共查询到19条相似文献,搜索用时 67 毫秒
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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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一种新的灵敏核探针——慢正电子束流装置 总被引:1,自引:0,他引:1
简要介绍了广泛应用于表面科学的灵敏核探针——慢正电子束设备的原理、构造和应用 ,阐述了北京慢正电子束流装置的设计原理和性能 ,讨论了北京慢正电子束流装置今后的研究前景. A novel and compact slow positron beam line——Beijing Slow Positron Beam Line was described. The basic physical concepts of the slow positron beam and its applications were reviewed. Recent experimental results showed the converting effcicency for the total positrons from the radioisotope to slow positrons was 8×10 -5 and the moderation efficiency was 1.7×10 -4 . The future development of Beijing Intense Slow Positron Beam, based on the BEPC LINAC, was also briefly discussed. 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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针对基于北京正负电子对撞机的慢正电子强束流系统对输运磁场的设计要求,本文对不同规格的磁场输运线圈模型、长螺线管端口处磁场的补偿以及地磁场和弯管道对正电子束流的影响等进行了计算,提出适用于本系统传输慢正电子束流的输运磁场分布、补偿线圈、调整线圈的加工参数,计算表明,系统的总体磁场不均匀度小于10髎.实际运行束流测试表明,所设计的磁场系统能够很好的将慢正电子束流输运到约16m远的样品测量室,慢正电子束斑尺寸基本没有变化,满足慢正电子束流系统的设计要求. 相似文献
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在慢正电子束研究表面的实验中,一般仍使用高纯Ge γ谱仪测量正电子湮没多普勒展宽能谱,对能谱的分析采用线形参数S,W,这些参数提供的信息有限. 例如,当电子与正电子在材料中形成电子偶素时,简单的线形参数非但不能表征它们,反而因它们的存在使得分析变得复杂. 本工作在对多普勒展宽能谱进行数据处理的过程中,引入正态电子偶素自衰变强度I3γ参数,建立了从能谱中获得I3γ参数值的方法. 以标准样品为基准,选用Ag盖帽的气凝硅胶进行I3γ参数计算,工作表明新参数对研究介孔材料及纳米薄膜能提供更丰富的信息. 相似文献
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利用射频磁控溅射方法制备了低介电常数材料多孔非晶SiOx薄膜,溅射压强从1Pa—3Pa变化,傅立叶变换红外吸收光谱测行x的范围为1≤x≤1.6.同步辐射X射线反射(XRR)测量结果显示了随着溅射压强的增大,薄膜的孔隙率(体积比)从6%上升到24%,同时估计了薄膜的厚度.慢正电子湮没多普勒展宽测量探测了薄膜中的缺陷分布信息,结果显示随着溅射压强的增加,薄膜中的E'中心缺陷增加,其抑制了电子偶素的生成,从而使S参数呈下降趋势,利用VEPFIT程序对正电子湮没结果进行了拟合,得到的膜厚与XRR结果较为接近. 相似文献
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WANG Ping MA Yan-Yun QIN Xiu-Bo ZHANG Zhe CAO Xing-Zhong YU Run-Sheng WANG Bao-Yi 《中国物理C(英文版)》2008,32(3)
The Beijing intense slow positron beam facility is based on the 1.3 GeV linac of Beijing ElectronPositron CoUider (BEPC) aiming to produce mono-energetic intense slow positron beam for material science investigation. The plugged-in 22Na based slow positron beam section has been newly constructed to supply continuous beam time for the debugging of positron annihilation measurement stations and improve the Beijing intense slow positron beam time using efficiency. Performance testing result of the plugged-in 22Na based slow positron beam facility are reviewed in this paper, with the measurement of the beam transport efficiency, the view of beam spot, the adjustment of beam position, the measurement of beam intensity and energy spread etc. included. 相似文献
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Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source. 相似文献
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WANG Bao-Yi MA Yan-Yun WANG Ping CAO Xing-Zhong QIN Xiu-So ZHANG Zhe YU Run-Sheng WEI Long 《中国物理C(英文版)》2008,32(2)
This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components.The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper,a prebuncher and a buncher has been constructed in order to meet the needs of materials science development.At present,the time resolution of the VEPLS can easily reach about 386 ps with a peak-to-background ratio of about 600:1.A plugged-in 22Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed.A slow positron beam with an intensity of 2.5x105 e+/s and the beam profile whose diameter is 10 mm has been obtained;the moderation efficiency of the tungsten mesh moderator reaches 5.1x 10-4 as calculated with an original positron source activity of 52 mCi. 相似文献
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Bangyun Xiong Xiuqin Tang Chunqing He Hui Cao Jingpei Huo Jie Luo Haiying He 《Chinese Journal of Physics (Taipei)》2018,56(1):355-361
Tunable mesoporous titania (TiO2) thin films were synthesized via a sol-gel method using an amphiphilic triblock copolymer F38 as the structural template. The dependence of crystalization, pore morphology and interconnectivity of TiO2 films on the weight ratio of F38 was studied by wide-angle X-ray diffraction, field emission scanning electron microscopy and Doppler broadening of positron annihilation radiation spectroscopy based on a slow positron beam. By loading more F38, the crystallization of TiO2 films is enhanced, accompanied by a decrement in oxygen vacancies/grain boundaries. Smaller and isolated mesopores are formed in the films prepared with F38 less than 15?wt%. The pore percolation occurs when the weight ratio of F38 is up to 20?wt% and larger and interconnected worm-like pores are formed. 相似文献
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A new slow pulsed positron beam, including a positron source, a moderator, a chopper, a pre-buncher, a main-buncher and a sample chamber, etc, has been installed and tested. It is necessary to simulate the acceleration, transportation and space focusing of positrons to meet the needs of beam debugging and further positron annihilation experiments. The result from SIMION simulations shows that the radius of the focused positron beam is less than 5 mm, which is further confirmed in our practical debugging process. 相似文献
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This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components.
The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper, a prebuncher and a buncher has been constructed in order to meet the needs of materials science development. At present, the time resolution of the VEPLS can easily reach about 386ps with a peak-to-background ratio of about 600:1. A plugged-in 22Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed. A slow positron beam with an intensity of 2.5×105e+/s and the beam profile whose diameter is 10mm has been obtained; the moderation efficiency of the tungsten mesh moderator reaches 5.1×10-4 as calculated with an original positron source activity of 52mCi. 相似文献
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Chunqing He Makoto Muramatsu Atsushi Kinomura Kenji Ito 《Applied Surface Science》2006,252(9):3221-3227
Positron annihilation lifetime spectra were measured for mesoporous silica films, which were synthesized using triblock copolymer (EO106PO70EO106) as a structure-directing agent. Different positron lifetime spectra for the deposited and calcined films indicated the formation of meso-structure after calcination, which was confirmed by Fourier transform infrared (FTIR) spectra and field emission-scanning electron microscopy (FE-SEM) observation. Open porosity or pore interconnectivity of a silica film might be evaluated by a two-dimensional positron annihilation lifetime spectrum of an uncapped film. Pore sizes and their distributions in the silica films were found to be affected by thermal treatments. 相似文献
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An intense slow positron beam using a 15 MeV LINAC (average current 1.25 × 1015 e−/s) at the Radiation and Photochemistry Group, Chemistry Division of Argonne National Laboratory (ANL) has been proposed and studied. Computer simulated results optimizing the positron yield and distribution of energy and angle show that a slow positron production at 1010 e+/s is possible. A proposed design of an intense slow positron beam with optimal conditions of incident electron, converter/moderator configurations, and extraction/transportation is presented. 相似文献