Physics of Atomic Nuclei, Vol. 64, No. 7, 2001, pp. 1157–1164. From Yadernaya Fizika, Vol. 64, No. 7, 2001, pp. 1235–1241. Original English TextCopyright c  2001 by Jones, Gore, Hamilton, Ramayya, de Lima, Dodder, Kormicki, Hwang, Beyer, Zhang, Zhu,Ter-Akopian, Oganessian, Daniel, Rasmussen, Lee, Cole, Drigert, Ma. Proceedings of the International Conference “Nuclear Structure and Related Topics” Shifted Identical Bands: A New Phenomenon * E.F. Jones 1) , P. M. Gore, J.H. Hamilton ** , A. V. Ramayya, A. P. de Lima 1) , R. S. Dodder, J. Kormicki, J. K. Hwang, C. J. Beyer, X. Q. Zhang, S.J.Zhu 2),3) , G. M. Ter-Akopian 3),4) , Yu. Ts. Oganessian 4) , A. V. Daniel 4) , J. O. Rasmussen 5) , I. Y. Lee 5) , J. D. Cole 6) , M. W. Drigert 6) , and W.-C. Ma 7) and the GANDS95 Collaboration Department of Physics and Astronomy, Vanderbilt University, Nashville, USA Received October 25, 2000 Abstract—The levels in 162 Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in 160 Gd. From that work, an analysis of yrast bands in even–even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount κ, so J 1a (1 + κ) = J 1b , from 2 + to 8 + and higher to 16 + . Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce–W nuclei with | ¯ κ| between 1.5% and 13%, where the spread in κ is less than ±1%, and only four identical bands (¯ κ ∼ = 0). As examples, we found for 158 Sm– 160 Gd, ¯ κ =(-3.2 +0.1 -0.2 )% (where the ± is the total spread in κ from -3.1 to -3.4); 156 Nd– 160 Gd, (-10.6 +0.4 -0.2 )%; 158 Sm– 160 Sm, (3.4 +0.5 -0.3 )%. The J 1 values were fitted to a variable moment of inertia model with parameters J 0 and C whose values correlate with the SIB J 1 values. The SIBs are not correlated either with deformation or with the N p N n product of the IBA model. c  2001MAIK “Nauka/Interperiodica”. 1. INTRODUCTION The discovery of identical bands (IB) in both su- perdeformed and normal deformed bands was a major highlight of nuclear structure research in the 1990s [1]. Bands in two neighboring nuclei with essentially equal transition energies and moments of inertia for every spin state in the band are classified as iden- tical bands. As noted [1], IBs test our theoretical understanding of large amplitude collective motion, demanding more precise microscopic approaches to calculating moments of inertia. Almost all IBs involve even–even and even–odd neighbors in proton-rich nuclei [1]. A series of nearly “IBs” was reported for the α chain 156 Dy to 172 W compared to 180 Os [2]. There, energy similarities were somewhat correlated ∗ This article was submitted by the authors in English. 1) Department of Physics, University of Coimbra, Portugal. 2) Department of Physics, Tsinghua University,Beijing, China. 3) Joint Institute for Heavy Ion Research, Oak Ridge, USA. 4) Flerov Laboratory for Nuclear Reactions, JINR, Dubna, Russia. 5) Lawrence Berkeley National Laboratory, Berkeley, USA. 6) Idaho National Engineering and Environmental Laboratory, Idaho Falls, USA. 7) Department of Physics, Mississippi State University, USA. ** e-mail: with N p N n . Two IBs have been reported in neutron- rich nuclei, 98, 100 Sr and 108-110 Ru [3]. While investigating the structure of neutron-rich nuclei in prompt γ –γ –γ coincidence studies in the spontaneous fission of 252 Cf, we discovered a new phenomenon, which we call shifted identical bands (SIB). We identified levels in 160 Sm and 162 Gd [3, 4] and new high spin states in the heavy partners in neutron-rich Ba to Gd nuclei [3]. The new 162 Gd yrast transition energies were so similar to 160 Gd that this initiated a comparison of the moments of inertia of neighboring even–even nuclei in the A = 140-162 region. We classified shifted identical bands as occurring when two yrast cascades in nuclei separated by two to eight nucleons have their transition energies and moments of inertia become identical when E γ and J 1 for one nucleus are shifted by a constant amount with less than ±1% total spread in the constant κ, where J 1a (1 + κ) = J 1b for every state from 2 + to 8 + and higher to 16 + . We extended this analysis to even–even nuclei from Ba to Pb, from proton- to neutron-rich nuclei, and to some excited superdeformed bands. The SIBs are grouped in stable to the most neutron-rich Sm to Yb nuclei known, while SIBs are not seen in their lighter mass nuclei nor in Ba, Ce, or Os nuclei, except 1063-7788/01/6407-1157$21.00 c  2001 MAIK “Nauka/Interperiodica”