Natural radioactivity has been around for billions of years. It can be found literally everywhere. Ionizing radiation existed on Earth long before the birth of life, and it has been present in space long before the appearance of Earth itself. About a billion years ago, complex chemical processes began on our planet, gradually leading to the formation of various molecules of various sizes necessary for the emergence of life.
At that time, nuclear radiation important physical factor contributing to these chemical processes since back then, the amount of radioactive substances and the level of nuclear radiation on Earth were immeasurably higher. Due to the absence of an atmosphere, the effect of gamma radiation from space was much more severe. The free radicals of the simplest carbon compounds that arose under the influence of radiation gave rise to ever new molecules. The very first organisms were significantly different from the ones that currently exist: radiation changed the structure of their macromolecules and caused the emergence of new and new variations. To put it shortly, radiation, being a powerful mutagenic factor, played an important role in the origin and evolution of life on Earth.
Radiation being discovered in the 19th century, despite being older than Earth itself
Millions of years have passed, during which, thanks to the continuing radioactive decay of radionuclides, the radiation level kept decreasing, and during the evolutionary development of modern life forms, the background radiation of our planet stabilized while the resulting atmosphere decreased the level of cosmic gamma radiation capable of reaching the inhabited surface of the Earth. For the last hundreds of thousands of years, the background radiation has been practically constant, and this is why modern organisms have not developed any special organs for the perception of nuclear radiation in the process of evolution. The absence of such receptors in human translated in the fact that thousands of years of history passed without us even suspecting the presence of radioactivity in our environment.
The first report on the discovery of radioactivity was made by French scientist Henri Becquerel on February 24th, 1896 at a meeting of the Academy of Sciences. The first active research on the matter was also carried out in France, this time by outstanding scientists Marie Skłodowska and Pierre Curie. Their discovery of chemical elements which they called radium and polonium attracted the attention of the entire scientific community, and the amount of new research grew rapidly at the beginning of the last century. One of the first scientists to appreciate the importance of the phenomenon of radioactivity was Vladimir Ivanovich Vernadsky. Here are words taken from the article he wrote in 1911:
“We are approaching a great upheaval in the life of mankind, one that no previously experienced event can be compared nor compete with. Soon will come the time when men will hold atomic energy in their own hands the source of a force that will allow them to build their lives the way they want. Will men be able to use this force for the sake of good and not self-destruction? Scientists should not turn a blind eye to the possible consequences of their research and progress. They must connect their work with the best organization of all mankind”.
By the first half of the 30s of the last century, a huge amount of data characterizing the radioactivity of various elements of the earth’s crust had already been collected, as well as data on the radioactivity in the atmosphere at various altitudes, on the radioactivity of water in oceans, seas, rivers and lakes. Repeated studies of meteorites collected by that time showed that they too, contain radioactive isotopes, which implies that the phenomenon of radioactivity is by no means limited to our planet. For those who have thoroughly forgotten all these facts, we shall recall them one more time: humans are surrounded by radioactive elements and radiation. The human body is also radioactive: not only do we live in a radioactive world, we ourselves are part of it. For millions of years, radioactivity hasn’t been hurting us, so before dramatically reacting to the next «radioactive horror story», it is always important to carefully study what this is actually all about.
Decay chain that are always with us
In order to understand what kind of radionuclides are involved, it is necessary to start any analysis with the question “aren’t they naturally radioactive?” This category includes substances that existed on Earth from the very beginning and whose emergence isn’t related to the presence of the human civilization on the planet, nor is it due either to the testing of nuclear and thermonuclear weapons, or to the development of nuclear energy, or to nuclear medicine. There isn’t much of such substances, since radioactive decay has lead led to the fact that only radionuclides with a long half-life are still around to this day. The Earth is fairly old, and over the course of its billion years of existence, short-lived radionuclides ended up, roughly speaking, “self-destructing”. All naturally radioactive substances are divided into three groups based on their origin.
We have already mentioned said groups (also called decay chains, or families) in a previous article on radioactivity. Uranium-238, Uranium-235 and Thorium-232 are the ancestors of these three chains which were named after them: the thorium series, the radium (or uranium) series, and the actinium series. Thorium-232 has a half-life of 14 billion years, so it is abundant in the earth’s crust. But it doesn’t mean that its atoms do not undergo radioactive decay during all this time: they actually do, only the probability of decay for each individual atom is negligible. But since there is a lot of thorium on the planet, its radioactive decay is substantial enough and easy to identify. Thorium-232 decays because of alpha radiation, that is, from time to time two pairs of protons and neutrons fly out of the nuclei of its atom in search of a better life.
After thee four have left the core, it ceases to be the core of thorium-232: what is left is now called radium-228. It is much less stable with a half-life of only 5.75 years, decays due to beta radiation, and when it does, its nucleus turns into an actinium-228 nucleus. This isotope is even less stable with a half-life of 6.15 hours and, once again, we are dealing with beta decay which results in the formation of the thorium-228 isotope. And so on until the decay ends as a lead isotope.
A similar situation occurs with the gradual decay of uranium-238: its chain of transformations begins with a thorium-234 isotope and, passing through radium-226, radon-222, polonium-218, ends as a lead due to alpha and beta decays. The actinium series starts with uranium-235, passes through a couple of radium isotopes, a couple of radon isotopes, a couple of polonium isotopes, and in the end, comes down to this very same lead. Despite its incredible cost, radium has been used in medicine for quite some time. In fact, the development of nuclear medicine was largely based on its isotopes. Sometimes, we hear questions about what kind of merit did Marie Sklodowska-Curie receive two Nobel prizes for (one in physics, one in chemistry), if she discovered “only” two chemical elements? Radium has four naturally-occurring isotopes, while polonium has five, and their half-lives last respectively 1602 years for radium-236 and 3.7 microseconds for polonium-213. Therefore, the question should be asked slightly differently: how was Marie Sklodowska-Curie able to achieve such results with the level of scientific technology that was available at the beginning of the 20th century?
In this group of naturally occurring radioactive materials, the radon-222 isotope with its half-life of 3.8 days is particularly worth paying attention to. It decays because of alpha radiation which, as you know, is the least dangerous when originating from an external source. Radon-222 is part of the radium series which begins with uranium-238. Despite the fact that the half-life of radon-22 is quite short, its concentration in the earth’s crust remains pretty stable due to the high prevalence of uranium. There is indeed a lot of uranium-238 on the planet, however, there are very few deposits. The average quantity of uranium-238 in the earth’s crust is about 1.4 ppm (parts-per-million), whereas in rocks and sandstones, it amounts to 2.0 ppm, and to 4.0 ppm in granite and phosphorite. If rock formations, sandstones and granite sound quite familiar, it’s because these are the components of such building materials as cement and concrete. Of course, the abovementioned concentrations of uranium-238 cannot cause any damage to human health. However, it doesn’t cancel out its alpha decay. We must thus take into account the fact that radon, regardless of the isotope, is, by its chemical properties, an inert gas.
Inert gases are gases that do not undergo chemical reactions with many other substances, as a result of which the radon contained in bricks and concrete can freely penetrate our living quarters. Radon-222 produces alpha radiation, and its high concentration can become a problem if it gets into the body through air or food. But radon-222 is seven and a half times heavier than air, and it therefore doesn’t accumulate towards the ceiling, but near the floor. The way to deal with it is by regularly ventilate the rooms in which we spend a lot of time. If you own a personal dosimeter, then you must note the following feature: indoors, the device shows a level of background radiation 2-3 times higher than the outdoor indicators, and this is completely normal. Keep ventilating the rooms and everything will be in order. It is also worth noting that baths of water containing radon are used in the treatment of diseases of the cardiovascular system, joints, peripheral nervous system and more. It has been used long and successfully enough to understand that natural radioactivity can be harmful to humans only if said humans really try and push for it.
Radioactivity within humans
The second group of naturally occurring radioactive materials consists of the radionuclides that are not a part of the radioactive series. They too arose during the Earth’s formation and their number gradually decreases due to the ongoing decays. Out of all the elements of this group, potassium is the most important one: it is necessary for the growth of plants and is an integral part of any living organism, including the human body. Natural potassium is a mixture of three isotopes: otassium-39, potassium-40 and potassium-41. Potassium-40 produces beta radiation, which brings us to the conclusion that every single person living on this planet is perfectly radioactive. The radioactivity of the human body in terms of potassium-40 is about 4-5 kilobecquerels depending on bodyweight. 1 Becquerel is a unit of measurement of the activity of a quantity of radioactive material in which one nucleus decays per second. Thus, 4 to 5 thousand beta decays of potassium-40 occur in our organisms, and this radioactivity cannot be “removed” by no means, since our life expectancy is slightly shorter than the half-life of this element, which for potassium-40 is of 1.25 billion years. Of course, on can try to get rid of potassium in their body, but this will inevitably end in fatigue, muscle weakness, dry skin, dull hair color, metabolic disorders, malfunctioning heart rate rhythms and even heart attacks. In order to avoid such problems, one should regularly eat potatoes, beans, watermelons, melons, bananas, carrots and, of course, rye bread. Increase your own potassium-40 radioactivity, be healthy and stop being scared of the word “radioactivity”.
We shall point out that the becquerel unit does not characterize the harm that is caused to the body by radioactivity, but what it does characterize is a radioactive source. The radioactive particles emitted by one source or another do not necessarily enter the body, since the body can be far enough so that they fly by or are absorbed by various obstacles along the path. The degree of harm caused to a living organism by ionizing radiation depends on the absorbed dose of said ionizing radiation, that is, the amount of ionizing radiation energy transferred to the organism, which is measured in grays (Gy). 1 Gy is 1 joule of energy from ionizing radiation per 1 kg of absorbing matter. But the gray unit is of most interest to theorists, not to the common folk whose main concern is their health. The absorbed dose does not say anything about the biological effect of radiation. After all, the unit itself doesn’t care whether it is being used in calculations for “living” or “non-living” matter, or whether it is used for alpha, beta or gamma radiation. Also, different organs and tissues of the human body react to radio emission in different ways, which is quite logical: our bones (which are mainly made up of calcium) are one thing, but our skin, stomach and lungs are completely different. Let us quote from one of our previous articles:
“In order to accurately assess the contribution that radiation in a specific organ or tissue makes to the overall health damage in cases of uniform exposure to the whole body, the International Commission on Radiation Protection has introduced dimensionless weighting factors for human organs and tissues. The idea is simple: the sum of all these coefficients should be equal to one, that is, the total harm to the body consists of several «harmful» elements for each of the 27 organs and tissues. Radiation is most harmful to the bone marrow, large intestine, stomach, and mammary glands, for each of which a weighting factor of 0.12 is taken into account. The weighting coefficient for the bladder, liver, esophagus and thyroid is 0.04 for each. Our skin, bone surface cells, brain and salivary glands are the least sensitive to radiation, each of them having a weighting coefficient of 0.01. The remaining 14 organs (tissues) taken together account for the remaining 0.32 units. All these weighting factors are calculated by the already mentioned International Commission on Radiological Protection. It’s not an easy task, and it is thus not surprising to see the values of the coefficients changing from time to time with the accumulation of new data.”
The use of weighting coefficients allows us to calculate what harm the absorbed dose causes to what organs. By multiplying the absorbed dose by a weighting coefficient for the liver, we get the force of radiation impact on the liver, and so on. The value obtained as a result of such a multiplication is called the equivalent dose and it is measured not in grays, but in sieverts (Sv). 1 sievert is a very large value, and we usually use decimal derivatives such as millisieverts (mSv) and microsieverts (μSv).
Now back to potassium-40: the average annual effective equivalent dose received by a person as a result potassium-40 decay in the body’s tissues is of 180 μSv. Sounds scary? Well, the level of radiation is considered safe at a value of approximately 0.5 µSv per hour, or 4’380 µSv per year. The equivalent dose of potassium-40 in our body comes to 4% of the safe limit. Therefore, we can only repeat this once again: natural radioactivity can only harm a person if said person really tries and pushes for it.
The third group of naturally occurring radioactive materials consists of radioactive isotopes that are formed in the biosphere as a result of exposure to cosmic rays. The most significant radionuclide of this group is radioactive carbon-14, since it is also found inside our organisms. This isotope contributes four times less to our internal radioactivity than potassium-40, which means that together, these two elements make up for almost its full volume.
This is how we, as the radioactive individuals we are, have been living in complete equilibrium with our radioactive environment, only experiencing problems in certain regions of the world where the radioactive background has increased. We can logically figure out that there are indeed such regions, and even what the characteristics of said regions are: the higher the surface level above the sea level, the thinner the layer of atmosphere above our heads—that very atmosphere that protects us from harsh cosmic gamma radiation. The second kind of problematic zones are lowlands, in the soil of which, in one form or another, there are accumulations of natural uranium and thorium, since their decay leads to the emergence of radium, and then radon (a gas that is heavier than air, and therefore accumulates in the lowlands).
But ever since the moment mankind has started to master new technologies such as nuclear energy and the creation of artificial radioactive elements for medical use, the situation has changed drastically. Nowadays, according to experts, the total amount of exposure to radioactivity sources consists of more than just natural background and exposure to radon and its decay products; their total contribution is about 65%. About 33.5% of the human exposure to radiation comes from ionizing radiation used in medical procedures, and another 0.25% comes from the use of air transport, the use of radioluminescent goods and nuclear facilities. The contribution of the global fallout of nuclear test products and nuclear incidents at nuclear power plants is a little more than 1%, but this one percent is enough for us to pay close attention to it, so that under no circumstances it will ever have reasons to grow bigger.
“Mayak”, year 1957
We consider the birth date of the nuclear energy field to be June 26th, 1954. It was on this day that the turbine of the Obninsk nuclear power plant (NPP) delivered its first kilowatts of electricity to the country’s energy network. But if you take a closer look at the history of the launch of the first NPP’s reactor, you’ll find quite an interesting coincidence for Russia. The reactor’s physical launch was scheduled for May 3rd, but due to bad weather, one of the launch’s research supervisors, Boris Grigorievich Dubovsky, was delayed in the city of Kharkov, and without his presence at the station’s console, Dmitry Ivanovich Blokhintsev, the director of the entire NPP project and director of the Physics and Energy Institute, decided to postpone the start of work. That spring, the bad weather in Ukraine lasted for 6 days, as a result of which the launch of the reactor of the First NPP took place on May 9th, 1954, at 7:07 PM. May 9th was therefore the day when Russian nuclear scientists won a symbolic victory in the upcoming peaceful nuclear race: there were two more years left before the launch of the Calder Hall nuclear power plant in the English county of Cumbria.
However, only three years after the start of the Obninsk NPP, the energy of the atomic nucleus, unfortunately, showed that it needed to be controlled extremely tightly. On September 29th, 1957, due to the failure of the cooling system at the Mayak industrial complex, an explosion of a capacity of 300 cubic meters occurred, which contained about 80 cubic meters of dried high-level radioactive waste. The explosion completely destroyed the stainless steel tank itself, which was located in a concrete canyon at a depth of more than eight meters, a concrete floor with a thickness of one meter and a weight of 160 tons was thrown back to a distance of 25 meters, and concrete floors of two similar neighboring tanks were also torn down. Within a radius of 3 km, window panes in all buildings were broken. The radioactive isotopes contained in the tanks rose into the air: strontium-90 (half-life of 28.8 years), cesium-137 (half-life of 30.17 years), cerium-144 (half-life of 285 days), zirconium-95 (half-life 64 days), niobium-95 (half-life of 35 days) and ruthenium-106 (half-life of 374 days).
According to the International Atomic Energy Agency’s INES hazard assessment, the so-called “Kyshtym disaster” belongs to category No. 6. For comparison, the No. 7 mark on the INES scale are accidents at the Chernobyl nuclear power plant and at the Fukushima Daiichi nuclear power plant. About 10% of the radioactive substances were blown up to a height where they were picked up by the air flows, which formed the East Ural Radioactive Trace (EURT). At the time of the explosion, a gusty southwest wind blew in the area of the Mayak plant, its velocity in the surface layer was about 5 meters per second, and even up to 10 meters per second at a 500 meters altitude. The fact that on that same evening, the winds happened to be heading this way and not otherwise is a truly fortuitous accident thanks to which radioactive substances did not go towards Chelyabinsk or Sverdlovsk. The fact that the wind was not strong is also luck, since as a result of that, 90% of the radioactive substances remained at the “Mayak”. Industrial buildings, steam locomotives, wagons, motor vehicles, concrete and railways, and much more were polluted.
The complex problem of radioactivity
However, this article is not about the details of the 1957 accident, but about the significance that it still has, surprisingly, to this day. First of all, it became clear to experts in the nuclear industry that radioactive waste requires no less attention and caution than the main production. According to the results of the investigation of the circumstances of the incident, it was found that neither the nuclear fission reactions nor the evolution of hydrogen, which theoretically could lead to a massive explosion, were the actual cause. Later, Scientists at the Academy of Chemical Protection managed to recreate in lab conditions the circumstances prevailing in tank No. 14 and prove that in the absence of properly calculated cooling, which leads to an increase in temperature, a mixture of nitrate and acetate salts (they were used to separate plutonium from irradiated uranium in the reactor) behaves like black powder. It is worth noting that never had anyone encountered anything like this before. It was a general, completely new “scientific discovery”, which fortuitously did not lead to human casualties. Because of this, none of Mayak’s employees was subjected to any criminal prosecution, and only one overall conclusion was drawn: the director of the plant Mikhail Antonovich Demyanovich was removed from his post and sent to work as director of the Siberian Chemical Plant.
A first consequence was that the radwaste management system at all enterprises of the nuclear weapons complex has been radically changed. Secondly, the attitude towards the production of measuring instruments has radically changed as well: the investigation showed that the control and measuring equipment supplied to the Mayak from the chemical industry was practically unable to function under conditions of high radioactivity. The staff of the working commission formed by the Ministry of Secondary Engineering was not enough to cope with the consequences of radioactive contamination at Mayak and throughout the EURT. For the first time in history, there was a need to deal with complex contamination with radioactive isotopes on a large scale and throughout a vast territory. Industrial buildings and equipment, infrastructure, forests, fields and meadows, several villages, farm animals, rivers and streams were impacted by the complex problem of radioactive pollution. The third Main Directorate of the Ministry of Health and the Ministry of Agriculture were involved in the work, and in the spring of 1958 an experimental biogeocenological research station was created 12 km from Ozersk. It involved the Institute of Biophysics of the Academy of Medical Sciences, the Institute of Biophysics of the Ministry of Health, the Institute of Applied Geophysics, the Timiryazevskaya Academy, the Agricultural Institute VASKHNIL, the Soil Institute of the Ministry of Agriculture, the Laboratory of Forestry AN, the All-Russian Research Institute for Experimental Veterinary Medicine and a number of others.
They studied the effect of radiation pollution on human health and on the condition of animals and plants. Protection measures were developed, safe levels of long-term exposure to ionizing radiation were determined, methods for the rehabilitation of affected areas in forests, agricultural land and water sources were developed, migration and behavior of radionuclides in the natural environment were studied.
Of course, such studies would have been carried out anyway, but it was the “Kyshtym disaster” that fanned the spark of all this research work and brought all these departments together to gather the acquired knowledge. Given that pollution in the EURT turned out to be equivalent to pollution that could be caused by a nuclear explosion with a capacity of 20-30 kilotons (such was the power of the American bombs detonated over Hiroshima and Nagasaki), the work done by scientists of different specialties in the Mayak area and throughout the EURT turned out to be of great significance even for the Ministry of Defense, since radioactive contamination is one of the damaging factors in the event of a nuclear war.
In a way, this was the first large-scale “experience” that turned out to be of particular importance in the development of nuclear energy by mankind. Unfortunately, it is by learning from its own mistakes that the country realized that the problem of the spread of radioactive substances is a complex one, and not just an “intradepartmental” problem that only the nuclear industry can solve. However, Rosatom is responsible for playing the role of the “radioactive cop”: not only does it have to provide the most complete, maximally tight isolation for radioactive substances resulting from the production activities of the industry itself, but also to control and handle radioactive substances that appear as the result of the work of any other sector of the economy.
In 1957, a decree of the Council of Ministers was issued “On measures to ensure safety when working with radioactive substances”. In 1958, “Radon” specialized enterprises were created not only in Chelyabinsk, but also in Leningrad (nowadays St. Petersburg), Blagoveshchensk , Irkutsk, Murmansk. Then in 1959, in Gorky (nowadays Nizhny Novgorod), in Grozny, in Khabarovsk, Kazan, Saratov and Novosibirsk. And in 1960, in Sverdlovsk and Moscow. In Soviet times, the “Radon” network worked throughout the country, but what these enterprises are and why was there a need to create the Federal State Unitary Enterprise “NO RAO”, the National Operator for Radioactive Waste Management, and what kind of work is being conducted at each of them, that we will discuss in another article.
Translated by Ellina Hensen
Original text: geoenergetics.ru