Nuclear Reactions with Neutrons

An atom is the smallest unit of a substance. Its size is approximately 10−8 cm (1Å), and it consists of a positively charged atomic nucleus and one or more electrons moving around the nucleus. The atomic nucleus which is at the center of an atom has a size of 10−12 cm, and it consists of Z protons and N neutrons. Here, Z, N, and A (= Z + N) are the atomic number, neutron number, and atomic mass number, respectively. These numbers are used to describe an atomic nucleus X as X. (As the atomic (chemical) symbol X and the atomic number Z represent the same thing, the atomic number is omitted and the atomic nucleus X is described as AX.) Nuclei having the same atomic numbers but different neutron numbers are known as isotopes. As the isotopes have the same atomic number, they show the same chemical behaviors (this is because chemical behaviors are determined by the number of the electrons around the nuclei), though the nuclei have different characterizations.