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The even-A stable Xe isotopes are placed in a mass region where a variety of nuclear phenomena emerge. In particular, $^{126}$Xe and $^{128}$Xe exhibit characteristics of transitional nuclei, a possible critical point in the shape transition from spherical to γ-soft, O(6)-like nuclei [1].
In order to probe the structure and collectivity of $^{126,128}$Xe, their properties were studied in low-energy Coulomb excitation measurements. An experiment was performed at the The National Superconducting Cyclotron Laboratory (NSCL) Re-accelerator facility at Michigan State University (MSU). The $^{126}$Xe and $^{128}$Xe nuclei were accelerated to 3.74 MeV/u and 3.81 MeV/u, respectively, and impinged on $^{196}$Pt and $^{208}$Pb targets. The scattered nuclei were detected in coincidence with de-excitation gamma-rays using the Joint Array for Nuclear Structure (JANUS) experimental setup. The detector configuration included a pair of segmented double-sided Si detectors and the Segmented Ge Array (SeGA) comprising of sixteen 32-fold segmented high-purity germanium detectors, placed around the target chamber.
Transition and diagonal matrix elements were determined from the experimental data using the GOSIA code [2]. They were further used to calculate E2 reduced transition probabilities and quadrupole moments for states in $^{126,128}$Xe. The results for the B(E2) values are in agreement with literature data from previous Coulomb excitation measurements [3,4]. The new results for quadrupole moments give a more detailed insight on the structure of the even-A Xe isotopes. The values suggest a deviation from the O(6) dynamical symmetry which was thought to describe well the properties of even-A Xe in this mass region.
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics. Work at LLNL is supported by the U.S. DOE under Contracts No. DE-AC52-07NA27344, 89233218CNA000001.
[1] R. M. Clark et al., Phys. Rev. C 69, 064322 (2004).
[2] T. Czosnyka, D. Cline, and C. Y. Wu, Bull. Am. Phys. Soc. 28, 745 (1983).
[3] L. Coquard et al., PRC 83, 044318 (2011).
[4] J. Srebrny et al., Nuclear Physics A 557, 663 (1993).