DOI 10.1140/epja/i2006-10005-1 Eur. Phys. J. A 27, 321–324 (2006) T HE EUROPEAN P HYSICAL JOURNAL A Rotational structures in the 125 Cs nucleus K. Singh 1 , S. Sihotra 1 , S.S. Malik 2 , J. Goswamy 3 , D. Mehta 1 , N. Singh 1, a , R. Kumar 4 , R.P. Singh 4 , S. Muralithar 4 , E.S. Paul 5 , J.A. Sheikh 6 , and C.R. Praharaj 7 1 Department of Physics, Panjab University, Chandigarh 160 014, India 2 Department of Physics, Guru Nanak Dev University, Amritsar 143 005, India 3 UIET, Panjab University, Chandigarh 160 014, India 4 Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India 5 Oliver Lodge Laboratory, University of Liverpool L69 7ZE, UK 6 Department of Physics, University of Kashmir, Hazrathbal, Srinagar, Kashmir, 190 006, India 7 Institute of Physics, Bhubaneshwar 751 005, India Received: 2 February 2006 / Published online: 3 April 2006 – c  Societ` a Italiana di Fisica / Springer-Verlag 2006 Communicated by D. Schwalm Abstract. The collective band structures of the 125 Cs nucleus have been investigated by in-beam γ-ray spectroscopic techniques following the 110 Pd ( 19 F, 4n) reaction at 75 MeV. The previously known level scheme, with rotational bands built on πg 7/2 , πg 9/2 and πh 11/2 orbitals, has been extended and evolves into bands involving rotationally aligned ν (h 11/2 ) 2 and π(h 11/2 ) 2 quasiparticles. A strongly coupled band has been reassigned a high-K πh 11/2 ⊗ νg 7/2 ⊗ νh 11/2 three-quasiparticle configuration and a new side band likely to be its chiral partner has been identified. Configurations assigned to various bands are discussed in the framework of Principal/Tilted Axis Cranking (PAC/TAC) model calculations. PACS. 21.10.Re Collective levels – 23.20.Lv γ transitions and level energies – 21.60.-n Nuclear-strucutre models and methods – 27.60.+j 90 ≤ A ≤ 149 The 55 Cs isotopes lying in the transitional region above the Z = 50 and below the N = 82 shell closures are pre- dicted to possess relatively flat potential-energy surfaces with respect to the quadrupole shape asymmetry param- eter (γ ) [1]. The triaxial deformation in this mass region has been evidenced by interpretation of observed cross- ing frequencies, staggering behaviour and ∆I = 1 doublet bands, which have been explained as the manifestation of chirality [2]. Chiral bands have been observed in var- ious odd-A [3] and odd-odd nuclei [4] with multiquasi- particle configurations that have substantial angular mo- mentum components along the three principal axes. An- other important feature is the magnetic dipole bands gen- erated through the shears mechanism and have also been reported in the odd-A 131 Cs [5] and doubly odd 132 Cs isotopes [4]. Among the 55 Cs isotopes, band-terminating states have been recently observed in 123 Cs at I ∼ 30¯ h [6]. The present in-beam gamma spectroscopic investigations are planned to probe for the above-mentioned structural features in the 125 Cs nucleus. The excited states in the 125 Cs nucleus were popu- lated using the 110 Pd ( 19 F, 4n) fusion-evaporation reac- a e-mail: nsingh@pu.ac.in tion at E lab = 75 MeV. The 19 F ion beam was delivered by the 15 UD pelletron accelerator at the Inter-University Accelerator Centre (IUAC), New Delhi. The target con- sisted of a self-supporting 1 mg/cm 2 thick 110 Pd foil. The emitted γ -rays were detected using the Gamma Detec- tor Array (GDA) comprising of 11 Compton-suppressed Ge detectors, one unsuppressed clover detector and a 14- element BGO multiplicity filter. The Ge detectors were mounted in three groups of four each making angles of 45 ◦ , 99 ◦ and 153 ◦ with the beam direction and having an inclination of ±23 ◦ with the horizontal plane. A total of 500 million coincidence events were collected in the ex- periment. Nuclides with major population in the reaction were 124 Cs (∼ 25%), 125 Cs (∼ 50%) and 124 Xe(∼ 10%). In the off-line analysis, the recorded coincidence data were sorted into 4k×4k E γ -E γ matrices. RADWARE graphical- analysis package [7] was used to establish coincidence and intensity relationships for various gamma transitions. The dipole/quadrupole nature of the γ -ray transitions was in- ferred from angular-correlation analysis based on the DCO method, which helped in level-spin assignments. The level scheme of 125 Cs is shown in fig. 1 with the band structures labeled 1-8.