Since Putin’s words cannot really be believed, immediately after his announcement about withdrawing from the Strategic Arms Limitation Treaty, experts from various sectors tried to explain the political, military and geostrategic nature of this step. Military observers point out that this agreement has not worked in practice for several years, so Putin’s high-profile announcement is more political than military in nature. Likewise, the statements of many commentators show a thinly veiled assumption that Russia’s nuclear arsenal is actually in such a bad state that it is a shame to show it to foreign inspectors.
At the level of sofa experts, there are versions that everything valuable there has been stolen a long time ago or is technically worn out. Let’s not forget that more than 30 years have passed since the last real tests of nuclear weapons. Also, most of the rockets and their nuclear warheads have survived from those prehistoric Soviet times. Therefore, it would not be a surprise if it turns out that these missiles cannot fly anywhere far at all. These talks reinforce the rumors that unsuccessful tests of the Russian strategic missile “Sarmat” took place in these days.
But even if these rockets were to go somewhere, it is not said that they will explode. Perhaps this version may turn out to be the closest to the truth. Why?
An atomic bomb is an extremely complex mechanism
Many who have even a little interest in the structure of the atomic bomb know its simplified scheme of operation. If two or more pieces of uranium (a heavy metal, similar to iron) isotope U-235 are joined and the critical mass is exceeded (it depends on the purity and geometric shape of the piece of U-235. The critical mass of a spherical ball of U-235 is 52 kg), then a chain reaction of nuclear fission began.
As a result of this reaction, a huge amount of energy is released and a nuclear explosion occurs. In principle, nothing changes if plutonium Pu-239 is used as nuclear fuel. For the sake of simplicity, in this article we will talk only about uranium – 235. Also, we will not get into the details of nuclear physics.
The energy of a nuclear explosion is divided approximately as follows: 50% – shock wave, 30% to 50% – light (heat) radiation; 5% – ionizing radiation (radiation); 5% to 15% – radioactive contamination. So the main destructive effect of an atomic bomb is the same as that of conventional weapons, only incomparably more powerful. Let me remind you that the power of the atomic bomb, which was detonated over Hiroshima in 1945, was equivalent to 13 kilotons of TNT. That is, the shock wave of the explosion was as strong as would be produced by detonating 13,000 tons of trinitrotoluene.
And now the most important thing: the total mass of the nuclear explosive U-235 of the bomb with the code name “Mazulis” (“Little Boy”) was 64 kilograms, but only 700 grams actually participated in the nuclear reaction. The remaining 63 kilograms of expensive U-235, which at that time was filled with enormous technical difficulties, flew through the air without participating in the reaction. What’s the matter?
The critical mass of U-235 depends on its purity or degree of enrichment. The higher the impurity of U-238, which is mostly found in ordinary uranium ore, the higher the critical mass. If the proportion of U-235 in a piece of uranium is less than 80%, then the chain reaction will not start at any mass. Therefore, it is important to enrich uranium in order to obtain the highest possible purity (usually – 85%). But this is not the atomic bomb’s most difficult technical problem.
The most important is another. Let’s imagine that we have managed to obtain enough U-235 to create a critical mass. We will, of course, keep this amount of uranium distributed so as not to start a spontaneous chain reaction. But how do we put these individual pieces together to make a nuclear explosion?
Usually people, including me when I was interested in it when I was young, don’t see any problem with this activity. Where’s the problem? We take a piece of uranium, put them together, and voila – half the city is gone.
In reality, everything looks completely different. The duration of one nuclear reaction has been measured to be 7 nanoseconds, or 7 billionths of a second. Bringing two uranium-235 hemispheres closer to each other, say, at a speed of 10 meters per second, they would cover a distance of 0.0000007 millimeters in 7 nanoseconds. In other words, an extremely tiny distance that cannot even be seen with the eye. This means that as these hemispheres approach, nearly touching the smooth surfaces, they would rapidly heat up to thousands of degrees in a few billionths of a second and push each other away with such force that only a few milligrams or less of U-235 nuclei could react mass. The two pieces of uranium would fly through the air like normal metal hemispheres.
Calculations show that even if these blanks are brought closer to each other at the speed of a cannon ball – a kilometer per second, the effect would be similar. So how do you fuse these pieces of U-235 together so that a critical mass is created and these pieces don’t fly away from each other before the chain reaction starts?
Generally, all popular scientific sources say that this problem was solved relatively simply by the technicians of the “Manhattan Project” in the USA – the so-called “mom” and “dad” connection was used. It is not the hemispheres that are zoomed in, but one piece of U-235 entering the other.
A ship’s cannon barrel was mounted inside the “Baby” bomb, with a uranium-235 cylinder (paps) attached to one end, on which a uranium-235 cylinder ring (mom) of the same size was shot from the other end of the barrel with an ordinary artillery charge. As one metal cylinder was driven into the other, it was much more difficult for both of them to fly away from each other to their respective sides. Technically, “mom” was slammed on top of motionless “dad” at a speed of one and a half kilometers per second.
I remind you that the mass of the nuclear fuel in this bomb was 64 kilograms, and the total mass of the bomb was 4.4 tons. Basically, this enormous weight was made up of the aforementioned cannon barrel and additional metal reinforcement around it, so that the structure would hold together for as long as possible, even a few millionths (not billionths) of a second.
Although the efficiency factor of “Baby” was pitifully small – only a little more than 1% of the mass of uranium was converted into the energy of the explosion – modern nuclear physicists are quite skeptical about this theory of the “mom” and “papa” model. It is believed that this is most likely a false model, because such a structure, even trapped in a multi-ton metal shell, would explode in the first over a hundred nanoseconds of a nuclear reaction, when only over a dozen chain fission steps would be involved in the reaction.
Since “Mazulim” still managed to deliver a rather impressive explosion of 13 kilotons of power, there is reason to believe that the design was different. It could be about the principle – bullet in bullet.
In this model, the smaller U-235 ball that must reach critical mass is inside a larger U-235 ball. At a certain point, this smaller sphere expands (explodes the bomb inside it), the pieces connect and a nuclear explosion is initiated. Such a design provides the theoretical maximum fusion effect. It has its weak point. It is extremely difficult to ensure uniform expansion of the inner sphere with nanosecond precision.
When any explosive is detonated, the chemical reaction of the explosion and the resulting shock wave spread seemingly uniformly in all directions. However, in a situation where everything is determined by billionths of seconds and millimetres, it turns out that the chemical reaction that creates the explosion did not proceed as smoothly as desired. To overcome this problem, the expansion of the inner U-235 sphere of the atomic bomb is ensured not by one, but by several synchronous internal explosions. Achieving the synchronicity of these explosions is an extremely difficult technical task that requires special technological precision.
What do I mean by that? The fact that an atomic bomb is not like an ordinary aviation bomb, which can lie in the ground for half a century, and it is enough only to activate the detonator for it to explode. An atomic bomb is a complex, technologically sensitive mechanism, which can cause various defects if it is kept in cold, damp shafts for a long time. Especially when the technological quality of these weapons is taken care of by the soldiers and officers of the Russian army, who are world-famous for their high sense of responsibility and honest attitude towards the duties assigned to them.
Let’s be realistic. It is clear that you cannot rely on the fact that Russia’s nuclear arsenal is useless and has lost its quality. Even if only one in two, one in five, or even one in ten atomic bombs in Russia’s possession were to explode, it would be enough to wreak havoc on the world and cause millions to suffer.
However, on the other hand, Russia’s fear of foreign inspectors (in the past, these inspections took place within the framework of the agreement) does not indicate much confidence. It doesn’t look like Putin is 100% sure that the moment he pushes the notional “red” button, exactly what he’s hoping and counting on will happen. Consequently, the suspension of participation in the said treaty indirectly indicates a decrease in the risk of the use of nuclear weapons, not an increase. Like Putin’s entire speech at the Federation Assembly.
