A bomb based on the hafnium isomer Hf-178-m2 could become the most expensive and most powerful in the history of non-nuclear explosive devices. But she didn't. Now this case is recognized as one of the most notorious failures of DARPA - the Agency for Advanced Defense Projects of the American military department.
The emitter was assembled from a discarded X-ray machine that was once in a dentist's office, as well as a household amplifier purchased from a nearby store. It was in stark contrast to the loud sign of the Center for Quantum Electronics, which was seen entering a small office building at the University of Texas at Dallas. However, the device coped with its task - namely, it regularly bombarded an inverted plastic cup with a stream of X-rays. Of course, the glass itself had nothing to do with it - it simply served as a stand under a barely noticeable sample of hafnium, or rather, its isomer Hf-178-m2. The experiment lasted for several weeks. But after careful processing of the data obtained, the director of the Center, Carl Collins, announced an undoubted success. Recording equipment suggests that his group has groped a way to create miniature bombs of colossal power - fist-sized devices capable of destructing the equivalent of tens of tons of ordinary explosives.
So in 1998, the history of the isomer bomb began, which later became known as one of the biggest mistakes in the history of science and military research.
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Hafnium
Hafnium is the 72nd element of Mendeleev's periodic table. This silvery-white metal takes its name from the Latin name for the city of Copenhagen (Hafnia), where it was discovered in 1923 by Dick Koster and Gyordem Hevesi, collaborators of the Copenhagen Institute for Theoretical Physics.
Scientific sensation
In his report, Collins wrote that he was able to register an extremely insignificant increase in the X-ray background, which was emitted by the irradiated sample. Meanwhile, it is X-ray radiation that is a sign of the transition of 178m2Hf from the isomeric state to the ordinary one. Consequently, Collins argued, his group was able to accelerate this process by bombarding the sample with X-rays (when an X-ray photon with a relatively low energy is absorbed, the nucleus goes to another excited level, and then a rapid transition to the ground level follows, accompanied by the release of the entire energy reserve). To force the sample to explode, Collins reasoned, it is only necessary to increase the power of the emitter to a certain limit, after which the sample's own radiation will be sufficient to trigger a chain reaction of the transition of atoms from the isomeric state to the normal state. The result will be a very palpable explosion, as well as a colossal burst of X-rays.
The scientific community greeted this publication with clear disbelief, and experiments began in laboratories around the world to validate Collins' results. Some research groups were quick to declare confirmation of the results, although their numbers were only marginally higher than the measurement errors. But most experts nevertheless believed that the result obtained was the result of an incorrect interpretation of the experimental data.
Military optimism
However, one of the organizations was extremely interested in this work. Despite all the skepticism of the scientific community, the American military literally lost their heads from Collins' promises. And it was from what! The study of nuclear isomers paved the way for the creation of fundamentally new bombs, which, on the one hand, would be much more powerful than ordinary explosives, and on the other, would not fall under international restrictions associated with the production and use of nuclear weapons (an isomer bomb is not nuclear, since there is no transformation of one element into another).
Isomeric bombs could be very compact (they have no lower mass limitation, since the process of transition of nuclei from an excited state to an ordinary state does not require a critical mass), and upon explosion they would release a huge amount of hard radiation that destroys all living things. In addition, hafnium bombs could be regarded as relatively "clean" - after all, the ground state of hafnium-178 is stable (it is not radioactive), and an explosion would practically not contaminate the area.
Thrown away money
Over the next few years, the DARPA agency invested several tens of millions of dollars in the study of Hf-178-m2. However, the military did not wait for the creation of a working model of the bomb. This is partly due to the failure of the research plan: in the course of several experiments using powerful X-ray emitters, Collins was unable to demonstrate any significant increase in the background of the irradiated samples.
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Attempts to replicate Collins' results have been made several times over the course of several years. However, no other scientific group has been able to reliably confirm the acceleration of the decay of the isomeric state of hafnium. Physicists from several American national laboratories - Los Alamos, Argonne and Livermore - were also engaged in this issue. They used a much more powerful X-ray source - Advanced Photon Source of the Argonne National Laboratory, but could not detect the effect of induced decay, although the radiation intensity in their experiments was several orders of magnitude higher than in the experiments of Collins himself. Their results were also confirmed by independent experiments at another US national laboratory - Brookhaven, where the powerful National Synchrotron Light Source synchrotron was used for irradiation. After a series of disappointing conclusions, the military's interest in this topic faded, funding stopped, and in 2004 the program was closed.
Diamond ammunition
Meanwhile, it was clear from the very beginning that for all its advantages, the isomer bomb also possesses a number of fundamental disadvantages. First, Hf-178-m2 is radioactive, so the bomb will not be entirely "clean" (some contamination of the area with "unworked" hafnium will still occur). Secondly, the Hf-178-m2 isomer does not occur in nature, and the process of its production is rather expensive. It can be obtained in one of several ways - either by irradiating a target of ytterbium-176 with alpha particles, or by protons - tungsten-186 or a natural mixture of tantalum isotopes. In this way, microscopic amounts of the hafnium isomer can be obtained, which should be quite enough for scientific research.
A more or less massive method of obtaining this exotic material is irradiation with hafnium-177 neutrons in a thermal reactor. More precisely, it looked - until scientists calculated that for a year in such a reactor from 1 kg of natural hafnium (containing less than 20% of the isotope 177), you can get only about 1 microgram of an excited isomer (the release of this amount is a separate problem). Do not say anything, mass production! But the mass of a small warhead should be at least tens of grams … It turned out that such ammunition turns out not even "gold", but downright "diamond" …
Scientific closure
But it was soon shown that these shortcomings were not decisive either. And the point here is not in the imperfection of technology or inadequacies of the experimenters. The final point in this sensational story was put by Russian physicists. In 2005, Evgeny Tkalya from the Institute of Nuclear Physics of Moscow State University published in the journal Uspekhi Fizicheskikh Nauk, an article entitled “Induced Decay of the Nuclear Isomer 178m2Hf and an Isomer Bomb”. In the article, he outlined all possible ways to accelerate the decay of the hafnium isomer. There are only three of them: the interaction of radiation with the nucleus and decay through an intermediate level, the interaction of radiation with the electron shell, which then transfers excitation to the nucleus, and the change in the probability of spontaneous decay.
After analyzing all these methods, Tkalya demonstrated that the effective decrease in the half-life of an isomer under the influence of X-ray radiation deeply contradicts the entire theory underlying modern nuclear physics. Even with the most benign assumptions, the values obtained were orders of magnitude smaller than those reported by Collins. So it is not yet possible to accelerate the release of the colossal energy that is contained in the hafnium isomer. At least with the help of real-life technologies.
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