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~(239)Pu作为一种用于快堆和核武器的重要的核燃料,它的裂变截面(记为~9σ_f)是一个很重要的数据,因此,近三十年来,人们用各种方法对这一数据进行了反复的测量。尽管如此,各家数据的分歧依然存在。由于~(235)U的裂变截面(记作~5σ_f)测量得比较仔细和系统,截面随能量的变化也比较平滑,常把~5σ_f作标准截面使用。因而通过测量~σ_f/~σ_f的比值即可定出~9σ_f。这样做的便利之处是避免了对中子通量的测量,修正量的考虑也可简单得多。值得注意的是,~(239)Pu是一种高α放射性的裂变物质,为了克服α堆垒脉冲对裂变计数的影响,必须在裂变室的设计与电子线路的使用上作一些特殊的考虑。为此,使用了上升时间快的快电离室与快线路系统。本工作的目的是在中子能量从30千电子伏到5.6兆电子伏和14—18兆电子伏区域内测量~(239)Pu和~(235)U裂变截面比值随中子能量变化的曲线,测量工作是在2.5兆伏静电加速器和600千伏高压倍加器上进行的。
As an important nuclear fuel used in fast reactors and nuclear weapons, Pu’s (~ 9σ_f) fission cross section (~ 9σ_f) is a very important data. Therefore, for nearly three decades, Pu has used various methods to calculate this A repeated measurement of data. In spite of this, differences in various data still exist. As ~ (235) U fission cross section (denoted as ~ 5σ_f) measured more carefully and the system, the section with the energy change is relatively smooth, often ~ 5σ_f standard cross section used. Thus by measuring the ratio of ~ σ_f / ~ σ_f can be set ~ 9σ_f. The convenience of doing so is to avoid the neutron flux measurement, the amount of correction can be considered much simpler. It is noteworthy that ~ (239) Pu is a high-alpha radioactive fission material. In order to overcome the effect of alpha-stack pulses on the fission count, special considerations must be placed on the design of fission chambers and the use of electronic circuits. For this purpose, fast ionization chambers and fast-track systems with fast rise times are used. The purpose of this work is to measure the curve of the ratio of ~ (239) Pu and ~ (235) U fission cross sections with the change of neutron energy in the region of neutron energies from 30 keV to 5.6 MeV and 14-18 MeV , The measurement was carried out on a 2.5-megawatt electrostatic accelerator and a 600-kv high voltage doubler.