高能质子照相中基于角度准直器设计的理论研究

角度准直器在高能质子照相中有着重要作用,既可以利用准直器提高图像对比度,又能通过二次成像实现材料诊断及密度重建,因此减小通过准直器后通量值的误差具有重要意义.本文通过理论分析,提出了一种高能质子照相中准直器设计的方法,通过Geant4程序建立了1.6 GeV的质子成像系统,该系统分别使用理想准直器、拉伸型准直器和利用该方法设计的准直器,并对比通过客体后的通量分布.结果表明,在使用理想准直器和该方法设计的角度准直器时,二者得到的客体的通量分布符合较好,而使用拉伸型准直器时,与使用理想准直器得到的结果相差较大.因此利用理想准直器方法设计的准直器可以很好地减小通量误差.     

Neutron collimator design of neutron radiography basedon the BNCT facility

For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy (BNCT) reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0·10⁶ n/cm²/s, the maximum collimation ratio (L/D) is 58, the Cd-ratio(Mn) is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.     

不同准直角双轴闪光照相

 为了降低闪光照相中散射的影响和提高法国试验客体（French test object,FTO）重建的精度,结合不同准直角下散射不同的特性,提出了不同准直角的双轴闪光照相布局,并进行了相应的数值模拟实验。研究结果表明：不同准直角双轴闪光照相中散射的相互干扰非常严重,且主要来于前保护器件,需使用铅板屏蔽。根据信息融合特性和降低散射影响的要求确定了FTO不同准直角双轴闪光照相的两个准直角分别为2.24°和1.15°。从该不同准直角的双轴闪光照相系统模拟得到的图像重建出了均方根误差小于5.8%的密度分布,结果远优于单轴照相23％的均方根误差。     

基于法国实验客体的X射线准直技术研究

通过研究法国实验客体(FTO)的闪光照相过程,设计了静态照相过程中采用的准直措施,除传统的一二级准直体外,还通过添加三级准直体来进一步控制入射到客体边缘部分的X射线,从而降低散射的影响。蒙特卡罗方法模拟结果表明,采用三级准直技术可以有效地控制散射的影响,图像接收平面各边界的直散比有了明显的提升。     

Characterization of a BNCT beam using neutron activation and indirect neutron radiography

This study aims to measure the neutronic characteristics of the 14-cm diameter boron neutron capture therapy beam at the Tsing Hua Open-pool Reactor and to provide essential information for the neutron source adjustment and validation. The measurements were performed both in air and inside a cubic PMMA phantom at the beam, with and without an 18-cm long extended PE collimator. The neutron intensity was determined by neutron activation analysis; the indirect neutron radiography and the cadmium difference method were coupled to provide the two-dimensional neutron flux distributions.According to the measurements, the angular distribution is highly forward for epithermal neutrons but much more divergent for thermal ones. A PE extended collimator will modify the beam characteristics and could benefit the treatment for head and neck tumors, which often needs higher therapeutical boron dose at the shallow region.     

Monte Carlo simulation for bremsstrahlung and photoneutron yields in high-energy x-ray radiography

This paper reports on the results of calculations using a Monte Carlo code (MCNP5) to study the properties of photons, electrons and photoneutrons obtained in the converted target and their transportations in x-ray radiography. A comparison between measurements and calculations for bremsstrahlung and photoneutrons is presented. The radiographic rule and the effect of the collimator on the image are studied with the experimental model. The results provide exact parameters for the optimal design of radiographic layout and shielding systems.     

由边界退化确定模糊尺寸

在高能闪光照相流体动力学实验中,模糊问题严重影响诊断结果的精度。模糊图像的边界检测结果与真实边界之间往往存在位置偏移,称为边界退化量。在照相布局和客体确定的条件下,模糊尺寸越大,边界退化量越大。利用边界退化量与模糊尺寸的这一关系,提出一种从边界检测中测量系统模糊尺寸的新想法,从闪光照相成像物理过程角度阐释了方法的原理,然后通过数值实验分析了方法的处理过程,建议测量实验利用倒锥准直器对球形客体成像。模拟结果表明:采用该方法模糊函数的FWHM误差小于1个像素。最后借助数值模拟对台阶客体照相实现了对模糊尺寸测量结果的验证。     

利用数值模拟测量闪光照相中H-D曲线

 在分析高能闪光照相中传统实验方法不足的基础上,提出了采用Monte Carlo模拟结果来建立底片光学密度与照射量之间的关系,并对一个球对称客体进行了实验照相。采用Monte Carlo方法分析了底片光学密度分布左右不对称的各种因素,认为底片光学密度分布左右不对称主要是照相器件几何对中不理想造成的,并说明了底片光学密度左右平均的合理性。在此基础上介绍了H-D曲线的生成方法,采用Silberstein理论得到了具有较高精度的H D曲线。这种结合Monte Carlo模拟的H-D曲线测量方法不但避免了照射量测量误差,而且还考虑了H-D曲线对X射线能谱的依赖关系,更能体现实际情况,具有较高的精度。可用于球对称客体或柱对称客体的辐射照相。     

Monte Carlo simulation and parameterized treatment on the effect of nuclear elastic scattering in high-energy proton radiography

A version of Geant4 has been developed to treat high-energy proton radiography. This article presents the results of calculations simulating the effects of nuclear elastic scattering for various test step wedges. Comparisons with experimental data are also presented. The traditional expressions of the transmission should be correct if the angle distribution of the scattering is Gaussian multiple Coulomb scattering. The mean free path(which depends on the collimator angle) and the radiation length are treated as empirical parameters, according to transmission as a function of thickness obtained by simulations. The results can be used in density reconstruction, which depends on the transmission expressions.     

高能闪光照相中网栅相机的性能分析

针对闪光照相基本布局, 从照相物理过程出发, 确立网栅相机下含各种物理参量的成像公式。为了获得尽量简化的成像公式, 采用数值模拟和理论分析方法, 探讨了网栅相机在抑制噪声、散射和模糊等方面的能力及其使用方法。结果表明:网栅相机不仅具有灵敏度高、降散射能力强和模糊小的特点, 采用有/无陡坡准直器和客体的两次照相可以获得主要含光源模糊的透射率图像, 极大减少了图像分析中的不确定性因素。     

A new method for analyzing the collimation angle of a neutron Soller collimator

A new method for analyzing the collimation angle of a neutron Soller collimator is described. A Gaussian distribution formula is used to define the angular distribution function of the neutron source and the neutron transmission function of the Soller collimator. A relationship between the FWHM of the collimator rocking curve and the collimation angle is derived. Using this method, some rocking curve experiment results are analyzed. The results show that the new function can be a good theoretical model for fitting the experimental data, especially for the data of two collimators with different collimation angles.     

大口径光学离轴平行光管研究——主反镜结构及光学检测

在长焦距大口径平行光管的应用中,平行光管物镜的定位精度以及在装调过程中高灵敏度的调试环节十分重要.介绍大口径离轴光学平行光管主镜结构及其检测方法,给出3种不同口径下的光学系统的装调方法,详细分析 700 mm的平行光管的主镜结构及精调装置,并利用4D干涉仪来检测装调装置对面形的影响.结果表明,该装调装置为自由移动装置,...     

准直物镜在变焦距镜头杂散光系数测试中的作用和影响分析

在对变焦距光学镜头进行杂散光系数测试的过程中,需要了解各测试环节的作用及对测量结果的影响。讨论了准直物镜使用与否对杂散光系数测量结果的影响。通过对杂散光形成机理的分析,将杂散光来源分为视场内与视场外两种,阐述不同来源杂散光的不同特点及这两种杂散光通过准直物镜后的状态。用两个参数不同的变焦距光学镜头在有无准直物镜两种情况下杂散光系数的测量结果,说明准直物镜在杂光测试中的作用。对于视场外入射光束形成的杂散光,准直物镜的使用与否对其测量结果影响巨大,而对视场内入射光束形成的杂散光影响很小,测量时可以利用准直物镜来判断光学镜头杂散光的来源。同时通过实验说明入射光线在准直物镜间的多次反射形成的杂散光约为1%,它可作为系统误差从测量结果中剔除。     

（n,2n）反应实验研究中的中子准直器设计

用3He球形4中子探测器,通过直接反应法可以对核素的（n,2n）反应截面进行测量。在此类实验中,要求对中子束进行很好的准直。好的准直器设计要求能够提高样品处的中子注量率的均匀性,同时保证中子束流边缘处的下降幅度,能够降低低能中子所占份额。本工作采用FLUKA和MCNPX对圆柱形准直器、单锥形准直器及三种不同斜率的双锥形准直器对中子注量率的均匀性和低能中子所占份额进行了对比研究,结果表明,低斜率的双锥形准直器可以满足实验对这两方面的要求。同时,在有样品和无样品两种条件下,对探测系统经由这五种不同准直器准直后的中子束流的响应做了对比,结果显示,经过低斜率的双锥形准直器准直的中子束流,探测系统在有样品时表现为较高的计数率,在无样品时表现为较低的本底。除此之外,对准直器出口处的斜率对准直效果的影响也做了比较。最终中子准直器选用为这种低斜率的双锥形准直器,材料选用为紫铜、不锈钢、聚乙烯和铅。准直孔开口处直径为2.64 cm,长度为137 cm,经准直后样品处的中子束斑直径为3.2 cm。     

微束X射线荧光分析

用能量色散微束X射线荧光分析仪实际测量了微束准直器孔径和X射线强度对微束空间分辨率的影响,在准直器孔径为0.1mm条件下,获得以FWHM定义的空间分辨率最好为0.073mm。通过微束扫描测量出某硫化锰矿微区内的Mn、Fe、Zn、Pb的三维等高线荧光强度分布图和不同小区域内的能谱。     

Calibrating the HXMT collimators using diffuse illumination

We propose a new method to calibrate the HXMT collimators by measuring the optical point spread function (PSF) of the hard X-ray modulation telescope (HXMT). The light transmission of the collimator at different viewing angles with a camera and a diffuse backlight placed behind the collimator is measured. This method is much easier to accomplish than measuring the PSF with a parallel optical beam. The experimental results are very consistent with the simulations. The PSF of the collimator of the high energy X-ray telescope on HXMT is found to be in good agreement with the design, with accuracy better than 1 arcmin.     

Large-aperture double-focus laser collimator for PAT performance testing of inter-satellite laser communication terminal

A laser collimator is necessary for testing and verification of the pointing, acquisition and tracking (PAT) performance of inter-satellite laser communication terminals on the ground. The laser collimator must have a large clear aperture to fit the PAT performance testing system. The PAT subsystem has a large field of view for the acquisition and a high angular accuracy for the fine tracking. To resolve the conflict between large field of view and fine angular resolution, a large-aperture double-focus laser collimator is proposed and its optical design and mechanical structure are described. The collimator mainly consists of a primary lens, a reflector, a beam-splitting plate, a secondary lens, two compensating lenses, two imaging sensors and a laser. The primary lens directly forms the long focal length arm of the collimator. The combination of the primary lens and the secondary lens form the short focal length arm of the collimator. The collimator has an angular resolution <0.75 μrad and a 10 mrad field of view. For the collimator, the incident beam is focused on the two imaging sensors by its two arms, and the beam emitted from the laser is collimated and transmitted. The collimator is combined with an optical scanner and a fine beam deflector to test and verify the PAT performance of the inter-satellite laser communication terminal in a full physical manner.     

CAFe DUMP前刮束器的设计研制

位于中国科学院近代物理研究所的超导直线加速器样机CAFe是一台质子超导直线加速器实验样机,围绕该装置的束流实验研究将为下一步设计研究加速器驱动次临界洁净核能系统(ADS)专用的超导直线加速器打下基础并提供经验。为了实现CAFe的10 mA束流指标,需要设计研制专门的束流收集器(DUMP)和对应的刮束器。本工作就CAFe DUMP前刮束器的研制进行了系统的设计和计算工作。刮束器面向束流侧的材料采用Al6063,确保束流轰击后的剩余放射性活度处于安全范围。基于蒙特卡罗粒子输运模拟,开展放射性核素及剩余剂量分析。结果表明,退役时刮束器外围剂量为可接受的百微希沃特每小时量级。通过ANSYS的热分析,计算了不同束流情况下刮束器的温度分布及温度变化,研究了刮束器在正常运行时移除热量的能力和在异常状况下应急保护的能力。计算结果表明,刮束器可以满足安全移除强流高功率束流束晕的设计需求。在CAFe高功率束流实验中,刮束器及DUMP运行正常,束流监测指标与设计一致,证明研制的刮束器实现了安全移除束晕、监测束流参数和保护DUMP的功能。     

Dose rate estimates due to gas bremsstrahlung for a photon shutter and collimator unit of the VESPERS beamline at the Canadian Light Source

A radiation shielding study against primary and secondary gas bremsstrahlung is carried out for a tungsten collimator/stop, which is one of the components employed in the VESPERS beamline at the Canadian Light Source. The dose and dose rate are obtained by calculating the energy deposition in a water phantom which surrounds the collimator/stop unit. The dose rate behind a vacuum hole of the collimator/stop which leads to the experimental hutch is closely examined. The dose rates are further investigated with the addition of a tungsten shutter that is positioned in front of the collimator/stop.     

校靶镜检定装置光学系统设计

根据校靶镜的检定需求,在传统检定装置的基础上,研究了一种新型的校靶镜检定装置,可针对不同口径的校靶镜进行检定,扩展了检定范围。运用ZEMAX软件设计可调焦平行光管,可在焦距500~1 000mm范围内实现连续变焦。设计过程中对可调焦平行光管结构进行分析,在0.707带对F光和C光校正了色差,获得了较好的像质。同时运用MATLAB软件拟合该变焦距光学系统的凸轮曲线。所设计的可调焦平行光管其光学传递函数在截止频率为33lp/mm时可达到0.3~0.5,成像质量良好,符合使用要求。