ATOMIC ENERGY — JOHNS 183 



was barium. Extensive experiments in both Europe and America had 

 by June 1939 confirmed this atomic fission.^ Here I only mention 

 three of the many then known facts, but will amplify them later. 



(1) The products of the atomic fission were two imequal fragments 

 near the middle of the table of atoms, for example, barium and krypton. 



(2) Tremendous amounts of energy were given off in the process. 



(3) From each atomic fission caused by one neutron, one to three 

 neutrons arose. 



Graphically the fission may be indicated thus : 



FISSION FRAGMENT 



MEUTRONS 



FISSION FP-AGMENT 



Figure 2. 



Here then was something new under the sun. Atomic fission was 

 a fact. The atom had been split. Then the black curtain of war 

 descended on the world and split the scientists also into isolated groups. 



THE MASS-DEFECT CURVE— BINDING ENERGY 



Let us return for a moment to the two illustrations cited of the 

 release of atomic energy in nature, namely, radioactivity and the 

 carbon cycle. It seems remarkable that energy can be released either 

 by the breaking down of the more complex radium atom to the less 

 complex lead atom or by the building up of the more complex helium 

 atom from the less complex hydrogen atom. That both processes 

 yield energy is possible because of the nature of the 92 elements them- 

 selves. It is a fact that the mass per particle (neutron or proton) in 

 the nucleus is greater for either the very light or the very heavy ele- 

 ments than it is for the elements midway between. Hence when hydro- 

 gen is transformed to helium or uranium to barium, mass is lost, and 



' For details I commend to your study Smyth's book, "Atomic Energy for Military 

 Purposes." 



777488—48 13 



