Elements in the universe 1869, a Russian chemist Mendeleev arranged 66 elements discovered at that time into a famous periodic table, and predicted the existence and properties of new elements.
Up to now, 1 18 elements have been found, of which 92 are natural elements and the other 26 are synthetic elements. Among natural elements, uranium element 92 is the element with the largest atomic number on the earth, while the artificial transuranic element with the atomic number greater than 92 is an extremely unstable radioactive element.
At present, our exploration of new elements is mainly carried out from two aspects: artificial synthesis and natural exploration. Artificial synthesis is mainly realized by modern experimental means such as long-term irradiation of high-energy neutrons, nuclear explosions and heavy ion accelerators. In addition, new elements can be found in cosmic rays, meteorites, satellite stones and natural minerals, and now we can create new elements through nuclear collisions in the laboratory.
For example, 20 14, Japan used rilac direct accelerator to accelerate zinc particles and hit one piece, thus creating the element 1 13? Unt？ However, these artificial components have a great disadvantage, that is, their life span is extremely short. Take 1 13 as an example, it only exists for three ten thousandths of a second, and then decays into other elements.
In 20 16, scientists hit calcium with artificial elements californium, thus creating a new atom with 1 18 protons in its nucleus. This element only exists in 1 millisecond, but it is the heaviest element made by human beings.
However, with the increase of atomic number, the repulsion between protons of elements increases, so the elements with high atomic number are very unstable, and the higher the atomic number, the more unstable they are, which also causes the elements with high atomic number to decay in a short time.
So there are almost no more than 92 elements (uranium) on the earth, and the newly discovered elements with high atomic number (transuranium elements) are all artificially synthesized, so the types of elements in the universe should be limited.
The production of light elements began with BIGBANG. According to the current mainstream theory, the universe was born in the Big Bang. In the early days of the universe, hydrogen and helium accounted for more than 99%, which were the earliest and most basic elements in the universe and the first two elements in the periodic table. Later, for a long time, the universe cooled until the birth of the first star, and because the mass of stars is generally relatively large.
Moreover, the temperature required to trigger the nuclear fusion reaction inside the supermassive star nucleus is very high, and such conditions can make the temperature of its outer layer just meet the reaction conditions required for hydrogen nuclear fusion. At this time, the outer layer of the star will gradually undergo nuclear fusion reaction, and different nuclear fusion reactions will be carried out layer by layer. As long as the mass of a star is large enough, its internal reactions can continue, from zero to zero, from deuterium and deuterium to helium, and then from helium to helium.
So the elements before iron are formed by nuclear fusion inside the star. So at the beginning of the birth of the universe 65.438+0.382 billion years ago, there were only the simplest elements.
So far, the known chemical elements in our universe are 1 18. Everything in the universe is made up of elements, but the evolution of stars can only reach 56 iron.
Why does nuclear fusion affect iron? Matter consists of microscopic particles, atoms contain nuclei and extranuclear electrons, while nuclei consist of neutrons and protons. These various particles get together, even positively charged protons get together, and there is a strong interaction between nucleons. In other words, if you want to separate these nuclei, you need huge energy.
This energy is called binding energy, in which? Specific binding energy? This means that the binding energy is divided by the total number of nuclei. The greater the binding energy, the tighter the atoms will be bound, and it takes a lot of energy to separate them. Among all the elements, the combined energy of iron 56 is the largest, indicating that iron 56 is the most stable and will not be easily separated.
In fact, we can understand that those heavier than iron 56 will split into iron 56, and those lighter than iron 56 will aggregate into iron 56. Generally speaking, iron 56 is composed of these elements? Chief. Elements on both sides will tend to it.
In fact, it is not impossible to melt iron, but it requires extremely harsh conditions. As mentioned above, the iron core needs a lot of energy to separate, so the nuclear fusion of the iron core can be realized by inputting a lot of energy in the whole process, but the released energy is very small, and the input is much greater than the output, which is generally difficult to achieve in the star core.
Heavy elements are produced because at the end of stellar evolution, iron? 56 will capture neutrons to form heavier elements, and supernova explosions will also form heavy elements, so let's briefly talk about this formation process, which is divided into two situations.
The first is that heavy elements are produced by slow neutron capture at the end of stellar evolution, and the second is that heavy elements are formed when supernovae explode. Therefore, the source of heavy elements after iron mainly depends on the huge energy generated by supernova explosion or neutron star collision, which will release a large number of high-energy neutrons, which will be captured by other elements, making the elements become heavier elements. This process is also called fast neutron capture process and slow neutron capture process.
0 1, slow neutron capture forms heavy elements.
The slow neutron capture process is also called s? This process usually occurs at the end of the evolution of stars, and it is in the ultra-high temperature core. Will the neutron be iron at this time? Capture and form iron? 57, and then iron? 57 will release another high-energy electron to form cobalt? 57, and so on, cobalt continues to form other heavier elements through the capture process of slow neutrons!
02, fast neutrons are captured to form heavy elements.
The capture process of fast neutrons generally occurs in the supernova explosion stage of stars, also known as R process. In this process, iron? 56 kinds of elements are mainly produced by continuous fast neutron capture, and the heavy elements formed by fast neutron capture account for more than half of the heavy elements formed by stars!
It is not difficult to find that no matter which process, iron? 56 is the most basic heavy element, and the heavy element is secondary generated during neutron capture with iron as the heavy element.