Effect of a Triaxial Nuclear Shape on Proton Tunneling: The Decay and Structure of ¹⁴⁵Tm

Gamma rays deexciting states in the proton emitter ¹⁴⁵Tm were observed using the recoil-decay tagging method. The ¹⁴⁵Tm ground-state rotational band was found to exhibit the properties expected for an h_11/2 proton decoupled band. In addition, coincidences between protons feeding the 2⁺ state in ¹⁴⁴Er and the 2⁺→0⁺ γ-ray transition were detected, the first measurement of this kind, leading to a more precise value for the 2⁺ excitation energy of 329(1) keV. Calculations with the particle-rotor model and the core quasiparticle coupling model indicate that the properties of the πh_11/2 band and the proton-decay rates in ¹⁴⁵Tm are consistent with the presence of triaxiality with an asymmetry parameter γ≈20°.