We have already mentioned the effects of radioactivity in living tissues when talking about radioactive particles . Indeed, radioactivity has harmful consequences but also very useful applications.
Among the harmful effects we have, for example, that the radioactive dust "rain" from nuclear weapons tests both in the atmosphere and underground during the decade of 1950 was so damaging to all living beings, including humans, that it led to the signing of an international treaty to stop such tests . But how does radioactive fallout affect specifically?
For example, strontium-90 is a radioactive isotope that is produced in fission reactions that can reach the upper layers of the upper atmosphere by non-underground nuclear explosions. The element strontium is just below calcium on the periodic table. When strontium-90 ends up falling to the ground, cows ingest it when they graze and it can replace calcium in the formation of milk, thus entering the food chain where it can damage internal organs, not just the cow and her calf. but also of humans who drink that milk.
These processes of radiation damage to biological organisms are the subject of considerable research today. Paradoxically, some of the results obtained have important applications in agriculture, medicine and other areas. An important area of research, with many ramifications, is discovering how radiation produces genetic changes. We now know that many of the key chemical processes in cells are organized by simple chains of molecules, including DNA. It seems obvious, therefore, that a single radioactive particle with sufficient energy can, by breaking a chemical bond in said chain, cause a permanent effect and perhaps a disastrous change in the cell.
The metabolism of plants and animals can be study with the help of extremely small amounts of radioactive nuclides called isotopic tracers . A radioactive isotope for example, 14 C, acts chemically (and therefore physiologically) as a stable isotope ( 12 C). Thus, we can follow a radioactive tracer with detectors and discover the behavior of a given chemical species as it goes through various metabolic processes. In this way, it is possible to study, for example, the role of micronutrients .
Similarly, agricultural experiments with fertilizers containing radioactive isotopes have shown at what point in the growth of a plant the fertilizer is essential. In chemistry, radioactive isotopes help in determining the details of chemical reactions and the structure of complex molecules, such as proteins, vitamins, and enzymes.
Perhaps the most directly related to our well-being uses of radioisotopes have been found in medical research, diagnosis and therapy. For example, tracers can help determine the rate of blood flow through the heart and extremities, thus aiding in the diagnosis of abnormal conditions. High doses of radiation can cause serious damage to all living cells, but diseased cells are often more easily damaged than normal cells. Therefore, radiation can be used to treat some diseases, for example, to destroy cancerous tumors. Some parts of the body preferably take concrete elements. For example, the thyroid gland absorbs iodine easily. Specially prepared radioisotopes of such elements can be administered to patients with certain diseases, thus delivering the desired radiation directly to the site of the disease.
This method has been used, in addition to the treatment of cancer of the thyroid gland, in diseases of the blood and brain tumors and in the diagnosis of diseases of the thyroid, liver or kidneys. Such a level of specificity has been reached that to destroy a malignant neoplasm in the prostate, "seeds" containing radioactive materials can be inserted into it.
An important use of radioactive elements, such as clocks, remains to be mentioned. But that deserves its own article.
 Unfortunately, the signing of a treaty does not mean that all countries respect it.
 Essential elements, in extremely small quantities, for the welfare of plants and animals.