Related Clues:

• 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
• Mighty bit
• Where electrons orbit
• Electron's locale
• Building block of matter
• Bit that may be split
• Molecule maker