蒙特卡罗方法选择TGS准进器的最佳形状

采用蒙特卡罗方法和技术，模拟了ＴＧＳ连续扫描模式，对不同形状的准直器，计算了被测量废物桶中各个像素内的纵向效率的最大百分差，从中选取了棱形准直器和调整后的棱形准直器作为ＴＧＳ装置的扫描直器。     

伽玛刀单束射线特性的Monte Carlo模拟

应用ＧＥＳ４ Ｍｏｎｔｅ Ｃａｒｌｏ程序模拟了单源情况下,＾６０Ｃｏγ射线经Ｌｅｋｓｅｌｌ Ｇａｍｍａ Ｕｎｉｔ准直系统后直射（未经散射）光子和散射光子在终准直器平面上的半径分布、能量分布及角度分布。模拟结果表明,在终准直器的外孔径范围内,直射光子数目约比散射光子数目高２－３个数量级,而在准直器孔径外,散射光子的份额不可忽略。对于光子的散射,又以康普顿散射为主,其它散射所占的份额很小,并且在准直器     

GZR－50型γ照射容器

本文介绍了一种用于工业计算机层析成像装置（ＩＣＴ）的ＧＺＲ－５０型γ照射容器。该容器根据装置的要求而研制，技术指标达到要求，具有重量轻、定位准、照射野均匀、安全性好等特点。通过更换前准直器，本容器还可用于γ探伤系统和辐射刻度系统。     

蒸汽发生器隔板和传热管束的水力学载荷分析

蒸汽发生器（ＳＧ）隔板和传热管束的水力学载荷分析ＳＧ隔板和传热管设计的基础，本文介绍了采用法国，ＡＴＨＩＳ和ＦＯＲＣＥＴ程序以及大亚湾核电站输入数据，对秦山二期ＳＧ在ＬＯＣＡ事故时隔板所受的最大压力和传热管束所受的最大水平载荷进行的建模和分析计算，并将计算结果与法马通过的计算结果进行了比较，比较结果表明，两者符合较好，对秦山二期ＳＧ而言其隔板设计的最大压差为８．０ＭＰａ，传热管束设计的最大水平力为     

轫致辐射显像的初步探讨

应用Ｓｏｐｈｙ ＤＳＸ ＳＰＥＣＴ系统，以＾９０Ｙ、＾３２Ｐ纯β类核素作为辐射源，通过模型实验选用不同准直器、不同能量窗宽等进行轫致辐射显像，以探讨最佳显像条件。结果发现：轫致辐射光谱是连续的，最大光子分布约在７０ｋｅＶ，以高能准直器，取８０ｋｅＶ６０％的能量范围及窗宽或经验性窗宽、且准直器与放射源之间距离较短时图像最为满意，２例病人的显像效果良好。结果表明ＳＰＥＣＴ可以用作轫致辐射显像。     

并列螺旋管圈管内两相流不稳定性程序OTSGI

研究了螺旋管直流蒸汽发生器两相流不稳定性。利用线性化频域理论，采用分相模型，考虑一邓管壁动态特性，建立了螺旋管直流蒸汽发生器两相充不稳定数学模型，编制了计算ＯＴＳＧＩ，分析了人口节流圈、系统压力等因素对不稳定性的影响，给出了螺旋管直流蒸汽发生器两相不稳定区域。     

GaAs FET辐射退化研究

低噪声ＧａＡｓ ＦＥＴ和功率ＧａＡｓ ＦＥＴ经中子辐射都未发生致命性的通或断失效，直流偏置伏态下，其失效模式仅仅表现为源漏饱和电流ＩＤＳＳ的退化降低，据此提出了ＩＤＳＳ退化失效与快中子注量φｎ之间的解析关键式ｌｎｙ＝ａ＋ｂｌｎφ。     

材料与构件深部应力场及缺陷无损探测中子谱仪径向准直器的设计

为设计材料与构件深部应力场及缺陷无损探测中子谱仪的径向准直器，实现大型工程构件的远距离准确取样，本文分析了径向准直器的实空间和相空间取样原理，介绍了目前径向准直器取样体积的解析与模拟计算方法，并利用0.2 mm尼龙线测试了德国E3残余应力谱仪径向准直器的取样尺寸，基于实验结果确定了采用JRR3解析方法作为径向准直器取样尺寸的计算依据。根据解析计算结果，研究了设计参数对径向准直器取样尺寸和传输效率的影响规律，并按照谱仪的空间几何结构，最终设计了谱仪1、2、3、4、5 mm径向准直器取样系统。     

螺旋管直流蒸汽发生器两相流不稳定性

研究了螺旋管直流蒸汽发生器两相流不稳定性。阐述了两相流不稳定性机理。利用线性化频域理论，建立了螺旋管直流蒸汽发生器两相流不稳定性数学模型，编制了计算程序ＨＴＯＴＳＧＩＡ，分析了入口节流圈，系统压力及不同螺旋管圈等因素对螺旋管直流蒸汽发生器两个流不稳定性的影响，给出了螺秘管直流蒸汽发生器两相流稳定区域。计算值与实验值基本一致。     

^90Y,^32P—GTMS介入治疗恶性肿瘤的实验研究与初步临床应用

采用介入治疗法，将＾９０Ｙ－ＧＴＭＳ和＾３２Ｐ－ＧＴＭＳ直接注入癌性肿块中，以达到杀灭癌细胞、抑制肿瘤生长、延长恶性肿瘤患者生存期的目的。在荷瘤裸鼠模型的瘤体上进行对照组、“冷”球组、不同剂量组（＾９０Ｙ－ＧＴＭＳ剂量分组为９２．５、１８５、３７０ＭＢｑ，＾３２Ｐ－ＧＴＭＳ剂量分组为３７、９２．５、１８５ＭＢｑ）的治疗，治疗后不同时间观察疗效，获得核素在单位体积中有效剂量后应用于临床。借助Ｂ超对肿     

Pinhole collimator design for nuclear survey system

A conventional knife-edge collimator, which is widely used in gamma camera for medical diagnosis, is not suitable for nuclear imaging system because many scattering radiations near the pinhole aperture happen and blur image. A new pinhole collimator, which shapes a channeled aperture for reducing image degradation induced by the scattering radiations, is introduced and its characteristics are analyzed by Monte Carlo simulation. Resolutions defined as the full-width at half-maximum (FWHM) of point spread function and efficiencies are calculated about several pinhole diameters from 4 to 8 mm and channel heights from 2 to 10 mm. For this calculation, we assumed that ¹³⁷Cs radiation sources with 662 keV mono-energies enter into our designed collimator at the 1 m distance from the detector plane. The efficiencies and resolutions of the channeled collimator are compared with those of the conventional collimator. By comparison results, it is verified that the new collimator takes advantage more than the conventional collimator. The optimum channel height and diameter of the pinhole collimator from simulation results are also proposed and designed. We finally acquired nuclear image mounting this collimator in the nuclear survey system.     

基于LaBr3(Ce)晶体耦合SiPM阵列的可变角分辨率伽玛相机的设计与研制

编码孔径成像技术由于探测效率高、信噪比高、角分辨率好、成像质量稳定可靠等优点而广泛应用于核安全、核设施的去污及退役的测量、核医学等领域。建立通过改变编码准直器和探测器之间距离进而实现可变角分辨的伽玛成像系统。整个成像系统主要由编码准直器、位置灵敏探测(position sensitive detector, PSD)、数据采集卡以及图像重建系统组成。该成像系统的编码准直器采用修正均匀冗余阵列(modified uniformly redundant array, MURA)编码方式,为了保障对较高能量射线的探测能力,编码准直器的材料采用含钨量90%的钨铜合金,PSD通过LaBr₃(Ce)晶体耦合SiPM阵列组成,重建算法采用的是直接互卷积算法,快速高效。测试结果显示,整个位置灵敏探测器的平均能量分辨率为4.96%(662 keV);该辐射成像系统可以准确地对Am-241、Cs-137、Co-60进行清晰成像,并通过改变编码准直器和探测器之间的距离成功分辨出两个Cs-137点源的位置。     

用于固体放射性废物无损定量测量的TGS图象重构技术

本文介绍了用于固体放射性废物无损测量的TGS图象重构技术的原理和技术,对TGS装置的准直器材料、屏蔽层厚度、准直孔的形状及其长／宽比的设计,以及对测量的效率矩阵的获取等关键问题进行了讨论。     

Monte-Carlo simulation of pinhole collimator of a small field of view gamma camera for small animal imaging

Needs in scintimammography applications,especially for small animal cardiac imaging,lead to develop a small field of view,high spatial resolution gamma camera with a pinhole collimator.However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity.In order to design a pinhole collimator with an optimized sensitivity and spatial resolution,the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters.The results show that the camera with pinhole of 1 mm,1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm,2.25 mm and 3 mm and geometric sensitivity of 0.016%,0.022% and 0.036%,while the source to collimator distance is 3 cm.We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the wade-off between sensitivity and resolution.     

Characteristics of parallel-hole and pinhole collimators for nuclear medicine imaging

In this paper,the spatial resolution and geometry sensitivity of parallel- and pin-hole collimators in compact gamma camera are presented,and quantitatively compared by GEANT4 code in Monte-Carlo library.The results show that the geometry sensitivity for pinhole collimator rapidly drops with increasing the gamma source-to- collimator distance(SCD);and for parallel-hole collimator,mildly.Meanwhile,the spatial resolution for pin-hole collimator mildly deteriorates;and for parallel-hole collimator,severely.The pin-hole collimator for close imaging objects has higher geometry sensitivity than parallel-hole collimator.Our findings are helpful for setting compact gamma camera collimators in nuclear medicine imaging.     

Study of intensity suppression in a gantry beamline for SC200 proton therapy system

ABSTRACT

For proton therapy, a beam intensity of 0.4 nA to 4 nA is typically used with a beam transmission factor of 10. However, because of energy degrading, emittance matching, and energy spread selecting, the ratio of beamline transmission (I_Max/I_Min) for our SC200 proton therapy facility (200 MeV/500 nA) should be far more than 10. Therefore, a novel intensity suppression scheme, based on the installation of two new collimators placed symmetrically with respect to the gantry coupling point, is proposed and verified. First, the feasibility of delivering a beam with variable size at the gantry isocenter is demonstrated. The beam delivery method uses waist-to-waist imaging optics, a symmetric beam method, and the principle of beam line inversion. The relationship between energy and isocenter beam size (in air) is then verified using an empirical formula and a Monte Carlo method. The intensity suppression and subsequent optimization of the gantry beam optics were accomplished through simulations. The results indicate that increases in the entrance beam radius at a specific collimator results in significant changes in the beam optics and intensity behind the collimator. This passive scheme, which produces intentional losses at the gantry coupling point, is demonstrated to be viable.     

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating, accelerating and guiding protons, using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism. In addition, the problems involved are studied by using two-dimensional particle-in-cell simulations. The results show that the proton beam can be collimated, accelerated and guided effectively through this type of target. Theoretically, a formula is derived for the combined electric field of accelerating protons. Compared with a proton beam without a beam collimator, the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10% respectively. Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field, and that the beam collimator plays a role in focusing energy. In addition, the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I. The more prominent point is that the proton number of type II is 2.2 times higher than that of type I. This kind of target has important applications in many fields, such as fast ion ignition in inertial fusion, high energy physics and proton therapy.     

基于束流环形高斯模型对上海硬X射线自由电子激光装置的束流刮束器进行活化分析

在建的上海硬X射线自由电子激光装置(Shanghai HIgh repetition rate XFEL aNd Extreme light facility,SHINE)的加速器隧道内,采用束流刮束器刮掉束晕外围张角比较大的电子,刮束器的束流损失率为0.1‰。本文采用蒙特卡洛程序FLUKA,用SOURCE程序实现电子束在3σ_beam外的高斯分布,以尽量真实模拟电子在束流刮束器处的丢失情况,解决了低功率刮束情况下蒙特卡洛模拟无统计性结果的难题。利用束流环形高斯模型对刮束器的活化进行了分析,结果表明环形高斯模型可以更真实地再现电子在束流刮束器的丢失情况;5年运行后距刮束器30 cm处的剩余剂量率达到了数百μSv/h至数mSv/h,和国外类似装置计算结果相当;通过对放射性核素的种类分析,结果证明刮束器(钨)的放射性废物处置难度不大。     

GEANT4 simulation of photo-peak efficiency of small high purity germanium detectors for nuclear power plant applications

GEANT4 – based Monte Carlo simulations have been carried out for the determination of photo-peak efficiency of heavily shielded small high purity germanium detector (HPGe) used for monitoring radiation levels in nuclear power plants. The GEANT4 simulated values of HPGe detector efficiency for point as well as for disk sources, for two different values of collimator diameter, have been found in good agreement with the corresponding published results obtained by using the MCNP code. The work has been extended to study the effect of radial displacement of a source relative to a detector on photo-peak efficiency for both point and disk source, and at various values of γ-ray energies. Also the effect of disk source radius on photo-peak efficiency has been studied. Besides the results of different available physics models in GEANT4 have also been compared. The computed values of efficiency for point as well as for disk sources using the Penelope and Livermore physics models have been found correspondingly consistent for various values of γ-ray energies while some differences (e.g., Penelope model yields 6.3% higher values of photo-peak efficiency for Eγ = 1.332 MeV, 10 mm collimator diameter) have been observed in the corresponding valued obtained by using the Standard physics model.