共查询到20条相似文献,搜索用时 15 毫秒
1.
《核技术(英文版)》2016,(5):125-130
To obtain multiple monoenergetic neutron sources and realize the on-site calibration of radiation monitoring equipment for nuclear-involved places,the structural characteristics and neutron source features of D-T neutron tube were analyzed;Monte Carlo method was adopted to simulate the effect of interaction between typical materials and different energy neutrons;multilayered shielding materials were combined and optimized to acquire the optimal scheme to shield the neutron sources from the neutron tube.On the base,a tapered alignment filtration construction was designed and Monte Carlo method was employed to simulate the effect of alignment construction.The result showed that the tapered alignment filtration construction can create monoenergetic neutrons including14.1 MeV,0.18 MeV and thermal neutrons and demonstrated good monochrome performance which provides multiple monoenergetic sources for the on-site calibration. 相似文献
2.
In relation to the establishment of thermal neutron radiography as a measurement method with high accuracy and reliability, this paper reviewed the present status on the development of high-frame-rate neutron radiography with a steady thermal neutron beam and its application to multiphase flow researches. This review included also the present progress on the quantification of neutron radiographic image at Kyoto University, i.e. (1) quantitative method to measure void fraction of two-phase flow with thermal neutron radiography (Σ-scaling method), (2) influence of scattered neutrons on void fraction measured by neutron radiography, (3) measurement error of neutrons in a low neutron flux field, (4) error in void fraction measurement due to low gray level, and (5) measurement error due to low imaging speed Moreover, a new experimental approach on a total macroscopic cross section for thermal neutrons measurement by neutron radiography was presented. This paper revealed neutron radiography to be a promising visualization and measurement method in thermal hydraulic research. 相似文献
3.
4.
In order to achieve the goal of nuclear security, the neutron generator is used to image shielded nuclear material by non-destructive analysis method. In order to improve the imaging quality, it is necessary to collimate the slowed neutrons. In this paper, the Monte Carlo software Geant4 was used to theoretically model a new compact thermal neutron collimator based on gadolinium-doped silicate, and the thermal neutron transmittance and collimation ratio of the collimator were simulated and calculated. The calculation results will be used to guide the subsequent construction of neutron-based nuclear material imaging systems. 相似文献
5.
6.
Ismail. Shaaban 《Progress in Nuclear Energy》2010,52(6):569-572
A permanent epithermal neutron irradiation site was designed in the Syrian Miniature Neutron Source Reactor (MNSR) by using cadmium as a thermal neutron shielding material. This site was designed by Cd-shielding the internal surface of the outer aluminum tube of the FOIS (First Outer Irradiation Site) in the MNSR. The MCNP-4C calculations showed that, to have a permanent epithermal neutron irradiation site for the ENAA using the cadmium, it is necessary to add the top beryllium shims of the reactor to compensate for the reactivity losses due to the neutrons absorption in the cylindrical cadmium shell. The activation detectors were used to measure the thermal and epithermal neutron fluxes in the FOIS. Distribution of the thermal neutron flux along the vertical direction of the outer irradiation capsule used in the FOIS has been found using MCNP-4C code, and experimentally by irradiating five copper wires. Good agreements were obtained between the calculated and the measured results. 相似文献
7.
Veerle Cnudde Manuel Dierick 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2008,266(1):155-163
Fluid flow through porous natural building stones is of great importance when studying their weathering processes. Many traditional experiments based on mass changes are available for studying liquid transport in porous stones, such as the determination of the water absorption coefficient by capillarity. Because thermal neutrons experience a strong attenuation by hydrogen, neutron radiography is a suitable technique for the study of water absorption by capillarity in porous stones. However, image contrast can be impaired because hydrogen mainly scatters neutrons rather than absorbing them, resulting in a blurred image. Capillarity results obtained by neutron radiography and by the European Standard 1925 for the determination of the water absorption coefficient by capillarity for natural building stones with a variable porosity were compared. It is illustrated that high-speed neutron radiography can be a useful research tool for the visualization of internal fluid flow inside inorganic building materials such as limestones and sandstones. 相似文献
8.
9.
This paper is devoted to the determination of dosimetric characteristics of intermediate-energy neutrons. A calculation of the interaction of neutrons with paraffin for the normal incidence of an extended beam of neutrons in the energy interval from 100 ev to 1 Mev, which has been performed by means of an electronic computer, is given here. The computation results are used for calculating the components of the neutron tissue dose resulting from the moderation process in the tissue. The dose resulting from the neutron capture is calculated on the basis of the authors' data on the distribution of slow neutrons in paraffin and on neutron reflection from the surface of a hydrogenous medium. The depth distributions of neutron dose components for thermal neutrons and neutrons with energies of 100 ev, 1, 30, 240, 500 kev, and 1 Mev were obtained. The depth distributions of the biological dose for neutrons of the same energy and the biological dose values pertaining to the unit neutron flux were obtained. 相似文献
10.
11.
目前教科书中介绍的反应堆热中子有效增殖系数keff,是对无源中子的反应堆内的中子变化情况的准确定义及相应表达式的准确介绍,它能准确解释并描述中子在反应堆内六种物理过程中的变化情况。但用它作为一个统一的定义及表达式来描述并解释和计算有源中子存在的实际反应堆时,对于部分情况它既不能准确、清楚,又不能正确解释相应的物理过程,它的表达式也不能作为一个统一的表达式,按照它的定义计算得到相应的结果。且,目前,国内外工程研究人员还没有给出过实际反应堆内有源中子存在情况下的热中子有效增殖系数的定义及表达式。因此,特撰写此文,对考虑了源中子后的实际反应堆的热中子有效增殖系数,给出一个正确且准确的定义及相应表达式。 相似文献
12.
《Journal of Nuclear Science and Technology》2013,50(12):1138-1146
Five neutron guide tubes have been installed in the upgraded JRR-3 (Japan Research Reactor No. 3). Two of them are for thermal neutrons and the other three are for cold ones. The characteristic wavelength of the thermal neutron guide tubes is 2 Å, and those of the cold neutron guide tubes are 4 and 6 Å. The longest guide tube is 59.9 m long and the total length of guide tubes is 232.1 m. The beam sizes are 2 cm × 20 cm for the thermal neutron beams and 2 cm × 12 cm for the cold neutron beams. A curved part of the neutron guide is assembled by a polygonal approximation with use of 85 cm long straight units. The neutron mirrors of these units are made of natural Ni deposited borosilicate glasses. The Ni layer is about 2,000 Å in thickness. The mean fabrication error of guide tube units is 4 μm. The mean installation errors are 8 μm for the positional abutment error and 5 × 10?6 rad for the angular error. The neutron losses by these errors will be about 5%, and the neutron fluxes at the exits of the neutron guides are estimated to be about 2 × 108 n/cm2·s. 相似文献
13.
A. Mameli A. Fidanzio S. Cilla L. Grimaldi G. Giannini P. Totaro L. Azario 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2008,266(16):3656-3660
PhoNeS (photo neutron source) is a project aimed at the production and moderation of neutrons by exploiting high energy linear accelerators, currently used in radiotherapy. A feasibility study has been carried out with the scope in mind to use the high energy photon beams from these accelerators for the production of neutrons suitable for boron neutron capture therapy (BNCT). Within these investigations, it was necessary to carry out preliminary measurements of the thermal neutron component of neutron spectra, produced by the photo-conversion of X-ray radiotherapy beams supplied by three LinAcs: 15 MV, 18 MV and 23 MV. To this end, a simple passive thermal neutron detector has been used which consists of a CR-39 track detector facing a new type of boron-loaded radiator. Once calibrated, this passive detector has been used for the measurement of both the thermal neutron component and the cadmium ratio of different neutron spectra. In addition, bubble detectors with a response highly sensitive to thermal neutrons have also been used. Both thermal neutron detectors are simple to use, very compact and totally insensitive to low-ionizing radiation such as electrons and X-rays. The resultant thermal neutron flux was above 106 n/cm2s and the cadmium ratio was no greater than 15 for the first attempt of photo-conversion of X-ray radiotherapy beams. 相似文献
14.
15.
16.
《IEEE transactions on nuclear science》2005,52(4):966-971
It is shown that pulse-height spectra acquired from a high-pressure$hbox Xe+ ^3!hbox He$ gas ionization chamber exposed to mixed gamma-neutron radiation fields can be unfolded into separate gamma ray and thermal neutron spectra. The procedure takes advantage of the unique shape of the recently discovered spectral response of thermal neutrons in this high pressure$hbox Xe+ ^3!hbox He$ mixture. A template spectrum formed from only the pulse-height distribution of neutron signals is subtracted from the combined gamma and neutron spectrum to provide an estimate for the count of thermal neutrons. This procedure leaves a pure gamma spectrum for standard gamma ray spectrum analyses and isotope identification. 相似文献
17.
Variation of environmental neutron flux with altitude and depthof both water and soil 总被引:1,自引:0,他引:1
K.KOMURA N.K.AHMED A.H.EL-KAMEL A.M.M.YOUSEF 《核技术(英文版)》2004,15(4):248-256
Applying the extreme low-level y-ray spectroscopic analysis the environmental neutron flux is measured using different moderator construction and environment through the reaction ^197Au (n, γ) ^198Au- The contribution of thermal and resonance neutrons is separated using the cadmium difference technique, while fast neutrons are measured by the paraffin moderator. The results of altitude dependence of the neutron flux are discussed. The thermal neutron flux near the surface of sea water is less than its value at 100 cm over ground near sea water, while the value over the surfaces of fresh water is higher than that near the surface of sea water. Also the thermal neutron flux at 5 cm soil depth increases, then decreases to its original value at 10 cm depth and still constant until 25 cm, then decreases rapidly to reach 27% of its original value at 60 cm depth. The soil compositions, corresponding neutron temperatures and effective absorption cross sections of earth are the most effective factors on the equilibrium region of thermal neutrons in the ground. 相似文献
18.
《Journal of Nuclear Science and Technology》2013,50(1):11-17
The reactivity cbange due to increase in the radius of empty hole was measured in a D2O moderated reactor and some results differing from experiments with ZEEP were obtained. It can be concluded that the streaming in a hole is not so effective for reactivity. In measuring neutron flux in a void, a flat thermal neutron flux distribution was obtained and it has been concluded that the neutrons leaking through the empty hole or the void do not consist of thermal neutrons but fast neutrons for the most part. The experimental result of reactivity change due to the void location in the core indicates that the relation between the void location and the reactivity change is independent of the neutron flux distribution. 相似文献
19.
This work is concerned with the study of the distribution and attenuation of doses of thermal neutrons emitted directly from the core of 235U research reactor in ordinary concrete shields. In practice it is not possible to identify the reactor thermal neutrons in the emitted continous neutron spectrum, therefore, measurements were carried out by using a direct and cadmium filtered beam of reactor neutrons. All measurements were performed using Li2B4O7:Mn thermoluminescent dosimeters.The data obtained were analysed and the dose distributions of reactor thermal neutrons were evaluated. A group of isodose curves were constructed which give directly the shape and thickness of the shield required to attenuate the intensity of doses of reactor thermal neutrons to specific values. In addition, the thermal neutron relaxation lengths in ordinary concrete were derived for disc collimated beam and infinite plane monodirectional sources. 相似文献
20.
《Annals of Nuclear Energy》1999,26(13):1131-1157
The conceptual Fast Energy Amplifier, proposed by Rubbia et al. consists of a combination of a U-233/Th-232 fuelled fast-neutron subcritical facility with a proton accelerator. An intense beam of 1 GeV protons is injected into liquid lead at the core centre and drives the reactor by producing spallation neutrons. The burst of spallation neutrons produced by a single proton alters the basic neutron statistics which are well known for thermal neutrons in conventional nuclear reactors. A short assessment of standard neutron noise analysis methods is made with respect to monitoring neutron parameter data. 相似文献