Lithium isotopes are widely used not only in the nuclear industry, but also in the manufacture of rechargeable batteries. There are several types, of which two are found in nature. Nuclear reactions with isotopes are accompanied by the release of a large amount of radiation, which is a promising direction in the energy industry.
Definition
Isotopes of lithium are varieties of atoms of a given chemical element. They differ among themselves in the number of neutrally charged elementary particles (neutrons). Modern science knows 9 such isotopes, seven of which are artificial, with an atomic mass of 4 to 12.
Of these, the most stable is 8 Li. Its half-life is 0.8403 seconds. 2 types of nuclear isomeric nuclides (atomic nuclei, which differ not only in the number of neutrons, but also in protons) were also revealed - 10m1 Li and 10m2 Li. They are different in the structure of atoms in space and in properties.
Being in nature
Under natural conditions, there are only 2 stable isotopes - with a mass of 6 and 7 units a. e. m ( 6 Li, 7 Li). The most common of these is the second lithium isotope. Lithium in the periodic system of Mendeleev has a serial number of 3, and its main mass number is 7 a. E. m. This element is quite rare in the earth's crust. Its mining and processing are expensive.
The main raw material for the production of lithium metal is its carbonate (or lithium carbonate), which is converted into chloride, and then electrolyzed in a mixture with KCl or BaCl. Carbonate is isolated from natural materials (lepidolite, spodumene pyroxene) by sintering with CaO or CaCO 3 .
In samples, the ratio of lithium isotopes can vary greatly. This occurs as a result of natural or artificial fractionation. This fact is taken into account when conducting accurate laboratory experiments.
Specifications
The lithium isotopes 6 Li and 7 Li differ in nuclear properties: the probability of interaction of elementary particles of the atomic nucleus and reaction products. Therefore, the scope of their application is also different.
When the lithium 6 Li isotope is bombarded with slow neutrons, superheavy hydrogen (tritium) is obtained. In this case, alpha particles are cleaved and helium is formed. Particles are ejected in opposite directions. This nuclear reaction is shown in the figure below.
This property of the isotope is used as an alternative to the replacement of tritium in fusion reactors and bombs, since tritium is characterized by less stability.
The liquid lithium isotope 7 Li has a large specific heat and a low nuclear effective cross section. In an alloy with sodium, cesium and beryllium fluoride, it is used as a coolant, as well as a solvent of U and Th fluorides in liquid salt nuclear reactors.
Kernel Layout
The most common arrangement of lithium atomic nuclei in nature includes 3 protons and 4 neutrons. The rest have 3 such particles. The arrangement of lithium isotope nuclei is shown in the figure below (a and b, respectively).
In order for a nucleus of a Li atom to form from the nucleus of a helium atom, it is necessary and sufficient to add 1 proton and 1 neutron. These particles combine their magnetic forces. Neutrons have a complex magnetic field, which consists of 4 poles; therefore, in the figure at the first isotope, the average neutron has three occupied contacts and one potentially free one.
The minimum binding energy of the lithium isotope 7 Li, necessary for the splitting of the nucleus of an element into nucleons, is 37.9 MeV. It is determined by the calculation method below.
In these formulas, variables and constant values have the following meaning:
- n is the number of neutrons;
- m is the neutron mass;
- p is the number of protons;
- dM is the difference between the mass of particles making up the nucleus and the mass of the nucleus of the lithium isotope;
- 931 meV is the energy corresponding to 1 a. eat.
Nuclear Transformations
Isotopes of this element can have up to 5 extra neutrons in the nucleus. However, the lifetime of such a variety of lithium does not exceed a few milliseconds. When a proton is captured, the 6 Li isotope turns into 7 Be, which then decays into an alpha particle and the 3 He helium isotope. When bombarded with deuterons, 8 Be reappears. When a deuteron is captured by a 7 Li nucleus, a 9 Be nucleus is obtained, which immediately decays into 2 alpha particles and a neutron.
As experiments show, during the bombardment of lithium isotopes, a wide variety of nuclear reactions can be observed. A significant amount of energy is released.
Getting
Separation of lithium isotopes can be carried out in several ways. The most common ones are:
- Separation in a stream of steam. For this, a diaphragm is placed in a cylindrical vessel along its axis. A gaseous mixture of isotopes is fed towards the auxiliary pair. On the left side of the apparatus, part of the molecules enriched in the light isotope accumulates. This is due to the fact that light molecules are characterized by a high diffusion rate through the diaphragm. They are discharged together with the steam flow from the upper pipe.
- Thermal diffusion process. In this technology, as in the previous one, the property of various speeds for moving molecules is used. The separation process takes place in columns in which the walls are cooled. Inside them, a hot wire is stretched in the center. As a result of natural convection, 2 flows arise - warm moves up along the wire, and cold moves down along the walls. In the upper part, light isotopes accumulate and are removed, and in the lower part - heavy isotopes.
- Centrifugation of gas. The mixture of isotopes is driven in a centrifuge, which is a thin-walled cylinder that rotates at high speed. Heavier isotopes are discarded by centrifugal force to the walls of the centrifuge. Due to the movement of the vapor, they are carried away downward, and light isotopes from the central part of the apparatus are carried upward.
- Chemical way. The chemical reaction proceeds in 2 reagents in a different phase state, which makes it possible to separate the flows of isotopes. There are varieties of this technology when they ionize certain isotopes with a laser and then separate them with a magnetic field.
- Electrolysis of chloride salts. This method is used for lithium isotopes only in laboratory conditions.
Application
Almost all spheres of lithium use are associated precisely with its isotopes. A variation of the element with mass number 6 is used for the following purposes:
- as a source of tritium (nuclear fuel in reactors);
- for industrial synthesis of tritium isotopes;
- for the manufacture of thermonuclear weapons.
Isotope 7 Li is used in the following fields:
- for the production of rechargeable batteries;
- in medicine - for the manufacture of antidepressants and tranquilizers;
- in reactors: as a coolant, to maintain operating conditions of water power reactors of nuclear power plants, to clean the coolant in demineralizers of the primary circuit of nuclear reactors.
The scope of lithium isotopes is becoming wider. In this regard, one of the pressing problems of industry is the production of high purity substances, including mono-isotopic products.
In 2011, the production of tritium batteries was also launched, which are obtained by irradiating lithium with lithium isotopes. They are used where small currents and a long service life are required (pacemakers and other implants, downhole sensors and other equipment). The half-life of tritium, and therefore the battery life, is 12 years.