Introduction to Nuclear Physics Vanderbilt （核物理范德比尔特的介绍）.pdfVIP

Introduction to Nuclear Physics 1.Atomic Structure and the Periodic Table According to the Bohr-Rutherford model of the atom, also called the “solar system model,”the atom consists of a central nucleus surrounded by electrons in orbits around the nucleus. The nucleus is very massive, and the electrons are very light. Both the electrons and the nucleus are very much smaller than the overall size of the atom (the electrons may actually have no size at all). Since the nucleus is positively charged and the electrons are negatively charged, the electrons are attracted toward the nucleus, like the planets are attracted toward the sun, and they orbit around the nucleus is somewhat the same way. While this model has deficiencies that we talk about later, it is sufficient for our present purposes. It turns out that the nucleus has exactly the same charge as the total of all the electrons, but of opposite sign. If the charge on a single electron is −q (negative), the nuclear e charge is Zq (positive), and the atom contains Z electrons, where the integer Z is e called the atomic number. Curiously, these electrons organize themselves into shells, filling first the shell closest to the nucleus and working outward as more electrons are added. Two electrons can fit in the first shell, eight in the second, eighteen in the third, and so on. Unfortunately, the filling of the shells is not completely regular beyond the first two shells. Beginning with the third shell, electrons begin to add to the fourth shell before the third shell is completed, and this complicates things. But this is more important to the chemists than to the nuclear physicists, so we won’t worry about the details here. The chemists tell us that the chemical properties of an atom depend on the electrons in the outermost