On the next anniversary of badabum on Hiroshima and Nagasaki, I decided to scour the Internet for questions of nuclear weapons, where why and how it was created was of little interest to me (I already knew) - I was more interested in how 2 pieces of plutonium do not melt but make a big broad.
Keep an eye on the engineers - they start with a seeder and end with an atomic bomb.
Marcel Pagnol
Nuclear physics is one of the most controversial areas of venerable natural science. It was in this area that mankind for half a century threw billions of dollars, pounds, francs and rubles, like into the locomotive furnace of a late train. Now the train seems to be no longer late. The raging flames of burning funds and man-hours died down. Let's try to briefly figure out what kind of train called "nuclear physics" is.
Isotopes and radioactivity
As you know, everything that exists is made up of atoms. Atoms, in turn, consist of electronic shells, living according to their mind-blowing laws, and a nucleus. Classical chemistry is not at all interested in the nucleus and his personal life. For her, an atom is his electrons and their ability to exchange interaction. And from the nucleus of chemistry, only its mass is needed to calculate the proportions of reagents. In turn, nuclear physics does not care deeply about electrons. She is interested in a tiny (100 thousand times smaller than the radius of the electron orbits) speck of dust inside an atom, in which almost all of its mass is concentrated.
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What do we know about the core? Yes, it consists of positively charged protons and neutrons with no electrical charge. However, this is not entirely true. The core is not a handful of two-colored balls, as in an illustration from a school textbook. There are completely different laws at work here called strong interaction, transforming both protons and neutrons into some kind of indistinguishable mess. However, the charge of this mash is exactly equal to the total charge of the protons included in it, and the mass - almost (I repeat, almost) coincides with the mass of neutrons and protons that make up the nucleus.
By the way, the number of protons of a non-ionized atom always coincides with the number of electrons that have the honor to surround it. But with neutrons it is not so simple. As a matter of fact, the task of neutrons is to stabilize the nucleus, since without them, similarly charged protons would not get along together even in microseconds.
Let's take hydrogen for definiteness. The most common hydrogen. His device is laughingly simple - one proton surrounded by one orbiting electron. Hydrogen in the Universe in bulk. We can say that the universe is composed mainly of hydrogen.
Now let's carefully add a neutron to the proton. From the point of view of chemistry, it is still hydrogen. But from the point of view of physics, no longer. Having discovered two different hydrogens, physicists got worried and immediately thought of calling ordinary hydrogen protium, and hydrogen with a neutron with a proton - deuterium.
Let's get the nerve and feed the nucleus another neutron. Now we have another hydrogen, even heavier - tritium. It, again, from the point of view of chemistry, practically does not differ from the other two hydrogens (well, except that it now enters into the reaction a little less willingly). I want to warn you right away - no efforts, threats and admonitions will be able to add another neutron to the tritium nucleus. Local laws are much stricter than human ones.
So protium, deuterium and tritium are isotopes of hydrogen. Their atomic mass is different, but their charge is not. But it is the nuclear charge that determines the location in the periodic table of elements. That is why isotopes were called isotopes. Translated from Greek, this means "occupying the same place." By the way, the well-known heavy water is the same water, but with two deuterium atoms instead of protium. Accordingly, superheavy water contains tritium instead of protium.
Let's take another look at our hydrogens. So … Protium in place, deuterium in place … Who else is this? Where did my tritium go and where did helium-3 come from? In our tritium, one of the neutrons clearly missed it, decided to change profession and became a proton. In doing so, he gave birth to an electron and an antineutrino. The loss of tritium is, of course, disappointing, but we now know that it is unstable. Feeding neutrons was not in vain.
So, as you understood, isotopes are stable and unstable. There are plenty of stable isotopes around us, but, thank God, there are practically no unstable ones. That is, they are available, but in such a scattered state that they have to be obtained at the cost of a lot of labor. For example, uranium-235, which caused so much hassle for Oppenheimer, is only 0.7% in natural uranium.
Half life
Everything is simple here. The half-life of an unstable isotope is the period of time during which exactly half of the atoms of the isotope decay and turn into some other atoms. The already familiar tritium has a half-life of 12.32 years. It is a fairly short-lived isotope, although compared to francium-223, which has a half-life of 22.3 minutes, tritium appears to be a gray-bearded aksakal.
No macroscopic external factors (pressure, temperature, humidity, the mood of the researcher, the amount of appropriations, the location of the stars) affect the half-life. Quantum mechanics is insensitive to such nonsense.
Popular Explosion Mechanics
The essence of any explosion is the rapid release of energy that was previously in an unfree, bound state. The released energy is scattered, predominantly turning into heat (kinetic energy of disordered movement of molecules), shock wave (here, too, motion, but already ordered, in the direction from the center of the explosion) and radiation - from soft infrared to hard short-wavelength quanta.
With a chemical explosion, everything is relatively simple. An energetically beneficial reaction occurs when certain substances interact with each other. Only the upper electronic layers of some atoms participate in the reaction, and the interaction does not go deeper. It is easy to guess that there is much more latent energy in any substance. But no matter what the conditions of the experiment, no matter how good the reagents we choose, no matter how we calibrate the proportions, chemistry will not let us go deeper into the atom. A chemical explosion is a primitive phenomenon, ineffective and, from the point of view of physics, obscenely weak.
The nuclear chain reaction allows you to dig a little deeper, including in the game not only electrons, but also nuclei. This sounds really weighty, perhaps, only for a physicist, and for the rest I will give a simple analogy. Imagine a giant weight around which electrified dust particles flutter at a distance of several kilometers. This is an atom, a "weight" is a nucleus, and "dust particles" are electrons. Whatever you do with these grains of dust, they will not give even a hundredth of the energy that can be obtained from a weighty weight. Especially if, for some reason, it breaks, and massive debris scatters at great speed in different directions.
A nuclear explosion uses the binding potential of the heavy particles that make up the nucleus. But this is far from the limit: there is much more latent energy in matter. And the name of this energy is mass. Again, for a non-physicist this sounds a little strange, but mass is energy, only extremely concentrated. Each particle: an electron, a proton, a neutron - all these are scanty bunches of incredibly dense energy, for the time being at rest. You probably know the formula E = mc2, which authors of anecdotes, editors of wall newspapers and designers of school classrooms love so much. She is exactly about this, and it is she who postulates mass as nothing more than one form of energy. And she also answers the question of how much energy can be obtained from a substance to the maximum.
The process of a complete transition of mass, that is, bound energy into free energy, is called annihilation. By the Latin root "nihil" it is easy to guess about its essence - it is transformation into "nothing", or rather - into radiation. For clarity, a few numbers.
Explosion TNT equivalent Energy (J)
F-1 grenade 60 grams 2.50 * 105
The bomb dropped on Hiroshima 16 kilotons 6.70 * 1013
Annihilation of one gram of matter 21.5 kilotons 8.99 * 1013
One gram of any matter (only mass is important) during annihilation will give more energy than a small nuclear bomb. Compared with such a return, the exercises of physicists on nuclear fission, and even more so the experiments of chemists with active reagents, seem ridiculous.
For annihilation, appropriate conditions are needed, namely, the contact of matter with antimatter. And, unlike "red mercury" or "philosopher's stone", antimatter is more than real - for the particles known to us there exist and are investigated similar antiparticles, and experiments on annihilation of pairs "electron + positron" have been repeatedly carried out in practice. But in order to create an annihilation weapon, it is necessary to put together a certain weighty volume of antiparticles, and also to limit them from contact with any matter up to, in fact, military use. This, pah-pah, is still a distant prospect.
Mass defect
The last question that remains to be clarified regarding the mechanics of an explosion is where does the energy come from: the one that is released during the chain reaction? Here again, it was not without mass. Rather, without her "defect".
Until the last century, scientists believed that mass is preserved under any conditions, and they were right in their own way. So we dipped the metal into the acid - the retort bubbled up and gas bubbles rushed up through the thickness of the liquid. But if you weigh the reagents before and after the reaction, without forgetting the released gas, the mass converges. And it will always be so, while we operate with kilograms, meters and chemical reactions.
But it is worth delving into the area of microparticles, as the mass also presents a surprise. It turns out that the mass of an atom may not be exactly equal to the sum of the masses of the particles that make it up. When a heavy nucleus (for example, uranium, for example) is divided into parts, the "fragments" in total weigh less than the nucleus before fission. The "difference", also called the mass defect, is responsible for the bond energies within the nucleus. And it is this difference that goes into heat and radiation during the explosion, and all according to the same simple formula: E = mc2.
This is interesting: it so happened that it is energetically advantageous to divide heavy nuclei, and unite light ones. The first mechanism works in a uranium or plutonium bomb, the second in a hydrogen bomb. And you can't make a bomb out of iron with all the desire: it is exactly in the middle in this line.
Nuclear bomb
In a historical sequence, let's first look at the nuclear bombs and carry out our little Manhattan Project. I will not bore you with boring methods of isotope separation and mathematical calculations of the theory of chain reaction of fission. You and I have uranium, plutonium, other materials, assembly instructions and the necessary share of scientific curiosity.
Fission Chain Reaction I have already mentioned that the uranium fission chain reaction was first carried out in December 1942 by Enrico Fermi. Now let's talk about the nuclear chain reaction in more detail.
All uranium isotopes are unstable to one degree or another. But uranium-235 is in a special position. With the spontaneous decay of the uranium-235 nucleus (also called alpha decay), two fragments (nuclei of other, much lighter elements) and several neutrons (usually 2-3) are formed. If the neutron formed during the decay hits the nucleus of another uranium atom, there will be a usual elastic collision, the neutron will bounce off and continue looking for adventure. But after a while it will waste energy (ideally elastic collisions occur only with spherical horses in a vacuum), and the next nucleus will turn out to be a trap - the neutron will be absorbed by it. By the way, physicists call such neutron thermal.
Look at the list of known uranium isotopes. There is no isotope with an atomic mass of 236 among them. Do you know why? Such a nucleus lives for fractions of microseconds, and then decays with the release of a huge amount of energy. This is called forced decay. An isotope with such a lifetime is somehow embarrassing to call an isotope.
The energy released during the decay of the uranium-235 nucleus is the kinetic energy of fragments and neutrons. If we calculate the total mass of the decay products of the uranium nucleus, and then compare it with the mass of the original nucleus, it turns out that these masses do not coincide - the original nucleus was larger. This phenomenon is called a mass defect, and its explanation is laid down in the formula E0 = mс2. The kinetic energy of the fragments, divided by the square of the speed of light, will be exactly equal to the difference in masses. The fragments are decelerated in the crystal lattice of uranium, giving rise to X-ray radiation, and neutrons, having traveled, are absorbed by other uranium nuclei or leave the uranium casting, where all events take place.
If the uranium casting is small, then most of the neutrons will leave it before they can slow down. But if each act of forced decay causes at least one more such act due to the emitted neutron, this is already a self-sustaining chain reaction of fission.
Accordingly, if the size of the casting is increased, an increasing number of neutrons will cause acts of forced fission. And at some point, the chain reaction will become uncontrollable. But this is far from a nuclear explosion. Just a very "dirty" thermal explosion, which will release a large number of very active and toxic isotopes.
Critical mass
Quite a natural question - how much uranium-235 is needed for the fission chain reaction to become an avalanche? In fact, not everything is so simple. The properties of the fissile material and the volume to surface ratio play a role here. Imagine a ton of uranium-235 (I'll make a reservation right away - it's a lot), which exists in the form of a thin and very long wire. Yes, a neutron flying along it, of course, will cause an act of forced decay. But the fraction of neutrons flying along the wire will be so small that it’s ridiculous to talk about a self-sustaining chain reaction.
Therefore, we agreed to consider the critical mass for a spherical casting. For pure uranium-235, the critical mass is 50 kg (this is a ball with a radius of 9 cm). You understand that such a ball will not last long, however, like those who cast it.
If a ball of smaller mass is surrounded by a neutron reflector (beryllium is perfect for it), and a material - a neutron moderator (water, heavy water, graphite, the same beryllium) - is introduced into the ball, then the critical mass will become much smaller. By using the most effective reflectors and moderators of neutrons, the critical mass can be increased to 250 grams. This, for example, can be achieved by placing a saturated solution of uranium-235 salt in heavy water in a spherical beryllium container.
The critical mass is not limited to uranium-235. There are also a number of isotopes capable of fission chain reactions. The main condition is that the decay products of a nucleus must cause acts of decay of other nuclei.
Uranium bomb
So, we have two hemispherical uranium castings weighing 40 kg. As long as they are at a respectful distance from each other, everything will be calm. And if you start moving them slowly? Contrary to popular belief, nothing mushrooming will happen. It's just that the pieces, as they get closer, will begin to heat up, and then, if you don’t change your mind in time, they will heat up. In the end, they will simply melt and spread, and everyone who moved the castings will give oak from neutron irradiation. And those who watched this with interest will glue the flippers together.
And if faster? Will melt faster. Faster still? They will melt even faster. Cool? Yes, even if you dip it into liquid helium, there will be no sense. And if you shoot one piece at another? ABOUT! The moment of truth. We just came up with a uranium cannon scheme. However, we have nothing to be proud of, this scheme is the simplest and most artful of all. Yes, and the hemispheres will have to be abandoned. As practice has shown, they are not inclined to stick together evenly by planes. The slightest distortion - and you get a very expensive "bunch", after which you will have to clean up for a long time.
Better to make a short thick-walled tube of uranium-235 with a mass of 30-40 kg, to the hole of which we attach a high-strength steel barrel of the same caliber, loaded with a cylinder of the same uranium of approximately the same mass. Let's surround the uranium target with a beryllium neutron reflector. Now, if you shoot a uranium "bullet" at the uranium "pipe" - there will be a full "pipe". That is, there will be a nuclear explosion. Only you need to shoot in a serious way, so that the muzzle velocity of the uranium projectile is at least 1 km / s. Otherwise, again, there will be a "bunch", but louder. The fact is that when the projectile and the target approach each other, they heat up so much that they begin to intensively evaporate from the surface, being slowed down by oncoming gas flows. Moreover, if the speed is insufficient, then there is a chance that the projectile simply does not reach the target, but evaporates along the way.
To accelerate to such a speed a disc weighing several tens of kilograms, moreover, over a distance of a couple of meters is an extremely difficult task. That is why you need not gunpowder, but powerful explosives capable of creating the proper gas pressure in the barrel in a very short time. And then you don't have to clean the barrel, don't worry.
The Mk-I "Little Boy" bomb dropped on Hiroshima was designed according to the cannon scheme.
There are, of course, insignificant details that we did not take into account in our project, but we did not completely commit against the principle itself.
Plutonium bomb
So. We detonated the uranium bomb. We admired the mushroom. Now we will blow up the plutonium one. Just don't drag a target, a projectile, a barrel and other rubbish here. This number will not work with plutonium. Even if we fire one piece into another at a speed of 5 km / s, the supercritical assembly will still not work. Plutonium-239 will have time to warm up, evaporate and spoil everything around. Its critical mass is just over 6 kg. You can imagine how much more active it is in capturing neutrons.
Plutonium is an unusual metal. Depending on temperature, pressure and impurities, it exists in six modifications of the crystal lattice. There are even modifications in which it shrinks when heated. The transitions from one phase to another can be made abruptly, while the plutonium density can change by 25%. Let's, like all normal heroes, go around. Recall that the critical mass is determined, in particular, by the ratio of volume to surface. Okay, we have a subcritical mass ball that has a minimum surface for a given volume. Let's say 6 kilograms. The radius of the ball is 4.5 cm. And if this ball is squeezed from all sides? The density will increase in proportion to the cube of linear compression, and the surface will decrease in proportion to its square. And this is what happens: the plutonium atoms will become denser, that is, the neutron stopping distance will be shortened,which means that the probability of its absorption will increase. But, again, compressing at the required speed (about 10 km / s) will still not work. Dead end? But no.
At 300 ° C, the so-called delta phase occurs - the most loose. If plutonium is doped with gallium, heated to this temperature, and then slowly cooled, then the delta phase can exist at room temperature. But it will not be stable. At high pressures (of the order of tens of thousands of atmospheres), an abrupt transition into a very dense alpha phase will occur.
Place the plutonium ball in a large (23 cm diameter) and heavy (120 kg) hollow uranium-238 ball. Don't worry, it doesn't have critical mass. But it perfectly reflects fast neutrons. And they will still be useful to us. Do you think they blew it up? No matter how it is. Plutonium is a damn capricious entity. We'll still have to work. Let's make two hemispheres of plutonium in the delta phase. Let's form a spherical cavity in the center. And in this cavity we will place the quintessence of nuclear weapons thought - a neutron initiator. This is such a small hollow beryllium ball with a diameter of 20 and a thickness of 6 mm. Inside it is another beryllium ball with a diameter of 8 mm. There are deep grooves on the inner surface of the hollow ball. All of this is generously nickel plated and gold plated. Polonium-210 is placed in the grooves, which actively emits alpha particles. Here is such a miracle of technology. How does it work? Wait a second. We still have a few things to do.
Let's surround the uranium shell with another one made of an aluminum-boron alloy. Its thickness is about 13 cm. In total, our "matryoshka" has now grown to half a meter and recovered from 6 to 250 kg.
Now we are going to make implosion lenses. Imagine a soccer ball. Classic, consisting of 20 hexagons and 12 pentagons. Let's make such a "ball" from explosives, and equip each of the segments with several electric detonators. The segment thickness is about half a meter. There are also a lot of subtleties in the manufacture of "lenses", but if you describe them, then there is not enough space for everything else. The main thing is maximum lens accuracy. The slightest error - and the entire assembly will be crushed by the blasting action of explosives. The complete assembly now has a diameter of about one and a half meters and a weight of 2.5 tons. The design is completed by an electrical circuit whose task is to detonate the detonators in a strictly defined sequence with an accuracy of a microsecond.
All. Before us is a plutonium implosion scheme.
And now the fun part.
When detonated, the explosive compresses the assembly, and the aluminum "pusher" does not allow the decay of the blast wave to propagate inward after its front. Having passed through uranium with a counter velocity of about 12 km / s, the compression wave will compact both it and plutonium. Plutonium at pressures in the compression zone of the order of hundreds of thousands of atmospheres (the effect of focusing the explosive front) will jump into the alpha phase. In 40 microseconds, the uranium-plutonium assembly described here will become not just supercritical, but several times greater than the critical mass.
Having reached the initiator, the compression wave will crush its entire structure into a monolith. In this case, the gold-nickel insulation will collapse, polonium-210 due to diffusion will penetrate into beryllium, the alpha particles emitted by it, passing through beryllium, will cause a colossal flux of neutrons that start a chain fission reaction in the entire volume of plutonium, and the flux of "fast" neutrons generated decay of plutonium, will cause an explosion of uranium-238. Done, we have grown a second mushroom, no worse than the first.
An example of a plutonium implosion scheme is the Mk-III "Fatman" bomb dropped on Nagasaki.
All the tricks described here are needed in order to force the maximum number of atomic plutonium nuclei to react. The main task is to keep the charge in a compact state as long as possible, to prevent it from scattering like a plasma cloud, in which the chain reaction will instantly stop. Here, every microsecond won is an increase of one or two kilotons of power.
Thermonuclear bomb
There is a widespread belief that a nuclear bomb is the fuse for a thermonuclear bomb. In principle, everything is much more complicated, but the essence is captured correctly. Weapons based on the principles of thermonuclear fusion made it possible to achieve such an explosion power that under no circumstances can be achieved by a fission chain reaction. But so far the only source of energy that allows "igniting" a thermonuclear fusion reaction is a nuclear explosion.
Thermonuclear fusion
Remember how we “fed” the hydrogen nucleus with neutrons? So, if you try to connect two protons together in this way, nothing will come of it. The protons will not stick together because of the Coulomb repulsive forces. Either they scatter, or beta decay occurs and one of the protons becomes a neutron. But helium-3 exists. Thanks to a single neutron, which makes protons more livable with each other.
In principle, based on the composition of the helium-3 nucleus, it can be concluded that one nucleus of helium-3 can be completely assembled from the nuclei of protium and deuterium. In theory, this is so, but such a reaction can only occur in the bowels of large and hot stars. Moreover, in the interiors of stars, helium can be collected even from protons alone, converting some of them into neutrons. But these are already questions of astrophysics, and an achievable option for us is to merge two nuclei of deuterium or deuterium and tritium.
One very specific condition is necessary for the fusion of nuclei. This is a very high (109 K) temperature. Only at an average kinetic energy of nuclei of 100 keV are they able to approach each other at a distance at which the strong interaction begins to overcome the Coulomb interaction.
Quite a legitimate question - why fence this garden? The fact is that the fusion of light nuclei releases an energy of about 20 MeV. Of course, with the forced fission of a uranium nucleus, this energy is 10 times more, but there is one caveat - with the greatest tricks, a uranium charge with a capacity of even 1 megaton is impossible. Even for a more advanced plutonium bomb, the achievable energy yield is no more than 7-8 kilotons per kilogram of plutonium (with a theoretical maximum of 18 kilotons). And don't forget that a uranium nucleus is nearly 60 times heavier than two deuterium nuclei. If we consider the specific energy yield, then thermonuclear fusion is noticeably ahead.
And yet - for a thermonuclear charge there are no restrictions on the critical mass. He simply does not have it. There are, however, other restrictions, but about them - below.
In principle, starting a thermonuclear reaction as a neutron source is not difficult enough. It is much more difficult to launch it as a source of energy. Here we are faced with the so-called Lawson criterion, which determines the energy advantage of a thermonuclear reaction. If the product of the density of the reacting nuclei and the time of their confinement at the fusion distance is greater than 1014 sec / cm3, the energy provided by the fusion will exceed the energy introduced into the system.
All thermonuclear programs were dedicated to achieving this criterion.
Classic super
The first thermonuclear bomb scheme that came to Edward Teller's mind was something akin to trying to create a plutonium bomb using a cannon scheme. That is, everything seems to be correct, but it does not work. The "classic super" device - liquid deuterium, in which a plutonium bomb is immersed - was indeed classic, but far from super.
The idea of an explosion of a nuclear charge in a liquid deuterium medium turned out to be a dead end initially. Under such conditions, a slightest yield of thermonuclear fusion energy could be achieved by detonating a 500 kt nuclear charge. And there was no need to talk about the achievement of the Lawson criterion at all.
Puff
The idea to surround a nuclear trigger charge with layers of thermonuclear fuel, interspersed with uranium-238 as a heat insulator and an explosion amplifier, Teller also came up with. And not only him. The first Soviet thermonuclear bombs were built exactly according to this scheme. The principle was quite simple: a nuclear charge heats a thermonuclear fuel to the temperature of the beginning of fusion, and fast neutrons generated during fusion explode layers of uranium-238. However, the limitation remained the same - at the temperature that the nuclear trigger could provide, only a mixture of cheap deuterium and incredibly expensive tritium could enter the fusion reaction.
Later, Teller came up with the idea of using the compound lithium-6 deuteride. This solution made it possible to abandon expensive and inconvenient cryogenic containers with liquid deuterium. In addition, as a result of irradiation with neutrons, lithium-6 was converted into helium and tritium, which entered into a fusion reaction with deuterium.
The disadvantage of this scheme was the limited power - only a limited part of the thermonuclear fuel that surrounded the trigger had time to enter the fusion reaction. The rest, no matter how much it was, went to the wind. The maximum charge power obtained when using the "puff" was 720 kt (British Orange Herald bomb). Apparently, it was a "ceiling".
Teller-Ulam scheme
We have already talked about the history of the development of the Teller-Ulam scheme. Now let's understand the technical details of this circuit, which is also called the "two-stage" or "radiation compression" circuit.
Our task is to heat the thermonuclear fuel and keep it in a certain volume in order to fulfill the Lawson criterion. Leaving aside the American exercises with cryogenic circuits, let us take lithium-6 deuteride, already known to us, as a thermonuclear fuel.
We will choose uranium-238 as the material for the container for the thermonuclear charge. The container is cylindrical. Along the axis of the container, inside it we will place a cylindrical rod made of uranium-235, which has a subcritical mass.
Note: the sensational neutron bomb at the time is the same Teller-Ulam scheme, but without the uranium rod along the container axis. The point is to provide a powerful flux of fast neutrons, but not to allow the burnout of all thermonuclear fuel, which will consume neutrons.
Fill the rest of the free space of the container with lithium-6 deuteride. We will place the container in one of the ends of the body of the future bomb (this will be the second stage), and at the other end we will mount a conventional plutonium charge with a capacity of several kilotons (first stage). Between the nuclear and thermonuclear charges, we will install a uranium-238 partition to prevent the premature heating of lithium-6 deuteride. Fill the rest of the free space inside the bomb body with solid polymer. In principle, the thermonuclear bomb is ready.
When a nuclear charge is detonated, 80% of the energy is released in the form of X-rays. Its propagation speed is much higher than that of plutonium fission fragments. In hundredths of a microsecond, the uranium shield evaporates, and the X-ray radiation begins to be intensively absorbed by the uranium of the thermonuclear charge container. As a result of the so-called ablation (removal of mass from the surface of the heated container), a reactive force arises that compresses the container 10 times. It is this effect that is called radiation implosion or radiation compression. At the same time, the density of the fusion fuel increases 1000 times. As a result of the colossal pressure of radiation implosion, the central rod of uranium-235 is also compressed, albeit to a lesser extent, and passes into a supercritical state. By this time, the thermonuclear block is bombarded with fast neutrons from a nuclear explosion. After passing through lithium-6 deuteride, they slow down and are intensely absorbed by the uranium rod.
A fission chain reaction begins in the rod, quickly leading to a nuclear explosion inside the container. Since lithium-6 deuteride is subjected to ablative compression from the outside and the pressure of a nuclear explosion from the inside, its density and temperature increase even more. This moment is the beginning of the start of the synthesis reaction. Its further maintenance is determined by how long the container will keep thermonuclear processes inside itself, preventing the release of thermal energy outside. This is what determines the achievement of the Lawson criterion. The combustion of thermonuclear fuel proceeds from the axis of the cylinder to its edge. The combustion front temperature reaches 300 million kelvin. It takes a couple of hundred nanoseconds to fully develop the explosion until the fusion fuel burns out and the container collapses - twenty million times faster than you read this phrase.
Reliable operation of the two-stage circuit depends on accurate container assembly and prevention of premature heating.
The power of the thermonuclear charge for the Teller-Ulam scheme depends on the power of the nuclear trigger, which ensures effective compression by radiation. However, now there are also multi-stage schemes in which the energy of the previous stage is used to compress the next one. An example of a three-stage scheme is the already mentioned 100-megaton "Kuz'kina mother".