pA级弱电子流的获取及测量研究

介绍了利用电子加速器进行内带电地面模拟试验研究的关键部分——弱束流的获取及测量方法研究。电子束在通过微孔板散射后得到了弱束流,并用法拉第筒进行了测量,得到了地面模拟试验需要的pA级的弱束流。     

中国散裂中子源(CSNS)LRBT输运线真空系统

中国散裂中子源(CSNS)质子加速器由产生能量为80Me V的负氢离子直线加速器、直线加速器到环(LRBT)和环到靶(RTBT)的束流输运线、以及积累和加速质子束到1.6Ge V的快循环同步环(RCS)组成,而总长约200米的LRBT段是该加速器的重要组成部分。本文介绍LRBT段真空系统,包括总体布局设计,物理需求,真空参数,关键设备,安装和调试工作;目前,LRBT动态真空在打靶功率50k W时优于2×10~(-6)Pa,满足物理需求,各非标真空设备、真空获得及测量设备等经过2年半的长期运行,稳定可靠无故障。     

重离子激发解吸测试装置设计与调试

束流与真空管壁碰撞后从腔体表面解吸出一定数量的分子和离子, 解吸出的粒子使加速器系统的真空度下降, 进而会影响束流的寿命。在重离子加速器中, 为了降低动态真空对束流的影响, 需找出一种低解吸率材料作为准直器镀膜材料。因此, 不同材料的解吸率测量已成为重离子加速器真空系统设计的关键所在。本文首先介绍了基于中科院近代物理研究所320 k V高电荷态离子综合研究实验平台设计的解吸率测量装置, 并利用Molflow+真空分析软件计算了该测试装置的静态真空分布。其次以无氧铜为测试靶材进行了解吸率实验研究, 得出了束流轰击靶材时动态真空变化的趋势, 同时计算了无氧铜在不同能量和不同流强Xe¹⁰⁺和O⁺束流作用下的解吸率和相对应的电子能损。结果表明粒子解吸引起的动态真空变化较明显, 无氧铜解吸率随着入射束流能量的增加而增加, 而且在长时间束流作用时会出现束流清洗效应, 即解吸出的粒子在束流长时间轰击下逐渐减少。电子能损的平方和解吸率成正比例关系, 与相关文献的结论一致, 说明实验装置运行稳定, 获得的数据具有一定的参考意义。     

NSRL储存环真空系统

国家同步辐射实验室储存环超高真空系统自建成至今已稳定运行了 10年。储存环正常运行时 ,在储存能量 80 0 Me V时储存流强 2 0 0 m A的束流寿命已超过 6 0 0 min。 NSRL正在进行的二期工程 ,要求光源性能有进一步的提高和改善 ,机器达到长期、稳定、可靠运行。为了达到储存环能量 80 0 Me V时储存流强 30 0 m A时的束流寿命 6 0 0 min以上 ,有必要对现有的环真空系统进行改造。本文详细分析了 NSRL真空系统的现状和存在的问题 ,根据光源改造对真空系统的要求 ,提出了具体措施和改进方案     

SC200超导质子回旋加速器束流传输真空系统及控制设计北大核心CSCD

束流传输系统真空是合肥超导质子医疗设备(SC200)的重要技术保障。研究束流传输系统真空对有效保证束流传输环境和束流最终品质,使束流在合理的偏差范围内到达治疗终端有着重要作用。SC200输运线上二极铁、四级铁、校正铁、束流阻断器和束测等部件分布密集,局部机械空间紧张。在此设计输入下,束流传输系统的真空部件和真空管结构既要有利于束流传输的品质,又要确保机械安装空间和后期设备维护的便利性。SC200超导质子回旋加速器束流传输真空系统总长约65 m,动态真空要求优于5×10^-4 Pa(局部可降低为5×10^-3 Pa)。研究结果表明,SC200超导质子回旋加速器束流传输系统真空设计满足设计输入要求。     

耦合系数和束流强度对驻波加速器性能的影响和耦合系数的测量

根据加速器和微波谐振腔的基本理论,采用微波电路理论,分析和计算了驻波加速器输入波导和加速腔之间的耦合系数和束流强度对能量、束流功率、效率和X射线辐射强度等性能的影响。当耦合系数大于1时,随着耦合系数增加,加速器最大输出能量下降。随着加速器束流强度增加,加速器能量V_s降低。对于给定的束流强度,随着耦合系数增加,加速器输出能量、电子注束流功率和X射线的辐射强度存在最大值。为了使加速器获得最佳性能,确定和测量耦合系数十分重要。论文在大功率速调管输出电路的外观品质因子测试方法的基础上,针对不同耦合系数,推导出了驻波加速管的外观品质因子、固有品质因子与加速管输入端处的群延迟和驻波比的相互关系,建立了相应的测试方法。采用矢量网络分析仪,通过测量加速管输入端的群延迟和驻波比,可测得耦合系数等相关参数,该方法已在实验中获得了验证。     

SC200超导质子回旋加速器束流传输真空系统及控制设计

束流传输系统真空是合肥超导质子医疗设备(SC200)的重要技术保障。研究束流传输系统真空对有效保证束流传输环境和束流最终品质,使束流在合理的偏差范围内到达治疗终端有着重要作用。SC200输运线上二极铁、四级铁、校正铁、束流阻断器和束测等部件分布密集,局部机械空间紧张。在此设计输入下,束流传输系统的真空部件和真空管结构既要有利于束流传输的品质,又要确保机械安装空间和后期设备维护的便利性。SC200超导质子回旋加速器束流传输真空系统总长约65 m,动态真空要求优于5×10^-4 Pa(局部可降低为5×10^-3 Pa)。研究结果表明,SC200超导质子回旋加速器束流传输系统真空设计满足设计输入要求。     

不锈钢的同步辐射光致脱附

电子储存环真空室壁及相连光束线的同步辐射光致脱附 (PSD)严重影响着束流质量和寿命。不锈钢是加速器真空室最常用的材料 ,合肥光源的真空系统即为不锈钢结构。合肥光源在B6a光出口建立了PSD光束线 ,选用长 12 1cm ,内径8 6cm的 30 4L不锈钢真空室作为首件样品 ,用于测试不锈钢不同表面状态的脱附情况 ,结果表明经辉光放电处理的表面脱附系数最低。     

原子能院自由电子激光器真空系统

介绍中国原子能科学研究院自由电子激光器的真空系统。激光器由Ｌ波段行波电子直线加速器、束流输运系统和包含１．５ｍ援摆器的光学谐振腔组成,１０台钛油射离子泵分布在各段以获得并保持超高真空。     

不锈钢的同步辐射光致脱附

电子储存环真空室壁及相连光束线的同步辐射致脱附（ＰＳＤ）严重影响着束流质量和寿命。不锈钢是加速器真空室最常用的材料,合肥光源的真空系统即为不锈钢结构。合肥光源在Ｂ６ａ光出口建立了ＰＳＤ光束线,选用长１２１ｃｍ,内径８．６ｃｍ的３０４Ｌ不锈钢真空室作为首件样品,用于测试不锈钢不同表面状态的脱附情况,结果表明经辉光放电处理的表面脱附系数最低。     

A tagging system for linearly polarized photons

A bremsstrahlung tagging system was installed at the Mainz microtron facility and was successfully used for experiments. At a primary electron energy of 184 MeV photons from 14 to 144 MeV could simultaneously be tagged. The magnetic electron optics for the tagging spectrometer were chosen in such a way, that the linear polarization of an off-axis tagged photon beam was considerably enhanced. The setup is described and results of performance tests are discussed.     

Monte Carlo simulation of a medical linear accelerator for radiotherapy use

A Monte Carlo code MCNPX (Monte Carlo N-particle) was used to model a 25 MV photon beam from a PRIMUS (KD2-Siemens) medical linear electron accelerator at the Centre Antoine Lacassagne in Nice. The entire geometry including the accelerator head and the water phantom was simulated to calculate the dose profile and the relative depth-dose distribution. The measurements were done using an ionisation chamber in water for different square field ranges. The first results show that the mean electron beam energy is not 19 MeV as mentioned by Siemens. The adjustment between the Monte Carlo calculated and measured data is obtained when the mean electron beam energy is approximately 15 MeV. These encouraging results will permit to check calculation data given by the treatment planning system, especially for small fields in high gradient heterogeneous zones, typical for intensity modulated radiation therapy technique.     

Dynamic micromagnetic field measurement by stroboscopic electronbeam tomography

A stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads is presented. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of the dynamic magnetic field are calculated using a tomographic reconstruction algorithm. To obtain enough current even in pulsed electron beam operation, a high-brightness Ti/W thermal field emitter is used. This system was successfully applied in measuring the field distributions of a thin-film recording head, with 0.1 μm spatial resolution and 1 ns time resolution at an operation frequency of 30 MHz     

合肥光源真空控制系统

合肥光源（HLS）是第二代专用同步辐射光源，由200MeV直线加速器、输运线和800MeV电子储存环组成。真空控制系统是基于EPICS（Experimental Physicsand Industrial Control System）的分布式控制系统，3台10C分别控制储存环上的7台Varian真空规控制器、直线加速器上的15台溅射离子泵电源控制器和输运线上16台溅射离子泵的电源控制器。采用Channel Arciver实现了储存环真空度及直线输运线溅射离子泵离子流数据的采集、存档及检索的功能。利用开发的CGI程序，改善了数据检索的性能，并对合肥光源储存环真空管道的束流清洗过程进行了分析。     

Workplace characterisation in mixed neutron-gamma fields, specific requirements and available methods at high-energy accelerators

A good knowledge of the radiation field present outside the shielding of high-energy particle accelerators is very important to be able to select the type of detectors (active and/or passive) to be employed for area monitoring and the type of personal dosemeter required for estimating the doses received by individuals. Around high-energy electron and proton accelerators the radiation field is usually dominated by neutrons and photons, with minor contributions from other charged particles. Under certain circumstances, muon radiation in the forward beam direction may also be present. Neutron dosimetry and spectrometry are of primary importance to characterise the radiation field and thus to correctly evaluate personnel exposure. Starting from the beam parameters important for radiation monitoring, the paper first briefly reviews the stray radiation fields encountered around high-energy accelerators and then addresses the relevant techniques employed for their monitoring. Recent developments to increase the response of neutron measuring devices beyond 10-20 MeV are illustrated. Instruments should be correctly calibrated either in reference monoenergetic radiation fields or in a field similar to the field in which they are used (workplace calibration). The importance of the instrument calibration is discussed and available neutron calibration facilities are briefly reviewed.     

Electron beam irradiation of denture base materials

Electron beam irradiation can be used to influence the properties of polymers. It was the aim of this study to investigate whether PMMA denture base materials can benefit from irradiation in order to have increased fracture toughness, work of fracture or hardness. Rectangular specimens of heat-and auto-curing denture base materials were electron beam irradiated (post-cured) with 25, 100 and 200 kGy using an electron acceleration of 10 MeV or 4.5 MeV respectively. Fracture toughness, work of fracture, Vickers hardness and colour changes were measured and compared with not-irradiated specimens.The toughness, work of fracture and hardness increased using 10 MeV with a dose of 25 kGy and with 100 kGy using 4.5 MeV. However, the clinical use may not benefit from the observed small changes. Higher dosage (200 kGy) decreased the values significantly. The colour changes reached a level which was found to be not clinically acceptable. Conclusion: PMMA denture base materials do not benefit from post-curing with electron beam irradiation.     

Development of GEM tracking detector for intermediate-energy nuclear experiments

We have developed a tracking detector with a gas electron multiplier (GEM) for nuclear experiments. The developed GEM detector was installed inside the dipole magnet used for transporting the primary beam to the beam dump and it was used to measure the momentum of charged particles. A sufficiently high spatial resolution was achieved at a high counting rate and a magnetic field for coherent pion production with a 392 MeV proton beam to study the short-range component of the residual nuclear interaction. The detector systems and development procedure are described.     

Fast neutron beams--prospects for the coming decade

The present status of neutron beam production techniques above 20 MeV is discussed. Presently, two main methods are used; white beams and quasi-monoenergetic beams. The performances of these two techniques are discussed, as well as the use of such facilities for measurements of nuclear data for fundamental and applied research. Recently, two novel ideas on how to produce extremely intense neutron beams in the 100-500 MeV range have been proposed. Decay in flight of beta delayed neutron-emitting nuclei could provide beam intensities five orders of magnitudes larger than present facilities. A typical neutron energy spectrum would be essentially monoenergetic, i.e., the energy spread is about 1 MeV with essentially no low-energy tail. A second option would be to produce beams of (6)He and dissociate the (6)He nuclei into alpha particles and neutrons. The basic features of these concepts are outlined, and the potential for improved nuclear data research is discussed.     

The peripheral dose outside the applicator in electron beams of Oncor linear accelerator

In this study, the peripheral dose outside the applicator was measured using electron beams produced by an Oncor linear accelerator and compared with the data of the treatment planning system (TPS). The dose profiles have been measured, by using a water-equivalent slab phantom and a parallel plate ionisation chamber, at 6, 9 and 15 MeV energy levels in 5×5, 10×10, 15×15, 20×20 and 25×25 cm(2) applicators and at 0, 10 and 20° gantry angles; and at the surface, 0.2, 0.5, 1 cm and d(max) depth for each electron energy level. The peripheral dose has been determined with these profiles by normalisation at the field central beam axis (CAX). It has been noticed that, using a 10×10 cm(2) applicator, there is a 1.4 % dose peak on the surface 6 cm away from the field edge where the field CAX is at 100 %, at a gantry angle of 0° with 6 and 9 MeV electron beams; also for the 15 MeV electron beam there is a 2.3 % dose peak. It has been discovered that the peak dose approaches a minimum depending on the increase in depth and reaches 2.5-4 % depending on the growth of the field dimension. At gantry angles of 10 and 20°, 6 and 9 MeV electron beams created small peaks and a maximum dose could be reached at 0.2 and 1 cm depth. Electron beam of 15 MeV did not peak at depths of 0.2 and 1 cm at gantry angles of 10 and 20°. The measured peripheral dose outside the applicators has been compared with the data from a TPS's computer using the Pencil Beam algorithm; it has been stated that dose calculations can be made as far as 3 cm outside the field. In conclusion, the TPS is not sufficient to measure the peripheral dose outside the applicators, and this dose can only be determined by direct measurement.     

POD Evaluation: The Key Performance Indicator for NDE 4.0

The magnified images of thin wires, plastic, steel and lead plates which were obtained using linear microfocus hard bremsstrahlung generated through interaction of an 18 MeV electron beam with a 13 μm thick Ta foil oriented along the internal beam of a B-18 betatron are presented. The images indicate high absorption contrast of the objects due to a small horizontal size of the radiation source the width of which is 115-fold smaller than the diameter of the electron beam. Some results have shown a few peculiarities in the images which were not earlier observed. Several results were compared with the ones obtained earlier using the microfocus bremsstrahlung generated by the 18 MeV electron beam of B-18 in a narrow Si target.