Historical Question about Nuclear Binding Fraction

Dear sci.physics.particle members,

I am researching George Gamow's liquid-drop model from the point of
view of analogical reasoning in theory construction, and I have run
into a historical question whose answer is eluding me. I hope you can
help.

When did physicists realize that the binding energy per nucleon is
proportional to the mass of the nucleus, for a large number of nuclei?
In other words, when did physicists understand that the nuclear binding
fraction is relatively constant, ranging from 8 to 9 Mev for 20<A<80?

Many thanks,

Joe

Dr. Joseph Little
Department of English
Niagara University
jlittle@xxxxxxxxxxx

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