Alpha and beta radiation are generally calledradioactive decays. This is a process, which is the emission of subatomic particles from the nucleus, which occurs at a tremendous rate. As a result, the atom or its isotope can turn from one chemical element to another. Alpha and beta decays of nuclei are characteristic of unstable elements. These include all atoms with a charge number greater than 83 and a mass number exceeding 209.
Reaction conditions
Disintegration, like other radioactivetransformations, is natural and artificial. The latter is due to the ingress of an extraneous particle into the core. How much alpha and beta decay is able to undergo an atom depends only on how soon a stable state will be reached.
Under natural circumstances, alpha and beta-minus decays occur.
Under artificial conditions, there are neutron, positron, proton and other, more rare species of decays and transformations of nuclei.
These names were given by Ernest Rutherford, who studied radioactive radiation.
The difference between a stable and unstable kernel
The ability to decay directly depends onstate of the atom. The so-called "stable" or non-radioactive nucleus is inherent in non-decaying atoms. In theory, observation of such elements can be carried out to infinity, to finally make sure of their stability. This is required in order to separate such nuclei from unstable ones, which have an extremely long half-life.
By mistake, such a "slow" atom can be taken as a stable one. However, tellurium, and more specifically, its isotope number 128, which has a half-life of 2.2 · 1024 years. This case is not unique. Lanthanum-138 is subject to half-life, the term of which is 1011 years. This term is thirty times the age of the existing universe.
The essence of radioactive decay
This process is arbitrary.Each decaying radionuclide acquires a velocity, which is a constant for each case. The rate of decay can not change under the influence of external factors. It does not matter, the reaction will occur under the influence of a huge gravitational force, at absolute zero, in the electric and magnetic field, during any chemical reaction, and so on. Affect the process can only be a direct impact on the interior of the atomic nucleus, which is almost impossible. The reaction is spontaneous and depends only on the atom in which it flows, and its internal state.
When mentioning radioactive decays is oftenthe term "radionuclide" is encountered. Those who are not familiar with it, you should know that this word denotes a group of atoms that have radioactive properties, their own mass number, atomic number and energy status.
Various radionuclides are used in technical,scientific and other spheres of human life. For example, in medicine, these elements are used in diagnosing diseases, processing medicines, tools and other items. There are even a number of therapeutic and prognostic radiopreparations.
Equally important is the determination of the isotope.This word is a special kind of atoms. They have the same atomic number as the ordinary element, but an excellent mass number. This difference is caused by the number of neutrons that do not affect the charge, like protons and electrons, but they change mass. For example, for simple hydrogen, there are as many as 3. This is the only element, whose isotopes have been named: deuterium, tritium (the only radioactive) and protium. In other cases, names are given in accordance with the atomic masses and the main element.
Alpha decay
This is a kind of radioactive reaction. Characterized by the natural elements from the sixth and seventh periods of the periodic table of chemical elements of Mendeleev. Especially for artificial or transuranic elements.
Elements subject to alpha decay
In the number of metals for which this is characteristicdecay, include thorium, uranium and other elements of the sixth and seventh period from the periodic table of chemical elements, counting from bismuth. The process also involves isotopes from the number of heavy elements.
What happens during the reaction?
With alpha decay, the emission of particles consisting of 2 protons and a pair of neutrons begins from the nucleus. The particle itself is the nucleus of a helium atom, with a mass of 4 units and a charge of +2.
As a result, a new element appears, whichlocated two cells to the left of the original in the periodic table. Such an arrangement is determined by the fact that the initial atom lost 2 protons, and with it the initial charge. As a result, the mass of the resulting isotope by 4 mass units decreases in comparison with the initial state.
Examples
During such decay, thorium is formed from uranium.Radium appears from thorium, radon comes from it, which ultimately produces polonium, and in the end lead. In this process, the isotopes of these elements arise, and not themselves. So, it turns out uranium-238, thorium-234, radium-230, radon-236 and further, up to the emergence of a stable element. The formula for this reaction is as follows:
Th-234 -> Ra-230 -> Rn-226 -> Po-222 -> Pb-218
The speed of the selected alpha particles at the time of emission is from 12 to 20 thousand km / s. Being in a vacuum, such a particle would go around the globe in 2 seconds, moving at the equator.
Beta decay
The difference of this particle from the electron is in placeappearances. Beta decay occurs in the nucleus of an atom, and not in the electron shell surrounding it. Most often occurs from all existing radioactive transformations. It can be observed in almost all existing chemical elements. It follows from this that each element has at least one isotope that is subject to decay. In most cases, as a result of beta decay Beta-minus decomposition occurs.
Reaction
In this process, ejection fromthe nucleus of an electron arising from the spontaneous conversion of a neutron into an electron and a proton. In this case, the protons due to the greater mass remain in the nucleus, and the electron, called the beta-minus particle, leaves the atom. And since the number of protons has increased by one, the core of the element itself is changing in a big direction and is located to the right of the original one in the periodic table.
Examples
The decay of beta with potassium-40 turns it into an isotopecalcium, which is located on the right. Radioactive calcium-47 becomes scandium-47, which can turn into a stable titanium-47. What does such a beta decay look like? Formula:
Ca-47 -> Sc-47 -> Ti-47
The beta particle emission rate is 0.9 of the speed of light equal to 270 thousand km / s.
In nature, beta-active nuclides are not too many.Significant ones are quite few. An example would be potassium-40, which in a natural mixture contains only 119/10000. Also natural beta-minus-active radionuclides from among the significant are the products of alpha and beta decay of uranium and thorium.
Beta decay has a typical example:thorium-234, which becomes alpha-decay into protaktinium-234, and then in the same way becomes uranium, but its other isotope, numbered 234. This uranium-234 again, due to alpha decay, becomes thorium, but its other kind . Then this Thorium-230 becomes Radium-226, which turns into radon. And in the same sequence, up to thallium, only with different beta transitions back. This radioactive beta decay ends with the appearance of stable lead-206. This transformation has the following formula:
Th-234 -> Pa-234 -> U-234 -> Th-230 -> Ra-226 -> Rn-222 -> At-218 -> Po-214 -> Bi-210 -> Pb-206
K-40 and elements from thallium to uranium are natural and significant beta-active radionuclides.
Decay beta plus
Также существует бета-плюс превращение.It is also called positron beta decay. It emits a particle called a positron from the nucleus. The result is the transformation of the original element in the left, which has a smaller number.
Example
When electron beta decay occurs, magnesium-23 becomes a stable isotope of sodium. Radioactive europium-150 becomes samarium-150.
The resulting reaction of beta decay can create beta + and beta emission. The particle escape velocity in both cases is equal to 0.9 of the speed of light.
Other radioactive decays
Apart from such reactions as alpha decay and beta decay, whose formula is widely known, there are other, more rare and characteristic of artificial radionuclides processes.
Neutron decay. The emission of a neutral particle 1mass units. During it, one isotope turns into another with a smaller mass number. An example would be the conversion of lithium-9 to lithium-8, helium-5 to helium-4.
When irradiated with gamma rays of a stable iodine-127 isotope, it becomes isotope with the number 126 and acquires radioactivity.
Proton decay. It is extremely rare. During it, the proton is emitted, having a charge of +1 and 1 mass unit. Atomic weight becomes less by one value.
Any radioactive transformation, in particular,radioactive decays, accompanied by the release of energy in the form of gamma radiation. It is called gamma-quanta. In some cases, there is x-ray radiation, which has less energy.
Gamma decay. Представляет собой поток гамма-квантов.It is electromagnetic radiation, more stringent than x-rays, which is used in medicine. As a result, gamma rays, or energy flows from the atomic nucleus, appear. X-rays are also electromagnetic, but they come from the electron shells of an atom.
Alpha particle run
Alpha particles with a mass of 4 atomic units and a +2 charge move in a straight line. Because of this, we can talk about the run of alpha particles.
Значение пробега зависит от изначальной энергии и ranges from 3 to 7 (sometimes 13) cm in the air. In a dense medium, it is one hundredth of a millimeter. Such radiation can not pierce a sheet of paper and human skin.
Because of its own mass and charge numberThe alpha particle has the greatest ionizing ability and destroys everything in its path. In this regard, alpha-radionuclides are the most dangerous for people and animals when exposed to the body.
Penetration ability of beta particles
In connection with the small mass number, which in 1836times smaller than a proton, a negative charge and size, beta radiation has a weak effect on the substance through which it flies, but flying longer. Also, the path of the particle is not straight. In this regard, they talk about penetrating ability, which depends on the energy received.
Penetrating abilities of beta particles arisingduring radioactive decay, in the air they reach 2.3 m, in liquids it is counted in centimeters, and in solids it is in fractions of a centimeter. The tissues of the human body pass radiation at 1.2 cm in depth. To protect against beta radiation, a simple layer of water up to 10 cm can serve. A stream of particles with a sufficiently large decay energy of 10 MeV is absorbed almost all by such layers: air — 4 m; aluminum - 2.2 cm; iron - 7.55 mm; lead - 5.2 mm.
Given the small size, the particles of beta radiation have a low ionizing ability compared to alpha particles. However, when ingested, they are much more dangerous than during external exposure.
Наибольшие проникающие показатели среди всех types of radiation currently has neutron and gamma. The mileage of these radiations in the air sometimes reaches tens and hundreds of meters, but with less ionizing indices.
Most gamma-ray isotopes are not energy efficient.exceed the performance of 1.3 MeV. The values of 6.7 MeV are rarely achieved. In this regard, to protect against such radiation, layers of steel, concrete and lead are used for the multiplicity of attenuation.
For example, to weaken tenfoldCobalt gamma radiation, lead protection about 5 cm thick is needed, 9.5 cm is required for 100-fold attenuation. Concrete protection will be 33 and 55 cm, and water protection - 70 and 115 cm.
Ionizing indicators of neutrons depend on their energy indicators.
In any situation, the best defensive method from radiation will be the maximum distance from the source and the least possible pastime in the high-radiation zone.
Nuclear fission
The division of the nuclei of atoms means spontaneous, or under the influence of neutrons, the division of the nucleus into two parts, approximately equal in size.
These two parts become radioactive isotopes of elements from the main part of the table of chemical elements. Start from copper to lanthanides.
During the selection of a couple of extra breaksneutrons and there is an excess of energy in the form of gamma quanta, which is much more than with radioactive decay. So, with one act of radioactive decay, one gamma-quantum appears, and during a fission event, 8.10 gamma-rays appear. Also scattered fragments have a large kinetic energy, turning into thermal performance.
The released neutrons are able to provoke the separation of a pair of similar nuclei, if they are located nearby and the neutrons hit them.
In this regard, there is a likelihood of a branching, accelerating chain reaction separating atomic nuclei and creating a large amount of energy.
Когда такая цепная реакция находится под control, it can be used for specific purposes. For example, for heating or electricity. Such processes are carried out at nuclear power plants and reactors.
If you lose control over the reaction, then an atomic explosion will occur. This applies to nuclear weapons.
Under natural conditions, there is only one element - uranium, which has only one fissile isotope number 235. It is a weapon.
In an ordinary uranium nuclear reactor fromuranium-238 under the influence of neutrons form a new isotope number 239, and from it - plutonium, which is artificial and is not found in natural conditions. At the same time, the resulting plutonium-239 is used for weapons purposes. This process of nuclear fission is the essence of all atomic weapons and energy.
Phenomena such as alpha decay and beta decay,formula which is studied in school, widespread in our time. Due to these reactions, there are nuclear power plants and many other industries based on nuclear physics. However, one should not forget about the radioactivity of many such elements. When working with them requires special protection and compliance with all precautions. Otherwise, it can lead to an irreparable catastrophe.
