Related Clues:

• Physicist's study
• U-235 or C-14, e.g.
• Minute amount
• Element form
• Molecule part
• Item of interest to Niels Bohr
• Itty-bitty bit
• First half of the files?
• Physics subject
• Smashed item
• Tiny part
• Molecule component
• Modicum
• Tiny power unit
• Basic bit