High Efficiency Neutron Spectrometer with Low Background PDF Download

Author: A. V. Arzannikov
Publisher:
ISBN:
Category :
Languages : en
Pages : 15

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10

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A transportable fast neutron detection system has been designed and constructed for measuring neutron energy spectra and flux ranging from tens to hundreds of MeV. The transportability of the spectrometer reduces the detector-related systematic bias between different neutron spectra and flux measurements, which allows for the comparison of measurements above or below ground. The spectrometer will measure neutron fluxes that are of prohibitively low intensity compared to the site-specific background rates targeted by other transportable fast neutron detection systems. To measure low intensity high-energy neutron fluxes, a conventional capture-gating technique is used for measuring neutron energies above 20 MeV and a novel multiplicity technique is used for measuring neutron energies above 100 MeV. The spectrometer is composed of two Gd containing plastic scintillator detectors arranged around a lead spallation target. To calibrate and characterize the position dependent response of the spectrometer, a Monte Carlo model was developed and used in conjunction with experimental data from gamma ray sources. Multiplicity event identification algorithms were developed and used with a Cf-252 neutron multiplicity source to validate the Monte Carlo model Gd concentration and secondary neutron capture efficiency. The validated Monte Carlo model was used to predict an effective area for the multiplicity and capture gating analyses. For incident neutron energies between 100 MeV and 1000 MeV with an isotropic angular distribution, the multiplicity analysis predicted an effective area of 500 cm2 rising to 5000 cm2. For neutron energies above 20 MeV, the capture-gating analysis predicted an effective area between 1800 cm2 and 2500 cm2. As a result, the multiplicity mode was found to be sensitive to the incident neutron angular distribution.

Author: Chul Mo Kim
Publisher:
ISBN:
Category : Fast neutrons
Languages : en
Pages : 78

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Author: Ka-Yu Fung
Publisher: Open Dissertation Press
ISBN: 9781361362211
Category :
Languages : en
Pages :

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This dissertation, "Study of 3He Neutron Spectrometer With Bonner Spheres and Its Application in Low Background Environment" by Ka-yu, Fung, 馮家裕, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: A Bonner Sphere neutron spectrometer for low background environment was developed. The spectrometer consists of a 3He neutron detector, eight high density polyethylene spheres with size ranging from 5-inch to 12-inch and two Lead shells with thickness 1cm and 2 cm, which is used to increase the detect efficiency at high energy range. The dead time of the spectrometer is about 3.7 microseconds, which is mainly contributed by the extended TTL signal from the DAQ. The background of 3He detector is measured in CJPL which is the deepest underground laboratory in the world. The detector background is 15.50 10-4 8.1 10-5 counts per second. The responses of Bonner Spheres were obtained by Geant4 Monte Carlo simulation. The responses were verified by a 241AmBe neutron source in HKU. A genetic algorithm unfolding program(GA) was developed and tested by unfolding the 241AmBe neutron source. The background neutron in HKU Observatory was measured by the spectrometer and unfolded by GA s. The unfolded neutron flux is (56.84 6.01) 10-4 s-1 cm-1 by NSUGA version 3 and (56.43 2.53) 10-4 s-1 cm-1from NSUGA_FORTRAN. Another unfolding program "Equalizer" with different algorithm, by scaling a initial guess spectrum, was also used to unfold the background spectrum in HKU Observatory. The unfolded neutron flux from "Equalizer" is (51.69 2.79) 10-4 s-1 cm-1. The neutron flux from three unfolding programs agree with each other. The measurement was repeated in Daya Bay EH1 and the results were used to unfold the background neutron spectrum. The unfolded spectrum flux was (34.50 3.13) 10-5 s-1cm-1from NSUGA version 3, (35.13 1.45) 10-5 s-1cm-1 from NSUGA_FORTRAN. The unfolded neutron fluxes from GA s agree with each other. However the shape of spectra shows a chaotic pattern in low energy region. The unfolded neutron flux from "Equalizer" is (30.85 1.95) 10-5 s-1c m-1. The unfolding programs show a dominant thermal neutron peak, a tiny (α, n) peak and a small cosmic-ray neutron peak. The Bonner Spheres Spectrometer has flaws due to the geometry and the nature of unfolding process. Some ideas are suggested to minimize the effect from the error sources. DOI: 10.5353/th_b5334883 Subjects: Neutrons - Spectra

Author: S. S. Kapoor
Publisher: New Age International
ISBN: 9780852264966
Category : Neutron counters
Languages : en
Pages : 252

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Author: A. Burger
Publisher:
ISBN:
Category :
Languages : en
Pages : 4

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Cryogenic microcalorimeter detectors operating at temperatures around {approx}0.1 K have been developed for the last two decades, driven mostly by the need for ultra-high energy resolution (0.1%) in X-ray astrophysics and dark matter searches [1]. The Advanced Detector Group at Lawrence Livermore National Laboratory has developed different cryogenic detector technologies for applications ranging from X-ray astrophysics to nuclear science and non-proliferation. In particular, we have adapted cryogenic detector technologies for ultra-high energy resolution gamma-spectroscopy [2] and, more recently, fast-neutron spectroscopy [3]. Microcalorimeters are essentially ultra-sensitive thermometers that measure the energy of the radiation from the increase in temperature upon absorption. They consist of a sensitive superconducting thermometer operated at the transition between its superconducting and its normal state, where its resistance changes very rapidly with temperature such that even the minute energies deposited by single radiation quanta are sufficient to be detectable with high precision. The energy resolution of microcalorimeters is fundamentally limited by thermal fluctuations to {Delta}E{sub FWHM} {approx} 2.355 (k{sub B}T{sup 2}C{sub abs}){sup 1/2}, and thus allows an energy below 1 keV for neutron spectrometers for an operating temperature of T {approx} 0.1 K . The {Delta}E{sub FWHM} does not depend on the energy of the incident photon or particle. This expression is equivalent to the familiar (F{var_epsilon}E{sub {gamma}}){sup 1/2} considering that an absorber at temperature T contains a total energy C{sub abs}T, and the associated fluctuation are due to variations in uncorrelated (F=1) phonons ({var_epsilon} = k{sub B}T) dominated by the background energy C{sub abs}T” E{gamma}. The rationale behind developing a cryogenic neutron spectrometer is the very high energy resolution combined with the high efficiency. Additionally, the response function is simple and the instrument is transportable. We are currently developing a fast neutron spectrometer with 0.1% energy resolution at 1 MeV neutron energy with an efficiency of 1%. Our fast-neutron spectrometers use boron-based and {sup 6}LiF absorber crystals with Mo/Cu thermistors readout. They have achieved an energy resolution of 5.5 keV FWHM for 2.79 MeV deposited in {sup 10}B by thermal neutron capture (fig. 1), and 46 keV FWHM for fast (MeV) neutrons absorbed in {sup 6}LiF (fig. 2). Since the energy resolution does not depend on the neutron energy, we expect a similar energy resolution for MeV neutron energies. The response function is given simply by the cross section of the capture reaction, offset from zero by the Q-value of the capture reaction. This allows straightforward discrimination against gamma-events, most of which deposit less that Q{sub 6Li} = 4.79 MeV in the {sup 6}LiF absorber, and easy deconvolution of the neutron spectrum, since there is only a single capture reaction in {sup 6}Li and the spectrum is not affected by edge effects or geometric broadening. The current challenge for microcalorimeters is their necessarily small effective pixel area, {approx}1cm{sup 3} for neutron spectrometer pixels, and their slow decay time, {approx}10ms for neutron spectrometers. The pixel size is limited by the requirement for low Cabs for high energy resolution; the decay time is set by the intrinsically weak thermal coupling between materials at low temperatures. Both issues can be addressed by fabricating large detector arrays. This will enable high-precision neutron spectrometry with high statistics, such as simulated for Pu analysis in fig 3.

Author: G. V. Muradian
Publisher:
ISBN:
Category :
Languages : en
Pages : 8

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Author: Lucy-Ann McFadden
Publisher: Elsevier
ISBN: 0080474985
Category : Science
Languages : en
Pages : 987

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Long before Galileo published his discoveries about Jupiter, lunar craters, and the Milky Way in the Starry Messenger in 1610, people were fascinated with the planets and stars around them. That interest continues today, and scientists are making new discoveries at an astounding rate. Ancient lake beds on Mars, robotic spacecraft missions, and new definitions of planets now dominate the news. How can you take it all in? Start with the new Encyclopedia of the Solar System, Second Edition.This self-contained reference follows the trail blazed by the bestselling first edition. It provides a framework for understanding the origin and evolution of the solar system, historical discoveries, and details about planetary bodies and how they interact—and has jumped light years ahead in terms of new information and visual impact. Offering more than 50% new material, the Encyclopedia includes the latest explorations and observations, hundreds of new color digital images and illustrations, and more than 1,000 pages. It stands alone as the definitive work in this field, and will serve as a modern messenger of scientific discovery and provide a look into the future of our solar system.· Forty-seven chapters from 75+ eminent authors review fundamental topics as well as new models, theories, and discussions· Each entry is detailed and scientifically rigorous, yet accessible to undergraduate students and amateur astronomers· More than 700 full-color digital images and diagrams from current space missions and observatories amplify the chapters· Thematic chapters provide up-to-date coverage, including a discussion on the new International Astronomical Union (IAU) vote on the definition of a planet· Information is easily accessible with numerous cross-references and a full glossary and index

Author: Janice L. Bishop
Publisher: Cambridge University Press
ISBN: 110718620X
Category : Language Arts & Disciplines
Languages : en
Pages : 655

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Comprehensive overview of the spectroscopic, mineralogical, and geochemical techniques used in planetary remote sensing.

Author: W. Brown
Publisher:
ISBN:
Category : Helium
Languages : en
Pages : 74

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