Comprehensive Notes on Radioactivity, Radionuclides, and Nuclear Applications

Fundamental Definition and Principles of Radioactivity

Radioactivity is defined as the inherent ability of certain substances to spontaneously emit invisible, highly penetrating radiation. This physical phenomenon occurs at the level of the atomic nucleus; during the process of radioactive emission, the parent atomic nuclei undergo a transformation, resulting in their conversion into different types of nuclei. Substances that are composed of atoms characterized by unstable nuclei which emit this radioactive radiation are formally referred to as radionuclides.

Classification and Characteristics of Radioactive Radiation

The nuclei of radionuclides are capable of emitting several distinct types of penetrating radiation, each categorized by its physical composition, level of penetration, and necessary shielding requirements. These types are:

Radiation alpha ( $\alpha$ ): This radiation consists of a stream of alpha particles. Physically, these particles are the nuclei of helium atoms ( $He$ ). While alpha radiation exhibits low penetrating power—it can be fully absorbed by a simple sheet of paper—it remains extremely hazardous if it enters the interior of a living organism, particularly through inhalation (breathing it in) or ingestion (swallowing).
Radiation beta ( $\beta$ ): This radiation is composed of a stream of fast-moving electrons or positrons. Positrons are identified as positively charged particles that possess the same mass as electrons. Beta radiation is significantly more penetrative than alpha radiation, though it can be halted and absorbed by a thin layer of sheet metal.
Radiation gamma ( $\gamma$ ): Gamma radiation is a form of short-wave electromagnetic radiation. It is produced during the transformation of atomic nuclei and is also present as cosmic radiation that reaches Earth from outer space. This type of radiation is utilized medically for the irradiation of malignant tumors. Due to its high energy, it requires a dense material such as a layer of lead to be absorbed.
Neutron radiation: This type of radiation consists of a stream of fast-flying neutrons. It is primarily generated within nuclear reactors and during the detonation of nuclear bombs. It is categorized as the most penetrative form of radiation mentioned, requiring substantial barriers such as a thick layer of water or concrete for effective absorption.

Half-Life, Natural Radionuclides, and Decay Series

A critical identifying property of any radionuclide is its half-life of transformation. This is defined as the specific duration of time required for exactly one-half of the total number of nuclei in a given quantity of a radionuclide to transform.

In the natural world, approximately 50 radionuclides have been identified. One of the most significant natural radionuclides is Uranium-238 ( $U-238$ ). Through the process of nuclear transformation, Uranium-238 creates a sequence of further radionuclides in a step-by-step manner. This process continues until a stable nuclide is formed that does not undergo any further transformation. In the specific case of Uranium-238, the sequence ends with the formation of the stable isotope Lead-206 ( $Pb-206$ ). This entire sequential progression is known as a radioactive decay series.

Beyond these natural occurrences, humans have the capability to manufacture artificial radionuclides. There are currently several thousand known artificial radionuclides, which find essential applications across the fields of science, technology, and clinical medicine.

The Labeled Atoms Method and Ecological Applications

Radionuclides serve vital functions in science, technology, and medicine due to the fact that many chemical elements possess radioactive isotopes in addition to their stable ones. This allows for a technique known as the "method of labeled atoms."

This method involves using a small amount of a specific radioactive isotope to track the movement and cycle of elements within living organisms or plants by measuring the emitted radiation. For example, researchers can observe how potassium ( $K$ ) accumulates in the seeds or leaves of plants, or how iodine ( $I$ ) concentrates within the thyroid gland. This technique is also employed to monitor the movement of harmful substances (pollutants) within the environment, which facilitates the implementation of measures for environmental protection.

Radiocarbon Dating and Historical Research

Radionuclides are indispensable for determining the age of organic substances and geological materials, such as wood, bones, clothing, and ancient documents. The primary tool for historians and archaeologists is the radiocarbon dating method.

This method is predicated on the fact that as long as a plant or animal organism is alive, it continuously takes in carbon from the atmosphere. This intake incluye both stable carbon ( $C$ ) and the radioactive isotope Carbon-14 ( $C-14$ ), or radiocarbon, which has a half-life of 5,730 years. When the organism dies, the intake of carbon stops immediately, and the radiocarbon already present begins to transform into other nuclides. By comparing the proportion of radiocarbon remaining in a sample to the proportion found in living organisms, scientists can accurately determine the sample's age.

Industrial and Medical Utility

In medical practice, radionuclides are utilized for the diagnostic identification of diseases, the sterilization of medical items, and the treatment of malignant tumors through targeted irradiation.

In the industrial sector, radionuclides are used for the measurement and quality control of manufactured products, a field referred to as defectoscopy. Furthermore, radionuclides are used in the production and acquisition of electrical energy.

Questions & Discussion

The following items and questions were noted in the transcript for further review:

Identifying Nuclides and Symbols: $N$ , ${214}_{83}F$ , ${27}_{14}Si$ , ${61}_{31}Gae$
Question: What types [of radiation are there]? (Jaké dru)
Fragment: 2-mal-
Fragment: B-MEE
Question: What is the half-life? (Co je poloc)