Author: 馮家裕Publisher:
ISBN:
Category : Neutrons
Languages : en
Pages : 0
Book Description
Study of 3He Neutron Spectrometer with Bonner Spheres and Its Application in Low Background Environment
Author: 馮家裕Study of 3he Neutron Spectrometer with Bonner Spheres and Its Application in Low Background Environment
Author: Ka-Yu FungPublisher: Open Dissertation Press
ISBN: 9781361362204
Category :
Languages : en
Pages :
Book Description
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
Design of a Moderated Multidetector Neutron Spectrometer for Optimal Specificity
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Neutron spectrometry can play an important role in the detection and identification of neutron-emitting sources in various security applications. In the present work, a portable filtered array neutron spectrometer, consisting of twelve 6LiF-based thermal neutron detectors embedded within a single heterogeneous volume was designed and its expected performance compared to that of a commercially available 12-sphere Bonner spheres spectrometer. Each detector within the volume was designed to optimally respond to a unique portion of the neutron spectrum by varying the type and thickness of materials used to filter the spectrum as well as the thickness of the moderator in front of the detector. The available design space was permuted and performance metrics developed to identify the optimal geometries. The top performing detector geometries were then combinatorially explored to identify the best array of geometries that yielded the most information about a neutron spectrum. The best performing filtered array was found to provide as much spectral information as, or more than, the commercially available 12-sphere Bonner spheres spectrometer to which it was compared.
Nuclear Science Abstracts
Author: Applications of Bonner Sphere Detectors in Neutron Field Dosimetry
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The theory of neutron moderation and spectroscopy are briefly reviewed, and moderators that are useful for Bonner sphere spectrometers are discussed. The choice of the neutron detector for a Bonner sphere spectrometer is examined. Spectral deconvolution methods are briefly reviewed, including derivative, parametric, quadrature, and Monte Carlo methods. Calibration is then discussed. (LEW).
A Broad Spectrum Neutron Spectrometer Utilizing a High Energy Bonner Sphere Extension
Author: Eric A. BurgettPublisher:
ISBN:
Category : Neutrons
Languages : en
Pages :
Book Description
A novel broad spectrum neutron spectrometer has been created to extend the useful energy range of existing neutron Bonner Sphere Spectrometers (BSS). Both an active LiI(Eu) scintillator probe and passive gold foil detector were utilized to extend the energy response of the existing BSS. Above 20 MeV the energy structure for the standard polyethylene BSS are poor because the response functions are not unique. MCNPX was used to investigate several modifications to the BSS system which resulted in the Bonner Sphere Extension (BSE). This cost effective extension uses several concentric spheres of copper, lead, and tungsten heavy metal downscatter materials to extend the useful range of the current BSS from 20 MeV to above 1 GeV. Using both a 3" and 5" inner polyethylene spheres, aluminum shell sets were made with a 1" cavity and filled with the high Z materials for six total sets of spheres. a 12" and 8" polyethylene sphere were also milled to accept the heavy metal spheres. The system was validated at the Los Alamos Neutron Science Center (LANSCE) neutron beam. The system was calibrated at LANSCE for neutrons up to 800 MeV on target 4's 15 degree right flightpath (4FP15R) at 90 meters. Detailed models in MCNPX were made of the BSS, BSE and LANSCE facilities. Fine group responses were made and compared to the unfolded data from LANSCE. A vast improvement over the BSS system alone was seen with reasonable agreement with time of flight data measured at LANSCE and MCNPX calculated neutron spectra.
High Efficiency Neutron Spectrometer with Low Background
Author: A. V. ArzannikovNeutron Spectra Measurements with the Bonner Sphere Spectrometer
Author: David Joseph WhitfillPublisher:
ISBN:
Category :
Languages : en
Pages : 422
Book Description
Journal of Nuclear Science and Technology
Author: Publisher:
ISBN:
Category : Nuclear energy
Languages : en
Pages : 560
Book Description
Includes English abstracts from Japanese articles in Nihon Genshiryoku Gakkai Shi (Journal of the Atomic Energy Society of Japan).
A Study of Photoneutron Spectra Around High-energy Medical Linear Accelerators Using Monte Carlo Simulations and Measurements
Author: Robert MaglieriPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
"During high-energy radiotherapy treatments, neutrons are produced in the head of the linac through photonuclear interactions. This has been a concern for many years as photoneutrons contribute to the accepted, yet unwanted, out-of-field doses that pose an iatrogenic risk to patients and an occupational risk to personnel. Presently, in-room neutron measurements are difficult and time-consuming and have traditionally been carried out using Bonner spheres with activation foils and TLDs. In this work, a new detector, the Nested Neutron Spectrometer (NNS) is investigated for use in radiotherapy bunkers. It is designed for easy handling and is more practical than the traditional Bonner spheres providing a quicker and more efficient method to measure neutron spectra. Operated in current mode, the NNS was evaluated around a medical linear accelerator at the Montreal General hospital by: determining the performance, comparing with bubble detectors and comparing with Monte Carlo simulations.Firstly, the performance of the NNS was evaluated in high dose-rate environments. Reproducibility, linearity and dose-rate tests showed, with coefficient of variation less than 1%, that the NNS consistently reproduced the same raw measured data in each case. Secondly, equivalent doses measured by bubble detectors were compared with those measured by NNS. Absolute differences ranged from 1% in the treatment room to 50% in the maze. Finally, there was good overall agreement between Monte Carlo simulated and NNS measured spectra at various treatment room locations. Spectral characteristics were similar except for a discrepancy in the peak heights. These tests validate the use of the NNS in radiotherapy.Additionally, the NNS was used to measure neutron spectra around a new linear accelerator operated in flattening filter free (FFF) mode. Our measurements revealed a decrease in total fluence, neutron source strength and equivalent dose of approximately 35 - 40% across the treatment room for measurements in FFF mode compared with those made in flattening filter mode for the same number of MU." --