Radioisotope

An atom (nuclear) with the same nuclear charge but different atomic mass is called an isotope. Since the discovery of radioactivity at the end of the 19th century, more than 30 radioactive elements have been discovered by the early 20th century, and it has been shown that some radioactive elements, although significantly different in radioactivity, are chemically identical. In 1910, the British chemist F. Soddy proposed a hypothesis that chemical elements have different physicochemical properties with different atomic weight and radioactivity. These variants should be in the same position of the periodic table, called isotopes. Soon, the atomic weight of a lead obtained from different radioactive elements was 206.08, and the other was 208. In 1897, British physicist W. Thomson discovered electrons. In 1912, he improved the instrument for measuring electrons and used magnetic fields. A magnetic separator (predecessor of the mass spectrometer) was fabricated. When he measured with helium, no matter how it was purified, two parabolas were obtained on the screen, one representing the mass of 20 and the other representing the mass of 22. This is the first stable isotope discovered, that is, a radioactive isotope. When FW Aston made the first mass spectrometer, it was further proved that helium did have two isotopes with different atomic masses and more than 200 isotopes were found from more than 70 other elements. So far, 109 elements have been discovered, and only 20 elements have not found stable isotopes, but all elements have radioisotopes. Most of the natural elements are a mixture of several isotopes, with more than 300 stable isotopes and more than 1,500 radioisotopes.