Related Clues:

• What the Bohr model models
• Bit to split
• Material
• See 101-Down
• Tiny bundle of energy
• Fundamental particle
• Physics bit
• Split bit
• Tiny power source
• Elemental unit
• Symbol of the post-1945 age
• Chemistry bit
• Film director Egoyan
• With 28-Across, particle accelerators
• Elemental building block