uranium-235

Etymology
From.

Noun

 * 1)  A fissile isotope of uranium, used for energy generation and in atomic weapons, containing one hundred and forty-three neutrons. It has a half-life of 7·038×108 years; it decays into thorium-231 and ultimately lead.

Usage notes

 * In scientific literature, the more technically correct abbreviation is used, rather than U-235.