缺中子同位素^(215-217)U的α衰变研究  

a decay studies of the neutron-deficient uranium isotopes ^(215-217)U

作　　者：甘再国[1] 姜舰[1,2] 杨华彬[1,2,3] 张志远[1] 马龙[1,2,3] 郁琳[1,2] 王建国[1] 田玉林[1] 丁兵[1] 黄天衡[1] 王永生[1] 郭松[1] 孙明道[1,2,3] 王凯龙[1,2] 周善贵[4] 任中洲[5] 周小红[1] 徐瑚珊[1] 

机构地区：[1]中国科学院近代物理研究所，兰州 730000 [2]中国科学院大学物理科学学院，北京 100049 [3]兰州大学核科学与技术学院，兰州 730000 [4]中国科学院理论物理研究所 ，北京 102413 [5]南京大学物理学院，南京 210093

出　　处：《科学通报》2016年第22期2502-2511,共10页Chinese Science Bulletin

基　　金：国家自然科学基金(11475226;11405225;11305230;11120101005;11405243;11205208);国家重点基础研究发展计划(2013CB834403)资助

摘　　要：通过重离子熔合蒸发反应^(180)W(^(40)Ar,xn)^(220-x)U,合成了两个缺中子新核素^(216)U和^(215)U.目标核由熔合反应产生后从薄靶中反冲出来,在飞行中被兰州充气谱仪从大量的本底离子中分离并偏转到探测系统.探测系统对目标核的注入以及随后将发生的α衰变进行探测.探测器上产生的信号经电子学处理后被数据获取系统转换成一定格式的数据保存下来.实验采用能量-位置-时间关联的数据分析方法来寻找和鉴别目标核.在束流能量为187.2 MeV的情况下,新核素^(216)U的两个α衰变态被观察到:一是基态,它的α粒子能量为10.384(30)MeV,半衰期为4.72_(-1.57)^(+4.72)ms;二是自旋宇称为8^+的同核异能素态,它的α粒子能量为10.582(30)MeV和8.182(30)MeV,半衰期为1.31_(-0.48)^(+1.80)ms.在束流能量为205.5 MeV的情况下,新核素^(215)U被观测到,它的α粒子能量和半衰期被确定为8.428(30)MeV和0.73_(-0.29)^(+1.33)ms.此外,实验还观测到从^(217)U的基态产生的两个新的α跃迁,它们的α粒子能量分别为8.210(30)MeV和8.098(30)Mev.The α-decay study is an important tool for obtaining information on the nuclear structure of heavy neutron-deficient nuclei. For the N=126 and 124 isotones with even proton number, an intruder state （πh9/2πf7/2）8＋ based on the attractive interaction offv/2 protons and f5/2 neutrons was observed, which increases the binding energy of this configuration with increasing proton number. Additionally, taking into account the octupole correlations, a large-scale shell model calculations predict that the （πh9/2πf7/2）8＋ state lies close or below the （πh2/9/2 ） 6＊ state in the 216Th and 218U. To extend the systematic of the r=8＋ isomeric state in N=124 isotones and search for the most neutron-deficient uranium isotopes, an experiment for the a-decay studies of 215-217U was performed at the gas-filled recoil separator SHANS at the Heavy Ion Research Facility in Lanzhou （HIRFL）. Heavy ion induced fusion evaporation reactions of the 180W（40Ar, xn）220-xU （x=3-5） were used to synthesize these neutron-deficient uranium isotopes. The 4OAr beam was delivered by the sector focusing cyclotron of the HIRFL. The evaporation residues recoiled from the thin target were separated in-flight from the primary beam particles by the gas-filled recoil separator SHANS. After passing through two multi-wire proportional counters, the residues were planted into a focal plane detection system. Based on the energy-position-time correlation measurement, the isotopes 215-217U were identified. At a beam energy of 187.2 MeV, two （x-decaying states were observed in 216U with Eα=8.384（30） MeV, T1/2= ＋4.72 4.72＋1.57 ms for the ground state and Eα=I0.582（30） MeV and 8.182（30） ＋1.80 MeV, T1/2= 1.3 14.48 ms for an isomeric state. Through the analysis of the α-decay reduced width, the isomeric state is suggested to have the configuration （75h9/2 Kf7/2）8＋. At the beam energy of 205.5 MeV, two decay chains of 215U were observed and they were assigned to the decays from ground state to ground s

关 键 词：缺中子新核素 熔合蒸发反应 充气谱仪 α粒子能量 半衰期 同核异能素 

分 类 号：O571.321[理学—粒子物理与原子核物理]