放ほう射しゃ性せい崩ほう壊かい

ほ

う

しゃ

せ

い

ほ

う

か

い

Meanings

1

noun

radioactive decay

Scientific term for the process by which an unstable atomic nucleus loses energy by emitting radiation.

set free, release, fire

射shoot, shine into, onto

性sex, gender, nature

崩crumble, die, demolish

壊demolition, break, destroy

放ほう射しゃ能のう
放射能 refers to radioactivity (the property or strength of emitting radiation), while 放射性崩壊 is the specific process of decay.
半はん減げん期き
半減期 is the half-life, the time required for half of a radioactive substance to decay, a concept closely related to 放射性崩壊.

Compound of 放射性 (radioactive) + 崩壊 (decay, collapse). A straightforward technical term.