The 10,000,000,000-Volt question: What is the best choice of proton energy to drive a pulsed spallation neutron source?

In pulsed spallation neutron sources, higher proton beam current or higher proton energy brings higher proton beam power, and from greater beam power come more neutrons. Consequently, accelerator scientists and target systems designers conceive systems to produce ever-higher intensities of neutrons, and the question arises: What is the best choice of proton energy to drive a pulsed spallation neutron source? Meanwhile target engineering, radiation shielding, and neutronic coupling to moderators must be accomplished effectively. This paper addresses the title question from the target side, assessing the neutron yield, the distribution of leakage neutrons, and the power density distribution as functions of proton energy.     

The use of recombination chambers at radiation therapy facilities

The paper presents an overview of the applications of recombination chambers for dosimetric measurements at radiotherapy facilities. The chambers were used at electron, proton and heavy ion accelerators, in the beam and in the vicinity of the accelerators at very different dose rates. The examples of measurements discussed in the paper include: the determination of the absorbed dose and radiation quality parameters of a 170 MeV proton beam and BNCT (boron neutron capture therapy) beam, neutron dose measurements at a phantom surface outside the beam of a 15 MV electron medical accelerator, determination of ambient dose equivalent, H1 (10) outside the irradiated phantom in the proton therapy treatment room at JINR (Dubna, Russia), and at working places outside the shielding of the heavy ion therapy facility at GSI (Darmstadt, Germany).     

先进核能系统结构材料辐照性能研究

首先简要介绍第一代到先进的第四代核能系统的发展、与核能系统发展密切的抗辐照结构材料研发进展、第四代核能系统结构材料辐照性能研究新方法。第四代核能系统发展中,辐照引起材料性能退化是一个需要研究和解决的瓶颈问题。现有中子源都不能满足第四代核能系统结构材料高剂量中子辐照性能研究的要求。为此,发展了用于核能系统结构材料高剂量辐照性能快速检测加速器重离子辐照方法和第四代核能系统实际辐照工况模拟的重离子与氢和氦三束同时辐照新方法,文中进行了详细的介绍。最后介绍了中国原子能科学研究院核能系统结构材料辐照性能研究现状和近期发展计划。该院在HI-13串列加速器器上建立了多种不同用途的重离子辐照装置、三个独立加速器构成的重离子与氢和氦三束同时辐照实验平台,开展了一系列核能结构材料,例如国产改进型奥氏体钢、CLAM钢、1515钢、钽、钨等的辐照性能的系统测试和研究。为了更好地开展核能结构材料性能研究,从国外引进了一台超导直线加速器和一台可变能量重离子回旋加速器。结合现有2×13 MeV,2×1.7 MV串列加速器、30 MeV和100 MeV质子回旋加速器、高压倍加器,中国实验快堆、中国先进研究堆、微堆等,CIAE将建成一个比较完整和先进的核能系统结构材料辐照实验平台系统供国内外用户使用。This paper introduces briefly the development of nuclear energy systems from the GEN I to the advanced GEN IV, the progress of manufacturing radiation resistant materials associated with the development of nuclear energy systems and the new methods of investigating radiation properties of the structural materials for the GEN IV nuclear energy systems at first. Irradiation induced deterioration of materials properties is a bottle neck problem, which must be investigated and solved for the development of the GEN IV nuclear energy systems. Unfortunately, all the currently available neutron sources cannot meet the requirements of investigating radiation properties of structural materials irradiated by high dose neutron irradiation in the GEN IV nuclear energy systems. Therefore, two new methods of the accelerator heavy ion irradiation that simulates the high-dose neutron irradiation and the triple beam irradiation that mimics the real neutron irradiation environment in the GEN IV nuclear energy systems have been developed. These two methods are introduced in this paper. The present status of the study on radiation properties of structural materials for nuclear energy systems of the new generation and the near future development plan at China Institute of Atomic Energy (CIAE) are described also. The accelerator heavy ion irradiation facilities for different applications and the simultaneous triple beam irradiation platform with three separate accelerators or implanters have been established at the HI-13 tandem accelerator of CIAE. A series of structural materials for nuclear energy systems, such as the home-made modified austenic steel, CLAM steel, 1515 steel, Tantalum, Tungsten, etc. have been tested and investigated systematically. A superconducting linear accelerator and a variable energy heavy ion cyclotron have been imported from abroad for a better performance of the study. Combined with the currently existing facilities of 2×13 MeV and 2×1.7 MV tandem accelerators, 30 and 100 MeV proton cyclotrons, China experimental fast reactor, China advance research reactor, Miniature neutron source reactor, etc. a comprehensive and advanced system of experimental irradiation platform for structural materials of nuclear energy systems will be established in the near future for both domestic and foreign users.     

Monitoring radiation levels in the FEL accelerator hall

The radiation control system for the Free Electron Laser (FEL) monitors the radiation in its workplaces and accelerator hall. Gas-filled detectors installed in the accelerator hall are used for radiation monitoring and controlling beam losses in the vacuum chamber and for beam orbit correction.     

First observation of intrabeam stripping of negative hydrogen in a superconducting linear accelerator

We report on an experiment in which a negative hydrogen ion beam in the Spallation Neutron Source (SNS) linear accelerator was replaced with a beam of protons with similar size and dynamics. Fractional beam loss in the superconducting part of the SNS accelerator was measured to be at least 2×10(-5) for the H(-) beam, and it was an order of magnitude lower for the protons. Also beam loss has a stronger dependence on intensity with H(-) than with proton beams. These measurements verify a recent theoretical explanation of unexpected beam losses in the SNS superconducting linear accelerator based on an intrabeam stripping mechanism for negative hydrogen ions. This previously unidentified mechanism for beam loss is important for the design of new high current linear ion accelerators and the performance improvement of existing machines.     

一种用于C-ADS低能束流传输线束流强度控制的新型可调限束光阑

为了实现超导直线加速器束流强度的连续可调,并满足加速器在线稳定可靠运行,针对我国加速器驱动次临界系统(C-ADS)低能束流传输线(LEBT)的束流强度调控,提出了一种新型的可调限束光阑。可调限束光阑采用两个相对旋转的镜像对称转芯,转芯的孔径在某一范围内可以实现连续变化,以刮除不需要的外部粒子,提高束流品质,降低束损,最重要的是可实现束流强度的在线连续可调,并满足圆形束的要求。仿真和试验结果表明,在0~10 mA范围内,可以有效地卡掉不需要的外部粒子束流,并实现束流强度的在线连续调节。该装置为质子直线加速器提供了一种方便的束流调试方法,能够满足ADS直线加速器稳定可靠的在线运行。     

一台2.45GHz强流中子源

A 2.45GHz microwave-driven ion source is being used to provide 40mA of deuterium ion beam (peak current) for an RFQ accelerator as part of a neutron source system.We have also designed a 60kV electrostatic LEBT using computer simulations.In our experiment,we measured the hydrogen and deuterium ion beam currents as functions of discharge power,gas flow,and magnetic field strength.The required beam current was obtained using leas than 700W of net microwave power with a gas flow of less than 1.5sccm.From the rise time data,it was determined that in order to obtain a high percentage of atomic ions in the beam, the beam extraction should start after 1ms of switching on the microwave power.At steady state,the proton fraction was above 90%.     

改进型Andersson-Braun中子雷姆仪对0.025eV-45.4MeV中子的能量响应

描述了一种适用于高能粒子加速器周围杂散辐射场测量的改进型Ａｎｄｅｒｓｓｏｎ－Ｂｒａｕｎ中子雷姆仪的原理与结构。利用国内外多种类型的中子源装置，进行了中子能量从０．０２５ｅＶ－４５．４ＭｅＶ的注量率能量响应实验，实验表明，这种改进型Ａｎｄｅｒｓｓｏｎ－Ｂｒａｕｎ中子雷姆仪，对能量大于２０ＭｅＶ中子的响应，比普通Ａｎｄｅｒｓｓｏｎ－Ｂｒａｕｎ中子雷姆仪有明显的改善。     

Regulation of the output energy of a backward-wave linear accelerator by the duration of the rf power pulse

The problems of regulating the output energy of the accelerated beam of a backward-wave linear proton accelerator over a wide range without altering the beam intensity are investigated. The proton energy is regulated by adjusting the duration of the rf power pulse delivered to the accelerator and by regulating the delay time between the instant of injection and the instant at which the leading edge of the rf pulse arrives at the output end of the accelerator. The method is tested on the interdigital-type accelerating section of length 1.25 m of a linear proton accelerator. It is shown experimentally that the electron beam energy at the accelerator output can be varied approximately threefold without any appreciable sacrifice of the beam intensity by varying the duration of the rf pulse in the given accelerator section. Zh. Tekh. Fiz. 68, 135–137 (May 1998)     

中能重离子碰撞中前平衡核子发射的同位旋效应

利用同位旋相关的输运理论,研究了中能重离子碰撞中丰中子和缺中子碰撞系统在较宽能区范围内前平衡发射核子的同位旋效应.结果表明除低能区外,在100MeV/u以上核子–核子碰撞动力学效应起主要作用的能区,前平衡发射的中子–质子比仍然对介质中核子–核子碰撞截面的同位旋效应不灵敏,然而对于对称势的改变非常灵敏.故从低能量到较高能量的较大能区内,前平衡发射的中子–质子比的理论值与实验值的比较是提取对称势形式和强度的灵敏探针.     

与散裂中子靶物理相关的理论计算程序探讨I薄靶计算

利用中能强流质子加速器形成的散裂中子源作为外加中子源驱动次临界反应堆的洁净核能系统是目前国际上的一个研究热点 .散裂中子源是这个系统的一个重要部分 ,也是一个急需解决的重点.有关散裂靶物理的理论计算程序的建立和基准检验是目前工作的一个重点.The research for intermediate energy proton accelerator driven radiologically clean nuclear power system has attracted considerable attention. The spallation neutron source induced by intermediate energy proton nucleus interaction is a key point and has not solved yet for the transmutation and applications. The theoretical programs related to the spallation neutron source for accelerator driven system (ADS) are discussed at present work.     

高能质子束流强度绝对测量的二次电子补偿原理研究

高能质子入射到金属接收体表面诱发的二次电子直接影响束流强度的测量精度,如何消除二次电子影响是实现束流高精度测量的关键.根据高能带电粒子在金属表面诱发二次电子发射理论,对高能质子束流强度测量的二次电子补偿原理进行了研究,设计了二次电子补偿结构.采用三块金属极板构成的实验装置在高能质子源上开展实验研究,实验测得在中间极板上输出的电流与入射质子束流强度的比值小于0.7%,中间极板上二次电子得到补偿,验证了二次电子补偿原理的正确性.研究表明,采用设计的二次电子补偿结构对高能质子束流强度进行测量时二次电子贡献小于1%.     

Design and construction of the first prototype ionization chamber for CSNS and PA beam loss monitor （BLM） system

Design and construction of the first prototype ionization chamber for CSNS and Proton Accelerator （PA） beam loss monitor （BLM） system is reported. The low leakage current （〈0.1 pA）, good plateau （≈800 V） and linearity range up to 200 Roentgen/h are obtained in the first prototype. All of these give us good experience for further improving the ionization chamber construction.     

Muon science in J-PARC

The intensity of proton accelerator has attained to the order to mega-watt, and several MW-class proton accelerators start to operate in the world. J-PARC is a complex of three accelerators, and generates a variety of secondary beams, i.e. muon beam, neutron beam, meson beam and neutrino beam. The muon facility is established in order to provide a pulsed muon beam for various experimental programs. The first muon beam is transported to the experimental area in September 2008. Although the accelerator is still under commissioning, and the beam power doesn’t reach the design value of 1 MW yet, the world strongest pulsed muon beam will be provided shortly. In this paper, we review the muon beam line in J-PARC, and discuss evolved scientific programs.     

4 MV静电加速器调试中出现的问题及解决方案

 4 MV静电加速器由高压系统、离子源及束流系统、控制系统和气体系统四部分组成。调试中出现了离子源不起弧、加速管破裂、控制系统失灵和输电带输电能力降低等技术问题,分析了出现这些问题的原因,然后分别采取了相应的措施加以解决：变换工作流程,在每次关机前先把引出电压降为零,开机时等离子源起弧后再把引出电压升到预定值;对过渡法兰进行车加工,重新封装;对高压端的控制设备采取屏蔽措施,在输入、输出端使用TVS二极管,对控制软件进行抗干扰设计;对绝缘气体进行循环干燥等。调试出了流强为100 μA、能量在3 MeV以上的稳定质子流。     

Proposal for muon and white neutron sources at CSNS

The China Spallation Neutron Source (CSNS) is a large scientific facility with the main purpose of serving multidisciplinary research on material characterization using neutron scattering techniques. The accelerator system is to provide a proton beam of 120 kW with a repetition rate of 25 Hz initially (CSNSⅠ), progressively upgradeable to 240 kW (CSNS-Ⅱ) and 500 kW (CSNS-Ⅱ'). In addition to serving as a driving source for the spallation target, the proton beam can be exploited for serving additional functions both in fundamental and applied research. The expanded scientific application based on pulsed muons and fast neutrons is especially attractive in the overall consideration of CSNS upgrade options. A second target station that houses a muon-generating target and a fast-neutron-generating target in tandem, intercepting and removing a small part of the proton beam for the spallation target, is proposed. The muon and white neutron sources are operated principally in parasitic mode, leaving the main part of the beam directed to the spallation target. However, it is also possible to deliver the proton beam to the second target station in a dedicated mode for some special applications. Within the dual target configuration, the thin muon target placed upstream of the fast-neutron target will consume only about 5% of the beam traversed; the majority of the beam is used for fast-neutron production. A proton beam with a beam power of about 60 kW, an energy of 1.6 GeV and a repetition rate of 12.5 Hz will make the muon source and the white neutron source very attractive to multidisciplinary researchers.     

Neutron-beam-shaping assembly for boron neutron-capture therapy

A neutron-beam-shaping assembly consisting of a moderator, a reflector, and an absorber is used to form a therapeutic neutron beam for the boron neutron-capture therapy of malignant tumors at accelerator neutron sources. A new structure of the moderator and reflector is proposed in the present article, and the results of a numerical simulation of the neutron spectrum and of the absorbed dose in a modified Snyder head phantom are presented. The application of a compositemoderator and of a composite reflector and the implementation of neutron production at the proton energy of 2.3MeVare shown to permit obtaining a high-quality therapeutic neutron beam.     

Beam dynamics in a C253-V3 cyclotron for proton therapy

In recent years, oncologic diseases have become a severe issue in developed countries. Proton therapy is viewed as one of the most efficient methods of treating oncologic diseases. The results of computing the beam dynamics in a C235 medical cyclotron intended for proton therapy are presented. The cyclotron was modified by teams of researchers at the Joint Institute for Nuclear Research and Ion Beam Application (IBA Group, Belgium). Possible reasons for losses in the beam under acceleration are considered, and the influence of the magnetic field radial component in the median plane of the accelerator is studied. The results of analysis and upgrading of the beam extraction system are presented. Based on analytical data, the design of the commercial C235 cyclotron is considerably modified. A new version of the C235-V3 cyclotron will be placed in commission at the Dimitrovgrad center of radiation medicine.     

基于2.5 MeV质子加速器BNCT装置的中子慢化材料性能模拟研究

基于加速器中子源的硼中子俘获治疗(Boron Neutron Capture Therapy, BNCT)是新一代的放射治疗方法,束流整形体(Beam Shaping Assembly, BSA)作为硼中子俘获治疗装置的重要组成部分,其作用是将中子源中的快中子束流慢化至超热中子能区(0.5 eV~10 keV),并尽可能减少快中子、热中子以及$\gamma $射线的成分,使其满足BNCT用于治疗的中子束要求。本工作基于蒙特卡罗软件包Geant4(Geometry and Tracking),以2.5 MeV,10 mA质子流强的7Li(p, n)7Be中子源为对象,研究分析了AlF₃ 、Fluental、Al₂O₃、Al作为慢化体材料时,不同的厚度对束流出口处的超热中子注量率、超热中子注量与热中子注量比值、快中子成分、$ \gamma $成分所产生的影响。计算表明,当选用厚度为25 cm的AlF₃作为慢化体材料时,经过整形慢化后的超热中子束的束流参数,均满足国际原子能机构(International Atomic Energy Agency, IAEA)的中子束流参数推荐值。