Helium, He, appears to be one of the main products of fusion reactions of this type and it will be noticed that such reaction products are not themselves radioactive. In this particular sense, fission systems contrast markedly with fusion systems.
     In order that the ionized nuclei of light elements may collisionally interact with each other, they must be accelerated to very high energies. Using the various high-voltage accelerator machines of modem nuclear physics, it is indeed possible to initiate such reactions in laboratory systems, but the yields are fantastically small and it appears dubious whether a weapon design could be perfected which included highly efficient accelerating devices of electrical type.

4. Thermonuclear Reactions and Triggering 

     As an extension of the fusion reaction concept, certain schools of thought are of the opinion that it might be possible to accelerate (or trigger) the nuclei of light elements, deuterons, tritons, etc., to reacting conditions if they were thermally energized in the core of a conventional fission weapon of plutonium or uranium. It is very simply calculable that a temperature of a million degrees Centigrade could only accelerate a proton to about 130 electron volts energy and this is not a very imposing figure when compared with the five million electron volt boost given by an ordinary laboratory Van der Graaf machine.
     Hydrogen and its companion isotopes, tritium and deuterium are all gases which are difficult to liquify and would require weapon refrigerating conditions of the order of -250₁C, before a liquid mixture could be located inside a fission weapon. This seems an insurmountable engineering problem, although some writers waver this may well have been the principle of the American "wet bomb".
     Others prefer the "dry bomb" concept and are of the opinion that it would be possible to use solid compounds of the hydrogen isotopes in the form of their alkali or metallic hydride derivatives and to subject such mixtures to the thermal boosting effect of a fission weapon.
    Stafan's radiation law establishes that at temperatures of many millions of degrees Centigrade the rate of loss of heat from a thermonuclear mass of this character is still proportional to the fourth power of the absolute temperature. To cope with this gigantic rate of heat loss, the fusion reaction would have to produce energy within the system at such a rate that no significant cooling of the reactants, with consequent efficiency loss, occurred in the minute interval of time associated with the functioning of the explosive device. There is no "critical size" consideration to dominate the character of a fusion reaction, but the break-up of the weapon components and the disintegration of the fusion mass at a time

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