Pseudo Spin Doublet Bands and Gallagher Moszkowski Doublet Bands in ¹⁰⁰Y

New transitions in the deformed neutron-rich ¹⁰⁰Y uniquely identified using the VAMOS++ spectrometer (A, Z) in conjunction with EXOGAM, produced in fission reactions of ²³⁸U on a ⁹Be target at energies around the barrier are reported. High spin states were obtained from an analysis of the large fold gamma coincidence data from the spontaneous fission of ²⁵²Cf using the Gammasphere detector array. The new K-π = 4⁺ band decaying to an isomeric state (1s) is assigned to be the high-K Gallagher-Moszkowski (GM) partner of the known K-π = 1⁺ band, and is also proposed to be the pseudo sπn (PS) partner of another new K-π = 5⁺ band. Constrained triaxial covariant density functional and quantal particle rotor model calculations for the band structure and electromagnetic transition probabilities are in good agreement with the measurements. The work shows for the first time a coexistence of GM and PS bands in the same nucleus and could point towards a common source of these bands despite their very different origins. (authors)