Concerning the Hydrogen Bomb
AT THE OUTSET let me say that I am a warmonger; that is, I am not a X Red, a Pink or a Yellow. (Those who do not have whiskers and bite must have feathers and scratch.) When it appears highly probable that war may come, though all human means should be used to avoid it, I believe that' every principle and device known to science should be used to perfect our means of waging war. But I do not believe in vast waste nor in engaging in a huge gamble.
A hydrogen bomb is one which presumably uses hydrogen as one of the essential materials producing the explosion. There are three forms of hydrogen: (1) the abundant and ordinary Hl, detected in 1766, the nucleus of which is a single postively charged particle, a proton; (2) heavy hydrogen, H2, or deuterium, D2 (1932); the nucleus, a deuteron, is a proton and a neutron; it constitutes one five-thousandth of all hydrogen, it is rather easily obtained; (3) hydrogen three, H3, tritium, T³; it is an artificial and radioactive atom with a half life of 12 years, thirty per cent of it would become helium in three years; it is enormously expensive.
In the ordinary bomb, the A bomb of uranium or plutonium, a nucleus is broken into two parts, fissioned, by the entrance of a neutron. The excess mass is charged into energy of about 200 million electron volts, 200 Mev (1 Mev will be our unit of energy). The neutron being uncharged does not experience any difficulty in entering the nuclei. But the nuclei of hydrogen repel one another. Thus a mass of H or of D will remain unchanged forever—unless the atoms are given enormous energies. This can be done now by the use of atomic guns. When D's are fired into heavy hydrogen, nuclei may momentarily merge and break up into or change over to form other nuclei. Thus we may have these reactions: (1) H2 +H2 = He4 + E1; (2) H2 +H2 = Hi +H³ + E2; (3) H2 +H2 = He3 + neutron + E3. The E's are the energies resulting from these reactions, Ex is about 23 Mev, E2 and Es each about 3.2 Mev. The large probability is that the last two reactions take place.
Consequently it results that the energy which may be obtained by the fusing of two atoms of deuterium is about one six- tieth of that due to the fission of one atom of plutonium. As there are 120 times as many atoms of deuterium in a pound as of plutonium, it follows that if all the atoms of deuterium would unite in pairs, we would have a production of energy nearly equal to that due to the fission of all the atoms of an equal weight of plutonium.
The only way in which the atoms of hydrogen can be given great energies is by heating hydrogen to temperatures of the order of fifty million degrees centigrade by the explosion of the A bomb. There is no doubt but that in the center of the A bomb such temperatures are produced. Now hydrogen ordinarily is a rare gas. Heavy hydrogen would have to be subjected to a pressure of 45 tons per squareinch to be given the density of water and that density would be required in order for the above reactions to take place. If we assume that the A bomb consists of 100 pounds of plutonium (that would be the mass of a six-inch diameter sphere), then 50 tons of deuterium would be required to give a power 1000 times that of the A bomb. The volume required would be 1600 cubic feet. This is smaller than a Sachem Village house, but would be larger than some students' rooms.
Our picture then is this—in the center an A bomb with its tamper of a few tons (it took the largest plane in the world to launch the A bomb) surrounded by 1600 cubic feet, 50 tons, of deuterium encased by a metal wall under an initial pressure of 4.5 tons per square inch. The whole volume of deuterium would have to be raised many million degrees. What would happento the pressure—and to the casing? It can be seen that the probability of making a bomb of the above power out of deuterium is very small.
DEUTERIUM AND TRITIUM
WHEN a D and a T nucleus, each having an energy represented by 50,000,000 degrees, impinge, this reaction may result: H2 + H3 = He4 + n + E. The energy is about 17 Mev, or five times that due to the collision of two deuterons. Hence we may cut down the mass from go tons to 10 tons (4. of D and 6 of T) and the volume from 1600 cubic feet to 320 cubic feet, still at an initial pressure of 45 tons per square inch. This looks more hopeful. But it would be necessary for the D's and the T's to behave properly, the D's should not impinge on the D's nor the T's on the T's. Then we revise our view. But let us look at another item. I have just received from the director of the Physics Division of Oak Ridge the new reduced price for tritium in a large lot. The cost is $1,315 for 10 cc. (one must have the permission of the A.E.C. to purchase this amount). This works out to be $526,000 per gram, or $240,000,000 a pound—if that much could ever be obtained. (Will the sophomores please check these figures?) Hence for one bomb the cost for tritium alone would be $2,880,000,000,000. Thus the contemplation of a combined D and T bomb might give even a U. S. Senator the DT's.
Of course, the point may be raised that the Oak Ridge Laboratory is only a few years old, that we have spent only a billion dollars or so on it, that the A.E.C. now spends only $700,000,000 a year on this and other laboratories. If we would erect a laboratory designed especially for the man- ufacture of tritium, its cost could be greatly reduced. But how much would this pre- liminary cost be? How many schools and hospitals could be built for the same money?
There is one great difference in the performance of the A bomb as compared with the D or T bomb. In the former, whenever an atom is fissioned two neutrons (on the average) are released ready to continue the work. But there is no such multiplying chain reaction in the other bombs, indeed there may be the opposite action. For gamma rays may be released and these may break up the D's or the T's into ordinary H's and neutrons. The H's are worse than useless. The neutrons might assist in increasing the efficiency of the A bomb, for a large fraction of the plutonium is now blown away unfissioned. (See No Placeto Hide by Dave Bradley, Dartmouth '3B).
Where would we test the new bomb? If it should work and be as deadly as some claim it would be, it dare not be tested any- where in the U.S. The adjacent regions would protest. An island in the-Pacific is no place for a test. Many different kinds of instruments or various' buildings should be placed at various distances from the center in order to test the shock and temperature effects. This cannot be done properly iri the Pacific.
There is another combination which might be used, but concerning it I do not care to write. The temperature required would be several times that required for the D or T bomb, and the mass and volume would be very large.
Mr. Hull is Appleton Professor of Physics, Emeritus, and a scientist of international reputation. During and for two years after World War I he was Physicist of the Technical Staff of the Ordnance Department of the U. S. Army. He introduced new methods and designed apparatus for measuring the acceleration of projectiles in guns, their speed and retardation in air, and the pressure and rate of change of pressure in the gun during firing. Practically all these methods are still used in the Aberdeen Proving Ground.
