γ射线级联衰变符合相加修正方法研究

γ射线级联衰变引起的符合相加干扰可导致被测量γ射线全能峰计数增加或减少,从而使测量结果偏离真实值。本文从级联符合相加产生的机理出发,以~(134)Cs为例研究了级联符合相加修正因子的数值计算方法。基于蒙特卡罗计算程序MCNP给出了γ射线全能峰效率和总效率的模拟计算方法。通过实验测量和软件计算验证了符合相加修正因子数值计算方法的准确性。针对核电厂周围环境监测中主要关注的人工放射性核素,计算了不同环境介质中γ核素测量的符合相加修正因子。计算结果表明,对于气溶胶、生物灰样品中核素~(110)Ag~m、~(134)Cs符合相加干扰可达20%以上,而对于全能峰效率相对较低的土壤样和水样符合相加干扰可大于10%,其余核素也不同程度地存在符合相加干扰。本文研究结果为γ放射性核素的准确测量和误差来源分析提供了技术参考。     

γ谱仪测量土壤样品探测效率模拟刻度研究

针对Ф75mm×25mm的土壤样品,利用HPGeγ谱仪,分别用241Am、137Cs、~(60)Co混合点源测量5种高度的样品剖面上不同位置的全能峰效率,确定点源全能峰效率随半径变化的函数关系,对该函数进行数值积分计算可以得到59.54keV、661.66keV、1173.2keV和1332.5keVγ射线的面源全能峰效率,进一步拟合确定面源全能峰效率随样品高度变化的函数参数,对样品高度进行数值积分计算得到Ф75mm×25mm样品的体源全能峰效率。结果表明,点源模拟计算的体源全能峰效率和标准体源全能峰效率进行比较,两者在10%以内符合。因此,在没有标准体源的情况下,用已知活度的标准点源模拟体源进行全能峰效率刻度的方法替代标准体源进行效率刻度方法是可行的。     

γ能谱符合相加效应修正方法及影响因素

在辐射环境质量监测中,多能核素的级联符合相加效应是影响γ能谱活度测量准确性的重要因素之一,为了提高待测样品分析的准确性,对结果进行符合相加修正是十分必要的。以¹⁵²Eu核素为例,根据峰总比不变性特点,获得探测器峰总比拟合公式,联合符合相加修正公式,全能峰效率公式,计算了¹⁵²Eu核素的符合相加修正因子,进一步采用Genie 2000符合相加蒙特卡罗程序对液体体源的¹⁵²Eu核素进行了符合相加修正。点源的修正结果与真值的相对偏差小于6%,体源修正结果与真值的相对偏差在±4%以内。通过点源符合相加修正因子与源到探测器距离的线性关系,可以得到符合相加效应可忽略的最小测量距离;体源样品的符合相加修正结果表明：同一介质的样品,高度越高,符合相加修正因子越小;自吸收效应会在低能端对样品的有效立体角产生较大影响,从而影响样品的符合相加修正因子。峰总比不变性与衰变纲图相结合的数值修正方法,不需要对不同位置处的点源总效率进行测量,与蒙特卡罗程序法相比,该方法无需对探测器进行工厂表征,不用对体源介质、密度和形状等参数进行描述;舍弃级联符合较...     

放射源~(152)Eu的能谱识别及和峰特性分析

使用低本底高纯锗(HPGe)探测器测量放射源~(152)Eu的γ能谱,识别能谱中出现的所有峰,分辨出干扰峰,并对和峰的特性进行分析,结合计数率随距离变化曲线以及通过分辨率比较和峰与特征峰的差异,为和峰的辨别提供判据。在和峰效应引起的全能峰计数率减少的情况下,修正各全能峰计数率,计算放射源中~(154)Eu杂质含量,结果显示,与修正前差异较明显,表明在能谱分析尤其是考查全能峰强度数据时,需要进行符合相加修正。     

γ射线谱中符合相加修正系数的Monte-Carlo模拟

用Monte Carlo方法模拟放射性核素的衰变过程,得到用HPGe探测器应能测到的多道γ能谱理论谱形,同时给出各特征能峰的探测效率和各特征峰的真符合相加修正系数。采用本方法开发的I、140Co、131Cool2000软件,可模拟60Co、88Y、134Cs、133Ba、95Nb、57Co、103Ru、106Ru、110Agm、124Sb、144Ce、65Zn、58La、241Am、99Mo、166Hom、152Eu、125Sb、214Bi、212Bi(α衰变链)和208T1,共计24种核素的衰变过程。对于60Co圆柱形体源发射的两条主要γ射线进行测量和分析结果表明:符合修正系数的模拟计算值与实验值在±1%的偏差范围内相符。同时给出了一种校正同轴探测器死层厚度和冷指尺寸的方法。     

塑料闪烁体环探测器作反符合屏蔽的NaI(Tl)γ能谱仪

本文报告了一个用塑料闪烁体环探测器作反符合屏蔽的NaI(T_1)γ能谱仪的结构及主要性能。它采用Φ76×76mmNaI(Tl)晶体作为主探测器和符合探测器,以自制的Φ500×520mm塑料闪烁体作环探测器。在有无井型反符合屏蔽条件下,能量范围0.1—2MeV时,谱仪的积分本底比为2.8,对~(137)Csγ源的康普顿减弱因子(积分比)为2.5。当源位于晶体表面中心时,谱仪对~(137)Cs源的能量分辨率和全能峰效率分别为9.5％和8.4％。     

干扰核素对便携式HPGeγ谱仪全能峰效率的影响

采用~(152)Eu点源作为干扰核素,模拟高本底复杂环境对~(57)Co、~(133)Ba低能核素全能峰效率的影响。用高、中、低能三种点源在距离便携式HPGeγ谱仪探头25 cm处,以不同次序叠加测量,分析所得全能峰效率与其单独放置时测量结果的相对偏差,并与固定式HPGeγ谱仪测量结果进行比较。结果显示:~(152)Eu点源对~(57)Co和~(133)Ba主要能量峰效率的影响量最大为7.1%,最小为1.3%;在三种特定叠加次序下,各能量峰效率的平均相对偏差均在4%以内。且与固定式HPGeγ谱仪测量结果一致。     

快速NaI全身计数器γ谱全能峰形函数的探讨

采用主高斯函数加高能尾、低能尾小高斯修正项共9个参数的经验函数可较好拟合γ谱的各全能峰,给出了相应的拟合参数及分析结果.考虑到NaI全身计数器要求γ谱分析快速可靠,在保证一定的准确度情况下,对该经验函数作了进一步的简化,忽略高能尾修正项,仅考虑低能尾修正项,并引入低能尾小高斯修正项的峰位和半高全宽分别与主高斯函数的峰位和半高全宽的相关关系.在γ谱分析软件中仅采用主高斯函数加低能尾小高斯修正项4个参数的经验函数.结果表明,对NaI全身计数器测得的57Co、137Cs、60Co和柏40K等所有全能峰拟合的解析型改进的优良指数AJFOM均小于0.01%,拟合优度达到优良.     

NaI(Tl)、Ge(Li)探测器对大圆柱体源的效率

本文介绍用蒙特卡洛方法,采用加权技巧计算 NaI(Tl)、Ge(Li)探测器对大体积圆柱形体源的效率。文中首先对计算方法作了简要叙述。然后介绍在 PDP11/34A 小型计算机上用蒙特卡洛方法计算了76×76mm NaI(Tl)晶体对76mm 直径的水圆柱体源的效率,在80—3000keV 能区,计算值与文献值在±1%内一致。对本实验室的一台 Ge(Li)探测器,分别计算了它对 NBS参考物质和水圆柱体源(源半径大于 Ge(Li)晶体半径)的效率,计算中对探测器 N 层和包装外壳等项因素作了修正。实验测定了点源的峰总比,得到 Ge(Li)探测器的峰效率。将 Ge(Li)探测器峰效率的计算值与用~(152)Eu、~(60)Co、~(137)Cs、U、U-Ra 和 Th 标准源测得的实验值进行了比较,在93—2614keV 能区,估计两者在±4%内一致。最后讨论了样品体积与探测下限的关系。     

HPGe探测器探测效率对γ能量及其探测距离的相关性研究

为了探究高纯锗谱仪探测效率与γ能量和探测距离的普适函数关系,本工作利用标准源133Ba、137Cs和60Co,刻度了探测器在高能段(E160ke V)的效率曲线;并通过调节探测器与标准源的距离,研究了效率曲线与探测距离的变化关系;最后通过拟合所有实验测量点,得到了普适函数关系式。为减小统计误差,各特征γ的全能峰计数大于2.0×105;同时利用了强源干扰法对较大死时间数据进行了修正。该结果可为开展大规模非标样品的实验测量和体样本探测效率的模拟计算提供参考。     

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.