The fine structure in C radioactivity of Ra was discussed for the first time by M. Greiner and W. Scheid in 1986. The superconducting spectrometer SOLENO of IPN Orsay has been used since 1984 to identify C clusters emitted from Ra nuclei. Moreover, it was used to discover the fine structure observing transitions to excited states of the daughter. A transition with an excited state of C predicted in Ref. was not yet observed.