Alpha and beta radiation are generally called radioactive decays. This is a process that is the emission of subatomic particles from the nucleus, occurring at tremendous speed. As a result, an atom or its isotope can transform 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 greater than 209.
Reaction conditions
Decay, like other radioactive transformations, is natural and artificial. The latter occurs due to the ingress of a foreign particle into the nucleus. How much alpha and beta decay an atom can undergo depends on how soon a stable state is reached.
Under natural circumstances, alpha and beta minus decays are found.
Under artificial conditions, there is neutron, positron, proton, and other, rarer types of decays and nuclear transformations.
These names were given by Ernest Rutherford, who studied radiation.
The difference between a stable and an unstable core
The ability to decay directly depends on the state of the atom. The so-called "stable" or non-radioactive nucleus is characteristic of non-decaying atoms. In theory, observation of such elements can be carried out indefinitely to finally verify 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 "slowed down" atom can be taken as stable. However, tellurium can be a striking example, and more specifically, its isotope number 128, which has a half-life of 2.2 · 10 24 years. This case is not an isolated one. Lanthanum-138 is subject to half-life, which lasts 10 11 years. This period is thirty times the age of the existing universe.
The essence of radioactive decay
This process occurs arbitrarily. Each decaying radionuclide acquires a speed that is constant for each case. The decay rate cannot change under the influence of external factors. No matter, the 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. The process can only be affected by a direct effect on the inside of the atomic nucleus, which is practically impossible. The reaction is spontaneous and depends only on the atom in which it flows and its internal state.
When mentioning radioactive decays, the term "radionuclide" is often found. Those who are not familiar with it should be aware that this word means 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 activity. For example, in medicine, these elements are used in diagnosing diseases, processing drugs, tools and other items. There are even a number of therapeutic and prognostic radiopharmaceuticals.
Equally important is the determination of the isotope. This word refers to a special kind of atom. They have the same atomic number as an 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 change the mass. For example, in simple hydrogen there are as many as 3. They are the only element whose names were assigned to the isotopes: 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 type of radioactive reaction. It is characteristic of natural elements from the sixth and seventh period of the periodic table of chemical elements. In particular for artificial or transuranic elements.
Alpha Decay Elements
Among the metals that are characterized by this decay include thorium, uranium and other elements of the sixth and seventh period from the periodic table of chemical elements, counting from bismuth. Also, isotopes from the number of heavy elements are exposed 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 emitted 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, which is located two cells to the left of the original in the periodic table. This arrangement is determined by the fact that the initial atom lost 2 protons and, at the same time, the initial charge. As a result, the mass of the resulting isotope by 4 mass units decreases compared with the initial state.
Examples
During such a decay, thorium is formed from uranium. Radium appears from thorium, from it - radon, which eventually gives polonium, and at the end - lead. At the same time, isotopes of these elements arise in the process, and not themselves. So, it turns out uranium-238, thorium-234, radium-230, radon-236 and beyond, until 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 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 have circled the globe in 2 seconds, moving along the equator.
Beta decay
The difference between this particle and the electron is in the place of occurrence. The decay of beta occurs in the nucleus of an atom, and not in the electron shell surrounding it. Most often found from all existing radioactive transformations. It can be observed in almost all currently existing chemical elements. It follows from this that each element has at least one isotope susceptible to decay. In most cases, beta decay beta minus decomposition occurs.
Reaction
In this process, an electron is thrown out of the nucleus that has arisen due to the spontaneous conversion of a neutron into an electron and a proton. In this case, due to the larger mass, protons 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 nucleus of the element itself changes upward and is located to the right of the original in the periodic table.
Examples
The 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 stable titanium-47. What does beta decay look like? Formula:
Ca-47 -> Sc-47 -> Ti-47
The beta particle ejection rate is 0.9 of the speed of light, equal to 270 thousand km / s.
There are not too many beta-active nuclides in nature. Significant of them are quite few. An example is potassium-40, which in a natural mixture contains only 119/10000. Significant natural beta-minus-active radionuclides are alpha and beta decay products of uranium and thorium.
The decay of beta has a typical example: thorium-234, which during alpha decay turns into protactinium-234, and then in the same way becomes uranium, but its other isotope number 234. This uranium-234 again becomes thorium due to alpha decay , but its different variety. Then this thorium-230 becomes radium-226, which turns into radon. And in the same sequence, up to thallium, with only different beta transitions back. This radioactive beta decay ends with the emergence 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.
Beta plus decay
There is also a beta plus conversion. It is also called positron beta decay. In it, a particle called a positron is emitted from the nucleus. The result is the transformation of the original element to the one on the left, which has a lower number.
Example
When electronic beta decay occurs, magnesium-23 becomes a stable sodium isotope. Radioactive europium-150 becomes samarium-150.
The resulting beta decay reaction can create beta + and beta emissions. The particle exit velocity in both cases is 0.9 of 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, more rare and characteristic processes for artificial radionuclides.
Neutron decay . Emission of a neutral particle of 1 unit of mass occurs. 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 gamma rays are irradiated with the stable isotope of iodine-127, it becomes the isotope number 126 and acquires radioactivity.
Proton decay . It is extremely rare. During it, the emission of a proton having a charge of +1 and 1 unit of mass occurs. Atomic weight is reduced by one value.
Any radioactive conversion, 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-ray radiation having less energy is observed.
Gamma decay. Represents a stream of gamma rays. 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-ray radiation is also electromagnetic, but arises from the electron shells of an atom.
Alpha particle mileage
Alpha particles with a mass of 4 atomic units and a charge of +2 move rectilinearly. Because of this, we can talk about the range of alpha particles.
The mileage value depends on the initial energy and ranges from 3 to 7 (sometimes 13) cm in air. In a dense medium, it is a hundredth of a millimeter. Such radiation cannot penetrate a sheet of paper and human skin.
Due to its own mass and charge number, an alpha particle has the greatest ionizing ability and destroys everything in its path. In this regard, alpha-radionuclides are most dangerous to humans and animals when exposed to the body.
Beta Penetration
Due to 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 is longer. Also, the particle path is not straightforward. In this regard, they talk about penetrating ability, which depends on the energy received.
The penetrating power of beta particles that occur during radioactive decay in air reaches 2.3 m, in liquids they are counted in centimeters, and in solids - in fractions of a centimeter. Tissues of the human body transmit radiation 1.2 cm in depth. A simple layer of water up to 10 cm can serve as protection against beta radiation. Particle flux 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.
Given the small size, beta particles have a low ionizing ability compared to alpha particles. However, when ingested, they are much more dangerous than during external exposure.
The largest penetrating indicators among all types of radiation are currently neutron and gamma. The range of these radiations in the air sometimes reaches tens and hundreds of meters, but with lower ionizing parameters.
Most of the isotopes of gamma rays do not exceed 1.3 MeV in energy. Occasionally, values of 6.7 MeV are reached. In this regard, to protect against such radiation, layers of steel, concrete and lead are used for the attenuation factor.
For example, to reduce cobalt gamma radiation tenfold, lead protection of about 5 cm thick is needed, 9.5 cm will be required for attenuation 100 times. Concrete protection will be 33 and 55 cm, and water protection will be 70 and 115 cm.
Ionizing indices of neutrons depend on their energy indices.
In any situation, the best protective method against radiation will be the maximum distance from the source and the least possible time spent in the zone of high radiation.
Atomic fission
By fission of nuclei of atoms 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. Start from copper to lanthanides.
During the emission, a pair of excess neutrons breaks out and an excess of energy appears in the form of gamma rays, which is much larger than during radioactive decay. So, during one act of radioactive decay, one gamma quantum occurs, and during the act of fission, 8.10 gamma rays appear. Also, the shattered fragments have a large kinetic energy, turning into thermal indicators.
Released neutrons can provoke the separation of a pair of similar nuclei if they are located close to and neutrons get into them.
In this regard, 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 of the reaction, an atomic explosion will occur. Similar 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 nuclear reactor, from uranium-238, under the influence of neutrons, a new isotope is formed under the number 239, and from it - plutonium, which is artificial and does not occur in natural conditions. In this case, the resulting plutonium-239 is used for weapons purposes. This process of fission of atomic nuclei is the essence of all atomic weapons and energy.
Phenomena such as alpha decay and beta decay, the formula of which is studied at 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 of these elements. When working with them, special protection and the observance of all safety measures are required. Otherwise, it can lead to an irreparable disaster.