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Radioactivity is a process in which an atom of one element transforms into one or more atoms of other elements. A byproduct of this decay is ionising radiation that carries the excess energy released. Some radioactive elements occur commonly in nature, e.g. uranium or radon. It is these elements that create the natural radiation to which we are exposed every day of our lives. However, if humans artificially create a radioactive material, we call this radiation artificial.

Ionising radiation is a flow of particles from a material undergoing a radioactive decay. Not all materials, however, emit the same particles. There are three basic kinds of such radiation:
Alpha, where particles are the helium nuclei and which cannot penetrate even a sheet of paper.
Beta, where particles are electrons or positrons and which can be stopped by a thin layer of a metal.
Gamma, where the particles are photons and which can be stopped only by a thick layer of lead or a similar material.

Atomic nuclei are made of two kinds of particles: protons and neutrons, where the number of protons determines what element it is. The ratio of the protons and neutrons then decides whether radioactive decay will occur. Simply put, if an element is not happy with its number of neutrons, it is radioactive.

In everyday life as well as in science until the beginning of 20th century, the world seemed to be well described by Newtonian mechanics. This means that objects change their positions and speeds according to forces that act upon them. However, many very accurate experiments lead physicists to develop a different model of the world called quantum mechanics that explained the experiment in a more accurate way. In quantum world objects can’t be assigned by macroscopic attributes like speed or trajectory, on the other hand we can talk about probability densities. As an example, if we take a positively charged atom nucleus and surround it with negatively charged electrons, we will not end up with an analogy of tiny solar system. Electrons do not fly around on different orbits like planets around the Sun. A better way of imagining it, is like a cloud of electrons surrounding the nucleus. The density of the cloud gives us the probability of finding an electron in that position.

Nuclei of radioactive atoms, both natural and artificial, undergo a decay into nuclei of different nuclides (atoms with different numbers of particles in their nuclei). However, many of these decays produce nuclides that are also radioactive. In that case the decay continues until a stable nucleus is created. This process is called a decay chain. In a cloud chamber, we can observe the decay of e. g. Radon-220 to polonium-216, which is so unstable that it almost immediately decays to lead-212. Thus we observe two alpha particles, one from each decay, originating from almost the same location. The radon decay chain then continues through three more decays to its final stable product, lead-208.

Ionising radiation is omnipresent, but if organisms are exposed to it in higher doses, it has undesirable health consequences. We could say that radiation is a good servant but a bad master. If we want to use ionising radiation to our advantage, we must at the same time ensure safety of all people as well as the environment. The Chernobyl disaster was not just a combination of coincidences but mainly a severe violation of safety regulations of nuclear power plants. If we adhere to all safety rules, nuclear power plants are a safe source of electric energy as shown by functioning power plants all around the world.

PET = positron emission tomography is a diagnostic method based on a radioactive material with a short half-life. This material is introduced into the body and accumulates in metabolically active tissues like cancer tumors. If we detect the radiation particles emitted, we can determine the position of the tumor. Proton therapy, on the other hand is a therapeutic method, in which the tumour is irradiated with a flow of protons. Protons are used for their smaller side effects compared to other forms of radiation.

Elementary particles are particles that have no internal structure, i. e. we cannot split them to any subparticles. In past, scientists once thought that the elementary particles are just proton, neutron, photon and electron. Today we know that only electron and photon are elementary particles and that protons and neutrons are composed of quarks and gluons. Also some new elementary particles were discovered: muon, tauon, bosons W+, W- a Z0, the Higgs’ boson and neutrinos. All other particles then necessarily must be composed of the elementary ones.

Composite particles are composed of the elementary particles. E. g. The alpha particle is made of two protons and two neutrons, each of which is made of three quarks and gluons.

Bananas are very rich source of dietary potassium and it is potassium that happens to be one of the elements with a relatively high natural radioactivity. Potassium-40 isotope is unusual because it can undergo three types of decay: gamma, beta+ and beta-. Beta+ radiation is made of antimatter, specifically of positrons, the antiparticles of electrons. However, do not panic, it is beyond the human limit to eat enough bananas for any effect of radiation to occur.

Ionising radiation does not originate only on our planet, but also in space. Fortunately, most of it is captured by the atmosphere or the magnetic field of the Earth. The secondary radiation is then emitted during interaction of the cosmic radiation with the molecules of air in the atmosphere. The so called Oh-My-God particle was a particle captured by a cosmic radiation detector in 1991. It got its name because its energy was many times higher than any other particle observed.

The standard model is a model of particles and interactions accepted in contemporary world. It is quite easy to imagine the model. Lets divide the particles of the standard model into two imaginary groups – bricks and grout. By bricks we can understand the first group of particles – they create the matter and the universe. Among particles of the matter belong quarks and leptons. Grout is the other group of particles – force carriers. Force carriers keep objects in the universe together and they are responsible for their interactions.
The standard model includes also the Higgs boson – particle the scientist were searching for half a century and finally found in CERN in 2013.
The standard model of particle physics used to seem like the final theory of everything that is capable of explaining all of physics. Similarly to other branches of physics, this theory also breaks in certain situations it cannot explain. That means that it is not entirely correct, but it does not mean it is not useful and it shows possible directions of further research.

The fastest particles we can encounter are those from the cosmic radiation or those artificially accelerated in particle accelerators. As predicted by Albert Einstein’s Special Theory of Relativity, we observe the particle’s time to run more slowly than ours. Particles do not have watches, but if they are unstable, we can observe the time it takes to decay and compare it to a stationary particle. Then we will find out that moving particles decay more slowly than stationary particles, i. e. their time is slower.

An element is radioactive if it is not happy with the number of neutrons in its nucleus. Therefore, if we wish to make a radioactive element, we need to foist some protons or neutrons onto it. Such a transformation is called a transmutation and is typically done by irradiating the material with ionising radiation e. g. alpha particles, protons or neutrons.

During radioactive decay a lot of energy is released in a form of radiation. Unfortunately, weh do not know, how to directly use the energy of particles so we absorb them in a material. The heat released in this process is used to evaporate water and subsequently we make electricity with a steam turbine. We could basically say that it is just a regular coal power plant with a different method of heating the water.

Ionising radiation, as the name suggests, has the ability to rip electrons from molecules. If this happens a so called “free radical” is created, which is a very reactive chemical species. Free radicals inside cells of our body can react with DNA, the carriers of the genetic information. Cells have many mechanisms of coping with this, but if there are too many such events, cancer or radiation sickness may emerge.