atomic warhead
Refers to the nuclear explosive device mounted on a missile or other delivery system. Technical and military term.
The missile is equipped with an atomic warhead.
核弾頭 is a broader term for 'nuclear warhead', while 原子弾頭 specifically emphasizes atomic (fission) as opposed to thermonuclear (fusion). In practice, they are often used interchangeably.
Compound of 原子 (げんし, 'atom') and 弾頭 (だんとう, 'warhead').