镭

Left-side metal radical, the compressed form of 金 used on the left of compound characters. Indexes 镭 in the chemical-element family — coined names where 钅 + a phonetic give a specific metal: 铀 uranium, 钚 plutonium, 铍 beryllium, 镭 radium. Modern Chinese coinage applied to the periodic table.

Right 雷 supplies the sound — same léi, same tone, a textbook phonetic. 雷 itself is 雨 rain over 田 field, originally picturing thunderclouds over farmland. The choice of phonetic also nods quietly to radium's electric, glow-in-the-dark character, fitting an element discovered for its lightning-like emanations.