Related Clues:
- Democritus' indivisible unit
- Nuclear fission target
- Very small matter
- Molecule bit
- Charged subatomic particle
- Minute matter
- It's split in a lab
- Quantum mechanics model
- Elemental combiner
- Basic unit of matter
- Bit of negativity?
- Bit for 38-Across
- "We have split the ___"
- Molecule building block
- With 4-Across, mushroom cloud producer