225 kV X光机管电压、管电流及固有过滤的研究北大核心CSCD

X光机的管电压、管电流及固有过滤是X射线光机质量控制的重要参数。X光机管电压、管电流以及固有过滤的测量,对于X光机的性能评价和参考辐射质的建立是非常必要的。以一台管电压上限为225kV的X光机为例,用能谱终点法测量对X光机的管电压进行测量,得出X光机能在±0.2%的范围内显示管电压值;用指型电离室PTW30013测量了高能X光机管电流的线性,测量得到的X光机的的管电流性能良好;用半值层法测量X光机的固有过滤,固有过滤为0.058mmAl.     

诊断X射线能谱影响因素的模拟与分析

诊断X射线的能谱分布受到一系列因素的影响。为了进一步了解影响诊断X射线能谱的因素,从而为评估光机自身特性导致诊断结果的差异提供技术基础,通过仿真模拟的方法建立了诊断X射线光机的物理模型。模拟计算和比较了诊断X射线光机在不同管电压、发射角、过滤材料、纹波等条件下的出射能谱。研究结果表明,管电压、发射角、过滤材料(包括厚度)以及管电压纹波都会影响射线能谱分布和平均能量。诊断X射线光机的上述关键参数可能会直接影响诊断结果的可靠性,在光机运行过程中,参数的选择和质量控制方面需要予以重视。     

工业钼靶X射线光机能谱的蒙特卡罗模拟

利用蒙特卡罗模拟程序EGSnrc,构建出工业钼靶X射线光机模型,进行了28 keV的电子束经过钼靶产生的光子在光机各组件中的传输模拟,得到距源焦点50 cm处, 射野半径为5 cm平面上的粒子相空间文件,通过对相空间文件分析得到粒子注量、能谱分布、角分布、平均能量等信息,模拟计算了过滤材料和管电压对钼靶X射线谱分布的影响。钼过滤下钼靶X射线的平均能量小于铑过滤,但对较高能量部分的影响要大于铑过滤;随着管电压的升高,钼靶光机的光子产生效率呈上升趋势,平均能量增加。25,28,30,35 kV 4组辐射质条件下,钼靶X射线能谱的平均能量分别为16.0,16.6,17.0,17.8 keV,与实验测量值接近,相对误差在1%以内。     

工业X射线光机管电压测量的研究

用非介入管电压测量仪测量了工业X射线光机标称管电压在70～120 kV的管电压,并与介入式测量方法的测量结果傲了比较;在用非介入式测量管电压时比较了不同附加过滤对测量结果的影响.结果显示,附加过滤的厚度会影响非介入式管电压测量结果的准确性,在实验条件下最大的标准偏差能达到2.5％,根据附加过滤对非介入式测量结果进行修正后最大偏差为0.4％.     

钨靶光管钼过滤X射线空气比释动能的量值复现北大核心CSCD

基于低能钨靶X射线光机,配置钼过滤材料参考建立了管电压为23kV、25kV、28kV、30kV、35kV的辐射质,其附加过滤均为0.06mm的钼片。测量了5个辐射质的半值层,结果显示,半值层值在0.346mmAl到0.405mmAl之间。有效能量在15.4~16.4keV之间,明显高于相同管电压激发钼靶光管产生的X射线辐射质。对乳腺X射线自由空气电离室进行了各个修正因子的测量,完成了空气比释动能的测量工作。     

对医用X射线机焦点检测条件的探讨

根据JJG774—2004《医用诊断用X射线辐射源》检定规程,对X射线球管焦点的检测采用星卡照相法,X射线管的焦点测量条件是：对于X射线机标称电压大于75kV时,将管电压调至75kV,对于X射线机标称电压小于或等于75kV时,将管电压调为标称电压;mA均调为标称电流一半,要求不用增感屏。现有的X射线机．30mA以上的标称电压均超过75kV以上。故检测时均调到75kV使用,如没有增感屏,低于75kV无法拍照。     

非介入技术在X光机管电流测量中的应用研究

X光机广泛应用于放射诊断、放射治疗、工业探伤等相关领域,在保障公民身体健康和促进社会经济进步方面发挥着重要作用。X光机管电流作为控制X射线强度的重要参数,对射线输出质量、拍片清晰度等方面产生重要影响。在保证检测数据准确、检定过程简易的情况下,设计采用了基于非介入式的X光机管电流测量方法,测试结果表明该方法能准确测量X光机管电流。     

X射线铅当量测量辐射质的建立和能谱模拟

医用诊断X射线防护器具的防护性能通常用铅当量表示,根据IEC 61331-1,防护材料衰减性能的测定主要是在40～150kV X射线范围内,研究纯铅、含铅和无铅材料在窄束、宽束以及逆向宽束条件下铅当量的大小。为进一步研究不同测量方法下防护材料的屏蔽性能,需要建立符合标准要求的X射线参考辐射质,并对其能谱进行模拟或测量。依托工业X射线光机,通过添加铝附加过滤和不同厚度铝吸收片,建立了40～150kV范围内8个X射线参考辐射质,测量半值层最大相对偏差为2.8%。利用EGSnrc蒙卡模拟程序,模拟了不同辐射质的X射线能谱,其平均能量与IEC推荐值的最大相对偏差不超过0.4%,满足防护材料X射线铅当量辐射质的要求。     

中能X射线照射量基准

中国计量科学研究院建立中能X射线照射量基准的研究工作，始于50年代末，是我国电离辐射计量创始阶段的重要组成部分n现行某准装置设计制法干70年代，于80年代初完成。1986年批准为国家计量基准，负责全国量值统一工作。该基准由基准电离室、电离电流测量装置和X射线源组成。基准电离室为平行平板型自由空气电离室，电离电流测量装置采用精密空气电容器的汤逊补偿线路，X射线源为高稳定X光机。在（60－25o）kV，半减弱层（0．06－2．5）mmCU的射线范围，基准复现X射线照射量的扩展不确定度为0．48％（k＝3）。基准量值稳定性0．则叽一0…     

X射线探伤机检定平台的研究与建立

X射线探伤机被广泛应用于各行业的工业探伤,但因长期频繁的现场作业致使很多射线探伤机的辐射角有偏移,遗留安全隐患。本文设计的X射线探伤机检定平台配合0.6cm~3电离室能完成X射线束(-400~400)mm的扫描范围,能完成X射线探伤机辐射角、辐射束重复性等参数的自动测量,为X射线探伤机的量值传递提供了技术支持,为工业探伤提供了计量基础。     

The performance of commercial photodiodes for dosimetry in mammography

This paper reports the results of an investigation carried out to determine the suitability of using a commercially available photodiode for dosimetry in mammography thereby providing a low cost dosemeter with a direct reading of the radiation dose. A mammographic X-ray generator (Siemens Mammomat 1000) with tube potential in the 23-30 kV range and a constant potential X-ray generator (Pantak) with a W/Mo anode/filter combination were used in this study. The results showed that the photodiode response is highly linear within mammographic dose ranges and that the energy dependence was <3% at tube potentials of 25-30 kV. Good agreement was observed between the incident air kerma measured with both the photodiode and the ionization chamber. These results show the viability of using the photodiode as a dosemeter system in mammography.     

一种基于射线照相的X射线衰减系数获得方法

提出了一种通过射线照相法计算X射线在物质中衰减系数的方法,通过简单实验以及计算快速获取不同能量X射线在物质中的衰减系数。设计实验找出了底片黑度与工件厚度的关系曲线,推导出表达式,并得出表达式的可信区间。用射线照相法实测了管电压为140、130、120kV时钢质台阶试块的X射线衰减系数与理论值对比,其标准误差＜3%,证明了该方法的可靠性。射线照相法求物质衰减系数计算简单、操作便捷、误差小,有望推广应用于材料中X射线衰减系数的估算。     

40~125kV脉冲X射线参考辐射场的建立

为解决用于X射线诊断、安检等涉及到的脉冲X射线剂量监测仪表的时间响应修正问题,建立了模拟上述辐射条件的40~125kV脉冲X射线参考辐射场。该参考辐射场同时具备了常规辐射场特性和脉冲辐射场特性。基于栅控技术的高压发生器可以调控光管产生不同脉冲特性的X射线,使用脉冲时间测量模块对产生X射线的脉冲特性(上升和下降沿时间、曝光时间等)进行测量,得到的结果表明该参考辐射场可用于主动式剂量监测设备的时间响应修正和剂量溯源。     

X射线石墨空腔电离室壁修正因子的蒙特卡罗模拟

在250～600 kV X射线宽谱系列辐射质下,运用EGSnrc蒙特卡罗程序模拟计算3种不同结构石墨空腔电离室的壁修正因子.根据辐射质和光机参数使用BEAMnrc程序包模拟8组规范下辐射质的X射线注量谱,将模拟得到的相空间文件作为X射线源,运用EGSnrcMP程序包中的cavity程序代码模拟计算得到石墨空腔电离室的壁修正因子.模拟结果表明:对于相同体积的球型电离室,收集极长的电离室其壁修正因子更大;对于收集极长度相同电离室,球柱球型电离室比球型电离室的壁修正因子数值大.并且当X射线能量增加时,电离室的壁修正因子都有减小的趋势.     

Pulse transformers

Pulse transformers capable of transmitting substantially rectangular voltage pulses, with durations of less than one microsecond, were developed for radar applications during World War II. Their primary functions were to match the impedances of high-power microwave radio-frequency electron-tube generators to electronic pulse generators and coaxial transmission cables, and to provide polarity reversal and impedance matching functions within pulse generator circuitry. The principle contributor to the development of satisfactory pulse transformers was the development of cores of thin-gauge magnetic materials having 1 μs pulse permeabilities in the range of 500 to 3500 for flux-density changes of 10 000 G. The development of void free dry-type insulation systems made it possible to produce dry-type pulse transformers for operation at pulse voltages below 12 kV. The pulse transformer development work was paralleled by analytical work which enabled pulse transformer designers to make designs to meet the requirements of the radar circuit designers. The analysis relates the three principle pulse transformer parameters, which are magnetizing inductance, leakage inductance, and effective distributed capacitance, in combination with the circuit parameters which are source resistance, effective load resistance, and load shunt capacitance, to the rise time, top ripple and droop, and fall time of the output pulse. Pulse transformers now cover a wide range of sizes and power levels and pulse widths. Small units in computer applications may deliver only a few volts at pulse widths less than 0.1 μs. Large units in linear accelerators, however, may deliver pulse powers of 70 MW at 270 kV with a pulse width of about 3 μs.     

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.     

Measurement of X-ray tube accelerating potential by differentialbeam filtration

Indirect determination of X-ray generator kilovoltage (kV) using the ratio of differentially filtered beam measurements has been known for 20 years. Measurement of generator potentials used for diagnostic computed tomography (CT), conventional X-ray, and mammography typically requires filter cassettes or special instruments in the X-ray beam; the resulting readings are usually accurate within ±2%. A related technique, free of many theoretical and practical restrictions, provides simplified generator potential measurements with significantly improved accuracy. Curve fitting provides a simple relationship predicting generator kV from a measured filter response ratio. Routine use has established that this technique is robust, reliable, repeatable, and more accurate than most working standards     

An experimental method for ripple minimization in transmission data for industrial X-ray computed tomography imaging system

Industrial Computed Tomographic (ICT) imaging systems based on X-rays require a high stability source. This emanates from the fact that in a computed tomographic imaging system, statistical variation inherent in the penetrating radiation used to probe the specimen, electronic noise generated in the detection system and reconstruction errors play an important role in the overall quality of the image. A conventional industrial X-ray machine used for routine radiography work is not suitable for tomographic imaging applications because of its output dose variations. In this paper, an experiment is described to utilise a general-purpose 160 kV constant potential industrial X-ray machine with significant ripple in its output beam, in an experimental Computed Industrial Tomographic Imaging System (CITIS) developed at Isotope Applications Division of Bhabha Atomic Research Centre. Studies carried out include the analysis of temporal profile of X-ray beam intensity and online averaging of detected signals for the minimization of periodic ripple, which mainly showed up, at the power line frequency. A tomographic image of a typical specimen, reconstructed with the processed projection data is analysed. It was observed that the mean value of reconstructed linear absorption coefficients and standard deviation computed over a window within a constant density region of the object were stable