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1.
研究堆慢正电子源是获得高强度慢正电子束流的有效方式,国际上己建成多座装置并获得广泛应用.与常规同位素慢正电子源相比,研究堆慢正电子源的物理过程复杂,影响末端束流强度的因素众多,对其进行深入研究与合理建模是未来在中国绵阳研究堆(CMRR)上构建慢正电子源的基础.本文厘清了研究堆慢正电子产生的关键过程与物理机理,建立了预测末端正电子束流强度的理论模型,找到了影响其末端强度的主要物理量:快正电子体产生率、慢化体有效表面积、慢化体扩散距离、慢正电子从表面被提取到靶环末端的效率、及束流系统提取效率.用多种实验结果对模型进行校验,包括多个同位素慢正电子源的效率测量值,以及PULSTAR研究堆慢正电子源测量结果,充分验证了模型正确性.根据模型对各物理量的影响因素进行了分析,找到了需着重关注的影响因素,对未来源/靶结构的设计给出建议. 相似文献
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正电子湮没技术是一种研究材料的微观缺陷和相变的灵敏工具,在通常的正电子谱仪中,正电子能量为MeV量级,在样品中注入深度比较学(-100μm),主要研究材料体内的平均缺陷密度,慢正电子束方法把正电子的能量降低为keV量级(而且可以调节),注入比较浅(-μm),所以是研究表面缺陷的探测手段,正电子慢化体是产生慢正电子的关键设备,对其研究有重要意义,文章综述了慢化体研究的历史和现状,从物理概念出发介绍使正电子慢化的四种可能方法和当今慢化体的五种几何排列方法,其中应用最广泛的是钨慢化体和百叶窗式的排列方式,效率最高的是惰性气体固体慢化体,而加电场慢化体是有待开发的高效慢化体。 相似文献
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综述了慢正电子技术的发展以及从放射源β衰变发射出的慢正电子的慢化原理,概述了利用慢正电子技术研究固体薄膜表面和界面的基本原理和方法,并讨论了慢正电子束技术在固体薄膜表面和界面研究中的应用。 相似文献
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综述了慢正电子束技术的发展以及从放射源衰变发射出的慢正电子的慢化原理,概述了利用慢正电子束技术研究固体薄膜表面和界面的基本原理和方法,并讨论了慢正电子束技术在固体薄膜表面和界面研究中的应用。 相似文献
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《中国科学院高能物理研究所年报》2003,(1):139-155
北京慢正电子强束流依托于北京正负电子对撞机(BEPC)电子直线加速器(LINAC),利用其完成注入后的剩余时间,产生高强度、高亮度、低能单色正电子束流,应用于材料科学尤其是材料表面特性的研究。该装置的建成弥补了我国现有的基于放射性同位素的慢正电子束流装置正电子强度较弱的不足,拓展了慢正电子技术在材料科学和微观核探针方法学中的应用领域,为进一步建立慢正电子湮没寿命测量、正电子诱导俄歇电子能谱测量以及低能正电子衍射和正电子显微镜等方法奠定了基础。 相似文献
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低能单色正电子束装置的原理、研制及应用 总被引:1,自引:0,他引:1
简要介绍了一种新的灵敏核探针--低能单色正电子(慢正电子)束流装置的原理及应用。同时介绍了北京慢正电子束流装置的建设进展情况。 相似文献
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Measurements were made on a low-energy positron beam apparatus in an attempt to increase the efficiency of the slow positron yield from radioisotopes. A study was made to sweep thermalized positrons to the surface of a silicon wafer with an applied electric field at 298 and 140 K. Temperature studies were also made on more conventional Pt and Pt+MgO powder moderators and the results are discussed. The role of the MgO powder has been clarified, though fundamental questions remain. The positron apparatus beam and relevant information regarding sources, temperature and magnetic fields are discussed in sufficient detail so that such a slow positron beam utilizing a “conventional” slow positron moderator could be easily duplicated for use in solid state studies. 相似文献
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V. D. Anan’ev A. A. Belyakov M. V. Bulavin A. E. Verkhoglyadov S. A. Kulikov K. A. Mukhin E. P. Shabalin 《Technical Physics》2014,59(2):283-286
The first criticality of a new KZ-202 neutron moderator on the IBR-2M reactor is achieved. The moderator consists of thermal and cold units. The former is a room-temperature comb water moderator; the latter, a moderator using a mixture of aromatic hydrocarbons (mesitylene and m-xylene). The cold moderator is filled with granules of this mixture, which are supplied by a cold helium flow, and operates at 30 K. The combination of two units in one moderator makes it possible to simultaneously take the thermal and cold neutron spectra for extracted-beam spectrometers. The arrangement of the thermal and cold moderators is numerically optimized by the Monte Carlo method. The use of the cold moderator allows a 13-fold increase in the cold neutron intensity from its surface. 相似文献
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M. V. Bulavin R. N. Vasin S. A. Kulikov T. Lokaichek D. M. Levin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2016,10(4):677-686
A unique cold moderator based on a mixture of mesitylene and m-xylene is developed for the IBR-2 pulsed reactor. If combined with a standard warm-water moderator, it provides a high neutron flux in a wide wavelength range. The advantages of the use of this composite moderator in neutron-diffraction texture analysis are discussed using the example of a sample of slate (formed from five minerals) studied using the SKAT diffractometer. The diffraction data obtained in experiments with warm-water and composite moderators are compared. 相似文献
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《Radiation measurements》2007,42(2):241-244
Performance of a prompt gamma ray neutron activation analysis (PGNAA) setup depends upon thermal neutron yield at the PGNAA sample location. For a moderator, which encloses a sample, thermal neutron intensity depends upon the effective moderator volume excluding the void volume due to sample volume. A rectangular moderator assembly has been designed for the King Fahd University of Petroleum and Minerals (KFUPM) PGNAA setup. The thermal and fast neutron yield has been measured inside the sample cavity as a function of its front moderator thickness using alpha particle tracks density and recoil proton track density inside the CR-39 nuclear track detectors (NTDs). The thermal/fast neutron yield ratio, obtained from the alpha particle tracks density to proton tracks density ratio in the NTDs, shows an inverse correlation with sample to moderator volume ratio. Comparison of the present results with the previously published results of smaller moderators of the KFUPM PGNAA setup confirms the observation. 相似文献
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The effect of the time of flight of neutrons escaping from the moderator on the measured time dependence of the neutron density, which in turn serves for determining the decay constant , has been analyzed. The measured values of a have been found to vary considerably with the distance of the detector from the moderator and also with its size described by the bucklingB
2. Measurement with light water and loose diphenyl has shown that the deviation in depends also on the type of moderator.The authors would like to thank Mr. J. Jirou and Mr. J. Jadavan for their collaboration in the measurements and for maintaining the electronic apparatus and the accelerator as well. The authors also acknowledge the help of Dr. M. Nepraová in preparing the computer programme. 相似文献
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A novel method is proposed for the efficient conversion of intermediate energy negative muons into a low-energy muon beam. It is based on using an electric field to eject muons from a moderator consisting of a large number of thin carbon foils placed perpendicularly to the axis of a high-field solenoid. High-energy muons are made to slow down within the moderator to an energy where further slowing down is inhibited by the electric field acceleration between the foils. The muons accumulate at low energy within the moderator hopping from one foil to the next until they come out as a low-energy muon beam. The resulting phase compression factor exceeds 1000. Efficient initial injection of the muons into the moderator is obtained either by letting the muons enter it in a direction opposite to the acceleration force or by producing the muons within a magnetic trap containing the moderator. A practical configuration based on the second scheme is presented. By implementing the method into the most intense muon production configurations a new pathway is opened that may ultimately compete with other schemes in the selection of the optimal source for high-energy muon colliders. 相似文献
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A. I. Kuklin A. D. Rogov Yu. E. Gorshkova P. K. Utrobin Yu. S. Kovalev A. V. Rogachev O. I. Ivankov S. A. Kutuzov D. V. Soloviov V. I. Gordeliy 《Physics of Particles and Nuclei Letters》2011,8(2):119-128
The results of experimental and computer-modeling investigations of neutron spectra and fluxes obtained with cold and thermal
moderators at the IBR-2 reactor (Joint Institute for Nuclear Research (JINR), Dubna) are presented. These studies are for
the YuMO small-angle neutron scattering (SANS) spectrometer (IBR-2 beamline 4). The neutron spectra have been measured for
two methane cold moderators for the standard configuration of the SANS instrument. The data from both moderators under different
conditions of their operation are compared. The ratio of experimentally determined neutron fluxes of cold and thermal moderators
is shown at different wavelengths. Monte Carlo simulations have been carried out to determine the spectra for cold-methane
and thermal moderators. The results of calculations of the ratio of neutron fluxes of cold and thermal moderators at different
wavelengths are demonstrated. In addition, the absorption of neutrons in the air gaps on the way from the moderator to the
investigated sample is presented. SANS with the protein apoferritin was done with both cold methane and a thermal moderator
and the data were compared. The prospects for the use of a cold moderator for a SANS spectrometer at IBR-2 are discussed.
The advantages of using the YuMO spectrometer with a thermal moderator with respect to the tested cold moderator are shown. 相似文献
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The performance of the upstream moderator for neutron beams 1, 4, 5, 6, and 9 extracted from the IBR-2 reactor is simulated towards selecting its optimum configuration. For different moderator options, gain factors with respect to the existing comb-shaped water moderator are computed. Taking into account the technological issues in manufacturing a combined moderator, the scheme with optimal physical characteristics is selected. 相似文献
19.
Liangxing Li Huixiong Li Takeshi Kawai Tingkuan Chen Qincheng Bi 《Physica B: Condensed Matter》2008,403(12):2036-2042
The mathematical model developed in a previous paper is improved in the present paper for analyzing and evaluating the void fraction profiles in the crescent-shape moderator cell of the Cold Neutron Source (CNS) of the China Advanced Research Reactor (CARR) which is now under construction in the China Institute of Atomic Energy (CIAE). The model is then applied to the case of the CARR-CNS with liquid hydrogen as a moderator and the void fraction in the crescent-shape moderator cell of the CARR-CNS is evaluated. The calculation results show that the void fraction in the crescent-shape moderator cell less than 20%. The model and the calculation results will help to obtain insight of the mechanism that controls the void fraction distribution in the crescent-shape moderator cell, and provide theoretical supports for the moderator cell construction. 相似文献
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We present a method of calculating the current of very cold neutrons emerging from a cold moderator applicable to any moderator whose spectral density is known. Results are shown for a hydrogenous moderator with a Debye spectrum. 相似文献