编码孔径辐射成像定位技术

随着核物理技术的广泛应用及其辐射防护对放射源的成像需求在不断增加。编码孔径成像定位系统作为一种高精度的放射源成像及定位装置,可以准确定位放射源的位置并重建放射源的大致形状,本文探究编码孔径成像定位中的多种重建算法对具有连续能谱的放射源位置及形状重建效果对比,从而确定不同重建算法的优缺点及其适用的场景。利用Geant4软件对编码孔径成像定位系统进行模拟,得到相关数据再使用δ解码算法、精细采样平衡解码算法、卷积神经网络算法、最大似然最大期望值法（MLEM）进行编程实现并重建放射源的位置。结果表明：4种重建算法都可以清晰地定位到放射源的位置;δ解码算法和精细采样平衡解码算法重建图像有伪影;卷积神经网络算法对于线源、面源重建效果较差,可以通过扩展训练集解决;MLEM算法的对比度-噪声比（CNR）值较高,重建效果较好,但是对线源和面源重建会丢失部分细节信息。     

MURA编码辐射成像系统的解码方法

近年来,随着核辐射成像技术的发展及应用的需求,核辐射成像设备在高灵敏度、高分辨率、高信噪比以及携带方便等方面受到越来越多的关注,编码孔径准直器代替传统的平行孔和针孔准直器顺应了这种发展趋势,成为核辐射成像领域的研究热点。本文主要介绍一种新型便携式辐射成像探测系统中修正均匀冗余阵列(Modified Uniformly Redundant Arrays,MURA)编码孔径准直器的成像方法,研究其解码过程、校正方法和解码矩阵的算法:δ解码算法和精细采样平衡解码算法。在MATLAB环境下对两种解码算法进行了对比仿真,并对单个放射源与多个放射源情况分别进行了图像重建实验。实验结果表明,精细采样算法要比δ解码算法更能使成像系统对单源或多源进行清晰成像。     

一种纵、横向视野不同的编码孔径伽玛相机的方法论述与模拟验证北大核心CSCD

对基于M-M编码方式的编码孔径成像系统的方法进行了论述,通过蒙特卡罗软件MCNP对基于M-M编码方式的成像系统建立模型。使用不同能量的放射源在不同的位置,对不同厚度的编码准直器进行照射,并对所获得的重建图像SNR进行了分析与说明,确定了最佳的码板厚度为10 mm。随后模拟了基于最佳码板参数的成像系统对单点源、多点源以及形状源的响应,其中单点源的重建图像SNR达到40.36,成像系统也成功重建出了形状源的形状,且背景都没有波动的旁瓣。以上结果证明M-M编码方式优异的性能,具备替代MURA或者URA在特殊场景的应用潜力。可为后续的基于M-M编码方式的编码孔径伽玛相机的研制奠定基础。     

近场条件下X射线位相衬度成像方法及其模拟

近场条件下的类同轴法位相衬度成像具有边缘突出效应，其强度分布与相位分布的拉普拉斯算子有直接关系。在近场成像过程中，成像距离决定了成像质量的好坏。本工作通过一维模拟几种具有特定几何构型样品的菲涅耳衍射图样，得到近场条件下最适宜的成像距离，并通过二维模拟验证了此结论。      

γ相机探测技术研究

<正>针对如何有效搜寻放射源、显示γ放射性污染区域强度分布,为后续处理提供依据,提高国民生活以及核设施的安全性,需发展γ相机探测技术来计算、分析和判断,快速查找放射源和放射性污染区域。编码孔径成像技术的不断发展为研制新型辐射成像设备提供了理论依据。γ相机的基本结构主要由编码孔准直器、闪烁体晶体探测器、数据采集与传输模块及用     

大孔径厚针孔成像数值模拟研究

为解决cm级尺寸射线源的空间分布诊断,本文提出大孔径厚针孔成像方法。采用Geant4软件编写蒙特卡罗程序模拟5、10和15 mm大孔径厚针孔的成像过程,采用Matlab软件实现逆滤波、Wiener滤波和Lucy-Richardson复原算法,以均方根误差σ作为复原效果评判标准,优化了Wiener滤波信噪比参数和Lucy-Richardson算法迭代次数参数。将复原算法应用于不同孔径厚针孔的图像复原,发现理想逆滤波算法会引起噪声放大;Wiener滤波算法图像复原解存在较严重的伪影;Lucy-Richardson算法可获得清晰的复原图像。结合Lucy-Richardson算法的5、10、15 mm大孔径厚针孔成像获取的图像的σ是0.5 mm孔径传统针孔成像结果的1.15、1.21、1.26倍。结果表明,结合图像复原算法的大孔径厚针孔成像技术能获得与传统针孔成像接近的源图像测量结果,初步验证了该方法具有可行性。     

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。     

基于电偶极子辐射模型的三维成像算法

提出了一种基于电偶极子辐射模型的三维成像算法.在研究后向投影算法原理的基础上,利用散射模型分析了近、远场成像的关系,提出先采用电偶极子辐射模型对采样数据进行近场化处理,再将处理后的数据反向投影到成像区域,获得成像图像.利用FDTD数值仿真实现对目标的三维成像,验证了算法的有效性,分析了耦合对成像效果的影响.     

X射线编码孔成像技术在近地太空核爆探测中的应用

根据X射线编码孔成像的原理,搭建了地面模拟成像系统,在此基础上建立了编码孔成像技术探测近地太空核爆当量和方位的理论计算方法,获得了系统响应（灰度）与X射线强度、重建图像质心位置与X射线入射角度之间的关系,并开展了核爆当量和方位的模拟探测实验,对实验数据和理论计算数据进行了对比和分析。结果表明,理论计算结果与实验结果吻合较好,验证了采用X射线编码孔成像技术探测近地太空核爆的可行性,同时证明X射线编码孔成像具有较多针孔成像更高的探测灵敏度、信噪比和抗干扰能力。     

线扫描探测器位移的测量

介绍了基于光学编码的线位移测量系统.系统由位移编码、光学成像和位移读出三个部分组成,位移读出包括光电转换器件(线阵CCD)及其外围电路(CCD驱动电路)、二级放大电路、巴特沃斯二阶低通滤波电路和二值化电路.介绍了编码方式,给出了各个电路的实验信号波形,给出了系统的线性实验测试结果,实验结果令人满意.     

Preparation of Zn/TiO2 powder and its photocatalytic performance for oxidation of P-nitrophenol

Zn-doped TiO2 catalysts were prepared using a sol-gel method and characterized by XPS,UV-Vis, BET, XRD in this study. Under the irradiation of simulant sunlight, the photocatalytic activity for the degradation of p-nitrophenol was studied too. After irradiation for 2.5 h, the degradation percentage of p-nitrophenol could rise to more than 80 %. The results showed that the spectrum absorption band edge of Zn/TiO2 powder does not broaden obviously comparing with pure TiO2 powder. Zinc exists as Zn （11）. When calcined at 973 K, there is a new phase as ZnTiO3 in Zn/TiO2 catalyst. The order of photocatalytic activity of Zn/TiO2 catalysts calcined at different temperatures for p-nitrophenol is 773 K 〉 673 K 〉 873 K 〉 573 K 〉 973 K and the photocatalytic activity of Zn/TiO2 catalyst calcined at 773 K is better than TiO2 catalysts heated at the same temperature, and outclasses that of commercial TiO2 catalyst. It also showed that the photocatalytic degradation of p-nitrophenol follows first-order kinetics under the irradiation of simulant sunlight.     

Current status of radiation therapy for prostate cancer

Radiotherapy for the treatment of prostate cancer has been extensively explored in the past. Along with the comprehensive understanding of the biology of prostate cancer and rapid advances in terms of technology, the out- come of treatment for the patients with prostate cancer has improved. The authors review radiotherapy as the primary treatment for the disease, with particular emphasis on the technological advances from both the radiobiological and radiophysics aspects. Nonconventional fractionated irradiation like hyper- or hypo-fractionation has been imple- mented in the clinic, the final results still need to be confirmed in the future. Technological advances like IMRT, IGRT, in the last two decades have significantly improved the delivery of external radiotherapy to the prostate. This has re- sulted in an overall increase in the total dose that can be safely delivered to the prostate, which has led to modest im- provements in the biochemical outcome. However, establishing the standard therapy for prostate cancer remains con- troversial. It is hoped that the next decades will bring continued advances in the development of biologicals that will further improve current clinical outcomes.     

The control system for SSRF injection and extraction

This paper introduces the injection and extraction control system design for SSRF,which is a distributed control system aimed at stability and reliability of the pulse power supplies,PPS(Personnel Protection System)and MPS(Machine Protection System).The hardware environment is mainly based on PLC(Programmable Logic Con- troller),and ARM(Advanced RISC Machine)is also applied for studying stability of the power supplies.WinCC and EPICS(Experimental Physics and Industrial Control System)have been selected as the platforms of SCADA(Super- visory Control and Data Acquisition).For unifying the interfacing to the control computer,all front-end equipments are connected via Industrial Ethemet.     

水平管内含空气蒸汽强制对流冷凝换热模型研究

为研究含空气蒸汽在水平管内强制对流冷凝换热特性,基于对传热传质过程的分析,建立了管内为环状流与波状流条件下的流动冷凝换热模型。从潜热、显热和液膜3个环节对整个换热过程进行建模,最终得到计算局部冷凝换热系数的理论关系式。模型预测结果与实验数据的对比表明,二者相对偏差在±20%以内,验证了该换热模型的准确性与适用性。通过进一步的研究发现：从换热管入口至出口,随着冷凝的进行,管内换热主要热阻由液膜热阻向气液界面的凝结热阻转变;主流气体对流换热过程基本可忽略。     

Investigations on landmine detection by BF3 detector

Experiments were carried out to investigate the possible use of neutron backscattering for the detection of polyethylene (PE) sample buried in the soil. In detection of landmine by neutrons, the neutron detector and its shield play an important role. In this paper, the effects of graphite, heavy water, polyethylene and boric acid moderators on the flux of back scattered neutrons were investigated. We have also experimentally verified the effect of BF3 detector shield and obtained good agreement with theory.     

Web Services interface of SSRF archive data analysis system

Accelerator database stores various static parameters and real-time data of accelerator. SSRF (Shanghai Synchrotron Radiation Facility) adopts relational database to save the data. We developed a data retrieval system based on XML Web Services for accessing the archive data. It includes a bottom layer interface and an interface applicable for accelerator physics. Client samples exemplifying how to consume the interface are given. The users can browse, retrieve and plot data by the client samples. Also, we give a method to test its stability. The test result and performance are described.     

有效探测面积大于1000 cm2的正比计数器测量系统性能测试

为对自制的活性面积高达1 000 cm²的大面积源进行表面发射率定值,同时作为现有2πα、2πβ表面发射率标准装置能力的扩充,研制了一套内置式大面积2π多丝正比计数器测量系统,并利用活性区直径为8 mm的²⁴¹Am点源及活性区面积为10 cm×15 cm的大面积²⁴¹Am和⁹⁰Sr-⁹⁰Y源对其进行计量学性能测试。结果表明：计数器内计数响应均匀性优于±0.4%,有效探测面积达1 400 cm²;所得²⁴¹Am源高压坪曲线的坪长为1 400 V,坪斜为0.27%/100 V,坪区内计数变化为0.87%;⁹⁰Sr-⁹⁰Y源高压坪曲线的坪长为300 V,坪斜为0.75%/100 V,坪区内计数变化为0.80%;10次测量重复性好于0.4%,8 h内短期稳定性好于0.3%,1 a内长期稳定性好于0.8%。     

Assessment of radioactivity levels in some oil samples from the western desert, Egypt

Distributions of natural gamma-emitting radionuclides were determined in 93 oil samples collected from some petroleum fields in the western desert of Egypt. The radioisotope activities in the area under investigation lay in the range of (21 ± 4) to (38 ± 13) Bq?L-1 for 226Ra, (9 ± 2) to (15 ± 5) Bq?L-1 for 232Th, and (154 ± 28) to (303 ± 54) Bq?L-1 for 40K. The mean values were 27, 12, and 201 Bq?L-1, respectively. Among oils, variations in radionuclide ac- tivities could be on account of differences in TDS, HCO3, and Ba, with high or low pH. In this environment, oil prop- erties differently affected the mobilization of natural radionuclides. The range of 226Ra variation had been compared with available data from other countries. The calculated absorbed dose rate ranged from 22.33 to 32.66 nGy?h-1 in lo- cation (B) and (E) respectively, which was less than the accepted value.     

Preparation and properties of 117m Sn(IV)-TTHMP in in-vitro and in small animals

In this work,TTHMP was synthesized and labelled with 117m Sn.The preparation conditions,stability and lipophilicity of 117m Sn(IV)-TTHMP were investigated.Biodistribution of the complex in rabbits and mice was studied.It was found that the quantity of TTHMP and pH value of the prepararion solution had vital effects on the labeling yield of 117m Sn(IV)-TTHMP.It was also found that 117m Sn(IV)-TTHMP was hydrophilic and stable at room temperature and 37℃ in open air 117m Sn(IV)-TTHMP showed unexpectedly high bone uptake and bone-to-blood ratio in the animals.This made it potentially useful as an reagent for skeletal scintigraphy and radiotherapy of bone tumors.     

The role of AGFA high-energy CR in the calibration and quality control of multileaf collimators （MLC）

Linear accelerators equipped with multileaf collimators （MLC） are becoming more common and are widely used in the intensity-modulated radiotherapy （IMRT）. There is an imperative need to ensure the commissioning specification of the linear accelerators for the sake of quality assurance （QA） and quality control （QC）. This paper is aimed to investigate the role of AGFA high-energy CR （Computed Radiography） in calibrating dynamic multileaf collimators and evaluating the accuracy of the leaf position. The result shows that AGFA high-energy CR can easily and conveniently be used to calibrate MLC and verify its position. Hence, the application of AGFA high-energy CR is proved to be an accurate and time-saving method for routine MLC QC, especially when MLC calibration adjustments are required.