ISSN 1063-7788, Physics of Atomic Nuclei, 2006, Vol. 69, No. 7, pp. 1198–1203. c  Pleiades Publishing, Inc., 2006. PROPERTIES OF ATOMIC NUCLEI Experiment Collective Bands in 104,106,108 Mo * E. F. Jones 1) , P. M. Gore 1)** , S. J. Zhu 1), 2)*** , J. H. Hamilton 1) , A. V. Ramayya 1) , J. K. Hwang 1) , R. Q. Xu 2) , L. M. Yang 2) , K. Li 1) , Z. Jiang 2) , Z. Zhang 2) , S. D. Xiao 2) , X. Q. Zhang 1) , W. C. Ma 3) , J. D. Cole 4) , M. W. Drigert 4) , I. Y. Lee 5) , J. O. Rasmussen 5) , Y. X. Luo 1), 5) , and M. A. Stoyer 6) Received November 24, 2005 Abstract—We have used our analysis of γ −γ −γ data (5.7 × 10 11 triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of 252 Cf to study the collective bands in 104,106,108 Mo. The one-phonon and two-phonon γ -vibrational bands and known two-quasiparticle bands in neutron-rich 104,106 Mo were extended to higher spins. The one- and two-phonon γ -vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in 104,106 Mo, along with the first β-type vibrational band in 106 Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in 106 Mo are strong. These are the first reported chiral vibrational bands in an even–even nucleus. PACS numbers : 21.10.Re, 21.60.Ev, 27.60.+j DOI: 10.1134/S1063778806070167 A γ −γ −γ coincidence study of prompt γ rays emitted in the spontaneous fission of 252 Cf was carried out using Gammasphere with 102 Compton- suppressed Ge detectors. In spontaneous fission, 252 Cf fissions into two primary fragments, which emit neutrons and become secondary fragments, which emit γ rays. In our experiment, these γ rays were detected by Gammasphere. By using a 252 Cf source of strength 62 mCi sandwiched between two Fe foils of thickness 10 mg/cm 2 and mounted in a 3-inch- diameter plastic ball, approximately 6 × 10 11 triple- and higher-fold coincidence events were recorded with a 1-μs time window. Further experimental details are found in Luo et al. [1]. Our 2000 ex- periment utilizing the spontaneous fission of 252 Cf yielded about 50 times greater statistics than previous ∗ The text was submitted by the authors in English. 1) Department of Physics, Vanderbilt University, Nashville, USA. 2) Department of Physics, Tsinghua University, Beijing, China. 3) Department of Physics, Mississippi State University, USA. 4) Idaho National Engineering and Environmental Laboratory, Idaho Falls, USA. 5) Lawrence Berkeley National Laboratory, Berkeley, USA. 6) Lawrence Livermore National Laboratory, Livermore, USA. ** E-mail: philip.m.gore@vanderbilt.edu *** Joint Institute for Heavy Ion Research, Oak Ridge, USA. experiments. Coincidence data were analyzed with the RADWARE [2] software package. In our work, collective bands in 104,106,108 Mo were investigated by measuring the prompt γ rays emit- ted in the spontaneous fission of 252 Cf. The ground and one- and two- phonon γ -vibrational bands were extended and new bands were observed. In 106 Mo, two sets of ΔI =1 bands were observed, which are proposed to be chiral doublets. Figure 1 shows the level scheme of 104 Mo. The ground band (1) is extended in our work from 12 + up to 16 + . Band (2) is extended from 10 + up to 14 + and crossing transitions at 394.3, 604.9, 1283.7, and 940.6 keV between bands (2) and (1), respectively, were found from our analysis, as well as transitions at 215.8, 168.9, 259.9, and 250.3 keV within band (2). Band (3) is extended from 7 + up to 9 + , and crossing transitions at 368.6, 609.1, 358.8, and 898.6 keV between bands (3) and (2), respectively, as well as crossing transition at 1022.4 keV between bands (3) and (1), were found from our work. Bands (5) and (8), with two levels each, and band (7), with four levels, and their depopulating transitions, were observed for the first time. Band (6) is extended from 9 - up to 13 - , and an additional level is identified at 5 - , The odd-spin level energies in band (2) are seen to be somewhat closer to the next higher even-spin level than to the next lower even-spin level in 104 Mo. 1198