β -delayed spectroscopy of Ge4880 and competition between Gamow-Teller and first-forbidden transitions in Ga49</mml…

The β-delayed spectroscopy of ⁸⁰Ge has been studied using sources of ground and low-lying isomeric states of ⁸⁰Ga. A hybrid γ-ray spectrometer was used, composed of high-purity germanium (HPGe) detectors for low-energy γ-ray detection, phoswich detectors from the PARIS array for high-energy γ rays and a plastic detector for β tagging. The new decay level schemes are presented, with 13 and 14 states β populated by ⁸⁰ᵍGa and ⁸⁰ᵐGa, respectively, being reported for the first time. We quantitatively compare summed intensities of first-forbidden and previously reported Gamow-Teller β transitions [R. Li et al., Phys. Rev. C 111, 034303 (2025)]. The upper-limit fractions of first-forbidden transitions contributing to the decays of ⁸⁰ᵍGa and ⁸⁰ᵐGa are (48.0±2.7)$%$ and (47.9±3.3)$%$ of the observed total β transition intensities of (78.2±2.5)$%$ and (82.2±3.7)$%$, respectively. Notably, the half-lives decrease in accordance with the upper limits of (48.0±6.0)$%$ [3.67(20) s →1.91(3)0.28em0exs] and (47.9±7.2)$%$ [3.01(19) s →1.57(1)0.28em0exs] for ⁸⁰ᵍGa and ⁸⁰ᵐGa, respectively, when including first-forbidden transitions, in contrast to those by Gamow-Teller transitions only.