Radioactive elements are produced in nature and scientific experiments.

Oxygen, which is one of the chemical elements, is necessary for us to breathe.

This rock is radioactive, so care must be taken when handling it.

Radium is a radioactive chemical element.

Hydrogen is the most abundant element in the universe.

Education about sex is very important.

He is majoring in chemistry at university.

Sufficient caution is necessary when handling radioactive materials.

This area is off-limits due to high radiation levels.

This radio is emitting music.