125 
hope of ever tapping the sources of energy within the nucleus. Only two 
years later came the crucial discovery which made it seem possible, 
and in Chicago in 1942, it was actually carried through successfully. 
In 1939 three German scientists discovered a new effect, the fission 
of uranium as a result of bombardment by neutrons. Up to this time, 
all transmutation e3q)eriments in which variovis nuclei were bombarded 
by high energy particles of one kind or another, the transmutation was 
to a new nucleus differing only by one, two or three particles from the 
target nucleus. That is to say, the product nucleus would differ by one 
or two orotons or one or two neutrons from the original nucleus. It has 
experiments on the 
chipping process. The 
that 
two uneqiial 
numbers 
and 135 particles approximately or indeed almost any two 
which add up to about 235. The resulting nuclei can be re< 
)airs of well known elements, for example, krypton and ba 
um 
with a huge amount 
tion. 
through 
Where does this energy come from? If you look at a list of the 
exact masses of the product nuclei, for example, krypton and barium 
and of the uranium nuclei you start with, you find that the combined 
masses of the products fall slightly short of the original mass before 
fission. It is indeed true that the mass which disappears is only 0,1 
this accounts for the hi^e energy 
exa 
xmdergoing fission (even though 
energy 
inemassis lost) is still rovighly 40,000,000 times greater than the ener 
gy release per molecule of CO 2 when coal is burned. 
I want to emphasize that, at this stage, we still have no inkling of 
now to turn on or to turn off the supply of energy known to be in the 
uranium nucleus. So far, to make the uranium atom undergo fission, it 
^ been necessary to supply millions of neutrons from an outside sour 
in order that one or two of them may produce fission in a lucky colli- 
sion. Scientifically 1939 and 1940 were exciting years; fission of ura- 
nium was studied with gusto. However, there was no more reason then 
«an there was twenty years before to believe that useful amounts of 
nuclear energy could be released at will. 
cnanged the situation radically. It was discovered that every time a 
uranium atom undergoes fission it also emits several new neutrons, 
^nis opened up the possibility of a chain reaction and the possibility 
nuclear bomb or atomic bomb as it more often is called, 
aai- °^® ^^ ^^ highly significant that, in 1940, when, for the 
Dea "T^^"^ of a possibility of using nuclear energy as a weai 
^red, scientists in this country, Canada and Britain quietl; 
^iish any further researches on uranium fission. This wa 
j^r?'.?^^"^°^P°sed, censorship adopted long before the Arm; 
* that a new and terrihlp wpunnn micrht nnssiblv develop. 
Then 
volun 
