CEBAF和质子G°实验研究

本文简单介绍了美国ＣＥＢＡＦ（连续电子束流加速器）的近况和研究方向,以及Ｃ厅将展开的研究核子内Ｓ夸克成分的极化电子与质子散射宇称破坏不对称性测量的实验,即质子味单态电形状因子Ｇ°实验． The current status and scientific goal of CEBAF (The continuous Electron Beam Accelerator Facility ) are briefly presented. The project of the measurement of the flavor Singlet form factor G°of proton at C hall is outlined. A precise measurement of Parity violating asymmetry in the scattering of polarized electron from a proton target enables one to explore the Strange quark content in the proton.     

1.30-2.21MeV质子在硅上的160°散射截面测量

采用薄靶对能量 1.30 - 2 .2 1MeV质子在纯度为 99.99%硅上的非卢瑟福弹性背散射截面(16 0°背散射角 )进行了测量 .质子束由 2× 1.7MV串列加速器提供 ,测量仪器采用金硅面垒探测能谱仪 .实验中最低能区进入卢瑟福弹性散射能区 ,测量结果与以前发表的结果进行了比较 .所测量数据可供从事背散射分析技术的有关人员参考 . The elastic backscattering cross sections of H + from silicon for a wide energy range are very useful parameters in the proton backscattering analysis for investigating silicon content and distribution profiles in the films. It is necessary to measure the scattering cross sections with good accuracy at a large scattering angle for the applications of proton backscattering analysis. The present paper reports our measured results of differential elastic backscattering cross sections of 1.30-2.21 MeV...     

Simulation and analysis of 13N+p elastic resonance scattering

The ^13 N＋p elastic resonance scattering has been studied at the secondary radioactive beam facility of CIAE in inverse kinematics via a thick-target method. The excitation function for the ^13N（p,p） scattering was obtained in the energy interval of Ecru ≈0.5-3.2 MeV with a ^13 N secondary beam of （47.8±1.5） MeV. Careful analysis of the secondary beam components and extensive Monte-Carlo simulations enable the resolution of the experimental proton spectra. The resonance parameters for five low-lying levels in ^14 O were deduced by Rmatrix fitting calculations with MULTI7 and SAMMY-M6-BETA. The present results show general agreement with those from a recent similar work, and thus confirm the observation of a new 0^- level at 5.7 MeV in 140 with an improved width of 400（45） keV.     

Energy calibration of a BC501A liquid scintillator using a γ-γ coincidence technique

An accurate energy calibration of a BC501A liquid scintillator by means of Compton scattering of γ-rays is described.The energy resolution and the position of the Compton edge have been precisely determined using a γ-γ coincidence technique and fitting the coincidence spectrum with a Gaussian function superimposed on a quadratic polynomial for the background.The position of the Compton edge relative to the position of the maximum and the half height of the distribution in dependence on the relevant energy resolution is discussed in detail.The results indicate that the maximum energy of the recoil Compton electron does not occur at the half height distribution but at 0.90±0.05 of the maximum height in the energy range considered.The energy resolution varies from 15.6% to 8.02% for electrons in the energy region from 0.5 MeV to 3 MeV.     

Off-axis dose distribution for rectangle proton beam

This papcr modifies an analytical algorithm originally developed for electron dose calculations to evaluate the off-axis dose distribution of rectangle proton bcam. This spatial distribution could be described by Fermi-Eyges theory since a proton undergoes small-angle scattering when it passes through medium. Predictions of the algorithm for relative off-axis dose distribution by a 6 cm ＊ 6 cm initial monoenergetic proton beam are compared with the results from the published Monte Carlo simulations. The excellent level of agreement between the results of these two methods of dose calculation （〈 2%） demonstrates that the off-axis dose distribution from rectangle proton beam may be computed with high accuracy using this algorithm. The results also prompts the necessity to consider the off-axis distribution when the proton is applied to clinical radiotherapy since the penumbra is significant at the distal of its range （about 0.6 cm at the Bragg-peak depth）.     

A CVD diamond film detector for pulsed proton detection

A chemical vapour deposition （CVD） diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo （MC） simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.     

Experimental study on scintillation efficiency of ZnO:In to proton response

Film ZnO:In crystal is a good candidate for a scintillation recoil proton neutron detection system and the response of ZnO:In to protons is a crucial point. The energy response of ZnO:In to mono-energetic protons in the range of 10 keV-8 MeV was measured. The experiment was carried out in current mode, and Au foil scattering was employed, where the forward scattering protons were used for exciting the sample, and the backward scattering protons were used for monitoring the beam intensity. According to the result, the yield of light non-linearly depends on proton energy, and drops significantly when proton energy is low. The scintillation efficiency as a function of proton energy was obtained, which is very useful for researching the scintillation recoil proton neutron detection system.     

Highlights from the COMPASS experiment

The Compass experiment at CERN is studying the nucleon spin structure with a 160 GeV polarized muon beam and polarized targets as well as hadron structure with 190 GeV pion,kaon and proton beams.The paper gives an overview of the results for the helicity and transverse spin structure of the nucleon.A first result from the spectroscopy experiments,the observation of a resonance with exotic J P C = 1-＋ quantum numbers at 1660 MeV is also presented.The paper ends with an outlook to future measurements.     

Experimental study of the elastic scattering of ~(10)Be on ~(208)Pb at the energy of around three times the Coulomb barrier

Elastic scattering of 10Be on a 208Pb target was measured at ELab=127 MeV,which corresponds to three times the Coulomb barrier.The secondary 10Be beam was produced at the Radioactive Ion Beam Line in Lanzhou of the Heavy-Ion Research Facility in Lanzhou.The angular distribution of elastic scattering in the 10 Be+208Pb system shows a typical Fresnel diffraction peak.Optical model analysis of the angular distribution was performed using the Woods-Saxon,double-folding and global potentials.With the global potential,different density distributions were used.The results indicate that different density distributions for the projectile induce distinct effects in the angular distribution.     

Influence of radial magnetic field on emittance in the median plane at CYCIAE-100

A 75—100 MeV H- compact cyclotron CYCIAE-100 is being constructed at China Institute of Atomic Energy (CIAE). About 200 μA proton beam will be provided by CYCIAE-100. The imperfection of magnetic fields will remarkably affect the acceleration orbit and beam envelope in CYCIAE-100. The effects to the accelerating beam by the imperfection fields, especially the field components Br on the mid-plane will be analyzed in detail with tracking code COMA. Poles misalignment that causes magnetic imperfection will be described in the paper. According to the simulation results, the tolerance of the poles machining and assembly will be illustrated in this paper.     

A system for measuring a low-intensity proton beam

A system for measuring proton beam intensity and energy for the medical channel of the Institute for Nuclear Research, Russian Academy of Sciences, at energies of 70–280 MeV and an average current of about 1 nA is presented. The reaction of elastic scattering of primary beam protons on the polyethylene target is used in the system to determine the intensity and energy of a therapeutic proton beam with accuracies of 1% and 1 MeV, respectively.     

100MeV质子双环双散射体扩束方案设计

为满足质子单粒子效应实验对大面积、均匀化质子束流的需求,针对中国原子能科学研究院100 MeV质子回旋加速器提供的100 MeV质子进行了双环双散射体扩束方案设计.Geant4模拟表明该方案可在2.4 m位置产生一个均匀性为±1.89%、半径为8 cm的照射野,在5 m位置产生一个均匀性为±5.32%、半径为20 cm的照射野.此外,利用Geant4对双环双散射体扩束方法的基本原理进行了进一步探索,并对第二散射体后加速器管道、初始束斑尺寸、照射野形成距离、改变入射质子能量等实际中各种可能因素对该方案扩束效果的影响进行了讨论.     

100 MeV质子束流品质诊断及剂量测量准确性评估方法研究

质子辐射生物学效应是太空放射生物学和质子束放疗研究的重要基础,可为空间环境下人员的危险性评估以及质子治疗优化设计提供科学依据。依托加速器建立相应的生物样本辐照技术是开展此类研究的前提条件。中国原子能科学研究院最近建立的100 MeV强流质子回旋加速器提供的中能质子束流为目前国内能量最高,特别适合用于太空放射生物学和质子治疗相关研究。本研究中,利用在束和离线等多种手段建立了中能质子束流诊断和剂量测量方法,对加速器引出的100 MeV质子照射野大小、均匀性等束流品质以及剂量测量系统准确性进行了分析和评估。结果表明,对光子剂量响应好的LiF(Mg, Ti)热释光探测器,对90 MeV质子同样具有良好的剂量响应关系,可作为中能质子剂量准确性评估的手段之一。在5.0 cm×5.0 cm照射野范围内,加速器引出的100 MeV质子束流的均匀性好于90%,在线剂量测量系统准确性好于93%,束流品质和剂量测量条件基本满足辐射生物学的要求,可为质子辐射生物学效应研究的开展提供可靠保障。     

Effects of Distorted Wave on Proton Elastic Scattering from Light Nuclei at 200 MeV

The distorted wave is introduced into the relativistic impulse approximation to generate the Dirac optical potentials for proton elastic scattering. Those potentials, produced by folding the target ground state wavefunction with the free nucleon-nucleon interactions, are used to reevaluate scattering observables, such as differential cross section, analysing power and spin rotation function, for proton elastic scattering from ^12C and ^16O at Elab = 200 MeV, respectively. The inclusion of the distorted wave in the original relativistic impulse approximation has brought out better results of the observables, especially at small scattering angles.     

医用质子直线加速器的设计研究

讨论用于治癌的低束流高能量质子直线加速器的初步物理设计.采用短脉冲和高重复频率的S波段的加速结构,类似于医用电子直线加速器.总长26m,由离子源、RFQ、DTL、SCDTL及SCL组成,能量经70—200MeV有八档可调,平均束流强度10—40nA.     

Complete Set of Deuteron Analyzing Powers for dp Elastic Scattering at Intermediate Energies and Three Nucleon Forces

With the aim of clarifying roles of the 3NFs in nuclei experimental programs with the polarized deuteron beam at intermediate energies are in progress at RIKEN RI Beam Factory. As the first step, we have measured a complete set of deuteron analyzing powers in deuteron–proton elastic scattering at 250 and 294 MeV/nucleon. The obtained data are compared with the Faddeev calculations based on the modern nucleon–nucleon forces together with the Tucson–Melbourne’99, and UrbanaIX three nucleon forces.     

Focusing crystal device for deflecting a divergent 50-GeV proton beam

At large accelerators, bent crystals are employed to deflect weakly divergent proton beams at the stages of extraction and collimation. We demonstrate that a divergent particle beam may be efficiently deflected using a crystal with a focusing edge. A proton beam with divergence near 1 mrad, which exceeds the Lindhard angle by a factor of 30, has been experimentally deflected by 1.8 mrad with efficiency near 15%. The proposed focusing crystal may serve as an element of a novel optical system for secondary-particle beams in the TeV energy region.     

散裂靶中质子束窗的散射效应

 质子束窗是在高功率靶区中的一个分界窗,它将质子输运线上高真空区域和氦容器中的氦环境分开。在其他散裂中子源中质子束窗的热效应以及机械问题都已经被研究过了,但质子束在该窗中散射效应的研究却很少被报导,然而在靶设计中如果没有处理好质子束窗的散射效应会有很大的问题。报导了质子束窗散射效应的模拟计算结果,包括不同质子束窗的材料和结构选择,并以中国散裂中子源（CSNS）为例,介绍了在CSNS一期和二期中质子束窗采用周边水冷的铝合金单层结构,CSNS三期采用中间水冷的铝合金夹层结构。文中给出了不同结构的质子束窗和不同的与靶距离散射效应对靶上经非线性磁铁均匀化的束流分布的影响的模拟计算结果。模拟结果显示质子窗的散射效应对束流损失和靶上的束流分布有重要的影响。     

Transverse asymmetries at backward angles in G0

The backward angle phase of the G0 experiment has measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton and made the first measurement in quasi-elastic scattering in deuterium at backward angles for Q²?=?0.22 GeV²/c² and 0.63 GeV²/c². The measurements were made at a lab scattering angle of 108° at beam energies of 362 MeV and 687 MeV respectively. Preliminary results for the proton are consistent with including ??N states in the calculation of the asymmetry in the resonance region. A preliminary estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasi-static deuterium model.     

入射质子的能量对质子与晕核弹性散射观测量的影响

用相对论脉冲近似(RIA)对不同的中能质子(200MeV, 400MeV和800MeV)与¹⁴Be, ¹⁶O和¹²C的弹性散射进行了研究, 讨论了不同的入射能量对3种观测量, 即微分散射截面、分析本领和自旋转动函数的影响. 研究发现在小散射角的区域晕中子对观察量的影响趋势保持一致, 不随入射质子能量的改变而改变.