25MeV/u　^(40)Ar+^(209)Bi裂变反应的断点激发能和裂变时标测量  

Measurement of Fission Time Scale and Excitation Energy at Scission for 25MeV/u ^(40)Ar+^(209)Bi Fission Reaction

作　　者：郑纪文[1] 邬恩九[1] 张纯[1] 肖志刚[1] 王素芳[1] 尹淑芝[1] 靳根明[1] 谭继廉[1] 金卫阳 宋明涛[1] 李祖玉[1] 吴和宇[1] 贺智勇 殷旭[1] 朋兴平[1] 江栋兴[2] 钱兴[2] 

机构地区：[1]中国科学院近代物理研究所,兰州730000 [2]北京大学技术物理系,北京100871

出　　处：《高能物理与核物理》1999年第10期946-953,共8页High Energy Physics and Nuclear Physics

基　　金：国家自然科学基金!19235011

摘　　要：对25MeV／u40Ar＋209Bi非完全熔合反应中形成的热核，测量了与裂变碎片相符合的α粒子能谱，用运动源模型分解α粒子能谱得到了裂变断前和断后发射α粒子多重性．由断后碎片发射α粒子多重性得到断点激发能约为172．5MeV．由断前α粒子多重性得到激发能在470—600MeV范围内的热核的裂变时标约为4×10－21S．Alpha particles detected in coincidence with two fission fragments in the reaction of 25MeV/u 4oAr + 209Bi have been measured at the backwards angles of 145° and 95°, respectively. The spectra at each angle are incremented in two different intervals of linear momentum transfer(LMT). These two intervals of LMT correspond to two considesably diffesent initial excitation energies, <E*> =472 and 595MeV, in the primordial hot nuclei formed in the reaction. The moving source analysis of the spectate has been used to extract the prescission and postScission alpha particlemultiplicities, as well as other relevant qualities such as the temperatures of the target-like residues and fission fragments. The excitation energies at scission, deduced from the postscission α pasticle multiplicity are about 166 and 179 MeV in the two LMT intervals, respectively. Compared with the considesable difference of initial excitation energies, the near equality shows that the excitation energy at scission are not explicitly dependant on the initial excited state of the fission nuclei. The fission bine scale of hot nuclei with excitation energy of 470-600MeV, deduced from prescission multiplicity, is about 4 × 10-21 sec, which indicates that the so-called fast fission dominates in the fission channel of hot nuclei in this excitation energy range.

关 键 词：断点 激发能 裂变时标 氩40 铋40 

分 类 号：O571.43[理学—粒子物理与原子核物理]