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Threats to the non-proliferation regime: “Fourth Generation” nuclear weapons

Angelo Baracca
Department of Physics, University of Florence

The whole non-proliferation regime seems at present in a serious stalemate, in particular after the failure of the 7th Review Conference, and as a consequence of the attitudes and projects of the nuclear States.

This is not the place for examining the pretexts that are adduced for these choices. It will be sufficient to say that thousands of warheads cannot be justifies by an alleged threat by North Korea or Iran: the latter country is a party to the NPT and hosts regular inspections from the IAEA, that has not found military projects; on the contrary, the nuclear States parties to the NPT are in a state of breach of the obligations of art. VI since decades (including two of the States which are negotiating with Teheran), and Israel has never adhered to the treaty and is not subject to the IAEA inspections. One could remark that Brazil has recently developed the technology of uranium enrichment, without international complaints; while there are other States that possess the materials and the know-how to build the bomb in a very short time (typically, but not only, Japan, as well as Germany, the third State that negotiates with Teheran).

The aim of this note is to call the attention towards a problem that seems widely disregarded, but threatens the whole non-proliferation regime.

As it is well known, nuclear proliferation is traditionally based on the techniques of uranium enrichment and plutonium separation. A third ingredient, the mechanism of boosting, has acquired a fundamental role in modern, compact and efficient warheads: a very small (around two grams) quantity of a deuterium-tritium mixture (DT) is placed in the core of the plutonium pit before the detonation (tritium is a radioactive substance, with a half-life of 12 years, and must be continuously produced). The implosion and priming of the chain reaction ignites the nuclear fusion reaction of the DT mixture (whose contribution to the yield is negligible), generating a strong flux of neutrons which, from the inside, enhances and exhausts the fission of plutonium before the warhead disassembles. Tritium technology is complex, since it is an extremely volatile and radioactive gas: it is produced bombarding litium-6 with neutrons (typically in a nuclear reactor, as India and Pakistan have done).

It is important to remark that the non-proliferation regime established since 1970 only deals with warheads based on the chain reaction in uranium or plutonium, and suffer from additional and severe limitations. In fact, not only the START-II and the CTBT never entered into force, but the latter bans only full-scale nuclear tests, which at present seem not really necessary for building new warheads, leaving the possibility of a wide set of subcritical tests. Campaigns of such tests regularly performed by the nuclear States should in fact put on the alert.

The risk that I would like to discuss here is that the present stalemate may hide the opening of a completely new, much more dangerous phase of nuclear proliferation. Traditional warheads present severe limitations against their effective use in the battlefield, mainly for their yield (critical mass) and residual radioactivity. One of the most debated issues deals at present with the projects for very low-yield, hearth penetrating warheads: but there are a lot of hoaxes on this subject. In fact, the U.S. (and probably also Russia) have built very low-yield bombs as early as in the 1950s (e.g. the gun projectile known as "Davy Crockett"), and more recently, e.g. with the B-61-11 warhead (although the Spratt-Furse Law was a cheat, its abrogation was not a good signal). This aspect conceals the search for completely new types of nuclear armaments, which circumvent international treaties and non-proliferation regime, and may be effectively used in "conventional" warfare.

The search for really new kinds of nuclear weapons, based on new processes, proceeds since decades, but one may suspect that is has been intensified in the last decade, besides other dangerous military projects (e.g. techniques for the simulation of nuclear tests), and the willingness to sign a comprehensive test ban could raise the suspicion that it could really be affording some results.

A further danger of these efforts lies in the fact that, besides the activities in the military laboratories, they benefit of the advances in many fields of fundamental research and civil technologies.

It is impossible to synthesize these trends, advanced results are classified, the scientific contents are complex, but it seems worth adding some preliminary comments and references.

  • Controlled nuclear fusion is a field that was developed since the beginning of the nuclear era, with the (unfulfilled) promise of producing cheap energy: but, at least inertial confinement fusion (ICF) by lasers or accelerated particles beams always had military purposes. As early as 30 years ago, an article in Science qualified it as "Laser fusion: an energy option, but weapons simulation is first" [1]. ICF is based on the implosion of a small DT pellet, igniting its nuclear fusion: such a process would constitute a micro-thermonuclear explosion (less than 1 ton of TNT), like in boosting, but without the first-stage fission explosion. Obviously, in order to make a weapon, the main problem, not at all irrelevant, consists in the miniaturization of lasers or particle accelerators: but big progress is done in these directions. Besides this purpose, fusion research is contributing to the understanding of still badly known aspects of the process, with direct military interest. It is worth recalling the giant plants under construction in the US (National Ignition Facility [2]) and France (Mégajoule [3]).
  • Tabletop superlasers have been constructed, having moreover many other possible military applications (missile defense, space-based weapons).
  • Deep advances are expected, if not already obtained, from a revolutionary field, nanotechnology, i.e., the science of designing microscopic structures in which the materials and their relations are machined and controlled atom-by-atom. Lying at the crossroads of engineering, physics, chemistry, and biology, nanotechnology may have considerable impact in all areas of science and technology. However, it is certain that "the most significant near term applications of nanotechnology will be in the military domain. In fact, it is under the names of 'micromechanical engineering' and 'microelectromechanical systems' (MEMS) that the field of nanotechnology was born a few decades ago - in nuclear weapons laboratories." [4]
  • A very tempting perspective, form the military point of view, would lie in the possibility of producing amounts of antimatter: this would allow new kinds of weapons based on matter-antimatter annihilation, with no critical mass limitation. We are probably still far from such a purpose. However, high energy laboratories have done great advances in the production and conservation of quantities of antimatter. Antimatter appears moreover as very promising for starting nuclear fusion.
  • New heavy isotopes are hunted for, with long half lives and fissile, with very low critical masses, in order to realize new low-yield fission warheads.
  • New nuclear processes, nuclear isomers with electromagnetic decay, that would allow new powerful electromagnetic weapons [5].
It seems very difficult to judge how far, or near the production of completely new nuclear arms is. But we cannot wait when it will be too late. If, and when, one of such weapon be carried out, the whole non-proliferation regime will be frustrated. The only solution we have is to demand and impose a full nuclear disarmament, i.e. the total elimination of every kind of nuclear armaments, present and future.


[1] Robert Gillette, Science, 188 (April 4, 1975), p. 30. It is interesting to cite some sentences: "[...] if the two superpowers do eventually come to terms on a comprehensive test ban, a remarkable and rapidly evolving new technology may, in important ways, help to circumvent it. [...] laser fusion has been widely hailed [...] as a potential shortcut to [...] cheap electric power [...]. Although there is no question about the sincerity of these hopes, it is not generally understood that the immediate practical objective [...] is to devise a laboratory technique for simulating weapons explosions. Indeed, there is a bold of opinion [...] which holds that weapons simulation may be the only practical application of laser fusion in the century. [...] laser fusion promises 'orders of magnitude' improvement over present methods of simulation [...] weapons experts expect laser fusion to become an extraordinarily valuable experimental tool for studying basic "weapons physics" and, in conjunction with increasingly refined computer simulation codes, for developing new warheads designs. Under any circumstance, laser fusion thus promises to save a great deal of time and money now spent in setting off bombs under the Nevada desert. [...] Thus, quite literally, laser fusion is emerging as a new means of bringing nuclear testing indoors [...]"

[2] Ray E. Kidder says ("Problems with the stockpile stewardship", Nature, 386, 17 April 1997, p. 646): "The relevance of National Ignition Facility to nuclear weapons science is that the states of matter produced, and the physical processes involved, are similar to those that govern the behavior of nuclear weapons. As a result, computer programs used in Internal Confinement Fusion research have much in common with those used in nuclear weapons design. The more powerful of these are therefore classified, at least at the three US nuclear weapons laboratories."

[3] Luc Allemand, "Mégajoule: le plus gros laser du monde", La Recherche, 360, gennaio 2003, pp. 60-67.

[4] André Gsponer, "From the lab to the battlefield" Nanotechnology and Fourth-Generation nuclear weapons", Disarmament Diplomacy, 67, October-November 2002.

[5] David Hambling, "gamma-ray weapon could trigger next arms race", New Scientist, 13 agosto 2003.


André Gsponer and Jean_Pierre Hurni, Fourth Generation Nuclear Weapons, INESAP (International Network of Engineers and Scientists Against Proliferation), Darmstad, Technical Report No. 1, Seventh Edition, September 2000.

Angelo Baracca, A Volte Ritornano: Il Nucleare. La Proliferazione Nucleare Ieri, Oggi e Soprattutto Domani, Milano, Jaca Book, 2005.