Study of negative parity Bands in 136 Ce

Abstract

Background: The band structures of Ce(Z=58) nuclei with A~135 were studied extensively with the physics interest such as triaxiality and rotation like-sequence i.e. shears mechanism etc. The level structures of 136Ce, with 58 protons and 78 neutrons, were predicted to arise from the interaction between valence proton particles above the Z = 50 major shell and four neutron holes in the N = 82 major shell. The γ-ray spectroscopy of 136Ce was performed here for experimental investigations.Purpose: Study the states of two negative parity bands B1 and B2 with band head Iπ = 5- andIπ = 6- with level energy 1979 keV and 2425 keV respectively. Methods: The excited states of 136Ce are populated via the 124Sn(16O, 4n ) 136Ce fusion evaporation reaction at Ebeam = 90 MeV. The emitted γ-rays from the excited nuclei were detected using the Indian National Gamma Array (INGA) spectrometer at IUAC, New Delhi India.Results: States of two negative parity bands, with band-head Iπ = 5- state at 1979 keV and Iπ = 6- state at 2425 keV have been studied in the present work. The placement of γ-ray transitions of negative parity band B1 has been changed from the earlier reported work and hence the level energy of this band revised and the systematics study of negative parity bands of isotones with N=78, the 136Ce, 134Ba, 138Nd has been carried out.Conclusions: The 806.3 keV γ-ray is found altered with the placement of 971 keV γ-ray transition in the earlier reported work and a 1015.2 keV γ-ray transition is placed in the place of the previously reported 1013 keV γ-ray transition above Iπ = 11- state in band B1. Previously, B1 and B2 bands were predicted as signature partner bands associated with two-quasiparticle, ν[h11/2⊗s1/2/d3/2] configuration. The present work does not support these bands as signature partner bands. Present results are discussed in view of systematics