3 sentences

1. 原子由原子核和电子组成。

   yuán​zǐ yóu yuán​zǐ​hé hé diàn​zǐ zǔ​chéng.

   Atoms are composed of a nucleus and electrons.

   Source: Dong Chinese Dictionary

2. 科学家们正在研究原子核的分裂过程。

   kē​xué​jiā men zhèng​zài yán​jiū yuán​zǐ​hé de fēn​liè guò​chéng.

   Scientists are studying the process of nuclear fission.

   Source: Dong Chinese Dictionary

3. 原子核是由质子和中子这两种核子构成的。

   yuán​zǐ​hé shì yóu zhì​zǐ hé zhōng​zǐ zhè liǎng zhǒng hé​zǐ gòu​chéng de.

   The atomic nucleus is composed of two types of nucleons: protons and neutrons.

   Source: Dong Chinese Dictionary