Related Clues:

• Lepton site
• It's smaller than a molecule
• Bit of matter
• With 41-Down, nuclear device
• Bit to be split
• Democritus' indivisible unit
• Nuclear fission target
• Very small matter
• Molecule bit
• Minute matter
• U-235, e.g.
• It's split in a lab
• Quantum mechanics model
• Elemental combiner
• Basic unit of matter