noun
synthetic element
Technical term used in physics and chemistry for elements not found naturally on Earth, produced artificially in laboratories or nuclear reactors.
プルトニウムは人工元素の一つです。
Plutonium is one of the synthetic elements.
天然元素 refers to naturally occurring elements, in contrast to 人工元素 which are artificially created.
Compound of 人工 (じんこう, 'artificial') and 元素 (げんそ, 'element').