How do nuclear weapons work? How do nuclear weapons work?

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 indistinguishable either in appearance or chemically, they are separated by a chasm in the properties of their 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 higher 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 (at a correspondingly higher or lower 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 that saves the greatest number of 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 maintain the noble shape of the ball during an explosion - for this, the layer of explosive must be detonated simultaneously along its entire outer surface, compressing 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 through the fission they produce to the substance of the assembly, 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 lower, 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 change 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: there is almost no substance left on the inside, 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 substance — 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 of transferring the energy of the fireball to the 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 also possible, when both mechanisms are effective.

The process captures new layers of air; 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 increases sharply (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 evaporates, further away it melts, but even further, where the heat flow is no longer sufficient to melt solids, soil, rocks, houses flow like liquid, under a monstrous pressure of gas that destroys all strong bonds, heated to the point of unbearable for the eyes radiance.

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 extreme 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 have been 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 duration of the pulse formed by the tube) 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 of a nuclear strike must be indicated, no one disassembles the charge in order 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.

Explosive character

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.

Critical assembly

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 fissioning, 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 Pu239 ball 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.

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 an explosion - for this, the layer of explosive must be detonated simultaneously along its entire outer surface, compressing 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.

Explosion within

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 lower, 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, electrons stripped from them 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

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: there is almost no substance left on the inside, 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 substance - more than 150,000 atm! The shell is not destined to become too thin; it bursts, forming “blisters”.

Shock wave and atomic mushroom

Near the explosion, everything around evaporates, further away it melts, but even further, where the heat flow is no longer sufficient to melt solids, the soil, rocks, houses flow like liquid, under a monstrous pressure of gas that destroys all strong bonds, heated to the point of unbearable for the eyes radiance.

Neutron initiation

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 (in the first American product less than a million neutrons were generated per microsecond), and polonium is very perishable - in just 138 days it reduces its activity by half. Therefore, isotopes have been replaced by less dangerous ones (which do not emit when not turned on), and most importantly, by neutron tubes that emit more intensely (see sidebar): in a few microseconds (the duration of the pulse formed by the tube) 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.

Nuclear misconceptions

The density of plutonium at the moment of explosion increases due to a phase transition

Metallic plutonium exists in six phases, the density of which ranges from 14.7 to 19.8 g/cm3. At temperatures below 119 °C there is a monoclinic alpha phase (19.8 g/cm3), 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 try to preserve 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, there will be no explosion - the workpiece will simply heat up, but nickel plating may be released (and plutonium is very toxic).

Neutron source

The first nuclear bombs used a beryllium-polonium neutron source. Modern charges use much more convenient neutron tubes

In a vacuum neutron tube, a pulse voltage of 100 kV is applied between the tritium-saturated target (cathode) (1) and the 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 that this was fusion, 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.

Neutrons - slow and fast

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 25 mm thick layer of beryllium, 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 rupture it - but this will be a thermal explosion, devoid of all the typical “nuclear” signs).

Video: Nuclear explosions

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Hundreds of thousands of famous and forgotten gunsmiths of antiquity fought in search of the ideal weapon, capable of evaporating an enemy army with one click. From time to time, traces of these searches can be found in fairy tales that more or less plausibly describe a miracle sword or a bow that hits without missing.

Fortunately, technological progress moved so slowly for a long time that the real embodiment of the devastating weapon remained in dreams and oral stories, and later on the pages of books. The scientific and technological leap of the 19th century provided the conditions for the creation of the main phobia of the 20th century. The nuclear bomb, created and tested under real conditions, revolutionized both military affairs and politics.

History of the creation of weapons

For a long time it was believed that the most powerful weapons could only be created using explosives. The discoveries of scientists working with the smallest particles provided scientific evidence that enormous energy can be generated with the help of elementary particles. The first in a series of researchers can be called Becquerel, who in 1896 discovered the radioactivity of uranium salts.

Uranium itself has been known since 1786, but at that time no one suspected its radioactivity. The work of scientists at the turn of the 19th and 20th centuries revealed not only special physical properties, but also the possibility of obtaining energy from radioactive substances.

The option of making weapons based on uranium was first described in detail, published and patented by French physicists, the Joliot-Curies in 1939.

Despite its value for weapons, the scientists themselves were resolutely against the creation of such a devastating weapon.

Having gone through the Second World War in the Resistance, in the 1950s the couple (Frederick and Irene), realizing the destructive power of war, advocated for general disarmament. They are supported by Niels Bohr, Albert Einstein and other prominent physicists of the time.

Meanwhile, while the Joliot-Curies were busy with the problem of the Nazis in Paris, on the other side of the planet, in America, the world's first nuclear charge was being developed. Robert Oppenheimer, who led the work, was given the broadest powers and enormous resources. The end of 1941 marked the beginning of the Manhattan Project, which ultimately led to the creation of the first combat nuclear warhead.

In the town of Los Alamos, New Mexico, the first production facilities for weapons-grade uranium were erected. Subsequently, similar nuclear centers appeared throughout the country, for example in Chicago, in Oak Ridge, Tennessee, and research was carried out in California. The best forces of the professors of American universities, as well as physicists who fled from Germany, were thrown into creating the bomb.

In the “Third Reich” itself, work on creating a new type of weapon was launched in a manner characteristic of the Fuhrer.

Since “Besnovaty” was more interested in tanks and planes, and the more the better, he did not see much need for a new miracle bomb.

Accordingly, projects not supported by Hitler moved at a snail's pace at best.

When things started to get hot, and it turned out that the tanks and planes were swallowed up by the Eastern Front, the new miracle weapon received support. But it was too late; in conditions of bombing and constant fear of Soviet tank wedges, it was not possible to create a device with a nuclear component.

The Soviet Union was more attentive to the possibility of creating a new type of destructive weapon. In the pre-war period, physicists collected and consolidated general knowledge about nuclear energy and the possibility of creating nuclear weapons. Intelligence worked intensively throughout the entire period of the creation of the nuclear bomb both in the USSR and in the USA. The war played a significant role in slowing down the pace of development, as huge resources went to the front.

True, Academician Igor Vasilyevich Kurchatov, with his characteristic tenacity, promoted the work of all subordinate departments in this direction. Looking ahead a little, it is he who will be tasked with accelerating the development of weapons in the face of the threat of an American strike on the cities of the USSR. It was he, standing in the gravel of a huge machine of hundreds and thousands of scientists and workers, who would be awarded the honorary title of the father of the Soviet nuclear bomb.

World's first tests

But let's return to the American nuclear program. By the summer of 1945, American scientists managed to create the world's first nuclear bomb. Any boy who has made himself or bought a powerful firecracker in a store experiences extraordinary torment, wanting to blow it up as quickly as possible. In 1945, hundreds of American soldiers and scientists experienced the same thing.

On June 16, 1945, the first ever nuclear weapons test and one of the most powerful explosions to date took place in the Alamogordo Desert, New Mexico.

Eyewitnesses watching the explosion from the bunker were amazed by the force with which the charge exploded at the top of the 30-meter steel tower. At first, everything was flooded with light, several times stronger than the sun. Then a fireball rose into the sky, turning into a column of smoke that took shape into the famous mushroom.

As soon as the dust settled, researchers and bomb creators rushed to the site of the explosion. They watched the aftermath from lead-encrusted Sherman tanks. What they saw amazed them; no weapon could cause such damage. The sand melted to glass in some places.

Tiny remains of the tower were also found; in a crater of huge diameter, mutilated and crushed structures clearly illustrated the destructive power.

Damaging factors

This explosion provided the first information about the power of the new weapon, about what it could use to destroy the enemy. These are several factors:

light radiation, flash, capable of blinding even protected organs of vision;
shock wave, a dense stream of air moving from the center, destroying most buildings;
an electromagnetic pulse that disables most equipment and does not allow the use of communications for the first time after the explosion;
penetrating radiation, the most dangerous factor for those who have taken refuge from other damaging factors, is divided into alpha-beta-gamma irradiation;
radioactive contamination that can negatively affect health and life for tens or even hundreds of years.

The further use of nuclear weapons, including in combat, showed all the peculiarities of their impact on living organisms and nature. August 6, 1945 was the last day for tens of thousands of residents of the small city of Hiroshima, then known for several important military installations.

The outcome of the war in the Pacific was a foregone conclusion, but the Pentagon believed that the operation on the Japanese archipelago would cost more than a million lives of US Marines. It was decided to kill several birds with one stone, take Japan out of the war, saving on the landing operation, test a new weapon and announce it to the whole world, and, above all, to the USSR.

At one o'clock in the morning, the plane carrying the "Baby" nuclear bomb took off on a mission.

The bomb, dropped over the city, exploded at an altitude of approximately 600 meters at 8.15 am. All buildings located at a distance of 800 meters from the epicenter were destroyed. The walls of only a few buildings, designed to withstand a magnitude 9 earthquake, survived.

Of every ten people who were within a radius of 600 meters at the time of the bomb explosion, only one could survive. The light radiation turned people into coal, leaving shadow marks on the stone, a dark imprint of the place where the person was. The ensuing blast wave was so strong that it could break glass at a distance of 19 kilometers from the explosion site.

One teenager was knocked out of the house through a window by a dense stream of air; upon landing, the guy saw the walls of the house folding like cards. The blast wave was followed by a fire tornado, destroying those few residents who survived the explosion and did not have time to leave the fire zone. Those at a distance from the explosion began to experience severe malaise, the cause of which was initially unclear to doctors.

Much later, a few weeks later, the term “radiation poisoning” was announced, now known as radiation sickness.

More than 280 thousand people became victims of just one bomb, both directly from the explosion and from subsequent illnesses.

The bombing of Japan with nuclear weapons did not end there. According to the plan, only four to six cities were to be hit, but weather conditions only allowed Nagasaki to be hit. In this city, more than 150 thousand people became victims of the Fat Man bomb.

Promises by the American government to carry out such attacks until Japan surrendered led to an armistice and then to the signing of an agreement that ended World War II. But for nuclear weapons this was just the beginning.

The most powerful bomb in the world

The post-war period was marked by the confrontation between the USSR bloc and its allies with the USA and NATO. In the 1940s, the Americans seriously considered the possibility of striking the Soviet Union. To contain the former ally, work on creating a bomb had to be accelerated, and already in 1949, on August 29, the US monopoly in nuclear weapons was ended. During the arms race, two nuclear tests deserve the most attention.

Bikini Atoll, known primarily for frivolous swimsuits, literally made a splash throughout the world in 1954 due to the testing of a specially powerful nuclear charge.

The Americans, having decided to test a new design of atomic weapons, did not calculate the charge. As a result, the explosion was 2.5 times more powerful than planned. Residents of nearby islands, as well as the ubiquitous Japanese fishermen, were under attack.

But it was not the most powerful American bomb. In 1960, the B41 nuclear bomb was put into service, but it never underwent full testing due to its power. The force of the charge was calculated theoretically, for fear of exploding such a dangerous weapon at the test site.

The Soviet Union, which loved to be the first in everything, experienced in 1961, otherwise nicknamed “Kuzka’s mother.”

Responding to America's nuclear blackmail, Soviet scientists created the most powerful bomb in the world. Tested on Novaya Zemlya, it left its mark in almost all corners of the globe. According to recollections, a slight earthquake was felt in the most remote corners at the time of the explosion.

The blast wave, of course, having lost all its destructive power, was able to circle the Earth. To date, this is the most powerful nuclear bomb in the world created and tested by mankind. Of course, if his hands were free, Kim Jong-un's nuclear bomb would be more powerful, but he does not have New Earth to test it.

Atomic bomb device

Let's consider a very primitive, purely for understanding, device of an atomic bomb. There are many classes of atomic bombs, but let’s consider three main ones:

uranium, based on uranium 235, first exploded over Hiroshima;
plutonium, based on plutonium 239, first exploded over Nagasaki;
thermonuclear, sometimes called hydrogen, based on heavy water with deuterium and tritium, fortunately not used against the population.

The first two bombs are based on the effect of heavy nuclei fissioning into smaller ones through an uncontrolled nuclear reaction, releasing huge amounts of energy. The third is based on the fusion of hydrogen nuclei (or rather its isotopes of deuterium and tritium) with the formation of helium, which is heavier in relation to hydrogen. For the same bomb weight, the destructive potential of a hydrogen bomb is 20 times greater.

If for uranium and plutonium it is enough to bring together a mass greater than the critical one (at which a chain reaction begins), then for hydrogen this is not enough.

To reliably connect several pieces of uranium into one, a cannon effect is used in which smaller pieces of uranium are shot into larger ones. Gunpowder can also be used, but for reliability, low-power explosives are used.

In a plutonium bomb, to create the necessary conditions for a chain reaction, explosives are placed around ingots containing plutonium. Due to the cumulative effect, as well as the neutron initiator located at the very center (beryllium with several milligrams of polonium), the necessary conditions are achieved.

It has a main charge, which cannot explode on its own, and a fuse. To create conditions for the fusion of deuterium and tritium nuclei, we need unimaginable pressures and temperatures at at least one point. Next, a chain reaction will occur.

To create such parameters, the bomb includes a conventional, but low-power, nuclear charge, which is the fuse. Its detonation creates the conditions for the start of a thermonuclear reaction.

To estimate the power of an atomic bomb, the so-called “TNT equivalent” is used. An explosion is a release of energy, the most famous explosive in the world is TNT (TNT - trinitrotoluene), and all new types of explosives are equated to it. Bomb "Baby" - 13 kilotons of TNT. That is equivalent to 13000.

Bomb "Fat Man" - 21 kilotons, "Tsar Bomba" - 58 megatons of TNT. It’s scary to think of 58 million tons of explosives concentrated in a mass of 26.5 tons, that’s how much weight this bomb has.

The danger of nuclear war and nuclear disasters

Appearing in the midst of the worst war of the twentieth century, nuclear weapons became the greatest danger to humanity. Immediately after World War II, the Cold War began, which several times almost escalated into a full-fledged nuclear conflict. The threat of the use of nuclear bombs and missiles by at least one side began to be discussed back in the 1950s.

Everyone understood and understands that there can be no winners in this war.

To contain it, efforts have been and are being made by many scientists and politicians. The University of Chicago, using the input of visiting nuclear scientists, including Nobel laureates, sets the Doomsday Clock a few minutes before midnight. Midnight signifies a nuclear cataclysm, the beginning of a new World War and the destruction of the old world. Over the years, the clock hands fluctuated from 17 to 2 minutes to midnight.

There are also several known major accidents that occurred at nuclear power plants. These disasters have an indirect relation to weapons; nuclear power plants are still different from nuclear bombs, but they perfectly demonstrate the results of using the atom for military purposes. The largest of them:

1957, Kyshtym accident, due to a failure in the storage system, an explosion occurred near Kyshtym;
1957, Britain, in the north-west of England, security checks were not carried out;
1979, USA, due to an untimely detected leak, an explosion and release from a nuclear power plant occurred;
1986, tragedy in Chernobyl, explosion of the 4th power unit;
2011, accident at the Fukushima station, Japan.

Each of these tragedies left a heavy mark on the fate of hundreds of thousands of people and turned entire areas into non-residential zones with special control.

There were incidents that almost cost the start of a nuclear disaster. Soviet nuclear submarines have repeatedly had reactor-related accidents on board. The Americans dropped a Superfortress bomber with two Mark 39 nuclear bombs on board, with a yield of 3.8 megatons. But the activated “safety system” did not allow the charges to detonate and a disaster was avoided.

Nuclear weapons past and present

Today it is clear to anyone that a nuclear war will destroy modern humanity. Meanwhile, the desire to possess nuclear weapons and enter the nuclear club, or rather, burst into it by knocking down the door, still excites the minds of some state leaders.

India and Pakistan created nuclear weapons without permission, and the Israelis are hiding the presence of a bomb.

For some, owning a nuclear bomb is a way to prove their importance on the international stage. For others, it is a guarantee of non-interference by winged democracy or other external factors. But the main thing is that these reserves do not go into business, for which they were really created.

Video

The nuclear reactor works smoothly and efficiently. Otherwise, as you know, there will be trouble. But what's going on inside? Let's try to formulate the principle of operation of a nuclear (nuclear) reactor briefly, clearly, with stops.

In essence, the same process is happening there as during a nuclear explosion. Only the explosion happens very quickly, but in the reactor all this stretches out for a long time. As a result, everything remains safe and sound, and we receive energy. Not so much that everything around would be destroyed at once, but quite sufficient to provide electricity to the city.

Before you understand how a controlled nuclear reaction occurs, you need to know what it is nuclear reaction at all.

Nuclear reaction is the process of transformation (fission) of atomic nuclei when they interact with elementary particles and gamma rays.

Nuclear reactions can occur with both absorption and release of energy. The reactor uses the second reactions.

Nuclear reactor is a device whose purpose is to maintain a controlled nuclear reaction with the release of energy.

Often a nuclear reactor is also called an atomic reactor. Let us note that there is no fundamental difference here, but from the point of view of science it is more correct to use the word “nuclear”. There are now many types of nuclear reactors. These are huge industrial reactors designed to generate energy in power plants, nuclear reactors of submarines, small experimental reactors used in scientific experiments. There are even reactors used to desalinate seawater.

The history of the creation of a nuclear reactor

The first nuclear reactor was launched in the not-so-distant 1942. This happened in the USA under the leadership of Fermi. This reactor was called the "Chicago Woodpile".

In 1946, the first Soviet reactor, launched under the leadership of Kurchatov, began operating. The body of this reactor was a ball of seven meters in diameter. The first reactors did not have a cooling system, and their power was minimal. By the way, the Soviet reactor had an average power of 20 Watts, and the American one - only 1 Watt. For comparison, the average power of modern power reactors is 5 Gigawatts. Less than ten years after the launch of the first reactor, the world's first industrial nuclear power plant was opened in the city of Obninsk.

The principle of operation of a nuclear (nuclear) reactor

Any nuclear reactor has several parts: core With fuel And moderator , neutron reflector , coolant , control and protection system . Isotopes are most often used as fuel in reactors. uranium (235, 238, 233), plutonium (239) and thorium (232). The core is a boiler through which ordinary water (coolant) flows. Among other coolants, “heavy water” and liquid graphite are less commonly used. If we talk about the operation of nuclear power plants, then a nuclear reactor is used to produce heat. Electricity itself is generated using the same method as in other types of power plants - steam rotates a turbine, and the energy of movement is converted into electrical energy.

Below is a diagram of the operation of a nuclear reactor.

As we have already said, the decay of a heavy uranium nucleus produces lighter elements and several neutrons. The resulting neutrons collide with other nuclei, also causing them to fission. At the same time, the number of neutrons grows like an avalanche.

It should be mentioned here neutron multiplication factor . So, if this coefficient exceeds a value equal to one, a nuclear explosion occurs. If the value is less than one, there are too few neutrons and the reaction dies out. But if you maintain the value of the coefficient equal to one, the reaction will proceed long and stably.

The question is how to do this? In the reactor, the fuel is in the so-called fuel elements (TVELakh). These are rods that contain, in the form of small tablets, nuclear fuel . Fuel rods are connected into hexagonal-shaped cassettes, of which there can be hundreds in a reactor. Cassettes with fuel rods are arranged vertically, and each fuel rod has a system that allows you to regulate the depth of its immersion into the core. In addition to the cassettes themselves, they include control rods And emergency protection rods . The rods are made of a material that absorbs neutrons well. Thus, control rods can be lowered to different depths in the core, thereby adjusting the neutron multiplication factor. Emergency rods are designed to shut down the reactor in case of an emergency.

How is a nuclear reactor started?

We have figured out the operating principle itself, but how to start and make the reactor function? Roughly speaking, here it is - a piece of uranium, but the chain reaction does not begin in it on its own. The fact is that in nuclear physics there is a concept critical mass .

Critical mass is the mass of fissile material required to start a nuclear chain reaction.

With the help of fuel rods and control rods, a critical mass of nuclear fuel is first created in the reactor, and then the reactor is brought to the optimal power level in several stages.

In this article, we tried to give you a general idea of the structure and operating principle of a nuclear (nuclear) reactor. If you have any questions on the topic or have been asked a problem in nuclear physics at the university, please contact to the specialists of our company. As usual, we are ready to help you resolve any pressing issue regarding your studies. And while we're at it, here's another educational video for your attention!

It is one of the most amazing, mysterious and terrible processes. The principle of operation of nuclear weapons is based on a chain reaction. This is a process whose very progress initiates its continuation. The principle of operation of a hydrogen bomb is based on fusion.

Atomic bomb

The nuclei of some isotopes of radioactive elements (plutonium, californium, uranium and others) are capable of decaying, while capturing a neutron. After this, two or three more neutrons are released. The destruction of the nucleus of one atom under ideal conditions can lead to the decay of two or three more, which, in turn, can initiate other atoms. And so on. An avalanche-like process of destruction of an increasing number of nuclei occurs, releasing a gigantic amount of energy for breaking atomic bonds. During an explosion, enormous energies are released in an extremely short period of time. This happens at one point. This is why the explosion of an atomic bomb is so powerful and destructive.

To initiate a chain reaction, the amount of radioactive substance must exceed a critical mass. Obviously, you need to take several parts of uranium or plutonium and combine them into one. However, this is not enough to cause an atomic bomb to explode, because the reaction will stop before enough energy is released, or the process will proceed slowly. In order to achieve success, it is necessary not only to exceed the critical mass of the substance, but to do this in an extremely short period of time. It is best to use several. This is achieved by using others, and alternating fast and slow explosives.

The first nuclear test was carried out in July 1945 in the USA near the town of Almogordo. In August of the same year, the Americans used these weapons against Hiroshima and Nagasaki. The explosion of an atomic bomb in the city led to terrible destruction and the death of most of the population. In the USSR, atomic weapons were created and tested in 1949.

H-bomb

It is a weapon with very great destructive power. The principle of its operation is based on the synthesis of heavier helium nuclei from lighter hydrogen atoms. This releases a very large amount of energy. This reaction is similar to the processes that occur on the Sun and other stars. Thermonuclear fusion occurs most easily using isotopes of hydrogen (tritium, deuterium) and lithium.

The Americans tested the first hydrogen warhead in 1952. In the modern understanding, this device can hardly be called a bomb. It was a three-story building filled with liquid deuterium. The first hydrogen bomb explosion in the USSR was carried out six months later. The Soviet thermonuclear munition RDS-6 was detonated in August 1953 near Semipalatinsk. The USSR tested the largest hydrogen bomb with a yield of 50 megatons (Tsar Bomba) in 1961. The wave after the explosion of the ammunition circled the planet three times.