Lithium isotopes are widely used not only in the nuclear industry, but also in the production of rechargeable batteries. There are several types of them, two of which are found in nature. Nuclear reactions with isotopes are accompanied by the release of large amounts 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 from each other in the number of neutrally charged elementary particles (neutrons). Modern science knows 9 such isotopes, seven of which are artificial, with atomic masses from 4 to 12.
Of these, the most stable is 8Li. Its half-life is 0.8403 seconds. 2 types of nuclear isomeric nuclides (atomic nuclei that differ not only in the number of neutrons, but also protons) have also been identified - 10m1Li and 10m2Li. They are different in the structure of atoms in space and in properties.
Being in nature
In natural conditions, there are only 2 stable isotopes - with a mass of 6 and 7 units a. eat(6Li, 7Li). The most common of these is the second isotope of lithium. Lithium in Mendeleev's periodic system has serial number 3, and its main mass number is 7 a.u. e. m. This element is quite rare in the earth's crust. Its extraction and processing are costly.
The main raw material for obtaining metallic lithium 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 CaCO3.
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.
Features
Lithium isotopes 6Li and 7Li differ in nuclear properties: the probability of interaction of elementary particles of the atomic nucleus and reaction products. Therefore, their scope is also different.
When the lithium isotope 6Li is bombarded with slow neutrons, superheavy hydrogen (tritium) is produced. In this case, alpha particles are split off 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 replace tritium in fusion reactors and bombs, since tritium is characterized by a smallerstability.
Lithium isotope 7Li in liquid form has a high specific heat and 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 for U and Th fluorides in liquid-s alt nuclear reactors.
Core layout
The most common arrangement of lithium atoms in nature includes 3 protons and 4 neutrons. The rest have 3 such particles. The layout of the nuclei of lithium isotopes is shown in the figure below (a and b, respectively).
To form the nucleus of a Li atom from the nucleus of a helium atom, it is necessary and sufficient to add 1 proton and 1 neutron. These particles connect their magnetic forces. Neutrons have a complex magnetic field, which consists of 4 poles, so in the figure for the first isotope, the average neutron has three occupied contacts and one potentially free one.
The minimum binding energy of the lithium isotope 7Li required to split the element's nucleus into nucleons is 37.9 MeV. It is determined by the calculation method given below.
In these formulas, variables and constants have the following meaning:
- n – number of neutrons;
- m – neutron mass;
- p – number of protons;
- dM is the difference between the mass of the particles that make up the nucleus and the mass of the nucleus of the lithium isotope;
- 931 meV is the energy corresponding to 1 a.u. e.m.
Nucleartransformations
Isotopes of this element can have up to 5 extra neutrons in the nucleus. However, the lifetime of this kind of lithium does not exceed a few milliseconds. When a proton is captured, the isotope 6Li turns into 7Be, which then decays into an alpha particle and a helium isotope 3 He. When bombarded by deuterons, 8Be reappears. When a deuteron is captured by the nucleus 7Li, the nucleus is obtained 9Be, which immediately decays into 2 alpha particles and a neutron.
As experiments show, when bombarding lithium isotopes, a wide variety of nuclear reactions can be observed. This releases a significant amount of energy.
Receive
Lithium isotope separation can be done in several ways. The most common ones are:
- Separation in steam flow. To do this, a diaphragm is placed in a cylindrical vessel along its axis. The gaseous mixture of isotopes is fed towards the auxiliary steam. Some of the molecules enriched in the light isotope accumulate on the left side of the apparatus. This is due to the fact that light molecules have a high rate of diffusion through the diaphragm. They are discharged together with the steam flow from the top nozzle.
- Thermodiffusion process. In this technology, as in the previous one, the property of different speeds for moving molecules is used. The separation process takes place in columns whose walls are cooled. Inside them, a red-hot wire is stretched in the center. As a result of natural convection, 2 flows arise - the warm one moves alongwires up, and cold - along the walls down. Light isotopes are accumulated and removed in the upper part, and heavy isotopes in the lower part.
- Gas centrifugation. A mixture of isotopes is run in a centrifuge, which is a thin-walled cylinder rotating at high speed. Heavier isotopes are thrown by centrifugal force against the walls of the centrifuge. Due to the movement of steam, they are carried down, and light isotopes from the central part of the device - up.
- Chemical method. The chemical reaction proceeds in 2 reagents that are in different phase states, which makes it possible to separate the isotope flows. There are variations of this technology, when certain isotopes are ionized by a laser and then separated by a magnetic field.
- Electrolysis of chloride s alts. This method is used for lithium isotopes only in laboratory conditions.
Application
Practically all applications of lithium are associated precisely with its isotopes. A variation of the element with a mass number of 6 is used for the following purposes:
- as a source of tritium (nuclear fuel in reactors);
- for the industrial synthesis of tritium isotopes;
- for making thermonuclear weapons.
Isotope 7Li 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 the operating conditions of waterpower reactors of nuclear power plants, to clean the coolant in the 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 the industry is to obtain a substance of high purity, 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 low currents and long service life are required (pacemakers and other implants, downhole sensors and other equipment). The half-life of tritium, and therefore the life of the battery, is 12 years.
