More specifically, they are often called atomic physicists or nuclear physicists.

Here's why:

* Physics is the branch of science that deals with the fundamental constituents of the universe and their interactions, including the nature of matter and energy.

* Atomic physics focuses specifically on the structure, properties, and behavior of atoms.

* Nuclear physics focuses on the nucleus of the atom, including its structure, composition, and the forces that hold it together.

While physicists are the primary scientists studying atoms, other fields like chemistry and materials science also deal with the behavior of atoms, but their focus is often more on the interactions between atoms to form molecules and materials.