曼哈顿计划的核科学及与当今ENDF数据的比较
Nuclear Science for the Manhattan Project and Comparison to Today's ENDF Data
摘要：
介绍了1939-1945年美国和英国核物理的进展。曼哈顿计划的工作导致了我们对核科学知识的爆炸。1943年4月在洛斯阿拉莫斯举行的一次会议提供了一个计算临界质量的简单公式，并制定了确定关键核常数所需的研究计划。在很短的时间内，在洛斯阿拉莫斯大学拆卸和重新组装了四个大学加速器，并建立了测量极小样品的方法，因为最初缺乏浓缩铀235和钚。我追踪了测量裂变截面、裂变发射中子多重性及其能谱和输运截面的程序，并将测量结果与我们今天在评价核数据文件ENDF/B-VIII.0中所体现的最佳理解进行了比较。在项目开始时，大的核数据不确定性通常超过25- 50%，到1945年减少到通常低于5- 10%。235 U和239 Pu裂变截面评估在快MeV范围内减少了更准确的测量，中子多重性增加。幸运的是，由于消除了误差，最初的临界质量估计值接近最终估计的质量。显示了我们洛斯阿拉莫斯档案馆历史文件中的一些图像。早年的许多原始测量结果以前并未广泛使用。通过这项工作，与原子能机构和布鲁克海文国家实验室合作，这些数据现已存入国际实验核反应数据库。
英文摘要：
Nuclear physics advances in the US and Britain, from 1939-1945, are described. The Manhattan Project's work led to an explosion in our knowledge of nuclear science. A conference in April 1943 at Los Alamos provided a simple formula used to compute critical masses, and laid out the research program needed to determine the key nuclear constants. In short order, four university accelerators were disassembled and reassembled at Los Alamos, and methods were established to make measurements on extremely small samples owing to the initial lack of availability of enriched 235 U and plutonium. I trace the program that measured fission cross sections, fission emitted neutron multiplicities and their energy spectra, and transport cross sections, comparing the measurements with our best understanding today as embodied in the Evaluated Nuclear Data File ENDF/B-VIII.0. The large nuclear data uncertainties at the beginning of the project, which often exceeded 25--50%, were reduced by 1945, often to less than 5-10%. 235 U and 239 Pu fission cross section assessments in the fast MeV range were reduced with more accurate measurements, and the neutron multiplicity increased. By a lucky coincidence of cancelling errors, the initial critical mass estimates were close to the final estimated masses. Some images from historical documents from our Los Alamos archives are shown. Many of the original measurements from these early years have not previously been widely available. Through this work, these data have now been archived in the international experimental nuclear reaction data library (EXFOR) in a collaboration with the IAEA and Brookhaven National Laboratory.
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