Читать книгу Essentials of Nuclear Medicine Physics, Instrumentation, and Radiation Biology - Rachel A. Powsner - Страница 14

Atoms initially were thought of as no more than small pieces of matter. Our understanding that they have an inner structure has its roots in the observations of earlier physicists that the atoms of which matter is composed contain electrons of negative charge. In as much as the atom as a whole is electrically neutral, it seemed obvious that it must also contain something with a positive charge to balance the negative charge of the electrons. Thus, early attempts to picture the atom, modeled on our solar system, showed the negatively charged electrons orbiting a central group of particles, the positively charged nucleus (Figure 1.4).

Figure 1.4 Flat atom. The standard two‐dimensional drawing of atomic structure.