclear materials. In addition, a recent detection technique based on measuring the lower energy particles that do not traverse the material (range radiography), allows to discriminate low and medium Z-materials. We have demonstrated it first using Monte Carlo simulations. More recently, using a Mini-Muon Tracker developed at Los Alamos National Laboratory, we performed various experiments to try out the radiation length technology. This paper presents the results from real experiments and evaluates the likelihood that soft cosmic ray tomography may be applied to detect high-explosives.

Active Proton Interrogation for Homeland Security

Energetic proton beams may provide an attractive technology for active interrogation of nuclear t... more Energetic proton beams may provide an attractive technology for active interrogation of nuclear threats because: they have large fission cross sections, long mean free paths and high penetration, and proton beams can be manipulated with magnetic optics. We have measured time-dependent cross sections for delayed neutrons and gamma rays using 800 MeV protons from the Los Alamos Neutron Science Center and 4 GeV protons from the Brookhaven Alternating Gradient Synchrotron for a set of bare and shielded targets. The results show significant signals from both unshielded and shielded nuclear materials. Results will be presented. )

A capture-gated neutron calorimeter using plastic scintillators and 3He drift tubes

A segmented neutron calorimeter using nine 4-inch x 4-inch x 48-inch plastic scintillators and si... more A segmented neutron calorimeter using nine 4-inch x 4-inch x 48-inch plastic scintillators and sixteen 2-inch-diameter 48-inch-long 200-mbar-³He drift tubes is described. The correlated scintillator and neutron-capture events provide a means for n/ discrimination, critical to the neutron calorimetry when the background is substantial and the signals are comparable in amplitude to the neutron signals. A single-cell prototype was constructed

Measurement of Proton-Induced Delayed Neutron Cross-Sections at 800 and 4000 MeV

Active interrogation using energetic protons

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