Deuterium and tritium allotropic modifications. Tritium - what is it? Mass of tritium
I think that those children who are just learning to crawl today will reach a reasonable age to admiringly watch broadcasts from the first ITER launches. And today we will talk about the fuel that is required for thermonuclear reactors, the futuristic future of Russia and our lunar program.
What is the connection? Let's figure it out.
Let's remember
A fusion reaction takes place in a thermonuclear reactor, i.e. As a result of heating, light atomic nuclei are accelerated and combined into a heavier nucleus of an atom. During the connection, a sea of \u200b\u200benergy is released, for the sake of which everything is started.
There are many difficulties in the task of designing a thermonuclear reactor, but they are being solved. In France, the joint efforts of several countries, including Russia, have already started the construction of the ITER mentioned. But I already wrote about it.
One of the difficulties of industrial launch of a thermonuclear reactor is fuel. It is planned to use various options.
Deuterium + tritium
This is the easiest option in terms of ensuring the reaction proceeds. Deuterium is heavy hydrogen. Getting it is not a problem. There are tens of billions of tons of it in water alone.We take water. We get heavy water from it, and then deuterium. Its production on earth at the moment is tens of thousands of tons per year. We can do it.
Tritium is more difficult. Tritium is superheavy hydrogen. It is formed in the high layers of the atmosphere when particles of cosmic radiation collide with the nuclei of atoms. As you understand, there is not much of it at all, and it is not possible to catch it at a height.
Therefore, tritium is produced on earth in nuclear reactors. Imagine, in total from 1955 to 1999, for example, in the USA, 225 kg were received.
Our reactors are also able to do this. One kilogram of this joy costs almost 2 billion rubles.Great investment? Yes, it was not there.
The problem here is that the half-life of tritium is -12-plus years. This means that after 12 years from 1 kg. tritium will remain only half a kilo. Not the best way to keep your money.Only one launch of ITER will require 3 kg. To start the next generation fusion reactor DEMO - 4-10 kg. And in the world now there are only 18 kg. this goodness. Yes, and I hasten to please: working fusion reactor with a power plant that produces gigawatts of electricity, will consume 56 kg (!) of tritium for each same gigawatt * year. Where can you get so many? Yes, thermonuclear energy is not cheap.
elegant solution
Already the DEMO thermonuclear plant will have to produce tritium for its needs on its own and even more for other reactors. Actually, this is one of the purposes of DEMO - to prove that the reactor can provide itself with tritium and produce a surplus. How so?
During thermonuclear fusion, a helium nucleus and a high-energy neutron are obtained from deuterium and tritium. This very neutron, rushing faster than the wind, must leave the electromagnetic chamber and hit a meter-long shell of lithium. When a neutron and a lithium nucleus collide, tritium will appear.
Well, we never had any problems with lithium. Anyone interested in how it is mined can look.
Well, what if it doesn't?
If tritium cannot be produced in large quantities, than the station itself needs it? What if the output is very small?A thermonuclear station is not a magic wand: one was built and that's it, the problem of energy consumption is solved. They will need to be built a lot all over the planet.
However, if you are not fed up with tritium alone, you can use helium-3 instead.
Deuterium + helium-3
Extremely difficult, at the limit of the possible reaction. And all because of the unimaginably high plasma temperatures that must be achieved. But who said it would be easy?
At the output, when connecting atoms of deuterium and Helium 3, helium 4, a proton and 18.4 MeV are obtained.
We have sorted out the issue with deuterium. But with Helium 3 problems.In nature, he is in a mantle, he has been lying around there since the creation of the earth. It enters the atmosphere through volcanoes and all sorts of faults.So far, we are not able to extract anything from the mantle, and there is so little Helium 3 in the atmosphere that this is a disastrous task.We have to get it artificially, for example, during the decay of tritium.
And then tritium?! Yes, no, if this was the only option, Helium 3 would not cost 65 thousand rubles per liter.There is another option to bombard lithium with alpha particles.
But in any case, the matter is quite costly and complicated, and this we are talking about kilograms, not to mention industrial production.
Where to get Helium-3?
Ours are now launching a satellite for mapping the lunar surface.
under construction spaceship to fly into Earth orbit. Many people do this, including us. But our engineers, although they are lagging behind in terms of launching tests, however, plan to send the ship further away from the earth's orbit - to the moon! The construction of a lunar base is planned.What the hell do we need from this piece of stone?
The point is that in lunar soil accumulated 10 million tons of Helium-3 - t some necessary and useful substance.
And you thought we were flying to the moon for the sake of curiosity? We are not vain Americans. They did a public relations campaign on a flight to the moon, and we will stir up Helium-3 on an industrial scale. We even have a plan.
Plan
Until 2025, we will send 4 interplanetary stations to the Earth's satellite. Their task will be to explore the polar regolith with water ice, as well as to search for a good place for a base near the South Pole.
Until the early 1930s, manned expeditions would go to the Moon without landing on the surface. In the 1930s and 1940s, the first landings on the lunar surface and the first laying of the base's future infrastructure will take place.
By 2050base to be!
And there we will see the first automatic machines that left their marks on the lunar soil. Bulldozer robots will form new lunar mountains from raw materials, and the enrichment plant will work around the clock, producing Helium-3. And only the launches of interplanetary cargo ships will break the silent routine of these works.
And on earth, we will still scold the government in the comments, not at all thinking about the path electricity takes from a thermonuclear reactor to our gadget.
Forms three isotopes with mass numbers 1, 2, 3:
() - deuterium;
() - tritium.
In nature, hydrogen is in the form of protium (99.98%). 0.0156% of natural hydrogen is accounted for by "heavy" hydrogen - deuterium, whose mass is twice that of protium. Protium and deuterium are not radioactive.
For the first time, deuterium was obtained in the form of heavy water D 2 O by electrolysis natural water.
Heavy water D 2 O - water, formed by atoms deuterium. In its physicochemical properties it differs from H 2 O:
Currently, deuterium is obtained from a natural mixture by isotope exchange between water and hydrogen sulfide:. To obtain 1 liter of heavy water, 41 tons of water and 135 tons of hydrogen sulfide are required.
Chemical reactions in heavy water proceed more slowly than in ordinary water, hydrogen bonds involving deuterium are somewhat stronger than usual. Heavy water is toxic. Heavy water has a detrimental effect on animals and humans. For example, replacing 1/3 H 2 O with D 2 O leads to infertility, carbohydrate imbalance and anemia.
However, some microorganisms are able to live in 70% heavy water (protozoa) and even in pure heavy water (bacteria). A person can drink a glass of heavy water without visible harm to health, all deuterium will be removed from the body in a few days. In this respect, heavy water is less toxic than table salt, for example.
Heavy water is an industrial product and is available in large quantities. The production of heavy water is very energy intensive, so its cost is quite high (approximately $200 - $250 per kg).
Deuterium nuclei have a nuclear spin of 1, which is the reason for the use of heavy water and other deuterated solvents (deuterochloroform CDCl 3 ) in nuclear magnetic resonance spectroscopy. Heavy water finds use in nuclear technology as a fast neutron moderator because it will quickly lower the energy of nuclear fission neutrons, and also because deuterium has a lower neutron capture cross section (does not absorb neutrons) than hydrogen, and therefore significantly reduces the neutron flow.
Deuterium is widely used in the study of reaction mechanisms and in kinetic studies.
Tritium differs from other isotopes in that it is radioactive. Tritium occurs in nature in very small amounts. The natural content of tritium is 1 atom per 10 18 hydrogen atoms, this is the result of nuclear reactions occurring in water by the action of cosmic rays in the upper atmosphere:
After testing the thermo nuclear weapons(1954) the concentration of tritium has increased hundreds of times, but now it has fallen as a result of the ban on atmospheric testing of nuclear weapons. Low tritium content earth's crust due to its radioactivity with a half-life of 12.35 years. AT last years The main source of technogenic tritium in the environment has become nuclear power plants, which annually emit several tens of kilograms of tritium.
At present, tritium is produced in nuclear reactors by irradiating lithium with neutrons: .
Lithium is used in the form of an alloy with magnesium or aluminum, which retains a lot of tritium, which is released when the irradiated alloy is dissolved in acid.
Note. The most convenient way to store tritium is to convert it into UT 3 by reaction with finely divided uranium. Tritium is easily released from this compound when heated above 400 ºС.
Heavy water based on tritium T 2 O has strong radioactivity. Therefore, dilute solutions containing 1% tritium water are usually used. Tritium is a pure β-emitter with no γ-component impurity, therefore it is relatively safe, since β-particles have a low penetrating power, therefore they are retained by a sheet of paper or a 3 mm layer of air. Tritium is one of the least toxic radioisotopes.
Tritium can serve as a radioactive label for studying various natural processes. Analysis of atmospheric tritium provides valuable information about cosmic rays. And tritium in sedimentary rocks may indicate the movement of air and moisture on Earth.
The richest natural springs tritium - rain and snow, since almost all the tritium formed under the action of cosmic rays in the atmosphere goes into water. The intensity of cosmic radiation varies with latitude, so precipitation, for example, in central Russia carries several times more tritium than tropical showers. And there is very little tritium in the rains that fall over the ocean, since their source is basically the same ocean water, and there is not much tritium.
It is clear that the deep ice of Greenland or Antarctica does not contain tritium at all - it has long since completely decayed there. Knowing the rate of formation of tritium in the atmosphere, it is possible to calculate how long moisture is in the air - from the moment it evaporates from the surface to falling in the form of rain or snow. It turned out that, for example, in the air over the ocean, this period is on average 9 days.
Most often, tritium is used as a label in the study of reaction mechanisms and their kinetics.
Synthesized tritium is relatively cheap and is used in scientific research and in industry. Tritium luminous paints, which are applied to instrument scales, have found wide application. These light compositions are less dangerous from the point of view of radiation than traditional radium ones. Such permanent light compositions are used for the manufacture of pointers, instrument scales, etc. Hundreds of grams of tritium are annually spent on their production.
Tritium is present in human body. It enters it with food, with inhaled air and through the skin. Interestingly, gaseous T 2 is 500 times less toxic than tritium water T 2 O. This is due to the fact that molecular tritium, getting into the lungs with air, is then quickly (in about 3 minutes) excreted from the body, while tritium in the composition water lingers in it for 10 days and manages to transfer a significant dose of radiation to it during this time.
Tritium is important in thermonuclear fusion reactions: occurring during the explosion of a hydrogen bomb.
Popular Mechanics has already written about modern nuclear weapons ("PM" No. 1 "2009) based on fission charges. This issue is a story about even more powerful fusion munitions.
Alexander Prishchepenko
In the time since the first test at Alamogordo, thousands of fission charge explosions have thundered, each of which yielded precious knowledge about the peculiarities of their functioning. This knowledge is similar to the elements of a mosaic canvas, and it turned out that this “canvas” is limited by the laws of physics: reducing the size of the ammunition and its power puts the limit on the kinetics of slowing down neutrons in the assembly, and achieving an energy release that significantly exceeds a hundred kilotons is impossible due to nuclear physics and hydrodynamic restrictions on the allowable dimensions of the subcritical sphere. But it is still possible to make ammunition more powerful if, together with fission, nuclear fusion is made to “work”.
Division plus synthesis
Heavy isotopes of hydrogen serve as fuel for fusion. The fusion of deuterium and tritium nuclei produces helium-4 and a neutron, the energy yield in this case is 17.6 MeV, which is several times greater than in the fission reaction (in terms of the mass unit of the reactants). In such fuel, under normal conditions, a chain reaction cannot occur, so its amount is not limited, which means that the energy release of a thermonuclear charge has no upper limit.
However, in order for the fusion reaction to begin, it is necessary to bring the nuclei of deuterium and tritium closer together, and this is hindered by the Coulomb repulsion forces. To overcome them, you need to disperse the nuclei towards each other and push them. In a neutron tube during the stall reaction to ion acceleration high voltage a lot of energy is wasted. But if you heat the fuel to very high temperatures of millions of degrees and maintain its density for the time necessary for the reaction, it will release much more energy than that spent on heating. It is thanks to this method of reaction that weapons began to be called thermonuclear (according to the composition of the fuel, such bombs are also called hydrogen bombs).
To heat the fuel in a thermonuclear bomb - as a "fuse" - a nuclear charge is needed. The body of the "fuse" is transparent to soft X-rays, which, during the explosion, are ahead of the expanding substance of the charge and turn into plasma an ampoule containing thermonuclear fuel. The substance of the ampoule shell is chosen so that its plasma expands significantly, compressing the fuel to the axis of the ampoule (this process is called radiation implosion).
Deuterium and tritium
Deuterium is "admixed" with natural hydrogen in approximately five times smaller amounts than "weapon-grade" uranium is with ordinary hydrogen. But the mass difference between protium and deuterium is double, so the processes of their separation in countercurrent columns are more efficient. Tritium, like plutonium-239, does not exist in nature in tangible quantities; it is mined by exposing the lithium-6 isotope to powerful neutron fluxes in a nuclear reactor, producing lithium-7, which decays into tritium and helium-4.
Both radioactive tritium and stable deuterium turned out to be dangerous substances: experimental animals that were injected with deuterium compounds died with symptoms characteristic of old age (brittle bones, loss of intelligence, memory). This fact served as the basis for the theory according to which death from old age and under natural conditions occurs with the accumulation of deuterium: many tons of water and other hydrogen compounds pass through the body during life, and heavier deuterium components gradually accumulate in cells. The theory also explained the longevity of the highlanders: in the field of gravity, the concentration of deuterium does decrease slightly with height. However, many somatic effects turned out to be contrary to the "deuterium" theory, and as a result it was rejected.
Hydrogen isotopes - deuterium (D) and tritium (T) - under normal conditions are gases, sufficient quantities of which are difficult to "collect" in a device of reasonable size. Therefore, their compounds are used in charges - solid lithium-6 hydrides. As the synthesis of the most “lightly ignitable” isotopes heats up the fuel, other reactions begin to occur in it - with the participation of both the nuclei contained in the mixture and the resulting nuclei: the fusion of two deuterium nuclei with the formation of tritium and a proton, helium-3 and a neutron, the fusion two tritium nuclei to form helium-4 and two neutrons, the fusion of helium-3 and deuterium to form helium-4 and a proton, and the fusion of lithium-6 and a neutron to form helium-4 and tritium, so that lithium is not quite "ballast".
…Plus division
Although the energy release of a two-phase (fission + fusion) explosion can be arbitrarily large, a significant part of it (for the first of the mentioned reactions - more than 80%) is carried away from the fireball by fast neutrons; their range in the air is many kilometers, and therefore they do not contribute to explosive effects.
If it is precisely the explosive effect that is needed, a third phase is also realized in a thermonuclear munition, for which the ampoule is surrounded by a heavy shell of uranium-238. The neutrons emitted during the decay of this isotope have too little energy to maintain a chain reaction, but uranium-238 is fissioned under the action of "external" high-energy thermonuclear neutrons. Non-chain fission in the uranium shell gives an increase in the energy of the fireball, sometimes exceeding even the contribution of thermonuclear reactions! For every kilogram of weight of three-phase products, there are several kilotons of TNT equivalent - they significantly exceed other classes of nuclear weapons in terms of specific characteristics.
However, three-phase ammunition has a very unpleasant feature - an increased yield of fission fragments. Of course, two-phase munitions also pollute the area with neutrons, which cause nuclear reactions in almost all elements that do not stop many years after the explosion (the so-called induced radioactivity), fission fragments and the remnants of "fuses" (during the explosion, only 10-30 % plutonium, the rest scatters around the neighborhood), but three-phase ones are superior in this regard. They are so superior that some ammunition was even produced in two versions: “dirty” (three-phase) and less powerful “clean” (two-phase) for use in the territory where the actions of their troops were expected. For example, the American bomb B53 was produced in two identical appearance variants: "dirty" B53Y1 (9 Mt) and "clean" version B53Y2 (4.5 Mt).
Types of nuclear explosions: 1. Space. It is used at an altitude of more than 65 km to destroy space targets. 2. Ground. Produced on the surface of the earth or at such a height when the luminous area touches the ground. It is used to destroy ground targets. 3. Underground. Produced below ground level. Characterized by severe contamination of the area. 4. High-rise. It is used at an altitude of 10 to 65 km to destroy air targets. For ground objects it is dangerous only by the impact on electrical and radio devices. 5. Air. Produced at altitudes from several hundred meters to several kilometers. There is practically no radioactive contamination of the area. 6. Surface. Produced on the surface of the water or at such a height that the light area touches the water. It is characterized by a weakening of the action of light radiation and penetrating radiation. 7. Underwater. Produced underwater. Light emission and penetrating radiation is practically absent. Causes severe radioactive contamination of water.
Explosion factors
From the energy of 202 MeV supplied by each fission event, the following are instantly released: the kinetic energy of fission products (168 MeV), the kinetic energy of neutrons (5 MeV), and the energy of gamma radiation (4.6 MeV). Thanks to these factors, nuclear weapons dominate the battlefield. If an explosion occurs in relatively dense air, two-thirds of its energy is converted into a shock wave. Almost the entire remainder is taken away by light radiation, leaving only a tenth of the penetrating radiation, and of this minuscule, only 6% goes to the neutrons that created the explosion. Significant energy (11 MeV) is carried away by neutrinos, but they are so elusive that it has not been possible to find practical application for them and their energy so far.
With a significant delay after the explosion, the energy of beta radiation of fission products (7 MeV) and the energy of gamma radiation of fission products (6 MeV) are released. These factors are responsible for the radioactive contamination of the area - a phenomenon that is very dangerous for both sides.
The action of the shock wave is understandable, therefore, the power of a nuclear explosion began to be evaluated by comparing it with an explosion of conventional explosives. The effects caused by a powerful flash of light were not unusual either: wooden buildings burned, soldiers were burned. But the effects that do not turn the target into firebrands or a trivial, undisturbed pile of ruins - fast neutrons and hard gamma radiation - were, of course, considered "barbaric".
The direct action of gamma radiation is inferior in combat effect to both the shock wave and light. Only huge doses of gamma radiation (tens of millions of rads) can cause trouble for electronics. At such doses, metals melt, and a shock wave with a much lower energy density will destroy the target without such excesses. If the energy density of gamma radiation is less, it becomes harmless to steel technology, and the shock wave can also have its say here.
Not everything is clear with “manpower” either: firstly, gamma radiation is significantly weakened, for example, by armor, and secondly, the features of radiation injuries are such that even those who received an absolutely lethal dose of thousands of rem (the biological equivalent of an X-ray, the dose of any type of radiation that produces the same effect in a biological object as 1 x-ray) tank crews would remain combat-ready for several hours. During this time, mobile and relatively invulnerable machines would have time to do a lot.
Death to electronics
Although direct gamma irradiation does not provide a significant combat effect, it is possible due to secondary reactions. As a result of the scattering of gamma rays on the electrons of air atoms (the Compton effect), recoil electrons arise. A current of electrons diverges from the explosion point: their speed is much higher than the speed of ions. The trajectories of charged particles in the Earth's magnetic field twist (and therefore move with acceleration), while forming an electromagnetic pulse of a nuclear explosion (EMP).
Any compound containing tritium is unstable, because half of the nuclei of this isotope itself decays into helium-3 and an electron in 12 years, and in order to maintain the readiness of numerous thermonuclear charges for use, it is necessary to continuously produce tritium in reactors. There is little tritium in the neutron tube, and helium-3 is absorbed there by special porous materials, but this decay product must be pumped out of the ampoule with a pump, otherwise it will simply be torn apart by gas pressure. Such difficulties led, for example, to the fact that British specialists, having received Polaris missiles from the United States in the 1970s, preferred to abandon American thermonuclear combat equipment in favor of less powerful single-phase fission charges developed in their country under the Chevaline program. In the neutron munitions intended to fight tanks, the replacement of ampoules with a significantly reduced amount of tritium with "fresh" ampoules was carried out in the arsenals during storage. Such ammunition could also be used with "blank" ampoules - as single-phase nuclear projectiles of kiloton power. It is possible to use thermonuclear fuel without tritium, only on the basis of deuterium, but then, ceteris paribus, the energy release will decrease significantly. Scheme of operation of a three-phase thermonuclear munition. The explosion of the fission charge (1) turns the ampoule (2) into a plasma that compresses the thermonuclear fuel (3). To enhance the explosive effect due to the neutron flux, a shell (4) of uranium-238 is used.
Only 0.6% of the energy of gamma quanta passes into the energy of EMP nuclear weapons, and in fact their share in the balance of the energy of the explosion is small in itself. A contribution is also made by dipole radiation, which arises due to the change in air density with height, and the perturbation of the Earth's magnetic field by a conducting plasmoid. As a result, a continuous frequency spectrum of EMP nuclear weapons is formed - a set of oscillations of a huge number of frequencies. The energy contribution of radiation with frequencies from tens of kilohertz to hundreds of megahertz is significant. These waves behave differently: megahertz and higher-frequency waves attenuate in the atmosphere, while low-frequency waves “dive” into the natural waveguide formed by the Earth’s surface and the ionosphere and can go around Earth. True, these "long-livers" remind of their existence only by wheezing in the receivers, similar to the "voices" of lightning discharges, but their higher-frequency relatives declare themselves with powerful and dangerous "clicks" for the equipment.
It would seem that such radiation should generally be indifferent to military electronics - after all, any device with the greatest efficiency receives waves of the range in which it emits them. And military electronics receive and radiate in much higher frequency ranges than EMP nuclear weapons. But EMP does not affect electronics through an antenna. If a rocket with a length of 10 m was “covered” by a long wave with an electric field strength of 100 V / cm that did not amaze the imagination, then a potential difference of 100,000 V was induced on the metal rocket body! Powerful pulsed currents "flow" into the circuits through the grounding connections, and the grounding points themselves on the case turned out to be at significantly different potentials. Current overloads are dangerous for semiconductor elements: in order to “burn out” a high-frequency diode, a pulse of scanty (ten millionth of a joule) energy is enough. EMP took the place of honor as a powerful damaging factor: sometimes they disabled equipment thousands of kilometers from a nuclear explosion - neither a shock wave nor a light pulse could do this.
It is clear that the parameters of the EMP-causing explosions were optimized (mainly the height of the detonation of a charge of a given power). Protective measures were also developed: the equipment was supplied with additional screens, security arresters. Not a single piece of military equipment was accepted into service until it was proved by tests - full-scale or on specially created simulators - that its resistance to EMP nuclear weapons, at least of such intensity, which is typical for not too large distances from the explosion.
Inhuman weapon
However, back to two-phase ammunition. Their main damaging factor is the flux of fast neutrons. This gave rise to numerous legends about “barbaric weapons” — neutron bombs, which, as Soviet newspapers wrote in the early 1980s, destroy all life in the explosion, and leave material values (buildings, equipment) practically intact. A real looting weapon - blew it up, and then come and rob! In fact, any objects exposed to significant neutron fluxes are life-threatening, because neutrons, after interacting with nuclei, initiate various reactions in them, causing secondary (induced) radiation, which is emitted for a long time after the last of the decays. neutrons irradiating matter.
What was this "barbaric weapon" intended for? The warheads of Lance missiles and 203-mm howitzer shells were equipped with two-phase thermonuclear charges. The choice of carriers and their reach (tens of kilometers) indicate that these weapons were created to solve operational and tactical tasks. Neutron munitions (according to American terminology - "with an increased output of radiation") were intended to destroy armored vehicles, in terms of which the Warsaw Pact outnumbered NATO by several times. The tank is sufficiently resistant to the effects of a shock wave, therefore, after calculating the use of nuclear weapons of various classes against armored vehicles, taking into account the consequences of contamination of the area with fission products and destruction from powerful shock waves, it was decided to make neutrons the main damaging factor.
Absolutely pure charge
In an effort to obtain such a thermonuclear charge, they tried to abandon the nuclear "fuse", replacing fission with ultra-high-speed cumulation: the head element of the jet, which consisted of thermonuclear fuel, was accelerated to hundreds of kilometers per second (at the time of the collision, temperature and density increase significantly). But against the background of the explosion of a kilogram shaped charge, the "thermonuclear" increase turned out to be negligible, and the effect was registered only indirectly - by the yield of neutrons. An account of these US experiments was published in 1961 in Atoms and Weapons, which, given the then paranoid secrecy, was in itself a failure.
In the seventies, in "non-nuclear" Poland, Sylvester Kaliski theoretically considered the compression of thermonuclear fuel by spherical implosion and received very favorable estimates. But experimental verification showed that, although the neutron yield, compared with the "jet version", increased by many orders of magnitude, front instabilities do not allow reaching the desired temperature at the wave convergence point and only those fuel particles react, the speed of which, due to the statistical spread , is much higher than the average value. So it was not possible to create a completely “clean” charge.
Expecting to stop the bulk of "armor", the NATO headquarters developed the concept of "fighting the second echelons", trying to move farther away the line of use of neutron weapons against the enemy. The main task armored forces- the development of success to the operational depth, after they are thrown into a breach in the defense, pierced, for example, by a nuclear strike of high power. At this point, it is too late to use radiation munitions: although 14-MeV neutrons are slightly absorbed by armor, damage to crews by radiation does not immediately affect combat capability. Therefore, such strikes were planned in waiting areas, where the main masses of armored vehicles were being prepared for introduction into the breakthrough: during the march to the front line, the effects of radiation should have manifested themselves on the crews.
neutron interceptors
Another use of neutron munitions was the interception of nuclear warheads. It is necessary to intercept the enemy warhead at high altitude, so that even if it is blown up, the objects it is aimed at do not suffer. But the absence of air around deprives the anti-missile of the opportunity to hit the target with a shock wave. True, during a nuclear explosion in airless space, the conversion of its energy into a light pulse increases, but this does not help much, since the warhead is designed to overcome the thermal barrier when entering the atmosphere and is equipped with an effective burning (ablative) heat-shielding coating. Neutrons, on the other hand, freely "jump" through such coatings, and having slipped through, hit the "heart" of the warhead - an assembly containing fissile material. Nuclear explosion in this case, it is impossible - the assembly is subcritical, but neutrons give rise to many damped fission chains in plutonium. Plutonium, which under normal conditions, due to spontaneous nuclear reactions, has an elevated temperature that is noticeable when touched, melts and deforms under powerful internal heating, which means that it will no longer be able to turn into a supercritical assembly at the right time.
Such two-phase thermonuclear charges are equipped with American Sprint anti-missiles guarding the mines of intercontinental ballistic missiles. The conical shape of the missiles allows it to withstand the huge overloads that occur during launch and subsequent maneuvering.
Energy is released from the fission of heavy nuclei in a reactor. Where is the source of this energy? Why is it released at the moment when the core splits into two parts?
The uranium-235 nucleus consists of 92 protons and 143 neutrons. This is not a simple mechanical mixture of elementary particles, like, say, a mixture of iron filings and sulfur powder. The particles that make up the nucleus of an atom are very strongly bound to each other by the so-called nuclear forces. This bond of particles in the nucleus is many millions of times stronger than the bond that exists between the atoms in the molecule of any chemical compound. Ignite the same iron filings mixed with sulfur, you get a chemical compound - iron sulfide. To break down all the iron sulfide molecules to the iron and sulfur atoms contained in one gram, energy is needed in the amount of about one large calorie. And in order to destroy to elementary particles all the nuclei that are in a piece of uranium weighing one gram, it would take energy of the order of 170 million large calories. This amount of energy is released by burning almost 20 tons of gasoline.
Neutrons and protons in the nuclei of various chemical elements are bound to each other in different ways: in some they are stronger, in others they are weaker. During the fission of the uranium nucleus, as already mentioned, two "fragments" are formed, which are the nuclei of the atoms of the middle periodic table elements of Mendeleev, for example, the nuclei of barium and krypton atoms. The protons and neutrons in these nuclei are bound together more strongly than they were bound in the nuclei of uranium or other heavy elements at the end of the periodic table. The destruction of one barium nucleus and one krypton nucleus to elementary particles (protons and neutrons) would require ten percent more energy than to destroy one uranium nucleus.
If a certain definite energy is needed for the splitting of a nucleus into separate elementary particles, then in the formation of nuclei from these particles, according to the law of conservation of energy, the same energy must be released.
Let us mentally divide the process of fission of the uranium nucleus into two stages. The first stage is the destruction of the uranium nucleus into protons and neutrons; this consumes energy in the amount of 170 million large calories per gram of pure uranium. The second stage is the formation of barium and krypton nuclei from elementary particles formed during the destruction of uranium nuclei. This process is accompanied by the release of energy in the amount of about 190 million large calories. As a result of carrying out both stages of the reaction, an energy gain of 20 million large calories is obtained. To obtain this amount of energy, it is necessary to burn about two tons of gasoline. Thus, the "calorific value" of uranium during its fission turns out to be two million times higher than during the combustion of gasoline.
Let us explain our reasoning with the following example. Let's say you are standing on a mountainside and drawing water from a well two meters deep. For each kilogram of water you expend work of two kilogram-meters. Then you pour this water through the chute onto the turbine wheel, located five meters below. If we neglect all kinds of energy losses, then the turbine will do work equal to five kilogram meters. As a result, we get three kilogram-meters more work than we spend.
During the fission of the nuclei of heavy elements, they do not disintegrate into individual elementary particles, they only split into two parts - fragments. Inside the resulting fragments, a rearrangement of elementary particles occurs instantly; they are "packed" more densely, and this process is accompanied by the release of energy, and more energy is released than it is spent on the destruction of a heavy nucleus.
Calculations show that the fission of heavy nuclei releases only part of the energy stored in the nucleus. Significantly more energy is obtained if the same nuclei of barium and krypton are synthesized (composed) directly from protons and neutrons. Then you don't have to expend energy of 170 million large calories to destroy heavy nuclei. In the example with water, this would correspond to the fact that it is not necessary to pull it up from the well, but to use the pool, the water in which is at the level of the upper edge of the gutter.
But for the synthesis atomic nuclei of neutrons and protons, it is necessary first of all to have these elementary particles at our disposal. They are not found in nature in finished form. They can only be obtained artificially. However, neutrons and protons isolated in the free state cannot be stored for future use. Protons are protium atoms deprived of a single electron; under normal conditions, they cannot exist for a long time. The protons will find their lost electrons and turn back into electrically neutral protium atoms.
Neutrons easily penetrate into the nuclei of atoms and are captured by them. In addition, neutrons are radioactive. The lifetime of neutrons in the free state is a matter of minutes. If the neutron managed to avoid capture by the nucleus, then it spontaneously turns into a proton and an electron. Where did the electron come from during the radioactive transformation of the neutron? The fact is that both the neutron and the proton are essentially the same elementary particle, only it is in different energy states. To emphasize the commonality of these particles, when they together constitute some kind of nucleus of an atom, they are even called by one name - nucleons. So they say, for example, the nucleus of the isotope chlorine-35 consists of 35 nucleons, without subdividing them into protons and neutrons. The process of transition of a neutron into a proton is a spontaneous transition from a higher energy level to a lower one; at the same time, an electron is “born”. Spontaneous transition of a proton into a neutron is impossible; this would correspond to a transition from a low energy level to a higher one, which contradicts the law of conservation of energy. A stone lying on the ground will never rise up by itself, without the intervention of an external force. If, on the other hand, the necessary amount of energy is imparted to the proton from the outside, it can turn into a neutron, and this act is accompanied by the appearance of a particle similar to an electron, but positively charged. It is called, as we already know, the positron. This is how it turns out that although there are no electrons in neutrons, and positrons in protons, these particles are released during their mutual transformation.
So, if it is possible to obtain neutrons and protons in a free form, then they must immediately be used for the synthesis of atomic nuclei.
The destruction of heavy nuclei such as uranium into elementary particles (nucleons) is associated with the expenditure of a large amount of energy. But are there no such nuclei in nature in which protons and neutrons are not bound together as strongly as in the nucleus of uranium? If such nuclei are available, then the first mental stage of the reaction - the destruction of the nucleus - would require less energy. Returning to the example with a well and a gutter, one should look for a shallow well if possible.
This is where hydrogen enters the scene with its heavy isotopes and now not one, but two.
What role did deuterium play in the operation of a nuclear reactor? Its role was auxiliary - to slow down fast neutrons to thermal speeds. He did not take a direct part in the release of nuclear energy. In many reactors, as you already know, carbon in the form of graphite blocks, or ordinary water, are successfully used as neutron moderators. There are reactors without a moderator at all - these are reactors operating on fast neutrons. In the processes with which we will now become acquainted, the isotopes of hydrogen have crucial in the release of nuclear energy.
In addition to the heavy isotope of hydrogen - deuterium, there is also a superheavy isotope - tritium; it is denoted by the letter T. In addition to the proton, the tritium nucleus includes not one neutron, as in deuterium, but two (Fig. 13). Unlike deuterium
(white circles denote protons, black circles denote neutrons that make up nuclei).
Half of all available tritium atoms decay in 12.2 years. This period is not long, but quite sufficient to always have tritium in stock in the right amount.
Tritium is a more complex isotope of hydrogen. In its properties, it differs from protium more than deuterium.
Like the first two isotopes, tritium can be condensed into a liquid. The boiling point of liquid tritium is already 4.65 degrees higher than the boiling point of protium. Its heat of vaporization is even higher than that of deuterium. When tritium combines with oxygen, water is formed, which is called tritium or superheavy water. Like deuterium, tritium, in combination with protay, deuterium, and oxygen isotopes, gives water of various isotopic compositions. To those nine varieties of water that deuterium gave, now the same number of new ones are added, the molecules of which include tritium atoms. The formulas of these molecules can be written as follows:
MSW16, LLP17 and LLP18.
Arguing in the same way as in the case of fission of uranium nuclei (see p. 50), we mentally divide the process into two stages: the first is the destruction of deuterium and tritium nuclei to individual nucleons, the second is the synthesis of helium nuclei from them. Neutrons and protons are bound together in deuterium and tritium nuclei much less strongly than in helium nuclei. Therefore, the destruction of the nuclei of two hydrogen isotopes consumes less energy in total than it is released during the synthesis of one helium nucleus from the resulting elementary particles. The calculation shows that when only one gram of helium-4 isotope atoms is formed from deuterium and tritium nuclei, about one hundred million large calories are released. This is five times the energy released by the fission of one gram of uranium under the influence of neutrons.
To carry out the reaction of fusion of helium nuclei, it is necessary to bring the nuclei of deuterium and tritium into collision with each other. This is the main difficulty in carrying out the reaction of fusion of helium nuclei. After all, both colliding nuclei are positively charged, and electrically, like-charged bodies repel each other. To overcome the electric repulsive forces, it is necessary to the nuclei at
lay down great strength. How to do it? Apparently, it is necessary to impart to the nuclei such an energy of motion that would be enough to overcome the repulsive forces acting between them.
The average speed of random motion of particles, and hence their energy, is determined by temperature. The higher the body temperature, the greater the average energy of the particles, the faster they move. This means that our isotopes must be heated and heated to a very high temperature, of the order of a million degrees and even higher. Only at such temperatures will the energy of the particles be sufficient to overcome the electric forces of repulsion between the nuclei. If we remember that even on the surface of the Sun the temperature is only 6000 degrees, then the difficulty of heating bodies up to a million degrees becomes obvious. The only source known in our time, with the help of which it is possible to reach such temperatures, is an explosion. atomic bomb, that is, a chain process of fission of uranium or plutonium nuclei. In the zone of such an explosion, deuterium and tritium will exist in the form of plasma - a medium consisting of "bare" atomic nuclei devoid of electron shells. Under such conditions, the nuclei of hydrogen isotopes get the opportunity to combine into helium nuclei when they meet, the so-called thermonuclear reaction is carried out. This or a similar process occurs during the explosion of a hydrogen bomb.
To use the energy released during thermonuclear reactions for peaceful purposes, it is necessary to learn how to control such reactions. Scientists from many countries of the world are now occupied with the solution of this very difficult problem. Big Research in this direction are carried out here, in the Soviet Union. The successful solution of this problem will remove from mankind the concern for the search for new sources of energy and lead to an unprecedented flourishing of science and technology.
Only two and a half decades separate us from the discovery of heavy water and the time when it was obtained in quantities that fit at the bottom of a small test tube. For that a short time heavy water has won a firm place in nuclear power engineering. It turned out to be the best moderator for nuclear reactors, work
Yushchikh on thermal neutrons. However, this is not the most important thing. Heavy water acquires the main significance in the implementation of thermonuclear reactions. For these reactions, first of all, it is necessary to have enough raw materials, that is, deuterium and tritium. Deuterium atoms are integral part heavy water molecules. Tritium atoms can be obtained, as we have seen, from deuterium atoms. Consequently, heavy water is the source that supplies the necessary elements for the implementation of the reaction of fusion of helium nuclei. Therefore, the production of heavy water in many countries of the world is now carried out on a large factory scale.
Usually, in order to emphasize the significance of this or that element, they say: if it were not there, then such and such would happen. But, as a rule, this is nothing more than a rhetorical device. But hydrogen may someday really not be, because it continuously burns out in the depths of stars, turning into inert helium. And when the hydrogen reserves run out, life in the Universe will become impossible - both because the sun will go out, and because there will be no water ...
Hydrogen and the Universe
Once people deified the Sun. But now it has become the object of precise research, and we rarely think about the fact that our very existence depends entirely on the processes taking place on it.
Every second, the Sun radiates energy equivalent to about 4 million tons of mass into outer space. This energy is born during the fusion of four hydrogen nuclei, protons, into a helium nucleus; The reaction proceeds in several stages, and its total result is written as follows:
4 1 1 H + → 4 2 He 2+ + 2e + + 26.7 MeV.
Is it a lot or a little -26.7 MeV per elementary act? A lot: the "burning" of 1 g of protons releases 20 million times more energy than the combustion of 1 g of coal. On Earth, no one has yet observed such a reaction: it takes place at a temperature and pressure that exist only in the depths of stars and have not yet been mastered by man.
It is impossible to imagine a power equivalent to a mass loss of 4 million tons every second: even with the most powerful thermonuclear explosion, only about 1 kg of matter is converted into energy. But if we attribute all the energy radiated by the Sun to its total mass, then the incredible will turn out: the specific power of the Sun will turn out to be negligible - much less than the power of such a “heat-generating device” as man himself. And calculations show that the Sun will shine without weakening for at least another 30 billion years.
Needless to say, enough for our lifetime.
Our Sun is at least half hydrogen. A total of 69 chemical elements have been found on the Sun, but hydrogen predominates. It is 5.1 times more than helium, and 10 thousand times (not by weight, but by the number of atoms) more than all metals combined. This hydrogen is used not only for energy production. In the course of thermonuclear processes, new chemical elements, and accelerated protons are ejected into space around the Sun.
The last phenomenon, called the "solar wind", was discovered relatively recently during space exploration using artificial satellites. It turned out that particularly strong gusts of this "wind" occur during chromospheric flares. Reaching the Earth, the stream of protons captured by her magnetic field, causes auroras and disrupts radio communications, and for astronauts the "solar wind" poses a serious danger.
But is the impact on the Earth of the flux of solar hydrogen nuclei limited only to this? Apparently not. First, the proton flux gives rise to secondary cosmic radiation reaching the Earth's surface; secondly, magnetic storms can affect life processes; thirdly, the hydrogen nuclei captured by the Earth's magnetic field cannot but affect its mass transfer with space.
Judge for yourself: now in the earth's crust, out of every 100 atoms, 17 are hydrogen atoms. But free hydrogen practically does not exist on Earth: it is part of water, minerals, coal, oil, living beings ... Only volcanic gases sometimes contain a little hydrogen, which dissipates in the atmosphere as a result of diffusion. And since the average speed of the thermal motion of hydrogen molecules due to their small mass is very high - it is close to the second cosmic velocity - these molecules fly away from the layers of the atmosphere into outer space.
But if the Earth is losing hydrogen, then why can't it get it from the same Sun? Since the "solar wind" is hydrogen nuclei that are captured by the Earth's magnetic field, why shouldn't they stay on it?
After all, there is oxygen in the Earth's atmosphere; reacting with the hydrogen nuclei that have flown in, it will bind them, and cosmic hydrogen will sooner or later fall on the surface of the planet in the form of ordinary rain. Moreover, the calculation shows that the mass of hydrogen contained in the water of all the earth's oceans, seas, lakes and rivers is exactly equal to the mass of protons carried by the "solar wind" throughout the history of the Earth. What is this - a mere coincidence?
We must realize that our Sun, our hydrogen Sun, is just an ordinary star in the Universe, that there are an innumerable number of similar stars hundreds, thousands and millions of light years away from the Earth. And who knows - maybe it is in the range of radio emission of interstellar hydrogen (remember - 21 centimeters!) that humanity will be able to contact alien civilizations for the first time ...
Hydrogen and life
Once again about the fact that it is absurd to say: "If nature did not have this and that, then this and that would not exist." The fact is that the picture of the world that we have the opportunity to observe now has developed precisely as a result of what exists in reality ...
For example, writers like to inhabit planets where water is replaced by hydrogen fluoride or ammonia, and life is based not on carbon, but on silicon. But why doesn't "silicon" life exist on our planet, where silicon is more than enough? Is it because silicon is simply not a suitable basis for life?
However, if both carbon and oxygen are sometimes replaced by sophisticated human imagination, then nothing can replace hydrogen. The fact is that all elements have analogues, but hydrogen does not. The nucleus of this atom is an elementary particle, and this cannot but affect the properties of the atom.
Any atom, with the exception of the hydrogen atom, under normal conditions cannot lose all the electrons: it has at least one more electron shell, and this shell, which carries negative charges, shields the nucleus. But the hydrogen ion is a “bare”, positively charged proton, and it can be attracted to the electron shells of other atoms, while experiencing a not particularly strong repulsion from the nucleus.
And here's what happens. Let's say that in a water molecule, both valences of the oxygen atom are saturated and, it would seem, no additional bond can arise between the two molecules. But when the hydrogen atom of one water molecule approaches the oxygen atom of another molecule, then an additional attraction force begins to prevail between the proton and the electron shell of oxygen, and a special, so-called hydrogen bond is formed:
Such connections are twenty times weaker than usual ones, but still their role is enormous. Take, for example, the very same water: many of its amazing properties are determined precisely by unusually developed hydrogen bonds. At least try to predict its melting point, based on the constants of hydrogen compounds with oxygen's neighbors in the periodic system - nitrogen and fluorine or analogues - sulfur and selenium.
Ammonia melts at -77.7°C, hydrogen fluoride at -92.3°C; therefore, water would seem to have an intermediate melting point of around -85°C. Selenium hydrogen melts at -64°C, hydrogen sulfide at -82.9°C; therefore, the melting point of water, as a similar derivative with a lower molecular weight, should be even lower ... But no, its actual melting point turns out to be almost a hundred degrees higher than theoretically predicted, and the reason for this is weak, but numerous intermolecular hydrogen bonds, which oxygen, due to the specific structure of the electron shell, is able to form to a much greater extent than nitrogen, fluorine, sulfur or selenium.
Hydrogen bonds underlie the most subtle phenomena of life. For example, it is thanks to these bonds that enzymes are able to specifically recognize the substances whose reactions they accelerate. The fact is that the protein chain of each enzyme has a strictly defined spatial configuration, fixed by a multitude of intramolecular hydrogen bonds between groups of atoms C \u003d O and N - H. In turn, a substance molecule has groups that can form hydrogen bonds with a certain part of the enzyme molecule - so called the active center. As a result, intramolecular bonds in this substance weaken, and the enzyme literally "bites" the molecule.
But this does not limit the role of weak hydrogen bonds in life processes. It is thanks to these connections that the exact copying of the DNA molecule occurs, which transmits all genetic information from generation to generation; hydrogen bonds determine the specificity of the action of many drugs; they are responsible both for taste sensations and for the ability of our muscles to contract ... In a word, in wildlife, the hydrogen atom is really irreplaceable.
Hydrogen and science
In the very late XVIII and early XIX in. chemistry entered a period of establishing quantitative laws: in 1803, John Dalton formulated the law of multiple ratios (substances react with each other in weight ratios that are multiples of their chemical equivalents). At the same time, he compiled the first table in the history of chemical science of the relative atomic weights of elements. In this table, hydrogen was in the first place, and the atomic weights of other elements were expressed in numbers close to integers.
The special position that hydrogen occupied from the very beginning could not but attract the attention of scientists, and in 1811 chemists were able to get acquainted with the hypothesis of William Prout, who developed the idea of the philosophers of ancient Greece about the unity of the world and suggested that all elements are formed from hydrogen as from the very light element. Jens Jakob Berzelius, who was in the process of refining atomic weights, objected to Prout: it followed from his experiments that the atomic weights of elements are not in integer ratios to the atomic weight of hydrogen. “But,” Prout’s supporters objected, “atomic weights have not yet been determined accurately enough” - and as an example they referred to the experiments of Jean Stas, who in 1840 corrected the atomic weight of carbon from 11.26 (this value was established by Berzelius) to 12, 0.
Nevertheless, Prout's attractive hypothesis had to be abandoned for a while: soon the same Stas, through careful and unquestionable research, established that, for example, the atomic weight of chlorine is 35.45, i.e. can never be expressed as a multiple of the atomic weight of hydrogen...
But in 1869, Dmitry Ivanovich Mendeleev created his own periodic classification of elements, based on the atomic weights of elements as their most fundamental characteristic. And in the first place in the system of elements, of course, was hydrogen.
With the discovery of the periodic law, it became clear that the chemical elements form a single series, the construction of which is subject to some internal regularity. And this could not fail to bring to life Prout's hypothesis again - albeit in a slightly modified form: in 1888, William Crookes suggested that all elements, including hydrogen, were formed by compacting some primary matter, which he called protyl. And since protyle, Crookes reasoned, apparently has a very small atomic weight, the emergence of fractional atomic weights is also understandable from this.
Against this hypothesis, Mendeleev objected: “... give something individualized and it will become easy to understand the possibility of visible diversity. Otherwise, how can the one give many? That is, according to the creator of the periodic system, one kind of particles cannot serve as the basis for constructing a system of elements with such diverse properties.
But here's what's interesting. Mendeleev himself was unusually occupied with the question: why should the periodic system begin precisely with hydrogen? What prevents the existence of elements with an atomic weight less than one? And in 1905, Mendeleev calls such an element ... "world ether". Moreover, he places it in the zero group above helium and calculates its atomic weight - 0.000001! An inert gas with such a low atomic weight, according to Mendeleev, should be all-penetrating, and its elastic vibrations could explain light phenomena ...
Alas, this prediction of the great scientist was not destined to come true. But Mendeleev was right in that the elements are not made up of identical particles: we now know that they are made up of protons, neutrons, and electrons.
But let me exclaim, because the proton is the nucleus of the hydrogen atom. So Prout was right after all?
Yes, he was indeed right in his own way. But it was, so to speak, prematurely right. Because at that time it could neither be truly confirmed nor truly refuted...
However, hydrogen itself has played a significant role in the history of the development of scientific thought. In 1913, Niels Bohr formulated his famous postulates, which explained on the basis of quantum mechanics the peculiarities of the structure of the atom and the inner essence of the law of periodicity. And Bohr's theory was recognized because the spectrum of hydrogen calculated on its basis completely coincided with the observed one.
And yet the story of the idea, expressed more than 150 years ago, is not yet over. One of the most puzzling tasks facing today's science is to find a pattern in the properties of the so-called elementary particles, which now number many dozens. Scientists are trying to bring them into a kind of periodic system, but doesn’t this indicate that there are still some “bricks of the universe” from which all elementary particles are built - both atoms and molecules, and we , eventually?
Physicists have suggested that such particles exist and even called them quarks. The only problem is that no one in the world has yet been able to prove that such particles are a reality, not a myth...
But remember Prout and the fate of his hypothesis. The idea of the particles from which everything is built remains as attractive as it was two millennia and a century and a half ago. And even if quarks turn out to be not what modern scientists think about them, the important thing is that the idea of the unity of the world lives and develops. And the time will come when it will receive its logical conclusion.
Hydrogen and practice
Let's make a reservation right away: in contrast to "science", as a field of pure ideas, "practice" we will call everything that serves the practical activity of a person - even if it is the activity of an experimental scientist.
The chemist deals with hydrogen primarily as a substance with the properties of an ideal reducing agent.
But where to get hydrogen? Of course, the easiest way is from a balloon. From a green cylinder with a red inscription "Hydrogen" and a valve with a "left" thread (combustible gas!). But if there is no balloon at hand?
Hydrogen can be produced by reacting metals with acids:
Zn + H 2 SO 4 → ZnSO 4 + H 2.
But this hydrogen cannot be perfectly pure, because a perfectly pure metal and acid are needed. Pure hydrogen was also obtained by Lavoisier, passing water vapor through a gun barrel heated on a brazier:
4H 2 O + 3Fe → Fe 3 O 4 + 4H 2.
But even this method is not very convenient, although in a modern laboratory one can get by with a quartz tube filled with iron shavings and heated in an electric furnace.
Electrolysis! Distilled water, to which a little sulfuric acid is added to increase electrical conductivity, decomposes when a direct current is passed:
2H 2 O → 2H 2 + O 2.
At your service - hydrogen of almost perfect purity, it only needs to be freed from the smallest droplets of water. (In industry, alkali is added to water, not acid - so that metal equipment does not collapse).
And now we will slowly pass this hydrogen through water in which palladium chloride is stirred up. Recovery will begin almost immediately, and the precipitate will turn black - you get palladium black:
PdCl 2 + H 2 → Pd + 2HCl.
Palladium black is an excellent catalyst for the hydrogenation of various organic compounds. A catalyst is needed here because molecular hydrogen is very inert: even with oxygen, under normal conditions, it reacts unusually slowly. After all, first a hydrogen molecule must dissociate into atoms, and for this, 104 kcal must be spent for each mole of hydrogen (that is, only 2 g!) But on the surface of the catalyst, this process takes place with much lower energy costs, hydrogen is sharply activated.
Perhaps it is not worth talking much about the role of catalysts in modern chemical technology: the vast majority of processes are carried out in their presence. And the most important among them is the synthesis of ammonia from hydrogen and atmospheric nitrogen:
3H 2 + N 2 → 2NH 3.
In this case, hydrogen is produced either from water and methane according to the so-called conversion reaction:
CH 4 + 2H 2 O → 4H 2 + CO 2.
or by splitting natural hydrocarbons in a reaction that is the reverse of the hydrogenation reaction:
CH 3 - CH 3 - CH 2 \u003d CH 2 + H 2.
Synthetic ammonia is indispensable in the production of nitrogen fertilizers. But hydrogen is needed not only to produce ammonia. The transformation of liquid vegetable fats into solid substitutes for animal oil, the transformation of solid low-quality coals into liquid fuels, and many other processes involve elemental hydrogen. It turns out that hydrogen is food for humans, plants, and machines...
But back to the lab. Here, hydrogen is used not only in its pure form, but also in the form of its compounds with metals - for example, lithium aluminum hydride LiAlH 4 , sodium boron hydride NaBH 4 . These compounds easily and specifically restore certain groups of atoms in organic substances:
Hydrogen isotopes - deuterium (2 H or D) and tritium (3 H or T) - make it possible to study the finest mechanisms of chemical and biochemical processes. These isotopes are used as "tags" because deuterium and tritium atoms retain all Chemical properties conventional light isotope - protium - and are able to replace it in organic compounds. But deuterium can be distinguished from protium by mass, and tritium by radioactivity. This makes it possible to trace the fate of each fragment of the labeled molecule.
Hydrogen and the future
The words "deuterium" and "tritium" remind us that today man has a powerful source of energy released during the reaction:
2 1 H + 3 1 H → 4 2 He + 1 0 n+ 17.6 MeV.
This reaction begins at 10 million degrees and proceeds in a tiny fraction of a second during the explosion of a thermonuclear bomb, and a gigantic amount of energy is released on the scale of the Earth.
Hydrogen bombs are sometimes compared to the Sun. However, we have already seen that slow and stable thermonuclear processes take place on the Sun. The sun gives us life, and the hydrogen bomb promises death...
But someday the time will come - and this time is not far off - when the measure of value will not be gold, but energy. And then hydrogen isotopes will save mankind from impending energy starvation: in controlled thermonuclear processes, each liter of natural water will provide as much energy as 300 liters of gasoline now provide. And humanity will remember with bewilderment that there was a time when people threatened each other with a life-giving source of heat and light...
Protium, deuterium, tritium...
The physical and chemical properties of the isotopes of all elements, except hydrogen, are almost the same: after all, for atoms whose nuclei consist of several protons and neutrons, it is not so important - one neutron less or one neutron more. But the nucleus of a hydrogen atom is a single proton, and if a neutron is added to it, the mass of the nucleus will almost double, and if there are two neutrons, it will triple. Therefore, light hydrogen (protium) boils at minus 252.6°C, and the boiling point of its isotopes differs from this value by 3.2° (deuterium) and 4.5° (tritium). For isotopes, this is a very big difference!
Surprising isotopes are not equally distributed in nature: one atom of deuterium is about 7000, and one atom of beta radioactive tritium is one billion billion protium atoms. Another extremely unstable isotope of hydrogen, 4 H, was obtained artificially.
Precision comes first
The relative mass of the light isotope of hydrogen is determined with fantastic accuracy: 1.007276470 (if we take the mass of the carbon isotope 12 C equal to 12.0000000). If, for example, the length of the equator were measured with such accuracy, the error would not exceed 4 cm!
But why is such precision necessary? After all, each new figure requires more and more efforts from experimenters... The secret is revealed simply: protium nuclei, protons, take part in many nuclear reactions. And if the masses of the reacting nuclei and the masses of the reaction products are known, then, using the formula E = mc 2, its energy effect can be calculated. And since the energy effects of even nuclear reactions are accompanied by only a slight change in mass, then these masses have to be measured as accurately as possible.
First or seventh?
What place should hydrogen occupy in the periodic table? It would seem a ridiculous question: of course, the first! Yes, but which group should I place it in? For a long time, hydrogen was placed above lithium, since it has one valence electron, like all monovalent metals. (By the way, the thermal conductivity of hydrogen for a gas is unusually high - hydrogen molecules move much faster than molecules of other gases and therefore transfer heat more intensively.)
In the modern table of elements, hydrogen is placed in group VII, above fluorine. The fact is that the logic of the law of periodicity requires that the charge of the nuclei of the analogous elements of the first three periods differ by eight units; therefore, hydrogen (atomic number 1) should be considered as analogous to fluorine (atomic number 9), and not as analogous to lithium (atomic number 3). And yet it must be remembered that the analogy here is not complete: although hydrogen, like fluorine, is capable of forming compounds with metals (hydrides), the hydrogen ion is a proton, a naked elementary particle, and cannot be compared at all with any other ions.
Alkali or acid?
Substances that split off a hydrogen ion, a proton, in solutions are called acids, and those that add this ion are called alkalis. The concentration of protons characterizes the reaction of the medium: 1 liter of a neutral aqueous solution, as well as 1 liter of pure water, contains 10–7 grams of hydrogen ions; if the concentration of protons is higher, the medium becomes acidic, and if it is lower, it becomes alkaline. (The logarithm of this concentration, taken with the opposite sign, is the “hydrogen index,” or pH.)
However, it should be remembered that there are no and cannot be free protons in aqueous solutions: the nucleus of the hydrogen atom is so small that it seems to be introduced into the electron shell of water and forms a special compound - the oxonium ion:
H + + H 2 O → H 3 O +.
However, the situation here is rather the opposite - it is not the oxonium ion that is formed because the proton is split off from the acid, but the acid dissociates because the oxonium ion is formed. Therefore, the dissociation scheme of, say, hydrogen chloride should be written as follows:
HCl + H 2 O → H 3 O + + Cl -.
This means that water, when hydrogen chloride is dissolved in it, behaves like an alkali (it attaches a proton); if, for example, ammonia dissolves in it, then water already acts as an acid:
NH 3 + H 2 O → NH 4 + + OH -.
In a word - everything in the world is relative ...
Miracles of occlusion
Imagine such an experience. In a water electrolysis device, the cathode is made in the form of a plate. You turn on the current, and... the plate starts to bend by itself! The secret of this trick lies in the fact that the plate is made of palladium and coated on one side with a layer of varnish. During electrolysis, hydrogen is released on the non-lacquered side of the plate and immediately dissolves in the metal; and as the volume of the palladium increases, a force arises that bends the plate.
But wait, you say, do gases dissolve in metals? Generally speaking, this phenomenon, called occlusion, is not surprising. Another thing is surprising: up to 850 volumes of hydrogen are dissolved in one volume of palladium! This is slightly less than the amount of ammonia that can be dissolved in one volume of water - and which gas dissolves better in water! Hydrogen, on the other hand, dissolves in water very slightly - about 0.02 volume per volume of water.
In statu nascendi
When hydrogen is burned in pure oxygen, temperatures up to 2800 ° C develop - such a flame easily melts quartz and most metals. But with the help of hydrogen, even higher temperatures can be achieved if it is used not as a source, but as a carrier and concentrator of energy.
Here's how it's done. A jet of hydrogen is passed through the flame of a voltaic arc. Under the action of high temperature, its molecules disintegrate, dissociate into atoms, absorbing a large amount of energy. The resulting atomic hydrogen does not combine into molecules instantly: after all, atoms must first give up their stored energy. And if a jet of atomic hydrogen is directed at some solid surface, then it is on it that the atoms are combined into molecules: dissociation energy is released, and the surface temperature rises to 3500...4000°C. With the help of such an atomic hydrogen burner, even the most refractory metals can be processed.
Atomic hydrogen is born not only in an arc flame: it is formed even when acids react with metals. At the moment of its release (in Latin - in statu nascendi) hydrogen has increased activity, and chemists use it to reduce organic matter.
How many hydrogens are there?
We have already talked about four varieties of hydrogen - its isotopes. And yet in nature there are many more different "hydrogens", if we talk not only about the atoms of this element, but also about its molecules. The fact is that under normal conditions, molecular hydrogen is a mixture of two unusual isomers - the so-called ortho- and steam hydrogen, which differ in the orientation of the magnetic moments of the nuclei of their constituent atoms. For orthohydrogen, these moments have the same orientation, and for hydrogen vapor, they have the opposite orientation; ortho- and para-isomers differ in their physical properties. And since both deuterium and tritium have similar isomers, and since HD, HT, and DT molecules can exist, each of which, apparently, can also exist in the form of ortho- and paraisomers, this means that there is twelve varieties of molecular hydrogen.
But that's not all. Not so long ago, scientists managed to obtain antihydrogen - an atom built from an antiproton and a positron, and after it, antideuterium and antitritium nuclei were obtained in high-energy accelerators. And then there are mesoatoms, in which a proton or an electron is replaced by one or another meson. They can also be considered as peculiar isotopes of hydrogen...
First metallic hydrogen
As we know, at least three hopes are connected with hydrogen today: for thermonuclear energy, for energy transfer with almost no losses (in superconducting devices at the temperature of liquid hydrogen, not liquid helium) and - as a fuel, harmless to environment. And all these hopes are associated primarily with metallic hydrogen, i.e. such hydrogen, which is solid, which has high electrical conductivity and other properties of the metal. Compact metallic hydrogen should be the most convenient hydrogen fuel. In addition, there are theoretical prerequisites according to which metallic hydrogen can exist at ordinary temperatures, while remaining a superconductor.
They tried (and continue to try) to obtain metallic hydrogen in various ways, by subjecting ordinary solid hydrogen to static or dynamic loads. The first report on possible success in solving this important and complex problem was published in February 1975 by a group of scientists from the Institute of High Pressure Physics of the USSR Academy of Sciences (headed by Academician L.F. Vereshchagin). Having deposited a thin layer of hydrogen on diamond anvils cooled to 4.2°K and acting on it very high pressure, observed unusual phenomenon. The electrical resistance of hydrogen has decreased millions of times - it has passed into a metallic state. This happened under a static pressure of about 3 million atm. When the pressure began to decrease, already at about a threefold decrease in pressure (1 million atm.), the reverse transition of hydrogen from the metallic state to the usual, dielectric state took place. However, the researchers did not perceive this fact as a fatal failure, meaning the impossibility of the existence of metallic hydrogen at normal pressure. They hope that metallic hydrogen will somehow be able to be “hardened” and eventually made available to scientists of various specialties. And for technology, apparently, too.