natural scientist
A person who studies natural sciences, such as physics, chemistry, biology, or earth science.
He is famous as a natural scientist.
科学者 is a broader term for 'scientist' in any field, while 自然科学者 specifically refers to a scientist in the natural sciences.
Compound of 自然 (しぜん, 'nature') + 科学 (かがく, 'science') + 者 (しゃ, 'person').