激发能升高级联裂变到瞬发多重碎裂的演化

Evolution from Cascade Fission to Prompt Multifragmentation with Increasing Excitation Energy

分析（４０）Ａｒ＋（１５９）Ｔｂ、（１９７）Ａｕ、（２０９）Ｂｉ（２５ＭｅＶ／ｕ）中心碰撞产生的三体碎片产物的角关联，配合Ａｒ＋Ａｕ（６０ＭｅＶ／ｕ）三体出射的数据，分析非完全熔合反应产生的高激发核衰变的演化过程，证明了在２５ＭｅＶ／ｕ入射能时激发核产生的三重大质量碎片是级联的两次出射的裂变形成的，其时间差尺度大约为１０００ｆｍ／ｃ，而对６０ＭｅＶ／ｕ入射能下的激发核观察到重碎片在１２０°附近出现强的角关联，这在理论上解释为发射时间差较短，即出现了瞬发的多重碎裂．

The correlation functions of relative angle distributions of mass-symmetric ternary fissions in the reactions Ar+Au、Bi、Tb at 25MeV/u are presented.The evolution of decay mode of hot nucleus is studied by comparing the present data with Ar+ An(60MeV/u)experimental results.It is shown that the time scale for fragment emission is reduced from the characteristic timeτ=1000fm/c at 25MeV/ufor standard sequential decay to prompt emission one at 60 MeV/u withτ=50 fm/c.