Small and low-yield nuclear warheads have historically been unlucky. In those blessed times, when nuclear charges of all types were actively developed and tested, there was no suitable isotope for them. Only plutonium-239 and uranium-235 were available, and you couldn't make a compact nuclear charge out of them. Of course, the American W54 warhead, weighing 23 kg, looked very favorably against the background of the "Fat Man" weighing 4.6 tons, but it was still not as compact as we would like.
This warhead, apparently, was one of the last, which was actually tested by a nuclear explosion. The subsequent moratorium on nuclear tests sharply slowed down work, due to which mainly powerful products remained in the nuclear arsenal. Now that the nuclear nonproliferation and limitation regime seems to be on the verge of its exhaustion, it is possible to return to the development of new types of nuclear charges that could diversify nuclear war.
Americium is the best candidate
Plutonium as a filling of a nuclear charge is good for everyone, only it does not allow creating a truly compact charge, since it has a rather large critical mass - 10.4 kg. With a plutonium density of 19.8 g per cubic centimeter, the volume of the sphere will be 525.2 cubic meters. cm, and its diameter is 10, 1 cm. In addition, in order for it to bump, one must take not one critical mass, but a little more, say, 1, 2 or 1, 35 critical mass. This is due to the fact that the detonation system and the neutron fuse in a compact charge are not as good as in an aerial bomb or missile warhead, and in order to achieve the effect, one must have a larger supply of fissile material. Therefore, compact plutonium charges usually used 13-15 kg of plutonium (for 13 kg the diameter of the ball is 10.7 cm), formed into an egg-shaped or cylindrical nucleus.
In principle, although heavy, but quite suitable for large-caliber artillery shells, missiles and mines, charges in the power range from several hundred kg to 10-15 kt of TNT equivalent were obtained. But there was a serious objection: why use precious weapons-grade plutonium for a low-power charge, if you can make a thermonuclear ammunition with an incomparably greater power? A 400-kiloton warhead will achieve an effect much greater than 10-15 kt or even less.
In general, there were two reasons for the retirement of low-power nuclear charges: not too compact dimensions, which made it difficult to use them, and military-economic arguments for the irrationality of spending the valuable isotope.
In the 1950s, there was nothing to replace uranium and plutonium as weapons-grade isotopes. But some time has passed since then and a good candidate has appeared - americium-242. This isotope is formed during the decay of plutonium-241 (formed during the capture of a neutron by uranium-238), and is contained in plutonium processing waste and spent nuclear fuel (SNF). After 26 years, all plutonium-241 will decay into americium-241, the half-life of which is much longer - 432.2 years. Thus, SNF unloaded from reactors and put into storage in the late 1980s and early 1990s should already contain a significant amount of americium-241. Its isolation, as far as can be judged, does not present any particular difficulties.
If am-241 is irradiated with neutrons, then an even more remarkable isotope of americium-242m will be obtained. Since a reactor based on americium-242 was designed in Obninsk, intended for obtaining neutron radiation for medical purposes, some data on its production were given. 1 gram of am-242m is formed by irradiation of 100 grams of am-241 (it was obtained at the now dismantled BN-350 reactor in Shevchenko, Kazakhstan), and to obtain this amount, it is enough to process 200 kg of aged SNF. We have a lot of this stuff: about 20 thousand tons of spent nuclear fuel and an annual production of about 200 tons more. The accumulated SNF is sufficient to produce about 1000 kg of am-242m.
What is AM-242M good for? Extremely low critical mass. The pure isotope has a critical mass of only 17 grams. With a density of americium of 13.6 g per cubic centimeter, it will be a ball with a diameter of 1.33 cm. If we take 1.35 of the critical mass, then the ball will be 1.45 cm in diameter. With a reflector and a blasting system, it is quite possible to keep within the size 40 -mm projectile. The energy release of 1 g of am-242m corresponds approximately to 4.6 kg of TNT, so that such a charge with 22.9 g of the isotope will give approximately 105 kg of TNT.
A mixture of am-241 and am-242m can be used. With the content of the latter at 8%, the critical mass will be 420 grams. The diameter of the ball will be 3.8 cm. It can be a nuclear grenade for an RPG, a mine for an 82-mm mortar, and so on. The energy release will be about 2 tons of TNT equivalent.
In general, the best candidate for the filling role for very compact nuclear charges, up to small-caliber nuclear projectiles. Americium is also good in that it emits little heat during decay, almost does not heat up, and therefore storage of nuclear ammunition stuffed with americium does not require refrigerators. The long half-life: am-241 - 433, 2 years, am-242m - 141 years, also allows the production and accumulation of americium for future use. Such ammunition can be stored for 30-40 years without significant changes in their characteristics, while plutonium should be sent for cleaning from decay products after 10-15 years.
The American charge can be used on its own, as well as as a nuclear-neutron fuse for more powerful charges. If it turns out that the americium charge can initiate a thermonuclear reaction (which may well be), then the possibility of creating very compact and lightweight, but at the same time powerful thermonuclear charges will open up.
Warhead for guided missiles
An important question is what such a very compact American charge can be used for. For example, we will take a charge equipped with about 500 grams of americium and an energy release of 2, 3-2, 5 tons of TNT equivalent. The total weight of this product can be only 2-3 kg. Where and how can it be applied?
Surface-to-air and air-to-air missiles, that is, anti-aircraft and aviation missiles, designed to destroy aircraft. For an aircraft, an overpressure of 0.2 kgf / cm2 is definitely dangerous (the load on the wing of a Su-35 can, for example, reach 0.06 kgf / cm2). An explosion of a compact nuclear charge with a capacity of 2.3 tons will create such an overpressure at a distance of about 210 meters, and an overpressure of 1.3 kgf / cm2, at which the destruction of the aircraft will surely occur, will create an explosion at a distance of 60 meters. Proximity fuses of aircraft missiles usually initiate a charge at a distance of 3-5 meters from the target, and in this case, the target aircraft definitely does not shine - guaranteed defeat! Fine splashes of metal and a cloud of radioactive vapors.
Anti-ship missiles. Small anti-ship missiles, such as the Kh-35 and similar, the most convenient for use (there are aircraft, helicopter, ship, ground and even container launchers), unfortunately, are so weak that they can not sink, but even seriously damage any large ship. This is clearly seen in the firing at the decommissioned tank landing ship USS Racine (LST-1191). It was hit by 12 anti-ship missiles, similar to the Kh-35, and the ship remained afloat. They finished with him only with a torpedo. This is not surprising if the warhead of the missiles has a weight of 150-250 kg and their power is relatively low. Equipping the X-35 missile with an American nuclear charge of the above characteristics makes this missile much more dangerous even for large ships. If an Arleigh Burke-class destroyer is hit by such a missile, it will, at its best, require lengthy factory repairs. But one can also count on sinking, since an explosion of such power may well destroy the ship's hull.
Torpedoes. In general, a charge with a capacity of 2.3 tons of TNT, installed in a torpedo, even not the most modern one, turns it into a compelling argument against even large ships and ships.
ATGM. If the weight of the entire ammunition is in the range of 2-3 kg, then they can be equipped with missiles for anti-tank missile systems, for example, "Kornet". It has a good firing range, up to 5.5 km, which makes it quite safe to use a compact and low-power nuclear charge. Any, even the latest and most protected tank, will be guaranteed to be destroyed by such a missile.
Already from this very brief overview it is clear that the best carrier for such very compact nuclear charges is various types of guided missiles. The American charge will turn out to be quite expensive and it will not be possible to produce so many of them, several hundred, perhaps up to a thousand pieces. Therefore, they need to shoot at something valuable and important, which at least economically will justify its use. Targets: aircraft, ships, air defense systems, radars, possibly also the latest (that is, the most expensive) tanks and self-propelled guns. The combination of the precision of guided missiles with the much higher yield of an American charge compared to standard explosives would make such a weapon very effective.
