Isotope thorium family

The natural radioelements are listed in Table 14.1. Isotopes of these elements are members of the uranium, actinium and thorium families (Table 1.2, and Tables 4.1 to 4.3). In the ores of U and Th the concentrations of natural radioelements are relatively high and proportional to the half-life. The average concentration of U in the earth s crust is about 2.9 mg/kg (ppm) and that of Th about 11 mg/kg (ppm). The... 

The mass numbers of all isotopes in the family of thori-um-232 are divided by four. Therefore, the thorium family is sometimes referred to as the 4re family. After division by four of the mass numbers of the isotopes in the two uranium families we get a remainder of two or three. Respectively, the uranium-238 family is known as the (4re + 2) family and the uranium-235 family as the (4re + 3) family. 

A radioactive element is an element that disintegrates spontaneously with the emission of various rays and particles. Most commonly, the term denotes radioactive elements such as radium, radon (emanation), thorium, promethium, uranium, which occupy a definite place in the periodic table because of their atomic number. The term radioactive element is also applied to the various other nuclear species, (which arc produced by the disintegration of radium, uranium, etc.) including (he members of the uranium, actinium, thorium, and neptunium families of radioactive elements, which differ markedly in their stability, and are isotopes of elements from thallium (atomic number 81) to uranium (atomic number... 

Now it is clear that radioelements are just isotopes of natural radioactive elements. The three emanations are the isotopes of the radioactive element radon, the number 86 in the periodic system. The radioactive families consist of the isotopes of uranium, thorium, polonium, and actinium. Later many stable elements were found to have isotopes. An interesting observation may be made here. When a stable element was discovered this meant simultaneous discovery of all its isotopes. But in the cases of natural radioactive elements individual isotopes were discovered first. The discovery of radioelements was the discovery of isotopes. This was a significant difference between stable and radioactive elements in connection with the search for them in nature. No wonder that the periodic system was badly strained when accommodation had to be found for the multitude of radioelements,—it was a classification of elements, after all, not isotopes. The discovery of the displacement law and isotopy greatly clarified the situation and paved the way for future advances. 

A decisive role in further developments was played by the radioelement UY, a thorium isotope discovered in 1911 by the Russian radiochemist G. Antonov who worked in Rutherford s laboratory. The radioelement UXi (also a thorium isotope) in the uranium family emits beta particles and gives rise to brevium (UXg). 

The natural isotopes of uranium and thorium in long series of successive radioactive transformations give rise to secondary chemical elements. In the first decade of the 20th century scientists had in their disposal about forty radioactive isotopes of the elements at the end of the periodic system, that is, from bismuth to uranium. These radioelements comprised three radioactive families headed by thorium-232, uranium-235 and uranium-238. Each radioactive element sent, its representatives to these families with the only exception of eka-iodine and eka-cesium. None of the three series had links that would correspond to the isotopes of element 85 or 87. This suggested an unexpected idea that eka-iodine and eka-cesium were not radioactive. But why Nobody dared to answer this question. Under this assumption it was meaningless to look for these elements in the ores of uranium and thorium which contained all the radioactive elements without exception. 

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