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~(239)U是不稳定的一种核素,很难在实验室中作为靶核,故其~(239)U(n,f)截面几乎没有测量值,但它有着极其重要的意义。Cramer和Brit等[1]早在实验上测量了Et=0.5～2.5MeV条件下的229,231Th(t,pf),233,235,237U(t,pf)和239,241Pu(t,pf)截面数据,并发现某些短寿命裂变核的(n,f)反应截面可用相应的长寿命核靶的(d,pf),(t,pf)或(3He,pf)等直接反应的测量数据来估量。同样,可由直接反应238U(18O,
U ~ (239) U is a kind of unstable nucleus, which is hard to be used as target nucleus in the laboratory. Therefore, there is almost no measured value of ~ (239) U (n, f) cross section, but it is of great significance. Cramer and Brit et al [1] measured 229,231 Th (t, pf), 233,235,237 U (t, pf) and 239,241 Pu (t, pf) cross section data at Et = 0.5-2.5 MeV as early as possible The (n, f) cross sections of some short-lived fission nuclei can be estimated using measurements of direct response to (d, pf), (t, pf) or (3He, pf) Similarly, by direct reaction 238U (18O,