强度平衡法测定138Csγ射线发射概率

短寿命裂变产物138Cs是测量裂变燃耗的重要核素,其半衰期为33.41min,经β-衰变到138Ba,共发射88条γ射线.根据母核衰变到子核基态上各种射线强度之和等于母核衰变活度的强度平衡法原理,用已标定好的峰效率曲线的HPGeγ谱仪准确测定了138Cs的γ射线发射概率,Pγ(1435.86keV)的测定结果为0.7599±0.0032.     

核衰变γ射线谱的测量

本文对我们实验室的探测系统和数据获取方法作了介绍,这两个系统即低本底反康普顿谱仪和γ-γ-t三参数快慢符合谱仪,我们核衰变谱学组常用这两套谱仪来测量伴随核衰变的γ射线.此外作为例子用这两套谱仪对252Cf自发裂变碎片衰变γ射线和伴随74As的β EC衰变γ射线的测量作了简要描述.     

稀土废渣现场γ射线剂量率分段计算方法

在现场γ射线剂量率筛选的过程中,由放射性核素的活度限值到剂量率限值的计算是其中重要部分。在稀土冶炼过程中,伴生的天然放射性~(232)Th、~(238)U、~(235)U系列平衡被破坏,使得稀土废渣现场γ射线剂量率的计算工作加大。本文基于核素的衰变规律和化学特性,将~(232)Th、~(238)U、~(235)U天然放射性系列进行分段处理,通过计算各段衰变子系的γ剂量率来求得整个衰变系列的γ射线剂量率,提出现场γ射线剂量率分段计算方法。在封闭的环境下,~(232)Th、~(238)U、~(235)U系列的主要辐射子系可在较短时间内达到衰变平衡,从而避免非平衡状态下衰变系列各代子体核素的活度随时间变化的问题,减小计算量,并基于蒙特卡罗方法建立各段衰变子系的比活度与现场γ剂量率之间的关系,利用实验室测量的各衰变核素的比活度,实现对现场γ射线剂量率的计算。     

关于~(196)Au的衰变

本文用Ge(Li)γ谱仪研究了~(196)Au衰变的γ能谱。在几种不同实验条件下,测量了~(196)Au通过电子俘获和β衰变所放出的十七条γ射线的能量和相对强度、并导出了分支比。所得结果与国外结果进行了比较。     

~(57)Fe共振过滤γ射线的时间相依性和穆斯堡尔谱

~(57)Fe 14.4keVγ射线的衰变几率在这个态形成后,随时间指数衰减。1960年R.E.Holland观察到当与14.4keV入射γ射线共振的~(57)Fe薄膜用作过滤片(即吸收体)时,由符合测量技术测得的γ射线数目偏离指数型。随后M.Hamermesh和S.Harris分别用经典力学和量子力学的方法推导出理论曲线,经过厚度修正,使理论和实验曲线符合较好。     

MC法模拟符合选择核素全能峰

利用Geant4对含有锰元素的混合材料进行热中子活化模拟,并进行γ射线的探测。符合测量技术利用核素衰变的级联γ射线,对56Mn的特征γ射线进行选取。模拟采用~(56_Mn的846 keV特征射线作为门信号,对与846 keV相级联的特征γ射线进行选择,获取~(56)Mn符合γ谱,根据符合γ能谱验证Geat4软件能模拟~(56)Mn的级联衰变。     

^147Pm低激发能级研究

用高分辨率、高探测效率的Ge(Li)、HPGe及高探测效率的柱状、环状NaI(Tl)探测器测量了~(147)Nd衰变的γ单谱及符合谱。为了避开本底干扰,对γ射线逐条进行了半衰期跟踪测量,结果给出了两条新能级和三条新γ射线,这是~(147)Nd迄今为止最新的一组数据。依据最新的实验结果,对各能级的J~x值及β~-衰变分支比做了系统评价。     

关于~(95)Zr和~(95)Nb的衰变

裂变产物~(95)Zr和~(95)Nb的衰变,特别是~(95)Zr衰变的分支比,是比较有用的核数据。因而,许多实验室在这方面作过不少工作,但至今结果仍有一定偏离。目前一般采用的衰变纲图如图1所示。我们用Ge(Li)γ谱仪,对~(95)Zr和~(95)Nb所放出的γ射线的能量及相对强度进行了测量。     

医用同位素~(125)I放射性强度的测定

~(125)I是发射低能γ的同位素,衰变纲图见图1。它通过电子俘获衰变到~(125)Te的激发态(其中产生的27.5keV KX射线,分支比为68.5％),然后经γ跃迁(发射35keVγ,分支比为6.4％)或发射内转换电子(也产生 上述KX射线,分支比为66.0％)退激到基态。 测定~(125)I溶液放射性强度的较好办法是采用单晶 NaI闪烁谱仪,利用γ能谱上的符合和峰(coincident sum peak)面积来推求之,它的γ能谱见图2。在这个 衰变过程中发射的LX射线能量3.8keV,很低,谱上记     

美国本土现代航空γ能谱测量和区域钾分布图

自然环境的航空γ测量是测量地表10—20cm内物质中由~(40)K、~(214)Bi和~(208)T1放射性衰变产生的γ射线通量。~(40)K是一种放射性钾同位素,它可以用来估测土壤和岩石中钾总量。~(214)B是~(238)U放射性衰变系列产物,用于测定铀浓度,~(208)Tl是~(232)Th放射衰变系列产物,用于测定钍浓度。包括美国本土48个州的航空γ射线资料     

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.     

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.     

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.     

微型X射线管空气比释动能和能谱的测量

为研究微型X射线管的特性,通过电离室测量光管出射口30 cm远处的空气比释动能,使用高纯锗探测器分别测量了Ag过滤和Cu过滤下的X射线能谱。结果表明,空气比释动能随电流的增加有线性增加的趋势,能谱图明显的观察到银的两个特征X射线。完成了微型X射线管空气比释动能和能谱的测量方法以及实验测量的工作,为微型x射线管下辐射质的建立提够了条件基础。     

Gamma-ray attenuation technique for measuring void fraction in horizontal gas-liquid two-phase flow

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a single-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.