60 years ago - on August 29, 1949 - the first Soviet atomic bomb RDS-1 with a declared yield of 20 kt was successfully tested at the Semipalatinsk test site. Thanks to this event, strategic military parity between the USSR and the United States was allegedly established in the world. And a hypothetical war with catastrophic consequences for the Soviet Union was realized in its cold state of aggregation.
In the footsteps of the Manhattan project
The Soviet Union (as, indeed, Germany) had every reason to become a leader in the nuclear race. This did not happen because of the great role that science played in the ideology of the new government. The leadership of the Communist Party, following the precepts of the immortal labor "Materialism and Empirio-Criticism", anxiously watched the flourishing of "physical idealism". In the 1930s, Stalin was inclined to trust not those physicists who argued that with the help of a certain chain reaction in isotopes of heavy elements it was possible to release enormous energy, but those who defended materialistic principles in science.
True, Soviet physicists started talking about the possibilities of military use of the energy of the atomic nucleus only in 1941. Georgy Nikolaevich Flerov (1913-1990), who before the war in the laboratory of Igor Vasilyevich Kurchatov (1903-1960) worked on the problem of the chain reaction of uranium fission, and then served as a lieutenant in the Air Force, twice sent letters to Stalin in which he regretted “a big mistake "And" voluntary surrender of the positions won before the war in research in nuclear physics. " But - in vain.
Only in September 1942, when intelligence became aware of the deployment of the American Manhattan Project, led by Robert Oppenheimer (1904-1967), which grew out of the activities of the Anglo-American Uranium Commission, Stalin signed a decree "On the organization of work on uranium." … It ordered the USSR Academy of Sciences "to resume work on studying the feasibility of using atomic energy by fission of uranium and to submit to the State Defense Committee by April 1, 1943, a report on the possibility of creating a uranium bomb or uranium fuel."
In mid-April 1943 in Moscow, in Pokrovsky-Streshnev, Laboratory No. 2 was created, which included the country's largest physicists. Kurchatov headed the laboratory, and the general management of the "uranium work" was initially assigned to Molotov, but then Beria replaced him in this function.
It is quite understandable that the resources of the Soviet Union were incomparable with the capabilities that the States, not too burdened by the war, possessed. However, this is hardly the only explanation for the huge gap in the scale of development carried out at Los Alamos and Moscow. 12 Nobel laureates from the USA and Europe, 15 thousand scientists, engineers and technicians, 45 thousand workers, 4 thousand stenographers, typists and secretaries, one thousand security personnel who ensured the regime of extreme secrecy took part in the Manhattan project. Laboratory No. 2 has 80 people, of which only twenty-five were research workers.
By the end of the war, work practically did not get off the ground: in Laboratory No. 2, as well as in Laboratories No. 3 and No. 4 opened in early 1945, methods were being sought for obtaining plutonium at reactors of various operating principles. That is, they were engaged in scientific, not experimental and design developments.
The atomic bombings of Hiroshima and Nagasaki actually opened the eyes of the USSR government to the level of the threat hanging over the country. And then a special committee was created, headed by Beria, which received emergency powers and unlimited funding. Sluggish research work has been replaced by an energetic innovative leap forward. In 1946, at the uranium-graphite reactor launched in the Kurchatov laboratory, they began to obtain plutonium-239 by bombarding uranium with slow neutrons. In the Urals, in particular in Chelyabinsk-40, several enterprises were created for the production of weapons-grade uranium and plutonium, as well as chemical components necessary to create a bomb.
In Sarov, near Arzamas, a branch of Laboratory No. 2 began to be created, called KB-11, he was entrusted with the development of the design of the bomb and its testing no later than the spring of 1948. And in the beginning it was necessary to make a plutonium bomb. This choice was predetermined by the fact that in Laboratory No. 2 there was a detailed diagram of the American plutonium bomb "Fat Man" dropped on Nagasaki, which was handed over to Soviet intelligence by the German physicist Claus Foocks (1911-1988) who took part in its development, who adhered to communist views. The Soviet leadership was in a hurry in the face of tense relations with the United States and wanted to get a guaranteed positive result. In this connection, the scientific leader of the project, Kurchatov, had no choice.
Uranium or Plutonium?
The classical scheme of a nuclear chain reaction in the isotope of uranium 235U is an exponential function of time with base 2. A neutron, colliding with the nucleus of one of the atoms, splits it into two fragments. This releases two neutrons. They, in turn, split already two uranium nuclei. At the next stage, twice as many fissions occur - 4. Then - 8. And so on, incrementally, until, again, relatively speaking, all matter consists of fragments of two types, the atomic masses of which are approximately 95/140. As a result, huge thermal energy is released, 90% of which comes from the kinetic energy of the flying fragments (each fragment accounts for 167 MeV).
But for the reaction to proceed in this way, it is necessary that not a single neutron was wasted. In a small volume of "fuel", neutrons released in the process of fission of nuclei fly out of it, without having time to react with uranium nuclei. The likelihood of the occurrence of a reaction also depends on the concentration of the 235U isotope in the "fuel", which consists of 235U and 238U. Since 238U absorbs fast neutrons that do not take part in the fission reaction. Natural uranium contains 0.714% 235U, enriched, weapons grade, it must be at least 80%.
Similarly, albeit with its own specifics, the reaction proceeds in the plutonium isotope 239Pu
From a technical point of view, it was easier to create a uranium bomb than a plutonium one. True, it required an order of magnitude more uranium: the critical mass of uranium-235, in which the chain reaction takes place, is 50 kg, and for plutonium-239 it is 5.6 kg. At the same time, obtaining weapons-grade plutonium by bombarding uranium-238 in a reactor is no less laborious than separating the uranium-235 isotope from uranium ore in centrifuges. Both of these tasks required at least 200 tons of uranium ore. And their solution required the maximum investment of both financial and production resources in relation to the entire cost of the Soviet nuclear project. As for human resources, the Soviet Union over time surpassed the United States many times over: in the end, 700 thousand people, mostly prisoners, were involved in the creation of the bomb.
"Kid" or "Fat Man"?
The uranium bomb dropped by the Americans on Hiroshima and dubbed "Kid" was collected in a barrel borrowed from a 75-millimeter anti-aircraft gun bored to the required diameter. There were laid six uranium cylinders connected in series with each other with a total mass of 25.6 kg. The length of the projectile was 16 cm, the diameter was 10 cm. At the end of the barrel there was a target - a hollow uranium cylinder with a mass of 38, 46 kg. Its outer diameter and length were 16 cm. To increase the power of the bomb, the target was mounted in a neutron reflector made of tungsten carbide, which made it possible to achieve a more complete "combustion" of uranium participating in the chain reaction.
The bomb had a diameter of 60 cm, a length of more than two meters and weighed 2300 kg. Its operation was carried out by igniting a powder charge, which drove the uranium cylinders along a two-meter barrel at a speed of 300 m / s. At the same time, the boron protective shells were destroyed. At the "end of the path" the projectile entered the target, the sum of the two halves exceeded the critical mass, and an explosion occurred.
The drawing of the atomic bomb, which appeared in 1953 at the trial in the case of the Rosenberg spouses, accused of atomic espionage in favor of the USSR. Interestingly, the drawing was secret and was not shown to either the judge or the jury. The drawing was only declassified in 1966. Photo: Department of Justice. Office of the U. S. Attorney for the Southern Judicial District of New York
The military, who were entrusted with the combat use of the "Malysh", feared that, if handled carelessly, any blow could lead to detonation of the fuse. Therefore, the gunpowder was loaded into the bomb only after the plane took off.
The device of the Soviet plutonium bomb, with the exception of its dimensions, fitted to the bomb bay of the Tu-4 heavy bomber, and the triggering equipment when the atmospheric pressure of a given value was reached, exactly repeated the "stuffing" of another American bomb - "Fat Man".
The cannon method of bringing two pieces of semi-critical mass closer to one another is not suitable for plutonium, since this substance has a significantly higher neutron background. And when the pieces are brought together at a speed attainable with the blasting pusher, before the start of a chain reaction due to strong heating, melting and evaporation of plutonium should occur. And this should inevitably lead to mechanical destruction of the structure and the release of unreacted substance into the atmosphere.
Therefore, in the Soviet bomb, as in the American one, the method of dynamic compression of a piece of plutonium by a spherical shock wave was applied. The wave speed reaches 5 km / s, due to which the density of the substance increases by 2, 5 times.
The hardest part of an implosion bomb is to create a system of explosive lenses, visually resembling the geometry of a soccer ball, which direct energy strictly to the center of a piece of plutonium, the size of a chicken egg, and squeeze it symmetrically with an error of less than one percent. Moreover, each such lens, made of an alloy of TNT and RDX with the addition of wax, had two types of fragments - fast and slow. When, in 1946, one of the participants in the Manhattan Project was asked about the prospects for creating a Soviet bomb, he replied that it would appear no earlier than 10 years later. And only because the Russians will struggle for a long time over the problem of ideal symmetry of implosion.
Soviet "Fat Man"
The Soviet bomb RDS-1 had a length of 330 cm, a diameter of 150 cm and weighed 4,700 kg. Concentrically nested spheres were placed inside the drop-shaped body with a classic X-shaped stabilizer.
In the center of the entire structure was a "neutron fuse", which was a beryllium ball, inside which there was a polonium-210 neutron source shielded by a beryllium shell. When the shock wave reached the fuse, beryllium and polonium were mixed, and neutrons "igniting" a chain reaction were released into plutonium.
Next came two 10-centimeter hemispheres of plutonium-239 in a state with a reduced density. This made plutonium easier to process, and the required final density was the result of implosion. The distance of 0.1 mm between the hemispheres was filled with a layer of gold, which prevented the premature penetration of the shock wave into the neutron fuse.
The function of a neutron reflector was performed by a layer of natural uranium 7 cm thick and weighing 120 kg. A fission reaction took place in it with the release of neutrons, which partially returned to the piece of plutonium. Uranium-238 gave 20% of the bomb's power.
The "pusher" layer, which is a sphere of aluminum 11.5 cm thick and weighing 120 kg, was intended to dampen the Taylor wave, which leads to a sharp drop in pressure behind the detonation front.
The structure was surrounded by an explosive shell 47 cm thick and weighing 2500 kg, which consisted of a complex system of explosive lenses focused towards the center of the system. 12 lenses were pentagonal, 20 were hexagonal. Each lens consisted of alternating sections of fast-detonating and slow explosives, which had a different chemical formula.
The bomb had two autonomous detonation systems - from hitting the ground and when the atmospheric pressure reached a predetermined value (high-altitude fuse).
Five RDS-1 bombs were manufactured. The first of them was blown up at a landfill near Semipalatinsk in a ground position. The power of the explosion was officially recorded at 20 kt, but over time it turned out that this was too high an estimate. Real - at half the level. By that time, the Americans already had 20 such bombs, and any claims for parity were groundless. But the monopoly was broken.
Four more of these bombs have never been lifted into the air. The RDS-3, an original Soviet development, was put into service. This bomb, with its smaller dimensions and weight, had a yield of 41 kt. This became possible, in particular, due to the enhancement of the fission reaction of plutonium by the thermonuclear reaction of fusion of deuterium and tritium.
