noun
actinium series
Refers to the radioactive decay chain starting with uranium-235 and ending with lead-207, named after actinium-227 which appears in the chain. The gloss 'Actinides' is a broader term and less precise here.
アクチニウム系列はウラン235から始まる崩壊系列です。
The actinium series is a decay chain that begins with uranium-235.
Compound of アクチニウム (actinium) and 系列 (series, chain), referring to the decay chain in which actinium-227 appears.