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nuclexis is to have two protons and two neutrons come together at exactly 
the same instant. Energy would be given out, but the chance of this oc- 
curring is so fantastically low that it is ruled out. The chance of two 
friends meeting each other at say the corner of Broadway and Olive, of 
course without previous planning, is extremely small, but the chance of 
four friends meeting at the same point at the same time without plan- 
ning is astronimically smaller. Consequently we restrict ourselves to 
collision between two nuclei. In this business of doodling symbols on 
paper to see what possible combinations there are, one has plenty of 
nuclei to start with. For example we have the proton which is the nu- 
cleus of deuterium or heavy hydrogen, the trlton which is the nucleus of 
tritium, or very heavy hydrogen, Li of mass 6, Li of mass 7, and Be of 
mass 9. The possible combinations of all these nuclei, two by two, are 
quite numerous and the possible yield of energy varies a great dealde- 
pending on the particular pair you are dealing with. However this is not 
the whole story by a long way. Some combinations go easily, others go 
with difficulty. So you have to know the probability of the type of com- 
bination you have under consideration. Consider the collision of two 
deuterons, the nuclei of heavy hydrogen, each containing one proton and 
one neutron stuck together. They can bounce off each other withoutany 
evolution of energy, they can coalesce into a helium nucleus, or they can 
result in one proton and one triton, the triton being the nucleus of very 
heavy hydrogen and having two neutrons and one proton stuck together. 
The latter process happens much more often than the first. 
Earlier I mentioned the numerous possible combinations of lighter 
nuclei to form slightly heavier nuclei. The probabilities of occurence 
of a few of these are well know, having been published in the scientific 
journals all over the world. The probabilities of occurrence of others 
are unknown as yet, at least no results have been published. 
In addition to knowing the amount of energy evolved in the synthesis 
of a nucleus from lighter nuclei, and the probability of the formation of 
a particular nucleus when certain light nuclei colUde, it is of the great- 
est importance to ensure these nuclear collisions will occur with suffi- 
cient frequency to evolve energy at such a rate that much of the availa- 
ble energy has been released before the material begins to fly apart, 
tarlier m my talk I mentioned that the electrons in an atom provided 
effective interference for the nucleus. What I meant was that when two 
atoms collide at temperatures even as high as in a blast furnace the 
electrons around each nucleias in the atoms are completely effective in 
preventmg the nuclei ever getting close to each other. As an analogy 
ZlTl ^^ °^ ^ "^°^^^^ o* peaches at the bottom of a basket wluchis 
ouPnH B^" violently so that the peaches colUde with each other fre- 
quently However, the fruit of the peaches, representing the electrons 
Spft lT°'''^^^ ^°^ *^ ^*°"«s o* the peaches representing the nu; 
P^rin f "" '^^''^^^ ^^* ^^^h other. Only by agitating the basket J^th 
D?/rh/ r^"^ y^^^^''^^ ^°^l<i itl»e possible to make the stones of the 
att in!hi ?^* ^"""^^ ^^ ^^^t and touch each other. In matter at aU 
wi? !f ^^"^Pt^^tures on the earth, the nuclei of colliding atoms neve 
^rl nf if "'f °! *°^*^^^S each other because of the effective interfer 
ence of the electrons. To overcome this interference and so make « 
