Plutonium

Large hopes and large fears of mankind are pined on a unit № 94.... In the beginning there were protons - galactic hydrogen. As a result of its squeezing and followed then nuclear reactions the most incredible were derivated “Bullion” nucleones. Among them, these “Bullion”, were, apparently, and containing on 94 protons. Appraisals of theorists allow to consider, that about hundred nucleon educations which one composition 94 protons and from 107 to 206 neutrons go into, are so stable, that it is possible to consider them as nucleuses of isotopes of a unit № 94.

But all these isotopes - hypothetical and real - are not so stable to be conserved up to now from the moment of education of units of a solar system. A half-life of the long-lived isotope of a unit № 94 - 75 million years. The age of Galactic is metered by billions years. Therefore, for “primary” plutonium was not chances to live up to now. If it also was derivated at great synthesis of units of the Universe, those its old atoms for a long time “dies” just as dinosaurs and mammoths have died out.

In the XX-th century of a new era, our era, this unit has been reconstructed. From hundred possible isotopes of plutonium twenty five are synthesised. For fifteen of them nuclear properties are learnt. Four have discovered operational use.

From that day when the first nucleuses of a unit № 94 have got to scientists, has driven a lot of time. In December, 1940 at bombarding radiation of uranium by nucleuses of heavy hydrogen bunch of the American radio chemists led by Glenn T. Seaborg has detected unknown before an emitter of alpha particles with a half-life of 90 years. The unit isotope № 94 with mass number 238 has appeared this emitter. The same year, but several months earlier Edwin McMillan and Philip Abelson have received the first unit, heavy-dutier, than uranium, - a unit № 93. This unit 94th have named neptunium, and - plutonium. The historian definitely will tell, that these titles originate in Roman mythology, but in effect the parentage of these titles is faster not mythological, but astonomical.

Astronomical parallel

The unit occupying 92nd cell periodic table, has been detected Martin Heinrich Klaproth in 1789 and named by uranium in honour of farthest of known then planets (it well-known astronomer William Herschel in 1781 for the first time watched, for eight years before hours Klaproth.)

Not Uranus it has appeared last planet of a solar system. Further away from the Sun there drives an orbit of Neptune, but also Neptune not last, behind it is Pluto, a planet about which one till now almost it is not known... Look-alike build-up is watched and on "the left flank" periodic table: uranium - neptunium-plutonium, however about plutonium the mankind knows much more, than about Pluto. By the way, Pluto astronomers have detected all ten years prior to plutonium synthesis, - almost same interval of time devided openings Herschel and Klaproth.

Energy of rocks

Let's size up the power resources concluded in natural reserves of uranium.

Uranium - a trace element, and practically it is everywhere. But very few people knows, that in granite ton on the average is maintained from 4 to 10 grammes of uranium. Granite compounds almost 20 % of weight of earth crust. If to consider only uranium-235 in granite ton it is concluded 6 • 106 large calories of energy. It is a lot of, but...

For waste-handling of a granite and extract from it uranium it is necessary to expend still larger quantity of energy - order of 106-107 large calories. If it was possible to use in the capacity of the energy source not only uranium-235, and and uranium-238 then a granite could be observed at least as potential power raw. Then the energy received from ton of a rock, would compound already from 8 •107 to 2 •108 large calories. It is interconvertible to 16 40 tons of coal. And in this case a granite could yield people almost a million times more energies, than all reserves of chemical combustible on the Earth.

But nucleuses of uranium-238 are not divided by neutrons. For atomic energetics this isotope is useless. More precisely, would be useless, if it did not manage to be transformed into plutonium-239. Also that is specially relevant: practically it is not necessary to spend energy for this nuclear change - vice-versa, in this process energy is effected!

Let's try to clear up, as it happens, but in the beginning some words about natural plutonium.

In 400 thousand times it is less, than radium

Grass-snake it was said, that plutonium isotopes were not conserved since time of synthesis of units at education of our planet. But it does not mean, that plutonium in the Earth is not present. It is all the time derivated in uranic ores. Trapping neutrons of a cosmic radiation and the neutrons organised at spontaneous (spontaneous) partition of kernels of uranium-238, some - very much the few - atoms of this isotope turn to atoms of uranium-239. These nucleuses are very unstable, they irradiate electrons and by that increase the charge. Neptunium - the first transuranium unit is derivated.

Neptunium-239 too is rather unstablis, and its nucleuses irradiate electrons. In total for 56 hours half of neptunium-239 turns to plutonium-239 which one half-life is already enough great - 24 thousand years.

Why do not mine plutonium from uranic ores? Density is too small. Therefore not only to get - even to detect "natural" plutonium unusually difficultly. To make it it was possible only after have been learnt physical and chemical properties of the plutonium received in atomic boilers.

When 2,70>> 2,23 Collect plutonium in nuclear reactors. In heavy-lift neutron fluxes there is a same response, as in uranic ores, but a generation rate and plutonium accumulatings in the choke much more above - in billion billions times. For response of conversion of ballast uranium-238 in power plutonium-239 form optimum (within admissible) conditions.

If the choke works on thermal neutrons from a natural mixture of isotopes of uranium receive quantity of plutonium the little smaller, that quantity of the "burnt out" uranium-235. The little, but smaller, plus plutonium inevitable losses at its chemical stressing from the irradiated uranium. Furthermore chain nuclear reaction is bolstered in a natural mixture of isotopes of uranium only until the inappreciable fraction of uranium-235 is expended. From here the leading-out is natural: the "thermal" choke on natural uranium - the basic phylum of current chokes - cannot ensure a breeding of nuclear fuel. But what then it is perspective? For the answer to this problem we will compare a course of chain nuclear reaction in uranium-235 and plutonium-239 and we will inject into our reasonings one more physical concept.

The major performance of any nuclear fuel - the median number of the neutrons irradiated after a nucleus has trapped one neutron. Physicists name it etha-figure mark out Grecian q character-. In "thermal" chokes on uranium such regularity is watched: each neutron "spawns" on the average 2,08 neutrons (q =2,08). The plutonium placed in such choke under the influence of thermal neutrons yields q =2,03. But after all there are still the chokes working on fast neutrons. A natural mixture of isotopes of uranium in such choke to load it is useless: the chain reaction will not go. But if to enrich "raw" with uranium-235, it can unstrand and, in the "sweeping" choke. Thus q will be peerly more narrow 2,23. And the plutonium, a positioned hearth raking by fast neutrons, will yield q peer 2,70. In our instruction will enter "a superfluous half-neutron". And it at all is not enough.

Let's trace, on what the received neutrons are spent. In any choke one neutron is necessary for maintenance of chain nuclear reaction. 0,1 neutrons it is captured by constructional materials of installation. "Overflow" goes on plutonium-239 accumulating. In one case "overflow" it is peer 1,13, other - 1,60. After "combustion" of a kilogramme of plutonium in the "sweeping" choke energy in 2,25 107 precipitates out and 1,6 kg of plutonium accumulate. And uranium and in the "sweeping" choke will yield the same energy and 1,1 kg of new nuclear fuel. And in that, and the breeding in case of the latter is available. But it is impossible to forget about economics.

Owing to a number of the technical reasons the plutonium cycle of reproduction occupies some years. We will admit, that five years. Means, in a year the quantity of plutonium will be augmented only by 2 %, if q = 2,23, and on 12 %, if q = 2,7! Nuclear fuel - the capital, and any capital should yield, say, 5 % of the annual. In case of the former it is available heavy losses, and in second - larger lost head. This primitive instance illustrates "weight" of every tenth of figure q in a nuclear power problem.

Was relevant and other. The nuclear power should ripen behind growth of requirement for energy. Accounts display: this condition possible in the future only when q comes nearer to three. If developing of nuclear power radiants loses requirements of a company for energy remains two paths: or "to brake advance", or to take energy from any other radiants.

Extract

When as a result of nuclear reactions in uranium the indispensable quantity of plutonium will accumulate, it is necessary for separateing not only from the uranium, but also from partition chips - both uranium, and the plutonium, burnt out in chain nuclear reaction. Besides, in Uranium-Plutonium to pulp there is also a neptunium quantity. It is the most complicated to separate plutonium from neptunium and rare-earth elements (lanthanoids).

To plutonium as to a chemical element in any measure has not carried. From the point of view of the chemist, a nuclear power main member - only one of fourteen actinides. Like the rare-earth elements, all units of an actinic number are very close among themselves on chemical properties, the constitution of outage electronic shells of atoms of all units from actinium to 103rd is equal. Was even more offensive, that chemical properties of actinides are look-alike to properties of rare-earth elements, and among chips of partition of uranium and plutonium of lanthanoids though take away. But 94th unit can be in five valent states, and it "edulcorates a pill" - helps to separate plutonium both from uranium, and from partition chips.

Valence of plutonium varies from three to seven. Are chemical most stable (and consequently, joints of tetravalent plutonium are most propagated and most learnt).

Segregation of relatives on chemical properties of actinides - uranium, neptunium and plutonium - can be grounded on a variance in properties of their four-and hexavalent joints. At first uranic bars dissolve in hydrogen nitrate. Hydrogen nitrate - the strong oxidising agent at dissolution and uranium, both plutonium, and impurities acidify. Zero-valent atoms of plutonium turn to ions Рu6 +. Plutonium dissolves together with uranium. From this solute it reduce to a tervalent status sulphur dioxide, and then precipitate lanthanum fluoride. The sediment except plutonium maintains neptunium rare-earth elements. But the great bulk of material uranium - remains in a solute and separates from plutonium.

The received sediment dissolve again and acidify neptunium to a tetravalent status a potassium bromate. On plutonium this reagent does not act, and at sec sedimentation by the same LаF3 tervalent plutonium transfers in a sediment, and neptunium remains in a solute.

To separate donation chips, plutonium again acidify to a hexavalent status and again add lanthanum fluoride. Now rare-earth elements transfer in a sediment, and plutonium remains in a solute...

From assemblage of methods of stressing of plutonium known nowadays it is necessary to mention extraction of plutonium by organic solvents and plutonium stressing on ion-exchange pillars. These methods are presented the chemists working with plutonium, the most perspective.

Metal

Now, at last, about metal. To evolve joints of plutonium from a solute - a commitment foolproof. Tens the modes are known, allowing it to make. Then the received joints of plutonium transform in chemically pure tetra-fluoride PuF4 which one at 1200 GradCel reduce in barium pairs. So receive pure plutonium. But it yet a structural material: fuel elements of power nuclear reactors (or even atomic bomb details) from it not to make. Why? It is necessary at least, "bar" - mould piece. At manufacture of plutonium items use predominantly a casting method. Melting point of metallic plutonium - 640GradCel - is quite accessible, but...

Spillover melted plutonium from a crucible in the necessary moulding box, start it to chill to an indoor temperature, - in the course of solidification in mould piece by all means there will be cracks. Perhaps, refrigeration goes too sweepingly? As changed conditions, mould piece was immutably blasted. Means, a hitch not in a temperature schedule. What then happens?

In molten metal atoms moving disorderly. With a temperature drop when metal starts to solidify, atoms fluctuate about the centres which have been had in strictly certain order, for example in apexes of becks, tetrahedrons etc. already., depending on a crystalline constitution of this or that metal.

In chips atoms are packaged, as a rule, more tightly, than in fluids. The majority of materials, excepting ice, a type-metal alloy regulus metal and few others, solidifying, are moderated in size - their tightness is augmented.

Plutonium starts to solidify at the temperature of 640°C, thus its atoms derivate a crystal lattice in the form of becks. In process of decrease of temperature tightness of metal by degrees grows. But here the temperature has attained 480°C, and here unexpectedly tightness of plutonium slumps. Of the reasons of this abnormality have got to the bottom quickly enough: at this temperature atoms of plutonium are rearranged in a crystal lattice. It becomes tetragonal and very "crumby". Such plutonium can float in a characteristic melt, as ice on water.

The temperature prolongs to fall, has here it is attained 451°C, and atoms have again derivated a cubic lattice, but have placed on larger, than in case of the former, spacing interval from each other. At further refrigeration the crate becomes at first trimetric, then monoclinic. In total plutonium derivates six various crystalline moulding boxes. Two of them differ remarkable property - a subzero coefficient of thermal expansion: with growth of temperature metal does not expand, and shrinks. Absolutely unusual behaviour!

When the temperature attains 122°C and atoms of plutonium in sixth time rearrange the rows, tightness varies specially hardly - from 17,77 to 19,82 g/sm3. It is More than on 10 %! The bullion size is accordingly moderated. If against the voltage originating on other transferrings, metal still could resist, during this moment collapse is imminent.

How then to fabricate a detail of this surprising metal? Metallurgists dope plutonium (add in it immaterial amounts of the necessary units) and receive mould pieces without a uniform crack. Of them also make plutonium charges of nuclear bombs. A charge weight (it is determined first of all by isotope chain-reacting amount) 5-6 kilogrammes. It would without difficulty be seated in a small cube with a size of a rib of 10 centimetres.

Heavy-duty isotopes

Plutonium-239 in an immaterial amount maintains also the highest isotopes of this unit - with mass numbers 240 and 241. The isotope 240Рu is practically useless is a ballast in plutonium. From 241st receive americium - a unit № 95. In the pure state, without impurity of other isotopes, plutonium-240 and plutonium-241 can be received at electromagnetic segregation of the plutonium collected in the choke. Before it plutonium follow-up irradiate with neutron fluxes with strictly certain performances. Certainly, all it is very complicated, as plutonium not only is radioactive, but also is rather toxic. Job with it requires exclusive guard.

- 242Рu it is possible to learn one of the most interesting isotopes of plutonium, irradiating a long time 239Рu in neutron fluxes. 242Рu very seldom traps neutrons and consequently "burns out" in the choke more slowly remaining isotopes; it is conserved and after remaining isotopes of plutonium almost have completely transferred in chips or have turned to plutonium-242.

Plutonium-242 is relevant as "raw" for rather sweeping accumulating of the highest transuranic elements in nuclear reactors. If in the routine choke to irradiate plutoniums-239 on accumulating from grammes of plutonium of microgram quantities, for example, kalifornija-251 it is required about 20 years.

It is possible to reduce storage time of the highest isotopes, having augmented neutron intensity in the choke. And make, but then it is impossible to irradiate a plutonium-239 lump. After all this isotope is divided by neutrons, and in high flows too much energy precipitates out. There are additional complications with cargo transporter and choke refrigeration. To avoid these complications, it should to moderate quantity of irradiated plutonium. Therefore, the californium yield would become again scanty. A vicious circle!

Plutonium-242 is not divided by thermal neutrons, it, and in lumps it is possible to irradiate in intense neutron fluxes... Therefore in chokes from this isotope "make" and collect in weight quantities all units from californium to einsteinium.

Every time when it was possible to scientists to receive a new isotope of plutonium, metered a half-life of its kernels. Half-lifes of isotopes of heavy-duty radioactive kernels with even mass numbers vary regularly. (It it is impossible to tell about odd isotopes.)

Look at the graph in which one association of a half-life of even isotopes of plutonium on mass number is mirrored. With a weight gain isotope "life time" grows also. Several years ago plutonium-242 was a climax of this graph. And further as this curve - with further growth of mass number will go? Exactly 1 which one matches to survival time of 30 million years, or exactly 2 which one responds already to 300 million years? The answer to this problem was very relevant for sciences about the Earth. In case of the former, if five billions years ago the Earth bodily consisted from 244Рu, now in all pulp, Earths there would be only one atom of plutonium-244.

If correctly second supposition plutonium-244 can be in the Earth in such densities which one could be detected. If has had the luck to discover in the Earth this isotope, the science would receive the most valuable information on processes "happening at making up of our planet.

Several years ago the front scientists has risen a problem: whether it is necessary to try to discover heavy-duty plutonium in the Earth? For the answer to it it was necessary to specify a plutonium-244 half-life first of all. Theorists could not count this rate with the necessary accuracy. All hope was only on experiment.

Plutonium-244 have collected in a nuclear reactor. Irradiated a unit № 95 - americium (an isotope 243Аm). Having trapped a neutron, this isotope transferred in americium-244; americium in one of ten thousand cases transferred in plutonium-244.

From a mixture of americium with a Curie unit have evolved a plutonium-244 drug. The formation sample weighed all some million-refill gramme. But they have sufficed to specify a half-life of this most interesting isotope. It has appeared to peer 75 million years. Plutonium-244 "has not held on" a little to be conserved in the Earth since times of synthesis of units in densities, which one else it is possible to detect.

Heavy-dutier isotopes of plutonium are subject b I-will dissolve, and their life time lies in the range from several days till several tenth sec. We know probably, that in thermonuclear shots all isotopes of plutonium, up to 257Рu are derivated. But their life time - the tenth fractions of a second and to learn many short-lived isotopes of plutonium yet it was not possible.

Tryings scientists undertook assemblage to discover the isotope of a transuranium unit living more longly, than 244Рu. But all of them remained vain. One time was rested by hopes on kjurij-247 but after this isotope has been collected in the choke, was clarified, that its half-life of all of 14 million years. To break a plutonium-244 record it was not possible, is most long-living of all isotopes of transuranic elements.

Plutonium-238 - very first of "man-made" isotopes of plutonium. It is subject an I-will dissolve, i.e. Its nucleuses spontaneously irradiate a-corpuscles - helium nucleuses. a the-corpuscles spawned by nucleuses of plutonium, carry larger energy; having scattered in material, this energy turns to heat.

This isotope seemed in the beginning unpromising.

But as its energy is great! Six million electron volts it is relieved at dissolving of one atomic nucleus of plutonium-238. In the radiant of an electricity containing one kilogramme of plutonium-238, the heat rate of 560 watt unstrands. Ultimate output same by weight a chemical electrical supply - 5 watt. In chemical reaction the same energy precipitates out at oxidising of several million atoms.

There are many emitters with look-alike power performances, but one singularity of plutonium-238 makes this isotope essential. Routinely the alpha-disintegration is escorted by the strong gamma-ray inpouring through larger strata of material. 238Рu - exclusion. An Energia g the-quanta escorting dissolving of its kernels, is insignificant, to shelter from it was foolproof: irradiation is captured by the thin-wall cargo transporter. The probability of spontaneous partition of kernels of this isotope is small also. Therefore it has found application not only in electrical supplies, but also in medicine. Batteries with plutonium-238 are for the energy source in special stimulants of warm activity. The design of artificial heart with an isotope radiant is created. For all these needs the proximate three-four years some tons of "light" plutonium is required.

But 238Рu not lightest of known isotopes of a unit № 94, isotopes of plutonium with mass numbers from 232 to 237 are received. The Half-life of the light isotope - 36 minutes.

Plutonium - a larger subject. It would be desirable to tell the main thing from the most important thing. After all the phrase became more narrow standard, that the plutonium chemistry is learnt much better than chemistry, such "old" units, as iron. About nuclear properties of plutonium the whole books are written. Plutonium metallurgy - one more surprising partition of human knowledge... Therefore it is not necessary to think, that, having read this story, you have really learnt plutonium - the major metal of the XX-th century.