Nuclear

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Across
  1. 1. apple ____ (4-letters)
  2. 4. energy that travels at the speed of light (9-letters)
  3. 7. heat (5-letters)
  4. 8. dirty ____ (4-letters)
Down
  1. 2. power (6-letters)
  2. 3. a splitting or breaking up into parts (7-letters)
  3. 5. smallest unit of matter (4-letters)
  4. 6. one that reacts (7-letters)