  In 1928 G. Gamow as well as Condon and Gurney gave the first explanation of
alpha decay as a quantum tunnelling of a preformed particle at the nuclear
surface. Soon after experimental discovery in 1984 by Rose and Jones of cluster
radioactivity, confirming earlier (1980) predictions by Sandulescu, Poenaru and
W. Greiner, a microscopic theory also explained the phenomenon in a similar
way. Here we show for the first time that in a spontaneous cold fission process
the shell plus pairing corrections calculated with Strutinsky's procedure may
give a strong argument for preformation of a light fission fragment near the
nuclear surface. It is obtained when the radius of the light fragment, $R_2$,
is increased linearly with the separation distance, $R$, of the two fragments,
while for $R_2=$~constant one gets the well known two hump potential barrier.
