122 
has 
practically the same mass as the proton which is the nucleus of thehy- 
1 that it has 
charge. 
that when uranium is 
two nuclei with a tre 
mendous evolution of energy. So far there was no glimmer of any idea 
as to how to control this release of energy. In 1940, there came the 
first indication of how a controlled chain reaction to utilize nuclear fis- 
sion could perhaps be devised. 
On December 2, 1942, in a small building under the bleachers of the 
Stagg Field at the University of Chicago, a group of men headed by A.H. 
Compton and E. Fermi, carried through the first successful experiment 
and 
On July 16, 1945, at Alamogardo, New M< 
was tested successfully. This was an explos 
gy, uncontrolled in the sense that once starte 
natural terminatinn 
activity 
physics which led to the first feeble steps in man's mastery of the re- 
energy 
Some of the points touched on need to be elaborated to >give a better 
understanding of the principles involved in utiUzing nuclear energy. 
Early in this century the physicists' picture of the atom had become 
fairly well stabilized. The atom consists of a heavy nucleus with a po- 
sitive charge at the center surrounded by a cloud of electrons, each with 
a negative charge, in rapid choatic motion around the nucleus. For ex- 
■ I • 
diiipie me aiom ot gold consists of a heavy nucleus carrying 79 posiuve 
charges surrounded by a cloud of 79 electrons in rapid motion. Each 
electron carries a single negative charge. The average distance bet- 
ween the electrons and between the electrons and the nucleus is roughly 
100,000 times the diameter of each. You then see that the atom is 
largely empty space. If you could blow up an atom of gold to the size of 
this room the nucleus would be represented by a large hornet motionless 
at the center of the room with 79 flies buzzing around in all direction 
withm the room. In spite of the emptiness of the atom, the electrons 
form an effective barrier shielding the nucleus. Even in the case of the 
hydrogen atom where there is but one electron, its rapid motion in all 
directions around and about the nucleus provides effective interference 
for the nucleus. The idea I want to put across is that the nucleus isweU 
protected m atoms by the electrons. Only a very high energy particle 
can crash through the interference. 
Chemistry is the study of the way atoms combine with each other to 
form molecules. Chemical combinations are bewildering in their num- 
ber and variety, but in the last analysis they are all describable as the 
tangling together of the superficial electrons in each atom involved. 
The 
clei. 
the 
the energy evolved when a compound 
is 
energy 
