共查询到19条相似文献,搜索用时 78 毫秒
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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. 相似文献
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用等效参数法研究含球形空腔弹性体的吸声性能 总被引:3,自引:0,他引:3
复合弹性材料已广泛应用于水声吸声材料中。本文研究的对象是含有球形空气空腔、以均匀粘弹性介质为基材的复合吸声结构。文中以散射理论和可变形粘弹性介质力学的基本理论为基础,建立了该复合结构的物理模型,引入了等效参数的概念来研究它的声学特性,并且分析了结构参数对其声学性能的影响。 相似文献
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潜艇吸声覆盖层在低频对抗主动声纳的探测是目前面临的一个重要技术难题,利用空腔共振时的吸收是解决低频吸声问题的一种有效途径,文中在假设入射球形纵波完全被腔壁反射的情形下,对球形空腔嵌入层的共振特性进行了理论分析,结果表明,在粘弹性介质中嵌入适当厚度的低剪切波速包覆层能有效地降低空腔共振的频率。 相似文献
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当使用基于空腔理论的石墨空腔电离室绝对测量γ射线空气比释动能时,需要考虑空腔体积的大小变化对测量结果准确度的影响。利用EGSnrc程序计算得到10~5 000 cm~3的球型石墨空腔电离室的石墨和空气的限制的阻止本领比■、入射光子与空腔气体直接作用沉积能量的份额F_(air)和Spencer-Attix空腔理论修正因子k_(SA)。结果表明对于~(60)Co和~(137)Cs能量的光子,在计算■时选择合适的?值可以使k_(SA)的值保持在0.998~1.000之间。此外k_(SA)的大小随空腔体积的增大有逐渐减小的趋势。表明在设计和使用较大体积(≥50 cm~3)的石墨空腔电离室时需要考虑合适大小的k_(SA)值,以保证空腔理论计算值和绝对测量结果的准确。 相似文献
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石墨空腔电离室由于对较高能量段有较好的能量响应,广泛应用于137Cs(有效能量为662keV)、60Co(有效能量为1250keV)以及平均能量为350keV的192Irγ射线空气比释动能的测量。运用EGSnrc程序模拟自制石墨空腔电离室在250~600kV窄谱辐射质下量值复现过程中的壁修正因子及物理常数。结果显示,石墨与空气的阻止本领比、空气与石墨的质能吸收系数之比、韧致辐射份额常数均与平均能量间有比较明显的关系可循,壁修正因子随着X射线能量的增加,则会有先变大后减小的趋势。蒙特卡洛模拟的结果为建立250~600kVX射线空气比释动能国家基准、实现量值复现提供了技术数据,达到了复现结果测量不确定度的预期要求。 相似文献
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Yu.T. Borzunov V.F. Chumakov L.B. Golovanov V.L. Mazarsky A.P. Tzvinev A.G. Zeldovich 《低温学》1983,23(3):151-152
A liquid hydrogen target is placed inside a streamer chamber which has an electric field equal to 20 kV cm?1. A flask of the target is made from mylar. Its diameter is 35 mm, its length is 198 mm and its thickness is 100 microns. The target box is made from polystyrene foam. The diameter of the box is 59 mm and its thickness is 7 mm. A source of cold for the target is a cooling gas machine having a power of 100 W. 相似文献
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碳纳米管冷阴极超高真空鞍场规的电场模拟与实验研究 总被引:1,自引:0,他引:1
在静电鞍场规的基础上研制了一种碳纳米管(CNT)冷阴极鞍场规(SFG).这种冷阴极鞍场规具有电极尺寸小,吸放气率低,热效应低,功耗低的特点.本文首先计算了碳纳米管冷阴极鞍场规的电场分布,计算结果表明,二极型碳纳米管电子枪的引出栅极的正电位在低于100 V的情况下对环形阳极鞍场规的轴向电位分布影响很少;并且在现有条件下对规管参数进行了测试,实验测定的规管对空气的灵敏度是1.05 Pa-1,规管功耗由热阴极规的0.9瓦减小到7毫瓦. 相似文献
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The dynamic spherical cavity expansion is treated through a complete analytical solution of the equations of motion for an elasto-plastic solid obeying von-Mises yield criterion. The solutions for various metals, with different elastic and plastic properties, are fitted with a third order polynomial which relates the normalized pressure inside the cavity with the normalized velocity of the cavity wall. An extensive search for material similarities is conducted in order to highlight the roles of the elastic properties of the solid, as well as its strength and equation of state parameters. Using the simple terms we derive, for the coefficients in the third order polynomial, one can easily calculate the relation between pressures inside the cavity and their wall velocities for any solid to within 1%. 相似文献
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By applying square wave AC voltage to the Au source electrode of tetracene based field-effect transistor (FET), electroluminescence (EL) was obtained. The results suggest that electrons and holes were injected alternately from the source electrode and recombined each other, and lead to the EL. This type of EL was localized at the interface between the source electrode and tetracene, and enhanced periodically with two relaxation times in accordance with the applied AC voltage cycle. We modeled the carrier behavior in the FET and explained the decay of EL, taking into account the space charge field contribution. Finally, using an AC voltage superposed on DC bias voltage, it was shown that electron injection was prompted only by space charge field. 相似文献
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Effect of an applied electric field on the oxidation rate of vacuum deposited aluminium thin films were studied at room temperature
in the laboratory atmosphere. Above the critical field, a negative potential applied to the film enhanced the rate of oxidation,
while a positive field retarded the rate. This suggests an oxidation mechanism involving cationic diffusion. The observed
change in the rate of oxidation for an applied field agrees with the Mott-Cabrera theory. 相似文献
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The method of calibration of a portable standard on equipment of the state standard GéT 45-94 for electric field strength
is presented. Analysis of the results of key comparisons CCEM.RF-K-20 is provided.
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Translated from Izmeritel’naya Tekhnika, No. 9. pp. 69–72, September, 2007. 相似文献