Complete the list of glossary terms with their corresponding definitions or explanations, based on the provided text.

Glossary Terms and Explanations:

• CAMOE ГЛАВНОЕ: The main part of the text, containing the most important information.
• ИТОГИ ГЛАВЫ: A summary or conclusion of the chapter.
• Радиоактивность [ ]: A phenomenon related to the emission of radiation, with a placeholder for further definition.
• ядерная (планетарная) модель строения атома [ ]: A model describing the structure of an atom, similar to a planetary system, with a placeholder for further definition.
• атомное ядро [ ]: The central part of an atom, with a placeholder for further definition.

Summary: The provided text introduces a section titled "ИТОГИ ГЛАВЫ" (Chapter Summary), highlighting "CAMOE ГЛАВНОЕ" (The Main Point). It then lists key concepts related to atomic structure and radioactivity: "Радиоактивность" (Radioactivity), "ядерная (планетарная) модель строения атома" (Nuclear (planetary) model of atomic structure), and "атомное ядро" (Atomic nucleus). Placeholders denoted by `[ ]` indicate that definitions or further explanations are expected to follow or are contained within the original text not fully visible.