铀表面腐蚀初始阶段的理论模型

本文使用数值模拟方法讨论了铀表面腐蚀初始阶段的氧化物形成过程.这个阶段发生在从清洁的铀表面吸附反应气体后到整个表面被一层氧化物所覆盖的过程之间.对储存在含有腐蚀气体气氛中的铀和铀合金材料,准确了解铀最初开始反应到表面被氧化物完全覆盖的反应速率是非常重要的.本文对该氧化物形成的过程进行了数学推导,讨论了等温情况下的近似分析数学表达式,得到了动力学方程,并与实验结果进行比较,表明理论模型是合理的.     

U与CO,CO2反应动力学的初步研究

在一定湿度下，将不同形态的铀样品密闭贮存在容器中并充入一定压力的高纯CO或CO2气体，通过定期测量贮存容器中气体组成，初步研究了铀与CO或CO2的反应动力学。结果表明，铀的形态，温度及气体种类对反应速度影响很大。与管状铀相比，铀粉与CO或CO2反应的速率要大得多；温度升高有利于铀与CO或CO2的反应；在相同温度条件下，CO与铀反应生成CO2的速度大于CO2与铀反应生成的CO的速度。     

铀及其合金的水氧腐蚀机理分析

铀及其合金是重要的核材料,其水氧腐蚀研究受到广泛关注。本文系统总结了铀及其合金在真空和大气环境下的氧化反应过程、腐蚀速率和产物,并对不同研究者提出的反应机理进行讨论分析。其中铀-氧反应过程为氧气在表面的吸附、解离,O2-在晶格中进行扩散,O2-在金属和氧化物界面发生反应,其中扩散是反应速率的控制步骤。铀-水体系反应机理存在争议:进行扩散反应的离子是O2-还是OH-还没有一致的认识。铀-氧-水体系的反应是氧气和水气共同作用的结果,反应速率介于前两种体系之间。     

氘/氚化铀热解吸的动力学同位素效应

在高真空金属系统上测定了氘/氚化铀在恒容体系和225～400℃范围内热解吸的压力-时间等温线,应用反应速率分析方法计算了各自在不同温度下的速率常数。随着温度的升高,热解吸反应的速率增大,反应的平衡压随之增高。由速率常数计算得到氘/氚化铀热解吸的表观活化能分别为(26.3±0.4)kJ/mol和(27.7±0.6)kJ/mol。活化能数据显示,氘/氚化铀热解吸反应的动力学同位素效应不明显。     

铀与氧气和二氧化碳的程序升温反应行为研究

利用程序升温分析方法研究了铀与氧气和二氧化碳的反应行为(TPO).结果表明在两种气氛中的反应过程均存在诱导期;当氧气分压处在16%～45%范围内时,铀的着火点温度为581～606 K,中间产物为UO2,最终产物为U3O8;铀在CO2气氛中的着火点温度相对较高,在反应过程中,CO2解离产生CO气体;反应的表观活化能随气体浓度的升高而降低.     

铀金属在H_2 CO气氛中表面反应的XPS研究

用X射线光电子能谱(XPS)分析研究了铀金属在H_2及H_2-CO气氛中的表面反应以及温度和CO对氢化反应的影响。在25℃条件下由于痕量水汽的作用,铀金属表面主要发生氧化反应。在200℃时铀金属表面发生氢化反应,氢化反应随H_2通入量的增加而增加。     

高氯酸体系中AHA与HNO_2的反应动力学研究

本工作研究HNO3体系下AHA与HNO2的反应动力学。研究得到该反应的反应动力学速率方程式为-dc(HNO2)/dt=kc(HNO2)c0.25(AHA)c(HNO3)。在t=10℃、I=0.5mol·kg-1条件下,反应速率常数k=(0.4814±0.0375)L1.25·mol-1.25·s-1。实验研究了反应温度对反应速率的影响。结果表明,随着反应温度的升高,反应速率明显加快,相应的反应活化能?E=46.92kJ·mol-1。在离子强度I=0.5～3.0mol·kg-1范围内,氧化还原反应的表观速率常数k′随离子强度I的增加而有所增大,但增大幅度不甚明显。对该反应的机理进行了简要讨论。高氯酸体系中AHA与HNO_2…     

铀金属在H_2 CO气氛中表面反应的XPS研究

用X射线光电子能谱(XPS)分析研究了铀金属在H_2及H_2-CO气氛中的表面反应以及温度和CO对氢化反应的影响。在25℃条件下由于痕量水汽的作用,铀金属表面主要发生氧化反应。在200℃时铀金属表面发生氢化反应,氢化反应随H_2通入量的增加而增加。当H_2含有一定量的CO气体时,表面氢化反应和氧化反应均受到抑制。     

纳米零价铁去除溶液中U(Ⅵ)的还原动力学研究

采用液相还原法制备纳米零价铁（nZVI）,用来去除溶液中的U(Ⅵ),讨论了溶液pH值、nZVI质量浓度、接触反应时间和温度对去除效果的影响,并从nZVI对U(Ⅵ)的还原角度探讨了还原动力学规律。研究结果表明：nZVI对溶液中的U(Ⅵ)有很好的去除效果,其去除过程包括还原沉淀和吸附,其中还原过程符合准一级还原动力学模型;溶液pH值对去除效果有明显的影响,在溶液pH值为5.0时,去除率达到最大值96.27%。温度对去除效果有一定的影响,表观速率常数k_obs随反应温度的升高而增大,还原速率与反应温度的关系符合Arrhenius定律,反应活化能E_a为16.54 kJ/mol,低于一般化学反应的活化能（60～250 kJ/mol）,表明该反应较易进行。     

水-氢同位素汽-气并流催化交换反应动力学研究

在憎水催化剂的作用下,于固定反应床中研究了水-氢同位素汽-气并流催化交换反应的宏观动力学,讨论了该反应的速率方程和反应级数,比较了反应温度和所研制的3种憎水催化剂对反应速率常数的影响关系.研究结果表明,在本工作所拟订的实验条件下,该反应具有一级反应的动力学特征;温度对反应速率常数的影响服从阿仑尼乌斯公式,温度越高,反应的速率常数越大;Pt-SDB类催化剂的活化能小于Pt-C-PTFE类催化剂.     

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.