Collective excitations in the 123, 125I nuclei

Abstract

The odd-proton nuclei 123I and 125I have been studied in the reactions 121Sb(α, 2n) 123I and 123Sb(α, 2n) 125I, respectively. The level schemes, spin and parity assignments are based on results obtained from singles γ-ray spectra ( E α = 27 MeV) and excitation functions, from measurements of delayed γ-rays, γ-γ coincidences, internal conversion electrons and γ-ray angular distributions. High-spin positive- and negative-parity bands with energies up to 2948 keV and spins up to 23 2 in 123I and with energies up to 3775 keV and spins up to 27 2 in 125 I have been established. In the decay schemes of both nuclei two separated structures of levels have been observed. One group of levels shows a strong ΔJ = 2 quasirotational pattern predicted by the particle-vibration coupling model. The ΔJ = 1 sequence on a 9 2 + state is assigned as a rotational structure built on the axially symmetric deformed state 9 2 +[404] . In 123I a 28 ns isomer at 2660.0 keV has been found.