在反应堆物理中,把燃料元件单位体积内的铀-238与铀-235裂变数之比定义为δ~(28);把铀-235的镉上裂变率与镉下裂变率之比定义为δ~(25)。 δ~(28)和δ~(25)的测量是在铀水棒栅的零功率堆上进行的。设计了十一种均匀栅装载,每个装载的元件栅距不同,因此有十一个水铀比,水铀比变化区域是从0.89到8.02,在如此宽的 In reactor physics, the ratio of uranium-238 and uranium-235 fission numbers per unit volume of a fuel element is defined as δ ~ (28); the ratio of the fission rate of cadmium to that of cadmium under uranium-235 is defined as δ ~ (25). The measurements of δ ~ (28) and δ ~ (25) were carried out on the zero-power reactor of the uranium water-bar grid. Eleven types of uniform grid loadings were designed, each loaded with a different pitch, so that there are eleven water-to-uranium ratios that vary from 0.89 to 8.02 for water to uranium at such a wide