Gammasphere上裂变丰中子核核结构若干前沿领域的新进展(Ⅱ:第三和第四部分)(英文)  

New Insights into Frontier of Nuclear Structure of Neutron-rich Nuclei by Means of Prompt Fission γ Ray Measurements at Gammasphere(Ⅱ: Section 3 & Section 4)

作　　者：罗亦孝 J.H.Hamilton J.O.Rasmussen A.V.Ramayya C.Goodin A.V.Daniel N.J.Stone 朱胜江 J.K.Hwang 刘少华 C.J.Beyer 李科 H.L.Crowell D.Al mehed S.Frauendorf A.Covello V.Di mitrov 张敬业 车兴来 姜卓 D.Fong A.Gelberg I.Stefanescu A.Gargano E.F.Jones P.M.Gore I.Y.Lee G.M.Ter-Akopian Yu.Ts.Oganessian M.A.Stoyer R.Donangelo 马文超 J.D.Cole J.Kormicki 张学谦 S.C.Wu J.Gilat T.N.Ginter S.J.Asztalos 

机构地区：[1]Physics Department, Vanderbilt University, Nashville, TN 37235, USA [2]Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA [3]Flerov Laboratory for Nuclear Reactions, JINR, Dubna, Russia [4]Joint Institute for Heavy Ion Research, Oak Ridge, TN 37831, USA [5]Department of Physics, Oxford University, Oxford OX1 3PU, United Kingdom [6]Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA [7]Physics Department, Tsinghua University, Beijing 100084, China [8]Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA [9]Institut far Strahlenphysik, FZD-Rossendorf, Postfach 510119, D-01314 Dresden, Germany [10]Dipartimento di Scienze Fisiche, Universita di Napoli Federico II, and Istituto Nazionale di Fisica Nuclear, Complesso Universitario di Monte S. Angelo, Via Cintia, 80126 Napoli, Italy [11]Idaho Accelerator Center, Idaho State University, Pocatello, ID-83209-8263, USA [12]Institut fur Kernphysik, Universitat zu Koln, 50937 Kdln, Germany [13]Department of Chemistry and Biochemistry, University of Maryland, MD 20742, USA [14]Lawrence Livermore National Laboratory, Livermore, CA 94550, USA [15]Instituto de Fisica, Facultad de Ingenieria, C. C. 30, 11300 Montevideo, Uruguay [16]Mississippi State University, Drawer 5167, Mississippi State, MS 39762, USA [17]Idaho National Laboratory, Bldg. IRCPL, MS2114, Idaho Falls, ID 83415, USA [18]Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 30013, China [19]National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA [20]Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

出　　处：《原子核物理评论》2010年第4期363-389,共27页Nuclear Physics Review

基　　金：The US Department of Energy Grants(DE-FG05-88ER40407,DE-FG02-95ER40934,DE-FG02-95ER40939,DE-FG05-87ER40311)and Contract(W-7405-ENG48,DE-AC03-76SF00098,DE-AC07-99ID13727,DE-AC07-761DO1570);The Work at Tsinghua University was supported by National Natural Science Foundation of China(19775028,10375032,10775078);by Major State Basic Research Development Program of China(2007CB815005,G2000077400)~~

摘　　要：使用Gammasphere多探测器系统对252Cf裂变源瞬发γ射线进行γ-γ-γ和γ-γ(θ)符合测量,A～100(Z～40,N>56)丰中子核区关于形状过渡、形状共存和形状突变的深入研究获得了新的进展。奇-Z核的系统研究揭示了从Z=39(Y)同位素的轴对称大四极形变到Z=43(Tc),44(Ru)和45(Rh)同位素中具有中等四极形变之大三轴形变的过渡。Nb(Z=41)同位素具有过渡核的特征。根据邻近同位素和同中素带交叉信息的系统性及推转壳模型(CSM)计算,Tc和Rh偶-N同位素中观察到的带交叉产生于一对h11/2中子的转动顺排。首次观察到100Nb(Z=41,N=59)的高自旋能级纲图和形变态,从而证实了100Nb中的形状共存,并确认,在Nb同位素链上,基态形状突变发生于N=58(球形)到N=59(大形变);而在Sr(Z=38),Y(Z=39)和Zr(Z=40)各同位素链上,基态形状突变均发生于N=59(球形)到N=60(大形变)。100Nb具有大形变基态,同现有理论预言相矛盾,其大形变的基态及转动带所具有的很大的和不规则的转动惯量具有重要的理论意义。对奇-质子Cs(Z=55)和La(Z=57)丰中子同位素八极激发的详细研究,发现了141,143,144Cs同位素链上电二极矩D0随中子数增加而减小的急剧变化,此前在145,147La中观察到的电二极矩D0的较缓和的减小似乎亦很陡地下延至148La。在Cs和La同位素中观察到的电二极矩D0的急剧下降很可能同偶-质子核146Ba和224Ra中观察到的电二极矩D0的急剧下降相类似,后者已获反射非对称平均场壳修正理论的成功解释。实验证明,141Cs具有很大电二极矩D0。141Cs和142Xe中观测到的很大的电二极矩D0和仅在141Cs中观察到的电二极矩D0的simplex量子数相关性需要进一步的理论研究。根据转动频率比值ω-(I)/ω+(I)的检定,同Xe同位素一样,认定Cs同位素中包括号143Cs的八极激发为八极振动,而在La同位素中存在八极形变。By means of γ-γ-γ and γ-γ（θ）measurements of prompt fission γ rays from 252↑Cf using Gammasphere,new insights have been gained into the A^100（Z^40,N56）neutron-rich region,which has long been of interest for shape transitions,shape coexistence and onset of deformations.The systematic investigations of odd-Z isotopes have revealed a shape transition from axially symmetric shapes with very large quadrupole deformations in Z=39（Y）to near maximum triaxial shapes with moderate quadrupole deformations in Z=43（Tc）,44（Ru）,45（Rh）isotopes.The Nb（Z=41）isotopes are found to be transitional with regard to this shape transition.The band-crossings observed in the even-N Tc and Rh isotopes are attributed to alignment of a pair of h11/2 neutrons.The long-expected sudden shape transition in Nb isotopic chain is now observed.The long-sought high-spin level scheme and deformed states in 100Nb（N=59）were identified.The ground state of 100↑Nb was found to be strongly deformed,in disagreement with existing theory.The shape coexistence was confirmed in the nucleus,and the sudden shape transition in the Nb isotopic chain was seen to occur between N=58（spherical）to N=59（strongly deformed）,in contrast to the sudden shape transition from N=59（spherical）to N=60（strongly deformed）in Sr（Z=38）,Y（Z=39）and Zr（Z=40）isotopic chains.The observation of strongly deformed ground state in 100Nb and its very large and irregular moments of inertia make 100↑Nb an especially interesting case for further theoretical studies.Recent detailed studies of octupole excitations in odd-Z Cs（Z=55）and La（Z=57）isotopes have discovered a sharp drop in electric dipole moments D0 in the Cs isotopic chain 141,143,144↑Cs,and,most likely,the previously reported moderate drop in D0 in↑ 145,147↑La is extended sharply down in 148La.The sharp drops of D0 in Cs and La are most likely analogous to those reported in 146↑Ba and 224↑Ra,which were accounted for by the reflection-asymmetric mean fie

关 键 词：形状过渡 轴对称形状 三轴形变 形状突变 带交叉 奇-质子 八极激发 B(E1)/B(E2)比值 电二极矩D0 二极矩的下降 八极振动 Cs La同位素 

分 类 号：O571.21[理学—粒子物理与原子核物理]