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possible for the nuclei themselves to collide with each other, it is ne - 
cessary to make the atoms move with extraordinary violence, and a way 
to effect this is to raise the temperature of the whole mass of material 
to many millions of degrees. This is perhaps the central problem of the 
hydrogen bomb, after selecting the nuclei which will give a good yield of 
energy on coalescing into a slightly heavier nucleus, and for which the 
probability of this particular synthesis is adequate. One way which has 
been repeatedly mentioned is to use a uranium or plutonium bomb as a 
starter to provide the very high temperatures needed and have the hy- 
drogen in close contact with it. The difficulties seem to be many and 
great. Since hydrogen is a gas, it would seem necessary to use liquid 
hydrogen to secure the necessary density of material. The problems of 
liquefying hydrogen and keeping it liquid are extraordinarily difficult. 
Perhaps one could get around this difficulty by combining Li 'and H^ in- 
to lithium hydride which at least does hot require to be held at extraor- 
dinary low temperatures. The nuclei of these atoms when in intimate 
contact, as is possible at high temperatures, can yield two helium nuclei 
with evolution of energy. 
So far as I know, we are, in respect to the hydrogen bomb, in the 
same situation as we were in 1941 with respect to the uranium bomb. 
Theoretically at that time, it was just possible to make an uranium bomb 
if many conditions, then unknown, all turned out to be favorable. They 
turned out to be favorable and the bomb was made . 
I want to recall my statement that, in the uranium bomb, only 0.1 per 
cent of the total mass disappears and this leads to the maximum energy 
ttat can be obtained theoretically per pound of uranium. Likewise In the 
formation of a helivmi nucleus out of lighter nuclei only a few tenths of 
one percent of the total mass disappears and this again leads to the maxi- 
mum energy that can be theoretically evolved. Obviously if one could 
devise a process whereby all the mass of any material were converted 
into energy, the theoretical efficiency would be a 1000 times greater 
than that of the uranium bomb. So far as I know, no one has the slightest 
idea of how to realize this. 
It is pertinent to quote a sentence from the Smyth report which dealt 
with the uranium bomb. "Initially many scientists could and did hope 
that some principle would emerge which would prove that atomic bombs 
were inherently impossible. This hope faded gradually." Smyth of 
course had in mind the uranium bomb. Maybe some principle or some 
technical difficulty may make the hydrogen bomb inherently impossible. 
Professor Urey recently stated that his guess was that there was afilty- 
fifty chance of success in making a hydrogen bomb. Until mankma 
learns to solve its difficulties without appeal to war, it may l>e J'jst as 
well if it was found that a hydrogen bomb could not be made. Umorru- 
nately man's skiU in science and technology goes ahead at an ^^°°^^''~ 
plosive pace while his abiUty to get along with his fellow men wiinoui 
war seems no better now than it was centuries ago. opttle 
So long as nations cannot work out acceptable P^<>^^°^^^®,JP^i ..„ . 
differences between themselves without appeal to war, It wouia oe 
realistic for us not to go ahead with the hydrogen bomb. 
un 
