The entire bulk of an intercontinental ballistic missile, tens of meters and tons of ultra-strong alloys, high-tech fuel and advanced electronics are needed for only one thing - to deliver the warhead to its destination: a cone a meter and a half high and as thick at the base as a human torso.
Let's look at a typical warhead (in reality, there may be design differences between warheads). This is a cone made of lightweight durable alloys. Inside there are bulkheads, frames, a power frame - almost everything is like in an airplane. The power frame is covered with durable metal casing. A thick layer of heat-protective coating is applied to the casing. It looks like ancient basket Neolithic period, generously coated with clay and fired in man's first experiments with heat and ceramics. The similarity is easy to explain: both the basket and the warhead have to resist external heat.
Inside the cone, fixed to their “seats,” there are two main “passengers” for the sake of which everything was started: a thermonuclear charge and a charge control unit, or automation unit. They are amazingly compact. The automation unit is the size of a five-liter jar of pickled cucumbers, and the charge is the size of an ordinary garden bucket. Heavy and weighty, the union of a can and a bucket will explode three hundred fifty to four hundred kilotons. Two passengers are connected to each other by a connection, like Siamese twins, and through this connection they constantly exchange something. Their dialogue is ongoing all the time, even when the missile is on combat duty, even when these twins are just being transported from the manufacturing plant.
There is also a third passenger - a unit for measuring the movement of the warhead or generally controlling its flight. IN the latter case working controls are built into the warhead, allowing you to change the trajectory. For example, actuator pneumatic systems or powder systems. And also an on-board electrical network with power supplies, communication lines with the stage, in the form of protected wires and connectors, protection against electromagnetic pulses and a thermostatting system - maintaining the required charge temperature.
The technology by which warheads are separated from the missile and set on their own courses is separate big topic, about which you can write books.
First, let’s explain what “just a combat unit” is. This is a device that physically houses a thermonuclear charge on board an intercontinental ballistic missile. The rocket has a so-called warhead, which can contain one, two or more warheads. If there are several of them, the warhead is called a multiple warhead (MIRV).
Inside the MIRV there is a very complex unit (it is also called a disengagement platform), which, after being launched by a launch vehicle outside the atmosphere, begins to carry out a number of programmed actions for individual guidance and separation of warheads located on it; in space, battle formations are built from blocks and decoys, which are also initially located on the platform. Thus, each block is placed on a trajectory that ensures it hits a given target on the Earth’s surface.
Combat units are different. Those that move along ballistic trajectories after separation from the platform are called uncontrollable. Controlled warheads, after separation, begin to “live their own lives.” They are equipped with attitude control engines for maneuvering in outer space, aerodynamic control surfaces for controlling flight in the atmosphere, they have an inertial control system on board, several computing devices, a radar with its own computer... And, of course, a combat charge.
A practically controllable warhead combines the properties of an unmanned spacecraft and a hypersonic unmanned aircraft. This device must perform all actions both in space and during flight in the atmosphere autonomously.
After separation from the breeding platform, the warhead flies for a relatively long time at a very high altitude - in space. At this time, the control system of the unit carries out a whole series of reorientations in order to create conditions for accurately determining its own movement parameters, making it easier to overcome the zone of possible nuclear explosions of anti-missile missiles...
Before entering the upper atmosphere, the on-board computer calculates the required orientation of the warhead and carries it out. Around the same period, sessions are held to determine the actual location using radar, for which a number of maneuvers also need to be made. Then the locator antenna is fired, and the atmospheric part of the movement begins for the warhead.
Below in front of the warhead lies a huge, contrastingly shiny from the menacing high altitudes, covered in a blue oxygen haze, covered with aerosol suspensions, the vast and boundless fifth ocean. Slowly and barely noticeably turning from the residual effects of separation, the warhead continues its descent along a gentle trajectory. But then a very unusual breeze gently blew towards her. He touched it a little - and it became noticeable, covering the body with a thin, receding wave of pale white-blue glow. This wave is breathtakingly high-temperature, but it does not burn the warhead yet, since it is too ethereal. The breeze blowing over the warhead is electrically conductive. The speed of the cone is so high that it literally crushes air molecules with its impact into electrically charged fragments, and impact ionization of the air occurs. This plasma breeze is called high Mach number hypersonic flow, and its speed is twenty times the speed of sound.
Due to the high rarefaction, the breeze is almost unnoticeable in the first seconds. Growing and becoming denser as it goes deeper into the atmosphere, it initially heats more than puts pressure on the warhead. But gradually it begins to compress her cone with force. The flow turns the warhead nose first. It does not unfold immediately - the cone sways slightly back and forth, gradually slowing down its oscillations, and finally stabilizes.
Condensing as it descends, the flow puts more and more pressure on the warhead, slowing down its flight. As it slows down, the temperature gradually decreases. From the enormous values of the beginning of the entry, the blue-white glow of tens of thousands of Kelvin, to the yellow-white glow of five to six thousand degrees. This is the temperature of the surface layers of the Sun. The glow becomes dazzling because the density of the air rapidly increases, and with it the heat flow into the walls of the warhead. The heat-protective coating becomes charred and begins to burn.
It does not burn from friction with the air, as is often incorrectly said. Due to the enormous hypersonic speed of movement (now fifteen times faster than sound), another cone diverges in the air from the top of the body - a shock wave, as if enclosing a warhead. The incoming air, entering the shock wave cone, is instantly compacted many times over and pressed tightly against the surface of the warhead. From abrupt, instantaneous and repeated compression, its temperature immediately jumps to several thousand degrees. The reason for this is the crazy speed of what is happening, the extreme dynamism of the process. Gas-dynamic compression of the flow, and not friction, is what now warms up the sides of the warhead.
The worst part is the nose. There the greatest compaction of the oncoming flow is formed. The area of this seal moves slightly forward, as if disconnecting from the body. And it stays in front, taking the shape of a thick lens or pillow. This formation is called a “detached bow shock wave.” It is several times thicker than the rest of the surface of the shock wave cone around the warhead. The frontal compression of the oncoming flow is the strongest here. Therefore, the disconnected bow shock wave has the highest temperature and highest heat density. This small sun burns the nose of the warhead in a radiant way - highlighting, radiating heat directly into the nose of the hull and causing severe burning of the nose. Therefore, there is the thickest layer of thermal protection. It is the bow shock wave that illuminates the area for many kilometers on a dark night around a warhead flying in the atmosphere.
Connected by one goal
The thermonuclear charge and the control unit continuously communicate with each other. This “dialogue” begins immediately after the warhead is installed on the missile, and it ends at the moment nuclear explosion. All this time, the control system prepares the charge for operation, like a trainer prepares a boxer for an important fight. And at the right moment he gives the last and most important command.
When placing a missile on combat duty, its charge is equipped to its full configuration: a pulsed neutron activator, detonators and other equipment are installed. But he is not ready for the explosion yet. Keeping a nuclear missile in a silo or on a mobile launcher for decades, ready to explode at any moment, is simply dangerous.
Therefore, during flight, the control system puts the charge in a state of readiness for explosion. This happens gradually, using complex sequential algorithms based on two main conditions: reliability of movement towards the goal and control over the process. If one of these factors deviates from the calculated values, the preparation will be stopped. The electronics transfer the charge to an increasingly higher degree of readiness in order to give a command to operate at the calculated point.
And when the fully prepared charge comes from the control unit to detonate, the explosion will occur immediately, instantly. A warhead flying at the speed of a sniper's bullet will only travel a couple of hundredths of a millimeter, not having time to shift in space even the thickness of a human hair, when the thermonuclear reaction in its charge begins, develops, completely passes and is completed, releasing all the normal power.
Having changed greatly both outside and inside, the warhead passed into the troposphere - the last ten kilometers of altitude. She slowed down a lot. Hypersonic flight has degenerated to supersonic speeds of three to four Mach units. The warhead is already shining dimly, fades away and approaches the target point.
An explosion on the surface of the Earth is rarely planned - only for objects buried in the ground, such as missile silos. Most targets lie on the surface. And for their greatest destruction, the detonation is carried out at a certain height, depending on the power of the charge. For tactical twenty kilotons this is 400-600 m. For a strategic megaton the optimal explosion height is 1200 m. Why? The explosion causes two waves to travel across the area. Closer to the epicenter, the blast wave will hit earlier. It will fall and be reflected, bouncing to the sides, where it will merge with the fresh wave that has just arrived here from above, from the point of explosion. Two waves - incident from the center of the explosion and reflected from the surface - add up, forming the most powerful shock wave in the ground layer, main factor defeats.
During test launches, the warhead usually reaches the ground unhindered. On board there is half a centner of explosives, detonated when falling. For what? First, the warhead is a secret object and must be securely destroyed after use. Secondly, this is necessary for the measuring systems of the test site - for prompt detection of the impact point and measurement of deviations.
A multi-meter smoking crater completes the picture. But before that, a couple of kilometers before the impact, an armored storage cassette is fired from the test warhead, recording everything that was recorded on board during the flight. This armored flash drive will protect against loss of on-board information. She will be found later, when a helicopter arrives with a special search group. And they will record the results of a fantastic flight.
Hundreds of books have been written about the history of nuclear confrontation between superpowers and the design of the first nuclear bombs. But there are many myths about modern nuclear weapons. “Popular Mechanics” decided to clarify this issue and tell how the most destructive weapon invented by man works.
Explosive character
The uranium nucleus contains 92 protons. Natural uranium is mainly a mixture of two isotopes: U238 (which has 146 neutrons in its nucleus) and U235 (143 neutrons), with only 0.7% of the latter in natural uranium. The chemical properties of isotopes are absolutely identical, therefore it is impossible to separate them by chemical methods, but the difference in masses (235 and 238 units) allows this to be done by physical methods: a mixture of uranium is converted into gas (uranium hexafluoride), and then pumped through countless porous partitions. Although the isotopes of uranium are not distinguishable by either appearance, nor chemically, they are separated by an abyss in the properties of nuclear characters.
The fission process of U238 is a paid process: a neutron arriving from outside must bring with it energy - 1 MeV or more. And U235 is selfless: nothing is required from the incoming neutron for excitation and subsequent decay; its binding energy in the nucleus is quite sufficient.
When hit by neutrons, the uranium-235 nucleus easily splits, producing new neutrons. Under certain conditions, a chain reaction begins.
When a neutron hits a fission-capable nucleus, an unstable compound is formed, but very quickly (after 10−23−10−22 s) such a nucleus falls apart into two fragments that are unequal in mass and “instantly” (within 10−16−10− 14 c) emitting two or three new neutrons, so that over time the number of fissile nuclei can multiply (this reaction is called a chain reaction). This is only possible in U235, because greedy U238 does not want to share from its own neutrons, whose energy is an order of magnitude less than 1 MeV. The kinetic energy of fission product particles is many orders of magnitude greater than the energy released during any chemical reaction in which the composition of the nuclei does not change.
Metallic plutonium exists in six phases, the densities of which range from 14.7 to 19.8 kg/cm 3 . At temperatures below 119 degrees Celsius, there is a monoclinic alpha phase (19.8 kg/cm 3), but such plutonium is very fragile, and in the cubic face-centered delta phase (15.9) it is plastic and well processed (it is this phase that they are trying to preserved using alloying additives). During detonation compression, no phase transitions can occur—plutonium is in a state of quasi-liquid. Phase transitions are dangerous during production: with large parts, even with a slight change in density, a critical state can be reached. Of course, this will happen without an explosion - the workpiece will simply heat up, but nickel plating may be released (and plutonium is very toxic).
Critical assembly
Fission products are unstable and take a long time to “recover”, emitting various radiations (including neutrons). Neutrons that are emitted a significant time (up to tens of seconds) after fission are called delayed, and although their share is small compared to instantaneous ones (less than 1%), the role they play in the operation of nuclear installations is the most important.
Explosive lenses created a converging wave. Reliability was ensured by a pair of detonators in each block.
Fission products, during numerous collisions with surrounding atoms, give up their energy to them, increasing the temperature. After neutrons appear in an assembly with fissile material, the heat release power can increase or decrease, and the parameters of an assembly in which the number of fissions per unit time is constant are called critical. The criticality of the assembly can be maintained with both a large and a small number of neutrons (with a correspondingly greater or lesser heat release power). The thermal power is increased either by pumping additional neutrons into the critical assembly from the outside, or by making the assembly supercritical (then additional neutrons are supplied by increasingly numerous generations of fissile nuclei). For example, if it is necessary to increase the thermal power of a reactor, it is brought to a regime where each generation of prompt neutrons is slightly less numerous than the previous one, but thanks to delayed neutrons, the reactor barely noticeably passes into a critical state. Then it does not accelerate, but gains power slowly - so that its increase can be stopped at the right moment by introducing neutron absorbers (rods containing cadmium or boron).
The plutonium assembly (a spherical layer in the center) was surrounded by a casing of uranium-238 and then a layer of aluminum.
The neutrons produced during fission often fly past surrounding nuclei without causing further fission. The closer to the surface of a material a neutron is produced, the greater the chance it has of escaping from the fissile material and never returning. Therefore, the form of assembly, saving greatest number neutrons is a sphere: for a given mass of matter it has a minimum surface area. An unsurrounded (solitary) ball of 94% U235 without cavities inside becomes critical with a mass of 49 kg and a radius of 85 mm. If an assembly of the same uranium is a cylinder with a length equal to the diameter, it becomes critical with a mass of 52 kg. The surface area also decreases with increasing density. That is why explosive compression, without changing the amount of fissile material, can bring the assembly into a critical state. It is this process that underlies the common design of a nuclear charge.
The first nuclear weapons used polonium and beryllium (center) as neutron sources.
Ball assembly
But most often it is not uranium that is used in nuclear weapons, but plutonium-239. It is produced in reactors by irradiating uranium-238 with powerful neutron fluxes. Plutonium costs about six times more than U235, but when it fissions, the Pu239 nucleus emits an average of 2.895 neutrons—more than U235 (2.452). In addition, the probability of plutonium fission is higher. All this leads to the fact that a solitary ball of Pu239 becomes critical with almost three times less mass than a ball of uranium, and most importantly, with a smaller radius, which makes it possible to reduce the dimensions of the critical assembly.
A layer of aluminum was used to reduce the rarefaction wave after the detonation of the explosive.
The assembly is made of two carefully fitted halves in the form of a spherical layer (hollow inside); it is obviously subcritical - even for thermal neutrons and even after being surrounded by a moderator. A charge is mounted around an assembly of very precisely fitted explosive blocks. In order to save neutrons, it is necessary to preserve the noble shape of the ball during the explosion - for this, the layer of explosive must be detonated simultaneously along its entire outer surface, pressing the assembly evenly. It is widely believed that this requires a lot of electric detonators. But this was only the case at the dawn of “bomb construction”: to trigger many dozens of detonators, a lot of energy and a considerable size of the initiation system were required. Modern charges use several detonators selected by a special technique, similar in characteristics, from which highly stable (in terms of detonation speed) explosives are triggered in grooves milled in a polycarbonate layer (the shape of which on a spherical surface is calculated using Riemann geometry methods). Detonation at a speed of approximately 8 km/s will travel along the grooves at absolutely equal distances, at the same moment in time it will reach the holes and detonate the main charge - simultaneously at all required points.
The figures show the first moments of the life of a fireball of a nuclear charge - radiation diffusion (a), expansion of hot plasma and the formation of “blisters” (b) and an increase in radiation power in the visible range during the separation of the shock wave (c).
Explosion within
The explosion directed inward compresses the assembly with a pressure of more than a million atmospheres. The surface of the assembly decreases, the internal cavity in plutonium almost disappears, the density increases, and very quickly - within ten microseconds, the compressible assembly passes the critical state with thermal neutrons and becomes significantly supercritical with fast neutrons.
After a period determined by the insignificant time of insignificant slowing down of fast neutrons, each of the new, more numerous generation of them adds an energy of 202 MeV by fission to the assembly substance, which is already bursting with monstrous pressure. On the scale of the phenomena occurring, the strength of even the best alloy steels is so minuscule that it never occurs to anyone to take it into account when calculating the dynamics of an explosion. The only thing that prevents the assembly from flying apart is inertia: in order to expand a plutonium ball by just 1 cm in tens of nanoseconds, it is necessary to impart an acceleration to the substance that is tens of trillions of times greater than the acceleration of free fall, and this is not easy.
In the end, the matter still scatters, fission stops, but the process does not end there: the energy is redistributed between the ionized fragments of the separated nuclei and other particles emitted during fission. Their energy is on the order of tens and even hundreds of MeV, but only electrically neutral high-energy gamma quanta and neutrons have a chance of avoiding interaction with matter and “escaping.” Charged particles quickly lose energy in acts of collisions and ionization. In this case, radiation is emitted - however, it is no longer hard nuclear radiation, but softer, with an energy three orders of magnitude less, but still more than sufficient to knock out electrons from atoms - not only from the outer shells, but from everything in general. A mixture of bare nuclei, stripped electrons and radiation with a density of grams per cubic centimeter (try to imagine how well you can tan under light that has acquired the density of aluminum!) - everything that a moment ago was a charge - comes into some semblance of equilibrium . In a very young fireball, the temperature reaches tens of millions of degrees.
Fire ball
It would seem that even soft radiation moving at the speed of light should leave the matter that generated it far behind, but this is not so: in cold air, the range of quanta of Kev energies is centimeters, and they do not move in a straight line, but changing the direction of movement, re-emitting with every interaction. Quanta ionize the air and spread through it, like cherry juice poured into a glass of water. This phenomenon is called radiative diffusion.
A young fireball of a 100 kt explosion a few tens of nanoseconds after the end of the fission burst has a radius of 3 m and a temperature of almost 8 million Kelvin. But after 30 microseconds its radius is 18 m, although the temperature drops below a million degrees. The ball devours space, and the ionized air behind its front hardly moves: radiation cannot transfer significant momentum to it during diffusion. But it pumps enormous energy into this air, heating it, and when the radiation energy runs out, the ball begins to grow due to the expansion of hot plasma, bursting from the inside with what used to be a charge. Expanding, like an inflated bubble, the plasma shell becomes thinner. Unlike a bubble, of course, nothing inflates it: with inside There is almost no matter left, it all flies from the center by inertia, but 30 microseconds after the explosion, the speed of this flight is more than 100 km/s, and the hydrodynamic pressure in the matter is more than 150,000 atm! The shell is not destined to become too thin; it bursts, forming “blisters”.
In a vacuum neutron tube, a pulse voltage of one hundred kilovolts is applied between a tritium-saturated target (cathode) 1 and anode assembly 2. When the voltage is maximum, it is necessary that deuterium ions be between the anode and cathode, which need to be accelerated. An ion source is used for this. An ignition pulse is applied to its anode 3, and the discharge, passing along the surface of deuterium-saturated ceramic 4, forms deuterium ions. Having accelerated, they bombard a target saturated with tritium, as a result of which an energy of 17.6 MeV is released and neutrons and helium-4 nuclei are formed. In terms of particle composition and even energy output, this reaction is identical to fusion - the process of fusion of light nuclei. In the 1950s, many believed so, but later it turned out that a “disruption” occurs in the tube: either a proton or a neutron (which makes up the deuterium ion, accelerated by an electric field) “gets stuck” in the target nucleus (tritium). If a proton gets stuck, the neutron breaks away and becomes free.
Which of the mechanisms for transmitting the energy of a fireball environment prevails, depends on the power of the explosion: if it is large, the main role is played by radiation diffusion; if it is small, the expansion of the plasma bubble plays a major role. It is clear that an intermediate case is possible when both mechanisms are effective.
The process captures new layers of air, and there is no longer enough energy to strip all the electrons from the atoms. The energy of the ionized layer and fragments of the plasma bubble runs out; they are no longer able to move the huge mass in front of them and noticeably slow down. But what was air before the explosion moves, breaking away from the ball, absorbing more and more layers of cold air... The formation of a shock wave begins.
Shock wave and atomic mushroom
When the shock wave separates from the fireball, the characteristics of the emitting layer change and the radiation power in the optical part of the spectrum sharply increases (the so-called first maximum). Next, the processes of illumination and changes in the transparency of the surrounding air compete, which leads to the realization of a second maximum, less powerful, but much longer - so much so that the output of light energy is greater than in the first maximum.
Near the explosion, everything around it evaporates, further away it melts, but even further away, where the heat flow is no longer sufficient for melting solids, soil, rocks, houses flow like liquid under the monstrous pressure of gas, destroying all strong bonds, heated to a radiance unbearable to the eyes.
Finally, the shock wave goes far from the point of explosion, where there remains a loose and weakened, but expanded many times, cloud of condensed vapors that turned into tiny and very radioactive dust from what was the plasma of the charge, and from what was close at its terrible hour to a place from which one should stay as far as possible. The cloud begins to rise. It cools down, changing its color, “puts on” a white cap of condensed moisture, followed by dust from the surface of the earth, forming the “leg” of what is commonly called an “atomic mushroom”.
Neutron initiation
Attentive readers can estimate the energy release during an explosion with a pencil in their hands. When the time the assembly is in a supercritical state is on the order of microseconds, the age of the neutrons is on the order of picoseconds, and the multiplication factor is less than 2, about a gigajoule of energy is released, which is equivalent to... 250 kg of TNT. Where are the kilo- and megatons?
Neutrons - slow and fast
In a non-fissile substance, “bouncing” off nuclei, neutrons transfer to them part of their energy, the greater the lighter (closer to them in mass) the nuclei. The more collisions neutrons take part in, the more they slow down, and finally they come into thermal equilibrium with the surrounding matter - they are thermalized (this takes milliseconds). Thermal neutron speed is 2200 m/s (energy 0.025 eV). Neutrons can escape from the moderator and are captured by its nuclei, but with moderation, their ability to enter into nuclear reactions increases significantly, so the neutrons that are “not lost” more than compensate for the decrease in numbers.
Thus, if a ball of fissile material is surrounded by a moderator, many neutrons will leave the moderator or be absorbed in it, but there will also be some that will return to the ball (“reflect”) and, having lost their energy, are much more likely to cause fission events. If the ball is surrounded by a layer of beryllium 25 mm thick, then 20 kg of U235 can be saved and still achieve the critical state of the assembly. But such savings come at the cost of time: each subsequent generation of neutrons must first slow down before causing fission. This delay reduces the number of generations of neutrons born per unit time, which means that the energy release is delayed. The less fissile material in the assembly, the more moderator is required to develop a chain reaction, and fission occurs with increasingly lower-energy neutrons. In the limiting case, when criticality is achieved only with thermal neutrons, for example, in a solution of uranium salts in a good moderator - water, the mass of the assemblies is hundreds of grams, but the solution simply periodically boils. The released steam bubbles reduce the average density of the fissile substance, the chain reaction stops, and when the bubbles leave the liquid, the fission outbreak is repeated (if you clog the vessel, the steam will burst it - but this will be a thermal explosion, devoid of all the typical “nuclear” signs).
The fact is that the fission chain in the assembly does not begin with one neutron: at the required microsecond, they are injected into the supercritical assembly by the millions. In the first nuclear charges, isotope sources located in a cavity inside the plutonium assembly were used for this: polonium-210, at the moment of compression, combined with beryllium and caused neutron emission with its alpha particles. But all isotopic sources are rather weak (the first American product generated less than a million neutrons per microsecond), and polonium is very perishable—it reduces its activity by half in just 138 days. Therefore, isotopes were replaced by less dangerous ones (which do not emit when not turned on), and most importantly, neutron tubes that emit more intensely (see sidebar): in a few microseconds (the pulse generated by the tube lasts for so long), hundreds of millions of neutrons are born. But if it doesn’t work or works at the wrong time, a so-called bang or “zilch” will occur—a low-power thermal explosion.
Neutron initiation not only increases the energy release of a nuclear explosion by many orders of magnitude, but also makes it possible to regulate it! It is clear that, having received a combat mission, when setting which the power must be indicated nuclear strike, no one dismantles the charge to equip it with a plutonium assembly that is optimal for a given power. In ammunition with a switchable TNT equivalent, it is enough to simply change the supply voltage to the neutron tube. Accordingly, the neutron yield and energy release will change (of course, when the power is reduced in this way, a lot of expensive plutonium is wasted).
But they began to think about the need to regulate energy release much later, and in the first post-war years there could be no talk of reducing power. More powerful, more powerful and more powerful! But it turned out that there are nuclear physical and hydrodynamic restrictions on the permissible dimensions of the subcritical sphere. The TNT equivalent of a hundred kiloton explosion is close to the physical limit for single-phase munitions, in which only fission occurs. As a result, fission was abandoned as the main source of energy, and they relied on reactions of another class - fusion.
To understand the operating principle and design of a nuclear reactor, you need to take a short excursion into the past. A nuclear reactor is a centuries-old, albeit not fully realized, dream of humanity about an inexhaustible source of energy. Its ancient “progenitor” is a fire made of dry branches, which once illuminated and warmed the vaults of the cave where our distant ancestors found salvation from the cold. Later, people mastered hydrocarbons - coal, shale, oil and natural gas.
A turbulent but short-lived era of steam began, which was replaced by an even more fantastic era of electricity. Cities were filled with light, and workshops were filled with the hum of hitherto unseen machines driven by electric motors. Then it seemed that progress had reached its apogee.
Everything changed at the end of the 19th century, when the French chemist Antoine Henri Becquerel accidentally discovered that uranium salts were radioactive. 2 years later, his compatriots Pierre Curie and his wife Maria Sklodowska-Curie obtained radium and polonium from them, and their level of radioactivity was millions of times higher than that of thorium and uranium.
The baton was picked up by Ernest Rutherford, who studied in detail the nature of radioactive rays. Thus began the age of the atom, which gave birth to its beloved child - the atomic reactor.
First nuclear reactor
“Firstborn” comes from the USA. In December 1942, the first current was produced by the reactor, which was named after its creator, one of the greatest physicists of the century, E. Fermi. Three years later, the ZEEP nuclear facility came to life in Canada. “Bronze” went to the first Soviet reactor F-1, launched at the end of 1946. I.V. Kurchatov became the head of the domestic nuclear project. Today, more than 400 nuclear power units are successfully operating in the world.
Types of nuclear reactors
Their main purpose is to support a controlled nuclear reaction that produces electricity. Some reactors produce isotopes. In short, they are devices in the depths of which some substances are converted into others with the release of a large amount of thermal energy. This is a kind of “furnace” where, instead of traditional fuels, uranium isotopes - U-235, U-238 and plutonium (Pu) - are burned.
Unlike, for example, a car designed for several types of gasoline, each type of radioactive fuel has its own type of reactor. There are two of them - on slow (with U-235) and fast (with U-238 and Pu) neutrons. Most nuclear power plants have slow neutron reactors. In addition to nuclear power plants, installations “work” in research centers, on nuclear submarines, etc.
How the reactor works
All reactors have approximately the same circuit. Its “heart” is the active zone. It can be roughly compared to the firebox of a conventional stove. Only instead of firewood there is nuclear fuel in the form of fuel elements with a moderator - fuel rods. The active zone is located inside a kind of capsule - a neutron reflector. Fuel rods are “washed” by the coolant – water. Because in the “heart” there is very high level radioactivity, it is surrounded by reliable radiation protection.
Operators control the operation of the plant using two critical systems - chain reaction control and a remote control system. If an emergency occurs, emergency protection is immediately activated.
How does a reactor work?
The atomic “flame” is invisible, since the processes occur at the level of nuclear fission. During a chain reaction, heavy nuclei decay into smaller fragments, which, being in an excited state, become sources of neutrons and other subatomic particles. But the process does not end there. Neutrons continue to “split”, as a result of which large amounts of energy are released, that is, what happens for the sake of which nuclear power plants are built.
The main task of the personnel is to maintain the chain reaction with the help of control rods at a constant, adjustable level. This is its main difference from atomic bomb, where the process of nuclear decay is uncontrollable and proceeds rapidly, in the form of a powerful explosion.
What happened at the Chernobyl nuclear power plant
One of the main reasons for the disaster at the Chernobyl nuclear power plant in April 1986 was a gross violation of operational safety rules during routine maintenance at the 4th power unit. Then 203 graphite rods were simultaneously removed from the core instead of the 15 allowed by regulations. As a result, the uncontrollable chain reaction that began ended in a thermal explosion and complete destruction of the power unit.
New generation reactors
Over the past decade, Russia has become one of the leaders in global nuclear energy. At the moment, the state corporation Rosatom is building nuclear power plants in 12 countries, where 34 power units are being built. Such a high demand is evidence of the high level of modern Russian nuclear technology. Next in line are the new 4th generation reactors.
"Brest"
One of them is Brest, which is being developed as part of the Breakthrough project. Now operating systems open-cycle systems operate on low-enriched uranium, which leaves a large amount of spent fuel that must be disposed of, which requires enormous costs. "Brest" - a fast neutron reactor is unique in its closed cycle.
In it, spent fuel, after appropriate processing in a fast neutron reactor, again becomes full-fledged fuel, which can be loaded back into the same installation.
Brest is distinguished by a high level of safety. It will never “explode” even in the most serious accident, it is very economical and environmentally friendly, since it reuses its “renewed” uranium. It also cannot be used to produce weapons-grade plutonium, which opens up the broadest prospects for its export.
VVER-1200
VVER-1200 is an innovative generation 3+ reactor with a capacity of 1150 MW. Thanks to its unique technical capabilities, it has almost absolute operational safety. The reactor is abundantly equipped with passive safety systems that will operate automatically even in the absence of power supply.
One of them is a passive heat removal system, which is automatically activated when the reactor is completely de-energized. In this case, emergency hydraulic tanks are provided. If there is an abnormal pressure drop in the primary circuit, a large amount of water containing boron begins to be supplied to the reactor, which quenches the nuclear reaction and absorbs neutrons.
Another know-how is located in the lower part of the protective shell - the melt “trap”. If, as a result of an accident, the core “leaks”, the “trap” will not allow the containment shell to collapse and will prevent radioactive products from entering the ground.
But this is something we often don’t know. And why does a nuclear bomb explode, too...
Let's start from afar. Every atom has a nucleus, and the nucleus consists of protons and neutrons - perhaps everyone knows this. In the same way, everyone saw the periodic table. But why are the chemical elements in it placed this way and not otherwise? Certainly not because Mendeleev wanted it that way. The atomic number of each element in the table indicates how many protons are in the nucleus of that element's atom. In other words, iron is number 26 in the table because there are 26 protons in an iron atom. And if there are not 26 of them, it is no longer iron.
But there can be different numbers of neutrons in the nuclei of the same element, which means that the mass of the nuclei can be different. Atoms of the same element with different masses are called isotopes. Uranium has several such isotopes: the most common in nature is uranium-238 (its nucleus has 92 protons and 146 neutrons, totaling 238). It is radioactive, but you cannot make a nuclear bomb from it. But the isotope uranium-235, a small amount of which is found in uranium ores, suitable for a nuclear charge.
The reader may have come across the expressions “enriched uranium” and “depleted uranium”. Enriched uranium contains more uranium-235 than natural uranium; in a depleted state, correspondingly, less. Enriched uranium can be used to produce plutonium, another element suitable for a nuclear bomb (it is almost never found in nature). How uranium is enriched and how plutonium is obtained from it is a topic for a separate discussion.
So why does a nuclear bomb explode? The fact is that some heavy nuclei tend to decay if they are hit by a neutron. And you won’t have to wait long for a free neutron – there are a lot of them flying around. So, such a neutron hits the uranium-235 nucleus and thereby breaks it into “fragments”. This releases a few more neutrons. Can you guess what will happen if there are nuclei of the same element around? That's right, a chain reaction will occur. This is how it happens.
In a nuclear reactor, where uranium-235 is “dissolved” in the more stable uranium-238, an explosion does not occur under normal conditions. Most of the neutrons that fly out from decaying nuclei fly away into the milk, without finding the uranium-235 nuclei. In the reactor, the decay of nuclei occurs “sluggishly” (but this is enough for the reactor to provide energy). In a single piece of uranium-235, if it is of sufficient mass, neutrons will be guaranteed to break up the nuclei, the chain reaction will start as an avalanche, and... Stop! After all, if you make a piece of uranium-235 or plutonium with the mass required for an explosion, it will explode immediately. This is not the point.
What if you take two pieces of subcritical mass and push them against each other using a remote-controlled mechanism? For example, place both in a tube and attach a powder charge to one so that at the right moment one piece, like a projectile, is fired at the other. Here is the solution to the problem.
You can do it differently: take a spherical piece of plutonium and attach explosive charges over its entire surface. When these charges detonate on command from the outside, their explosion will compress the plutonium from all sides, compress it to a critical density, and a chain reaction will occur. However, accuracy and reliability are important here: all explosive charges must go off at the same time. If some of them work, and some don’t, or some work late, no nuclear explosion will result: the plutonium will not be compressed to a critical mass, but will dissipate in the air. Instead of a nuclear bomb, you will get a so-called “dirty” one.
This is what an implosion-type nuclear bomb looks like. The charges, which are supposed to create a directed explosion, are made in the form of polyhedra in order to cover the surface of the plutonium sphere as tightly as possible.
The first type of device was called a cannon device, the second type - an implosion device.
The "Little Boy" bomb dropped on Hiroshima had a uranium-235 charge and a cannon-type device. The Fat Man bomb, detonated over Nagasaki, carried a plutonium charge, and the explosive device was implosion. Nowadays, gun-type devices are almost never used; implosion ones are more complicated, but at the same time they allow you to regulate the mass of the nuclear charge and spend it more rationally. And plutonium has replaced uranium-235 as a nuclear explosive.
Quite a few years passed, and physicists offered the military even more powerful bomb– thermonuclear, or, as it is also called, hydrogen. It turns out that hydrogen explodes more powerfully than plutonium?
Hydrogen is indeed explosive, but not that explosive. However, there is no “ordinary” hydrogen in a hydrogen bomb; it uses its isotopes - deuterium and tritium. The nucleus of “ordinary” hydrogen has one neutron, deuterium has two, and tritium has three.
In a nuclear bomb, the nuclei of a heavy element are divided into nuclei of lighter ones. In thermonuclear fusion, the opposite process occurs: light nuclei merge with each other into heavier ones. Deuterium and tritium nuclei, for example, combine to form helium nuclei (otherwise known as alpha particles), and the “extra” neutron is sent into “free flight.” This releases significantly more energy than during the decay of plutonium nuclei. By the way, this is exactly the process that takes place on the Sun.
However, the fusion reaction is possible only at ultra-high temperatures (which is why it is called thermonuclear). How to make deuterium and tritium react? Yes, it’s very simple: you need to use a nuclear bomb as a detonator!
Since deuterium and tritium are themselves stable, their charge in a thermonuclear bomb can be arbitrarily huge. This means that a thermonuclear bomb can be made incomparably more powerful than a “simple” nuclear one. The "Baby" dropped on Hiroshima had a TNT equivalent of around 18 kilotons, and the most powerful H-bomb(the so-called “Tsar Bomba”, also known as “Kuzka’s Mother”) – already 58.6 megatons, more than 3255 times more powerful than the “Baby”!
The “mushroom” cloud from the Tsar Bomba rose to a height of 67 kilometers, and the blast wave circled the globe three times.
However, such gigantic power is clearly excessive. Having “played enough” with megaton bombs, military engineers and physicists took a different path - the path of miniaturization of nuclear weapons. In their conventional form, nuclear weapons can be dropped from strategic bombers like aerial bombs or launched from ballistic missiles; if you miniaturize them, you get a compact nuclear charge that does not destroy everything for kilometers around, and which can be placed on an artillery shell or an air-to-ground missile. Mobility will increase and the range of tasks to be solved will expand. In addition to strategic nuclear weapons, we will receive tactical ones.
A variety of delivery systems have been developed for tactical nuclear weapons - nuclear cannons, mortars, recoilless rifles (for example, the American Davy Crockett). The USSR even had a nuclear bullet project. True, it had to be abandoned - nuclear bullets were so unreliable, so complicated and expensive to manufacture and store that there was no point in them.
"Davy Crockett." A number of these nuclear weapons were in service with the US Armed Forces, and the West German Minister of Defense unsuccessfully sought to arm the Bundeswehr with them.
Speaking about small nuclear weapons, it is worth mentioning another type of nuclear weapon - the neutron bomb. The plutonium charge in it is small, but this is not necessary. If a thermonuclear bomb follows the path of increasing the force of the explosion, then a neutron bomb relies on another damaging factor - radiation. To enhance radiation, a neutron bomb contains a supply of beryllium isotope, which upon explosion produces a huge number of fast neutrons.
According to its creators, a neutron bomb should kill enemy personnel, but leave equipment intact, which can then be captured during an offensive. In practice, it turned out somewhat differently: irradiated equipment becomes unusable - anyone who dares to pilot it will very soon “earn” radiation sickness. This does not change the fact that a neutron bomb explosion is capable of hitting an enemy through tank armor; neutron ammunition was developed by the United States specifically as a weapon against Soviet tank formations. However, tank armor was soon developed that provided some kind of protection from the flow of fast neutrons.
Another type of nuclear weapon was invented in 1950, but never (as far as is known) produced. This is the so-called cobalt bomb - a nuclear charge with a cobalt shell. During the explosion, cobalt, irradiated by a stream of neutrons, becomes an extremely radioactive isotope and is scattered throughout the area, contaminating it. Just one such bomb of sufficient power could cover the entire globe with cobalt and destroy all of humanity. Fortunately, this project remained a project.
What can we say in conclusion? A nuclear bomb is a truly terrible weapon, and at the same time it (what a paradox!) helped maintain relative peace between the superpowers. If your enemy has nuclear weapons, you will think ten times before attacking him. No country with a nuclear arsenal has ever been attacked from outside, and there have been no wars between major states in the world since 1945. Let's hope there won't be any.
The world of the atom is so fantastic that understanding it requires a radical break in the usual concepts of space and time. Atoms are so small that if a drop of water could be enlarged to the size of the Earth, each atom in that drop would be smaller than an orange. In fact, one drop of water consists of 6000 billion billion (6000000000000000000000) hydrogen and oxygen atoms. And yet, despite its microscopic size, the atom has a structure to some extent similar to the structure of our solar system. In its incomprehensibly small center, the radius of which is less than one trillionth of a centimeter, there is a relatively huge “sun” - the nucleus of the atom.
Tiny “planets” - electrons - revolve around this atomic “sun”. The nucleus consists of the two main building blocks of the Universe - protons and neutrons (they have a unifying name - nucleons). An electron and a proton are charged particles, and the amount of charge in each of them is exactly the same, but the charges differ in sign: the proton is always positively charged, and the electron is negatively charged. The neutron does not carry an electrical charge and, as a result, has a very high permeability.
In the atomic scale of measurements, the mass of a proton and a neutron is taken as unity. The atomic weight of any chemical element therefore depends on the number of protons and neutrons contained in its nucleus. For example, a hydrogen atom, with a nucleus consisting of only one proton, has an atomic mass of 1. A helium atom, with a nucleus of two protons and two neutrons, has an atomic mass of 4.
The nuclei of atoms of the same element always contain the same number of protons, but the number of neutrons may vary. Atoms that have nuclei with the same number of protons, but differ in the number of neutrons and are varieties of the same element are called isotopes. To distinguish them from each other, a number is assigned to the element symbol, equal to the sum all particles in the nucleus of a given isotope.
The question may arise: why does the nucleus of an atom not fall apart? After all, the protons included in it are electrically charged particles with the same charge, which must repel each other with great force. This is explained by the fact that inside the nucleus there are also so-called intranuclear forces that attract nuclear particles to each other. These forces compensate for the repulsive forces of protons and prevent the nucleus from spontaneously flying apart.
Intranuclear forces are very strong, but act only at very close distances. Therefore, the nuclei of heavy elements, consisting of hundreds of nucleons, turn out to be unstable. The particles of the nucleus are in continuous motion here (within the volume of the nucleus), and if we add some additional amount of energy to them, they can overcome internal forces- the core will split into parts. The amount of this excess energy is called excitation energy. Among the isotopes of heavy elements, there are those that seem to be on the very verge of self-disintegration. Just a small “push” is enough, for example, a simple neutron hitting the nucleus (and it does not even have to accelerate to high speed) for the nuclear fission reaction to occur. Some of these “fissile” isotopes were later learned to be produced artificially. In nature, there is only one such isotope - uranium-235.
Uranus was discovered in 1783 by Klaproth, who isolated it from uranium tar and named it after the recently discovered planet Uranus. As it turned out later, it was, in fact, not uranium itself, but its oxide. Pure uranium, a silvery-white metal, was obtained
only in 1842 Peligo. The new element did not have any remarkable properties and did not attract attention until 1896, when Becquerel discovered the phenomenon of radioactivity in uranium salts. After this, uranium became an object scientific research and experiments, but practical application still didn't have it.
When, in the first third of the 20th century, physicists more or less understood the structure of the atomic nucleus, they first of all tried to fulfill the long-standing dream of alchemists - they tried to transform one chemical element into another. In 1934, French researchers, the spouses Frédéric and Irene Joliot-Curie, reported the following experience to the French Academy of Sciences: when bombarding aluminum plates with alpha particles (nuclei of a helium atom), aluminum atoms turned into phosphorus atoms, but not ordinary ones, but radioactive ones, which in turn became into a stable isotope of silicon. Thus, an aluminum atom, having added one proton and two neutrons, turned into a heavier silicon atom.
This experience suggested that if you “bombard” the nuclei of the heaviest element existing in nature - uranium - with neutrons, you can obtain an element that does not exist in natural conditions. In 1938, German chemists Otto Hahn and Fritz Strassmann repeated general outline the experience of the Joliot-Curie spouses, taking uranium instead of aluminum. The results of the experiment were not at all what they expected - instead of a new superheavy element with a mass number greater than that of uranium, Hahn and Strassmann received light elements from the middle part of the periodic table: barium, krypton, bromine and some others. The experimenters themselves were unable to explain the observed phenomenon. Only the following year, physicist Lise Meitner, to whom Hahn reported his difficulties, found the correct explanation for the observed phenomenon, suggesting that when uranium is bombarded with neutrons, its nucleus splits (fissions). In this case, nuclei of lighter elements should have been formed (that’s where barium, krypton and other substances came from), as well as 2-3 free neutrons should have been released. Further research made it possible to clarify in detail the picture of what was happening.
Natural uranium consists of a mixture of three isotopes with masses 238, 234 and 235. The main amount of uranium is isotope-238, the nucleus of which includes 92 protons and 146 neutrons. Uranium-235 is only 1/140 of natural uranium (0.7% (it has 92 protons and 143 neutrons in its nucleus), and uranium-234 (92 protons, 142 neutrons) is only 1/17500 of the total mass of uranium (0 , 006%. The least stable of these isotopes is uranium-235.
From time to time, the nuclei of its atoms spontaneously divide into parts, as a result of which lighter elements of the periodic table are formed. The process is accompanied by the release of two or three free neutrons, which rush at enormous speed - about 10 thousand km/s (they are called fast neutrons). These neutrons can hit other uranium nuclei, causing nuclear reactions. Each isotope behaves differently in this case. Uranium-238 nuclei in most cases simply capture these neutrons without any further transformations. But in approximately one case out of five, when a fast neutron collides with the nucleus of the isotope-238, a curious nuclear reaction occurs: one of the neutrons of uranium-238 emits an electron, turning into a proton, that is, the uranium isotope turns into a more
heavy element - neptunium-239 (93 protons + 146 neutrons). But neptunium is unstable - after a few minutes, one of its neutrons emits an electron, turning into a proton, after which the neptunium isotope turns into the next element in the periodic table - plutonium-239 (94 protons + 145 neutrons). If a neutron hits the nucleus of unstable uranium-235, then fission immediately occurs - the atoms disintegrate with the emission of two or three neutrons. It is clear that in natural uranium, most of the atoms of which belong to the 238 isotope, this reaction has no visible consequences - all free neutrons will eventually be absorbed by this isotope.
Well, what if we imagine a fairly massive piece of uranium consisting entirely of isotope-235?
Here the process will go differently: neutrons released during the fission of several nuclei, in turn, hitting neighboring nuclei, cause their fission. As a result, a new portion of neutrons is released, which splits the next nuclei. Under favorable conditions, this reaction proceeds like an avalanche and is called a chain reaction. To start it, a few bombarding particles may be enough.
Indeed, let uranium-235 be bombarded by only 100 neutrons. They will separate 100 uranium nuclei. In this case, 250 new neutrons of the second generation will be released (on average 2.5 per fission). Second generation neutrons will produce 250 fissions, which will release 625 neutrons. In the next generation it will become 1562, then 3906, then 9670, etc. The number of divisions will increase indefinitely if the process is not stopped.
However, in reality only a small fraction of neutrons reach the nuclei of atoms. The rest, quickly rushing between them, are carried away into the surrounding space. A self-sustaining chain reaction can only occur in a sufficiently large array of uranium-235, which is said to have a critical mass. (This mass under normal conditions is 50 kg.) It is important to note that the fission of each nucleus is accompanied by the release of a huge amount of energy, which turns out to be approximately 300 million times more than the energy spent on fission! (It is estimated that the complete fission of 1 kg of uranium-235 releases the same amount of heat as the combustion of 3 thousand tons of coal.)
This colossal burst of energy, released in a matter of moments, manifests itself as an explosion of monstrous force and underlies the action of nuclear weapons. But in order for this weapon to become a reality, it is necessary that the charge consist not of natural uranium, but of a rare isotope - 235 (such uranium is called enriched). It was later discovered that pure plutonium is also a fissile material and could be used in an atomic charge instead of uranium-235.
All these important discoveries were made on the eve of World War II. Soon, secret work on creating an atomic bomb began in Germany and other countries. In the USA, this problem was addressed in 1941. The entire complex of works was given the name “Manhattan Project”.
Administrative management of the project was carried out by General Groves, and scientific management was carried out by University of California professor Robert Oppenheimer. Both were well aware of the enormous complexity of the task facing them. Therefore, Oppenheimer's first concern was recruiting a highly intelligent scientific team. In the USA at that time there were many physicists who emigrated from Nazi Germany. It was not easy to attract them to create weapons directed against their former homeland. Oppenheimer spoke personally to everyone, using all the power of his charm. Soon he managed to gather a small group of theorists, whom he jokingly called “luminaries.” And in fact, it included the greatest specialists of that time in the field of physics and chemistry. (Among them are 13 Nobel Prize laureates, including Bohr, Fermi, Frank, Chadwick, Lawrence.) Besides them, there were many other specialists of various profiles.
The US government did not skimp on expenses, and the work took on a grand scale from the very beginning. In 1942, the world's largest research laboratory was founded at Los Alamos. The population of this scientific city soon reached 9 thousand people. In terms of the composition of scientists, the scope of scientific experiments, and the number of specialists and workers involved in the work, the Los Alamos laboratory had no equal in world history. The Manhattan Project had its own police, counterintelligence, communications system, warehouses, villages, factories, laboratories, and its own colossal budget.
The main goal of the project was to obtain enough fissile material from which several atomic bombs could be created. In addition to uranium-235, the charge for the bomb, as already mentioned, could be the artificial element plutonium-239, that is, the bomb could be either uranium or plutonium.
Groves and Oppenheimer agreed that work should be carried out simultaneously in two directions, since it was impossible to decide in advance which of them would be more promising. Both methods were fundamentally different from each other: the accumulation of uranium-235 had to be carried out by separating it from the bulk of natural uranium, and plutonium could only be obtained as a result of a controlled nuclear reaction when uranium-238 was irradiated with neutrons. Both paths seemed unusually difficult and did not promise easy solutions.
In fact, how can one separate two isotopes that differ only slightly in weight and chemically behave in exactly the same way? Neither science nor technology has ever faced such a problem. The production of plutonium also seemed very problematic at first. Before this, the entire experience of nuclear transformations was limited to a few laboratory experiments. Now they had to master the production of kilograms of plutonium on an industrial scale, develop and create a special installation for this - a nuclear reactor, and learn to control the course of the nuclear reaction.
Both here and here a whole complex of complex problems had to be solved. Therefore, the Manhattan Project consisted of several subprojects, headed by prominent scientists. Oppenheimer himself was the head of the Los Alamos Scientific Laboratory. Lawrence was in charge of the Radiation Laboratory at the University of California. Fermi conducted research at the University of Chicago to create a nuclear reactor.
At first, the most important problem was obtaining uranium. Before the war, this metal had virtually no use. Now that it was needed immediately in huge quantities, it turned out that there was no industrial method of producing it.
The Westinghouse company took up its development and quickly achieved success. After purifying the uranium resin (uranium occurs in nature in this form) and obtaining uranium oxide, it was converted into tetrafluoride (UF4), from which uranium metal was separated by electrolysis. If at the end of 1941 American scientists had only a few grams of uranium metal at their disposal, then already in November 1942 its industrial production at Westinghouse factories reached 6,000 pounds per month.
At the same time, work was underway to create a nuclear reactor. The process of producing plutonium actually boiled down to irradiating uranium rods with neutrons, as a result of which part of the uranium-238 would turn into plutonium. The sources of neutrons in this case could be fissile atoms of uranium-235, scattered in sufficient quantities among atoms of uranium-238. But in order to maintain the constant production of neutrons, a chain reaction of fission of uranium-235 atoms had to begin. Meanwhile, as already mentioned, for every atom of uranium-235 there were 140 atoms of uranium-238. It is clear that neutrons scattering in all directions had a much higher probability of meeting them on their way. That is, a huge number of released neutrons turned out to be absorbed by the main isotope without any benefit. Obviously, under such conditions a chain reaction could not take place. How to be?
At first it seemed that without the separation of two isotopes, the operation of the reactor was generally impossible, but one important circumstance was soon established: it turned out that uranium-235 and uranium-238 were susceptible to neutrons of different energies. The nucleus of a uranium-235 atom can be split by a neutron of relatively low energy, having a speed of about 22 m/s. Such slow neutrons are not captured by uranium-238 nuclei - for this they must have a speed of the order of hundreds of thousands of meters per second. In other words, uranium-238 is powerless to prevent the beginning and progress of a chain reaction in uranium-235 caused by neutrons slowed down to extremely low speeds - no more than 22 m/s. This phenomenon was discovered by the Italian physicist Fermi, who lived in the USA since 1938 and led the work here to create the first reactor. Fermi decided to use graphite as a neutron moderator. According to his calculations, the neutrons emitted from uranium-235, having passed through a 40 cm layer of graphite, should have reduced their speed to 22 m/s and begun a self-sustaining chain reaction in uranium-235.
Another moderator could be so-called “heavy” water. Since the hydrogen atoms included in it are very similar in size and mass to neutrons, they could best slow them down. (With fast neutrons, approximately the same thing happens as with balls: if a small ball hits a large one, it rolls back, almost without losing speed, but when it meets a small ball, it transfers a significant part of its energy to it - in the same way a neutron during an elastic collision bounces off a heavy nucleus, slowing down only slightly, and when colliding with the nuclei of hydrogen atoms, it very quickly loses all its energy.) However, ordinary water is not suitable for slowing down, since its hydrogen tends to absorb neutrons. That is why deuterium, which is part of “heavy” water, should be used for this purpose.
In early 1942, under Fermi's leadership, construction began on the first nuclear reactor in history in the tennis court area under the west stands of Chicago Stadium. The scientists carried out all the work themselves. The reaction can be controlled in the only way - by adjusting the number of neutrons participating in the chain reaction. Fermi intended to achieve this using rods made of substances such as boron and cadmium, which strongly absorb neutrons. The moderator was graphite bricks, from which the physicists built columns 3 m high and 1.2 m wide. Rectangular blocks with uranium oxide were installed between them. The entire structure required about 46 tons of uranium oxide and 385 tons of graphite. To slow down the reaction, rods of cadmium and boron were introduced into the reactor.
If this were not enough, then for insurance, two scientists stood on a platform located above the reactor with buckets filled with a solution of cadmium salts - they were supposed to pour them onto the reactor if the reaction got out of control. Fortunately, this was not necessary. On December 2, 1942, Fermi ordered all control rods to be extended and the experiment began. After four minutes, the neutron counters began to click louder and louder. With every minute the intensity of the neutron flux became greater. This indicated that a chain reaction was taking place in the reactor. It lasted for 28 minutes. Then Fermi gave the signal, and the lowered rods stopped the process. Thus, for the first time, man freed the energy of the atomic nucleus and proved that he could control it at will. Now there was no longer any doubt that nuclear weapons were a reality.
In 1943, the Fermi reactor was dismantled and transported to the Aragonese National Laboratory (50 km from Chicago). Was here soon
Another nuclear reactor was built in which heavy water was used as a moderator. It consisted of a cylindrical aluminum tank containing 6.5 tons of heavy water, into which were vertically immersed 120 rods of uranium metal, encased in an aluminum shell. The seven control rods were made of cadmium. Around the tank there was a graphite reflector, then a screen made of lead and cadmium alloys. The entire structure was enclosed in a concrete shell with a wall thickness of about 2.5 m.
Experiments at these pilot reactors confirmed the possibility of industrial production of plutonium.
The main center of the Manhattan Project soon became the town of Oak Ridge in the Tennessee River Valley, whose population grew to 79 thousand people in a few months. Here, in short term The first enriched uranium production plant in history was built. An industrial reactor producing plutonium was launched here in 1943. In February 1944, about 300 kg of uranium was extracted from it daily, from the surface of which plutonium was obtained by chemical separation. (To do this, the plutonium was first dissolved and then precipitated.) The purified uranium was then returned to the reactor. That same year, construction began on the huge Hanford plant in the barren, bleak desert on the south bank of the Columbia River. Three powerful nuclear reactors were located here, producing several hundred grams of plutonium every day.
In parallel, research was in full swing to develop an industrial process for uranium enrichment.
Having considered different variants, Groves and Oppenheimer decided to focus their efforts on two methods: gaseous diffusion and electromagnetic.
The gas diffusion method was based on a principle known as Graham's law (it was first formulated in 1829 by the Scottish chemist Thomas Graham and developed in 1896 by the English physicist Reilly). According to this law, if two gases, one of which is lighter than the other, are passed through a filter with negligibly small holes, then slightly more of the light gas will pass through it than of the heavy one. In November 1942, Urey and Dunning from Columbia University created a gaseous diffusion method for separating uranium isotopes based on the Reilly method.
Since natural uranium is solid, then it was first converted into uranium fluoride (UF6). This gas was then passed through microscopic - on the order of thousandths of a millimeter - holes in the filter partition.
Since the difference in the molar weights of the gases was very small, behind the partition the content of uranium-235 increased by only 1.0002 times.
In order to increase the amount of uranium-235 even more, the resulting mixture is again passed through a partition, and the amount of uranium is again increased by 1.0002 times. Thus, to increase the uranium-235 content to 99%, it was necessary to pass the gas through 4000 filters. This took place at a huge gaseous diffusion plant in Oak Ridge.
In 1940, under the leadership of Ernst Lawrence, research began at the University of California on the separation of uranium isotopes by the electromagnetic method. It was necessary to find physical processes that would allow isotopes to be separated using the difference in their masses. Lawrence attempted to separate isotopes using the principle of a mass spectrograph, an instrument used to determine the masses of atoms.
The principle of its operation was as follows: pre-ionized atoms were accelerated by an electric field and then passed through a magnetic field, in which they described circles located in a plane perpendicular to the direction of the field. Since the radii of these trajectories were proportional to their mass, light ions ended up on circles of smaller radius than heavy ones. If traps were placed along the path of the atoms, then different isotopes could be collected separately in this way.
That was the method. In laboratory conditions it gave good results. But building a facility where isotope separation could be carried out on an industrial scale proved extremely difficult. However, Lawrence eventually managed to overcome all difficulties. The result of his efforts was the appearance of calutron, which was installed in a giant plant in Oak Ridge.
This electromagnetic plant was built in 1943 and turned out to be perhaps the most expensive brainchild of the Manhattan Project. Lawrence's method required a large number of complex, not yet developed devices associated with high voltage, high vacuum and strong magnetic fields. The scale of the costs turned out to be enormous. Calutron had a giant electromagnet, the length of which reached 75 m and weighed about 4000 tons.
Several thousand tons of silver wire were used for the windings for this electromagnet.
The entire work (not counting the cost of $300 million in silver, which the State Treasury provided only temporarily) cost $400 million. The Ministry of Defense paid 10 million for the electricity consumed by calutron alone. Much of the equipment at the Oak Ridge plant was superior in scale and precision to anything that had ever been developed in this field of technology.
But all these costs were not in vain. Having spent a total of about 2 billion dollars, US scientists by 1944 created a unique technology for uranium enrichment and plutonium production. Meanwhile, at the Los Alamos laboratory they were working on the design of the bomb itself. The principle of its operation was, in general terms, clear for a long time: the fissile substance (plutonium or uranium-235) had to be transferred to a critical state at the moment of the explosion (for a chain reaction to occur, the mass of the charge must be even noticeably greater than the critical one) and irradiated with a beam of neutrons, which entailed is the beginning of a chain reaction.
According to calculations, the critical mass of the charge exceeded 50 kilograms, but they were able to significantly reduce it. In general, the value of the critical mass is strongly influenced by several factors. The larger the surface area of the charge, the more neutrons are uselessly emitted into the surrounding space. A sphere has the smallest surface area. Consequently, spherical charges, other things being equal, have the smallest critical mass. In addition, the value of the critical mass depends on the purity and type of fissile materials. It is inversely proportional to the square of the density of this material, which allows, for example, by doubling the density, reducing the critical mass by four times. The required degree of subcriticality can be obtained, for example, by compacting the fissile material due to the explosion of a charge of a conventional explosive made in the form of a spherical shell surrounding the nuclear charge. The critical mass can also be reduced by surrounding the charge with a screen that reflects neutrons well. Lead, beryllium, tungsten, natural uranium, iron and many others can be used as such a screen.
One possible design of an atomic bomb consists of two pieces of uranium, which, when combined, form a mass greater than critical. In order to cause a bomb explosion, you need to bring them closer together as quickly as possible. The second method is based on the use of an inward-converging explosion. In this case, a stream of gases from a conventional explosive was directed at the fissile material located inside and compressed it until it reached a critical mass. Combining a charge and intensely irradiating it with neutrons, as already mentioned, causes a chain reaction, as a result of which in the first second the temperature increases to 1 million degrees. During this time, only about 5% of the critical mass managed to separate. The rest of the charge in early bomb designs evaporated without
any benefit.
The first atomic bomb in history (it was given the name Trinity) was assembled in the summer of 1945. And on June 16, 1945, the first atomic explosion on Earth was carried out at the nuclear test site in the Alamogordo desert (New Mexico). The bomb was placed in the center of the test site on top of a 30-meter steel tower. Recording equipment was placed around it at a great distance. There was an observation post 9 km away, and a command post 16 km away. The atomic explosion made a stunning impression on all witnesses to this event. According to eyewitnesses' descriptions, it felt as if many suns had united into one and illuminated the test site at once. Then a huge fireball appeared over the plain and a round cloud of dust and light began to rise towards it slowly and ominously.
Taking off from the ground, this fireball soared to a height of more than three kilometers in a few seconds. With every moment it grew in size, soon its diameter reached 1.5 km, and it slowly rose into the stratosphere. Then the fireball gave way to a column of billowing smoke, which stretched to a height of 12 km, taking the shape of a giant mushroom. All this was accompanied by a terrible roar, from which the earth shook. The power of the exploding bomb exceeded all expectations.
As soon as the radiation situation allowed, several Sherman tanks, lined with lead plates on the inside, rushed to the area of the explosion. On one of them was Fermi, who was eager to see the results of his work. What appeared before his eyes was a dead, scorched earth, on which all living things had been destroyed within a radius of 1.5 km. The sand had baked into a glassy greenish crust that covered the ground. In a huge crater lay the mangled remains of a steel support tower. The force of the explosion was estimated at 20,000 tons of TNT.
The next step was to be the combat use of the bomb against Japan, which, after the surrender of Nazi Germany, alone continued the war with the United States and its allies. There were no launch vehicles at that time, so the bombing had to be carried out from an airplane. The components of the two bombs were transported with great care by the cruiser Indianapolis to Tinian Island, where the 509th Combined Air Force Group was based. These bombs differed somewhat from each other in the type of charge and design.
The first bomb, “Baby,” was a large-sized aerial bomb with an atomic charge made of highly enriched uranium-235. Its length was about 3 m, diameter - 62 cm, weight - 4.1 tons.
The second bomb - "Fat Man" - with a charge of plutonium-239 was egg-shaped with a large stabilizer. Its length
was 3.2 m, diameter 1.5 m, weight - 4.5 tons.
On August 6, Colonel Tibbets' B-29 Enola Gay bomber dropped "Little Boy" on the major Japanese city of Hiroshima. The bomb was lowered by parachute and exploded, as planned, at an altitude of 600 m from the ground.
The consequences of the explosion were terrible. Even for the pilots themselves, the sight of a peaceful city destroyed by them in an instant made a depressing impression. Later, one of them admitted that at that second they saw the worst thing a person can see.
For those who were on earth, what was happening resembled true hell. First of all, a heat wave passed over Hiroshima. Its effect lasted only a few moments, but was so powerful that it melted even tiles and quartz crystals in granite slabs, turned telephone poles at a distance of 4 km into coal and, finally, incinerated human bodies so much that only shadows remained from them on the asphalt of the pavements or on the walls of houses. Then a monstrous gust of wind burst out from under the fireball and rushed over the city at a speed of 800 km/h, destroying everything in its path. Houses that could not withstand his furious onslaught collapsed as if knocked down. There is not a single intact building left in the giant circle with a diameter of 4 km. A few minutes after the explosion, black radioactive rain fell over the city - this moisture turned into steam condensed into high layers atmosphere and fell to the ground in the form of large drops mixed with radioactive dust.
After the rain, a new gust of wind hit the city, this time blowing in the direction of the epicenter. It was weaker than the first, but still strong enough to uproot trees. The wind fanned a gigantic fire in which everything that could burn burned. Of the 76 thousand buildings, 55 thousand were completely destroyed and burned. Witnesses of this terrible disaster they remembered torch people, from which burnt clothes fell to the ground along with rags of skin, and about crowds of maddened people, covered with terrible burns, rushing screaming through the streets. There was a suffocating stench of burnt human flesh in the air. There were people lying everywhere, dead and dying. There were many who were blind and deaf and, poking in all directions, could not make out anything in the chaos that reigned around them.
The unfortunate people, who were located at a distance of up to 800 m from the epicenter, literally burned out in a split second - their insides evaporated and their bodies turned into lumps of smoking coals. Those located at a distance of 1 km from the epicenter were affected by radiation sickness in an extremely severe form. Within a few hours, they began to vomit violently, their temperature jumped to 39-40 degrees, and they began to experience shortness of breath and bleeding. Then non-healing ulcers appeared on the skin, the composition of the blood changed dramatically, and hair fell out. After terrible suffering, usually on the second or third day, death occurred.
In total, about 240 thousand people died from the explosion and radiation sickness. About 160 thousand received radiation sickness in a milder form - their painful death was delayed by several months or years. When news of the disaster spread throughout the country, all of Japan was paralyzed with fear. It increased further after Major Sweeney's Box Car dropped a second bomb on Nagasaki on August 9. Several hundred thousand inhabitants were also killed and injured here. Unable to resist the new weapons, the Japanese government capitulated - the atomic bomb ended World War II.
War is over. It lasted only six years, but managed to change the world and people almost beyond recognition.
Human civilization before 1939 and human civilization after 1945 are strikingly different from each other. There are many reasons for this, but one of the most important is the emergence of nuclear weapons. It can be said without exaggeration that the shadow of Hiroshima lies over the entire second half of the 20th century. It became a deep moral burn for many millions of people, both contemporaries of this catastrophe and those born decades after it. Modern man can no longer think about the world the way they thought about it before August 6, 1945 - he understands too clearly that this world can turn into nothing in a few moments.
Modern man cannot look at war the way his grandfathers and great-grandfathers did - he knows for certain that this war will be the last, and there will be neither winners nor losers in it. Nuclear weapons have left their mark on all areas public life, and modern civilization cannot live by the same laws as sixty or eighty years ago. No one understood this better than the creators of the atomic bomb themselves.
"People of our planet , wrote Robert Oppenheimer, must unite. Terror and destruction sown the last war, dictate this thought to us. The explosions of atomic bombs proved it with all cruelty. Other people at other times have already said similar words - only about other weapons and about other wars. They weren't successful. But anyone who today would say that these words are useless is misled by the vicissitudes of history. We cannot be convinced of this. The results of our work leave humanity no choice but to create a united world. A world based on legality and humanity."