Related Clues:

• Quark's milieu
• Orbit site
• Unseen energy source
• __ bomb
• Hard thing to split
• Elemental bit
• Splitting it releases energy
• Vowel before omicron
• Minimal trace
• Excitable one
• Mr. ___, radioactive enemy of Captain Marvel
• Matter constituent
• Concern for Edward Teller
• Molecular bit
• Small amount of Greek?