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A researcher takes a water sample in Seoul, South Korea, to test for radioactivity.
Uranium has a bad reputation, like all radioactive elements.
With good reason, in part, because unfortunately uranium was the main fuel for the first nuclear bomb dropped on a population, the one known as
Little Boy
, which fell on Hiroshima on August 6, 1945. In addition, uranium is used for energy at nuclear power plants, which are also frowned upon by many people.
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The universe is empty
Despite its bad reputation, uranium is a great source of knowledge for astrophysicists or geologists, as it is one of our best clocks for dating from human bones to lunar rocks, meteorites older than the Solar System or the universe itself.
And thanks to uranium and others like it, life on Earth exists as we know it.
We break a spear from radioactivity and explain why.
A professor of mine from the Faculty of Physical Sciences of the Complutense University of Madrid said that the evolution of stars is the result of a continuous struggle between two great physical concepts: gravity and the pressure of a gas.
Similarly, the nucleus of atoms is the result of a fight between titans: the electromagnetic interaction and the so-called strong and weak interactions.
The interaction that joins the nucleons in the atoms, and the quarks within each nucleon, is called strong
Indeed, in the nuclei of all atoms except hydrogen, electrostatic repulsion between particles with the same charge, the protons, coexists with the attraction between nucleons, as both protons and neutrons are known. This attraction is more than 100 times stronger than electromagnetic repulsion at distances on the order of a billionth of a meter, which is known as a femtometer (with a prefix created in 1964 and coming from Danish and Norwegian, not Greek or created! millennia ago as we are used to!). At that scale, gravity is negligible, sextillions of times less intense. For this reason, the interaction that binds nucleons in atoms, and the quarks within each nucleon, is called strong.
The struggle between the strong and electromagnetic interactions remains in tables for many combinations of protons and neutrons, giving rise to the periodic table of the elements. But other combinations of nucleons are unstable, their equilibrium is easily broken and the atomic nucleus tends to break down into parts, emitting radiation in the form of particles with mass (for example, electrons, neutrinos or helium atoms) and / or without mass, such as photons. This is what is known as radioactive decay.
The first radioactive element to be discovered was uranium, thanks to the experiments of Henri Becquerel in the late 19th century, later continued by Marie Skłodowska-Curie, the first person to receive two Nobel Prizes. Uranium is the second most abundant radioactive element, after thorium. In the earth's crust there are almost 50 non-radioactive elements more abundant than both, only 3-4 grams of each ton of earth's rock is uranium, four times more in the case of thorium.
A chemical element is characterized by its atomic number, which is the number of protons in its nucleus. Uranium (U) has 92 protons and thorium (Th) 90. The same chemical element can exist in the form of several isotopes, which are distinguished from each other by the number of neutrons in their nucleus. On Earth, we can find uranium with those 92 protons accompanied by between 140 to 146 neutrons, forming the 6 main isotopes of uranium, all unstable. The most abundant are U-238, more than 99% of uranium is in this form, and U-235 practically all the rest. Both tend to disintegrate in times of the order of 1 billion years. Something similar happens with thorium: there are 7 isotopes, but one dominates over all the others, only two out of every 10,000 thorium atoms are not Th-232, which disintegrates in times similar to the age of the universe,on the order of 15 billion years.
Our planet has been releasing energy for the 4.5 billion years of its existence, cooling in the process from the great ball of rock to thousands of degrees that it originally was.
When a single atom of thorium or uranium decays, it releases four megaelectronvolts (MeV) of energy (let's see when the electricity bill comes in MeV, the unit of energy / mass used by high-energy physicists!), Which it can increase the temperature of a liter of water by a trillionth of a degree centigrade.
It seems very little, but the thing changes if we add all the thorium and all the uranium that is disintegrating on our planet, surely most of it in the mantle and the earth's crust.
Our planet has been releasing energy for the 4.5 billion years of its existence, cooling in the process from the great ball of rock to thousands of degrees that it originally was. The Earth loses energy at the rate of tens of trillions of watts, the equivalent of what a couple of thousand power plants as powerful as the Three Gorges hydroelectric plant, the largest ever built, would produce. Without the continuous warming of the Earth's interior produced by radioactive elements such as uranium-238, thorium-232 or potassium-40, it is possible that the Earth would have completely solidified long ago. Today less than half or even only a quarter of our planet's internal heat comes from the initial energy it acquired from gravitational collapse and collisions of planetesimals. The rest,that dominates the warming, comes from the radioactive decay, mainly from the 3 elements mentioned above. It's no coincidence, those radioactive elements have typical decay times similar to the age of the Earth, so we can still count on them to do their job.
The fact that the Earth's interior is hot and partially fluid is responsible for having plate tectonics, which is noticeable in phenomena such as earthquakes and volcanoes. We have already broken spears in honor of them, not in vain the composition of our atmosphere is intimately linked to the existence of those phenomena that have also been key to regulating the earth's temperature. As a consequence, the temperature is warm on our planet, on average about 16ºC. Having a partially molten and moving interior also allows us to have a magnetosphere, which protects us from more energetic solar radiation and wind.
Radioactivity, and specifically radioactive elements such as uranium, named in honor of the sky god Uranus, or thorium, named in honor of the thunder god Thor, are key in the evolution of our planet and, therefore, in the appearance and evolution of life as we know it.
Radioactivity is clearly a gift from the gods.
Pablo G. Pérez González
is a researcher at the Astrobiology Center, dependent on the Higher Council for Scientific Research and the National Institute of Aerospace Technology (CAB / CSIC-INTA)
Cosmic Void
is a section in which our knowledge about the universe is presented in a qualitative and quantitative way. It is intended to explain the importance of understanding the cosmos not only from a scientific point of view but also from a philosophical, social and economic point of view. The name "cosmic vacuum" refers to the fact that the universe is and is, for the most part, empty, with less than 1 atom per cubic meter, despite the fact that in our environment, paradoxically, there are quintillion atoms per meter cubic, which invites us to reflect on our existence and the presence of life in the universe. The section is made up of
Pablo G. Pérez González
, researcher at the Center for Astrobiology;
Patricia Sánchez Blázquez
, Professor at the Complutense University of Madrid (UCM);
and
Eva Villaver
, researcher at the Center for Astrobiology
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