The concept of “radioactivity” was introduced by Marie Skłodowska-Curie. It is identical to the concept of radioactive decay. This process is accompanied by the emission of particles and electromagnetic radiation. The composition of the atomic nucleus is changed: its charge and mass number. Radioactivity is a phenomenon in which the nuclei of one chemical element spontaneously transform into the nuclei of another element or isotopes of the same element, by several types of mechanisms and for different reasons.
Radioactive radiation is a flux of high energy particles escaping from an unstable nucleus. Modern chemistry distinguishes between natural and artificial radioactivity. Natural radioactivity is a phenomenon of spontaneous decay of atomic nuclei in nature. An example of natural radioactivity is solar radiation. In the core of the sun, thermonuclear reactions are constantly taking place, where hydrogen is converted into helium.
Artificial radioactivity is the phenomenon of spontaneous decay of atomic nuclei produced artificially through appropriate nuclear reactions. Man-made radioactivity is used by humans; at nuclear power plants, for example, electrical energy is obtained through artificially created nuclear reactions.
Experiments have established that all elements in Mendeleev’s periodic system, starting with bismuth, are radioactive. Their ordinal number is greater than 82. There are several units for measuring radioactivity in chemistry:
- becquerel;
- curie;
- Reservoir.
In the International System of Units, the unit for measuring the activity of a radionuclide is the becquerel. In Russian it is referred to as Bq, in international format as Bq. This unit was named after Antoine Becquerel, one of the discoverers of radioactivity. One Becquerel is equal to one decay per second. In the International SI, a second to the minus first power is not only a Becquerel, but also a Hertz. It is important not to confuse the two: the becquerel is used to measure random decay processes, while the hertz is used for periodic processes. Their nature is different (Mcgregor 35). One Becquerel is a small unit of measurement, so in practice it is common to use multiples. An off-system but widely used unit is the curie. It is used to measure the activity of radionuclides. Based on the radiation, there are 3 main types of radioactive decay:
- alpha decay;
- beta decay;
- Gamma decay, or isomeric transition.
Decays with emission of protons (one or two), neutrons and cluster radioactivity are also known. The process of radioactive decay can be lengthy. If a daughter nucleus resulting from radioactive decay is also radioactive, it will eventually decay as well. This continues until a stable, non-radioactive nucleus is formed. Moreover, some isotopes may experience more than one type of decay at the same time. Alpha decay – a type of spontaneous decay of an atomic nucleus into a daughter nucleus, in which an alpha particle, the nucleus of a helium atom, is emitted. The mass number of the daughter nucleus is reduced by 4, and the atomic number is reduced by 2.
Alpha decay, i.e. the flux of positively charged particles, is characteristic of isotopes of all heavy elements, starting with bismuth. Alpha particles leave the nucleus with velocities from 9400 to 23700 km/s (Mcgregor 63). In air, however, under normal conditions, alpha radiation is only able to travel a distance of 2.5 to 7.5 cm (Mcgregor 67). The radioactive radiation of alpha particles can be effectively trapped by a few tens of micrometers of dense material. For example, a sheet of paper or even a keratinized layer of skin – the human epidermis. This makes it relatively safe for humans (Mcgregor 23). However, if a source of alpha radiation does enter the body (e.g. in the form of dust), it can lead to serious consequences. Alpha particles cause about 20 times more damage than beta and gamma particles of the same energy.
Beta decay is a type of spontaneous decay of an atomic nucleus into a daughter nucleus, in which a flux of electrons and antineutrinos is emitted. The mass number remains the same, because the number of nucleons in the nucleus remains unchanged (Mcgregor 39). Beta radiation, as negative radiation of low mass, has a greater penetrating power than alpha particles. It can be trapped by aluminum foil.
Gamma decay is more commonly referred to as isomeric transition. This name is justified by the existence of isomeric states of nuclei. Most nuclei are able to exist in an excited state for a very short amount of time – less than a nanosecond. Some nuclei are able to exist longer – microseconds, days, or even years; such long-lived states are called isomeric states. In gamma decay, isomeric states of nuclei go to the ground state with the emission of one or more gamma rays. Gamma radiation has much greater penetrating power than alpha and beta radiation. It has no electrical charge, has tremendous energy, and can only be stopped by a thick layer of reinforced concrete, steel, lead, or other serious obstacle.
Thus, the term radiation is extremely versatile in chemistry. It assumes two kinds of radioactivity, artificial and natural. The decay of particles can be accomplished by three different mechanisms, such as alpha decay, beta decay, and gamma decay. Among all types of radioactive decay, beta decay is the most common. It is especially characteristic of man-made radionuclides.
Work Cited
Mcgregor, Douglas. Radiation Detection and Measurement : Concepts, Methods and Devices. Crc Press, 2018.