TNAG-1508-FCO40-2066-Guangdong-nuclear-power-station-project-at-Daya-Bay-safety-c-1987 — Page 111

Translation

Nuclear Technology Exhibition

Information Article 1

Nucleus, Isotopes and Rays

Atoms and nucleus

Although substances exist in the natural world in multifarious forms, they are all composed of chemical elements. Up to now 108 elements have been discovered. Different elements are composed of different atoms.

Atoms are very small in size.

The radius of an atom is only 10-8 cm. An atom consists of a positively charged nucleus and negatively charged

Even electrons which orbit the nucleus. The mass of an atom is very small. in the case of the uranium atom, which is comparatively heavy, 2,500 trillion such atoms merely weigh 1 gm.

The size of an atom is extremely big when compared with its nucleus. If we assume that the size of the former is like a hotel, then the latter merely equals to the size of a sesame seed. Despite the extremely small size of the nucleus, nearly all the mass of an atom is concentrated at its nucleus.

The structure of a nucleus is very complicated. It is composed

The chemical properties of positively charged protons and neutral neutrons.

While of an atom are determined by the number of protons in its nucleus. the numbers of protons in the nuclei of the same element are the same, those of neutrons may vary. For example, hydrogen, which is the simplest element, has 3 different nuclei, with hydrogen having only one proton, deuterium one neutron as well as one proton and tritium two neutrons in addition to one proton.

Isotopes

Isotopes are atoms of the same element having different mass numbers. Their chemical properties are almost identical and they take up the same position in the Periodic Table. Hydrogen, deuterium and tritium are isotopes of the same element. So, isotopes are in fact nuclides in nuclei with the same numbers of protons but different numbers of neutrons. So far, over 2,500 isotopes have been discovered.

Depending on the stability of their nuclei, isotopes are categorised

Because of its unstable into stable isotopes and radioactive isotopes. nucleus, a radioisotope spontaneously emits rays and then become a different isotope.