In this article we will familiarize ourselves with the term “radioactivity”. We will consider this concept in general terms, from the point of view of the decay process. Let us analyze the main types of radiation, the decay law, historical data, and much more. Let us dwell separately on the concept of “isotope” and get acquainted with the phenomenon of electronic decay.
Introduction
Radioactivity is a qualitative parameter of atoms, which allows some isotopes to decay spontaneously and emit radiation. The first confirmation of this statement was made by Becquerel, who conducted experiments on uranium. It is for this reason that the rays emitted by uranium were named after him. The phenomenon of radioactivity is the release of an alpha or beta particle from the nucleus of an atom. Radioactivity expresses itself in the form of decomposition of the atomic nucleus of a particular element and allows the latter to transform from the atom of one element to another.
During this process, the decay of the original atom occurs, followed by transformation into an atom that characterizes another element. The result of the ejection of four alpha particles from the atomic nucleus will be a decrease in the mass number that the atom forms by four units. This leads to a shift in the periodic table by a couple of positions to the left. This phenomenon is caused by the fact that during the "alpha shot" 2 protons and 2 neutrons were ejected. And the element number, as we recall, corresponds to the number of protons in the nucleus. If the beta particle (e - ) was thrown out, then the neutron transforms from the nucleus into one proton. This leads to a shift in the periodic table by one cell to the right. Mass changes to extremely small values. The emission of negatively charged electrons is associated with the emission of gamma rays.
Decay law
Radioactivity is a phenomenon during which the isotope decays in a radioactive form. This process is subject to the law: purely atoms (n), which decay in a unit of time, is proportional to the number of atoms (N) that are available at a particular time:
n = λN.
In this formula, the coefficient λ means a constant value of the decay of a radioactive nature, which is associated with the half-life of the isotope (T) and corresponds to the following statement: λ = 0.693 / T. From this law it follows that after a period of time equal to the half-life, the quantitative value of the isotope will become less than half. If the atoms that were formed in the course of radioactive (decay) decay begin to possess the same nature, then their accumulation will begin, which will last until the establishment of a radioactive equilibrium between two isotopes: the daughter and the mother.
Theory and radioactive decay
Radioactivity and decay are interrelated objects of study. The first (r-nost) becomes possible thanks to the second (decay process).
The concept of radioactive decay characterizes itself as a transformation of the composition or structure of the structure of an atomic unstable nucleus. Moreover, this phenomenon is spontaneous. The emission of an elementary particle (p-ts) or gamma-ray occurs, as well as the emission of nuclear fragments. Nuclides corresponding to this process are called radioactive. However, this term also refers to substances whose nuclei are also radioactive.
Natural radioactivity is the decay of atomic nuclei that occur naturally in nature spontaneously. Artificial rtyu is called the same process that we mentioned above, but it is carried out by humans using artificial pathways that correspond to special nuclear reactions.
Maternal and daughter are called those nuclei that decay, and those that are formed as the final product of this decay. The mass number and charge of the daughter structure is described in the Soddy Displacement Rule.
The radioactivity phenomenon includes various spectra that depend on the type of energy. In this case, the spectrum of alpha particles and y-quarks belong to the discontinuous (discrete) type of spectrum, and beta particles are continuous.
Today, we know not only alpha-gamma and beta decays, but also the emission of protons and neutrons has been discovered. The concept of cluster radioactivity and spontaneous fission was also discovered. The capture of electrons, positrons and double decay of beta particles are included in the beta decay section and are considered as a variation thereof.
There are isotopes that can undergo two or more types of decay simultaneously. An example is bismuth 212, which, with a 2/3 probability, forms thallium 208 (when alpha decay is used) and 1/3 leads to polonium 212 (when beta decay is used).
The nucleus that was formed during such a decay can sometimes have the same radioactive properties, and after a while it will be destroyed. The p-decay phenomenon is simpler in the absence of a stable nucleus. The sequence of similar processes is called the decay chain, and the nucleotides arising from this are called radioactive nuclei. The series of such elements, which begin with uranium 238 and 235, as well as thorium 232, eventually come to the state of stable nucleotides, respectively, of lead 206 and 207 and 208.
The phenomenon of radioactivity allows some nuclei (isobars) with the same mass number to turn into each other. This is possible due to beta decay. Each isobaric chain includes from one to three stable beta-type nuclides (they do not have the ability to beta-decay, but they can be unstable, for example, in relation to other types of p-decay). The rest of the set of cores in this chain is beta-unstable. By using β-minus or β-plus decay, the nucleus can be converted into a nuclide with a β-stable form. If such nuclides are in the isobaric chain, then the nucleus may begin to undergo beta-positive or negative decay. This phenomenon is called electronic capture. An example is the decay of the potassium 40 radionuclide into neighboring β-stable states of argon 40 and calcium 40.
About isotopes
Radioactivity is, first of all, the decay of isotopes. Currently, more than forty isotopes with radioactivity and in vivo are known to humans. The predominant amount is located in the r-ranks: uranium-radium, thorium and sea anemone. All these particles exist and spread in nature. They can be present in rocks, waters of the oceans, plants and animals, etc., and they also cause the phenomenon of natural radioactivity.
In addition to the natural series of r-isotopes, more than a thousand artificial species were created by man. The production method most often implements itself in nuclear reactors.
Many r-isotopes are used and used for medical purposes, for example, to fight cancer. They are very important in the field of diagnosis.
General information
The essence of radioactivity is that atoms can spontaneously transform from one to another. Moreover, they acquire a more stable or stable structure of the nucleus. During the transformation, the nth core actively releases the energy resources of the atom, which take the form of charged particles or reach the state of gamma rays; the latter, in turn, form either the corresponding (gamma) or electromagnetic radiation.
We already know about the existence of radioactive isotopes of artificial and natural nature. It is important to understand that there is no particular and / or fundamental difference between them. This is due to the properties of the nuclei, which can only be determined in accordance with the structuring of the nucleus, and they do not depend on the paths of creation.
From the history
As mentioned earlier, the discovery of radioactivity occurred due to the works of Becquerel, which were committed in 1896. This process was identified during experiments on uranium. More specifically, the scientist tried to cause the effect of blackening of the emulsion and subject the air to ionization. Madame Curie-Skłodowska was the first person to measure the magnitude of the radiation intensity U. And at the same time as a scientist from Germany Schmidt, she revealed the r-thorium. It was the Curie couple, after the discovery of invisible radiation, who called it radioactive. In 1898, they also discovered polonium, another p-element that was deposited in uranium resin ores. Radium was discovered by the Curie spouses also in 1898, but a little earlier. The work was completed with Bemon.
After the discovery of many p-th elements, a considerable number of authors proved and demonstrated that all of them cause radiation of three types, which change their behavior in a magnetic field. The unit of radioactivity is becquerel (Bq, or Bq). Rutherford suggested calling the detected rays alpha, beta and gamma rays.
Alpha radiation is a collection of particles with a positive charge. Beta rays are formed by electrons, particles with a negative charge and low mass. Gamma rays are an analogue of x-rays and are presented in the form of electromagnetic quanta.
In 1902, Rutherford and Soddy explained the phenomenon of radioactivity through the arbitrary transformation of an atom of one element into another. This process obeyed the laws of randomness and was accompanied by the release of energy resources, which took the form of gamma, beta, and alpha rays.
Natural radioactivity was investigated by M. Curie together with Debierne. In 1910, they received metal - radium - in its pure form, and investigated its properties. In particular, attention has been paid to measuring continuous decay. Debierne and Gisel made the discovery of sea anemone, and Gan discovered atoms such as radiotorium and mesotorium. Ionium was described by Boltwood, and Hahn and Meitner discovered the protactinium. Each isotope of these elements that have been discovered has radioactive properties. Pierre Curie and Labord in 1903 described the decay of radium. They showed that the reaction products of 1 gram of Ra release about one hundred forty kcal in one hour of decay. In the same year, Ramzai and Soddy found that a sealed ampoule with radium also contained helium in a gaseous form.
The works of scientists such as Rutherford, Dorn, Debierne and Gisel, show us that in the general list of decay products U and Th includes some rapidly decaying substances - gases. They have their own radioactivity, and they call them thorium or radium emanations. This also applies to sea anemone. They proved that when decayed, radium creates helium and radon. The law of radioactivity on the transformation of elements was first formulated by Soddy, Russell and Faience.
Types of radiation
The discovery of the phenomenon that we study in this article was first undertaken by Becquerel. It was he who discovered the phenomenon of decay. Because units of radioactivity are called becquerels (Bq). However, one of the biggest contributions to the development of the doctrine of r-nosti made Rutherford. He focused his own attention resources on the analysis of the decay under study and was able to establish the nature of these transformations, as well as determine the radiation that accompanies them.
The basis of his conclusions is the postulation about the presence of alpha, gamma and beta radiation, which are emitted by natural radioactive elements, and the measurement of radioactivity made it possible to isolate the following types:
- Β-radiation is endowed with strong penetrating properties. It is much more powerful than alpha radiation, but it also lends itself to deviation in the magnetic and / or electric field in the direction opposite to the greater distance. This serves as an explanation and proof that these particles are negatively charged e - . Rutherford was able to draw conclusions about the fact that it is electrons that are emitted based on an analysis of the ratio of mass to charge.
- Α-radiation - waves of rays that, under atmospheric pressure, can only overcome small distances (usually not more than 7.5 centimeters). If you place it in x vacuum, you can observe how the magnetic and electric fields affect alpha radiation and lead to its deviation from the original trajectory. By analyzing the direction and magnitude of the deviation, and also taking into account the ratio between the charge and the mass (e / m), we can conclude that this radiation is a stream of particles with a positive charge. The ratio of the parameters of weight and charge is identical to the value of a doubly ionized helium atom. Based on his work and using spectroscopic studies, Rutherford established that alpha radiation is produced by helium nuclei.
- γ-radiation is a type of radioactivity that has the largest penetrating power among other types of radiation. It is not amenable to deviation through the influence of a magnetic field, and also does not have a charge. This is "hard" radiation, which in the most undesirable way is able to affect living matter.
Radioactive conversion
Another point in the establishment and concretization of the definition of radioactivity is the discovery by Rutherford of nuclear structures of atoms. No less important is the establishment of a relationship between a number of properties of an atom and the structure of its nucleus. Indeed, it is the “core" of a particle that determines the structure of the electron shell and all the properties of a chemical nature. This is what made it possible to fully decipher the principles and mechanism by which the radioactive transformation occurs.
The first successful transformation of the nucleus was made in 1919 by Ernest Rutherford. He used the “bombardment” of the N nucleus using alpha polonium particles. The consequence of this was the emission of protons by nitrogen, followed by conversion to oxygen nuclei - O17.
In 1934, the Curie spouses received radioactive isotopes of phosphorus through artificial radioactivity. They acted on aluminum with alpha particles. The obtained P30 nuclei had some differences from the natural p-forms of the same element. For example, in the course of decay, not electron particles, but positron ones, were emitted. Then they transformed into stable silicon nuclei (Si30). In 1934, the discovery of artificial radioactivity and the phenomenon of positron decay was made.
Electron capture
One of the classes of radioactivity is electronic capture (K-capture). In it, electrons are captured directly from the shells of atoms. As a rule, the K-shell emits a certain amount of neutrons, and then it is converted into a new “core” of the atom with the same mass number index (A). However, the atom number (Z) becomes less by 1, in comparison with the original nucleus.
The process of nuclear transformation during electron capture and positron decay is an action similar to each other. Therefore, they can be seen simultaneously while observing a set of atoms of the same species. Electronic capture is always accompanied by the emission of radiation in x-ray form. This is explained by the transition of an electron from a more distant nuclear orbital to a closer lying one. This phenomenon, in turn, is explained by the fact that electrons break out from orbits that are closer to the nucleus, and particles from remote levels tend to fill their place.
The concept of isomeric transition
The phenomenon of the isomeric transition is based on the fact that the emission of alpha and / or beta particles leads to the excitation of some nuclei that are in a state of excess energies. The emitted resources "flow out" in the form of excited gamma rays. A change in the state of the nucleus during p-decay leads to the formation and release of all three types of particles.
A study of the strontium 90 isotope made it possible to determine that they emit only β particles, and nuclei, for example, sodium 24, can also emit gamma rays. The predominant number of atoms are very few in an excited state. This value is so short-term (10 -9 ) and small that it cannot yet be measured. Accordingly, only a small percentage of nuclei is able to remain in a state of excitation for a relatively long period of time (up to months).
Nuclei capable of "living" for so long are called isomers. The concomitant transitions that are observed during the transformation from one state to another and are accompanied by the emission of gamma-quantum particles are called isomeric. In this case, the radioactivity of radiation acquires high and life-threatening values. Nuclei that emit only beta and / or alpha particles are called pure nuclei. If gamma rays are emitted in the nucleus during its decay, then it is called a gamma emitter. A pure emitter of the latter type can only be called a core that undergoes many isomeric transitions, which is possible only with prolonged existence in an excited state.