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The nuclei around the A ∼ 130 mass region belong to the category of transitional nuclei, where the axial symmetry is broken, and the non-axial degree of freedom plays an essential role in determining the properties of these nuclei. The Xe isotopes in the A∼ 130 region are of particular interest as recent investigations of the excited states of the 125,127Xe have indicated triaxial shapes using gamma ray spectroscopy [1,2]. The existing level scheme of 129Xe has not been extended much compared with those of 127Xe and 131Xe. As a result, the structure and collective behaviour of 129Xe are not yet fully understood.
The high-spin states of 129Xe have been investigated using the fusion-evaporation reaction of a 124Sn target with a 9Be beam of energy of 40 MeV. The experiment was performed at the TIFR-BARC Pelletron LINAC Facility at TIFR-Mumbai, India. The γ-rays emitted in the reaction have been identified with the INGA, consisting of 18 Compton-suppressed HPGe detectors [3]. The previously known level scheme reported for 129Xe [4] has been verified, and new gamma-transitions have been observed. An extended level scheme has been constructed using γ–γ coincidence techniques [5]. Using the Ratio of directional correlation (Rdco) and Polarisation, spin-parity of the new levels and multipolarity of the gamma transitions have been assigned.
A detailed microscopic investigation of the γ-vibrational band structures has been done using the Triaxial Projected Shell Model (TPSM) approach [6]. The band crossing phenomenon is observed because of the particle alignment, showing the simultaneous crossing of both the yrast and γ band. The wavefunction analysis reveals a clean transition from one-quasiparticle dominance at low spin to three-quasiparticle dominance after the crossing. The extended TPSM approach [7] provides a unified and microscopic description of the rich band structures observed in 129Xe. These results contribute to a better understanding of the structure of nuclei in the A ~ 130 mass region.
References
[1] S. Chakraborty et al., Phys. Lett. B 811, 135854(2020).
[2] Mamta Prajapati et al. PRC 109, 034301(2024)
[3] R. Palit et al., Eur. Phys. J. A (2025) 61:74
[4] Y. Huang et al., Phys. Rev. C 93, 064315 (2016).
[5] R. Palit et al., NIM A, 680, pp. 90–96,(2012)
[6] S. Jehangir et al. Eur. Phys. J. A (2021) 57:308
[7] S. Jehangir et al., P.R.C 105, 054310 (2022).