热核三重碎裂中的两种模式

Two Modes in Three-fold Fragmentation of hot Nuclei

在30MeV／u40Ar＋159Tb反应中测量了热核碎裂成三块差不多大小的碎片的出射道．这种碎裂可能有两种模式：一种是接续的两体过程，如跟随裂变和级联裂变；另一种是瞬发的三重碎裂（3F）．从实验上区分了这两种模式并特别关注其中具有集体多轴形变的3F模式，对3F中的碎片质量分布和最可几碎片质量比进行拟合后找出了通用规律．用碎片发射平面的定向角分布来测量碰撞参数，从而将中心碰撞的3F事件与跟随准弹性散射或深部非弹性散射后的裂变事件分开．

Splitting of a hot nucleus into three comparable pieces in the 40 Ar+159 Tb reaction at 30MeV / u was measured. For the splitting there are two modes: one is a successive binary process, such as sequential fission or a cascade fission, another is a prompt threefold fragmentation (3F). The paper presents the identification between the two modes of the threefold fragmentation by the experimental results, such as the mass distribution of the fragments, the orientation of the fragmentation plane, etc.. In the two modes, the prompt one with collective deformation is emphasized.Furthermore fitting the mass distribution and finding a scaling law about the most-probable mass ratio in the 3F are given. In addition, the orientation of the fragmentation plane could also be used to measure the impact parameters, there for to distinguish 3F events associated with cental collision from the sequential fission after a quasi-elastic scattering or deep-inelastic collision.