Related Clues:

• Tiny bundle of energy
• Fundamental particle
• Physics bit
• Split bit
• Tiny power source
• Greek 'I'
• Elemental unit
• Symbol of the post-1945 age
• Greek "i"
• Chemistry bit
• Ninth in a series
• Kappa's preceder
• Film director Egoyan
• With 28-Across, particle accelerators
• Elemental building block