What is alpha decay and beta decay? Beta decay, alpha decay: formulas and reactions

Alpha and beta radiation in the general case are called radioactive decays. This is a process that 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 into 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 radioactive transformations, 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 achieved.

Under natural circumstances, alpha and beta-minus decays occur.

Under artificial conditions, there are neutron, positron, proton and other, more rare varieties 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 on the state of the atom. The so-called "stable" or non-radioactive nucleus is inherent in non-decaying atoms. In theory, the observation of such elements can be carried out to infinity in order 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 · 10 ²⁴ years, can become a vivid example. This case is not unique. Lanthanum-138 is subject to half-life, the term of which is 10 ¹¹ 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. No matter, a reaction will occur under the influence of a huge gravitational force, at absolute zero, in an 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 referring to radioactive decays, the term "radionuclide" is often 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 called a special kind of atoms. They have the same atomic number as a normal 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, in 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. Characteristic for natural elements from the sixth and seventh period of the table of chemical elements of Mendeleyev. Especially for artificial or transuranic elements.

Elements subject to alpha decay

Among the metals for which this decomposition is characteristic, include thorium, uranium and other elements of the sixth and seventh period from the periodic table of chemical elements, counting from bismuth. Isotopes from the number of heavy elements are also subjected to the process.

What happens during the reaction?

In alpha decay, the emission from the nucleus of particles consisting of 2 protons and a pair of neutrons begins. The very isolated particle is the nucleus of the helium atom, with a mass of 4 units and a charge of +2.

As a result, a new element appears, which is located two cells to the left of the source in the periodic table. Such an arrangement is determined by the fact that the initial atom lost 2 protons and, together with this, the initial charge. As a result, the mass of the isotope formed by 4 mass units decreases in comparison with the initial state.

Examples

During this decay, thorium is formed from uranium. From thorium appears radium, from it - radon, which as a result gives polonium, and in the end - lead. In this process, isotopes of these elements appear in the process, and not themselves. So, we get uranium-238, thorium-234, radium-230, radon-236 and further, up to the appearance of a stable element. The formula for this reaction is as follows:

Th-234 -> Ra-230 -> Rn-226 -> Po-222 -> Pb-218

The velocity of the extracted alpha particle at the time of emission is from 12 to 20 thousand km / sec. Being in a vacuum, such a particle would round the globe in 2 seconds, moving along the equator.

Beta decay

The difference between this particle and the electron is in the place of its appearance. The beta decay arises in the nucleus of the atom, rather than the electronic shell surrounding it. Most often occurs from all existing radioactive transformations. It can be observed in almost all existing chemical elements at the present time. It follows that each element has at least one isotope that is disintegrated. In most cases, as a result of beta decay There is a beta-minus decomposition.

Reaction of the reaction

In this process, an electron is ejected from the nucleus, which arises from the spontaneous conversion of a neutron into an electron and a proton. In this case, protons due to a larger 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 changes to the larger side and is located to the right of the source in the periodic table.

Examples

Decay of beta with potassium-40 turns it into a calcium isotope, 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 speed of emission of the beta particle is 0.9 times the speed of light, 270 thousand km / sec.

In the nature of beta-active nuclides, not too much. Significant of them is rather small. An example is potassium-40, which in the natural mixture contains only 119/10000. Also natural beta-minus-active radionuclides from the number of significant are alpha and beta decay products of uranium and thorium.

The beta decay has a typical example: thorium-234, which transforms into protactinium-234 during alpha decay, and then becomes uranium in the same way, but its other isotope at number 234. This uranium-234 again becomes thorium due to alpha decay , But already a different kind of it. Then this thorium-230 becomes radium-226, which turns into radon. And in the same sequence, down to thallium, only with various 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

Natural and significant beta-active radionuclides are K-40 and elements from thallium to uranium.

Decay of beta-plus

There is also a beta-plus transformation. It is also called positron beta decay. It emits a particle from the core called a positron. The result is the transformation of the source element to the one on the left, which has a smaller number.

Example

When electronic beta decay occurs, magnesium-23 becomes a stable isotope of sodium. Radioactive europium-150 becomes samarium-150.

The resulting beta-decay reaction can create beta + and beta-emission. The velocity of emission of particles in both cases is 0.9 times the speed of light.

Other radioactive decays

Apart from such reactions as alpha decay and beta decay, the formula of which is widely known, there are other processes that are more rare and characteristic for artificial radionuclides.

Neutron decay . A neutral particle of 1 unit of mass is emitted. During it, one isotope is converted into another with a smaller mass number. An example is the conversion of lithium-9 to lithium-8, helium-5 to helium-4.

When gamma rays are irradiated with a stable isotope of iodine-127, it becomes an isotope with the number 126 and acquires radioactivity.

Proton decay . It is extremely rare. During this process, a proton is produced, which has a charge of +1 and 1 unit mass. The atomic weight becomes smaller by one value.

Any radioactive transformation, in particular, radioactive decays, is accompanied by the release of energy in the form of gamma radiation. It is called gamma rays. In some cases, X-rays are observed, which have a lower energy.

Gamma decay. It is a stream of gamma quanta. It is electromagnetic radiation, more rigid than X-ray, which is used in medicine. As a result, gamma quanta, or energy fluxes from the atomic nucleus, appear. X-ray radiation is also electromagnetic, but arises from the electron shells of an atom.

Mileage of alpha particles

Alpha particles with a mass of 4 atomic units and a charge of +2 move rectilinearly. Because of this, we can talk about the alpha particle path.

The mileage depends on the initial energy and varies from 3 to 7 (sometimes 13) cm in air. In a dense environment, a hundredth of a millimeter. Such radiation can not penetrate a sheet of paper and human skin.

Because of its own mass and charge number, the alpha particle has the greatest ionizing ability and destroys everything on the way. In this regard, alpha-radionuclides are most dangerous for humans and animals when exposed to the body.

Penetration of beta particles

In connection with the small mass number, which is 1836 times smaller than the proton, negative charge and size, beta radiation has a weak effect on the substance through which it flies, but the flight lasts longer. Also the path of the particle is not rectilinear. In this regard, talk about the penetrating ability, which depends on the energy received.

The penetrating powers of beta particles that have arisen during radioactive decay in the air reach 2.3 m, in liquids counting is carried out in centimeters, and in solids - in fractions of a centimeter. The tissues of the human body transmit radiation at 1.2 cm depth. A simple layer of water up to 10 cm can serve to protect against beta radiation. A stream of particles with a sufficiently high decay energy of 10 MeV is almost completely absorbed by such layers: air - 4 m; Aluminum - 2.2 cm; Iron - 7.55 mm; Lead - 5,2 mm.

Considering the small size, the beta-radiation particles have a low ionizing ability in comparison with the alpha particles. However, when ingested, they are much more dangerous than during external exposure.

The largest penetrating indicators among all types of radiation currently have neutron and gamma. The run of these emissions in the air sometimes reaches tens and hundreds of meters, but with less ionizing parameters.

The majority of gamma-ray isotopes in energy do not exceed 1.3 MeV. Occasionally, values of 6.7 MeV are 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 reduce the gamma radiation of cobalt tenfold, lead shielding of about 5 cm in thickness is necessary, and 9.5 cm will be required for a 100-fold weakening. Concrete protection is 33 and 55 cm, and water protection is 70 and 115 cm.

Ionizing indicators of neutrons depend on their energy parameters.

In any situation, the best protective method from radiation will be maximum distance from the source and as little as possible pastime in the zone of high radiation.

Fission of atomic nuclei

By fission of atomic nuclei is meant spontaneous, or under the influence of neutrons, 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. They start from copper to lanthanides.

During the extraction, a pair of superfluous neutrons break out and an excess of energy is produced in the form of gamma quanta, which is much larger than in radioactive decay. Thus, one gamma quantum occurs during one act of radioactive decay, and 8.10 gamma quanta appear during the fission event. Also, the scattered fragments have a large kinetic energy, which translates into thermal indices.

The released neutrons are capable of provoking the separation of a pair of similar nuclei, if they are located near and the neutrons are in them.

In this connection, there arises the probability of a branching, accelerating chain reaction of the separation of atomic nuclei and the creation of a large amount of energy.

When such a chain reaction is under control, it can be used for certain 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 there will be an atomic explosion. This is used in nuclear weapons.

Under natural conditions, there is only one element - uranium, which has only one fissile isotope with the number 235. It is a weapon.

In an ordinary uranium atomic reactor from uranium-238 under the influence of neutrons form a new isotope at number 239, and from it - plutonium, which is artificial and does not occur under natural conditions. In this case, the arisen plutonium-239 is used for weapons purposes. This process of nuclear fission is the essence of all atomic weapons and energy.

Such phenomena as alpha decay and beta decay, the formula of which is studied in school, are widespread in our time. Thanks to these reactions, there are nuclear power plants and many other industries based on nuclear physics. However, do 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 disaster.