Alarm Clock

Two new methods of designing a thermonuclear weapon were subsequently invented in the years immediately after World War II. Both inventions were due to Teller.

The "Alarm Clock" was invented in 1946, and the "Booster" in 1947. The "Alarm Clock" was actively worked on by Richtmyer, Nordheim, and others. However, at the time, there seemed to be no way of putting it into practice. The Booster was different from all the others in that thermonuclear reactions are used only in a minor way, for weapons of relatively small yield. This method seemed quite promising from the start, and as early as the Summer of 1948 it was added to the devices to be tested in the Greenhouse tests.

The "Alarm Clock" design (so named because it will awaken the world) featured massive imploded enveloping spherical layered shells. The proposed structure consisted of alternating spherical layers of fissionable materials and thermonuclear fuel (deuterium, tritium, and, possibly, their chemical compounds). This design held several potential advantages. Fast neutrons generated in thermonuclear reactions were expected to initiate fissions in neighbouring layers of fissionable materials, which would result in a considerably higher energy yield.

The large dimensions and weight of the structure required in this case made its compression by chemical explosives very difficult, or practically impossible.

The "Alarm Clock" device was described in a report by Teller issued on 31 August 1946, two and a half months after Fuchs left Los Alamos. Intensive calculations on this device were carried out by Nordheim, Richtmyer and others from the time of its invention to the end of 1947.

After Teller proposed a new thermonuclear system, which later came to be called the TX-14, Richtmyer took up the problem of estimating performance. In January-February 1947 Richtmyer started to develop an improved theory of efficiency of the TX-14. He began discussions with Teller and von Neumann of possible application of advanced electronic computing equipment (then in early stage of design at Princeton) to Los Alamos problems.

Even before the completion of the ENIAC, the group associated with its development was discussing the logical and engineering design of the next-generation electronic computer, the EDVAC (electronic, discrete variable automatic computer) project.

In the case of a fission explosion, a modest number of experimental facts which could be determined in the laboratory (and had mostly been roughly ascertained before the Manhattan District was formed), along with rather elementary theoretical considerations, sufficed to show that a fission explosion was feasible. The major part of the wartime theoretical work at Los Alamos was required to ascertain the detaile of a favorable design, the mechanics of its assembly, and estimates of its performance.

With respect to thermonuclear weapons [and the classical Super in particular], the very proof of feasibility required the fully detailed calculation of its behavior during an explosion. Without this, no conclusive ex-periment was possible short of a successful stab in the dark, since a failure would not necessarily establish unfeasibility, but possibly only that the system chosen was unsuitable, or that the required ignition conditions had not been met.

Theoretical work on the "classical super," Method A, proceeded continually, since this method was considered the most important of all thermonuclear devices. New plans for calculations were made frequently, mostly by consultation between Teller and the senior staff of the theoretical division. However, the required scientific effort is clearly much larger than that needed for the first fission weapon. In particular, the theoretical computations required were of such complication that they could not be handled in any reasonable time by any of the computing machines then available. Some greatly simplified calculations were done but it was realized that they left out many important factors and were therefore quite unreliable.

By the end of September 1947, calculations had been made on several TX-14 models. The results are discussed by Teller in a report: "Because of the great technical difficulties that would be encountered in constructing such a bomb, we have not further pursued this possibility ...." The most favorable calculation available at that time indicated the possibility of obtaining 10 megatons from a certain configuration weighing from about 40 to 100 tons.

In the same report it was suggested that 6LiD might be used as a fuel. With lithium-6 included in the fuel, the quantity of tritium produced during the explosion would be considerably larger, which would notably increase the thermonuclear reaction efficiency. This would simplify some problems but require the production of separated lithium and leave the problem of the required initiating explosion to be solved.

After September 1947, in consideration of the enormous difficulties of igniting a TX-14 system of the type considered, or of achieving a practically useful object by any means then envisaged, further study of TX-14 was soon laid aside.

A faction of the scientific community, including Teller, felt that it would only be a matter of time before the Soviets developed a hydrogen bomb. To maintain the balance of power, it was imperative for the US to develop a hydrogen bomb first. A majority of the scientific community had doubts about the morality or the practicality of developing such a bomb.

After the summer of 1947, work on large-scale thermonuclear reactions was curtailed, first because no idea for a thermonuclear weapon seemed to exist that offered great and immediate promise, and second because it was felt that the Los Alamos Laboratory, with its limited scientific personnel, could not carry this work in addition to its more immediate responsibilities of improving fission weapons.

By the middle of 1948, Teller had invented the booster, in which a fission bomb initiates a thermonuclear reaction in a moderate volume of a mixture of T and D, and this reaction in turn serves to enhance the yield of the fission bomb. Substantial theoretical work on the booster was done in 1948, and on the basis of this work it was proposed in the Fall of 1948 to include the booster in the next weapons test. In the first part of 1949, a more thorough theoretical investigation of the booster was carried out.

But as Chuck Hansen noted, "One Super design in early 1949 included a fission trigger that in itself weighed 30,000 lbs.; the overall length of the bomb was estimated at approximately 30 feet, with a diameter in excess of 162 feet. Under these circumstances, the scientists at Los Alamos preferred not even to estimate the gross weight: this configuration represented essentially a huge fission trigger in the middle of a container of liquid deuterium the size of a large oil storage tank."

At the end of January 1950, the understanding and prospects of the TX-14 was that systems of this kind were believed to be feasible in principle, and capable of providing arbitrarily large yields. However, the system required to obtain a significant amplification of the initiating yield was so large and heavy as to appear to be of little practical value.