The lowest β-vibrational phonon in the second minimum of 236,238U

Vibrational exci tat ions of f i ss ion isomers have d i r ec t l y been observed for the f i r s t time using conversion electron spectroscopy. A new experimental setup has been developed whidh allows the measurement of prompt conversion electrons from electromagnetic t ransi t ions in delayed coincidence with the f i ss ion decay of the isomer. The large amount of low energy a-electrons was suppressed by special geometrical arrangement of the detectors in the magnetic f i e l d of the solenoid.