ATOMIC POWER—RICHARDSON LS7 
this corresponds to the escape of an alpha particle or electron from 
radioactive elements. Ifa drop of water is violently disturbed it may 
break into several parts. Similarly, if the nucleus receives a powerful 
shock, as when struck by a neutron, it may divide in two, the process 
which has since become known as “nuclear fission.” 
Meitner and Frisch also called attention to the tremendous energy 
released by the fission of uranium. When uranium, the heaviest ele- 
ment of all, is split into two elements of roughly half its weight, there 
is an excess of mass which is converted into energy of an amount given 
by Einstein’s mass-energy relation. 
The energy released by fission of one uranium atom is in engineering 
units 0.000320 ergs, which means that to produce one horsepower we 
would have to split 23,300 billion uranium atoms per second. Let us 
try to visualize these figures in terms of familiar things. To toast a 
slice of bread in an electric toaster takes about 15,500 calories. Assum- 
ing 100-percent efficiency in the atom-splitting process, the same energy 
could be obtained from thirty-billionths of an ounce of uranium. Or 
for an entirely different example, a 100-ton locomotive could run 
from New York to San Francisco on 0.02 ounce of uranium metal. 
Most important of all, uranium fission releases neutrons which are 
more effective in splitting nuclei than protons or alpha particles would 
be, since, having no charge, they are not repelled as they approach 
the positively charged nucleus. In the ideal case, the reaction would 
spread with increasing rapidity and if uncontrolled would lead to 
an explosion of tremendous violence. Even if the chain spreads much 
more slowly than in the ideal case the release of energy would still be 
of unprecedented violence, providing that the multiplying factor were 
always greater than unity, and was “compounded” very rapidly. 
According to reports, this entire detonation problem was and still is 
one of the most difficult encountered in designing a highly efficient 
atomic bomb. 
Further work indicated that the uranium involved in the fission re- 
action is a rare isotope of atomic weight 235, which comprises only 
0.7 percent (144, part) of the metal occurring in nature, most of which 
is of atomic weight 238. 
In the light of recent events, it is interesting to look back at some of 
the comments on uranium fission made about 1940. One writer," 
after mentioning several points in connection with the new process, 
remarked : “These five points are the fancy which may or may not 
come true within our time. There are others, like the uranium bomb, 
which go beyond fancy into the fantastic.” Again, E. O. Lawrence ™* 
spoke of the 
13 Robert D. Potter, Sci. Month., vol. 50, p. 571, 1940. 
14From an address given at Stanford University in June 1941; reprinted in Ann. Rep. 
Smithsonian Inst., 1941, p. 163. 
