Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1932 Chadwick made a very important discovery : he discovered the particle in the nucleus of an atom that became known as the neutron because it has no electric charge .
Simplified: In 1932 , Chadwick discovered a previously unknown particle in the atomic nucleus . This particle became known as the neutron because of its lack of electric charge .