Studying the phenomenon of radioactivity, each scientist turns to his most important characteristic, such as half-life. As you know, the law of radioactive decay states that every second in the world there is a decay of atoms, while the quantitative characteristic of these processes is directly related to the number of atoms available. If over a certain period of time, half of the total number of atoms available decays, then ½ of the remaining atoms will require the same amount of decay. It is this time period that is called the half-life. It is different for different elements - from thousandths of a millisecond to billions of years, as, for example, when it comes to the half-life of uranium.
Uranium, as the heaviest of all elements in the natural state on Earth, is generally the most wonderful object for studying the process of radioactivity. This element was discovered back in 1789 by the German scientist M. Klaprot, who gave it a name in honor of the recently discovered planet Uranus. The fact that uranium is radioactive was accidentally established at the end of the 19th century by the French chemist A. Beckerel.
The half-life of uranium is calculated by the same formula as the corresponding periods of other radioactive elements:
T_ {1/2} = au ln 2 = frac {ln 2} {lambda},
where "au" is the average lifetime of an atom, "lambda" is the main decay constant. Since ln 2 is approximately 0.7, the half-life is only 30% shorter on average than the total atom lifetime.
Despite the fact that to date, scientists know 14 isotopes of uranium, in nature there are only three of them: uranium-234, uranium-235 and uranium-238. The half-life of uranium is different: for U-234, it is “only” 270 thousand years, and the half-life of uranium-238 exceeds 4.5 billion. The half-life of uranium-235 is in the "golden mean" - 710 million years.
It is worth noting that the radioactivity of uranium in natural conditions is quite high and allows, for example, to illuminate photographic plates for only an hour. At the same time, it is worth noting that in all of the isotopes of uranium, only U-235 is suitable for the manufacture of nuclear bomb fillings . The thing is that the half-life of uranium-235 in industrial conditions is less intense than its "counterparts", therefore, the yield of unnecessary neutrons is minimal here.
The half-life of uranium-238 significantly exceeds 4 billion years, however, it is also now actively used in the nuclear industry. So, in order to start a chain reaction for the fission of heavy nuclei of this element, a significant amount of neutron energy is needed. Uranium-238 is used as protection in fission and synthesis apparatuses. However, most of the extracted uranium-238 is used to synthesize plutonium used in nuclear weapons.
Scientists use the half-life of uranium to calculate the age of individual minerals and celestial bodies as a whole. Uranium clocks are a fairly universal mechanism for this kind of calculations. At the same time, in order for age to be calculated more or less accurately, it is necessary to know not only the amount of uranium in certain rocks, but also the ratio of uranium and lead as the final product into which the uranium nuclei turn.
There is another way to calculate rocks and minerals, it is associated with the so-called spontaneous fission of uranium nuclei. As is known, as a result of spontaneous fission of uranium under natural conditions, its particles bombard nearby substances with tremendous force, leaving behind special traces - tracks.
It is precisely by the number of these tracks, knowing at the same time the half-life of uranium, that scientists make a conclusion about the age of a particular solid - be it an ancient rock or a relatively “young” vase. The thing is that the age of the object is directly proportional to the quantitative indicator of uranium atoms, the nuclei of which bombarded it.