Related Clues:

• Label on the first of two file drawers, maybe
• Lepton's locale
• Particle with a 'flavor'
• Physicist's subject
• Small matter?
• Small bit
• Bit of nuclear physics
• Supercollider projectile
• Sometimes it gets smashed
• Proton's place
• Cyclotron bit
• Teeny bit
• Source of nuclear energy
• Nuclear energy source
• Smallest amount