Скачать или смотреть Introduction to The Study of Unstable Isotopes - Isotope Geology

Studies of unstable isotopes are carried out based on the concept that radioactive elements decay from alpha and beta particles in order to achieve their stability.

One of the important things to know to carry out this type of study is where we find the elements for dating. Well, most of the elements used in these studies are incompatible elements, a topic addressed in another video on our channel.

Among the dating methods used are the K-Ar, Rb-Sr, Sm-Nd, and U-Th-Pb systems, all of them elements of the incompatible groups. However, even though they are generally classified as incompatible, these elements have varied compatibility with specific minerals and therefore, depending on the rock mineralogy, these methods can be used, after all, if there is no expectation of U existing in the rock minerals, one should not spend resources trying to use this method.

Firstly, the isotopic study consists on studying an isotope of a certain element i.e. Sm147 (called the parent isotope) that undergoes decay and "turns" into an isotope of another element Nd143 (called the daughter isotope). It is worth mentioning that, obviously, they are not isotopes among themselves, after all, they are not even the same element.

This transformation occurs from the emission or capture of the previously mentioned particles. In the case of the alpha particle, it is composed of 2 protons and 2 neutrons, and is then responsible for a decrease of 4 units of mass and 2 positive charges. For example: Sm147 - Nd143.

The beta particle can be emitted or captured. In the case of emission, it happens due to a breakdown of 1 neutron into 1 proton and 1 electron and then that electron is released by the element. In this way, there is an increase of positive charge in the nucleus of the element, but without loss of mass. For example: K19 - Ca20.

In the case of capture, 1 electron is captured by the element's nucleus and it takes the opposite path, bonding with 1 proton and forming 1 neutron. In this way, there is a reduction in the positive charge on the element's nucleus, but again without changing the atomic mass. For example: K19 - Ar18.

In this way, ideally, it is possible to know how long the rock has crystallized or undergone some metamorphic processes, evaluating how much of the daughter element is in it. After all, the decay time has already been studied in the laboratory and is known, so if it were possible to consider that the daughter element did not exist in the rock and today it is possible to identify it in it, it means that it is the product of the decay of the parent element. However, as we will see when we study the methods individually, this is not quite how it works.

These are the factors that determine the path of the decay, which element will be the product and, which method will be the most suitable for the study and dating of the rock. Terms like half-life are important for these studies and are widely addressed by other authors, but if you want us to make a video about it, leave a comment below.

Decay animations from:    / virtualschooluk  

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