1.
nucleus, core, kernel
The central and most important part of something. Used in biology for the cell nucleus, in physics for the atomic nucleus, and figuratively for the core member or central element of a group or organization.
細胞の核を観察する。
To observe the cell nucleus.
彼はチームの核となる選手だ。
He is a core player on the team.
この研究グループの核となっているのは、若手の研究者たちだ。
It is the young researchers who form the core of this research group.
2.
nuclear (as prefix)
Used as a prefix in compound words related to nuclear energy, nuclear weapons, or nuclear science.
核エネルギーの利用。
The use of nuclear energy.
核実験に反対する。
To oppose nuclear testing.
核の脅威は冷戦時代から続いている。
The nuclear threat has continued since the Cold War era.
COMMON COMPOUNDS (sense 2, nuclear):
- 核兵器: nuclear weapons
- 核実験: nuclear test
- 核融合: nuclear fusion
- 核分裂: nuclear fission
- 核家族: nuclear family
COMMON COLLOCATIONS (sense 1, core):
- 核となる: to serve as the core
- 核を成す: to form the nucleus of
- 組織の核: the core of an organization
NOTE:
核家族 (nuclear family) uses 核 in the sense of "core/nucleus" rather than "nuclear weapons," though the English term "nuclear family" has the same etymological origin.