The atomic weight of X is (a * a% + B × B%)

The atomic weight of X is (a * a% + B × B%)

Because of the existence of isotopes, and the mass fraction (abundance) of various isotopes are different

Atomic weight of radioactive elements
Why can thorium, plutonium and uranium still be measured as radioactive elements?

The choice between Rutherford's and Picard's hypotheses can be determined by the determination of the atomic weight of actinides. However, since the radioactivity of actinides is only 3% of that of uranium, and the half-life of each member is very short, it is very difficult to determine the atomic weight, Because its content in uranium ore can be compared with radium. However, due to the peculiarity of its nature, the large-scale production of plutonium has not been successful
It was known at that time that the final decay products of uranium, thorium and actinium are all lead. Lead 206 is the final decay product of uranium, so the content of lead 206 in this uranium mineral is particularly high. In addition, this uranium mineral also contains thorium, so there should be more final decay product of thorium, lead 208. However, it is strange that lead 208 is less than lead 207
It can only be concluded that lead 207 is formed from another radioactive source in uranium ore, and it should be the final decay product of actinides. Rutherford added a suggestion at the end of Aston's article, pointing out that actinides should be independent
Picard's hypothesis has been confirmed. However, the basis of his hypothesis is not sufficient. First, uranium does not have heavier natural isotopes; second, the relationship between the energy and half-life of α - rays was not accurate enough at that time
This process shows that it is very important to make bold hypotheses in scientific research. If we have sufficient factual or theoretical basis, we can put forward some hypotheses, which will certainly increase the possibility that the hypotheses will be finally confirmed. However, if we put forward some hypotheses based on clues, as long as there is no contradiction with the facts known at that time, we should still say that they are valuable, Because it opens up a new way to find truth. It is worth recalling that Becquerel made the important discovery of radioactive phenomenon just along with Poincare's wrong hypothesis. Of course, in the end, he is good at discarding the unreasonable part of the hypothesis, which is the key to the success of scientific workers
It is known that the final decay product of actinides is lead 207, so the atomic weight of actinides can be deduced to be 227, while the atomic weight of uranium actinides is supposed to be 235 (or 239). In 1935, Dempster analyzed uranium by spark ion source method, and found the spectral line of uranium actinides (uranium 235). So far, the original isotope of actinides was finally determined, and its mass number was confirmed to be 235