Uranium bomb and a bomb made from "unearthly" material. Uranium bomb Dimensions of modern uranium and plutonium bombs

neutron initiator.
The first stage, the neutron initiator, also called Urchin, is a beryllium spherical shell 2 cm in diameter and 0.6 cm thick. Inside it is a beryllium insert 0.8 cm in diameter. The total weight of the structure is about 7 grams. 15 wedge-shaped slots, 2.09 mm deep, were made on the inner surface of the shell. The shell itself is obtained by hot pressing in an atmosphere of carbonyl nickel, its surface and the inner sphere are covered with a layer of nickel and gold. 50 curies of polonium-210 (11 mg) were deposited on the inner sphere and slits in the shell. Layers of gold and nickel protect beryllium from alpha particles emitted by polonium or plutonium surrounding the initiator. The initiator is mounted on a bracket inside a cavity 2.5 cm in diameter in the plutonium core.
Urchin is activated when the shock wave reaches the center of the charge. When the shock wave reaches the walls of the internal cavity in the plutonium, the shock wave from the evaporated plutonium acts on the initiator, crushing the slots with the polonium and creating the Munroe effect - strong jets of substance that quickly mix the polonium and beryllium from the outer and inner spheres. Alpha particles emitted by Po-210 are absorbed by beryllium atoms, which in turn emit neutrons.

plutonium charge.
9 cm sphere, with a 2.5 cm cavity in the center for the neutron initiator. This form of charge was proposed by Robert Christy to reduce asymmetry and instability during implosion.
The plutonium in the core is stabilized in the low density delta phase (density 15.9) by fusing it with 3% gallium by weight (0.8% by weight). The advantages of using the delta phase over the denser alpha phase (density 19.2) are that the delta phase is malleable and pliable while the alpha phase is brittle and brittle, furthermore, stabilization of the plutonium in the delta phase allows avoid shrinkage during cooling and deformation of the workpiece after casting or hot working. It might seem that using a lower density material for the core might be disadvantageous, as a denser material is preferable due to increased efficiency and reduced plutonium requirement, but this is not entirely true. Delta-stabilized plutonium undergoes a transition to the alpha phase at a relatively low pressure of tens of thousands of atmospheres. The pressure of several million atmospheres that occurs during an implosion explosion makes this transition along with other phenomena that arise during such compression. Thus, with plutonium in the delta phase, there is a greater increase in density and a greater input of reactivity than would occur in the case of a dense alpha phase.

The core is assembled from two hemispheres, probably originally cast into billets and then hot-pressed in a carbonyl nickel atmosphere. Since plutonium is a chemically very active metal, and, in addition, representing a danger to life, each hemisphere is coated with a layer of nickel (or silver, as reported for the Gadget's core). This coating created a nuisance with the Gadget's core, since fast electroplating plutonium with nickel (or silver) led to the formation of shells in the metal and its unsuitability for use in the core. Careful grinding and layering of layers of gold restored the defects received by the hemispheres. However, a thin gold layer (about 0.1 mm thick) between the hemispheres was in any case a necessary part of the design, serving to prevent premature penetration of the shock wave jets between the hemispheres, which could prematurely activate the neutron initiator.

Uranium body/neutron reflector.
The plutonium charge is surrounded by a casing of natural uranium weighing 120 kg and 23 cm in diameter. This casing forms a seven-centimeter layer around the plutonium. The thickness of uranium is due to the problem of neutron conservation, so a layer of several centimeters is sufficient to ensure neutron deceleration. The thicker body (over 10 cm thick) additionally provides significant neutron conservation for the entire structure, however, the "temporal absorption" effect inherent in fast, exponentially developing chain reactions reduces the benefits of using a thicker reflector.
About 20% of the bomb's energy is released from the rapid fission of the uranium hull. The core and body together form a minimally subcritical system. When an assembly is compressed by up to 2.5 times its normal density with the help of an implosion explosion, the core begins to contain about four to five critical masses.

"Pusher" / absorber of neutrons.
The layer of aluminum surrounding the uranium, 11.5 cm thick, weighs 120 kg. The main purpose of this sphere, called the "pusher", is to reduce the effect of the Taylor wave, the rapid decrease in pressure that occurs behind the detonation front. This wave tends to increase during implosion, causing a more and more rapid drop in pressure as the detonation front converges to one point. The partial reflection of the shock wave occurring at the explosive (composition "B")/aluminum interface (due to the density difference: 1.65/2.71) sends a secondary front back into the explosive, suppressing the Taylor wave. This increases the pressure of the transmitted wave, increasing the compression at the center of the core.
The aluminum "pusher" also contains a fraction of boron. Since boron itself is a brittle non-metallic substance, difficult to handle, it is highly likely that it is contained in the form of an easy-to-machine aluminum alloy called borax (35-50% boron). Although its total share in the shell is small, boron plays the role of a neutron absorber, preventing neutrons emitted from there, which have slowed down in aluminum and explosives to thermal velocities, from getting back into the plutonium-uranium assembly.

Explosive shell and detonation system.
The explosive shell is a layer of high explosive. Its thickness is about 47 cm, and its weight is at least 2500 kg. This system contains 32 explosive lenses, 20 of which are hexagonal and 12 are pentagonal. The lenses are joined together in the fashion of a soccer ball, forming a spherical explosive assembly, about 130 cm in diameter. Each has 3 parts: two of them are made of explosive (BB) with a high detonation velocity, one - with a low one. The outermost part of the rapid detonating explosive has a cone-shaped recess filled with explosives with a low detonation velocity. These mating parts form an active lens capable of creating a circular, growing shock wave directed towards the center. The inside of the fast detonating explosive almost covers the aluminum sphere to enhance the converging impact.
The lenses were made by precision casting, so the explosive had to be melted down before use. The main fast detonating explosive was "composition B", a mixture of 60% hexagen (RDX) - a very fast detonating, but poorly melting high explosive, 39% TNT (TNT) - a highly exploding and easily melting explosive and 1% wax. The "slow" explosive was baratol - a mixture of TNT and barium nitrate (the share of tol is usually 25-33%) with 1% wax as a binder.
The composition and density of the lenses were precisely controlled and remained unchanged. The lens system was fitted to a very close tolerance, so that its parts were connected to each other with an accuracy of less than 1 mm, to avoid inhomogeneities in the shock wave, but the alignment of the surface of the lenses was even more important than fitting them to each other.
To achieve very accurate detonator timing, standard detonators lacked primary/secondary explosive combinations and had electrically heated conductors. These conductors are pieces of thin wire that instantly evaporate from the surge of current received from a powerful capacitor. An explosive detonator is detonated. The discharge of the capacitor bank and the evaporation of the wire for all detonators can be done almost simultaneously - the difference is +/-10 nanoseconds. The downside of such a system is the need for large batteries, a high-voltage power supply, and a powerful bank of capacitors (called the X-Unit, about 200 kg in weight) designed to fire 32 detonators simultaneously.
The finished explosive shell is placed in a duralumin case. The hull design consisted of a central belt, assembled from 5 machined duralumin castings, and the upper and lower hemispheres, forming a complete shell.

final assembly stage.
The final project of the bomb provides for a special "lid" through which fissile materials are laid at the end. The charge can be made as a whole, with the exception of the plutonium insert with the initiator. For safety reasons, assembly is completed immediately before practical use. The duralumin hemisphere is removed along with one of the explosive lenses. The neutron initiator is installed between the plutonium hemispheres and mounted inside a 40-kilogram uranium cylinder, and then the whole structure is embedded inside the uranium reflector. The lens returns to its place, a detonator is connected to it, a cover is screwed into place on top.
Fat Man presented a serious hazard in terms of delivery and storage in a ready-to-use state, however, even in the worst case, the hazard was still less than that of Little Boy. The critical mass of a core with a uranium reflector is 7.5 kg of plutonium for the delta phase, and only 5.5 kg for the alpha phase. Any accidental detonation of the explosive shell can lead to the compression of Fat Man's 6.2-kilogram core "a into the supercritical alpha phase. The estimated explosion power from such an unauthorized charge will be from tens of tons (roughly an order of magnitude more than the explosive charge in a bomb) to a couple of hundred tons of TNT equivalent.But the main danger lies in the flow of penetrating radiation during the explosion.Gamma rays and neutrons can cause death or serious illness far beyond the shock wave propagation zone.Thus, a small nuclear explosion of 20 tons will cause a fatal radiation dose of 640 rem at a distance of 250 m.
The transportation of Fat Man "and for safety reasons was never carried out in a fully assembled form, the bombs were completed immediately before use. Due to the complexity of the weapon, this process took at least a couple of days (taking into account intermediate checks). The assembled bomb could not be in working order for a long time condition due to the X-Unit's batteries being discharged.
The outlines of a combat plutonium bomb mainly consist of the design of an experimental Gadget, packed in a steel shell. Two halves of a steel ellipsoid are attached to the explosive system bandage along with an X-Unit, batteries, fuses and starting electronics are placed on the front side of the shell.
As in Little Boy, the high-altitude fuse in Fat Man is the Atchis radar rangefinder system (Archies - its antennas can be seen from the side in Little Boy's photographs). When the charge reaches the correct height above the ground (set to 1850+-100 feet), it issues a signal to detonate. In addition to it, the bomb is also equipped with a barometric sensor that prevents an explosion above 7000 feet.

Combat use of the plutonium bomb.
The final assembly of the Tolstyak took place on about. Tinian.
On July 26, 1945, a plutonium core with an initiator was sent by C-54 aircraft from Kirtland Air Force Base to Tinian.
On July 28, the core arrives on the island. On this day, three B-29s leave Kirtland for Tinian with three pre-assembled Fat Mans.
August 2 - arrival of B-29. The date of the bombardment is set as August 11, the target is the arsenal in Kokura. The non-nuclear part of the first bomb was ready by 5 August.
On August 7, a forecast comes in about weather conditions unfavorable for the flight on the 11th, the date of the flight is shifted by 10, then to 9 August. Due to the shift in the date, accelerated work is underway to assemble the charge.
On the 8th morning, the assembly of Fat Man is completed, by 22:00 he is loaded into the B-29 "Block" s Car.
August 9:
03:47 Aircraft takes off from Tinian, target identified as Kokur arsenal. Pilot - Charles Sweeney.
10:44 Time of approach to Kokura, but the target is not visible in conditions of poor visibility. Anti-aircraft artillery fire and the appearance of Japanese fighters force them to stop searching and turn towards the alternate target - Nagasaki.
There was a layer of clouds over the city - like over Kokura, there was only fuel left for one run, so the bomb was dropped into the first suitable gap in the clouds a few miles from the intended target.
11:02 An explosion occurs at a height of 503 m near the border of the city, the power according to measurements in 1987 is 21 kt. Despite the fact that the explosion occurred on the border of the populated part of the city, the number of victims exceeded 70,000 people. Mitsubishi's arms production was also destroyed.

uranium bomb

Operating principle

Nuclear weapons are based on an uncontrolled nuclear fission chain reaction. There are two main schemes: "cannon", otherwise called ballistic, and implosive.

« Cannon" the scheme is typical for the most primitive models of nuclear weapons of the 1st generation, as well as artillery and small arms nuclear munitions, which have restrictions on the caliber of weapons. Its essence lies in the "shooting" towards each other of two blocks of fissile material of subcritical mass. This method of detonation is possible only in uranium ammunition, since plutonium has a higher neutron background, which leads to an increase in the required speed of connection of parts of the charge, exceeding technically achievable.

"Implosive" the scheme implies obtaining a supercritical state by compressing a fissile material with a focused shock wave created by an explosion of a conventional chemical explosive, which is given a very complex shape for focusing and undermining is carried out simultaneously at several points with precision.

Nuclear charge power operating exclusively on the principles of fission of heavy elements, limited to hundreds of kilotons . It is possible, but extremely difficult, to create a more powerful charge based only on nuclear fission. The most powerful munition in the world, based only on nuclear fission, was tested in the USA on November 15, 1952, the explosion yield was 500 kt.

In order for the reaction to be able to support itself, an appropriate “fuel” is needed, which was used in the first stages as a uranium isotope.

Uranium occurs in nature in the form of two isotopes - uranium-235 and uranium-238. When uranium-235 absorbs a neutron during the decay process, from one to three neutrons are released:

Uranium-238, on the other hand, does not release new neutrons when it absorbs moderate-energy neutrons, preventing a nuclear reaction. It turns into uranium-239, then into neptunium-239, and finally into the relatively stable plutonium-239.

To ensure the operability of a nuclear bomb, the content of uranium-235 in nuclear fuel must be at least 80%, otherwise uranium-238 will quickly extinguish the nuclear chain reaction. Almost all natural uranium (about 99.3%) consists of uranium-238. Therefore, in the production of nuclear fuel, a complex and multi-stage uranium enrichment process is used, as a result of which the proportion of uranium-235 increases.

The uranium-based bomb became the first nuclear weapon used by man in combat conditions (the "Kid" bomb dropped on Hiroshima). Due to a number of shortcomings (difficulties in obtaining, developing and delivering), they are not currently common, yielding to more advanced bombs based on other radioactive elements with a lower critical mass.

The first nuclear weapon detonated for test purposes was the Gadget nuclear device, the Thing. gadget- fixture, trinket) - a prototype of the Fat Man plutonium bomb dropped on Nagasaki. The tests were carried out at a test site near the city of Alamogordo in New Mexico.

Structurally, this bomb consisted of several spheres nested in each other:

1. Pulsed neutron initiator (INI, "hedgehog", "urchin" (eng. urchin)) - a ball with a diameter of about 2 cm made of beryllium, covered with a thin layer of an alloy of yttrium-polonium or metallic polonium-210 - the primary source of neutrons for a sharp decrease in the critical mass and acceleration of the onset of the reaction. It fires at the moment of transferring the combat core to a supercritical state (during compression, a mixture of polonium and beryllium occurs with the release of a large number of neutrons). Currently, short-lived polonium-210 has been replaced by long-lived plutonium-238, which is also capable of producing a powerful neutron pulse when mixed with beryllium.
2. Plutonium. The purest plutonium-239 isotope is desirable, although to increase the stability of physical properties (density) and improve the compressibility of the charge, plutonium is doped with a small amount of gallium.
3. shell (English) tamper), which serves as a neutron reflector (from uranium).
4. squeezing sheath pusher) from aluminium. Provides greater uniformity of compression by the shock wave, while at the same time protecting the internal parts of the charge from direct contact with explosives and hot products of its decomposition.
5. An explosive with a complex detonation system that ensures the detonation of the entire explosive is synchronized. Synchronicity is necessary to create a strictly spherical compressive (directed inside the ball) shock wave. A non-spherical wave leads to the ejection of the material of the ball through inhomogeneity and the impossibility of creating a critical mass. The creation of such a system for the location of explosives and detonation was at one time one of the most difficult tasks. A combined scheme (lens system) is used from "fast" and "slow" explosives - boratol and TATV.
6. The body is made of duralumin stamped elements - two spherical covers and a belt connected by bolts.

Combat railway missile system BZHRK 15P961 "Molodets" with an intercontinental nuclear missile

Rocket RT-23 UTTH and missile system generally developed in<КБ>South in Dnepropetrovsk, General Designer Academician V.F. Utkin. The train and the launcher were developed in KBSM, Leningrad, chief designer academician A.F. Utkin. In 1987-1991 12 complexes built .

The composition of the BZHRK includes:

1.Three minimum launch modules

2. Command module consisting of 7 cars

3. Tank car with stocks of fuels and lubricants

4. Three locomotives DM62

The minimum launch module includes three cars:

1. Launcher control room 2.

2. Launcher

3. 3. Supply unit

On the next anniversary of the badaboom 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 big broads.

Keep an eye on the engineers - they start with a seeder and end with an atomic bomb.

Nuclear physics is one of the most scandalous branches of venerable natural science. It is in this area that humanity has been throwing billions of dollars, pounds, francs and rubles for half a century, like into a locomotive furnace of a late train. Now the train doesn't seem to be late anymore. The raging flames of burning assets and man-hours subsided. Let's try to briefly understand 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 electron shells that live according to their mind-blowing laws, and the nucleus. Classical chemistry is completely uninterested in the nucleus and its private life. For her, an atom is its electrons and their ability to exchange interaction. And from the core of chemistry, only its mass is needed to calculate the proportions of the reagents. In turn, nuclear physics does not give a damn about electrons. She is interested in a tiny (100 thousand times smaller than the radius of electron orbits) dust grain inside an atom, in which almost all of its mass is concentrated.

What do we know about the nucleus? Yes, it is made up of positively charged protons and electrically uncharged neutrons. However, this is not entirely true. The core is not a handful of balls of two colors, as in an illustration from a school textbook. There are completely different laws at work here called strong interaction, which turn both protons and neutrons into some kind of indistinguishable mess. However, the charge of this mess is exactly equal to the total charge of the protons entering it, and the mass almost (I repeat, almost) coincides with the mass of the 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 of surrounding it. But with neutrons, the matter is not so simple. Strictly speaking, the task of neutrons is to stabilize the nucleus, because without them, similarly charged protons would not get along together even for microseconds.

Let us take hydrogen for definiteness. The most common hydrogen His device is laughably simple - one proton surrounded by one orbital electron. Hydrogen in the universe in bulk. We can say that the universe consists mainly of hydrogen.

Now let's carefully add a neutron to the proton. Chemically, it's still hydrogen. But from the point of view of physics, no. Having discovered two different hydrogens, physicists became worried and immediately came up with the idea of ​​calling ordinary hydrogen protium, and hydrogen with a neutron with a proton - deuterium.

Let's get bold and feed the nucleus another neutron. Now we have another hydrogen, even heavier - tritium. Again, from the point of view of chemistry, it 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 exhortations will be able to add one more neutron to the tritium nucleus. The 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 charge of the nucleus that determines the location in the periodic system of elements. That is why isotopes are 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 look again at our hydrogens. So ... Protium is in place, deuterium is in place ... And who else is this? Where did my tritium go and where did the helium-3 come from? In our tritium, one of the neutrons clearly got bored, decided to change his 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 now we know that it is unstable. Feeding neutrons was not in vain.

So, as you understand, isotopes are stable and unstable. There are a lot of stable isotopes around us, but, thank God, there are practically no unstable ones. That is, they are available, but in such a dispersed state that they have to be obtained at the cost of very great labor. For example, uranium-235, which caused so much hassle to Oppenheimer, is only 0.7% of 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 isotope's atoms decay and turn into some other atoms. Tritium, already familiar to us, has a half-life of 12.32 years. This is a fairly short-lived isotope, although compared to francium-223, which has a half-life of 22.3 minutes, tritium will seem like a gray-bearded aksakal.

No macroscopic external factors (pressure, temperature, humidity, the mood of the researcher, the amount of allocations, the location of the stars) affect the half-life. Quantum mechanics is insensitive to such nonsense.

Popular explosion mechanic

The essence of any explosion is the rapid release of energy that was previously in a non-free, bound state. The released energy is dissipated, mainly turning into heat (the kinetic energy of the disordered movement of molecules), a shock wave (there is also movement, but already ordered, in the direction from the center of the explosion) and radiation - from soft infrared to hard short-wavelength quanta.

In a chemical explosion, everything is relatively simple. An energetically favorable 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 whatever the conditions of the experiment, no matter how successful the reagents we choose, no matter how we adjust 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.

Nuclear chain reaction allows you to dig a little deeper, including not only electrons, but also nuclei. This sounds really weighty, perhaps, only for a physicist, and I will give the rest a simple analogy. Imagine a giant weight, around which electrified dust particles flutter at a distance of several kilometers. This is an atom, the “weight” is the nucleus, and the “dust particles” are electrons. Whatever you do with these dust particles, they will not give even a hundredth of the energy that can be obtained from a weighty weight. Especially if, for some reason, it splits, and massive fragments scatter in different directions at great speed.

A nuclear explosion activates 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 unusual, but mass is energy, only extremely concentrated. Each particle: an electron, a proton, a neutron - all these are tiny clumps of incredibly dense energy, which for the time being remains at rest. You probably know the formula E=mc2, which was so loved by the authors of jokes, editors of wall newspapers and designers of school classrooms. It is about this, and it is she who postulates mass as nothing more than a form of energy. And it also gives an answer to the question of how much energy can be obtained from a substance to the maximum.

The process of complete transition of mass, that is, bound energy, into free energy is called annihilation. From the Latin root "nihil" it is easy to guess about its essence - this is a 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

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) will give more energy during annihilation than a small nuclear bomb. Compared with such a return, the exercises of physicists on the splitting of the nucleus seem ridiculous, and even more so the experiments of chemists with active reagents.

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 particles known to us, similar antiparticles exist and have been studied, and experiments on the annihilation of pairs "electron + positron" have been repeatedly carried out in practice. But in order to create an annihilation weapon, it is necessary to bring together a certain significant amount of antiparticles, as well as limit them from contact with any matter up to, in fact, combat use. This, pah-pah, is still a distant prospect.

mass defect

The last question that remains to be clarified regarding the mechanics of the explosion is where does the energy come from: the same one that is released during the chain reaction? Here again, there was a mass. Or rather, without its "defect".

Until the last century, scientists believed that mass is conserved under any conditions, and they were right in their own way. So we lowered the metal into acid - the retort began to boil and bubbles of gas rushed up through the thickness of the liquid. But if we weigh the reactants before and after the reaction, without forgetting the evolved gas, the mass converges. And it will always be so, as long as we operate with kilograms, meters and chemical reactions.

But it is worth delving into the field of microparticles, as well as the mass also surprises. 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 dividing into parts of a heavy nucleus (for example, the same uranium), the "fragments" in total weigh less than the nucleus before fission. The "difference," also called the mass defect, is the responsibility of the bond energies within the nucleus. And it is this difference that goes into heat and radiation during the explosion, 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 to unite light nuclei. 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 your desire: it stands exactly in the middle in this line.

Nuclear bomb

In historical order, let's take a look at nuclear bombs first and do our little Manhattan Project. I will not bore you with boring methods of isotope separation and mathematical calculations of the theory of fission chain reaction. We have uranium, plutonium, other materials, assembly instructions and the necessary amount of scientific curiosity.

All isotopes of uranium are unstable to some degree. But uranium-235 is in a special position. During the spontaneous decay of the uranium-235 nucleus (it is also called alpha decay), two fragments are formed (the nuclei of other, much lighter elements) and several neutrons (usually 2-3). If the neutron formed during the decay hits the nucleus of another uranium atom, there will be an ordinary elastic collision, the neutron will bounce off and continue to search for adventures. But after some time, it will waste energy (ideally elastic collisions occur only in 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, such a neutron is called a thermal neutron in physics.

Look at the list of known isotopes of uranium. Among them there is no isotope with an atomic mass of 236. 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 even somewhat 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 match - the original nucleus was larger. This phenomenon is called the mass defect, and its explanation lies 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-rays, and the 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 without having time to slow down. But if each act of forced decay causes at least one more of the same act due to the emitted neutron, this is already a self-sustaining fission chain reaction.

Accordingly, if you increase the size of the casting, an increasing number of neutrons will cause acts of forced fission. And at some point the chain reaction will become uncontrollable. But it's still far from a nuclear explosion. Just a very "dirty" thermal explosion, in which a large number of very active and poisonous isotopes will be released.

Quite a logical 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 ratio of volume to surface play a role here. Imagine a ton of uranium-235 (I'll make a reservation right away - this is 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 turn out to be so small that it is simply 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, however, a ball of smaller mass is surrounded by a neutron reflector (beryllium is perfect for it), and a neutron moderator material (water, heavy water, graphite, the same beryllium) is introduced into the ball, then the critical mass will become much smaller. Using the most efficient neutron reflectors and moderators, it is possible to increase the critical mass to 250 grams. This, for example, can be achieved by placing a saturated solution of uranium-235 salt in heavy water into a spherical beryllium container.

Critical mass exists not only for uranium-235. There are a number of isotopes capable of a fission chain reaction. The main condition is that the decay products of the nucleus must cause acts of decay of other nuclei.

So, we have two hemispherical uranium castings weighing 40 kg each. As long as they are at a respectful distance from each other, everything will be calm. And if you start to move them slowly? Contrary to popular belief, nothing mushroom-like will happen. It’s just that the pieces will start to heat up as they get closer, 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 stick their flippers together.

What if it's faster? Melt faster. Even faster? Melt even faster. Cool down? Yes, even lower 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 particularly proud of, this scheme is the simplest and most artless of all possible. Yes, and hemispheres will have to be abandoned. They, as practice has shown, do not tend to evenly stick together with planes. The slightest distortion - and you get a very expensive "bunch", after which it will take a long time to clean up.

It is better to make a short thick-walled uranium-235 tube with a mass of 30-40 kg, to the hole of which we will attach a high-strength steel barrel of the same caliber, loaded with a cylinder of the same uranium of approximately the same mass. Let us surround the uranium target with a beryllium neutron reflector. Now, if you shoot a uranium "bullet" at a uranium "pipe" - there will be a full "pipe". That is, there will be a nuclear explosion. You just need to shoot seriously, 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 will not reach the target, but will evaporate along the way.

To disperse to such a speed a disc weighing several tens of kilograms, and on a segment of a couple of meters, is an extremely difficult task. That is why you will need not gunpowder, but a powerful explosive 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 exactly according to the cannon scheme.

There are, of course, minor details that we did not take into account in our project, but we did not completely sin against the principle itself.

So. We detonated the uranium bomb. Enjoyed the mushroom. Now we will blow up plutonium. Just don't drag a target, projectile, barrel and other rubbish here. This number with plutonium will not work. Even if we shoot one piece at another at a speed of 5 km / s, a 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 terms of neutron capture.

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. Transitions from one phase to another can be made abruptly, while the density of plutonium can change by 25%. Let's, like all normal heroes, take a detour. Recall that the critical mass is determined, in particular, by the ratio of volume to surface. Okay, we have a ball of subcritical mass, which has a minimum surface area for a given volume. Let's say 6 kilos. The radius of the ball is 4.5 cm. And if this ball is compressed 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 stopping distance of the neutron will be reduced, which means that the probability of its absorption will increase. But, again, compressing at the desired speed (about 10 km / s) will still not work. Dead end? And here it is not.

At 300°C, the so-called delta phase sets in - the loosest. If plutonium is doped with gallium, heated to this temperature, and then slowly cooled, then the delta phase can also exist at room temperature. But it won't be stable. At high pressure (on the order of tens of thousands of atmospheres) there will be an abrupt transition to a very dense alpha phase.

Let us place a plutonium ball in a large (diameter 23 cm) and heavy (120 kg) hollow ball of uranium-238. 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. Plutonium is a hell of a capricious entity. 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 ball of beryllium with a diameter of 8 mm. There are deep grooves on the inner surface of the hollow ball. All this is generously nickel-plated and covered with gold. Polonium-210 is placed in the grooves, which actively emits alpha particles. This is the 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 aluminum alloy with boron. Its thickness is about 13 cm. In total, our “matryoshka” has now grown fat up to half a meter and recovered from 6 to 250 kg.

Now let's make the implosion "lenses". Imagine a soccer ball. Classic, consisting of 20 hexagons and 12 pentagons. We will make such a “ball” from explosives, and we will supply each of the segments with several electric detonators. The thickness of the segment is about half a meter. In the manufacture of "lenses" there are also a lot of subtleties, but if they are described, then there will not be enough space for everything else. The main thing is the maximum accuracy of the lenses. 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 mass of 2.5 tons. The design is completed by an electrical circuit, the task of which is to blow up the detonators in a strictly defined sequence with an accuracy of a microsecond.

All. Before us is a plutonium implosion scheme.

And now - the most interesting.

During detonation, the explosive compresses the assembly, and the aluminum "pusher" does not allow the decay of the blast wave to spread, propagating inward after its front. Having passed through uranium with a counter velocity of about 12 km/s, the compression wave will condense 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 will penetrate into beryllium due to diffusion, the alpha particles emitted by it passing through beryllium will cause a colossal flux of neutrons that start a fission chain reaction in the entire volume of plutonium, and the flux of "fast" neutrons born the decay of plutonium will cause an explosion of uranium-238. Done, we have grown the 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 plutonium atomic nuclei to react. The main task is to keep the charge in a compact state for as long as possible, not to let it scatter into a plasma cloud, in which the chain reaction will instantly stop. Here, each microsecond gained is an increase in one or two kilotons of power.

thermonuclear bomb

There is a popular belief that a nuclear bomb is a fuse for a thermonuclear one. 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 the only source of energy so far that allows you to "ignite" a thermonuclear fusion reaction is a nuclear explosion.

Remember how you and I "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 won't stick together because of the Coulomb repulsive forces. Either they will fly apart, or beta decay will occur and one of the protons will become a neutron. But helium-3 exists. Thanks to a single neutron, which makes protons more accommodating with each other.

In principle, based on the composition of the helium-3 nucleus, it can be concluded that one helium-3 nucleus can be completely assembled from protium and deuterium nuclei. Theoretically, this is true, but such a reaction can only take place in the depths of large and hot stars. Moreover, in the depths of stars, even from protons alone, helium can be collected, turning some of them into neutrons. But these are questions of astrophysics, and the achievable option for us is to merge two deuterium nuclei or deuterium and tritium.

Nuclear fusion requires one very specific condition. This is a very high (109 K) temperature. Only when the average kinetic energy of the nuclei is 100 kiloelectronvolts are they able to approach the distance at which the strong interaction begins to overcome the Coulomb one.

Quite a legitimate question - why fence this garden? The fact is that during the synthesis of light nuclei, an energy of the order of 20 MeV is released. Of course, with the forced fission of the uranium nucleus, this energy is 10 times greater, 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 almost 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 doesn't have it. There are, however, other restrictions, but about them - below.

In principle, starting a thermonuclear reaction as a source of neutrons is quite easy. It is much more difficult to run it as a source of energy. Here we are faced with the so-called Lawson criterion, which determines the energetic advantage of a thermonuclear reaction. If the product of the density of the reacting nuclei and the time of their retention at the fusion distance is greater than 1014 sec/cm3, the energy given by the fusion will exceed the energy introduced into the system.

It was the achievement of this criterion that all thermonuclear programs were devoted to.

Edward Teller's first idea for a thermonuclear bomb was like trying to build a plutonium bomb from a cannon design. 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 medium of liquid deuterium turned out to be a dead end from the very beginning. Under such conditions, a small amount of energy yield of thermonuclear fusion could be achieved by detonating a nuclear charge with a power of 500 kt. And there was no need to talk about achieving the Lawson criterion at all.

The idea to surround the nuclear trigger-charge with layers of thermonuclear fuel, interspersed with uranium-238 as a heat insulator and explosion amplifier, also came to Teller's mind. And not only to him. The first Soviet thermonuclear bombs were built according to this scheme. The principle was quite simple: a nuclear charge heats the thermonuclear fuel to the temperature of the beginning of fusion, and the fast neutrons born during the fusion blow up layers of uranium-238. However, the limitation remained the same - at the temperature that a nuclear trigger could provide, only a mixture of cheap deuterium and incredibly expensive tritium could enter into a fusion reaction.

Teller later came up with the idea of ​​using a lithium-6 deuteride compound. This decision 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 surrounding the trigger had time to enter into the fusion reaction. The rest, no matter how much it was, went down the drain. The maximum charge power obtained using the "puff" was 720 kt (British Orange Herald bomb). Apparently, it was the "ceiling".

We have already talked about the history of the development of the Teller-Ulam scheme. Now let's look into the technical details of this scheme, which is also called the "two-stage" or "radiation compression scheme".

Our task is to heat the fusion fuel and keep it in a certain volume in order to fulfill the Lawson criterion. Leaving aside American exercises with cryogenic schemes, let's take lithium-6 deuteride already known to us as thermonuclear fuel.

Let's choose uranium-238 as the material of the container for the thermonuclear charge. The container is cylindrical. Along the axis of the container inside it, we place a cylindrical rod of uranium-235, which has a subcritical mass.

Note: the neutron bomb that made a splash at the time is the same Teller-Ulam scheme, but without a uranium rod along the axis of the container. The point is to provide a powerful stream of fast neutrons, but not to allow the burnout of all the thermonuclear fuel, which will consume neutrons.

The rest of the free space of the container will be filled with lithium-6 deuteride. We will place the container at one end of the body of the future bomb (this will be the second stage for us), and at the other end we will mount the usual plutonium charge with a capacity of several kilotons (the first stage). Between the nuclear and thermonuclear charges, we will install a partition of uranium-238, which prevents premature heating of lithium-6 deuteride. Let's fill the rest of the free space inside the bomb body with a 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. The rate of its propagation is much higher than the rate of propagation of plutonium fission fragments. After hundredths of a microsecond, the uranium screen 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 (ablation of mass from the surface of a heated container), a reactive force arises that compresses the container 10 times. It is this effect that is called radiation implosion or compression by radiation. In this case, the density of thermonuclear fuel increases by a factor of 1000. As a result of the colossal pressure of radiation implosion, the central rod of uranium-235 is also subjected to compression, although to a lesser extent, and goes into a supercritical state. By this time, the thermonuclear unit is being bombarded by fast neutrons from a nuclear explosion. After passing through lithium-6 deuteride, they slow down and are intensively 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 fusion reaction. Its further maintenance is determined by how long the container will keep thermonuclear processes inside itself, without letting thermal energy out. This is what determines the achievement of the Lawson criterion. Burnup of thermonuclear fuel proceeds from the axis of the cylinder to its edge. The combustion front temperature reaches 300 million kelvin. The full development of the explosion up to the burnout of the fusion fuel and the destruction of the container takes a couple of hundred nanoseconds - twenty million times faster than you read this phrase.

Reliable operation of the two-stage circuit depends on the precise assembly of the container and the prevention of its premature heating.

The power of a 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 "Kuzkin's mother".

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