"Physics package" occurs as euphemism for the portion of the nuclear weapon that includes a actual explosive part of a weapon: the detonating device explosives, the fissile material, and (for fusion weapons) fusion fuel.

Numerous nuclear weapons come built within a modular fashion, by using the equivalent natural philosophy pack existence utilized for many different warhead applications. E.g., a physical science pack of the B61 nuclear bomb is also utilized in the W80 ALCM warhead, W81 for the cancelled nuclear Standard SM-2 SAM, W84 GLCM warhead, and W85 Pershing II missile.

When photo of payload casings come quite most common, exposure of the "physics package" come quite uncommon, possibly for the oldest & unrefined nuclear weapons.