How much tritium would be required for the kindling mixture? On this we can only speculate at present. Since the D-T kindling calls for the fusion of one atom of tritium with one atom of deuterium, and the atomic weight of tritium is three as compared with two for deuterium, the weight of the two substances will be in the ratio of 3 for tritium to 2 for deuterium. Thus if the amount to be used for the kindling mixture is to be one kilogram, it will be made up of 600 grams of tritium and 400 grams of deuterium. Since, as we have seen, it would take eighty kilograms of plutonium to produce one kilogram of tritium, we would have to use up only 48 kilograms of plutonium to create the 600 grams, or the equivalent of one and a half to about five A-bombs, according to Dr. Oliphant’s estimate.
But would we need as much as 600 grams of tritium? Such an amount, mixed with 400 grams of deuterium, would yield an explosive power equal to 80,000 tons of TNT, an energy equivalent of 100 million kilowatt-hours. A twentieth part of this amount would still be equal in power to 4,000 tons of TNT, equivalent in terms of energy to 5,000,000 kilowatt-hours. Now one twentieth of 600 grams, just 30 grams of tritium, could be made at a cost of no more than 2.4 kilograms of plutonium. Thus we would be paying only one twelfth to one fourth of an A-bomb (in addition to the one used as the trigger) to get the equivalent of ten A-bombs in blasting power and of thirty times the incendiary power, which would totally devastate an area of more than 300 square miles by blast and of more than 1,200 square miles by fire.
Would 30 grams of tritium be enough to serve as the superkindling for exploding, let’s say, 1,000 kilograms (one ton) of deuterium? We shall probably not know until we actually try it. It will largely depend on the temperature generated by our more powerful A-bomb models. If it is true, as Senator Johnson informed his television audience, that they have “six times the effectiveness of the bomb that was dropped over Nagasaki” (which, by the way, had more than twice the effectiveness of the Hiroshima model), it is quite possible that their temperature is as high as 150 million, or even 200 million, degrees. In that case, the extra kindling of a 20–30 gram D-T mixture, with its tremendous burst of 5,000,000 kilowatt-hours of energy in 0.28 to 0.38 microseconds (added to the vast quantity already being liberated by the exploding plutonium, or U-235), might well heat the deuterium to the proper ignition temperature and keep it hot long enough for its mass to explode well within 1.2 microseconds. In any case it would appear logical to expect that a mixture of 150 grams of tritium and 100 grams of deuterium, which would release an energy equal to that of the Hiroshima bomb, should be able to do the job with plenty of time to spare.
We thus have a threefold answer to the question: Can the H-bomb actually be made? As we have seen, the deuterium bomb is definitely not possible. The tritium bomb is theoretically possible, but definitely not practicable. But a large deuterium bomb using a reasonably small amount of a deuterium and tritium mixture as extra kindling is both possible and feasible.
We now also stand on solid ground in dealing with the questions of cost and of the time it would take us to get into production. With these questions answered, we can then decide whether the H-bomb, if made, will add enough to our security to make the effort worth while.
We know at this stage that the H-bomb requires three essential ingredients. It needs, first of all, an A-bomb to set if off. We have a sizable stockpile of them. It needs large quantities of deuterium. We have built several deuterium plants during the war, and they should be large enough to supply our needs. Since it is extracted from water, the raw material will cost us nothing. The only item of cost will be the electric power required for the concentration process, and this should not be above $100 per kilogram, and probably less. The third vital ingredient, tritium, can be made in the giant plutonium plants at Hanford, Washington. Thus it can be seen that all the essential ingredients of the H-bomb, the costliest and those that would take longest to produce, as well as the multimillion-dollar plants required for their production, are already at hand.
This means that as far as the essential materials are concerned, we are ready to go right now. And as for the cost, it would appear to require hardly any new appropriations by Congress, or, at any rate, only appropriations that would be mere chicken feed compared with the five billion we have already invested in our A-bomb program.
The raw material out of which tritium is made is the common, cheap light metal lithium, the lightest, in fact, of all the metals. It has an atomic weight of six, its nucleus consisting of three protons and three neutrons. When an extra neutron invades its nucleus, it becomes unstable and breaks up into two lighter elements, helium (two protons and two neutrons) and tritium (one proton and two neutrons). They are both gases and they are readily separated. And while lithium of atomic weight six constitutes only 7.5 per cent of the element as found in nature (it comes mixed with 92.5 per cent of lithium of atomic weight seven), there is no need to separate it from its heavier twin, since the latter has no affinity for neutrons and nearly all of them are gobbled up by the lighter element.
The production of tritium, even in small amounts, will nevertheless be a formidable process. As we have seen, it takes eighty times as many neutrons to produce any given amount of tritium as to produce a corresponding amount of plutonium. Since the lithium will have to compete with uranium 238 (parent of plutonium) for the available supply of neutrons, and since the number of atoms of U-238 per given volume is nearly forty times greater than the number of lithium atoms, the rate of tritium production would be very much slower than that of plutonium. On the other hand, even if it took as much as two hundred times as long to produce a given quantity of tritium, the handicap would be considerably overcome because of the relatively small amounts that may be required. If, for example, we should need only 30 to 150 grams of tritium per bomb, it would take our present plutonium plants only six to thirty times longer to produce these quantities than it takes them to produce one kilogram of plutonium. A hypothetical plant such as the one mentioned in the official Smyth Report, designed to produce one kilogram of plutonium per day, would thus yield 30 grams of tritium in six days.
How much tritium would be needed for an adequate stockpile of H-bombs? Since our primary reasons for building it are to deter aggression, to prevent its use against us or our allies, and as a tactical weapon against large land armies, it would appear that as few as twenty-five, or fifty at the most, would be adequate for the purpose. On the basis of the larger figure (assuming 30 to 150 grams of tritium per bomb), it would mean an initial stockpile of only 1.5 to 7.5 kilograms of tritium, which would entail the sacrifice of about 120 to 600 kilograms of plutonium. Once this initial outlay had been made, however, our plutonium sacrifice would be reduced annually to only one twenty-fourth of the original respective amounts—namely, 5 to 25 kilograms a year—just enough to make up for the decay of the tritium at the rate of fifty per cent every twelve years.