β decay of Ra228 and possible level structures in Ac228

An iron-free beta spectrometer with pre- and post-acceleration of electrons was used to study β branches and conversion electrons at very low energies in the β decay of Ra228. Results of conversion-electron and γ-ray spectroscopy are analyzed using β selection rules and two-quasiparticle-rotor model considerations. A tentative Ac228 level scheme, including model-dependent spin-parity and configuration assignments consistent with the available …