(Transcript of the video commentary.)
When passing through matter, ionizing radiation can disrupt molecules, damage organic tissue or lead to structural changes in matter. It is a natural part of the environment, so we are constantly exposed to its effects. Ionizing radiation comes both from radioactive elements contained in the Earth’s crust and from cosmic radiation. We also receive a certain dose of radiation from man-made sources. Each type of ionizing radiation has its own specific properties and for each type there is a way to effectively shield it or, on the contrary, use its properties.
The essence and effects of ionizing radiation would not have been possible to explain in the past without the discovery of radioactivity and an understanding of the composition of the atom. A number of scientists took care of this, starting with Wilhelm Conrad Röntgen with his mysterious gas-discharge radiation, Henri Becquerel studying the radiation of unexposed uranium ore and Maria Skłodowska-Curie, who named the ability of matter to emit radiation by radioactivity.
Ernest Rutherford contributed greatly to the expansion of knowledge about mysterious radiation but also about the structure of the atom. First, he divided the radiation into three groups according to the depth of their penetration and based on the well-known experiment with the bombardment of gold foil with alpha particles, he came to the conclusion that almost all the mass of an atom is concentrated in a very small volume of positively charged nucleus and significantly lighter electrons rotating around it.
The correctness of Rutherford’s planetary model of the atom was later explained using quantum physics by Niels Bohr, according to which electrons rotate around the nucleus in certain orbits without losing their energy. The discoveries of subatomic particles of the nucleus — the proton, discovered in 1917 by Rutherford, and the neutron, discovered by James Chadwick in 1932 — contributed to a complete understanding of the composition of the atom.
An atomic nucleus consists of protons and neutrons, with the number of protons uniquely identifying the element. Atoms with the same number of protons but different numbers of neutrons are referred to as isotopes of that element. Isotopes have the same chemical properties but differ in their physical properties. Some of them are unstable and by releasing the particles from the nucleus, they move to a more stable state. This process is called radioactive decay or transmutation.
We can call radiation not only electromagnetic waves, but they can also be a stream of particles. The penetration of the radiation depends on the distance it travels before the moving particle is stopped by the successive ionization of the atoms or the photon is absorbed by the atom. Ionizing radiation can be divided into alpha, beta and gamma rays, X-rays, cosmic rays and neutrons.
Alpha radiation has the smallest depth of penetration into matter. It is actually a stream of positively charged helium nuclei that can be reliably shielded even with an ordinary sheet of paper. Typical sources of this radiation are uranium, thorium and radium.
Beta radiation, on the other hand, is a stream of electrons or positrons that arise in the nucleus of an atom during the decay of a neutron or proton. Beta radiation can be shielded by a few centimetres of water or a few millimetres of aluminium.
The third type is gamma radiation. It is a stream of photons that has a very high penetration and ionizes indirectly through particles that are created after the interaction of gamma rays with matter. Gamma radiation can be shielded with a thick layer of lead.
X-rays are also indirectly ionizing short-wave radiation. It has a great penetration depth and can be shielded with a thick layer of concrete or lead. This radiation is produced by the transition of an electron to a lower orbit.
The last type of indirect ionizing radiation is a stream of elementary subatomic particles without electric charge — neutrons. Neutrons are created mainly during fission in nuclear reactors, they spread over long distances but they can be shielded by several meters of water.
Almost everything around us can be a source of ionizing radiation. Radioactive elements found in soil, air, water, food, and even in the human body constitute “natural” sources and the dose of radiation from them is called “natural background”. About 4/5 of the total annual dose that a person receives is from natural sources.
The amount of natural background depends on the location where we live. At higher altitudes, we are exposed to even stronger cosmic radiation.
The source of cosmic rays is primarily our Sun and some comes from space. Most of the cosmic rays are intercepted by the Earth’s magnetic field. In the upper layers of the atmosphere, particles create showers of secondary radiation when they collide with air molecules.
Soil & Bedrock
Soil and bedrock contain a certain amount of radioactive elements, so the annual dose in a given place depends mainly on the composition of the bedrock. In some places in the world, the natural background is many times higher than the average due to the bedrock.
Radioactive elements absorb plants as they grow from the soil and they continue to enter the food chain, so everything we eat and drink is radioactive to some extent. The amount of radioactive substances in food depends on the way the plant or animal absorbs the radioactive elements.
Radioactive sources of radiation are also in the air. This is mainly the radioactive gas radon, which can accumulate in unventilated residential buildings located above rocks containing uranium and thorium. When inhaled, radon in the lungs can emit alpha radiation as it decays.
The human body itself is also a natural source of radiation. It contains the very important elements carbon and potassium and both of these elements have their radioactive isotopes. Every second, several thousand radioactive changes occur in our body.
Science and Medicine
In addition to natural radioactive sources, the number of artificial sources of ionizing radiation also increases with the development of scientific knowledge and medicine. And medicine is the area where these man-made resources are used the most. Modern medicine cannot be imagined without X-ray diagnostic equipment. Liquid radioisotopes are also used in the diagnosis of internal organs. High and precisely focused doses of radiation have their place in medicine in the treatment and removal of tumours.
Strong sources of gamma radiation destroy harmful microorganisms and are therefore used, for example, to sterilize surgical instruments, to protect historical monuments against fungi and mould or to extend the shelf life of food products.
In industry, gamma radiation sources are used as precision gauges to measure the thickness or density of materials and examine their internal structure or to assess the quality of welds and detect invisible defects. Some radioisotopes are used as markers to detect leaks in closed systems.
Spent nuclear fuel from nuclear power plants is also a strong artificial source of ionizing radiation, but due to its strict isolation from the environment, its contribution to human exposure is practically negligible. Conversely, burning coal, which always contains small amounts of uranium, thorium or radium, concentrates radioactive isotopes so that a coal-fired power plant contributes about three times more to the radiation burden of local residents than a nuclear power plant.