noun
heavy oxygen
Scientific term referring to oxygen isotopes heavier than the common oxygen-16, especially oxygen-18.
重酸素は古気候の研究に使われる。
Heavy oxygen is used in paleoclimate research.
重水 is heavy water (D₂O), which contains deuterium; 重酸素 is about oxygen isotopes, not hydrogen.
Compound of 重 (heavy) and 酸素 (oxygen), a straightforward calque of English 'heavy oxygen'.